Symposium Organizers
Craig J. Fennie Cornell University
Lane W. Martin University of Illinois, Urbana-Champaign
Beatriz Noheda University of Groningen
Tsuyoshi Kimura Osaka University
Manuel Bibes Thales Research and Technology/CNRS
P4: Poster Session: Multiferroic Materials and Applications
Session Chairs
Tuesday AM, November 29, 2011
Exhibition Hall C (Hynes)
P1: Coupled Ferroic Instabilities
Session Chairs
Philippe Ghosez
Jim Scott
Monday PM, November 28, 2011
Room 302 (Hynes)
9:30 AM - **P1.1
Revisiting the Hexagonal Manganite Multiferroics.
Nicola Spaldin 1
1 Materials Theory, ETH Zurich, Zurich Switzerland
Show AbstractThe hexagonal manganite multiferroics, of which YMnO3 is the prototype, have recently been shown to exhibit a fascinating ferroelectric domain structure [1] which is a consequence of their improper geometric ferroelectricity [2,3]. Here we discuss how first-principles electronic structure calculations are contributing to understanding and predicting novel behaviors in the hexagonal manganites, including the origin of the unusual ferroelectric vortices, the coupling between ferroelectricity and magnetism, and the behavior of the ferroelectric domain walls.[1] Choi, T. et al. Insulating interlocked ferroelectric and structural antiphase domain walls in multiferroic YMnO3. Nature Mater. 9, 253-258 (2010)[2] Fennie, C. J. & Rabe, K. M. Ferroelectric transition in YMnO3 from first principles. Phys. Rev. B 72, 100103 (2005).[3] Van Aken, B. B., Palstra, T. T. M., Filippetti, A. & Spaldin, N. A. The origin of ferroelectricity in magnetoelectric YMnO3. Nature Mater. 3, 164-170 (2004).
10:00 AM - P1.2
Engineered Domain Structures in Multiferroic Materials: The Vortex Domain State.
Nina Balke 1 , Benjamin Winchester 2 , Wei Ren 3 , Ying-Hao Chu 4 , Anna Morozovska 6 , Eugene Eliseev 6 , Mark Huijben 7 , Rama Vasudevan 8 , Petro Maksymovych 1 , Jason Britson 2 , Stephen Jesse 1 , Igor Kornev 9 , Ramamoorthy Ramesh 5 , Laurent Bellaiche 3 , Long-Qing Chen 2 , Sergei Kalinin 1
1 CNMS, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , Pennsylvania State University, University Park, Pennsylvania, United States, 3 , University of Arkansas, Fayetteville, Arkansas, United States, 4 , National Chiao Tung University, Hsinchu Taiwan, 6 , National Academy of Science of Ukraine, Kiev Ukraine, 7 , University of Twente, Enschede Netherlands, 8 , University of New South Wales, Sydney, New South Wales, Australia, 9 , Ecole Centrale Paris, Chatenay-Malabry Cedex France, 5 , University of California, Berkeley, California, United States
Show AbstractTopological defects in condensed matter systems offer a powerful paradigm for nanoscale device engineering due to combination of unique physical properties and capability for manipulation by external magnetic, electric, or strain fields without the disruption of the host lattice. The examples include vortices in superconductors, defects in topological insulators, and topological defects such as domain walls in ferroics. Here, we report on the controlled creation and probing of the electronic properties of 1D topological defects. Specifically, we explore the physical properties of artificially engineered domain junctions forming vortex or anti-vortex states in multiferroic BiFeO3 (BFO). We demonstrate the creation of 1D conductive channels through the topological defects activated at voltages as low as 1 V, as compared to ~ 3V for domain walls. The electronic and polarization structure of the defect is analyzed, and enhanced conductivity is shown to be induced the interplay between symmetry driven band gap lowering and field-driven carrier segregation. For vortices, the presence of positive disclination results in strong tendency for vacancy segregation. Finally, the electroelastic fields at the topological defects are found to be controlled by the polarization twist at the core, universal for all defect types in (100) rhombohedral materials. This controlled creation of conductive 1D channels pens pathway for design and implementation of integrated oxide electronic devices based on domain patterning.This research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Division of Scientific User Facilities, U.S. Department of Energy.
10:15 AM - P1.3
Hidden Roto Symmetries and Roto Properties in Ferroics.
Venkatraman Gopalan 1 , Daniel Litvin 1
1 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractSymmetry is a powerful framework to perceive and predict the physical world. The structure of materials is described by a combination of rotations, rotation-inversions and translational symmetries. By recognizing the reversal of static structural rotations between clockwise and counterclockwise directions as a distinct symmetry operation, here we show that there are many more structural symmetries than are currently recognized in right- or left-handed handed helices, spirals, and in antidistorted structures composed equally of rotations of both handedness. For example, though a helix or spiral cannot possess conventional mirror or inversion symmetries, they can possess them in combination with the rotation reversal symmetry. Similarly, we show that many antidistorted perovskites possess twice the number of symmetry elements as conventionally identified. These new symmetries, referred to as “roto” symmetries, predict new forms for roto properties that relate to static rotations, such as rotoelectricity, piezorotation, and rotomagnetism. They also enable a symmetry-based search for new phenomena, such as multiferroicity involving a coupling of spins, electric polarization and static rotations. We will present the measurement of electrogyration tensor in handed crystals as a roto property to test for the presence of hidden symmetries predicted by this theory. This work is relevant to structure-property relationships in all material structures with static rotations.
10:30 AM - **P1.4
Tuning Multiferroic Order Parameters with Epitaxial Strain in BiFeO3.
Agnes Barthelemy 1 , I. Infante 1 2 , H. Bea 1 , J. Juraszek 3 , S. Jouen 3 , K. Bouzehouane 1 , S. Fusil 1 , F. Pailloux 5 , E. Jacquet 1 , G. Geneste 2 , J. Pacaud 5 , J. Iniguez 4 , L. Bellaiche 6 , B. Dkhil 2 , M. Bibes 1
1 , Unité Mixte de Physique CNRS/Thales, Palaiseau France, 2 Laboratoire Structures, Proprietes et Modelisation des Solides,, Ecole Centrale, Chatenay Malabry France, 3 Groupe de Physique des Matériaux, Université de Rouen, Rouen France, 5 Institut Pprime, Université de Poitiers, Poitiers France, 4 , ICMAB, Barcelona Spain, 6 Physics Department, University of Arkansas, Fayetteville, Arkansas, United States
Show AbstractStrain engineering has recently emerged as a powerful way to tune the various remarkable physical properties of perovskite oxide thin films. While epitaxial strain controls the Néel temperature in antiferromagnetic films by modifying oxygen octahedral tilt angles, it usually enhances the Curie temperature of ferroelectric films by increasing polar cation shifts. In the antiferromagnetic ferroelectric BiFeO3, both antiferrodistortive and polar instabilities coexist and are expected to respond differently to epitaxial strain. Combining advanced characterization techniques (X-ray and neutron diffraction, Mössbauer spectroscopy and piezoresponse force microscopy) and ab initio calculations, we have established the very rich phase diagram resulting from the influence of epitaxial strain on ferroic phase transitions and order parameters in a strain range spanning over 5% [1]. We will show that these results not only shed light on the interplay between polar and oxygen tilting instabilities but also reveal the possibility to strain-drive the magnetic and ferroelectric transition temperatures close together, offering an original approach to achieve enhanced magnetoelectric responses. We will also present results on the “T-like” phase of BFO films grown on highly mismatched LaAlO3 substrates that impose a misfit srtain around -5%. , This study reveals the coexistence of two differently distorted polymorphs that leads to striking features in the temperature dependence of the structural and multiferroic properties. Notably, the highly distorted phase quasi-concomitantly presents an abrupt structural change, transforms from a hard to a soft ferroelectric and transitions from antiferromagnetic to paramagnetic at 360 K. These coupled ferroic transitions just above room temperature hold promises of giant piezoelectric, magnetoelectric and piezomagnetic responses, with potential in many applications fields [2]. .[1] I.Infante et al. ; PRL 105, 057601 (2010) ; B. Dupé et al. ; PRB 81, 144128 (2010) ; [2] H. Béa et al. PRL 102, 217603 (2009) ; I. Infante et al. ; Cond. Mat 1105.6016 (2011)
11:30 AM - **P1.5
Materials with Built-in Competition: Coupled Phase Transitions and Functional Properties from First Principles.
Karin Rabe 1 , Jun Hee Lee 1 , Joseph Bennett 1
1 Physics and Astronomy, Rutgers, Piscataway, New Jersey, United States
Show AbstractDue to the interplay of structural, magnetic and electronic degrees of freedom, many complex oxides have one or more low-energy alternative phases distinct from the bulk, and therefore can be driven by a perturbation such as compositional substitution, epitaxial strain or artificial structuring through a first-order phase transition with coupled changes in magnetic, structural and electronic properties. At the phase boundary, these systems will have functional behavior arising from switching through the transition with applied fields or stress, with possibilities including piezoelectricity, electric-field or stress control of magnetism, and electric-field or stress induced metal-insulator transitions. In this talk, we will demonstrate how first principles calculations can be used to identify systems with distinct low-energy alternative phases distinct from the bulk and to explore perturbations that will drive candidate systems through a first-order phase transition. Examples will be drawn from recent work on magnetic perovskite oxides and ternary chalcogenides.
12:00 PM - P1.6
Coexistence of Ferroelectricity and Octahedral Rotations in ABX3 Perovskites.
Nicole Benedek 1 , Craig Fennie 1
1 School of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States
Show AbstractNearly all cubic perovskite materials are unstable to energy-lowering structural distortions. The most intensively studied distortions are those that induce ferroelectricity and tilts or rotations of the anion octahedra. The phonon dispersion curves of many perovskites contain both types of instability, although competition between the different types of distortions usually leads to ground-state structures in which one type of instability has been eliminated. Hence, whereas there are many perovskites that are either ferroelectric or have rotated octahedra, there are very few perovskites that are both ferroelectric and have rotated octahedra. A good understanding of the energetic competition between different structures has been built up from first-principles studies of the lattice dynamics of these materials and it is now generally possible to predict which particular structure a perovskite will adopt in its ground state. However, there is no chemically intuitive picture – one that combines lattice dynamics with a local description of bonding – to explain why, for example, the majority of ferroelectric perovskites with rotated octahedra form in only a select few space groups. Such knowledge is at the foundation of the current materials-by-design effort, which attempts to use design rules, based on both chemical and energetic criteria, to create new materials with desired properties. We use a combination of Density Functional Theory, classical simulations, group theoretical techniques and crystal chemistry arguments to study the interaction between ferroelectric and octahedral rotation distortions in a family of perovskite fluorides and oxides. By considering both ‘long-range’ distortions (phonons) and the local bonding environment of each ion in a particular structure, we are able to show that, in contrast to the common assumption, ferroelectricity and octahedral rotations do not always compete. In particular, we explain why many ferroelectric perovskites form in space group R3c and show how ferroelectricity is suppressed in space group Pnma, in which most perovskites form.
12:15 PM - P1.7
Ferroelectric Instabilitis in Lead-Free Na0.5Bi0.5TiO3-Based Ferroelectric Materials Studied by First-Principles Methods.
Melanie Groeting 1 2 , Silke Hayn 1 , Igor Kornev 2 , Brahim Dkhil 2 , Karsten Albe 1
1 Materials Science, TU Darmstadt, Darmstadt Germany, 2 Laboratoire SPMS, UMR8580 Ecole Centrale Paris-CNRS, Chatenay-Malabry France
Show AbstractNa0.5Bi0.5TiO3-based materials show extraordinarily high strains and are thus promising environmentally friendly alternatives to the toxic lead-containing standard piezoelectric materials. Na0.5Bi0.5TiO3 is considered as a model relaxor ferroelectric with a complex perovskite structure having two different cations (Na+ and Bi3+) on the A-site. In addition to local polar and chemical order/disorder, responsible for the relaxor behavior, Na0.5Bi0.5TiO3 structures combine long-range polar shifts along different directions and both in- and out-of-phase oxygen octahedral tilts offering a rich playground to investigate coupling/competing between different degrees of freedom. In this contribution, the influence of hydrostatic pressure and chemical substitution on ferroelectric instabilities and octahedral tilt in Na0.5Bi0.5TiO3-based solid solutions is studied by first-principles methods.Under positive (compressive) pressure an orthorhombic Pnma phase is stabilized above few GPa in good agreement with experimental data. Very interestingly, while the polarization is ”killed” leaving only tilts under positive pressure, for negative (tensile) pressure the polarization survives whereas the tilts are suppressed. We find that tilts can also be suppressed by substituting the A-cations by bigger cations like Ba or K, while smaller cations have the same effect as the application of hydrostatic pressure, favoring the orthorhombic Pnma phase. Studying Na0.5Bi0.5TiO3-BaTiO3 at different BaTiO3 contents, we find that while one end member Na0.5Bi0.5TiO3 is a purely A-site active ferroelectric the other end member BaTiO3 is pureley B-site active. At 0-20% BaTiO3 content the crossover between both regimes occurs, which we believe is part of the origin of the highly increased piezoelectric response found near the morphotropic phase boundary about 7% BaTiO3. At that concentration the A-site is still active while locally also some B-cations become activated.
12:30 PM - **P1.8
Manipulating the Band Structure of SrTiO3 via Strain-Controlled Ferroelectric Phase Transitions.
Charles Brooks 1 2 , Robert Berger 3 , Dagmar Chvostova 4 , Vladimir Trepakov 4 , Nik Podraza 5 , Lena Kourkoutis 6 , Tassilo Heeg 1 , Margitta Bernhagen 7 , Reinhard Uecker 7 , Jürgen Schubert 8 , David Muller 6 9 , Alexandr Dejneka 4 , Craig Fennie 6 , Jeffrey Neaton 3 , Darrell Schlom 1 9
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Department of Materials Science and Engineering , Pennsylvania State University, University Park, Pennsylvania, United States, 3 Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 4 , Institute of Physics ASCR, Prague Czechia, 5 Department of Electrical Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 6 School of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, 7 , Liebniz Institute for Crystal Growth, Berlin Germany, 8 Institute of Bio and Nanosystems, JARA-Fundamentals of Future Information Technologies, Research Centre Jülich, Jülich Germany, 9 Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, New York, United States
Show AbstractThe family of crystal structures known as perovskites are nature’s garbage can, able to accommodate nearly all elements as major constituents in a dense structure that is awash with phase transitions. These phase transitions accompany the many novel properties of perovskites—pyroelectricity, piezoelectricity, ferromagnetism, multiferroicity, non-linear optical effects, superconductivity, and much more—all with huge property coefficients. SrTiO3, the hydrogen atom of perovskites, exhibits many of these extraordinary and useful properties when suitably doped or strained, and is a very stable photocatalyst for water splitting. In this talk we will show how the bandgap of SrTiO3 can be altered by 10% (0.3 eV) by a ferroelectric phase transition or morphed from indirect to direct bandgap through an antiferrodistortive phase transition. In agreement with theory and experiment, both of these phase transitions can be manipulated using experimentally realizable biaxial strains providing a new means to accomplish bandgap engineering of SrTiO3 and related perovskites.
P2: Structure and Dynamics of Ferroelectric Domains
Session Chairs
Monday PM, November 28, 2011
Room 302 (Hynes)
2:30 PM - **P2.1
Phase-Field Modeling of Domain Structures and Charged Defects in Ferroelectric Crystals.
Long-Qing Chen 1
1 Department of Materials Science and Engineering, Penn State University, University park, Pennsylvania, United States
Show AbstractWhile ferroelectric crystals always contain domains, they also contain charged defects such as oxygen vacancies. The presence and migration of oxygen vacancies are believed to be responsible for a number of processes such as leakage current, dielectric degradation, ferroelectric fatigue, etc. This presentation will discuss a general phase-field formulation for modeling the simultaneous evolution of ferroelectric domain structures and ionic and electronic species. The thermodynamics of an inhomogeneous microstructure containing spatial distributions of polarization, strain, and ionic and electronic defects is written in a standard diffuse-interface description. The ionic/electronic transport equations as well as the electrostatic Poisson equation and the elasticity equation are then derived from the thermodynamic free energy. Implementation of spectral methods to solving the systems of equations under non-periodic boundary conditions will be discussed. Application of the set of transport equations to defect segregation to domain walls, formation of space charges, and ionic/electronic transport under a voltage bias will be presented.
3:00 PM - P2.2
Structure and Dynamics of Ferroelectric Domains.
Xiaoqing Pan 1 , Christopher Nelson 1 , Peng Gao 1 , Jacob Jokisaari 1 , Colin Heikes 2 , Carolina Adamo 2 , Alexander Melville 2 , Benjamin Winchester 3 , Yijia Gu 3 , Seung-Hyub Baek 4 , Chad Folkman 4 , Chang-Beom Eom 4 , Long-Qing Chen 3 , Darrell Schlom 2
1 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 3 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 4 Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin, United States
Show AbstractThe ability of an electric field to switch the spontaneous polarization in a crystal between energetically degenerate states is the defining characteristic of a ferroelectric and provides the underlying storage mechanism in an important class of nonvolatile memories. This switchable polarization couples with electronic transport properties, surface chemistry, strain, and magnetic order, enabling multifunctional devices. Domain motion and stability is influenced by defects within the ferroelectric as well as by electrical and mechanical boundary conditions. Dislocations, for example, are known to destroy ferroelectric order; neighboring grains and interfaces subject the ferroelectric to localized strain, electric fields, or the screening of electric fields. As advances in ferroelectric synthesis have enabled ferroelectric materials to be integrated with other functionalities with atomic precision, understanding the ferroelectric switching in such increasingly complex structures has come to the fore, requiring improvements in both theory and characterization. In this talk we show that the atomic scale polarization map in ferroelectrics can be determined using aberration-corrected transmission electron microscopy (TEM) owing to the large atomic displacements responsible for the dipole moment. This study reveals how interfaces in complex multidomain geometries lead to the formation of polarization vortices with electric flux closure domains. Using aberration-corrected transmission electron microscopy (TEM) in combination with in-situ scanning probing holder the kinetics and dynamics of ferroelectric switching is followed at millisecond temporal and sub-angstrom spatial resolution. We directly observe localized nucleation events at the interface, domain wall pinning on point defects, and the formation of metastable ferroelectric states localized to the ferroelectric and ferromagnetic interface. These results show how defects and interfaces impede full ferroelectric switching of a thin film.
3:15 PM - P2.3
A Quantitative Understanding of Domain Relaxation Behavior in BiFeO3-Based Multiferroic Systems Using In Situ TEM.
Mitra Taheri 1 , Christopher Winkler 1 , Jennifer Sloppy 1 , Steven Spurgeon 1 , Lane Martin 2 , Juan Idrobo 3 , Charudatta Phatak 4 , Jianguo Wen 4 , Dean Miller 4
1 Materials Science & Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 2 Materials Science & Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 , Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractMagneto-electric coupling in BiFeO3 (BFO) allows for control of the ferroelectric and magnetic domain structures via applied electric fields. Because of these unique properties, BFO and other magneto-electric multiferroics constitute a promising class of materials for incorporation into high-density ferroelectric and magnetoresistive devices. However, the magneto-electric coupling in BFO is mediated by volatile ferroelastically switched domains that make it difficult to incorporate this material into devices. To facilitate device integration, an understanding of the microstructural factors that affect ferroelastic relaxation and ferroelectric domain switching is needed. In this study, domain switching behavior was examined using in situ biasing in TEM. Specifically, the evolution of ferroelastically switched ferroelectric domains in BFO thin films during many switching cycles was investigated. Evidence of varying domain behavior mimicking nucleation, propagation, and switching was found, even at applied electric fields below the coercive field. Quantitative kinetic data extracted from these in situ videos indicates that the occurrence of ferroelastic relaxation in switched domains, and the stability of these domains, is influenced by the local microstructure of the BFO film. Local regions surrounding domains in the BFO thin film device structures were examined using aberration corrected TEM. This technique provides a high resolution view of microstructural dependence of domain relaxation. Additionally, this work was extended to Lorentz TEM using a ferromagnetic layer atop the BFO film device to gain an understanding of the deterministic control on ferromagnetic domain behavior of a BFO-based composite system.The in situ TEM biasing experiments presented provide a real time view of the complex dynamics of domain switching that provide a critical complement to data obtained from established methods such as scanning probe techniques. Research at Oak Ridge (MT, JS, JCI) is supported by the Shared Research Equipment (SHaRE) User Facility, Oak Ridge National Laboratory, sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences. Research at Argonne (MT, CW, SS, JS, CD, DM, JW) is sponsored by the U.S. DOE, Office of Science - Basic Energy Sciences, under contract DE-AC02-06CH11357. The Electron Microscopy Center at Argonne is supported by the Office of Science. The research was funded in part by the Office of Naval Research under contract #N00014-11-1-0296.
3:30 PM - P2.4
Incomplete Ferroelectric Domain Switching Driven by Built-in Potential and Defects.
Myung-Geun Han 1 , Lijun Wu 1 , Marvin Schofield 4 , Chao Ma 1 , Toshihiro Aoki 2 , Jason Hoffman 3 , Matthew Marshall 3 , Frederick Walker 3 , Charles Ahn 3 , Yimei Zhu 1
1 Condensed Matter Physics & Materials Science, Brookhaven National Lab, Upton, New York, United States, 4 Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, United States, 2 , JEOL USA Inc., Peabody, Massachusetts, United States, 3 Department of Applied Physics and Center for Research on Interface Structures and Phenomena, Yale University, New Haven, Connecticut, United States
Show AbstractSwitchable spontaneous polarization in ferroelectric thin films has received intense interests for applications to energy-efficient nonvolatile memories. However, long-term reliability issues, especially associated with polarization stability and incomplete domain switching, have been recognized as an open question for practical applications. Understanding the microscopic origins of domain switching is therefore indispensible to ensuring long-term performance, thus the utility of the devices. In this presentation, we show that incomplete domain switching is often caused by the built-in potential across the heterojunction between epitaxial ferroelectric thin film and substrate and the domain wall pinning by existing in-plane domain walls. Domain switching behavior observed by in situ electrical biasing in electron microscope is quantitatively correlated with electrostatic potential distribution measured with off-axis electron holography. The atomic structure of induced 180o domain walls revealed by annular-bright-field imaging showed systematic lattice translations of cations and anions along applied electric field across the domain wall.
3:45 PM - P2.5
Polar Domains in CaTiO3 Single Crystals.
Tom Lummen 1 , Eftihia Vlahos 1 , Charles Brooks 1 , Ekhard Salje 3 , Darrell Schlom 2 , Clive Randall 1 , Venkatraman Gopalan 1
1 Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania, United States, 3 Department of Earth Sciences, University of Cambridge, Cambridge United Kingdom, 2 Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show AbstractIn bulk CaTiO3, the established room temperature lattice is orthorhombic (space group Pbnm), with point group symmetry mmm. This structure sets in at high temperature (∼1500 K), involving strong rotations and tilts of the oxygen octahedra as compared to the parent cubic perovskite structure, but remaining non-polar [1]. Thus, bulk CaTiO3 is thought to be non-ferroelectric, although it has been referred to as an ‘incipient’ ferroelectric based on its low temperature dielectric behavior [2]. Recently, first principles theory predicted a ferroelectric instability for CaTiO3 thin films under tensile strain [3], though this has not yet been verified experimentally. Intriguingly, confocal Second Harmonic Generation (SHG) and micro-Raman imaging studies were carried out on perovskite CaTiO3 crystal surfaces, unambiguously revealing a multitude of highly regular, uniform polar domains. The individual domains are clearly delineated by twin walls, possessing different in-plane polarization components. Cross-correlation with optical birefringence images indicates domain polarity being linked to the existing ferroelastic domain structure that sets in at very high temperature (1500 K). Polarization dependent SHG analysis indicates that the highest compatible symmetry of the polar domains still preserving the strong octahedral tilts is monoclinic (point group m, space group Pc), with the ferroelectric polarization symmetry-allowed to freely rotate in the single symmetry plane at 45 degrees to the surface. To clarify the origin of this fascinating phenomenon, we present a combination of multi-scale X-ray diffraction data, SHG poling experiments and Thermally Stimulated Depolarisation Current (TDSC) results. [1] M. Yashima and R. Ali, Solid State Ionics 180, 120 (2009)[2] V.V. Lemanov, A.V. Sotnikov, E.P. Smirnova et al., Solid State Communications 110, 611 (1999)[3] C.-J. Eklund, C.J. Fennie and K.M. Rabe, Physical Review B 79, 220101(R) (2009)
4:00 PM - P2: Domains
Break
P3: BiFeO<sub>3</sub> and the Morphotropic Phase Boundary
Session Chairs
Monday PM, November 28, 2011
Room 302 (Hynes)
4:15 PM - P3.1
Interfacial Analysis in a Bismuth Ferrite - Lanthanum Aluminate Heterostructure.
P. Sankara Ramakrishnan 1 , Jan-Chi Yang 3 , Quentin Ramasse 2 , Yinh-Hao Chu 3 , Nagarajan Valanoor 1 , Paul Munroe 1
1 Materials Science and Engineering, University of New South Wales, Sydney, New South Wales, Australia, 3 Materials Science and Engineering, National Chiao Tung University, Hsin Chu City Taiwan, 2 , SuperSTEM Laboratory, Daresbury United Kingdom
Show AbstractMultiferroic bismuth ferrite (BiFeO3) has attracted considerable attention since it is both lead-free and exhibits ferroelectric ordering coupled with anti-ferromagnetism. The simultaneous presence of switchable ferroelectric and anti-ferromagnetic ordering in a single phase material leads to additional functionality, where electric-field induced control of magnetic ordering is possible. In addition to the parent rhombohedral phase, a tetragonally-distorted perovskite with large spontaneous polarization has also been identified. Epitaxial strain between a substrate and a BiFeO3 film can be used to stabilize the tetragonal polymorph and induce a morphotropic phase transition between these polymorphs. In this study, multiphase bismuth ferrite was deposited on a lanthanum aluminate (LaAlO3) substrate using pulsed laser deposition assisted by high pressure RHEED. Cross-sectional high resolution transmission electron microscope studies were performed using an aberration-corrected dedicated scanning transmission electron microscope (STEM) operating at 100 kV. Electron energy loss spectroscopy (EELS) analysis provided chemical information across the phase boundary. It was found that the LaAlO3-BiFeO3 interface was dislocation-free. However, EELS analysis revealed diffusion of Fe into the LaAlO3 substrate to a depth of ~ 2nm. Further, there was some La diffusion into BiFeO3, but to shallower depths. It is speculated that this diffusion accommodates misfit strain. High resolution Z-contrast images confirm the presence of rhombohedral and tetragonal phases adjacent to each other without there being dislocations present at their interfaces. EELS analysis also revealed subtle changes in oxygen and iron edge fine structure across the domain wall, which could potentially be linked to the relative movement of oxygen octahedra at that boundary and variations in the valance of the iron ions. Modelling has been used to support these observations.
4:30 PM - **P3.2
Temperature-Driven Phase Transitions in Tetragonal-like BiFeO3.
Hans Christen 1 2 , Wolter Siemons 1 , Michael Biegalski 2 , Joong Hee Nam 3 , Gregory MacDougall 4 , Jerel Zarestky 4 , Stephen Nagler 4 , Shuhua Liang 1 5 , Elbio Dagotto 1 5
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 , Korea Institute of Ceramic Engineering and Technology (KICET), Seol Korea (the Republic of), 4 Neutron Scattering Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 5 Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee, United States
Show AbstractThe recent discovery of a stress-induced tetragonal-like (T-like) phase in BiFeO3 (BFO) has illustrated how epitaxial constraints can fundamentally alter the properties of this multiferroic. While much work has been performed on samples with a mix of structural phases, the temperature dependence of the magnetic and structural properties of the T-like phase, especially in phase-pure samples, remains largely unknown. In this presentation we will focus on both structural and magnetic phase transitions that occur in T-like BFO. First we will focus on the magnetic properties, which we have analyzed using neutron diffraction over a temperature range of 10-500 K, allowing us to deduce the type of anti-ferromagnetic ordering and the ordering temperature (Néel temperature), and show that the measured Néel temperature agrees with predictions from a classical Heisenberg model.In addition, we have analyzed the structural properties using x-ray diffraction over the same temperature range and find a structural phase transition from the room-temperature monoclinic MC (T-like) phase to a monoclinic MA (T-like) phase at elevated temperature, with implications on the ferroelectric properties.In combination, these measurements shed light on the complexity of the phase diagram of BFO, and provide routes to explore how the material’s properties can be tuned by external parameters.Research supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division (H.M.C., W.S., S.L., E.D., H.M.C) and Scientific User Facilities Division (M.D.B., G.J.M, J.L.Z, S.E.N.).
5:00 PM - P3.3
In Situ Studies of an Electric-Field Induced Structural Transition in Rare-Earth Substituted BiFeO3 Thin Films at a Morphotropic Phase Boundary.
Anbusathaiah Varatharajan 1 , Daisuke Kan 1 , Mark Reese 1 , Samuel Lofland 2 , Ichiro Takeuchi 1
1 Department of Materials Science and Engineering, University of Maryland, College Park, Maryland, United States, 2 Department of Physics and Astronomy, Rowan University, Glassboro, New Jersey, United States
Show AbstractIn our recent work (Appl. Phys. Lett. 92, 202904, 2008), we have found a morphotropic phase boundary in BiFeO3 through systematic A-site cation (Sm3+) substitution using combinatorial film synthesis. We have observed significant enhancement in the piezoelectric and dielectric properties at the morphotropic phase boundary which occurs at 14% Sm. It has further been demonstrated that this composition is a boundary between a ferroelectric (FE) rhombohedral and paraelectric (PE) orthorhombic phases. One of the most intriguing findings is that the polarization hysteresis loops measured at the boundary show clear transition from square-shaped ferroelectric hysteresis loops to antiferroelectric-like double hysteresis loops. It was proposed that an electric-field induced structural transformation from the non-polar orthorhombic to polar rhombohedral phase is the origin for the double hysteresis behavior and the concomitant enhanced properties at the boundary. Here, we report on an in-situ electric-field dependent Raman spectroscopy measurement. Experiments were carried out on capacitors with a transparent conducting top electrode, which is used for Raman measurements. This work indeed confirmed the structural transition between PE and the FE phases as a systematic function of applied electric field. We expect the intrinsic piezoelectric coefficient due to the structural transition to be substantially larger than the one we have observed for epitaxially clamped thin films. To this end, we are fabricating nanopillar capacitors out of Sm-doped BFO thin films at the morphotropic phase boundary.
5:15 PM - P3.4
Phase Evolution and Stabilization in Highly-Strained Epitaxial BiFeO3 Films: Routes to Enhanced Electromechanical Response.
Anoop Damodaran 1 , Lane Martin 1
1 Materials Science and Engineering and Materials Research Laboratory, University of Illinois, Urbana Champaign, Urbana, Illinois, United States
Show AbstractThe multiferroic perovskite BiFeO3 exhibits a strain-induced structural phase transition (occurring at a critical strain level of ~4.5% compressive strain) that gives rise to enhanced electromechanical strains as large as 4-5%. The enhanced electromechanical response in this material has been attributed to the emergence of a complex mixed-phase structure and the ability for this material to reversibly transform under applied electric fields between these various phases. This is exciting as it opens up the possibility of using BiFeO3 as the candidate piezoelectric for use in a wide array of technologies. In an attempt to better understand the mechanisms for this strong electromechanical response and to identify ways to extend the magnitude of response in this system, we have investigated the thickness evolution of the various phases, the competition between the thermodynamically stable equilibrium rhombohedral-phase and these strain-induced polymorphs, and route to provide further enhanced responses.Epitaxial thin films of Bi1-xPbxFeO3 (x = 0, 0.25, and 0.50) have been grown on a range of substrates including LaAlO3 (001) using pulsed laser deposition. We have investigated the thickness dependent evolution of the phase competition in these films using a combination of X-ray reciprocal space mapping, high-resolution atomic force microscopy (AFM), and piezoresponse (PFM) force microscopy and have observed intriguing phase evolution in films between 20 and 350 nm. As part of this presentation, we will first present detailed X-ray diffraction and AFM studies of pure BiFeO3 films that reveal a complex phase evolution including the development of non-epitaxial versions of the bulk-like rhombohedral phase in films in excess of 200 nm thick. Such transformation to the parent phase, in turn, places strict limits on the magnitude of the electromechanical response achievable in these films. In order to overcome this thickness and strain-dependent phase evolution, we have investigated chemical alloying routes to further stabilize the mixed-phase structures necessary for large electromechanical response. As part of this work, we will present a study of Pb-alloyed BiFeO3 films and demonstrate how chemical alloying can be used to tune the lattice parameter of the film to provide a favorable strain state. This allows us to stabilize the complex mixed-phase structure in these films to thickness in excess of 500 nm and, in turn, achieve larger electromechanical responses. PFM-based switching experiments on 500-600 nm thick films will be presented that demonstrate net surface displacements as high as 20-25 nm. These results provide insight into the competing nature of the phases in this system and a pathway to achieve large electric-field induced displacements by stabilizing the desired mixed-phase structures in these exciting and technologically relevant materials.
5:30 PM - P3.5
Strain-Induced Low Symmetry Phases and Polarization Rotation Paths in Epitaxial BiFeO3 Thin Films.
Zuhuang Chen 1 , Ping Yang 2 , Sergey Prosandeev 3 , Zhenlin Luo 4 , Wei Ren 3 , Yajun Qi 1 , Chen Gao 4 , Junling Wang 1 , Thirumany Sritharan 1 , Laurent Bellaiche 3 , Lang Chen 1
1 School of Materials Science and Engineering, Nanyang Technological University, Singapore Singapore, 2 Singapore Synchrotron Light Source (SSLS),, National University of Singapore, 5 Research Link, Singapore Singapore, 3 Institute for Nanoscience and Engineering and Physics Department, University of Arkansas, Fayetteville, Arkansas, United States, 4 National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei China
Show Abstract Epitaxial BiFeO3 films grown by pulsed laser deposition on (001) substrates inducing different misfit strains (LaSrAlO4, LaAlO3, NdGaO3, LSAT, SrTiO3, DyScO3,GdScO3 and PrScO3) have been studied by piezoelectric force microscopy and synchrotron x-ray diffractometry . In-plane piezoelectric force microscopy studies showed clear signals and self-assembled nanoscale stripe domain structure for the tetragonal-like phase, and the polarization of the tetragonal-like phase lies in the (100) planes and tilts at certain angles with respect to [001] direction. Our experimental results reveal that the T-like phase of BFO films is monoclinic MC, which is different from MA type monoclinic phase reported in films grown on low misfit substrates, and further suggest that the strain-induced phase transition is MA--Mc. Besides the T-like MC and R-like MA phases, two other tilted triclinic ferroelectric phases have been revealed in the BiFeO3 films under large compressive strain. Furthermore, first-principles calculations strongly suggest an interesting scenario (involving phase separation from a single monoclinic state and elastic matching) for explaining the simultaneous observation of these two triclinic phases, as well as, the observed enhancement of piezoelectricity in the highly strained films.
5:45 PM - P3.6
Atomic Level View at the Ferroelectric-Antiferroelectric Transition and Phase Coexistence at Morphotropic Phase Boundary by Quantitative Aberration-Corrected STEM.
Albina Borisevich 1 , Ching-Jong Cheng 2 , J. Lin 3 , Ying-Hao Chu 3 , Ichiro Takeuchi 4 , Valanoor Nagarajan 2 , Sergei Kalinin 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , University of New South Wales, Sydney, New South Wales, Australia, 3 , National Chiao Tung University, Hsinchu Taiwan, 4 , University of Maryland, College Park, Maryland, United States
Show AbstractFor materials with competing or multidimensional order parameters the competition between close ground states often results in mesoscopic structural instabilities and associated complex nanoscale morphologies, such as monoclinic phases in the vicinity of morphotropic phase boundaries (MPB)[1] in ferroics and ferroelectric-antiferroelectric (FE-AFE) boundaries[2]. The detailed internal structure of the domains, and especially the size and atomic structure of boundaries between them cannot be addressed with diffraction-based or mesoscopic approach. Here, we report direct atomically-resolved mapping of structural transformations at the ferroelectric-antiferroelectric boundary in Sm-doped BiFeO3 using quantitative aberration-corrected Scanning Transmission Electron Microscopy (STEM) [3,4].Sm-doped BiFeO3 exhibits FE-AFE morphotropic phase boundary at ~14% Sm substitution.[2,5] We focused our attention on the 4x modulated bridging phase for antiferroelectric (10% Sm) and MPB (14% Sm) compositions. For both compositions, Bi-Bi spacings in the 4x ordered structure were strongly modulated. For the 10% Sm composition (away from the MPB) Fe-Fe spacings were uniform, thus creating an oscillating pattern of relative displacements resulting in ultrathin lamellar domain structure. In contrast, for the 14% Sm composition (MPB) Fe-Fe spacings were also modulated in such a way as to suppress relative cation displacements and hence the polarization of lamellar domains.These observations suggest that the bridging phase is a complex interplay of polarization and strain. For lower rare earth concentrations, patterns of oscillating Bi displacements are formed, while Fe sublattice is undisturbed. As A cation radius is reduced with Sm doping, Fe sublattice is also driven to distort to accommodate increasingly asymmetric environment. These conjectures are corroborated by O-K NEXAFS data on the two compositions. Possible theoretical framework for the behavior of this system will also be discussed.Research sponsored by ORNL’s Shared Research Equipment (SHaRE) User Facility, which is sponsored by the Office of Basic Energy Sciences, U.S. Department of Energy.[1] B. Noheda, Curr. Opinion Solid State and Mat. Sci. 6, 27 (2002).[2] C.J. Cheng et al., Phys. Rev. B 80, 014109 (2009).[3]C.L. Jia et al. , Nature Mat. 6 (2007), p. 64.[4] A. Borisevich et al., Phys. Rev. Lett., 105, 087204 (2010)[5]C.J. Cheng, A.Y. Borisevich et al., Chem. Mat. 22, 2588 (2010).
P4: Poster Session: Multiferroic Materials and Applications
Session Chairs
Tuesday AM, November 29, 2011
Exhibition Hall C (Hynes)
9:00 PM - P4.1
Rhombohedral-Orthorhombic Phase Transition Induced Enhancement on the Electrical Behavior of K0.5Na0.5NbO3-BiScO3-BiCoO3 Lead-Free Piezoelectric Ceramics.
Wenjuan Wu 1 , Dingquan Xiao 1 , Jiagang Wu 1 , Jing Li 1 , Wenfeng Liang 1 , Jianguo Zhu 1
1 , Sichuan University, Chengdu China
Show AbstractPerovskite-type structure (K0.5Na0.5)NbO3 (KNN)-based ceramics have been considered a promising candidate for lead-free piezoelectric ceramics because of its excellent properties. The polymorphic phase transition (PPT), rhombohedral to orthorhombic (R–O) transition or orthorhombic to tetragonal (O–T) transition, plays an important role in the dielectric and piezoelectric properties of KNN-based ceramics. Moreover, rhombohedral to orthorhombic phase transition temperature (TR-O) of KNN-based ceramics can be tuned close to room temperature, and better piezoelectric properties are induced by the theory of two-phase coexistence. KNN ceramics doped with BiScO3 or BiCoO3, respectively, have attracted more attention for the excellent piezoelectric properties owing to the rhombohedral to orthorhombic phase transition near room temperature. In this work, the (1-x)K0.5Na0.5NbO3-x(0.97BiScO3-0.03BiCoO3) (KNN-xBSC) piezoelectric ceramics were prepared by the conventional solid-state sintering method, and the effects of the BSC addition on the phase structure, microstructure, and electrical properties of the KNN ceramics were systematically investigated. The rhombohedral to orthorhombic phase transition around room temperature was identified for the KNN-xBSC ceramics in the composition range of 0.015≤ x ≤0.0175, and the improved electrical properties (d33~205 pC/N, kp~0.43, εr~1315, and tan δ~0.054) were induced by this phase transition. These results indicate that the enhanced piezoelectric properties for alkali niobate piezoelectric ceramics can be achieved by forming the coexistence of rhombohedral and orthorhombic phases at room temperature. Furthermore, the KNN-xBSC ceramics result in a relaxor ferroelectric behavior owing to a more complex occupation of A and B sites in the ABO3 perovskite structure. Our preliminary results show that the KNN-xBSC ceramics by doping magnetic elements (Co) exhibit a weak ferromagnetic order at room temperature.
9:00 PM - P4.10
Enhancing the Multiferroic Properties of BiFeO3 at the Nanoscale.
Georgia Papaefthymiou 1 , Tae-Jin Park 2 4 , Arthur Viescas 1 , Stanislaus Wong 2 3
1 Physics, Villanova University, Villanova, Pennsylvania, United States, 2 Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York, United States, 4 Radioactive Waste Technology Development Division, Korea Atomic Energy Research Institute, 1045 Daedeok-daero, Yuseong, Daejeon, 305-353 Korea (the Republic of), 3 Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York, United States
Show AbstractBismuth ferrite (BiFeO3) is a multiferroic material of special interest because it possesses both long-range magnetic and ferroelectric order at room temperature. Specifically, BiFeO3 is a canted antiferromagnet with a superimposed helical spin arrangement on the resulting small magnetic moment, rendering bulk bismuth ferrite an antiferromagnet. To enhance its multiferroic properties, one must release the latent magnetization locked within the spiral spin structure. To this end, we have pursued two distinctly different approaches: (a) the synthesis of single crystalline BiFeO3 nanoparticles of decreasing size, 245 > d > 14 nm, where d is the diameter of the particle and (b) the formation of single crystalline (BiFeO3)x-(BaTi O3)1-x solid solution nanocubes of ~ 200 nm on a side, for 1 > x > 0.5. The first approach is expected to impart a net magnetic moment to nanoparticles with d < 62 nm, the magnitude of the spiral spin wavelength in bulk BiFeO3, whereas the second seeks to induce a net magnetic moment by introducing structural modifications. Magnetic and 57Fe-Mössbauer measurements were used to characterize, respectively, the macroscopic and microscopic magnetic properties of the resulting nanostructures. The experimental observations indicate that both approaches succeed in releasing the inherent latent magnetization of BiFeO3. Additional finite size effects at the nanoscale further enhance the observed magnetization due to uncompensated spins at the surface. Furthermore, comparative studies of hysteresis loops obtained at T = 4.2 K and 300 K for the solid solution nanostructures point to the presence of magneto-electric coupling in these systems.
9:00 PM - P4.11
Phonon Assignments in Multiferroic BiFeO3 Single Crystal.
Arun Singh 1 2 , R. Palai 1 , R. Katiyar 1
1 Physics, University of Puerto Rico, San Juan United States, 2 Department of Physics, Jamia Millia Islamia University, New Delhi, Delhi, India
Show AbstractMultiferroic materials, which combine the two or more properties of ferromagnetism, ferroelectricity, and ferroelasticity, have attracted much attention owing to their physical mechanisms and potential for the design of multifunctional device applications. Multiferroics one of great interest for understanding the fundamental aspects of the mechanism that gives rise to magnetoferroelectric coupling, and potential device applications including electro-optic and data storage. BiFeO3 (BFO) is one of the attractive and stimulating multifer-roic materials which possess ferroelectric and antiferromagnetic properties in same phase. It has been revealed to possess a rhombohedrally distorted perovskite structure with space group R3c at room temperature. In the present study Physical properties of BFO single crystal have been examined by X-ray diffraction, back scattering Micro-Raman spectroscopy has been used to study lattice dynamics associated with the ferroelectric domains of a BiFeO3 crystal at different temperatures. Based on polarization orientation, and temperatures dependent Raman scattering studies we have identified all possible phonons in BFO single crystal and the results will be discussed.
9:00 PM - P4.12
Exchange Coupling Behavior between Ferromagnetic Metal and BiFeO3 Thin Films with Various Domain Structures.
Wittawat Saenrang 1 2 , Seung Hyub Baek 1 , Mark Rzchowski 2 , Chang-Beom Eom 1 2
1 Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 Physics, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractMultifunctional oxide materials exhibit interesting coupled piezoelectric, magnetoelectric and ferroelectric properties. Multiferroic BiFeO3 has been extensively studied due to its intriguing multifunctionality. It’s strong magnetoelectric coupling made it been considered as a promising candidate for new magnetoelectric devices. However, the antiferromagnetism in BiFeO3 is not easily used in applications. We need to make use of coupling interactions between the BiFeO3 film and ferromagnetic layer. There are two types of exchange interactions that have been observed at the interface between a ferromagnet and an antiferromagent. The first is an exchange bias and the second is an enhancement of the coercive field of the ferromagnet. Here, we report on the exchange coupling behavior between ferromagnetic metal and BiFeO3 thin films with controlled domain structures. Domain structure of BiFeO3 was configured with miscut directions and angle. Magnetic properties of the heterostructures were characterized by vibrating sample magnetometry (VSM). Our work will probe the exchange coupling behavior between ferromagnetic metal and controlled domain structure BiFeO3 thin films for applications to magnetoelectric devices.
9:00 PM - P4.13
Nonlinearity and Frequency Dependance of Direct Piezoelectric Response in BiFeO3 Ceramics.
Tadej Rojac 1 , Andreja Bencan 1 , Goran Drazic 1 , Marija Kosec 1 , Nava Setter 2 , Dragan Damjanovic 2
1 Electronic Ceramics Department, Jozef Stefan Institute, Ljubljana Slovenia, 2 Ceramics Laboratory, Swiss Federal Institute of Technology-EPFL, Lausanne Switzerland
Show AbstractBiFeO3 is attracting a lot of interest, primarily because it shows both antiferromagnetic and ferroelectric ordering, enabling magnetoelectric coupling. In addition, the ferrite has a high Curie temperature (825°C), which might be useful in high-temperature piezoelectric applications. However, data on piezoelectric properties of BiFeO3 ceramics, such as the dependence of piezoelectric coefficients on the frequency and amplitude of the driving field, are still lacking. There are several other critical issues that need to be worked out before this material can be considered for piezoelectric applications; the most important are related to processing, especially the strong influence of impurities on phase composition [1], high electrical conductivity and high coercive field (>70 kV/cm). We have developed a processing route, based on mechanochemical activation, with reduced number of processing steps that resulted into dense BiFeO3 ceramics with minimum concentration of secondary phases and capable to withstand large DC electric fields (100 kV/cm) [2]. Here, we present a study of the direct piezoelectric response of these BiFeO3 ceramics at room temperature, in particular its frequency and stress field dependence. The results revealed a considerable nonlinearity in the piezoelectric response, characterized by an increase of d33 of up to 25% at 0.01 Hz and maximum AC stress of 3.2 MPa peak-to-peak. The origin of the nonlinearity is discussed in relation to the results of the transmission electron microscopy and strain–electric-field measurements, performed above coercive field. Dispersion of d33 in the frequency range 0.1–100 Hz suggests possible Maxwell-Wagner piezoelectric effects. We observed a strong relationship between nonlinearity and dispersion that could be mediated by the conductivity. Finally, the influence of secondary phases, thermal quenching and sintering temperature on the piezoelectric response is discussed in more details. References:[1] Valant et al., Chem. Mater. 19, 5431 (2007).[2] Rojac et al, J. Appl. Phys. Lett. 108, 074107 (2010).
9:00 PM - P4.16
Nanoscale Switching of BiFeO3 Thin Films Grown by Pulsed Electron Deposition.
Hongxue Liu 1 , Ryan Comes 1 , Yonghang Pei 1 , Jiwei Lu 1 , Stuart Wolf 1
1 Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia, United States
Show AbstractRecent years have seen tremendous research interest in BiFeO3 (BFO) due to its simultaneous ferroelectric and magnetic order and great potential for new device applications. While BFO has been grown by various methods such as pulsed-laser deposition (PLD) and rf sputtering, there exist no reports yet of growth by pulsed electron deposition (PED) which offers a cost effective alternative to PLD while featuring a wider materials deposition capability. Here we demonstrate the epitaxial growth of BFO by PED and discuss the resulting crystal quality, magnetic and nanoscale switching properties. X-ray diffraction shows single phase, epitaxial (001) oriented films grown on SrRuO3 (SRO) buffered SrTiO3 (001) substrates with rocking curve full width at half maximum value of 0.7°, suggesting the extremely high quality and epitaxial nature of the films. The morphology of the BFO films reveals a combination of growth mode of step flow following the underlying topography of the SRO layer and also island formation. The magnetic measurement reveals a pure linear field dependent magnetization curve, consistent with an antiferromagnetic arrangement of the Fe3+ magnetic moments and indicating the absence of ferromagnetic impurities which could form, for example, as consequence of Bi loss. The piezoelectric force microscopy measurement shows a homogenous out-of-plane piezoresponse over a large scan area with mosaic domain patterns. A clear domain switching process at the scale as small as 50 nm is demonstrated, suggesting the good ferroelectric property in the local area of the BFO films.
9:00 PM - P4.17
Growth, Characterization and Multiferroic Properties of β-SrMnO3 Epitaxial Films.
Jose Pardo 1 2 , L. Maurel 1 , E. Gallardo 1 , J. Blasco 3 4 , L. Marin 1 , I. Lucas 1 , D. Sanzol 1 , J. Ordonez 1 , C. Magen 1 4 6 , P. Algarabel 3 4 , L. Morellon 1 4
1 Instituto de Nanociencia de Aragon (INA), Universidad de Zaragoza, 50018 Zaragoza Spain, 2 Dpto. de Ciencia y Tecnologia de Materiales y Fluidos, Universidad de Zaragoza, 50018 Zaragoza Spain, 3 Instituto de Ciencia de Materiales de Aragon (ICMA), CSIC-Universidad de Zaragoza, 50009 Zaragoza Spain, 4 Dpto. de Fisica de la Materia Condensada, Universidad de Zaragoza, 50009 Zaragoza Spain, 6 Laboratorio de Microscopias Avanzadas (LMA) and Fundacion ARAID, Universidad de Zaragoza, 50018 Zaragoza Spain
Show AbstractSrMnO3 is known to present several crystal structures at room temperature [1]. The metastable, cubic perovskite form (β-SrMnO3) shows G-type antiferromagnetic ordering and paraelectric behaviour in the bulk. However, first-principles calculations [2] predict possible epitaxy-driven ferromagnetic and ferroelectric ordering for compressive or tensile strain.In this work we report on the growth of epitaxial films of β-SrMnO3 by pulsed laser deposition. Ceramic targets were prepared by solid state reaction from SrCO3 and MnO2 powders at several temperatures. Different substrates were used in order to induce varying degrees of in-plane stress. The films structure and microstructure were studied by X-ray diffraction and transmission electron microscopy. We present a systematic research on the dependence of the films stoichiometry and crystal quality on deposition temperature and oxygen pressure, film thickness and substrate lattice parameter.Zero-field cooled and field-cooled susceptibility curves measured by SQUID in optimized samples suggest a correlation between epitaxial strain and magnetic ordering. Preliminary polarization vs. electric field results will be presented.[1] T. NEGAS and R. ROTH: "The SrMnO3-x system". J. Solid State Chem. 1, 409 (1970).[2] J. H. LEE and K. M. RABE: "Epitaxial-Strain-Induced Multiferroicity in SrMnO3 from First Principles". Phys. Rev. Lett. 104, 207204 (2010).
9:00 PM - P4.18
Ferroelectricity Origin and Magnetic-Field-Induced Polarization Switching in Multiferroic TbMn2O5: A First-Principles Study.
Jung-Hoon Lee 1 , Min-Ae Oak 1 , Hyun Myung Jang 1 2
1 1Department of Materials Science and Engineering, and Division of Advanced Materials Science (AMS), Pohang University of Science and Technology (POSTECH), Pohang Korea (the Republic of), 2 Department of Physics, Pohang University of Science and Technology (POSTECH), Pohang Korea (the Republic of)
Show AbstractOrthorhombic TbMn2O5 is a well-known multiferroic manganite with its exotic property of the polarization reversal under an applied magnetic field along the a-axis of Pb21m. In spite of extensive experimental and theoretical studies on TbMn2O5 during the last decade, however, little progress has been made in our understanding of the ferroelectricity origin as well as the atomic mechanism behind the observed extraordinary polarization reversal.In order to clarify the origin of orthorhombic ferroelectricity in TbMn2O5, we have carried out first-principles density-functional theory (DFT) calculations by considering the spin-orbit interaction and by adopting a 2a × b × 3c supercell that closely imitates the ground-state incommensurate wave- vector of k = (0.48,0,0.32). Our DFT calculations predict that the ferroelectric polarization develops along the b-axis of Pb21m with its value slightly less than 150 nC/cm2. More importantly, the present calculations clarify the ferroelectricity origin that the magnetically-induced improper polarization is mainly caused by an exchange striction mechanism (S . Sj). On the contrary, the polarization driven by the spin canting between neighbouring moments, i.e., the cross product (Si × Sj), contributes only ~1.2 % to the net polarization. We have further successfully reproduced the field-induced polarization switching by adopting a spin configuration which is likely to occur under a bias magnetic field. Although the atomic displacements of Mn3+ are very small (~0.01Å), the off-centering distortion clearly switches its direction from (+) to (-) b-axis under a bias field.
9:00 PM - P4.2
Transverse Electric Field Induced Magnetization Reversal Using Multiferroics.
Morgan Trassin 1 , John Heron 1 , Khalid Ashraf 2 , Qing He 1 , Ying-Hao Chu 3 , Sayeef Salahuddin 2 , Ramamoorthy Ramesh 1
1 Department of Materials Science and Engineering, University of California, Berkeley, California, United States, 2 Department of Electrical Engineering and Computer Science, University of California, Berkeley, California, United States, 3 Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan
Show AbstractThe discovery of the electrical control of the antiferromagnetic ordering in the multiferroic magnetoelectric bismuth ferrite (BiFeO3)[1] drew an increasing interest in the pursuit for low energy consumption data storage devices in the form of non-volatile magnetic bits that are switched by an electrical field[2]. In this magnetoelectric system using planar electric field, a magnetization reversal can be achieved.We report the magneto-transport evidence of a ferromagnetic CoFe layer in-plane magnetization reversal induced solely by an out of plane voltage applied to the multiferroic BiFeO3 film at room temperature using Pt / CoFe / BiFeO3(001) / SrRuO3(001) / DyScO3(110) heterostructures. The presence of an ultra thin conducting SrRuO3 bottom electrode allows ferroelectric characterization of the films and the in situ application of the out of plane voltage in the anisotropic magnetoresistance measurement architecture. The correlation between the ferroelectric state in the multiferroic layer and the CoFe ferromagnetic order is evidenced. The nature of the specific ferroelectric switching events induced by out of plane electric fields, resulting in the magnetization reversal will be discussed. The transverse configuration allows a reduction of the switching voltage as well as increases the device density since no in-plane electrodes are needed. References:1. T. Zhao et al. Nature Materials. 5, 823–829 (2006)2. Manuel Bibes and Agnès Barthélémy Nature Materials 7, 425 - 426 (2008)
9:00 PM - P4.20
Electronic Structure Calculations of CuCl2 Using First Principles DFT Method.
Kanagaraj Chinnadurai 1 , Baskaran Natesan 1
1 Physics, National Institute of Technology, Tiruchirappalli India
Show Abstract Recent experimental investigations revealing the multiferroic nature of CuCl2 system has motivated us to carry out detailed first principles electronic structure studies on this system. CuCl2 crystallizes in monoclinic structure and undergoes AFM ordering below 24 K. The first principles calculations were done using plane wave pseudo potential (PWPP) and linear muffin tin orbital (LMTO) implementation of DFT using 4x4x4 monkhorst grid in the frame work of generalized gradient approximations (GGA). Initially, the lattice constants and the atomic positions were optimized by minimizing the total energy of the system. The optimized cell constants and the atomic positions were then used to calculate the band structure, density of states and Born effective charges of different magnetic structures of CuCl2. Our total energy calculations carried out on different magnetic structures confirms that the AFM is a stable magnetic ground state of CuCl2, well in agreement with earlier reports. The band structure and density of states results reveal that both AFM and FM structure of CuCl2 exhibits a gap at the Fermi level indicating that the system is an insulator. A well separated half-filled anti bonding bands observed between 0.8 and 1.7eV with a width of 0.9eV originate from Cu-Cl pdsigma states of CuCl2. The exchange coupling constants for different magnetic structures are being carried out. Based on these results, the origin for the stability of AFM structure and the polarization resulting from the long range AFM ordering in CuCl2 will be discussed.
9:00 PM - P4.21
First Principles Study of Hexagonal and Orthorhombic YMnO3.
Sathya Sheela Subramanian 1 , Baskaran Natesan 1
1 Physics, National Institute of Technology, Tiruchirappalli India
Show Abstract Rare-earth manganites (RMnO3, R = Y - Lu) have attracted intense research interest in recent years, due to their various technological applications. In these family of manganites, YMnO3 is a unique geometrically frustrated multiferroic compound, which exists in hexagonal and orthorhombic phases, under different conditions. YMnO3 is a widely studied, because of its unusual structures and the possibility that both phases of YMnO3 can exhibit multiferroic properties. However, the origin for the coupling of magneto-electric ordering in YMnO3 is still not understood completely. In this work, we propose to carry out detailed electronic structure calculations of both these phases with different magnetic ordering, using plane wave pseudo potential (PWPP) and local muffin tin orbital (LMTO) implementations of density functional theory (DFT), in order to understand the structure and the origin of magneto-electric coupling in YMnO3. The lattice constants and atomic positions for both phases were optimized by minimizing the total energy of the respective phases. The spin polarized calculations were done by initializing different spins on neighbouring magnetic ions. For non magnetic case, we initialize zero spin on Mn ions. The AFM spin ordering was initialized by doubling the unit cell along c-axis (111) direction. The electronic band structure, density of states and the ionic polarization were calculated for different magnetic ordering of both phases. Similar calculations for cubic YMnO3 is also been carried our for comparison. The nature and the origin for the coupling of magneto-electric ordering in both phases of YMnO3 are analysed and the results will be discussed.
9:00 PM - P4.24
Domain Walls in Orthorhombic TbMnO3 Thin Films.
Saeedeh Farokhipoor 1 , Christophe Daumont 1 , Beatriz Noheda 1
1 , Zernike Institute for Advanced Materials, Groningen Netherlands
Show AbstractIn bulk orthorhombic TbMnO3 below 28K, the competition between nearest neighbor and next-nearest neighbor magnetic interactions leads to a spin cycloidal structure of the Mn sublattice. The magnetic cycloid breaks the inversion symmetry, allowing for a macroscopic electrical polarization[1],[2]. The magnetoelectric coupling is thus very strong in this material. Moreover, an intermediate sinusoidal antiferromagnetic phase exists between 28K and the Neel temperature of 42K. The magnetic moment of Tb orders at 7K but is less important for the appearance of the electrical polarization and magnetoelectric coupling. We have grown thin layers of TbMnO3 by pulsed laser deposition on (001)-oriented SrTiO3 substrates. Interestingly, unlike the bulk materials, the thin films display, below the Neel temperature, a net magnetic moment[3] with increasing magnitude as the thickness decreases[4]. A recent work reports that spin canting due to strain is responsible for the observed magnetic moment [5]. In a previous study we have shown that the films grown on (001)-SrTiO3 are (001)-oriented and form in-plane crystallographic domains with the density of domain walls increasing with decreasing thickness[6]. Thus, the thinner the films, the more evident the domain wall character should appear. This is important because 1) symmetry breaking takes place at domain walls and allows for the appearance of physical responses distinct from those in the domains; 2) huge stress values are able to concentrate at crystallographic domain walls, locally modifying the film properties. In addition, the long range spin spiral ordering is destroyed by the domain micro-structure, which will also affect the overall response of the films. By a combined magnetic, electrical and microscopic analysis we investigate the character and possible functionality of domain walls in TbMnO3. [1] M. Kenzelmann et al., Phys. Rev. Lett. 95 , 087206 (2005).[2] M. Mostovoy, Phys. Rev. Lett. 96 , 067601 (2006).[3] D. Rubi et al. Phys. Rev. B 79 , 014416 (2009).[4] C.J.M. Daumont et al., arXiv:1008.0315v3.[5] X. Marti et al Appl. Phys. Lett. 96 , 222505 (2010).[6] C.J.M. Daumont et al., Phys. Condens. Mat. 18 , 182001 (2009).
9:00 PM - P4.26
Chiral Order of Ferroelectric Domains in Multiferroic RMnO3
Keisuke Kobayashi 1 , Tsukasa Koyama 1 , Shigeo Mori 1 , Yoichi Horibe 2 , Sang-wook Cheong 2
1 , Osaka Prefecture University, Sakai Japan, 2 , Rutgers University, Piscataway, New Jersey, United States
Show Abstract
Recently it is revealed that RMnO3 (R=Y, Yb, Ho, Lu) with hexagonal structure exhibit some unconventional physical properties due to intricate coupling among structural Mn trimerization, ferroelectricity, magnetism and charge conduction [1]. These properties have strong connection with the characteristic ferroelectric (FE) and structural antiphase domain configuration, which is referred to as a cloverleaf pattern [1].
In this work, we prepared single crystals of both hexagonal RMnO3 (R=Y, Yb, Ho, Lu) and Ti-doped YMnO3 (YMn1-xTixO3) by Floating Zone method and carefully examined structural features of the cloverleaf FE domain configuration in hexagonal RMnO3 by the transmission electron microscopy (TEM). The cloverleaf patterns of six domains emerging from one point can be seen in the FE phase of hexagonal RMnO3 (R=Y, Yb, Ho, Lu), which implies that the cloverleaf FE patterns are inherent to the FE phase in hexagonal RMnO3. Since the cloverleaf FE domains are compromised by combination of two different polarization orientations along the [001] direction and structural antiphase domains due to the Mn trimerization, 180° FE domains along the [001] direction are possibly formed. Our high-resolution TEM experiments revealed the presence of the 180° FE domains due to the two different polarization orientations along the [001] direction in the (110) plane. However, since the formation of the 180° FE domains along the [001] direction is energetically unstable, the antiphase boundaries tend to arrange in a line elongating along the [001] direction. To clarify the stability of the cloverleaf patterns of YMnO3 against the impurity doping, we examined changes of the FE domain configuration by partial substitution of Ti for Mn. In YMn0.95Ti0.05O3, FE cloverleaf domain configuration remains intact and with increasing the Ti concentration up to x=0.2, the FE cloverleaf domains changed into FE nanodomains with ~20 nm size.
This work was partially supported by a Grant-in-Aid for Scientific Research on Priority Areas “Novel States of Matter Induced by Frustration” (No.19052002) from the MEXT in Japan.
[1] T. Choi et al., Nature Mater. 9 253-258(2010)
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Fabrication of Multiferroic RMnO3 and RMn2O5 by Containerless Processing.
Vijaya Kumar Malahalli 1 , Jianding Yu 1 , Kazuhiko Kuribayashi 1 , Shinichi Yoda 1
1 Department of Microgravity Sciences, Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), Sagamihara Japan
Show AbstractRecently, rare-earth manganites have attracted great interest towards their wide applications in the field of electronic industry. Among the manganites, new multiferroic hexagonal phases with a space group of P63cm are technologically important materials because of multiferroic characteristics, i.e., the coexistence of ferroelectricity and magnetism in one compound. In the present study, containerless solidification of the RMnO3 and RMn2O5 melts were carried out to fabricate multiferroics under the controlled Po2. Containerless processing is a promising technique to explore the new materials using rapid solidification of an undercooled melt because it provides large undercooling prior to nucleation. In order to undercool the melt deeply below the melting temperature, under a precisely controlled oxygen partial pressure, an aerodynamic levitator (ADL) combined with ZrO2 oxygen sensor was designed. A spherical sample was levitated and completely melted by a CO2 laser in an atmosphere with predetermined Po2. The samples were levitated and completely melted and solidified by cutting off the CO2 laser. The surface temperature and an in-situ observation of the solidification behavior was monitored using two-color pyrometer and color high speed video camera (HSV), respectively. X-ray diffractometry and scanning electron microscopy results showed the existence of single multiferroic phases. Thermodynamic stabilities of the as-solidified phases were studied up to 1673 K using TG/DTA. As a result no change in the crystal structure was observed even after cooling down to room temperature. The ferroelectric and ferromagnetic measurements were carried out with an impedance analyzer from 5 to 300 K over a frequency range of 100 Hz to 1 MHz. A characteristic dielectric peak was observed between 70-130 K for RMnO3 and 30-40 K for RMn2O5. These results suggest that the synthesized sample belongs to the group of multiferroics.
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Atomic Layer Control of Magnetism and Conductivity in Thin Film Manganites.
Matthew Marshall 1 , Jarrett Moyer 1 , Fred Walker 1 , Charles Ahn 1
1 CRISP, Dept. Applied Physics, Yale University, New Haven, Connecticut, United States
Show AbstractMultiferroic oxide heterostructures of PbZr0.2Ti0.8O3/La0.8Sr0.2MnO3/SrTiO3 (PZT/LSMO/STO) have been shown to undergo a large charge-driven magnetoelectric coupling. In this system, switching the polarization of PZT causes a spin and charge reconstruction in the top atomic layer of LSMO. The top unit cell of LSMO undergoes a transformation from ferromagnetic to antiferromagnetic ordering, with an accompanying large change in the magnetic moment and in-plane conductivity [1]. One way to enhance the magnetic switching and conductivity change for the heterostructures is to replace a portion of the LSMO thin film with LaMnO3, which is insulating and antiferromagnetic in the bulk. We have used oxide molecular beam epitaxy (MBE) to grow epitaxial thin films of LaMnO3(001) and La0.8Sr0.2MnO3/LaMnO3 heterostructures on SrTiO3(001) with atomic layer control. Thin films of LaMnO3 alone are found to be ferromagnetic [2] and undergo a spin glass transition. Heterostructures of LSMO/LMO grown on SrTiO3(001) show evidence of a first order transition in the magnetization. Optimization of the ferromagnetic layer can lead to improved electrical switching properties and an enhanced magnetoelectric coupling effect.References:[1] CAF Vaz, et al. Phys. Rev. Lett. 104, 127202 (2010); doi:10.1103/PhysRevLett.104.127202[2] CAF Vaz, et al. J. Appl. Phys. 109, 07D905 (2011); doi:10.1063/1.3540694
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Metal to Insulator Transition in Ultrathin La0.67Sr0.33MnO3 Films.
Arturas Vailionis 1 , Hans Boschker 2 , Jaap Kautz 2 , Evert Houwman 2 , Mark Huijben 2 , Gertjan Koster 2 , Dave Blank 2 , Guus Rijnders 2
1 Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California, United States, 2 MESA+ Institute for Nanotechnology, University of Twente, Enschede Netherlands
Show AbstractStrained La1-xSrxMnO3 (LSMO) films exhibit rich variety of electronic and magnetic phenomena that are closely coupled to lattice distortions. Among many structural degrees of freedom MnO6 octahedral distortions represent an important tuning mechanism of the physical properties in LSMO thin films [1]. Here we demonstrate that electric and magnetic properties of LSMO (x = 0.33) thin films are strongly coupled to the MnO6 octahedral rotations. The specific pattern of octahedral rotations that controls properties of the grown layer depends not only on overall strain in the film but also on BO6 rotation pattern of the perovskite substrate at the interface. For ultrathin layers the coupling of octahedral rotations at the film-substrate interface might become dominant and such films might reveal properties that are not observed in thicker films. We show that the conducting LSMO films grown on STO(110) become insulating as film thickness is reduced below 10 unit cells [2]. X-ray diffraction data show that, as films get thinner and reach 10 uc, the unit cell symmetry increases from monoclinic to orthorhombic. The symmetry change alters octahedral distortions at the interface which originate from dissimilar BO6 rotational patterns between the substrate and the coherently grown layer. We believe that insulating phase of LSMO films is related to the stabilization of static Jahn-Teller distortions due to the symmetry mismatch between substrate and the layer.
[1] A. Vailionis, et al., Phys. Rev. B 83, 064101 (2011).
[2] H. Boschker, et al., (submitted).
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Multiferroic Properties and Microstructures in BiFeO3-BaTiO3.
Tomoatsu Ozaki 1 , Shigeo Mori 1 , Yoichi Horibe 2
1 Materials Science, Osaka Prefecture University, Sakai Japan, 2 Rutgers Center for Emergent Materials and Department of Physics & Astronomy, Rutgers University, Piscataway, New Jersey, United States
Show AbstractBiFeO3 is one of typical multiferroic materials, in which magnetic and ferroelectric orderings coexist. BiFeO3 exhibits a ferroelectric phase transition at TC~1110K and subsequently an anti-ferromagnetic transition occurs at TN~650K [1]. We have reported in (1-x)BiFeO3-xBaTiO3 bulk samples that structural changes from the rhombohedral structure to the cubic one occured around the BaTiO3 concentration (x) of x=0.33. In addition, anomalies in dielectric and magnetic susceptibilities were found around x=0.33 [2,3]. Recently neutron diffration experiment, combined with the magnetic measurement, revealed that the size of magnetic domains is almost identical to the size of polar nanoregions (PNR) in (1-x)BiFeO3-xBaTiO3 with x~0.33 [4]. This implies that this compound has both polar and magnetic nanodomains in single phase, which should be referred to as multiferroic relaxor. In this work, we carefully investgated dielectric/magnetic properties and related microstructures in (1-x)BiFeO3- xBaTiO3 mainly by a Lorentz-type transmission electron microscopy (TEM) experiment, in combination with conventional dielectric and magnetic measurements. Temperature dependence of the relative dielectric permittivity in the x=0.33 compound, which sits on the structural phase boundary region, was investigated. Dielectric dispersion over a wide temperature range was found, which is similar to that in relaxor ferroelectric materials such as Pb(Mg1/3Nb2/3)O3. This indicates that there exist polar nano regions in the x=0.33 compound. On the other hand, field-cooled M-H hysteresis curves in the x=0.33 compound at 2 K. Asymmetric hysteresis curves under the applied magnetic fields of 500 and 1000 Oe were found at 2 K. These asymmetric hysteresis curves should stem from the existence of spin clusters, which should be characterized as the micto magnetism found in Au-Fe alloys. These dielectric and magnetic measurements suggested that the polar nanoregions coexist with the magnetic nanoregions in the structural phase boundary regions of (1-x)BiFeO3-xBaTiO3 around x~0.33. [1] T. Zhao et al., Nat. Mater. 5,823(2007). [2] T. Ozaki et al., Ferroelectrics 385, 155 (2009). [3] S. Kitagawa et al., Transactions of MRS-J 33(1), 27(2008). [4] M. Soda et al., JPSJ.
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Switchable Induced Polarization in LaAlO3/SrTiO3 Heterostructures.
Chung Wung Bark 1 , P. Sharma 3 , Seung Hyub Baek 1 , Sanghan Lee 1 , Sangwoo Ryu 1 , Chad Folkman 1 , A. Kumar 3 , Sergei Kalinin 3 , Evgeny Tsymbal 4 , Mark Rzchowski 2 , Alexei Gruverman 4 , Chang-Beom Eom 1
1 Department of Materials Science and Engineering, Univ Wisconsin-Madison, Madison, Wisconsin, United States, 3 Physics, University of Wisconsin-Madison, Madison, Wisconsin, United States, 4 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Physics and Astronomy, University of Nebraska, Lincoln, Nebraska, United States
Show Abstract Demonstration of a tunable conducting layer at the LAO/STO interfaces drew significant attention to the development of oxide electronic structures where electronic confinement can be reduced to the nanometer range. Specifically, scanning probe microscopy (SPM) studies allowed controllable change of interface conductivity at the nanoscale using the electrically biased SPM probe. While the mechanisms for the conductivity modulation are quite different and include metal-insulator phase transition and surface charge writing, in both cases it is implied that this effect is a result of electrical modification of the LaAlO3 surface (either due to electrochemical dissociation of surface adsorbates or free charge deposition) leading to the change in the two-dimensional electron gas (2DEG) density at the LaAlO3/SrTiO3 (LAO/STO) interface. Using a combination of piezoresponse force microscopy (PFM) and electrostatic force microscopy (EFM) we demonstrate a switchable electromechanical response of the LAO overlayer, which we attribute to the motion of oxygen vacancies through the LAO layer thickness. These electrically-induced reversible changes in bulk stoichiometry of the LAO layer is a signature of a possible alternative mechanism for nanoscale oxide 2DEG control on LAO/STO interfaces.
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Highly Spin-Polarized Conducting State at the Interface between Non-Magnetic Band Insulators: LaAlO3/FeS2 (001).
John Burton 1 , Evgeny Tsymbal 1
1 Physics and Astronomy, University of Nebraska Lincoln, Lincoln, Nebraska, United States
Show AbstractInterface engineering of complex oxide heterostructures allows creating interfaces with properties and functionalities distinct from those typical for the respective bulk constituents. In the spirit of the well known conducting LaAlO3/SrTiO3 interface we study a similar interface with the added functionality of being unambiguously ferromagnetic. Our first-principles density functional calculations demonstrate that such a spin-polarized two-dimensional conducting state can be realized at the (001) interface between the two non-magnetic band insulators FeS2 and LaAlO3. The (001) surface of FeS2(pyrite), a diamagnetic insulator, supports a localized surface state deriving from the Fe d-orbitals near the conduction band minimum. We find that, similar to the LaAlO3/SrTiO3 system, the deposition of a few unit cells of the polar perovskite oxide LaAlO3 leads to electron transfer into these surface bands, thereby creating a conducting interface. The occupation of these narrow bands leads to an exchange splitting between the spin sub-bands, yielding a highly spin-polarized conducting state quite distinct from the rest of the non-magnetic, insulating bulk. We show that the ferromagnetism in the occupied surface bands is consistent with the Stoner model for itinerant magnetism. Such an interface supporting a spin-polarized two-dimensional electron gas presents intriguing possibilities for spintronics applications.
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Exchange-Bias in LaNiO3 /LaMnO3 Superlattices.
Marta Gibert 1 , Raoul Scherwitzl 1 , Pavlo Zubko 1 , Jorge Iniguez 2 , Jean-Marc Triscone 1
1 , University of Geneva, Genève Switzerland, 2 , ICMAB-CSIC, Bellaterra Spain
Show AbstractTransition-metal based oxides display a wide range of physical properties triggered by complex interactions between their spin, charge, orbital and lattice degrees of freedom. The combination of these materials in artificially layered structures enables not only further tuning of their already outstanding properties, but also gives access to hidden phases and emergent physical phenomena. Here, we present high crystalline quality LaNiO3 /LaMnO3 (LNO/LMO) superlattices grown on (111)-oriented SrTiO3 substrates. LNO is the only member of the perovskite nickelate family lacking any magnetic order in its bulk form, whereas LMO is antiferromagnetic in bulk, but is found to be ferromagnetic when grown as a thin film. The LNO/LMO superlattices investigated here exhibit ferromagnetic behavior below 200K, with a temperature-dependence of the magnetization very similar to that of the LMO thin films. However, at lower temperatures, the magnetization loops become asymmetric indicating that exchange bias (EB) develops in this regime. Such biasing is a signature of the emergence of two interface-driven features in the system. First, there is a strong interfacial coupling between LNO and LMO layers. We show that both experimental and theoretical analyses support ferromagnetic exchange between the Mn and Ni cations at the interface and that the (111)-orientation seems key to the enhancement of these interactions. Second, magnetic order is induced within the paramagnetic material (LNO) when embedded between ferromagnetic LMO layers. A lower temperature limit for the onset of magnetism in LNO is extracted from the EB blocking temperature around 20-25K. First-principles calculations point towards a spin-density wave as the most plausible type of magnetic order induced in the LNO layers. Other possible magnetic scenarios will also be explored.
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Magnetoelectric Transport Properties of Multiferroic Tunnel Junctions.
Dong Jik Kim 1 , H. Lu 1 , A. Stamm 1 , X. Liu 1 , J. Burton 1 , Chung Wung Bark 2 , Chang Beom Eom 2 , E. Tsymbal 1 , A. Gruverman 1
1 Department of Physics & Astronomy, University of Nebraska - Lincoln, Lincoln, Nebraska, United States, 2 Department of Material Science & Engineering, University of Wisconsin - Madison, Madison, Wisconsin, United States
Show AbstractPolarization-dependent resistance switching - tunnel electroresistance (TER) effect – in ferroelectric tunnel junctions (FTJs) is considered as a basis for the next-generation nonvolatile memory technology. In FTJ, a writing pulse aligns the polarization and subsequent current-voltage (I-V) measurements detect high or low resistance states depending on the writing pulse polarity. We investigated the properties of FTJ in Au/Co/BaTiO3/La2/3Sr1/3MnO3 junctions grown on NdGaO3 single-crystal substrates, which have 6 and 12 monolayers (MLs) of BaTiO3 (BTO). Prior to TER, we confirmed the ferroelectricity of the junctions via piezoelectric hysteresis loop measurements. We observed more than 5 × 104 % and 1 × 103 % of TER values in 6 MLs and 12 MLs BTO junctions, respectively. The tunneling current at ON state showed a remarkable writing pulse dependence as a longer pulse with higher voltage gave a higher tunneling current. However, the tunneling current at OFF state showed no change with different writing pulses. We measured I-V curves with different delay times after the writing pulse. The tunneling current at ON state decayed with time and the difference between ON and OFF states vanished within several seconds. Temperature dependence of the ON/OFF resistance states had been measured in the range from RT up to 150 °C. It is assumed that in our system, asymmetry of Co/BTO and BTO/La2/3Sr1/3MnO3 interfaces might play an important role. Additionally, tunneling magnetoresistance (TMR) effect had been demonstrated at room temperature in the same heterostructures. It is shown that the main problem faced by the multiferroic tunnel junctions is the stability of polarization in ferroelectric tunnel barrier.
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Development of Multiferroic Tunnel Junctions: Structure, Magnetic and Transport Properties of Ferromagnetic/Ferroelectric Multilayers.
Laura Steren 1 2 , Luis Aviles Felix 3 2 , Santiago Carreira 1 8 , Federico Fernandez Baldis 3 2 , Enrique Kaul 3 2 , Martin Sirena 3 2 , Jerome Lesueur 5 , Nicolas Bergeal 5 , Rozen Bernard 6 7 , Javier Briatico 6 7 , Giancarlo Faini 4 , Javier Villegas 6 7
1 Condensed Matter, Centro Atomico Constituyentes, San Martin Argentina, 2 , CONICET, Buenos Aires Argentina, 3 , Centro Atómico Bariloche & Instituto Balseiro, Bariloche Argentina, 8 , Universidad de Buenos Aires, Buenos Aires Argentina, 5 Physique Quantique, UPR5-LPEM-CNRS, ESPCI, Paris France, 6 , Unité Mixte de Physique CNRS/Thales, Palaiseau France, 7 , Université Paris Sud 11, Orsay France, 4 , Laboratoire de Photonique et Nanostructures, CNRS, Marcoussis France
Show AbstractFerromagnetic/ferroelectric (FM/FE) bilayers, trilayers and superlattices were grown by DC sputtering. X-ray diffraction indicates that the samples present a textured growth with the c axis perpendicular to the substrate. Magnetization measurements show that the ferromagnetic layers are weakly coupled, probably due to magnetostatic interactions. A phenomenological approach is proposed to analyze the electrical transport in the FM/FE bilayer systems, measured by conductive atomic force microscopy. The influence of the substrate in the electrical properties of the bilayers was studied in the frame of this model. Substrate roughness was found to increase the barrier height distribution and increase the attenuation length in the material, reducing the barrier quality. Lithography based microtemplates were developed for the fabrication of multifferoic tunnel junctions.
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E-Field Control of Exchange Coupling and Deterministic Magnetization Switching in AFM/FM/FE Multiferroic Heterostructures.
Ming Liu 1 2 , Jing Lou 1 , Shandong Li 1 , Nian Sun 1
1 Electrical and Computer Engineering , Northeastern University, Boston, Massachusetts, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractIn the past decade, the ever-increasing demand for faster, smaller and ultra-low power electronics for both information processing and data storage has propelled the exploration of controlling magnetic states by using an electric field (E-field) instead of a magnetic field.(1) Multiferroic materials, which simultaneously exhibit ferroelectricity and ferromagnetism, could provide such capability of electric manipulating magnetisim through magnetoelectric (ME) coupling and realize magnetoelectric random access memories (MERAMs).(2,3,4) However, It has been challenging to achieve 180 degeree deterministic switching of magnetization by E-field, which is crucial for MERAMs. Here we demonstrate E-field tunable exchange coupling and near 180 degree deterministic switching of magnetization at room temperature in novel antiferromagnetic/ferromagnetic /Ferroelectric (AFM/FM/FE) hetoerstructure of FeMn/FeGaB/PZN-PT (lead zinc niobate – lead titanate) through the competition between the E-field induced uniaxial anisotropy and unidirectional anisotropy. The FeMn/FeGaB film was deposited under an in-situ magnetic bias field, which led to an in-plane magnetic easy axis either alone [100] (d31) or [011] (d32) of PZN-PT. E-field dependence of magnetic hysteresis loops for both configurations were achieved, indicating a giant E-field induced effective magnetic anisotropy. Angular dependence of exchange-bias field under various electric fields showed an dramatic E-field induced exchange-bias field shift, which is up to (ΔHex)/Hex =218%. The E-field switching of magnetization in time domain was demonstrated, showing a near 180 degree deterministic magnetization switching by reducing E-field. This E-field control exchange bias and realization of near 180 degree dynamic magnetization switching at room temperature in AFM/FM/FE mulitferroic heterostructures constitute one important step toward MERAMs and all sorts of energy efficiency magnetic devices.Reference1. C. W. Nan, M. I. Bichurin, S. X. Dong, D. Viehland, G. Srinivasan, J Appl Phys 2008, 1032. X. He, Y. Wang, N. Wu, A. N. Caruso, E. Vescovo, K. D. Belashchenko, P. A. Dowben, C. Binek, Nature Materials 2010, 9, 5793. M. Liu, O. Obi, J. Lou, Y. J. Chen, Z. H. Cai, S. Stoute, M. Espanol, M. Lew, X. Situ, K. S. Ziemer, V. G. Harris, N. X. Sun, Adv Funct Mater 2009, 19, 18264. J. Lou, M. Liu, D. Reed, Y. H. Ren, N. X. Sun, Adv Mater 2009, 21, 4711
9:00 PM - P4.37
Large Magnetoelectric Coupling Effect at Ni0.65Zn0.35Fe2-xAlxO4/PZT(Lead Zirconate Titanate) Multiferroic Heterostructures.
Ming Li 1 , Ziyao Zhou 1 , Jing Lou 1 , Ming Liu 1 , Nian Sun 1
1 Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts, United States
Show AbstractFerrites with low saturation magnetic moment, narrow ferromagnetic resonance (FMR) linewidth and large magnetostriction effect are urgently needed for electrostatically tunable microwave and radio frequency devices. In this paper, Aluminum substituted NiZn ferrites (Ni0.65Zn0.35Fe2-xAlxO4, x=0, 0.1,0.2, 0.3, 0.4, 0.6, 0.8, and 1) were fabricated by sintering process and characterized. The hysteresis loop obtained by vibrating sample magnetometer (VSM) indicated that the saturation magnetic moment of these spinel ferrites went down rapidly as the doping Aluminum proportion went up. The FMR linewidth became narrow as higher proportion of Aluminum was doped. Magnetostriction measurements were also performed and showed that magnetostriction effect became weaker when Aluminum substituted more iron in the ferrites. Measurements showed that NiZn ferrites with large magnetostriction and low FMR linewith (340Oe) were obtained. Magnetoelectric (ME) coupling was successfully demonstrated in the Ni0.65Zn0.35Fe2-xAlxO4/PZT(Lead zirconate titanate) multiferroic heterostructures. A large electrostatically tunable FMR field shift up to 40 Oe was observed for this spinel and piezoelectric multilayer structure bonded by polymer binders. These results provide great opportunity for the electrical tuning microwave devices.
9:00 PM - P4.38
Interfacial Layer Growth Condition Dependent Electrical Conduction in HfO2/SiO2 Heterostructured Thin Films.
Santosh Sahoo 1 , D. Misra 1
1 Electrical and Computer Engineering, New Jersey Inst. of Technology, Newark, New Jersey, United States
Show AbstractRecently, high K materials play an important role in microelectronic devices such as capacitors, memory devices, and microwave devices. Now a days HfO2 appears promising due to its high dielectric constant, large band gap and compatible with the conventional CMOS process. Heterostructured thin films have taken more interest because of its low leakage current compared to single layer films. In this work the effect of growth condition of SiO2 interfacial layer on the electrical conduction process of HfO2/SiO2 heterostructured film is studied. The HfO2 film is deposited on SiO2 interfacial layer by ALD process. It is observed that Poole-Frenkel conduction is the dominant leakage mechanism in the high field region whereas Ohmic conduction is dominant in the low field region for both ISSG and chemically grown SiO2 heterostructured films. Also it is observed that the growth condition affects the trap level energy and activation energy for Poole-Frenkel and Ohmic condction processes respectively.
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Selective Growth of ZnO Nanorods for PZT Nanorods Device Applications.
Masaru Shimizu 1 , Yasunori Imi 1 , Hironori Fujisawa 1 , Seiji Nakashima 1 , Yasutake Kotaka 2 , Koichiro Honda 2
1 , University of Hyogo, Himeji Japan, 2 , Fujitsu Lab. Ltd., Atsugi Japan
Show AbstractInterest in the ferroelectric nanorods, nanowires, and nanotubes has increased greatly from the view point not only their unique physical properties but also potential applications. Most commonly, solution-phase decomposition process, sol-gel process and hydrothermal method were employed to synthesis of ferroelectric nanowires, nanorods and nanotubes. We have already reported the synthesis of PbTiO3 and PZT nanorods and nanotubes by MOCVD using a ZnO nanorod positive template. PbTiO3/ZnO and PZT/ZnO core-shell heterostructured nanorods were successfully fabricated.However, it is important to have good control of the spatial arrangement and properties of nanorod arrays for the realization of future nanodevices such as 3D nanorod-stack capacitors and ferroelectric surrounded gate transistors. In this study, we demonstrate selective growth of ZnO nanorods for ferroelectric PbTiO3 and PZT nanorod device applications.In the first stage of our experiments, ZnO nanorods with a high aspect ratio were prepared on SiO2/Si and Pt/SiO2/Si substrates by MOCVD using Zn(C2H5)2 as a Zn precursor and oxygen as an oxidizing gas. VS (Vapor-Solid) growth process was used. In the next stage, PbTiO3 and PZT were deposited on ZnO nanowire positive template at around 550oC by MOCVD. PbTiO3/ZnO and PZT/ZnO core-shell heterostructured nanorods were successfully fabricated.When growth conditions of ZnO were optimized (reaction pressure : 1-4 Torr., substrate temperature : 550-700oC), ZnO nanorods were selectively grown on patterned Pt on SiO2/Si. On Pt/SiO2 holes on Si substrate, ZnO was also grown selectively. PZT/ZnO nanorods were also fabricted on Pt.
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Polarization Vortices, Dielectric Response, Order Parameters and Phase Transitions in PbTiO3 Nanowires from First Principles.
Ghanshyam Pilania 1 , R. Ramprasad 1
1 Materials Science, University of Connecticut, Storrs, Connecticut, United States
Show AbstractRecent experiments and simulations based on parameterized effective Hamiltonians have contributed to the mounting evidence for the presence of dielectric ferrotoroidic domains in ferroelectric nanostructures [1-3]. Dielectric ferrotoroidic domains are characterized by non-rectilinear arrangements of the electric dipole polarization vectors in vortex form such that their toroidal moment is the order parameter (rather than the polarization itself). Here, for the first time using parameter-free density functional theory (DFT) computations, we demonstrate the existence of a spontaneous toroidal moment of polarization in ultrathin PbTiO3 [001] nanowires [4]. We present the evolution of the polarization vortices with nanowire size, axial strain and electric field. Combined with the axial rectilinear polarization of the PbTiO3 nanowires (possible under strained states), the ferrotoroidic properties could be of practical interest for ternary logic applications.Our computations involve relaxed as well as axially strained free-standing nanowires with varying sidewall terminations (either PbO- or TiO2-terminated) and diameters. For the TiO2-terminated nanowires above a critical diameter of 16 Å, we predict the spontaneous appearance of polarization vortices. On the other hand, the stress-free PbO-terminated nanowires display purely rectilinear axial polarization at all sizes. More interestingly, we find the existence of novel stress-induced phase transitions between the mutually exclusive unconventional-vortex and conventional-axial polarization states in both the PbO- and TiO2-terminated nanowires. In general, our results indicate that axial compression always favors the ferrotoroidic ground state while the tensile stress along the nanowire axis tends to stabilize the rectilinear polarization with vanishing toroidal moment. We further confirm the validity of these results through normal mode frequency/eigenvector analysis. To probe the effect of such unconventional polarization states on the dielectric response of the ferroelectric nanowires, we used density functional perturbation theory to calculate the dielectric susceptibility tensor for both the (4x4)-PbO- and (4x4)-TiO2-terminated nanowires. Our results revealed an enhancement in both electronic and ionic contributions to the dielectric constant of the nanowires as compared to the bulk. Moreover, the total dielectric constant was found to be significantly high in the nanowires with the vortex polarization states as compared to those with the axial polarization state indicating that exotic unconventional polarization states can significantly improve the dielectric properties of ferroelectric nanostructures.[1] I. Naumov, L. Bellaiche, and H. Fu, Nature (London) 432, 737 (2004).[2] A. Gruverman et al. Phys.: Condens. Matter 20, 342201 (2008).[3] P. Aguado-Puente and J. Junquera, Phys. Rev. Lett. 100, 177601 (2008).[4] G. Pilania and R. Ramprasad, Phys. Rev. B 82, 155442 (2010).
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Complex Polarization Ordering at Twist Boundaries in Ferroelectric PbTiO3: First-Principles Simulations.
Xiaoyuan Wang 1 , Takahiro Shimada 1 , Takayuki Kitamura 1
1 Department of Mechanical Engineering and Science, Kyoto University, Kyoto Japan
Show AbstractBased on the first-principles density-functional theory calculations within the local density approximation, we investigated the ferroelectricity as well as the atomic and electronic structures at Σ5(001) twist boundaries in PbTiO3. The twist boundary structure with the coincidence site lattice (CSL) was found to be energetically favorable. We found the coexistence of both the rectilinear polarization and the vortex in-plane polarization at the twist boundary. The rectilinear spontaneous polarization in the normal to the boundary direction is highly enhanced due to the locally strengthened covalent Pb-O bond, which predominates ferroelectricity in PbTiO3. The vortex in-plane polarization is induced by rotational in-plane displacement resulting from the twisted misorientation of lattices. An applied tensile strain tends to increase the rectilinear polarization, especially at the twist boundary. The vortex polarization on the PbO layer is also enhanced with the increase of tensile strain, whereas the vortex polarization on the TiO2 layer decreases and finally disappears at a critical strain.
9:00 PM - P4.42
Improper Ferroelectricity in Ultrathin PbTiO3 Nanotubes.
Takahiro Shimada 1 , Xiaoyuan Wang 1 , Takayuki Kitamura 1
1 Department of Mechanical Engineering and Science, Kyoto University, Kyoto Japan
Show AbstractWe simulate from first-principles the energetic, structural, and electronic properties of ferroelectric PbTiO3 ultrathin nanotubes. The ferroelectric (FE) state with the spontaneous polarization along the tube axis can be stabilized in the ultrathin nanotube with only the single-unit-cell wall-thickness, which is below the limit of the ultrathin films. Emergence of anti-ferrodistortive (AFD) instability (a periodic tilting of the oxygen octahedra) is found in the nanotube and stabilizes the ferroelectric distortions as well as the tubular structure, indicating the improper ferroelectricity. The tensile strain along the axial direction enhances the ferreoelectric distortions incorporated with the AFD displacement. On the other hand, under compression, the spontaneous polarization changes from the axial to the circumferential direction to form the vortex state. Moreover, the nanotubes exhibit the wider bang-gap energy with respect to that of the bulk, thus has a strong resistivity to the current-leakage. These exotic properties suggest the possibility for the promising new-class of ferroelectric devices.
9:00 PM - P4.43
Photoluminescence and Ferroelectric Properties of Pr3+-doped (1-x)K0.5Bi0.5TiO3-xNa0.5Bi0.5TiO3 Ferroelectric Thin Films.
Hong Zhou 1 , Ni Qin 1 , Dinghua Bao 1
1 State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou, Guangdong, China
Show AbstractStructural, photoluminescence, dielectric and ferroelectric properties of lead-free perovskite Pr3+-doped (1-x)K0.5Bi0.5TiO3-xNa0.5Bi0.5TiO3 (x=0~1.0) thin films were studied. The thin films were prepared by a chemical solution deposition method combined with a rapid thermal annealing process at 700 oC. Under 350 nm UV radiation, a strong red emission at 611 nm assigned to 1D2→3H4 transitions of the Pr3+ ions was observed in all the thin films. The thin film at x = 0.15 showed the strongest red emission, also a very large dielectric constant and a large remanent polarization appeared in the same film. The good properties of the thin film with x =0.15 may be related to the morphotropic phase boundary of the thin films. The relationship between photoluminescence and other properties has been discussed.
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Limit of Functionality in Ultrathin Ferroelectric Thin Film Capacitors with Frozen-in and Diffusive Depletion Charges.
Hamidreza Khassaf 1 , Burc Misirlioglu 1 , Mehmet Yildiz 1
1 Faculty of Engineering & Natural Sciences, Sabanci University, Istanbul Turkey
Show AbstractDepletion charges due to impurity and vacancy concentrations in ferroelectric thin films have nearly always been neglected in the discussion of limits of functionality in these systems. The hysteresis curves and capacitance-voltage data have often been used to characterize their density and type. In this work, we quantitatively study the thickness dependence of the depletion charge induced domains and their stabilities under applied fields both for frozen-in and diffusive charge accumulations. We consider films both with ideal and real electrodes. A thermodynamic approach coupled with the electrostatic energy and interface conditions is used to simulate the field dependence and phase stability of ferroelectric thin films. We show that the electrical domains with a saw-tooth-like configuration form in relatively thick films and that a single-domain state with a built-in polarization is stable in ultrathin films (at the order of 4-6 nm) for nearly homogeneous depletion charge densities. For thick films with large densities of depletion charge, the phase transition is always into a multidomain state, destroying any hysteresis effects. We then show that this scenario can change if the charges have a diffusive character and that traps can emit charges due to band bending driven by the applied field. BaTiO3 on substrates that impose compressive and tensile misfit strains is considered as an example case. Depletion charges have a tremendous impact on the domain structures in addition to possible charge transport related phenomena. We also demonstrate that the depletion charge effects can compete with the depolarizing fields originating from the dead layers at the oxide-electrode interfaces.
9:00 PM - P4.45
The Operational Mechanism of Ferroelectric-Driven Organic Resistive Switches.
Martijn Kemerink 1 , Kamal Asadi 2 , Paul Blom 2 3 , Dago de Leeuw 2 4
1 Applied Physics, Eindhoven University of Technology, Eindhoven Netherlands, 2 Zernike Institute for Advanced Materials, University of Groningen, Groningen Netherlands, 3 , Holst Centre, Eindhoven Netherlands, 4 , Philips Research Laboratories, Eindhoven Netherlands
Show AbstractThe availability of a reliable memory element is crucial for the fabrication of ‘plastic’ logic circuits. Resistive switching and non-destructive read-out were recently demonstrated in diodes with a phase separated blend of the ferroelectric polymer P(VDF-TrFE) and a semiconducting polymer like P3HT as active layer. [1] Excellent current rectification and high on/off current ratios were reported. [2] Although it was realized that the functionality was based on modulation of the injection barrier, the operational mechanism so far remained elusive.Here, we develop a 2D device model that explains the operation of these all-polymer memories. The model reproduces all characteristic features in the device characteristics. Moreover, it allows us to assess the minimum feature size and hence the maximum memory density.In order to design memories based on phase separated ferroelectric / semiconductor blends, the vital question is to understand the true origin of the switching and of the modulation of the injection barrier. We address these questions by adopting a simplified morphological model. We consider straight, alternating slabs of ferroelectric and semiconducting phases, standing perpendicular to the (metallic) electrode surfaces. By numerical drift-diffusion simulations of diodes with this simplified morphology we reproduce the switching between an injection-limited Off-state and a space charge limited On-state. We demonstrate that the driving force for resistance switching of the diode is the stray field of the polarized ferroelectric phase. Furthermore, we quantitatively reproduce the experimentally observed exponential scaling of the on/off current modulation ratio with injection barrier height. Finally, we estimate the optimum diameter of the semiconducting domains in a ferroelectric matrix and hereby predict the ultimate memory density that can be realized to be around 1 Gb/cm2.[1] K. Asadi, D. M. de Leeuw, B. de Boer, and P. W. M. Blom, Nature Mater. 2008, 7, 547.[2] K. Asadi, T. G. de Boer, P. W. M. Blom, D. M. De Leeuw, Adv. Funct. Mater. 2009, 19, 3173.
9:00 PM - P4.48
Phase Transition Studies in Magnetoelectric Multiferroic Solid Solution of Lead Zirconate Titanate with Lead Iron Tantalite.
Dilsom Sanchez 1 , Ashok Kumar 1 , Nora Ortega 1 , Jim Scott 2 , Ram Katiyar 1
1 Physics, University of Puerto Rico, San Juan United States, 2 Physics, University of Cambridge, Cambridge United Kingdom
Show AbstractSingle-phase multiferroic material with magnetoelectric coupling at room temperature was fabricated by making solid solution of Lead Zirconate Titanate with Lead Iron Tantalite (PZTFT). At room temperature the material presented high dielectric constant, low dielectric loss and low leakage current; with dominant Poole-Frenkel conduction mechanism; antiferromagnetic behavior, square saturated ferroelectric hysteresis loops with saturation polarization Pr = 25 uC/cm2, which actually increased to 40 uC/cm2 at high temperatures, representing an exciting new room temperature oxide multiferroic to compete with BiFeO3. X-ray spectra as a function of temperatures revealed that PZTFT ceramic undergo a tetragonal to orthorhombic phase transition during cooling. The X-ray scattering analysis revealed two possible orthorhombic symmetries at room temperature, viz P222 (D2) or Pmm2 (C2v), and two possible tetragonal phases at elevated temperatures: P4/m (C4h) or P4mm (C4v). However, the square polarization hysteresis in both phases and a second-order dielectric divergence (at 460 K) requires an unambiguous assignment as a C2v-C4v (Pmm2-P4mm) transition. In addition, we find evidence from Raman scattering and dielectric loss measurements that this system becomes cubic above ca. 1300 K (but below its melting point) and its symmetry becomes lower than orthorhombic at slightly below room temperature (275K). We have investigated ferroelectric properties in each phase verifying that the transition is second-order thermodynamically, so that a group-subgroup relation exists between the upper and lower symmetries. Additional transitions at high temperatures (cubic at T>1200 K) and low temperatures (rhombohedral or monoclinic at T<250 K) were found. The material showed extremely low dielectric loss, found in any known room-temperature multiferroic that is of great advantage for magnetoelectric devices.
9:00 PM - P4.49
Piezoelectric Energy Harvesting of Flexible Device Based on PZT Ribbons by Laser Lift-off Process.
Young Ho Do 1 , Min Gyu Kang 1 , Seung Min Oh 1 , Hyun Cheol Song 1 , Won Hee Lee 1 , Chong Yun Kang 1 , Seok Jin Yoon 1
1 Electronic Materials Center, Korea Institute of Science and Technology, seoul Korea (the Republic of)
Show AbstractThe piezoelectric energy harvesting of PbZr0.52Ti0.48O3 (PZT) ribbons on a flexible polymer substrate has been applied to convert mechanical energy to electrical energy. The PZT ribbons were fabricated by conventional rf sputtering system on PZT (sacrificial layer)/Al2O3 substrates. The PZT ribbons were transferred to flexible polymer substrates by using laser lift-off process (LLO) to delaminate the films from the Al2O3 substrates and connected by metal electrodes (interdigitated pattern). Structural properties of PZT ribbons films are characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ferroelectric and piezoelectric characterization was done on a RT66A test system and a Keithley 6517A electrometer/high resistance meter. The flexible device based on PZT ribbons generated stable out current and power density, at periodically bending motion. In addition, the flexible device based on PZT ribbons has showed dependent out current and voltage with the shape of the PZT ribbons. These flexible devices by LLO can be employed as new approaches for flexible energy harvesting and flexible electronics applications.
9:00 PM - P4.5
Concurrent Transition of Ferroelectric and Magnetic Ordering in a Quasi-Layered Multiferroic.
Chan-Ho Yang 1 8 , Kyung Tae Ko 2 , Min Hwa Jung 2 , Qing He 3 , Jin Hong Lee 1 , Chang Su Woo 1 , Kanghyun Chu 1 , Jan Seidel 3 4 , W. Liang 5 , H. Chen 5 , Ying-Hao Chu 5 , Yoon Hee Jeong 2 , R. Ramesh 3 4 6 , Jae Hoon Park 2 7
1 Physics, KAIST, Daejeon Korea (the Republic of), 8 Institute for the NanoCentury, KAIST , Daejeon Korea (the Republic of), 2 Physics, POSTECH, Pohang Korea (the Republic of), 3 Physics, University of California, Berkeley, California, United States, 4 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 5 Materials Science and Engineering, National Chao-Tung University, HsinChu Taiwan, 6 Materials Science and Engineering, University of California, Berkeley, California, United States, 7 Division of Advanced Materials Science, POSTECH, Pohang Korea (the Republic of)
Show AbstractMany novel phenomena have been discovered in transition metal oxides with a structure of either perovskite(ABO3) or layered perovskite(A2BO4) structures. A highly elongated perovskite provides another class of perovskite-based crystal structure, which has the same stoichiometry as the normal perovskite(ABO3) but show similar anisotropic characteristics to the layered structure. The quasi-layered perovskites will broaden our scope in exploring new materials. In this talk, we will focus on a highly elongated multiferroic BiFeO3 thin film, which has been newly discovered as a quasi-layered phase stabilized through a misfit strain.[1,2] We report that the magnetic Néel temperature of multiferroic BiFeO3 (BFO) compound is unusually suppressed to near room temperature by heteroepitaxial misfit strain. Remarkably the ferroelectric state undergoes a first-order transition to another ferroelectric state simultaneously at the magnetic transition temperature. Our findings provide a unique example to show concurrent magnetic and ferroelectric transition at the same temperature among proper ferroelectrics. [1] R. J. Zeches et al., Science 326, 977-980 (2009).[2] H. Bea et al., Phys. Rev. Lett. 102, 217603 (2009).
9:00 PM - P4.50
A Model Operando Approach to Study Atomically Controlled Surfaces of Complex Oxide Catalysts.
Chad Folkman 1 , Seong-Keun Kim 1 , Edith Perret 1 , Matt Highland 1 , Jason Hoffman 1 , Liliana Stan 2 , Pete Baldo 1 , Carol Thompson 3 , Jeff Eastman 1 , Dillon Fong 1
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Center for Nanoscale Materials, Argonne National laboratory, Argonne, Illinois, United States, 3 Department of Physics, Northern Illinois University, Dekalb, Illinois, United States
Show AbstractThe development of state-of-the-art catalysts has benefited from in-situ studies that combine measurements of catalytic performance with advanced spectroscopy of the catalyst material. More recently, these so-called operando studies have been extended to atomically controlled model catalyst surfaces, like that of (111) Pd [1]. Although they lack the high surface area necessary for practical applications, model surfaces permit the systematic investigation of complex interfacial processes, even those occurring on transition metal oxides, where identifying specific catalytic mechanisms can be particularly challenging. Heterostructures comprised of perovskites, spinels, and Ruddlesden-Popper compounds are known to exhibit a fascinating array of novel materials behavior, and their surface properties in various gaseous environments are currently of significant interest. We investigate the surface reactivity of prototypical ferroelectric BaTiO3 using a three component approach: (i) growth of singly-terminated, epitaxially strained (001) BaTiO3 films by molecular beam epitaxy, (ii) use of a custom-designed low-volume reactor chamber in-line with a gas chromatograph / mass spectrometer, and (iii) integration with surface sensitive grazing incidence x-ray scattering measurements at the Advanced Photon Source. We will present preliminary results on oxidation/reduction reactions at the (001) BaTiO3 surface. Work supported by the U. S. Department of Energy under Contract No. DE-AC02-06CH11357.[1] van Rijn R., Achermann M. D., Frenken J. W. M., et. al. Review of Scientific Instruments. Ultrahigh vacuum/high-pressure flow reactor for surface x-ray diffraction and grazing incidence small angle x-ray scattering studies close to conditions for industrial catalysis. 81, 014101 (2010)
9:00 PM - P4.51
Photovoltage Study of the Intergrain Photovoltaic Effect in Polycrystalline M/Pb(ZrTi)O3/M Structures.
Liubov Delimova 1 , Valentin Yuferev 1 , Igor Grekhov 1
1 Solid State Electronics Division, Ioffe Institute of the RAS, St.Petersburg Russian Federation
Show AbstractA polycrystalline Pb(ZrTi)O3 (PZT) film sandwiched between electrodes is known to be the basic element of nonvolatile ferroelectric random access memory, which reliability depends on charge transport properties of PZT. We study MOCVD prepared 100-nm-thick PZT films, where (111) textured PZT grains are separated by ultrathin interlayers of semiconductor PbO phase, forming conducting channels between electrodes. Under illumination of the poled structure by light with the quantum energy lower than the PZT band gap but higher that the PbO band gap, the short-circuit photovoltaic current is observed. Opaque top electrodes are employed and the steady-state photocurrent is caused by illumination of the area adjacent to the top electrode. Earlier, we showed that this photovoltaic current is driven by the depolarization field, which is generated by residual uncompensated polarization charge located on PZT grain boundaries near electrodes [1]. Here, we study a photovoltage of the intergrain photovoltaic effect in M/PZT/M structures with Pt or Ir top electrode and with and without 5-nm-thick PbTiO3 (PTO) layer between PZT film and Ir bottom electrode. The photovoltage is measured using compensation of the photovoltaic current by the external transport current at different preliminary polarizations of the structure. To erase a prehistory before each measurement, the studied structure was firstly depolarized using Sawyer-Tower method then poled in the dark by applying the bias pulse to the bottom electrode. We found that all the depolarized structure have some remanent polarization, which is directed from the bottom electrode to the top one. At low bias, the remanent polarization varies weakly and grows significantly only when the bias is above the coercive field. Therefore, the short-circuit photocurrent measured in depolarized state is controlled by internal intergrain electric field produced by non-symmetrical top and bottom interfaces rather than the remanent polarization. We show that in structures with Pt top electrode this internal electric field is directed from the bottom to top electrode, whereas in the structures with Ir top electrode and PTO interlayer the internal intergrain field is directed from the top to bottom electrode. In all the poled structures, the photovoltage is directed against the polarization and its value depends on the magnitude of the remanent polarization, which agrees with our conception of the intergrain photovoltaic effect. For major structures, the photovoltage measured in positively poled structure is larger than that measured in negatively poled one by the value of ~0.1-0.2 V. This difference is much more than the photovoltage measured in the depolarized structures, which is ~0.02-0.08 V.1. Appl. Phys. Lett. 91, 112907 (2007), J. Appl. Phys. 108, 084110 (2010)The study is supported by the Grant of RFFI # 10-02-00562a, the Program of the Presidium of the RAS “Fundamental study of nanotechnology and nanomaterials”
9:00 PM - P4.52
Direct and Converse Magnetoelectric Coupling Coefficients in Multiferroics: Are They Equal to Each Other?
Jing Lou 1 , Gerry Pellegrini 1 , Ming Liu 2 , Nian Sun 1
1 Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show Abstract Multiferroics are the group of materials that consist of two or more primary ferroic properties, which are of great current interests, as they offer the possibility of magnetoelectric (ME) coupling, that is, electric field manipulation of magnetic properties (converse ME effect) or vice versa (direct ME effect),[1] and have led to many novel multiferroic devices, such as ultra-sensitive magnetometer, electrostatically tunable inductors,[2] electrostatically tunable microwave signal processing devices,[3, 4] etc. Two different groups of ME coupling coefficients have been defined for characterizing the strength of the direct and converse ME coupling, namely direct ME coefficient and converse ME coefficient. Direct ME coefficient quantifies the strength of the magnetic field induced electric polarization change; while converse ME coefficient measures electric field induced magnetization change. For reversible ME processes, the “Maxwell Relations” are demanded by standard thermodynamics, which dictates that the direct and converse ME coefficients should be equal under any bias condition. Up to now however, the equality of direct and converse ME coefficients has never been experimentally verified, due to the challenge in achieving strong ME coupling, the difficulty of precise measurement of both coefficients, and due to the existence of different versions of ME coefficients. In this paper, for the first time, a novel approach that combines the VSM and searching coil techniques was used to dynamically measure the converse ME coefficient of a multiferroic heterostructure of FeGa/PZN-PT/FeGa. The direct ME coefficients of the same sample under same bias conditions were also measured and compared. With the bias magnetic field changing from 0 to 300 Oe, and the bias electric voltage changing from 0 to 500 V, the magnitude of both direct and converse ME coefficients showed nearly identical behaviors with the two coefficients being equal to each other at arbitrary bias magnetic and electric fields with only a small difference of 1.6%, which is within measurement error. The experimental finding of such relation can lead to better understanding of multiferroics, and can be further used to guide the research in ME multiferroic systems.Reference:1. C. W. Nan, M. I. Bichurin, S. X. Dong, D. Viehland and G. Srinivasan, J. Appl. Phys. 103, 031101 (2008).2. J. Lou, D. Reed, M. Liu, N. X. Sun, Appl. Phys. Lett. 94, 112508 (2009).3. J. Lou, M. Liu, D. Reed, Y. Ren, and N. X. Sun, Adv. Mater., 21, 4711 (2009).4. M. Liu, O. Obi, J. Lou, Y. Chen, Z. Cai, S. Stoute, M. Espanol, M. Lew, X. Situ, K. S. Ziemer, V. G. Harris, and N. X. Sun, Adv. Funct. Mater. 19, 1826 (2009)
9:00 PM - P4.53
Challenges in Magnetic Exchange Coupling within Electrospun Fibers: Mixed Superparamagnetic-ferromagnetic Nanoparticle Composite.
Trevor Simmons 1 2 3 , Minoru Miyauchi 4 2 3 , Jianjun Miao 4 2 3 , Jennifer Gagner 4 2 3 , Zachary Shriver 5 , Udayanath Aich 5 , Jonathan Dordick 4 2 3 , Robert Linhardt 4 1 2
1 Chemistry & Chemical Biology, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York, United States, 3 Rensselaer Nanotechnology Center, Rensselaer Polytechnic Institute, Troy, New York, United States, 4 Chemical & Biological Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 5 Biological Engineering, Massachussetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractElectrospun polymer fibers were prepared containing mixtures of different proportions of ferromagnetic and superparamagnetic nanoparticles. The magnetic properties of these fibers were then explored using a superconducting quantum interference device. Mixed superparamagnetic/ferromagnetic fibers were examined for mesoscale magnetic exchange coupling, which was not observedas theoretically predicted. Anomalous data suggests a magnetic interaction of the mixed nanoparticles and will be discussed. This study includes some of the highest magnetic nanoparticle loadings (up to 50 wt %) and the highest magnetization values (≈ 25 emu/g) in an electrospun fiber to date and also demonstrates a novel mixed superparamagnetic/ferromagnetic system.
9:00 PM - P4.6
Thermodynamics and Strain-Induced Morphotropic Phase Boundary in Multiferroic BiFeO3 Films: A Theoretical Study.
Zhi-Gang Mei 1 , Shunli Shang 1 , Yi Wang 1 , Zi-Kui Liu 1
1 Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractBismuth ferrite (BiFeO3) is the only known multiferroic material at room temperature, which is of interest for a number of applications. Due to its small processing window, high quality BiFeO3 films are difficult to obtain in single-phase form. With coupled first-principles and CALPHAD approaches, we study the growth conditions for BiFeO3 thin films by thermodynamic calculations. The formation enthalpy of BiFeO3 from oxides is obtained by first-principles density-functional theory. It is predicted to be a small negative value by local density approximation plus U (LDA+U) calculations, which is used to study the phase equilibria and chemical potential-temperature phase diagram of BiFeO3. The predicted processing window for BiFeO3 agrees well with experimental oxygen partial pressure-temperature conditions. We further predict that Bi chemical potential represented by its partial pressure can be used to adjust the stability window of BiFeO3. This opens a new dimension in tailoring processing conditions for optimal growth of BiFeO3 films.Recent experiments reveal that epitaxial strain can effectively stabilize a tetragonal structure of BiFeO3 and drive the formation of a morphotropic phase boundary (MPB). However, the coexistence of the rhombohedral and tetragonal phases and MPB with intermediate compressive strain is still not well understood theoretically. Using LDA+U calculations, we study the effect of epitaxial strain on the structure and properties of BiFeO3. A first order rhombohedral-like (R) to tetragonal-like (T) phase transition is predicted at a critical compressive strain of 5.15%, and this iso-symmetric phase transition enables the coexistence of these two phases and MPB-like behavior recently reported in strained BiFeO3 thin films. The phase stability of the strained films with respect to c/a ratio is studied to understand the evolution of the phase mixture under different substrates. The calculated c/a ratio vs in-plane strain phase diagram of BiFeO3 provides helpful guidance for the appropriate epitaxial substrates in order to obtain the coexistence of the R and T phases within the strained BiFeO3 films, and a useful estimate of the relative amount of each phase.
9:00 PM - P4.7
Nanoscale Visualization of Domain Switching Dynamics during Fatigue in Epitaxial Ferroelectric Thin Film Capacitors.
Sang Mo Yang 1 , Tae Heon Kim 1 , Jong-Gul Yoon 2 , Tae Won Noh 1
1 ReCFI, Department of Physics and Astronomy, Seoul National University, Seoul Korea (the Republic of), 2 Department of Physics, University of Suwon, Suwon Korea (the Republic of)
Show Abstract Polarization fatigue, a systematic loss of the switchable polarization under electrical cyclilng, is a well-known and long-standing problem in ferroelectric materials. It has been a serious problem hindering the full commercialization of ferroelectric based electronic devices, such as ferroelectric random access memories. To overcome it, there have been numerous efforts over the last decades. However, the microscopic mechanism of fatigue is still unclear; it remains contentious. Many different microscopic mechanisms have been suggested, for instance, electromigration of oxygen vacancies to form extended defects capable of pinning domains, interface nucleation inhibition due to charge injection, domain locking with electronic charges, local phase decomposition, and so on [1]. Note that the conventional electrical measurements, such as polarization-electric field hysteresis loop measurement, provide no further insights on the fatigue mechanism. For a clarification on this controversy, the best way is to observe directly the time-dependent domain switching dynamics during fatigue process with nanoscale resolution. Here, we present our recent studies on nanoscale visualization of time-dependent ferroelectric domain switching dynamics during fatigue in high-quality epitaxial PbZr0.4Ti0.6O3 thin film capacitors. To visualize it, we used the modified-piezoresponse force microscopy (PFM) [2], which has advantages to monitor directly the domain nucleation and wall motion in the capacitor geometry samples [3]. We found that domain wall velocity decreased significantly during fatigue process. The amplitude signals of piezoresponse also decreased as fatigue cycles increased. Interestingly, we observed that the nucleation sites changed during fatigue. In other words, the several nucleation sites at fatigued states were different from those at virgin state. From these PFM image results with ten nanometer resolution, we found that domain wall pinning is the dominant origin of fatigue in our epitaxial ferroelectric thin film capacitors. This work provides us a critical clue to clarify the controversy on fatigue mechanism.[1]X. J. Lou et al., Phys. Rev. Lett. 97, 177601 (2006) and references theirin.[2]S. M. Yang et al., Appl. Phys. Lett. 92, 252901 (2008); D. J. Kim et al., Appl. Phys. Lett. 91, 132903 (2007).[3]J. Y. Jo et al., Phys. Rev. Lett. 102, 045701 (2009); S. M. Yang et al., J. Korean Phys. Soc. 55, 820 (2009); T. H. Kim et al., Appl. Phys. Lett. 95, 262902 (2009).
9:00 PM - P4.8
Large Reversible Strain on Phase Transition in Relaxor-Ferroelectric Pb(In1/2Nb1/2) O3–Pb (Mg1/3Nb2/3)O3–PbTiO3 Single Crystals.
Peter Finkel 1 , Ahmed Amin 1
1 , NUWC, Newport, Rhode Island, United States
Show AbstractWe present experimental evidence that under relatively low level drive (< 0.1MV/m) the large strain (~0.5%) associated with ferroelectric rhombohedral FR- ferroelectric orthorhombic FO phase transition in domain engineered relaxor–ferroelectric single crystals under compressive stress and bias electric field can be captured. We have demonstrated this in mechanically confined ternary Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals poised at the rhombohedral side of the morphotropic phase boundary (MPB). Experimental strain-field results and methods of mechanical confinement and drive are presented.
Symposium Organizers
Craig J. Fennie Cornell University
Lane W. Martin University of Illinois, Urbana-Champaign
Beatriz Noheda University of Groningen
Tsuyoshi Kimura Osaka University
Manuel Bibes Thales Research and Technology/CNRS
P9: Poster Session: Ferroic Materials and Properties
Session Chairs
Tuesday PM, November 29, 2011
Exhibition Hall C (Hynes)
P5: Magnetoelectric Multiferroics
Session Chairs
Tuesday PM, November 29, 2011
Room 302 (Hynes)
9:30 AM - **P5.1
New Magnetoelectric Multiferroics.
James Scott 1 2
1 Physics, Cambridge University, Cambridge United Kingdom, 2 Physics Department, University of Puerto Rico, San Juan United States
Show AbstractA discussion is presented of two new families of magnetoelectric multiferroics epitomized by PbFe(1/2)Ta(1/2)O3 combined with PbZr(0.4)Ti(0.6)O3 [PFT/PZT] at 30:70% and 40:60%, and by Pb5Cr3F19. The oxide work was done with Ashok Kumar, Nora Ortega, and Ram Katiyar in San Juan, Puerto Rico; and the fluoride work with Denis Arcon, Robert Blinc, and others in Ljubljana. PFT/PZT is a room-temperature multiferroic with low-loss ferroelectric and magnetic hysteresis loops at room temperature, and a linear magnetoelectric effect. It exhibits the same four phases as does BaTiO3, including a (nearly) second-order ferroelectric-ferroelectric C4v-C2v (4mm -- mm2) transition near 520K. Note that unlike BiFeO3, in PFT/PZT the magnetic ion is the ion responsible for ferroelectricity (Fe at the B-site), suggesting stronger magnetoelectric coupling.
10:00 AM - P5.2
Hysteretic Flopping of Magnetic Chiral Domains in Cycloidal Multiferroic Thin Films.
Ignasi Fina 1 , Lourdes Fabrega 1 , Florencio Sanchez 1 , Josep Fontcuberta 1
1 , Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Bellaterra Spain
Show AbstractAntiferromagnetic perovskites with cycloidal magnetic order are known to display ferroelectric polarization (P) due to the so-called inverse Dzyaloshinskii-Moriya interaction. P develops in a direction contained within the plane of rotation of the cycloidal order and perpendicular to its propagation vector. The sense of P is dictated by the chirality of the cycloid. Upon cooling the material through its Néel temperature, domains of distinct chirality and ferroelectric polarization, are expected to be formed. It is also known that the cycloidal plane can be flopped from bc(ac) to ac(bc) by an appropriate magnetic field.As in any ferroic material, where existing ferroic domains lead to hysteresis and coercivity, the chiral domains, upon flopping under a magnetic field and field-retreating, may preserve memory of the applied field(s) history. Here we will explore in detail the flopping process by monitoring the population of chiral domains after different H-E trajectories. The ultimate goal is to elucidate if chiral domains can display hysteresis. Orthorhombic YMnO3 thin films were grown by PLD on SrTiO3 (110) substrates. They are antiferromagnetic below around 40 K and display typical characteristics of bc-cycloidal order. Detailed analysis of the polarization, allows concluding that in absence of any bias field (electric or magnetic), the nucleation of chiral domains occurs randomly. Similarly, field induced magnetic switching of the cycloids occurs with equality probably chiral distribution. However, remarkably enough, when the sample has been forced to be single-domain by applying a suitable electric poling, field induced magnetic switching is not longer random but flopping occurs more favourably in a direction determined by the poling field. We will argue that these results indicate that electric poling produces a lock-in of chirality among distinct domains, likely related to the energy cost of formation of multiferroic domain walls, which thus display memory effects.
10:15 AM - P5.3
Lattice Modulation in the Magnetoelectric Hexaferrite Ba0.5Sr1.5Zn2Fe12O22 Examined by Electron Diffraction.
Toru Asaka 1 , Yuji Hiraoka 2 , Xiuzhen Yu 3 , Koichiro Fukuda 1 , Koji Kimoto 3 , Tsukasa Hirayama 4 , Yoshio Matsui 3 , Tsuyoshi Kimura 2
1 Department of Materials Science and Engineering, Nagoya Institute of Technology, Nagoya, Aichi, Japan, 2 Department of Condensed Matter Physics, Osaka University, Toyonaka, Osaka, Japan, 3 , National Institute for Materials Science, Tsukuba, Ibaraki, Japan, 4 Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya, Aichi, Japan
Show AbstractThe discovery of the magnetoelectric (ME) effect in a Y-type hexaferrite, Ba0.5Sr1.5Zn2Fe12O22 (BSZFO), [1] provided a precedent for recent studies on various ME hexaferrites functioning even in low fields and/or at room temperature. BSZFO exhibits ferroelectricity induced by a helical magnetic order at low temperature. Furthermore, it is worth noting that the magnetic order persists above room temperature (~320 K). We investigated crystal-lattice modulations for BSZFO by means of an electron diffraction technique. Single crystals of BSZFO were grown by a flux method. The crystals were cut into thin plates with the c axis on wide surfaces and thinned by mechanical grinding and Ar+ ion sputtering. During electron diffraction measurements, magnetic fields normal to the thin plate, that is, perpendicular to the c axis, between 0 and 2 T were applied using pole pieces of an electromagnetic objective lens of the electron microscope. We observed satellite spots along the c* axis in the electron diffraction patterns below 320 K, indicating a lattice modulation with a wave vector Qs = (0,0,3δ). The value of δ varies between ~0.23 and 0.5 as a function of temperature and corresponds well to that of the magnetic modulation vector, Qm, that is Qs = Qm. By applying magnetic fields, BSZFO exhibits successive transitions with regard to the lattice modulation, accompanied by the modifications of the helical magnetic order. We consider that the observed lattice modulations were induced by the helical magnetic order via exchange magnetostriction which is related to the ferromagnetic components in the helical magnetic orders.[1] T. Kimura et al., Phys. Rev. Lett. 94, 137201 (2005).
10:30 AM - P5.4
Enhanced Room Temperature Magnetization in LaxBi1-xMnyFe1-yO3 Multiferroics Thin Films.
Shrawan Mishra 1 , Morgan Trassin 2 , Suresha Jagannatha 3 , John Heron 2 , Pim Rossen 2 , Di Yi 2 , Qing He 2 , Ying-Hao Chu 2 , Elke Arenholz 4 , Ramamoorthy Ramesh 1 2
1 Department of Physics, University of California, Berkeley, Berkeley, California, United States, 2 Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 3 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 4 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractDoping-driven competition between energetically similar ground states leads to many exciting materials phenomena such as the emergence of high-Tc superconductivity, diluted magnetic semi-conductors, and colossal magnetoresistance. Adopting this generic concept, here we will present a novel series of room temperature co-doped multiferroics material LaxBi1-xMnyFe1-yO3 (LBMFO) that offers unprecedented room temperature co-existence of ferroelectricity and fully controlled ferromagnetism. Doped multiferroics materials demonstrate this notion of rich phenomenology via modied ground spins states. We provide a direct evidence of site engineering that enables us to manipulate the ground spin states causing an enhanced room temperature magnetization.Detailed x-ray diraction and transmission electron microscopy employed to understand the crystal structure of pulse laser deposited high quality LBFMO films. PFM imaging has been used to probe the ferroelectric properties of LBMFO thin films. The SQUID magnetometery suggests that Fe site substitution resulted in the enhancement of saturation magnetization, coercive field and clarity of magnetic hysteresis loops. In addition, La substitution provides a means to control the ferroelectric properties in doped multiferroics thin films. By measuring x-ray linear dichroism and measuring the element specific magnetic hysteresis loops, here we will described the microscopic origin of enhanced ferromagnetism as well as modulation of antiferromagnetic orderings in LBMFO thin films. Probing the X-ray absorption spectra at O K-edge, explore the role of modified local environment of Fe ions in doped multiferroics materials.
10:45 AM - P5.5
Observation of E-Field Induced Switching of Antiferromagnetic Domains in Epitaxial BiFeO3 Thin Films Using Neutron Diffraction.
Anbusathaiah Varatharajan 1 , Tieren Gao 1 , Karunakar Kothapalli 2 , Paul Kienzle 2 , William Ratcliff 2 , Ichiro Takeuchi 1
1 Department of Materials Science and Engineering, University of Maryland, College Park, Maryland, United States, 2 NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractDirect evidence of controlling the magnetic domains in BiFeO3 (BFO) thin films through electric field is presented using neutron diffraction. In our previous work (Ratcliff II et al., Adv. Func. Mater. 21, 1567, 2011), we demonstrated that the parameters such as the film orientation, geometry and epitaxial strain determine the magnetic structure in BFO thin films. For instance, the (110) oriented monoclinic BFO film shows single-domain modulated magnetic structure, whereas the (111) oriented rhombohedral film shows a modulated magnetic structure superimposed on the G-type order. In this work, by depositing a BFO thin film on a vicinal SrTiO3 substrate, we have achieved a single antiferromagnetic modulated domain structure coupled to a ferroelectric monodomain as confirmed by neutron diffraction and piezoresponse force microscopy (PFM). Further, the application of an electric field between the bottom SrRuO3 and the top electrode switches the ferroelectric domain state which concomitantly switches the magnetic state. The neutron diffraction patterns obtained for the BFO thin film before and after the application of electric field show significant change in the magnetic domain populations. The observed magneto-electric switching behavior by neutron diffraction is compared with the magneto optical Kerr effect (MOKE) measurement on patterned pads of exchange coupled Co film deposited on top of the BFO films.
P6: Control of Ferroic Order via Oxide Interfaces
Session Chairs
Tuesday PM, November 29, 2011
Room 302 (Hynes)
11:30 AM - **P6.1
Engineering New Phenomena at Oxide Interfaces.
Philippe Ghosez 1
1 Physique, Universite de Liege, Liege Belgium
Show AbstractComplex transition metal oxides form an important class of compounds, exhibiting a wide variety of functional properties exploited in many devices. Thanks to advances in deposition techniques, these oxides can nowadays be combined in heterostructures, with a structural quality comparable to what is achieved for conventional semiconductors. Creating such heterostructures gives not only the possibility to combine the intrinsic properties of different compounds but also to induce totally new phenomena at their interfaces. Relying on first-principles calculations, I will discuss few selected examples including : the trilinear coupling between structural instabilities in oxide superlattices as a promizing route to enhanced magneto-electric coupling and the electroresistance effect in ferroelectric tunnel junctions with symmetric electrodes. Work done in collaboration with Z. Zanolli, D. Bilc, E. Bousquet, A. Safari, H. Djani, A. Prikockyte, J. Wojdel, J. Iniguez, P. Ordejon, F. Novaes, and funded by the projects OxIDes (EC-FP7), QCN (IAP-Belgian) and TheMoTherm (ARC-ULG).
12:00 PM - P6.2
Ferroelectricity in Noncentrosymmetric Structures from Centric Polyhedral Building Blocks.
James Rondinelli 1 , Craig Fennie 2
1 Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 2 School of Applied Engineering Physics, Cornell University, Ithaca, New York, United States
Show AbstractIncreasing demands for highly versatile field-tunable electronic, medical, and security technology materials has renewed interests in the fundamental mechanisms producing electric polarizations and their coupling to lattice-derived properties. In complex perovskite oxides, ferroelectricity is routinely induced by polar cation displacements; however, these distortions are largely decoupled from the centric octahedral framework, which specifies the dielectric, magnetic and optical responses, limiting their use in advanced field-based applications. Here we report an innovative route to realize perovskite-structured ferroelectric oxides with sizable electric polarizations that are both induced by and strongly coupled to the ubiquitous octahedral building blocks. Using density functional calculations, we outline the crystal-chemistry criteria guiding the rational design of octahedral rotation-induced ferreoelectricity and subsequently show how to produce ferroelectric oxides from bulk materials, which have no electric polarizations, through changes in chemical composition and cation order. By uniting switchable electric polarizations to the connectivity of the transition-metal oxygen octahedra, electric-field control over materials properties is possible. We anticipate that these findings will contribute to our understanding of not only new forms of ferroelectricity, but also the behavior of most ferroics materials in reduced dimensionalities and artificial geometries.
12:15 PM - P6.3
Interface Control of Bulk Ferroelectric Polarization.
Pu Yu 1 , Weidong Luo 2 3 , Jinxing Zhang 1 , Marta Dacil Rossell 4 , Chan-Ho Yang 5 , Guneeta Singh-Bhalla 6 , Seung-Yeul Yang 1 , Qing He 1 , Quentin Ramasse 4 , Erni Rolf 4 , Lane Martin 7 , Sokrates Pantelides 3 2 , Stephen Pennycook 2 3 , Ying-Hao Chu 8 , Ramamoorthy Ramesh 1 6
1 Department of Physics and Department of Materials Science and Engineering, University of California, Berkeley, California, United States, 2 Materials Science and Technology Division, ORNL, Oak Ridge, Tennessee, United States, 3 Department of Physics and Astronomy, Vanderbilt University, Nashvilla, Tennessee, United States, 4 National Center for Electron Microscopy, LBNL, Berkeley, California, United States, 5 Department of Physics, KAIST, Daejeon Korea (the Republic of), 6 Materials Science Division, LBNL, Berkeley, California, United States, 7 Department of Materials Science and Engineering, UIUC, Urbana, Illinois, United States, 8 Department of Materials Science and Engineering, National Chiao Tung University, TsinChu Taiwan
Show AbstractOver the past few years, the study of precisely constructed, atomically sharp perovskite oxide heterointerfaces has led to novel electronic properties and functionalities that are different from those inherent to the individual components and become focal points for condensed-matter-physics and materials-science research. However, the focus on interfacial properties sidesteps possible macroscopic implications of interfacial atomic-scale control on the broad range of properties and order parameters that are present in bulk complex oxides. We have so far not answered a simple question: is it possible to use interfacial structure to control the bulk phase state of an epitaxial layer away from the interface? Such an approach could be particularly intriguing if one of the layers is highly polar and electrically switchable, i.e. ferroelectric in nature. In this talk, using a combination of experimental measurements and theoretical calculation, we demonstrate the ability to deterministically control a bulk property, namely ferroelectric polarization, of a heteroepitaxial bilayer by precise atomic-scale interface engineering. More specifically, the control is achieved by exploiting the interfacial valence mismatch (polar discontinuity) to influence the electrostatic potential step across the interface, which further manifests itself as the internal field in ferroelectric hysteresis loops and determines the ferroelectric state. Clearly, such a coupling effect between interface properties and the bulk order parameters of the thin films is, in principle, not limited to the electrostatic degree of freedom. Imbalance in the other degrees of freedom (for example, the spin or the orbital degrees of freedom) may be used to control the properties of the bulk as well.
12:30 PM - P6.4
Electronic and Structural Coupling at Complex Oxide-Semiconductor Interfaces.
Divine Kumah 1 , Joseph Ngai 1 , James Reiner 1 , Alexie Kolpak 1 , Diana Qiu 1 , Sohrab Ismail-Beigi 1 , Y. Zhu 3 , D. Su 3 , Zhan Zhang 2 , Charles Ahn 1 , Fred Walker 1
1 Center for Research on Interface Structure and Phenomena, Yale University, New Haven, Connecticut, United States, 3 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States, 2 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States
Show AbstractStructural distortions that occur at complex oxide-semiconductor interfaces depend directly on the chemistry and electrical structure at the interface. We use synchrotron x-ray diffraction and transmission electron microscopy to measure such distortions with picometer resolution. In the SrTiO3/Si system, sub-angstrom [001] cation-anion displacements observed leading to a film polarized out-of-plane. The polar distortions are found to arise from an interplay between compressive strain in the SrTiO3 and an interface dipole. This interface dipole couples to the zone center soft mode in SrTiO3 to cause the observed polarization. For BaTiO3 on Ge we have discovered a more complex atomic structure involving both a rotation of the oxygen octehedra and cation displacements. We show that the observed structure arises from an interplay between the tendency of the truncated Ge (001) surface to dimerize and the complex lattice dynamics of BaTiO3.
12:45 PM - P6.5
Electrostatic Coupling and Structural Distortions at Interfaces in Ferroelectric/Paraelectric Superlattices.
Pavlo Zubko 1 , Almudena Torres-Pardo 1 2 , Noemie Jecklin 1 , Celine Lichtensteiger 1 , Alex Gloter 2 , Odile Stephan 2 , Jean-Marc Triscone 1
1 Department of Condensed Matter Physics, University of Geneva, Geneva Switzerland, 2 Laboratoire de Physique des Solides, Université Paris-Sud, Paris France
Show AbstractSuperlattices composed of ferroelectric and paraelectric oxides have been the subject of numerous studies, motivated by fundamental questions about ferroelectric size effects, by the emergence of novel interfacial phenomena, and by the possibilities these artificially layered materials offer for tailoring their functional properties. Theoretically, much attention has been devoted to the effects of epitaxial strain and polarization continuity across the different layers. In this contribution we examine the role of periodic 180° ferroelectric nanodomains on the structural and electrical properties of PbTiO3/SrTiO3 superlattices. Using a combination of X-ray diffraction and electrical measurements, nanoscale motion of domain walls under applied field has been detected and linked to the large enhancement of the dielectric response of these materials [P. Zubko et al., Phys. Rev. Lett. 104, 187601 (2010)]. Electrostatic interactions between the ferroelectric layers have been studied in detail, revealing an unexpected decoupling of the ferroelectric layers once the paraelectric layer thickness exceeds just a few perovskite unit cells. Recent advances in transmission electron microscopy allowed us to map out the local structural distortions across the superlattice using electron energy loss spectroscopy (EELS) with unit-cell resolution, revealing highly inhomogeneous polarization profiles near the interfaces and giving new microscopic insight into the behavior of these fascinating materials.
P7: Magnetoelectric Interfaces
Session Chairs
Tuesday PM, November 29, 2011
Room 302 (Hynes)
2:30 PM - **P7.1
Charge-Based Magnetoelectric Coupling in Complex Oxide Interface Structures.
Charles Ahn 1
1 , Yale University, New Haven, Connecticut, United States
Show AbstractThe doped manganites are strongly correlated complex oxides exhibiting a strong interplay between charge, spin, and lattice effects. This coupling leads to a range of electronic and magnetic properties, including magnetic and charge ordered states, “colossal” magnetoresistance (CMR), and a variety of electron transport behavior. The possibility of integrating this multifunctional behavior with other types of functionalities has motivated the development of artificially structured oxide-based materials systems, such as multiferroic composite heterostructures. In this talk, we describe the observation of a charge-driven, magnetoelectric coupling in epitaxial La1-xSrxMnO3/PbZryTi1-yO3(LSMO/PZT) multiferroic heterostructures. Magnetization and magnetooptic Kerr effect magnetometry measurements show a large change in the magnetic critical temperature and magnetic moment of the LSMO layer that depends upon the two polarization states of the PZT layer, which modulates the charge-carrier concentration at the LSMO interface. This magnetoelectric coupling is electronic in origin, corresponding to changes in the Mn valency. We also observe the change in Mn valency directly using near-edge x-ray absorption spectroscopy. Further investigations of the electrical and magnetic properties of the LSMO layer also reveal evanescent phonon coupling across the substrate/film interface.
3:00 PM - P7.2
Electric Control of the Magnetization in BiFeO3/LaFeO3 Superlattices.
Zeila Zanolli 1 , Jacek Wojdel 2 , Jorge Iniguez 2 , Philippe Ghosez 1
1 Physics, Universite' de Liege, Liege Belgium, 2 , ICMAB-CSIC, Bellaterra Spain
Show AbstractTransition-metal oxides of perovskite structure can present a wide variety of physical properties such as ferroelectricity, piezoelectricity, colossal magnetoresistance, spin-dependent transport and superconductivity, which can be exploited in various technological applications. In particular, there is nowadays a strong interest in multiferroic materials that are simultaneously ferroelectric and magnetic, since the so-called 'magnetoelectric' coupling between electrical polarization and magnetism could permit electrically writable and magnetically readable data storage.Due to the scarcity of natural magnetoelectric multiferroics and thanks to the recent advances in the epitaxial growth techniques, the idea of designing new magnetoelectric multiferroic heterostructures seems the most promising approach to succeed in this quest. In this talk, we will discuss the possibility of achieving electric control of the magnetization, possibly at room temperature, through a specific (trilinear) coupling of the polarization with two other non-polar lattice instabilities which occurs in the so-called hybrid improper ferroelectrics [1-3]. First-principles modeling techniques are used to investigate a promising system: BiFeO3/LaFeO3 superlattice. We found this system to exhibit magnetism at room temperature, trilinear coupling of structural instabilities, improper ferroelectricity and magneto-electric coupling. Electric switching of magnetization in this material will be discussed.[1] E. Bousquet et al., Nature 452, 732 (2008).[2] N.A. Benedek, C.J. Fennie, Phys. Rev. Lett. 106, 107204 (2011).[3] Ph. Ghosez and J. M. Triscone, Nature Materials 10, 269 (2011).
3:15 PM - P7.3
Interface-Induced Room-Temperature Multiferroicity in BaTiO3.
Sergio Valencia 2 , Arnaud Crassous 1 , Laura Bocher 3 , Vincent Garcia 1 , Xavier Moya 5 , Cyrile Deranlot 1 , Karim Bouzehouane 1 , Stephane Fusil 1 , Ryan Cherifi 1 , Alberto Zobelli 3 , Alexandre Gloter 3 , Neil Mathur 5 , Andreas Gaupp 2 , Radu Abrudan 4 , Florin Radu 2 , Agnes Barthelemy 1 , Manuel Bibes 1
2 , Helmholtz-Zentrum-Berlin für Materialen und Energie, Berlin Germany, 1 , Unité Mixte de Physique CNRS/Thales, Palaiseau France, 3 , Laboratoire de Physique des Solides, Orsay France, 5 Department of Materials Science, University of Cambridge, Cambridge United Kingdom, 4 , Institut für Experimentalphysik/Festkörperphysik, Bochum Germany
Show AbstractMultiferroic materials possess two ferroic orders but have not been exploited in devices due to the scarcity of room-temperature examples. Those which are ferromagnetic and ferroelectric have potential applications in multi-state data storage if the ferroic orders switch independently, or in electric-field controlled spintronics if the magnetoelectric coupling is strong. Future applications could also exploit toroidal moments and optical effects that arise from the simultaneous breaking of timereversal and space-inversion symmetries. Here, we use soft X-ray resonant magnetic scattering and piezoresponse force microscopy to reveal that at the interface with Fe, ultrathin films of the archetypal ferroelectric BaTiO3 simultaneously possess a magnetization and a polarization that are both spontaneous and hysteretic at room temperature. Ab initio calculations of realistic interface structures provide insight into the origin of the induced moments and validate this new approach for creating room temperaturemultiferroics.
3:30 PM - P7.4
Electric-Field Induced Magnetization Reversal in a Multiferroic-Based Heterostructure.
John Heron 1 , M. Trassin 2 , K. Ashraf 3 , M. Gajek 2 , Q. He 2 , S. Yang 2 , D. Nikonov 4 , Y. Chu 5 , S. Salahuddin 3 , R. Ramesh 1 2 6
1 Materials Science and Engineering, University of California Berkeley, Berkeley, California, United States, 2 Physics, University of California Berkeley, Berkeley, California, United States, 3 Electrical Engineering and Computer Science, University of California Berkeley, Berkeley, California, United States, 4 Components Research, Intel, Santa Clara, California, United States, 5 Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan, 6 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractSpintronics applications utilize either an externally applied magnetic field or a large current density to achieve magnetization reversal, which is accompanied by significant energy dissipation. A reversal of magnetization requiring only the application of an electric field can lead to low-power devices. Using multiferroics, previous approaches have seen limited success by only achieving rotations (≤ 90°) of the magnetization by applying an electric field. To pave the way to new low-power devices, the more desirable electric-field driven magnetization reversal must be achieved and read out with a small current. Here we show a reversal of the magnetization of a Co.90Fe.10 layer, in contact with BiFeO3, with only an applied electric field and at room temperature in a magnetotransport-based device. Anisotropic magnetoresistance (AMR) measurements revealed that this electrically-driven 180° reorientation of the magnetization is non-volatile and reversible. An angle-dependent X-ray PEEM study of the magnetic domain structure of the ferromagnetic layer and piezoresponse force microscopy images of the domain structure of the multiferroic unveils a domain structure in the ferromagnet that is dependent on the magnetic order within each ferroelectric domain in the multiferroic. Equipped with this knowledge, GMR type heterostructures are then integrated into a device structure designed towards establishing the electric field control of the magnetization of the pinned layer. Contrary to the contemporary method of controlling the resistance state of a GMR device (magnetic field switching of the free layer), our approach envisions the purely electrical control of a spin valve by manipulating the magnetization that is coupled to a magnetoelectric multiferroic.This research was made with Government support under and awarded by DOD, Air Force Office of Scientific Research, National Defense Science and Engineering Graduate (NDSEG) Fellowship, 32 CFR 168a.
3:45 PM - P7.5
Ferroelectric Tunnel Junctions for Novel Electronics and Spintronics Devices.
Vincent Garcia 1 , Arnaud Crassous 1 , Andre Chanthbouala 1 , Karim Bouzehouane 1 , Stephane Fusil 1 , Laura Bocher 2 , Xavier Moya 3 , Sergio Valencia 4 , Cyrile Deranlot 1 , Alexandre Gloter 2 , Julie Grollier 1 , Neil Mathur 3 , Manuel Bibes 1 , Agnes Barthelemy 1
1 , Unité Mixte de Physique CNRS/Thales, Palaiseau France, 2 Laboratoire de Physique du Solide, Universite Paris-Sud, Orsay France, 3 Department of Materials Science, University of Cambridge, Cambridge United Kingdom, 4 , BESSY, Berlin Germany
Show AbstractAfter being conceptualized in the early 1970's, ferroelectric tunnel junctions have remained elusive for more than 30 years. Only through the recent tremendous progress in ultrathin film growth, characterization and modeling has it been possible to fabricate and study quantum-mechanical tunneling across ferroelectric barriers. At room temperature, we use piezoresponse force microscopy to show robust ferroelectricity in BaTiO3 ultrathin films, and conductive-tip atomic force microscopy to demonstrate the resistive readout of the polarization state via its influence on the tunnel current [1]. This giant electroresistance nondestructive readout paves the way for ferroelectric memories with simplified architectures, higher densities and faster operation. Additionally, ferroelectric tunnel junctions with ferromagnetic electrodes were engineered to demonstrate local, large and non-volatile control of carrier spin polarization by switching ferroelectric polarization [2]. Our results represent a giant interfacial type of magnetoelectric coupling and suggest a new low-power approach for spin-based information control.[1] V. Garcia et al., Nature 460, 81 (2009)[2] V. Garcia et al., Science 327, 1106 (2010)
4:00 PM - P7: ME Inter
Break
P8: Integrating Oxides on Semiconductors
Session Chairs
Tuesday PM, November 29, 2011
Room 302 (Hynes)
4:15 PM - P8.1
Interfacing SrTiO3 with Silicon Using Pulsed Laser Deposition.
Matjaz Spreitzer 1 , Hajo Molegraaf 2 , Dave H.A. Blank 2 , Guus Rijnders 2
1 Advanced Materials, Jozef Stefan Institute, Ljubljana Slovenia, 2 Faculty of Science & Technology, University of Twente, Enschede Netherlands
Show AbstractInterfacing an oxide with silicon is a great challenge that has attracted a lot of interest so far. Solving the problem would enable the further scaling of microelectronic devices to smaller dimensions and the growth of epitaxial thin films with different functionalities, which can be exploited in micro-electro-mechanical systems, random-access memories, and other oxide-based nano-electronic devices. Using molecular beam epitaxy (MBE) high-quality SrTiO3 has already been prepared on silicon using a silicide intermediate layer. However, since the process is slow and expensive it is less attractive for industrial applications. In our work, small-area pulsed laser deposition has been used to grow SrTiO3 on (001) silicon. In contrast to MBE procedures, which use a combination of high temperature and ultra-high vacuum to remove the native oxide from the surface of the silicon substrate, a HF treatment was applied in our work. The second simplification involves the exchange of a strontium metal source with a SrO target, which is chemically more stable.The results show that the optimal conditions for the direct growth of SrTiO3 involve a two-step procedure, in which the initial vacuum and the lower deposition temperature have an important role. The obtained films are flat and mainly (100) oriented; however, they do not exhibit any in-plane crystal relation with the substrate, in contrast to most MBE studies. The polycrystallinity of the film is presumably related to the formation of the silicate phase between the SrTiO3 and the silicon, as determined using X-ray photoemission spectroscopy (XPS). Improved growth characteristics were observed in the case when SrO was used as a buffer layer. In this case the SrTiO3 film is epitaxial with STO(110)//Si(100) and STO[100]//Si[110]. In addition, XPS shows that the SrO and Sr2SiO4 layers are formed at the interface, which influence the growth direction of the SrTiO3 layer considerably.
4:30 PM - **P8.2
Giant Piezoelectricity on Si for Hyper-Active MEMS.
Chang-Beom Eom 1
1 Materialas Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractSmart materials that can sense, manipulate, and position are crucial to the functionality of micro- and nano-machines. Integration of single crystal piezoelectric films on silicon offers the opportunity of high performance piezoelectric microelectromechanical systems (MEMS) incorporating all the advantages of large scale integration on silicon substrates with on-board electronic circuits, improving performance and eliminating common failure points associated with heterogeneous integration. We have fabricated oxide heterostructures with the highest piezoelectric coefficients and figure of merit for piezoelectric energy harvesting system ever realized on silicon substrates by synthesizing epitaxial thin films of Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) on vicinal (001) Si wafers using an epitaxial (001) SrTiO3 template layer. We have also demonstrated fabrication of PMN-PT cantilevers, whose mechanical behavior is consistent with theoretical calculations using the material constants of a bulk PMN-PT single crystal. These epitaxial heterostructures with giant piezoelectricity can be used for MEMS or NEMS devices that function with low drive voltage such as transducers for ultrasound medical imaging, micro-fluidic control and energy harvesting. Beyond electromechanical devices, our approach will open a new avenue to tune and modulate the properties of other multifunctional materials by dynamic strain control.This work was done in collaboration with S. H. Baek, J. Park, D. M. Kim, V. Aksyuk, R. R. Das, S. D. Bu, D. A. Felker, J. Lettieri, V. Vaithyanathan, S. S. N. Bharadwaja, N. Bassiri-Gharb, Y. B. Chen, H. P. Sun, H. W. Jang, D. J. Kreft, S. K. Streiffer, R. Ramesh, X. Q. Pan, S. Trolier-McKinstry, D. G. Schlom, M. S. Rzchowski, R. Blick.This work was supported by the National Science Foundation through grants ECCS-0708759.
5:00 PM - P8.3
Giant Flexoelectric Effect in Ferroelectric Epitaxial Thin Films.
Tae Won Noh 1 , Daesu Lee 1 , Aram Yoon 2 , Seung Yup Jang 1 , Jong-Gul Yoon 3 , Jin-Seok Chung 4 , Miyoung Kim 2 , James F. Scott 5
1 Department of Physics and Astronomy, Seoul National University, Seoul Korea (the Republic of), 2 Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of), 3 , University of Suwon, Suwon Korea (the Republic of), 4 , Soongsil University, Seoul Korea (the Republic of), 5 , University of Cambridge, Cambridge United Kingdom
Show AbstractThe flexoelectric effect describes an electric field that is generated by a strain gradient, and vice versa, whereas conventional electromechanical couplings such as piezoelectricity generally assume homogeneous strain conditions. Because strain gradients break inversion symmetry, flexoelectricity allows the generation of electric responses from lattice deformations in every dielectric material. Owing to this universal nature, flexoelectricity has inspired a wide range of scientific interest and has broad application potential, particularly in flexible systems. In solids, however, there has been little investigation into the flexoelectric effect, due to its minuscule magnitude by limited elastic deformation in solids. In this presentation, we will develop a general framework for realizing and modulating the giant flexoelectric effect in epitaxial oxide thin films, emphasizing the key role of flexoelectricity in solids [1]. In epitaxial oxide thin films, a lattice mismatch between the film and the substrate can result in strain relaxation within tens of nanometers of the film/substrate interface, inducing a large strain gradient. We observed the nanoscale strain gradients in ferroelectric HoMnO3 epitaxial thin films, which were 6 or 7 orders of magnitude larger than typical values reported for bulk oxides. Giant flexoelectric effect by the nanoscale strain gradient provides a means of tuning the physical properties of ferroelectric epitaxial thin films, such as domain configurations and hysteresis curves [2].[1] D. Lee et al., Phys. Rev. Lett. (in press).[2] D. Lee et al., Phys. Rev. B 81, 012101 (2010).
5:15 PM - P8.4
Integration of Ferrimagnetic CoFe2O4 and Ferroelectric BaTiO3 with Si(001).
Florencio Sanchez 1 , Romain Bachelet 1 , Nico Dix 1 , Patricia de Coux 1 2 , Ignasi Fina 1 , Carles Carrillo 1 , Benedicte Warot-Fonrose 2 , Lourdes Fabrega 1 , Vassil Skumryev 3 4 , Josep Fontcuberta 1
1 , ICMAB - CSIC, Bellaterra Spain, 2 , CEMES - CNRS, Toulouse France, 3 , ICREA, Barcelona Spain, 4 , Universitat Autonoma de Barcelona, Barcelona Spain
Show AbstractThe room-temperature ferrimagnetism of CoFe2O4 (CFO) and ferroelectricity of BaTiO3 (BTO) make these materials of interest for applications. The combination of both materials can permit multiferroic properties and magnetoelectric effects. CFO and BTO are thus extremely appealing for new electronic devices. But this will critically depend on the possibility for integration with silicon, which requires a buffer layer avoiding chemical interaction. We have grown epitaxial CFO and BTO films on yttria-stabilized zirconia (YSZ) buffered Si(001), using pulsed laser deposition assisted by reflection high-energy electron diffraction (RHEED). First, we report the fabrication of ultrathin epitaxial heterostructures of a few nanometers thick in total, combining CFO, YSZ buffer-layer, and SiOx. The ultrathin epitaxial buffer layers were fabricated using RHEED to monitor in real time the crystallization of YSZ, permitting to fabricate buffers around 2 nm thick with remaining SiOx interfacial layer below 1 nm in thickness. Then, CFO films were subsequently deposited. The thickness of the SiOx layer increased to around 2 nm due to oxygen diffusion. CFO films are found to be very flat, with magnetization close to the bulk value. These properties extend the possibilities of using spinel oxides in new applications, even including tunnelling devices.We also report on ferroelectric BTO grown on Si(001). It is well known that BTO on Si(001) tends to orient its polar axis in-plane due to the thermal mismatch between both materials. Buffer layers causing relatively-high epitaxial compressive stress can be used to favour c-axis orientation of BTO, and aiming for this objective we have used the multiple buffer layer LaNiO3/CeO2/YSZ. Carefully controlled growth conditions permitted two-dimensional epitaxial growth of BTO as confirms the presence of RHEED intensity oscillations. X-ray diffraction and ferroelectric loops measurements revealed that the polar axis is out-of-plane. Finally, we report on multiferroic bilayers of CFO-BTO on buffered Si(001) substrates.
5:30 PM - P8.5
Monolayer Insertion at the a-Al2O3/Si (001) Interface – Switchable Interface Dipoles.
Stephanie Fernandez-Pena 1 , Divine Kumah 2 , Zhan Zhang 4 , Alexie Kolpak 5 , Sohrab Ismail-Beigi 2 , Charles Ahn 2 3 , Fred Walker 2
1 Condensed Matter physics, Geneva University, Geneva Switzerland, 2 Crisp, Applied Physics, Yale University, New Haven, Connecticut, United States, 4 Chemistry Division, Argonne National Laboratory, Argonne, Illinois, United States, 5 Materials Science and Engineering, MIT, Boston, Massachusetts, United States, 3 Materials Science and Mechanical engineering, Yale University, New Haven, Connecticut, United States
Show AbstractWe describe experimental evidence for a new type of ferroelectric on silicon, which is made of a monolayer (ML) of ZrO2 in between Si (001) and amorphous-Al2O3. Density functional theory predicts two stable configurations for a single ML of ZrO2 on Si, having both an up and down polarizations. Such structures can be made by reacting Zr and oxygen on a clean Si (001) surface. One key requirement is to avoid SiO2 formation at the interface, which is monitored experimentally using X-Ray Photoelectron Spectroscopy (XPS) to determine the oxidation state of the Si at the interface. For heterostructures where the ZrO2 is in direct contact with the Si, band offset changes for the a-Al2O3 are observed to be 0.58 [eV]. This shift indicates the presence of a dipole at the interface. We test whether the dipole can be switched with an external electric field by performing capacitance-voltage (CV) measurements. In the CV data, hysteresis is observed, indicating that the dipoles can be switched at the interface. The microscopic origin of these dipoles is investigated by extended x-ray absorption fine structure (EXAFS) near the Zr K edge. These results are compared with the predicted coordination of zirconium with oxygen and silicon derived from DFT calculations of the interface structures for both polarizations.
5:45 PM - P8.6
Surfactant-Assisted Growth of Smooth Epitaxial Oxides on GaN.
Elizabeth Paisley 1 , Michael Biegalski 2 , James LeBeau 1 , Benjamin Gaddy 1 , Seiji Mita 1 , Ramon Collazo 1 , Zlatko Sitar 1 , Douglas Irving 1 , Jon-Paul Maria 1
1 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractEpitaxial integration of polar oxides with wide band gap polar semiconductors presents the possibility of tunable 2D charge carriers at polar interfaces and integration of non-linear dielectric properties if defect densities are low, and interfaces are smooth. Achieving this in materials with such highly dissimilar structure and symmetry remains a serious challenge. For example, many cubic oxides form rough (100)-oriented low-energy facets when prepared with the (111) orientation that is compatible with (0002) GaN. In this presentation we will first discuss a newly-developed surfactant approach to MBE growth of rocksalt oxides (MgO, CaO) on GaN, where water vapor is utilized during growth to hydroxylate the rocksalt (111) surfaces, changing the equilibrium habit from cubic to octahedral, eliminating the (100)-faceting tendency. We demonstrate unambiguously using RHEED that surfactant incorporation enables a 2D growth mode of (111) CaO. MBE deposition cannot access processing space to stabilize (111) MgO. To do so, higher surfactant partial pressures are required. These pressures, however, are achievable using PLD. We report a companion experiment performed at the ORNL CNMS using PLD, that demonstrates similar outcomes, i.e., 2D growth and step-and-terrace morphology. For both MgO and CaO, temperature dependent ab initio surface energy calculations predict the observed temperature and pressure windows supporting layer-by-layer growth.Collectively, these results demonstrate that one can engineer surface chemistry in situ creating a local equilibrium promoting a crystallographic habit and growth mode that is otherwise unavailable. Demonstrating this using two materials and growth techniques suggests a generic methodology. The utility of this method is illustrated by electrical property measurements that reveal drastically reduced leakage current densities (~1000X lower) for surfactant-assisted films as compared to those grown using conventional means. Solid solutions between MgO and CaO by both PLD and MBE that offer perfect lattice match to (0002) GaN are presented. In all cases, epitaxy stabilizes the system against phase separation and RHEED shows layer-by-layer growth. TEM analysis of defects of the lattice-matched interface will be presented. Current efforts focus on samples designed to probe the possibility of conductive oxide-GaN interfaces using GaN heterostructures containing carrier donor layers.Finally, we will report the current extension of this work to the BaTiO3/GaN interface. We present XRD and TEM data showing PLD growth of epitaxial BT on c+ and c- polarity-patterned GaN, with a focus on piezoforce imaging. PFM measurements show that the permanently polar GaN can template simultaneously the BT polarity in physically adjacent regions, a critical first step in realizing functional polar interfaces. Current efforts are transitioning this surfactant approach to complex oxides like BT where similar faceting tendencies are present.
P9: Poster Session: Ferroic Materials and Properties
Session Chairs
Wednesday AM, November 30, 2011
Exhibition Hall C (Hynes)
9:00 PM - P9.1
Does the Concept of Solid Solution Always Make Sense in Perovskites?
Aneta Slodczyk 1 , Philippe Colomban 1
1 , LADIR CNRS UPMC, Paris France
Show AbstractSolid solutions are obtained when a substitution atom does not modify the mean structure determined by X-ray/neutron diffraction. Consequently, some properties vary almost linearly with the atomic substitution and can be tailored by composition adjustment. However, special behaviours are observed in relaxor ferroelectrics [1 and ref. therein]. Competition between two or more sublattices related to different types of chemical bonds and structure/symmetry as well as compositional heterogeneity lead to the coexistence of different symmetries with long and short scales, especially in morphotropic phase boundary (MPB) region. Structure modifications involving the species forming a local bond (e.g. proton) may highly depend on the local composition and thus on the vicinity of certain substituted atom. Analysis sensitive to the common mean structure (e.g. diffraction) may give different views than that probing the short range scale (e.g. Raman scattering). Our results performed on different perovskites, for example (1-x)PbMg1/3Nb2/3O3-xPbTiO3 (PMN-PT) relaxor ferroelectrics [1] and (Ba,Sr)Zr1-xLnxO3-dHz proton conductors [2] show that the intrinsic short range heterogeneity of a compound makes the boundary between the different symmetries not straightforward what questions the concept of solid solution. 1.A. Slodczyk, Ph. Colomban Materials 2010, 3, 5007-5028.2.A. Slodczyk et al. J. Raman Spectrosc. 40 (2009) 513-521
9:00 PM - P9.10
Nonlinear Dielectric and Piezoelectric Responses in (Bi, La)FeO3-Pb(Ti, Mn)O3 Ceramics.
Guiyang Shi 1 , Shundong Bu 1 , Rui Dai 1 , Shengwen Yu 1 , Jinrong Cheng 1
1 , Shanghai University, Shanghai China
Show AbstractPolycrystalline solutions of Mn modified 0.6(Bi0.9La0.1)FeO3-0.4Pb(Ti1-xMnx)O3 (BLF-PTM) for x=0, 0.01 and 0.02 have been fabricated by so-gel process combined with a solid state reaction method. Linear dielectric behavior is almost confined to relatively low applied electric field, and the dielectric properties of BLF-PTM exhibits obviously nonlinearity above certain “threshold” values of electric fields. The threshold of electric field effectively increases by Mn substitutents. Furthermore, nonlinearity in the converse piezoelectric effect is also observed in x-E of BLF-PTM. According to the Rayleigh Law, the initial piezoelectric coefficient and the Rayleigh coefficient are calculated. The Rayleigh coefficient of Mn modified BLF-PTM is less than that of BLF-PTM without Mn modification, showing that Mn substitutions markedly reduce the piezoelectric nonlinearity of BLF-PTM.
9:00 PM - P9.12
Computational Modelling of Ba1-xCaxTiO3, Ca1-xBaxTiO3 and Ba1-xSrxTiO3 Solid Solutions.
James Dawson 1 , Colin Freeman 1 , John Harding 1 , Derek Sinclair 1
1 Engineering Materials, Univ Sheffield, Sheffield United Kingdom
Show AbstractBoth the BaTiO3 and CaTiO3 perovskite structures can accommodate a wide range of both isovalent and aliovalent dopant ions and these dopant ions have a significant effect on the electrical properties of the material. The solid solubility limit for Sr2+ in BaTiO3 is 100 mol%, whereas for Ca2+ the limit is only 25 mol% due to the increasing size mismatch between the larger Ba cations and smaller Ca cations [1,2]. For Ba-doped CaTiO3 a solid solubility limit of ~ 15% has been observed [3]. These dopants have a significant effect on the ferroelectric Curie temperature, Tc. For example the doping of Sr2+ in BaTiO3 causes Tc to decrease by 4 °C per mol%. Doping of Ca2+ in the same material causes a slight increase in Tc up to 8 mol% and then a decrease of ~ 1 °C per mol% at larger concentrations [2]. This behaviour has been attributed to a strain effect resulting from competition between the A-site size mismatch and mean A-cation radius [4].Lattice statics simulations, using the GULP code [5] on Ba1-xCaxTiO3, Ca1-xBaxTiO3 and Ba1-xSrxTiO3 solid solutions have been completed using a recently developed potential set designed for BaTiO3 [6] combined with new Sr-O and Ca-O interatomic potentials. Energies of mixing for the solutions have been obtained over a range of concentrations and excellent correlation with experimental findings has been observed. Ca-O and Ba-O interatomic distances in Ca-BaTiO3 are reported, which show significant local disorder that provides insight on the unusual Tc behaviour observed in the Ba1-xCaxTiO3 (BCT) system. References1. Matra D., Ferroelectric Ceramics, 1966: Maclaren and Sons Ltd. 2. Mitsui T. and Westphal W. B., Phys. Rev., 1961, 124(5): p. 1354-1359.3. Lee S., Levi R. D., Qu W., Lee S. C. and Randall C. A., J. Appl. Phys., 2010, 107: 023523. 4. Sinclair D. C. and Attfield J. P., Chem. Commun., 1999, p. 1497-1498. 5. Gale J. D., J. Chem. Soc. Faraday Trans., 1997, 93: p. 629-637.6. Freeman C. L., Dawson J. A., Chen H.-R., Harding J. H., Ben L.-B. and Sinclair D. C., J. Mater. Chem., 2010, 21: p. 4861-4868.
9:00 PM - P9.13
Quantitative Local Characterization of Bulk Ferroelectric Ceramics.
Maria Torres 1 , Guannan Chen 1 , Vincent West 2 , Peter Davies 2 , Andrew Rappe 3 2 , Jonathan Spanier 1
1 Materials Science & Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 2 Materials Science & Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 3 Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractSolid-state synthesis, e.g. via reactive sintering of powders at high temperature and/or pressure, remains the most facile and versatile route for producing new complex ceramic oxide materials with a high degree of control of structure, composition, phase purity and stoichiometry. While the production of thin films of novel complex oxide materials is needed for characterization of functional and device properties, for many materials, solid-state syntheses may be the only known and accessible synthetic pathway. For ferroelectrics, measurement of the local ferroelectric switching is typically limited by sample thickness, requiring high voltages for its investigation in pellets, resulting in high field concentration-induced artifacts, and even damage to the sample. Here we report on a new procedure to extract, locate and electrically interface 100-150 nm thick lamellae in the form of mesoscopic near-surface cross-sections of bulk pellets, thereby facilitating measurement of thin film-equivalent properties associated with these bulk materials, and spatial mapping of the properties as a function of distance from the pellet surface. The procedure is based on a designed and optimized sequence of high and low-accelerating voltage focused ion beam milling and extraction of lamellae that can render the vast majority of the specimen in its as-formed phase and microstructure. We demonstrate that milling of these lamellae, their transfer to selected substrate materials, and post-extraction thermal processing enable a range of local physical, electronic and functional property measurements, with an example of a mesoscopic cross-section of a KNbO3 pellet and its local ferroelectric and piezoelectric response. Work supported by the ECI of the Commonwealth of Pennsylvania and by the ARO under W911NF-08-1-0067, and in part by NSF under DMR-0907381.
9:00 PM - P9.15
A Complex Lead Based Perovskite Structure Material with Diffuse Phase Transition Behavior.
Venkata Puli 1 , Ricardo Martinez 1 , Ashok Kumar 1 , James Scott 1 2 , Ram Katiyar 1
1 Physics, University of Puerto Rico, San Juan United States, 2 Physics, University of Cambridge, Cambridge United Kingdom
Show AbstractA lead based quaternary compound composed of 0.25(PbZr0.52Ti0.48O3) + 0.25(PbFe0.5Ta0.5O3)+ 0.25 (PbF0.67W0.33O3)+0.25( PbFe0.5Nb0.5O3)--(PZT-PFT-PFW-PFN) was synthesized by conventional solid-state reaction techniques. It showed moderate high dielectric constant, low dielectric loss, and two diffuse phase transitions, one below the room temperature ~261K and other above ~410K. X-ray diffraction (XRD) patterns revealed a tetragonal crystal structure at room temperature where as scanning electron micrograph (SEM) indicates inhomogeneous surface with an average grain size of 500nm-3µm. Well saturated ferroelectric hysteresis loops with good saturation polarization (spontaneous polarization, Ps ~ 30.68 µC/cm2) were observed. Temperature-dependent ac conductivity displayed low conductivity with kink in spectra near the phase transition. In continuing search for developing new ferroelectric materials, in the present study we report stoichiometric compositions of complex perovskite ceramic materials: (PZT-PFT-PFW-PFN) with diffuse phase transition behavior. The crystal structure, dielectric properties, and ferroelectric properties were characterized by XRD, SEM, dielectric spectroscopy, and polarization. The compositional variation on the phase transition temperature, dielectric constant, and ferroelectric to paraelectric phase transitions are discussed.
9:00 PM - P9.17
Effect of A-Site Doping Using Various Elements on the Phase Transition Temperatures in Perovskite Multiferroic BiFeO3 of Thin Films.
Hamidreza Khassaf 1 , Burc Misirlioglu 1 , Ebru Alkoy 2 , Sedat Alkoy 3
1 Faculty of Engineering & Natural Sciences, Sabanci University, Istanbul Turkey, 2 Faculty of Engineering, Maltepe University, Istanbul Turkey, 3 Materials Science and Engineering, Gebze Institue of Technology, Kocaeli Turkey
Show AbstractBiFeO3 remains as a material that attracts considerable interest since the discovery of both ferroelectric and magnetic ordering existing in this system. Growth of these structures in good quality using cost effective and fabrication-friendly methods is another aspect that deserves attention along with shedding light on how the paraelectric-ferroelectric transition would be altered in such structures. In this work, we grow pure and doped films of BiFeO3 on misfitting (001)SrTiO3 and (001)MgO substrates that induce different signs of misfit. We use a metallorganic route to grow the films and get strongly textured, near epitaxial, films as confirmed by our X-ray diffraction results. It is demonstrated that films with very good crystalline quality can be obtained. We find that addition of La and Gd, A-site dopants either expands or shrinks the lattice parameters respectively and also reduces the transition temperatures in bulk form compared to pure bulk BiFeO3. Films grown with various concentrations of doping on (001)SrTiO3 show a variety of surface morphologies where relatively high A-site doping levels favor island-like features whereas pure BiFeO3 structures grow with a smoother surface confimed by High Resolution Scanning Electron Microscopy and Atomic Force Microscopy. An exactly opposite trend appears to be the case for films synthesized on (001)MgO. We compare the structural data and the results of our thermal analysis to detect phase transition temperatures both for doped bulk samples and for doped strongly textured films and investigate the competition between the lattice strain due to dopants and misfit strains induced by the substrates.
9:00 PM - P9.18
Effect of Chemical Doping on the Structure and Properties of a Strain Induced Morphotropic Phase Boundary System.
Weigang Chen 1 , Zuhuang Chen 1 , Chuanwei Huang 1 , Lu You 1 , Ping Yang 2 , Junling Wang 1 , Lang Chen 1
1 School of Materials Science and Engineering, Nanyang Technological University, Singapore Singapore, 2 Singapore Synchrotron Light Source (SSLS), National University of Singapore, Singapore Singapore
Show AbstractMorphotropic phase Boundary (MPB), which refers to a boundary between two or more phases, shows enhanced dielectric and electromechanical properties. MPB can be induced by either chemical doping, such as Bi1-xSmxFeO3 with a MPB at Sm%=14%, or epitaxial strain, such as BiFeO3 on LaAlO3 or LaSrAlO3 substrates. For a better understanding of the interplay of epitaxial strain and chemical doping, we present here our study of the effect of Samarium doping on the structure and properties of strain-induced BFO MPB. Epitaxial BSFO films with different Sm concentrations were deposited on to LAO substrates. Structural and ferroelectric characterizations were carried out. RSM analysis confirms that BSFO have similar phases with pure BFO films. However, the critical thickness at which mixed phase shows up increases with the Samarium doping. The domain arrangement of T-like and R-like phases also shows different features. Furthermore, the piezoelectric coefficient of the MPB was enhanced with the Sm doping. Our results confirms that Samarium doping can increase the critical thickness and enhance the piezoresponse of the strain induced BFO MPB.
9:00 PM - P9.19
The Role of Intermediate Polarization Variants on Domain Switching Behavior in Epitaxial BiFeO3 Thin Films Investigated by Angle-Resolved Piezoresponse Force Microscopy.
Moonkyu Park 1 , Seungbum Hong 2 , Jeffrey Klug 2 , Orlando Auciello 2 3 , Kwangsoo No 1
1 Dept. of Materials Science & Engineering, KAIST, Daejeon Korea (the Republic of), 2 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 3 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractWe present results from our recent studies on the role of intermediate polarization variants on domain switching behavior and the influence of electric field on the domain structure in an epitaxially grown, cube-on-cube (001) BiFeO3 multiferroic thin film using angle-resolved piezoresponse force microscopy (AR-PFM). We constructed the precise in-plane ferroelectric domain configuration based on the in-plane phase images and sample rotation angle, θ, around the direction normal to the substrate surface. In-/out-of plane phase and amplitude images of polarization domains were obtained while rotating the sample from 0° to 180° with an interval of 30° between each domain image. We found that twelve in-plane polarization variants, within 30° angular displacements, form a complicated domain structure, and that under an external dc electric field polarization domain reversal initiates predominantly at the intermediate polarization variants deviating from the ferroelectric easy axes, i.e. <111> directions. After application of -7 V over a 2 µm × 2µm area, the twelve in-plane polarization variants are reduced to four, which include two prevailing variants oriented along ferroelectric easy axes and two intermediate variants which remain after polarization reversal. These results imply that application of an electric field larger than the coercive field rearranges the complicated and delicately balanced domain structure determined by the competition between electrostatics, strain, and growth kinetics into simple interweaving one that shows an electrostatically lower energy state.
9:00 PM - P9.20
Deterministic Control of Phase Variants Assembly in Highly Strained BiFeO3 Thin Films.
Jian Zhou 1 , Morgan Trassin 1 , Qing He 2 , Nobumichi Tamura 2 , Martin Kunz 2 , Jinxing Zhang 1 , Wen-I Liang 3 , Ying Hao Chu 3 , Ramamoorthy Ramesh 1 , Junqiao Wu 1 4
1 Department of Material Science and Engineering, University of California - Berkeley, Berkeley, California, United States, 2 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Department of Materials Science and Engineering, National Chiao Tung University, Hsin Chu, Taiwan, China, 4 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractIn the past decade, much attention has been attracted to the multiferroic BiFeO3 (BFO). As a single phase material, BFO shows a wealth of fascinating physical properties, including magnetoelectric coupling, domain wall conduction and even photovoltaic effects. Very recently, large compressive epitaxial strain was successfully achieved in this interesting material, driving the film into a mixture of self-assembled rhombohedral-like (R’) phase nano-lamellae embedded in tetragonal–like (T) phase matrix. Q. He et al. reported an enhanced spontaneous magnetization of 20-30 emu/cc emerging from these highly strained R’ phase nano-lamellae, making this system extremely attractive for realizing electric-field controllable magnetic devices. However, in such films, the R’ nano-lamellae with different morphologies and orientations coexist, and self-assemble into bands roughly along two orthogonal, in-plane directions of the films. Because the spontaneous magnetization of each R’ phase lamella lies along its long axis, multiple lamellae orientations result in ambiguity of local magnetization easy axis. This is undesirable if the R-phase lamellae are to be used as nanoscale device elements, such as data storage bits. Therefore, deterministic controlling of both the orientation and structure of these R’ phase nano-lamellae is necessary for understanding the origin of their magnetization and realizing their potential applications in nano-scale magnetic devices controlled by electric fields.In this report, we show that, for the first time, an in-plane electric field can modify the R’ phase lamellae assembly in a unique way. The applied in-plane electric field lifts the system’s structural degeneracy, and creates distinctive R’ phase nano-lamellae assembly with single variant precision, making possible the study of fundamental mechanism driving the complex assembly. Scanning probe microscopy combined with synchrotron micro-X ray diffraction techniques are employed to probe the local structural change induced by electrical switching. We find that the T-phase matrix between the R’ phase lamellae plays a crucial role in determining the morphology and structure of the R’ phase lamellae embedded in it. At last, the spontaneous magnetization in these artificially created R’ phase nano-lamellae assembly is investigated by X-ray magnetic circular dichroism based photoemission electron microscopy. This confirms that the magnetic easy axis in our system is readily controlled by electric field. Interesting correlation between the structure and magnetization direction is also observed. Our result represents an important step towards the understanding and ultimate controlling of the spontaneous magnetization in this highly strained multiferroic system. Besides their potential applications in nanoscale magnetic devices, the photovoltaic effect and electromechanical response of these well ordered R’ phase nano-lamellae also provide exciting opportunities for future studies.
9:00 PM - P9.21
Role of Substrate Clamping Effect on the Piezoelectric Response of Epitaxial xPb(Mg1/3Nb2/3)O3 –(1-x)PbTiO3 Thin Films.
Josh Frederick 1 , Seung-Hyub Baek 1 , Chang-Beom Eom 1 , David Felker 2 , Mark Rzchowski 2 , Darrell Schlom 3
1 Department of Materials Science & Engineering, University of Wisconsin, Madison, Wisconsin, United States, 2 Department of Physics , University of Wisconsin, Madison, Wisconsin, United States, 3 Department of Materials Science & Engineering, Cornell University, Ithaca, New York, United States
Show AbstractThe marriage of giant piezoelectric thin films with silicon substrates allows integration such high-performance materials into the well-established processing techniques employed in silicon-based micro- and nanoelectromechanical systems (MEMS and NEMS) for both sensing and actuation purposes. For example, epitaxial heterostructures of the relaxor ferroelectric material Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) and SrRuO3 grown on silicon with a template SrTiO3 layer exhibit high operating efficiencies (i.e. low driving voltages) relative to electrostatic actuators. However, the substrate clamping effect can drastically reduce the longitudinal piezoelectric coefficient (d33). In order to explore methods of alleviating the substrate clamping effect, we have grown high-quality epitaxial PMN-PT/SrRuO3 thin film heterostructures of varying thickness and composition on substrates of varying rigidity: (001) SrTiO3 (higher modulus) and (001) silicon (lower modulus). In each case, micro-pillars of the PMN-PT film have been fabricated using a focused ion beam to isolate the piezoelectric layer, thereby reducing the influence of the substrate clamping effect. For the various compositions and pillar sizes, the piezoelectric coefficients of the PMN-PT thin films were determined by double-beam laser interferometry and piezo-force microscopy. The role of mechanical boundary conditions and the dependence of piezoelectric response on composition will be discussed, which will help guide the geometrical design and chemistry of MEMS for optimal performance.
9:00 PM - P9.22
Design of Large Piezoelectricity in Novel Piezoelectric Thin Films Using High-Pressure Synthesis Phase Materials.
Shintaro Yasui 1 , Jun-ichi Nagata 1 , Hitoshi Morioka 2 , Hiroshi Uchida 3 , Minoru Kurosawa 1 , Hiroshi Funakubo 1
1 , Tokyo Institute of Technology, Yokohama Japan, 2 , Bruker AXS, Yokohama Japan, 3 , Sophia University, Tokyo Japan
Show AbstractFor design of large piezoelectric property using morphtropic phase boundary (MPB), tetragonal ferroelectric materials are very important. It is well known that Pb(Zr,Ti)O3, Pb(Mg1/3Nb2/3)O3-PbTiO3 and Pb(Zn1/3Nb2/3)O3-PbTiO3 systems having large piezoelectricity are used this concept, and included tetragonal PbTiO3 as an end member. To design novel piezoelectric materials, the discovery of alternative to PbTiO3 are key point. In the past, the investigation of tetragonal lead-free ferroelectric materials was limited only BaTiO3 and (Bi,K)TiO3 family. In 2006, Bi-based tetragonal ferroelectric materials of BiCoO3 and Bi(Zn1/2Ti1/2)O3 were synthesized under high pressure.[1, 2] In this study, we focused on these tetragonal materials and prepared solid solution epitaxial thin films of rhombohedral BiFeO3 and tetragonal BiCoO3/Bi(Zn1/2Ti1/2)O3 by metalorganic chemical vapor deposition(MOCVD). Crystal structure, electrical and piezoelectric properties of films were investigated systematically. BiCoO3-BiFeO3 and Bi(Zn1/2Ti1/2)O3-Bi(Mg1/2Ti1/2)O3-BiCoO3 epitaxial films grown on (100), (110) and (111)SrRuO3//SrTiO3 substrates showed perovskite structure without impurity phase within the limited composition region. Phase boundary between tetragonal and rhombohedral symmetries as a function of film composition variation was obtained in these films. Tetragonality of the films was controlled by substitution Mg ion to Zn ion site in Bi(Zn1/2Ti1/2)O3. Leakage current density of the films decreased with decreasing BiFeO3 and BiCoO3 contents or increasing Bi(Zn1/2Ti1/2)O3 and Bi(Mg1/2Ti1/2)O3. This result suggests that important factor of leakage current is the B-site ion occupied in perovskite structure having valence stable ion; Zn2+(d10), Mg2+(d0) Ti4+(d0). Maximum piezoelectric coefficient of approximately 300 pm/V was obtained for (110)/(101)-oriented films near phase boundary composition. Bi perovskite materials including tetragonal structure shows large piezoelectricity as same as PbTiO3-based ones.[1] A. A. Belik, S. Iikubo, K. Kodama, N. Igawa, S. Shamoto, S. Niitaka, M. Azuma, Y. Shimakawa, M. Takano, F. Izumi, and E. Takayama-Muromachi, Chem. Mater. 18 (2006) 798.[2] M. R. Suchomel, A. M. Fogg, M. Allix, H. Niu, J. B. Claridge, M. J. Ro sseinsky, Chem. Mater. 18 (2006) 4987.
9:00 PM - P9.23
Ferroelectric and Piezoelectric Properties of Lead-Free NKN Thin Films Fabricated by RF Magnetron Sputtering Using High Density Ceramic Target.
Hye Yeon Jeong 1 , Hyung-Won Kang 1 , Hak In Hwang 1 , Hyeung-Gyu Lee 1 , Chang Won Ahn 2 , Ill Won Kim 2 , Seung Ho Han 1
1 Electronic Materials & Device Research Center, Korea Electronics Technology Institute, Seongnam Korea (the Republic of), 2 Department of Physics, University of Ulsan, Ulsan Korea (the Republic of)
Show AbstractPZT-based materials have been investigated for a variety of engineering applications such as actuators and sensors due to their high ferroelectric and piezoelectric properties. However, recent environmental issues around the world have limited the use of Pb-based materials. Therefore, lead-free piezoelectric materials have been attracting great attention due to their eco-friendly nature as compared with PZT-based toxic materials. Among the various lead-free piezoelectric materials, (Na0.5K0.5)NbO3 (NKN) is considered to be a more promising candidate because it has good ferroelectric and piezoelectric properties as well as a high Curie temperature. There have been several reports on NKN thin films fabricated by sol-gel process [1,2], pulsed laser deposition [3], and RF magnetron sputtering [4,5]. In particular, NKN thin films fabricated by RF magnetron sputtering have been scarcely reported because it is difficult to form high quality thin film with highly preferred orientation on Pt coated Si substrate. Shibata et al. reported a highly preferred NKN thin film on Pt(111)/Ti/SiO2/Si substrate deposited by RF magnetron sputtering [4]. However, the P-E loop was not well-saturated. Meanwhile, Lee et al. showed well-saturated P-E hysteresis loop for NKN thin film on Pt(111)/Ti/SiO2/Si substrate deposited by RF magnetron sputtering. However, the NKN thin film had polycrystalline behavior without preferred crystal orientation. In addition, the target was enriched with excessive amount of Na, K (Na:K:Nb=1.5:1.5:0.5), which made it very unstable in the moisture condition.In this study, lead-free piezoelectric NKN thin films were fabricated on Pt(111)/Ti/SiO2/Si substrate by RF magnetron sputtering method. The stoichiometric NKN ceramic target was fabricated by conventional solid state reaction. The experimental conditions were varied to form highly oriented thin film with enhanced ferroelectric properties. The NKN thin film deposited at optimum condition showed highly preferred orientation without second phases and with well-saturated P-E hysteresis loop. [1] F. Lai, J.-F. Li, Z.-X. Zhu, and Y. Xu, Jpn. J. Appl. Phys. 106 (2009) 106[2] F. Lai, J.-F. Li, Z.-X. Zhu, and Y. Xu, and Ying Xu, J. Appl. Phys. 106 (2009) 064101[3] M. Abazari, E. K. Akdogan, and A. Safari, J. Appl. Phys. 103 (2008) 104106[4] K. Shibata, F. Oka, A. Ohishi, T. Mishima, and I. Kanno, Appl. Phys. Express 1 (2008) 011501[5] H. J. Lee, I. W. Kim J. S. Kim, C. W. Ahn, and B. H. Park, Appl. Phys. Lett. 94 (2009) 092902
9:00 PM - P9.24
Electric Power Measurement of Unimorph-Type Piezoelectric Energy Harvester Using Various Piezoelectric Ceramics.
Seung Ho Han 1 , Hwi-Yeol Park 1 , Hyung-Won Kang 1 , Chan-Sei Yoo 1 , Woo Sung Lee 1 , Hyeung-Gyu Lee 1
1 Electronic Materials & Device Research Center, Korea Electronics Technology Institute, Seongnam Korea (the Republic of)
Show AbstractScavenging and converting environmental energy into exploitable electric energy have been gaining wide spread popularity. Renewable power can be obtained from various environmental energy sources such as solar energy, temperature gradient, and kinetic energy present within devices’ environment. Among the various environmental energies, piezoelectric energy harvesting is promising because it can generate sufficient energy for many applications with low to medium power requirements. In the piezoelectric energy harvesting applications, it has been considered that the harvested energy per unit volume is proportional to the product of piezoelectric strain constant (d) and piezoelectric voltage constant (g).In this study, electric power of unimorph-type piezoelectric energy harvester fabricated by using four kinds of piezoelectric ceramic materials was measured. The electric power of all four generators was measured under their resonant frequencies, with optimal resistance loads, and at equivalent acceleration condition. The experimental values were compared with simulated results to confirm the reliability. We could investigate the relationship between the electric power and piezoelectric material constant, such as d31, g31, and d31×g31.
9:00 PM - P9.25
Tilt Transitions in Compressively Strained AgTaxNb1-xO3 Thin Films.
Raegan Johnson-Wilke 1 , Daniel Tinberg 1 , Charles Yaeger 1 , Yisong Han 2 , Ian Reaney 3 , Igor Levin 4 , Tim Fister 5 , Dillon Fong 5 , Susan Trolier-McKinstry 1
1 , Penn State, University Park, Pennsylvania, United States, 2 Nanoscale Physics Research Laboratory, University of Birmingham, Birmingham United Kingdom, 3 Department of Engineering Materials, University of Sheffield, Sheffield United Kingdom, 4 Ceramics Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 5 , Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractPhase transitions in coherently strained epitaxial AgTa0.5Nb0.5O3 films grown on SrTiO3 (001) substrates were characterized by high resolution x-ray diffraction and transmission electron microscopy. It was found that coherently strained films undergo the same phase transition sequence as bulk materials: cubic (C) ↔ tetragonal (T) ↔ orthorhombic (O) ↔ orthorhombic (M3). However, the compressive in-plane strain stabilized the tetragonal and orthorhombic phases, expanding these phase fields by ≈ 250 °C. Moreover, in response to the smaller in-plane lattice parameters, the films exhibit c-axis domain texture; the complex octahedral tilt system, a-b-c-/a-b-c+, in the M3 phase and the in-phase tilt of the T phase both occur around the out-of-plane direction. In contrast, bulk materials and relaxed films are poly-domain, with the complex tilt system occurring along all three of the orthogonal axes. These results demonstrate unambiguously that strain engineering in systems with complex tilt sequences such as AgTa0.5Nb0.5O3 is feasible and open up the possibility of modifying properties by manipulation of the pertinent octahedral tilt transition temperature in a wide range of functional ceramics.
9:00 PM - P9.26
First-Order Reversal Curve Probing of Polarization Dynamics in Ferroelectric Nanocapacitors.
Yunseok Kim 1 , Amit Kumar 1 , Oleg Ovchinnikov 1 , Stephen Jesse1 1 , Hee Han 2 , Ionela Vrejoiu 3 , Woo Lee 2 , Dietrich Hesse 3 , Marin Alexe 3 , Sergei Kalinin 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , Korea Research Institute of Standards and Science, Daejeon Korea (the Republic of), 3 , Max Planck Institute of Microstructure Physics, Halle (Saale) Germany
Show AbstractPolarization switching in ferroelectric materials directly underpins memory devices including ferroelectric based data storages and random access memories. The intrinsic feature of switching in ferroelectrics is the presence of multiple remnant states dependent on field history, enabling multi-level storage devices in classical capacitor configuration. These modes of polarization switching are strongly related to local microstructure and disorder that allows multiple metastable states to exist. Hence, understanding of polarization reversal processes and the effect of local microstructure is required to efficiently control the device functionalities and further to achieve high memory density with proper binary or multiple-state functionalities. Here, we explore the polarization switching process of BiFeO3 (BFO) nanocapacitors using the first order reversal curve (FORC) method based on switching spectroscopy piezoresponse force microscopy (SS-PFM) techniques, which allows us to explore the field history of the hysteresis loop. Spatial maps of switching coefficients and FORCs reveal that individual polarization switching inside the nanocapacitors depends on the local microstructure. In order to analyze the switching behavior of the FORCs in BFO nanocapacitors, the classical Kolmogorov-Avrami-Ishibashi (KAI) model, which describes the polarization switching dynamics of ferroic materials on the time domain, has been adapted to the voltage domain. The polarization switching dynamics of the FORCs are well approximated by the adapted KAI model. The proper obtained values from the adapted KAI model also shows that the present model well describes polarization switching dynamics of BFO nanocapacitors. The results both show nanoscale switching dynamics of capacitor structures and provide a correlation between polarization switching and local microstructure. Acknowledgment: This research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Office of Basic Energy Sciences, U.S. Department of Energy.
9:00 PM - P9.27
Unusual Interplay between Thermal and Switching Behavior of Multiferroic Nanocapacitor.
Yunseok Kim 1 , Stephen Jesse 1 , Amit Kumar 1 , Alexander Tselev 1 , Hee Han 2 , Ionela Vrejoiu 3 , Woo Lee 2 , Dietrich Hesse 3 , Marin Alexe 3 , Sergei Kalinin 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , Korea Research Institute of Standards and Science, Daejeon Korea (the Republic of), 3 , Max Planck Institute of Microstructure Physics, Halle (Saale) Germany
Show AbstractPolarization switching in ferroelectric and multiferroic materials has been intensively investigated in the context of memory devices including ferroelectric based data storage, and ferroelectric random access memories. In parallel to these studies, conduction mechanisms in these materials have been also studied, owing to relationships between leakage currents, device reliability, and degradation. These studies have received broad attention recently since correlation between conduction and polarization state of materials was established using a combination of local scanning probe microscopy (SPM) techniques such as piezoresponse force microscopy (PFM) and conductive atomic force microscopy. In addition to physical mechanisms of interest such as bias-induced polarization switching and current flow, a broad spectrum of thermal and electrochemical effects can emerge. In particular, Joule heating induced by current flow will result in material expansion that can contribute to the measured PFM signal. Similarly, local temperature rise can facilitate the domain nucleation and growth. However, there is still lack of information on the interplay between the conduction and the domain switching behavior. In this presentation, we discuss the interplay between polarization dynamics, conduction, and electromechanical response in model BiFeO3 nanocapacitor structures combining SPM and modeling. We have developed a PFM-based technique that allows us to selectively probe the non-linear responses associated with Joule heating effects, and established quantitative guidelines for their observation. The non-linear responses associated with Joule heating effects and their contributions to polarization dynamics have been investigated. The finite element modeling also proved the Joule heating contributions to the non-linear response. This Joule heating induced by current flow will result in material expansion that can contribute to the measured PFM signal, and in locally increased temperature that can facilitate the polarization switching. These effects allow to improve SPM techniques and to open a possible pathway to nanoscale memory applications.Acknowledgment: This research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Office of Basic Energy Sciences, U.S. Department of Energy.
9:00 PM - P9.28
The Electrical Characterization of BiFeO3-PbTiO3 Ferroelectric Thin Films by PUND Technique.
Dongmei Sun 1 , Shengwen Yu 1 , Guiyang Shi 1 , Jinrong Cheng 1
1 School of Materials Science and Engineering, Shanghai University, Shanghai China
Show AbstractBiFeO3 (BFO) material is unique for the multiferroic phenomena exhibiting above room temperature. However, insulation is the most harassing issue in BFO film material. BiFeO3-PbTiO3 (BFO-PT) thin film is accordingly derived to improve the insulation while inheriting the multiferroic feature from the BFO parent. In this report, xBiFeO3-(1-x)PbTiO3 (0≤x≤1) thin films were prepared on FTO glass substrates. Positive-up-negative-down (PUND) characterization was adopted to measure the electrical properties of the BFO-PT thin films. The PUND technique can accurately describe the ferroelectric polarization information of the BFO-PT thin films by eliminating the effect stemming from the leakage conductance. Combining with the typical dielectric and ferroelectric measurements, such as capacitance-voltage curves and P~E hysteresis loops, the ferroelectric feature and insulation of the BFO-PT thin films with diverse composition x will be analyzed in detail in this work. The composition dependence mechanism will be discussed as well.
9:00 PM - P9.29
Probing Nanoscale Ferroelectric Domain Switching Mechanisms with Band Excitation Piezoresponse Spectroscopy.
Vasudeva Aravind 1 , Senli Guo 2 , Stephen Jesse 2 , Amit Kumar 2 , Sergei Kalinin 2 , Venkatraman Gopalan 3
1 Physics, Clarion University, Clarion, Pennsylvania, United States, 2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Clarion, Pennsylvania, United States, 3 Materials Science and Engineering and Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractFerroelectric domain walls, long believed to be static topological defects, have recently been demonstrated to exhibit a rich panoply of nanoscale switching behaviors, due to interplay between wall bowing and bulk-like nucleation (V. R. Aravind et al, Physical Review B 82, 024111 (2010)). In this presentation, we report the study of a single 180-degree domain wall response to electrical excitation at multiple frequencies, probed with band excitation piezoresponse spectroscopy. We demonstrate that domain wall acts like an energy dissipation center, owing to bending and bowing of the wall for applied electric fields, and that the resonance frequency of the cantilever shows local variations on either side of the domain wall, providing insights into micromechanics of domain formation.
9:00 PM - P9.30
Switching Charge Density of Ferroelectric PbTiO3 Nanoislands.
Hironori Fujisawa 1 , Kosei Yamada 1 , Seiji Nakashima 1 , Masaru Shimizu 1
1 , University of Hyogo, Himeji Japan
Show AbstractWe report switching charge density (Qsw) of PbTiO3 nanoislands with an average height of 4~5 nm and a width of less than 100 nm. PbTiO3 nanoislands were prepared at 540-600oC on Pt/SrTiO3(100) by self-assembly using metalorganic chemical vapor deposition (MOCVD). The Qsw was measured using scanning probe microscopy (SPM) and a commercially available cantilever with a blunt SPM tip. The tip has a well-defined circular end-face with a plateau diameter of 1.8 μm. A 100-nm-thick Ir film with a 20-nm-thick Ti adhesion layer was sputtered to add electrical conductivity to the tip. The SPM tip was directly contacted to PbTiO3 nanoislands as a top electrode, which enabled electrical characterization of as-prepared samples without fabricating top electrodes or any preprocessing. A pulse train with a preceding negative pulse, two consecutive positive pulses and two negative pulses was applied to the Pt bottom electrode, and the current transient detected by the series resistance was amplified by the high-speed voltage amplifier. The output of the amplifier and voltage pulse were observed using a digitizing oscilloscope. The minimum detectable current in the system was less than 1μA. Using this SPM system, switching current transients were successfully observed for PbTiO3 nanoislands and discontinuous films with surface coverage ranging from 13 to 56 %. Current transients observed using the SPM system were derived from polarization switching, leakage and charging currents to the parasitic capacitance, which were similar to those observed for ferroelectric capacitors. Therefore, Qsw was calculated by subtracting the non-switching current from the switching current. The maximum Qsw were 138 and 155μC/cm2 for nanoislands with coverage of 13 and 28 %, and 170μC/cm2 for discontinuous film with coverage of 56%, respectively. This proves that PbTiO3 nanoislands with an average width of 50 nm and average height of 5 nm did indeed yield spontaneous polarizations as large as those of the continuous films. Switching current measurements on individual PbTiO3 nanoislands and the size dependence of spontaneous polarization of ferroelectric nanoislands will also be discussed.
9:00 PM - P9.31
Structural Dynamics in Ferroelectric PbTiO3 Films.
Agnes Szoekefalvi-Nagy 1 , Miguel Castro-Colin 1 , Valentin Iov 1 , Celine Lichtensteiger 2 , Matthew Dawber 2 , Jean-Marc Triscone 2 , Peter Wochner 1
1 Low Dimensional and Metastable Materials, Max-Planck-Institut fuer Intelligente Systeme, Stuttgart, Baden-Wuerttemberg, Germany, 2 DPMC, U. of Geneva, Geneva Switzerland
Show AbstractA novel experimental setup has been constructed for studying the polarization-switching phenomena in ferroelectric thin films. The equipment is capable of detecting the time-dependent diffraction pattern obtained from monochromatic synchrotron X-rays, using a time resolution of 1-100 μs, and a full time range of the applied electric field corresponding to 1-100 ms. In the present case experiments have been performed at the synchrotron radiation source ANKA MPI-Beamline (Karlsruhe, Germany) on a ferroelectric perovskite thin film sample: PbTiO3 (40 nm) epitaxially grown onto SrTiO3 substrate covered by a conductive ceramic SrRuO3 (20 nm) layer (lower electrode). On top of the sample a gold layer serves as an upper electrode. In the experiment the sample is exposed to a periodic electrostatic field E(t) with varying polarity but constant magnitude. The magnitude of the electric field was changed up to 1 MV/cm. The diffraction pattern is registered in the vicinity of the (002) peak with a resolution of 1/1000 r.l.u. Both, the applied electric field and the probing momentum transfer are perpendicular to the sample surface. This setup enables us to disclose the time-dependent elastic strain induced by the electric field E(t), which can be interpreted in terms of the ferroelectric polarization of the layer, via the so-called butterfly loop. Details of the polarization switching process can be obtained from measurements of the intensity ratio and broadening of the diffraction peaks, corresponding to the two opposite electric field polarities.
9:00 PM - P9.32
Modulated Structures and Related Microstructures in Pb(In1/2Nb1/2)O3 with the Perovskite B-Site Randomness.
Shigeo Mori 1 , Kousuke Kurushima 2 , Hidehiro Ohwa 3 , Naohiko Yasuda 3 , Kenji Ohwada 4
1 Dept. of Material Sceince, Osaka Prefecture University, Sakai, Osaka, Japan, 2 , Toray Research Center, Ohtsu, Shiga Japan, 3 , Gifu University, Gifu Japan, 4 , Spring 8, Japan Atomic Energy Agency, Hyogo Japan
Show AbstractPerovskite oxide, Pb(In1/2Nb1/2)O3 (PIN), exhibits ferroelectric (FE), antiferroelectric (AFE) and relaxor behaviours, which depend strongly on the perovskite B-site randomness. Note that the randomness is characterized as spatial distribution of In and Nb ions on the perovskite B-site and can be controlled by the annealing treatment [1,2]. In order to clarify influences of the B-site randomness on physical properties such as dielectric dispersion, we have investigated microstructures in both the AFE and relaxor states by a transmission electron microscopy (TEM). Note that in the AFE state In and Nb are 1 : 1 ordered along the <111> direction and, on the other hand, In and Nb are disordered in the relaxor state. We carried out electron diffraction experiments and revealed that the AFE state is characterized as the modulated structure with the modulation vector of q=1/4 1/4 0 at 298 K. High-resolution TEM images clearly show the coexistence of two types of domains comprising the modulated and the non-modulated structures. On the other hand, in the relaxor state there appear two types of diffuse scatterings in the ED patterns with the [001] incidence. One is diffuse spots at the 1/2 1/2 0-type reciprocal positions and the other is diffuse streaks elongating along the <110> direction around the fundamental spots. We examined microstructures giving rise to the diffuse streaks by obtaining the real-space TEM images and found that there exist nanodomains with the size of ~ 5 nm. These nanodomains in the relaxor state should be responsible for the characteristic dielectric properties, as in the case of the relaxor state of PMN [3]. [1]. N. Yasuda et al., J. Phys. Soc. Jpn. 67, 3952 (1998). [2]. K. Ohwada et al., Phys. Rev. B 77, 094136 (2008). [3]. D. Fu et al., Phys. Rev. Lett., 103, 207601 1-4 (2009).
9:00 PM - P9.35
Evaluation of X-Ray Source Using Multiple LiTaO3 Single Crystals.
Hiroyuki Honda 1 , Shinji Fukao 1 , Yoshikazu Nakanishi 1 , Yuuki Sato 1 , Yoshiaki Ito 2 , Shinzo Yoshikado 1
1 , Doshisha University, Kyotanabe, Kyoto, Japan, 2 , Kyoto University, Uji, Kyoto, Japan
Show Abstract Pyroelectric crystals have recently been used to generate X-rays. A miniaturized X-ray source based on a pyroelectric crystal can be used in portable analytical instruments such as portable X-ray fluorescence spectrometers because the X-ray source can be activated by batteries. However, this method suffers from discontinuous X-ray emission and low and/or unstable intensity. Moreover, the X-ray intensity is unstable at current stage. These problems make it difficult to use these X-ray sources in practical applications. The problems can be substantially overcome by using multiple pyroelectric crystals and supplying sufficient electrons. If these problems can be overcome, it should be possible to use these sources for radiation therapy and in portable diagnostic devices. In this study, six LiTaO3 crystals are used to achieve continuous emission of high-intensity X-rays, and the interaction between X-rays and the case of the X-ray source is used to generate electrons. Furthermore, the effect of the shape of a target is investigated. Six nonstoichiometric LiTaO3 single crystals with dimensions of 5 mm × 5 mm × 5 mm were used. The electrical surfaces (z surfaces), which were perpendicular to the c-axis, were mirror polished. The cases were made from stainless steel, oxygen-free copper or aluminum. The conical niobium targets with various apex angles and heights were used. The target was placed at the center of the case. The positively charged surface (+z surface) of each crystal was attached to a Peltier device using silver paste. The six crystals were arranged hexagonally around the target so that the negatively charged surface (–z surface) of the crystal faced the target. The case, target, and +z surface were electrically grounded. The temperatures of the crystals were controlled by applying triangular voltages to the Peltier devices. A temperature range ΔT of approximately 40 °C was used. The phase difference between the temperature changes of adjacent crystals was adjusted 60 °. The temperature change period was 1000 sec. The ambient gas was air and the pressure in the case was high vacuum. Continuous X-ray emission was obtained and fluctuation in the X-ray count rate was reduced. The shape of the target also affected the X-ray count rate. Moreover, it was suggested that the X-ray count rate was dependent on the case materials. The X-ray count rate was the highest when using the aluminum case. This is probably because the amount of the electrons supplied through the interaction between emitted X-rays and the inner wall of the case was different. The photoelectric effect will occur readily if the work function is low, and decreasing the fluorescence yield of the case material is also important for the Auger process. Aluminum has lower fluorescence yield as compared with stainless steel or copper. It was suggested that more Auger electrons were supplied when using the aluminum case.
9:00 PM - P9.37
X-Ray Nanodiffraction Study of Intermediate Monoclinic Phase in BaTiO3 Single Crystals.
Tom Lummen 1 , Martin Holt 2 , Jianjun Wang 1 , Amit Kumar 1 , Eftihia Vlahos 1 , Sava Denev 1 , Long-Qing Chen 1 , Venkatraman Gopalan 1
1 Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractThe structural symmetry of domains in perovskite materials plays a pivotal role in determining their ferroelectric properties. In particular, low-symmetry monoclinic phases in ferroelectric materials are of considerable interest, due to their associated enhanced electromechanical coupling. Such phases have been found in Pb-based perovskite solid solutions such as lead zirconate titanate (PZT), where they form structural bridges between the rhombohedral and tetragonal ground states in compositional space [1]. The low symmetry phase, being a shared symmetry subgroup of the phases on either side of this so-called ‘morphotropic’ phase boundary, constitutes a natural intermediate phase, facilitating a symmetry-allowed continuous rotation of the ferroelectric polarization, thereby inducing the high piezoelectric coupling observed in the material [2,3]. For BaTiO3, it has been shown through biaxial strain engineering [4] that low-symmetry phases with strongly enhanced electromechanical properties can be stabilized in thin films, with first principles calculations [5] and phase field modeling [6] linking these properties to monoclinic structural distortions. Furthermore, poling BaTiO3 with electric fields along specific crystallographic directions has been shown to yield induced monoclinic phases and enhanced piezoelectricity in single crystals [7 ,8]. In preceding work, we have directly imaged a metastable monoclinic phase in BaTiO3 crystals at room temperature. Using optical Second Harmonic Generation (SHG) and micro-Raman imaging, this phase was observed just above the thermal tetragonal-orthorhombic phase boundary. Moreover, complementary phase-field modeling has revealed that the origin of this monoclinicity lies in the evolution of the ferroelectric domain micro-structure as the material is cycled through this transition. In this work we focus on quantifying the structural distortion of this metastable phase, by employing X-ray Nano-Diffraction (XND) imaging at a resolution of ~60 nm. The obtained X-ray-based images show excellent correlation to complementary SHG images, with the contrast in both corresponding to varying degrees of distortion. Analysis of X-ray data shows alternatingly distorted domains on a scale of 400 nm. The induced metastable phase, observed to persist for months at room temperature, is found to be ferroelectrically softer than the tetragonal phase, with the corresponding monoclinic domains easily moved by electric fields as low as 0.5 kV cm-1.[1] B. Noheda et al., Appl. Phys. Lett. 74, 2059 (1999)[2] B. Jaffe et al., J. Appl. Phys. 25, 809 (1954)[3] R. Guo et al., Phys. Rev. Lett. 84, 5423 (2000)[4] K.J. Choi et al., Science 306, 1005 (2004)[5] O. Diéguez et al., Phys. Rev. B 69, 212101 (2004)[6] Y.L. Li and L.Q. Chen, Appl. Phys. Lett. 88, 072905 (2006)[7] S.-E. Park et al., J. Appl. Phys. 86, 2746 (1999)[8] H. Cao et al., Appl. Phys. Lett. 94, 032901 (2009)
9:00 PM - P9.38
Nanoscale Modulation of High-Temperature Superconductivity via Ferroelectric Field Effects.
Arnaud Crassous 1 2 , Rozenn Bernard 1 2 , Stephane Fusil 1 2 3 , Karim Bouzehouane 1 2 , Shaima Enouz-Vendrenne 4 , Javier Briatico 1 2 , Manuel Bibes 1 2 , Agnes Barthelemy 1 2 , Javier Villegas 1 2
1 , Unite Mixte de Physique CNRS/Thales, Palaiseau France, 2 , Université Paris Sud 11, Orsay France, 3 , Université d’Evry-Val d’Essonne, Evry France, 4 , Thales RT, Palaiseau France
Show AbstractThe electrostatic tuning of physical properties in materials offers significant potential in a large variety of systems [1]. For example, the application of an electric field allows depressing or enhancing superconductivity in certain oxides [2]. Using heterostructures that combine a large-polarization ferroelectric (BiFeO3) and a high-temperature superconductor (YBa2Cu3O7-δ), we demonstrate here the nanoscale modulation of the superconducting condensate via ferroelectric field effects. The ability to design the ferroelectric domain structure at will enables us to create nanoscale “patterns” of normal regions within the superconductor, in a reversible and modifiable way. This allows us to create energy landscapes that govern the dynamics of flux quanta. The nanoscale ferroelectric field effects demonstrated here pave the road towards reconfigurable superconducting electronics, and may be extended to different strongly correlated electron systems for the fabrication of tunable nanoscale circuits.Work supported by French ANR via “Superhybrids-II”, “OXITRONICS”, and “Méloic” grants.[1] C. H. Ahn, J. M. Triscone, J. Mannhart, Nature 424 1015 (2003).[2] C. H. Ahn et al., Science 284, 1152 (1999) ; K. S. Takahashi et al., Nature 44, 195 (2006)..
9:00 PM - P9.39
Temperature-Strain Phase Diagram in BaTiO3/SrTiO3 Superlattices.
Dmitri Tenne 1 , A. Farrar 1 , J. Schmidt 1 , E. Vlahos 2 , A. Soukiassian 3 , P. Wu 2 , L. Chen 2 , S. Nakhmanson 4 , X. Xi 5 , M. Bernhagen 6 , P. Reiche 6 , R. Uecker 6 , C. Bark 7 , C. Eom 7 , V. Gopalan 2 , D. Schlom 3
1 Physics, Boise State University, Boise, Idaho, United States, 2 Materials Science and Engineering, the Pennsylvania State University, University Park, Pennsylvania, United States, 3 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 4 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 5 Physics, Temple University, Philadelphia, Pennsylvania, United States, 6 , Leibniz Institute for Crystal Growth, Berlin Germany, 7 Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin, United States
Show AbstractStrain effect on phase transitions in nanoscale BaTiO3/SrTiO3 ferroelectric superlattices has beenstudied by ultraviolet Raman spectroscopy and second harmonic generation. A series of coherentlystrained BaTiO3/SrTiO3 superlattices have been grown by molecular beam epitaxiy on various rareearth scandate ReScO3 (Re = Dy, Tb, Gd, Eu, Sm, Nd, and Pr), and SrTiO3 substrates. Therefore, a systematic variation of strain state in superlattices was achieved by varying the in-plane latticeconstant from 0.3905 nm to 0.4022 nm. Theferroelectric phase transition temperature was found from Raman and second harmonic generationdata to vary in a broad temperature range from 400 to about 700 K. Experimental data indicated thepresence of different ferroelectric phases with out-of-plane and in-plane components of polarizationin superlattices, depending on strain and temperature. Experimental results are supported byfirst-principles calculations of lattice instabilities in BaTiO3/SrTiO3 superlattices the temperature-strain phase diagram calculated within the phase-field model. Supported part by the NSF DMR-0705127 (D.A.T), DMR-1006136 (D.A.T.), DMR-0820404 (L.Q.C, V.G), NSF-0908718 (L.Q.C, V.G), ECCS-0708759 (C.B.E.), and by the DoE contract No. DE-AC02-06CH11357 (S.M.N.).
9:00 PM - P9.40
Solid-State Memories Using Ferroelectric Tunnel Junctions.
Andre Chanthbouala 1 , Vincent Garcia 1 , Arnaud Crassous 1 , Ryan Cherifi 1 , Karim Bouzehouane 1 , Stephane Fusil 1 , Xavier Moya 2 , Julie Grollier 1 , Stephane Xavier 3 , Neil Mathur 2 , Manuel Bibes 1 , Agnes Barthelemy 1
1 , Unité Mixte de Physique CNRS/Thales, Palaiseau France, 2 Department of Materials Science, University of Cambridge, Cambridge United Kingdom, 3 , Thales Research and Technology, Palaiseau France
Show AbstractBecause they show an hysteretic dependence with their conjugate field, ferroic order parameters are excellent state variables for information storage (such as magnetization in hard-disk drives). Coupling ferroics with quantum-mechanical tunneling permits a simple and fast readout of the stored information through the influence of ferroic orders on the tunnel current. For example, tunnel junctions with ferromagnetic electrodes display tunnel magnetoresistance (corresponding to their OFF/ON ratio) through which magnetization-encoded information is read in magnetic random access memories (MRAMs). Despite continuous efforts to improve performance and scalability, MRAMs still rarely show OFF/ON ratios larger than 4, with inherently power consuming write operations (>106 A/cm2). Here, we report OFF/ON ratios as large as 100 with very low write current densities (<104 A/cm2) in tunnel junctions integrating another ferroic – in this case a ferroelectric – as the barrier. The junctions show large, stable, reproducible and reliable tunnel electroresistance, with resistance switching related to ferroelectric polarisation reversal. They emerge as an alternative to other resistive memories, with the additional advantage of not being based on voltage-induced migration of matter at the nanoscale, but on a purely electronic mechanism .
9:00 PM - P9.41
Evaluation of Al-Doped ZnO Top Electrodes for PbLaZrTiOx Capacitors.
Toru Tsuji 1 , Youko Takada 1 , Naoki Okamoto 1 , Takeyasu Saito 1 , Kazuo Kondo 1 , Takeshi Yoshimura 2 , Norifumi Fujimura 2 , Akira Kitajima 3 , Akihiro Oshima 3
1 chemical engineering, Osaka Prefecture University, Sakai, Osaka, Japan, 2 electronic physics, Osaka Prefecture University, Sakai, Osaka, Japan, 3 , Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka, Japan
Show Abstract Ferroelectric Random Access Memory (FeRAM) is one of the most promising devices which have advantages as fast access time, non volatility and low energy consumption. For example, the application of FeRAM includes transportation, IC tags, mobile cards, and so on. However, conventional noble metal electrodes for ferroelectric materials, Pt, Ir or IrO2, causes price and resource issues for FeRAM device fabrication. In this study, we used conductive Al-doped (3 at%) ZnO as an alternative for Pt top electrodes of PbLaZrTiOx (PLZT) capacitors and evaluated the ferroelectric properties. This replacement decreases device cost and also eliminates supply instability. The substrates were highly (111)-oriented sputtered Pt as lower electrodes. PLZT films (450nm) were prepared by the sol-gel method. Al-doped ZnO were formed by pulse laser deposition (PLD) as top electrodes, in which deposition was performed with a metal through mask having 75um - 500um diameter. Based on the deposition rate, electrodes thickness was changed from 50nm to 140nm. The measurements of ferroelectric properties was carried out with the sample as prepared and after heating in 200°C, 1Torr, 3% hydrogen atmosphere for prescribed period. The various encapsulation oxide thin films were deposited by PLD or by radio frequency sputtering on top electrodes of ferroelectric PbLaZrTiOx (PLZT) capacitors. Initial polarization values (2Pr) of PLZT with Pt and with Al-doped ZnO as top electrodes (200um diameter) were 62uC/cm2 and 67uC/cm2, respectively, which indicates Al-doped ZnO is promising electrodes for PLZT capacitors. The remained polarization values of PLZT with Pt and with Al-doped ZnO electrodes after 15 minutes heating in 3% hydrogen atmosphere were 50% and 70%, respectively, which indicates Al-doped ZnO should be robust electrodes compared with Pt for FeRAM integration. Electrodes thickness dependency as well as encapsulation oxide insulator dependency will be discussed.
9:00 PM - P9.42
1D Ferroelectric - Carbon Nanotubes Composites.
Paula Vilarinho 1 , Amit Mahajan 1 , Rubaiyet Haque 1 , Angus Kingon 2
1 Department of Ceramics and Glass Engineering, University of Aveiro, Aveiro Portugal, 2 Division of Engineering, Brown University, Providence, Rhode Island, United States
Show AbstractMiniaturization of microelectronics device size is currently not only about reducing dimensions but also encompasses the development of devices that incorporate new and combined functionalities. One-dimension (1D) structures could allow miniaturization and at the same time facilitate new functionalization if the structures can be utilized as the “backbone” for new composite materials. We explore the case of 1D carbon nanotubes (CNTs) / ferroelectric (FE) structures, which have not yet previously been systematically addressed. CNTs have a unique set of mechanical, chemical and electrical properties which make them very promising for the development of nanostructures and nanocomposites. In particular the ballistic electron transport and a huge current - carrying capacity, are of interest for the above-mentioned future microelectronics.In this work 1D advanced functional composites nanostructures of the ferroelectrics PbZrxTi1-xO3 (PZT) and BaTiO3 (BT) with CNTs were synthesised using low cost mass production routes in which CNTs were used as the conductor. Two critical aspects were addressed in this work: the wetability of the tubes surface by the FE solution and the crystallization temperature of the FE phase. Electrophoretic deposition (EPD) was used to prepare CNTs films on conducting substrates. Due to high van der Waals forces CNTs tend to agglomerate. Thus CNTs were functionalized using both covalent (e.g., nitric acid and sulfuric acid functionalized) and non-covalent (e.g., anionic surfactant sodium dodecyl sulfate (SDS) functionalized) methods to yield charged CNT surfaces that helped the dispersion of the tubes and simultaneously optimized the affinity towards the FE precursors. Functionalised CNTs resulted in good wetability and excellent tube surface coverage. The FE precursors of PZT and BT were deposited by chemical solution deposition on the surface of CNTs. A key aspect is the crystallization temperature of the FE phase to ensure the integrity of CNTs if the tubes are to act as bottom electrodes. The combination of diphasic sol-gel based precursors and controlled atmospheres allowed the synthesis of the FE phase at temperatures lower than 550 degree C. The physical properties of FE / CNTs composites were addressed by piezoresponse force microscopy. Relationships between the pre-treatments of CNTs, wetting properties and crystalline phase formation are described.
9:00 PM - P9.47
Modeling and Evaluation of Output Power of a Transverse Mode Piezoelectric Energy Harvester Using Conformal Mapping.
Seon-Bae Kim 1 , Hosang Ahn 1 , Clyde Wikle 1 , Seung-Hyun Kim 2 , Dong-Joo Kim 1
1 Materials Research and Education Center, Auburn University, Auburn, Alabama, United States, 2 School of Engineering, Brown University, Providence, Rhode Island, United States
Show AbstractThe operational life of portable or wireless electronic devices is often limited by battery capacity which may be supplemented or even supplanted by alternative energy sources to prolong operational time and reduce maintenance. Among alternative energy sources, vibration is the most common and well suited for mobile applications. Piezoelectric energy harvesters have the highest efficiency for vibration energy harvesting, and are compatible with miniaturization for small scale devices. During vibration, electrical charge is collected employing either d31, or d33 mode depending upon the electrode configuration in piezoelectric energy harvesters. Electrodes for d31 mode devices consist of top and bottom electrodes (TBE), and d33 mode devices utilize interdigital electrodes (IDE). In case of lead zirconate titanate (PZT), the most popular piezoelectric material, the piezoelectric constant d33 is more than two times greater than d31. Devices based on d31 mode have been widely studied and modeled due to their simplicity, but research on d33 mode devices has been limited due to their more complicated nature. The dipoles in d31 mode devices with TBE are aligned with the electrodes; however, in d33 mode devices with IDE the dipoles are bent through the material between the electrodes. Previously, d33 mode devices have been modeled in a similar fashion to d31 mode devices by converting the dimensions of the IDE to that of a TBE device. The conversion is calculated as the product of the interdigitated finger length and the thickness of the piezoelectric layer, ignoring the finger width and the bent dipoles. In this research, conformal mapping was used as an alternative technique to account for the shortcomings of the IDE to TBE conversion method. Conformal mapping has been used with success to exactly model the capacitance of the dielectric layer with IDEs. MEMS scale d33 mode cantilevers were fabricated using PZT thin film. The dimension of the cantilever was 5000 x 1000 x 21 (μm3) (length x width x thickness). The width of the IDE fingers varied from 8 to 16 μm, and the finger gap varied from 4 to 16 μm. Measured capacitance and power under 0.5 g (1 g=9.8 m/s2) excitation matched with the simulation results employing conformal mapping. For a given IDE area and fixed finger gap, the power increased as the finger width decreased because of the greater number of electrode pairs within the IDE area. If the electrode finger width was fixed, maximum power was obtained when the finger gap was less than or equal to the finger width. These results indicate that charge is collected not only across the surface layer between electrode fingers, but also through the bulk of the piezoelectric material between the electrodes. In summary, conformal mapping was shown to more closely model the power conversion capability of a piezoelectric d33 mode vibrational energy harvester than the previous IDE-to-TBE conversion method.
9:00 PM - P9.48
Thin Film Electro-Optic Modulators Based on Bismuth Ferrite Heterostructures.
Daniel Sando 1 , Julie Allibe 1 , Eric Jacquet 1 , Stephane Fusil 1 , Karim Bouzehouane 1 , Cecile Carretero 1 , Cyrile Deranlot 1 , Jerome Bourderionnet 2 , Denis Crete 1 , Jean-Claude Mage 1 , Agnes Barthelemy 1 , Manuel Bibes 1
1 , Unité Mixte de Physique CNRS/Thales, Palaiseau France, 2 , Thales Research & Technology, Palaiseau France
Show AbstractBismuth ferrite (BFO), in addition to its considerable promise in spintronics, exhibits potentially valuable optical properties [1]. Its visible range bandgap, large birefringence, low absorption in the technologically-relevant infrared range, large value of spontaneous polarization, and high Curie temperature, make it a prime candidate as the active medium in thin-film heterostructure integrated electro-optic modulators (EOMs).The bandwidth of traveling-wave EOMs is primarily limited by the phase velocity mismatch between the lightwave and microwave, thus for high performance devices it is desired to bring the microwave index as close as possible to the optical index. A promising approach to achieve this is to use a ferroelectric film grown on a substrate with a low dielectric constant [2]. Various optical properties of BFO have been described by a number of authors, however in particular the electro-optic (EO) coefficients of this material are not well known. The knowledge of these properties is an important step for the potential integration of BFO into high-bandwidth, compact EOM devices.There are two commonly-used geometries for determining the EO coefficients of thin films. One method relies on injecting a light beam into a waveguide structure in which the ferroelectric film forms the core of the waveguide and planar electrodes enable the application of an electric field. The EO coefficients of the medium are determined by observing the effect of the applied electric field on the polarization state of the output optical field.The reflection method [3], on the other hand, involves using an optical field reflected from a thin film structure while an electric field is applied between a transparent top electrode and a reflective bottom electrode. This approach is similar in principle to conventional ellipsometry, whereby the change in polarization of the optical field induced by the electric field is related to the EO coefficients. The reflection method offers the advantage of not requiring the construction of a waveguide structure.In this work we will present the results of our efforts in determining the EO coefficients of BFO using both approaches. We will describe the fabrication of smooth epitaxial BFO films suitable for either waveguide structures [4] or reflection measurement geometries, the preliminary findings of our determination of the EO coefficients, and in a more general sense, the potential of these thin film heterostructures in electro-optical modulation applications.References[1] G. Catalan and J.F. Scott, Adv. Mater. 21, 1 (2009).[2] B.W. Wessels, Annu. Rev. Mater. Res. 37, 659 (2007).[3] C.C. Teng and H.T. Man, Appl. Phys. Lett. 56, 1734 (1990).[4] J. Allibe et al., Appl. Phys. Lett. 96, 182902 (2010).
9:00 PM - P9.5
New Crystallochemical Criteria for Analyzing Fluorite-Related (A2B2O7) Electroceramics.
Juan Claudio Nino 1 , Beverly Hinojosa 1 , Christopher Turner 1
1 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractEstablishing fundamental structure-dielectric property relationships in ceramics is essential for the understanding and tailoring of their electrical behavior. In this talk we will introduce two concepts, tolerance factor and continuous shape measure, newly apapted to analyze fluorite-related A2B2O7 compounds (e.g. pyrochlores, weberites, etc.). Currently, the tolerance factor for perovskites is well accepted and widely used for structure-property relationships among those compounds, most recently in the development of high temperature piezoelectrics. Here, two distinct tolerance factors are proposed from geometrical considerations of the A2B2O7 coordination polyhedra. This work will present trends and correlations between structure and dielectric response identified using the proposed equivalent tolerance factor formulae on previously studied pyrochlores. In addition to the tolerance factor, we will also introduce continuous shape measures (CShM) as another criterion for crystallochemical analysis. CShM is used here to quantify the degree of distortion of the different cation polyhedra and correlate it with the observed properties. Derivation of the tolerance factor, the tolerance factor field of existence, tolerance factor-property relationships, and CShM calculations for the family of pyrochlores and weberites (both fluorite-related ceramics) will be presented.
9:00 PM - P9.50
Electrical and Structural Diagnostics of `Stacked’ Barium Strontium Titanate (BST) Thin Films for RF Tunable Devices.
Supriya Ketkar 1 , Manoj Kumar 2 , Ashok Kumar 2 3 , Thomas Weller 1 , Andrew Hoff 1
1 Electrical Engineering, University of South Florida, Tampa, Florida, United States, 2 Mechanical Engineering, University of South Florida, Tampa, Florida, United States, 3 Nanotechnology Research and Education Center, University of South Florida, Tampa, Florida, United States
Show AbstractThe enormous growth in wireless communication industry and the need for low cost, reliable data links has resulted in a demand for active circuits that operate in the microwave frequencies. Barium strontium titanate (BST), a solid solution perovskite, is an attractive candidate for RF and microwave applications due to its high figure of merit, thermal stability and ease of integration into microelectronic circuits. High-k films in general exhibit variable conductance due to small band offsets and defect issues. In a previous report, the properties of rf-magnetron sputter deposited BST thin film were investigated and compared with spin coated sol-gel BST thin films. It could be inferred from the studies that it is difficult for either of the deposition technique to achieve the desired tunability or for the thin films to hold adequate fields typical of tuning. Hence, we adopted the stacking approach, wherein, BST (Ba0.6Sr0.4TiO3) was rf-magnetron sputter deposited on Silicon/SiO2/TiO2/Pt wafers and subsequently, BST sol-gel was spin-coated on the same samples. These samples were then characterized for the film structure, and the electric field dependence of the dielectric permittivity.The stoichiometry of the rf magnetron sputtering target was Ba0.6Sr0.4TiO3 and for that of the sol-gel was also maintained the same for obtaining similar phase in the thin film. The power was 200 Watts and deposition temperature 400. The Ar/O2 gas ratio was maintained at 9:1. The substrates were then annealed in different ambient conditions (Air, Oxygen and Argon) and at different temperatures (600, 800 and 900°C). The leakage current behavior was studied corresponding to the crystal structure of these films. The prepared thin films were physically characterized using tools like XRD, SEM and TEM. Parallel plate capacitors were fabricated and measured in the frequency range of 1–500 MHz. The dielectric properties for the BST film capacitors are measured at 20 V using a HP4284A LCR. Noncontact corona-kelvin based metrology was used to calculate key parameters like dielectric effective oxide thickness (EOT), dielectric voltage in valence band tunneling range (VB), interface trapped charge (Qit) and flatband voltage.
9:00 PM - P9.51
Epitaxial Growth, First-Principles Simulations and Characterization of Structural and Magnetic Properties of Cobalt-Doped SrTiO3 for Multiferroic Switching.
Mehmet Cengiz Onbasli 1 , Juan Manuel Florez 1 , Dong Hun Kim 1 , Lei Bi 1 , Caroline A. Ross 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractPerovskites, ABO3 oxides, offer a range of functionalities such as room-temperature ferromagnetism, piezoelectricity, ferroelectricity, thermoelectricity, colossal magnetoresistance, spin-dependent transport, magneto-optical activity and multiferroic switching. SrTiO3 is a paraelectric and nonmagnetic perovskite at room temperature with cubic lattice structure and bulk lattice parameter a = 0.3905nm. By embedding magnetic dopants in a nonmagnetic lattice, reducing oxygen fraction, tuning lattice strain through the choice of buffers, deposition temperature and pressure, materials with room temperature ferromagnetism can be produced.In this study, we report the epitaxial growth, density-functional theory simulations and characterization of micro- and nanostructure and magnetic properties of 30% Cobalt-doped SrTiO3 (STCo) on Silicon. We grew STCo epitaxially using pulsed laser deposition (PLD) on two sets of buffer layers, TiN and CeO2-on-YSZ (CeO2/YSZ, yittria-stabilized zirconia) on Si. Films were grown with a Coherent KrF (248 nm) laser with 10 Hz pulse frequency and 2.5 J cm-2 fluence, base pressure of 3.0e-6 torr. PLD targets of Sr(Ti70Co30)O3 were used for 300nm of STCo growth. By changing oxygen pressure, oxygen stoichiometry of the STCo films was tuned. X-ray photoelectron spectroscopy indicates that there are at least two Cobalt chemistries (binding energies 780.2 and 795.6 eV). The existence of two Sr chemistries (Eb = 134.8, 123.0eV) and two Ti chemistries (463.9 and 458.1eV) suggests that doping the host with Co displaces Strontium as well as Titanium. Cobalt resides in the lattice with 3+ and 4+ valence states. Increasing Cobalt doping (or reducing oxygen pressure during growth) decreases oxygen fraction in the lattice and the thin film STCo lattice expands with increasing Co fraction. The magnetic response of STC films measured with vibrating sample magnetometer indicates that the films have ferromagnetic behavior with coercivity of a few Oe. Saturation magnetization upto 0.5 uB/Co-ion for STCo films indicates antiferromagnetic coupling between some of the nearest neighbors. Magnetic hysteresis of STCo films has strong out of plane anisotropy. Temperature-dependent saturation magnetization measurement indicates that magnetization does not vanish even at 1000K and has been successfully described using a magnetoelastic model, suggesting high-temperature ferromagnetic behavior originates from strain-induced enhancement of magnetic response.We performed density functional theory (DFT) simulations for understanding electronic structure and magnetic properties of the STCo based on both generalized gradient approximation (GGA) for structural relaxation and GGA+U energy functional, and a Heyd-Scuseria-Ernzerhof functional. Projected augmented wave pseudopotentials are used along 8x8x8 k-point meshes and 450 eV energy cut-offs for STCo, SrTiO3 and SrCoO3. Differences between GGA+U and the Hybrid HSE06 DFT predictions are discussed.
9:00 PM - P9.52
Dielectric Response of Ultrathin Epitaxial CoFe2O4 Films.
D. Gutierrez 1 , M. Foerster 1 , M. Rubio-Roy 1 , I. Fina 1 , G. Herranz 1 , F. Sanchez 1 , Josep Fontcuberta 1
1 , Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Bellaterra Spain
Show AbstractThe trend of device miniaturization requires the knowledge of material properties on a smaller, nanometric scale, where they can differ considerably from known bulk properties. Magnetic insulators, such as ferrites, are nowadays being considered for potential use as magnetic tunnel barriers in spin filters and thus dielectric properties of nanometric films of these materials should be addressed.We explore here the dielectric properties of epitaxial CoFe2O4 (CFO) ultrathin (4-50 nm) films prepared by pulsed laser deposition on La2/3Sr1/3MnO3 and SrRuO3 bottom electrodes. Small (~ micron) metallic top contacts were contacted with a conducting AFM setup connected to an impedance analyzer. The dielectric response of the CFO films was measured as function of thickness, frequency and voltage. The frequency dependence is fitted most consistently by an equivalent circuit containing a constant phase element (CPE) with a parallel resistance. From the thickness dependence, the contribution of an interfacial layer is identified, allowing the quantification of the intrinsic dielectric properties of the CFO thin films as well as the interfacial layers. The capacitances of thinner samples show no significant dependence on the applied bias voltage, while for the thicker samples the capacitance decreases when increasing the bias voltage. Both latter observations agree quantitatively well with the assumption that the interface layer is comprised of a charge carrier depleted layer (Schottky barrier) of reduced permittivity. The presence of the Schottky contribution precludes determination of any possible variation of permittivity with thickness. The influence of the electrode materials on the results is discussed.
9:00 PM - P9.7
Finite Element Analysis of Heterogeneous Electroceramics.
Julian Dean 1 , Colin Freeman 1 , Kieth Butler 1 , Derek Sinclair 1 , John Harding 1
1 Department of Materials Science and Engineering, University of Sheffield, Sheffield United Kingdom
Show AbstractImpedance spectroscopy (IS) is a widely used methodology to study and examine the electrical properties of heterogeneous electroceramics [1]. Experimentally the choice of the correct equivalent circuit fitted to such data in order to extract material parameters is critical to analysis [2]. The strategy and reliability of this however is still under much debate today within the ceramics community. One method to help overcome this is to simulate the impedance spectroscopy of such systems, comparing directly to experimental data.In the work presented here an in-house code has been developed using a time domain finite element method for calculating Maxwell’s equations in space and time. This provides the time evolution of the spatial distribution of the electric field within the sample allowing the simulation of impedance spectroscopy of heterogeneous electroceramics. The method of using finite element analysis has previously been used to study heterogeneous electroceramics [3], however the complete treatment of a three-dimensional granular system with grain boundaries and contacts has previously been missing. The simulations take into account the complexities of the three dimensional granular structure using a hybrid mesh. Both tetrahedrons and prisms are used to represent the large size of the grains and grain boundary respectively, allowing extremely high bulk to grain boundary ratios of up to 1000:1.We present a numerical study over a large frequency range (1 mHz – 100 MHz) to highlight the how certain structural changes emerge in such impedance spectra. Results presented here show how contact size and grain boundary angle influences the depression angle measured in the Debye plots and how this can lead to a discrepancy of the calculated grain boundary conductance. These results are then used to describe the phenomena observed in a realistic sample of irregular shaped grains, here simulated using a Voronoi granular structure. Furthermore we provide an insight into the limitations in the design of an equivalent circuit and provide a possible solution. [1] A. R. West, D. C. Sinclair and N Hirose, J. Electroceramics 1:1 65-71, 1997[2] E. J. Abram, D. C. Sinclair and A. R. West, J. Electroceramics 10, 165-177, 2003[3] J. Fleig, B. Rahmati, S. Rodewald, J. Maier, J. European Ceramics Society 30, 215-220, 2010
9:00 PM - P9.8
An Artificial Multiferroic Memory Element.
Julian Dean 1 , Mathew Bryan 1 , Dan Allwood 1
1 Department of Materials Science and Engineering, University of Sheffield, Sheffield United Kingdom
Show AbstractArtificial multiferroic systems, combining piezoelectric and piezomagnetic materials, offer novel methods of controlling material properties. Many proposed memory and logic devices have been previously based on propagating magnetic domain walls (DWs) around nanowire circuits using magnetic fields or spin-polarised currents [1,2]. Key to the operation of the devices is the requirement that consecutive walls do not collide. Conventionally, geometrical features such as notches are used to pin walls within defined regions, ensuring wall separation. However, different depinning fields from the notch can occur due to the structure of the wall pinned [3]. Furthermore, stochastic variations in the depinning field can result from thermal activation [4], thus geometric pinning cannot guarantee wall separation. We present an alternative pinning method, based on a multiferroic system, coupling a ferroelectric piezoelectric material to a magnetic magnetostrictive nanowire. Localised strains result in an electrical controlled pinning sites that are unaffected by wall structure or thermal activation. A micromagnetic finite element software [5] is linked to COMSOL to calculate the Cauchy stress tensor and the subsequent effect in the magnetic response throughout a 5 nm thick, 100 nm wide nanowire sandwiched between a Si substrate and a 200 nm thick piezoelectric (PZT-5H) layer. As a proof of concept, potentials applied to a number of electrical contacts (100 nm wide, separated by 200 nm) on top the piezoelectric are shown to allow localised stresses in the wire to be generated. Further analysis reveals that the energy gradients generated by the stress could be used to propagate a DW without the need to apply a magnetic field or spin-polarised current. As a proof of principle we simulate a five contact device to highlight a memory element. This is shown to be capable of switching one bit of data every 1ns and maintain thermally of over 4eV, allowing this to also be used for storage. An upper estimate of the energy required to switch between states 0 and 1 is 74 keV, suggesting that the device could be used as a low power consumption memory cell. Read-out is shown to be achieved via the stress generated in the nanowire due to the presence of a DW, which induces a potential of 80 μV in the piezoelectric layer.[1] D. A. Allwood, et al., Science 309, 1688 (2005).[2] S. S. P. Parkin, et al., Science 320, 190 (2008).[3] M. Hayashi, et al., Phys. Rev. Lett. 97, 207205 (2006).[4] E. Martinez, et al., Phys. Rev. Lett. 98, 267202 (2007).[5] J. Dean, et al., J. Appl. Phys. 108, 073903 (2010).
Symposium Organizers
Craig J. Fennie Cornell University
Lane W. Martin University of Illinois, Urbana-Champaign
Beatriz Noheda University of Groningen
Tsuyoshi Kimura Osaka University
Manuel Bibes Thales Research and Technology/CNRS
P10: New Materials
Session Chairs
Wednesday AM, November 30, 2011
Room 302 (Hynes)
9:30 AM - **P10.1
Multiferroic Behavior Associated with Order-Disorder Phase Transition in Metal-Organic-Frameworks with Perovskite Topology.
Prashant Jain 1 , Harry Kroto 2 , Naresh Dalal 2 , Anthony Cheetham 3
1 Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Chemistry and Biochemistry, Florida State University, Tallahassee, Florida, United States, 3 Materials Science, University of Cambridge, Cambridge United Kingdom
Show AbstractMetal-Organic-Frameworks (MOFs) are crystalline compounds consisting of metal ions or clusters coordinated to organic molecules to form one-, two-, or three-dimensional structures. Nanoporous MOFs, due to their exceptionally high surface areas, are of great interest for applications in gas storage, separation and purification, catalysis, and sensors. However, it is also possible to make use of their organic and inorganic building blocks to combine otherwise difficult to combine ferroelectric and ferromagnetic properties simultaneously in one system and design rare multiferroic compounds. We recently showed that cation templated MOFs, with the same topology as those of ABX3 perovskites, undergo an order-disorder phase transition similar to that of potassium dihydrogen phosphate. The room temperature phase has the amine cation at the center of ReO3 type cage, disordered equally over three different sites due to hydrogen bonding. Upon cooling below 200K this phase becomes ordered, leading to a polar structure. These hybrid perovskites are highly tunable, and it is possible to modulate their transition temperatures by changing the central cation, as well as the type of metal. In some cases, we show that it is also possible to make room temperature ferroelectric MOFs. MOFs synthesized with paramagnetic transition metals are also magnetic and show weak ferromagnetic ordering below 40K. Theoretically, some of these MOFs also show weak magnetoelectric effect.
10:00 AM - **P10.2
Polar Inorganic Materials: Design Strategies and Functional Properties.
Shiv Halasyamani 1 , Hong-Young Chang 1 , Jeongho Yeon 1 , Weiguo Zhang 1 , Sang-Hwan Kim
1 , University of Houston, Houston, Texas, United States
Show AbstractPolar oxide materials – those with a macroscopic dipole moment – are ubiquitous in advanced technologies, i.e. computer memories, sensors, etc. The design and synthesis of new polar oxides, however, remains an ongoing challenge. Macroscopic polarity implies microscopic polarity, in other words some of the coordination polyhedra must be polar. As is often the case, the local dipole moment in the coordination polyhedra is directed in opposite directions resulting in a non-polar material. In this presentation we will discuss strategies toward designing new polar oxide materials, as well as the characterization of their functional properties. Specifically we will demonstrate that by exploiting second-order Jahn Teller distortions, we can design and synthesize new polar oxide materials. We will describe the synthesis of characterization of several new polar oxide materials, as well as crystal growth. Functional properties will be presented, and structure-property relationships will be discussed and explored.
10:30 AM - P10.3
Functional Nano-Ferroelectrics on Carbon Nanotubes.
Sai Shivareddy 1 , Ashok Kumar 3 , Youngjin Choi 1 , Geunhee Lee 3 4 , Hyunwoo Choi 4 , Seungbum Hong 4 , Jim Scott 2 , Gehan Amaratunga 1
1 Engineering, University of Cambridge, Cambridge United Kingdom, 3 Physics, University of Puerto Rico, San Juan United States, 4 Materials Science, Argonne National Lab, Lemont, Illinois, United States, 2 Physics, University of Cambridge, Cambridge United Kingdom
Show Abstract A range of perovskite type materials have been deposited on vertically aligned multiwalled carbon nanotube (MWNT) arrays by pulsed laser deposition. By this technique, we have deposited high dielectric constant, ferroelectric and multiferroic materials like BaTiO3, BaxSr1-xTiO3 and PZT. The as deposited films on MWNTs are conformal with high aspect ratios, nano - crystalline and retain their respective 2-D material properties. We find that the MWNTs are robust and endure the high temperature range ~ 450-800 deg C that is a prerequisite for high quality film growth. They also withstand the partial oxygen atmosphere that is required by perovskite oxides in the entire temperature range. In addition, we demonstrate ferroelectric switching from a single BaTiO3 coated vertical MWNT and the ferroelectric properties of these nanotubes will be presented. These multi-functionalized nanotubes could be used in a range of nanoscale devices from 3D ferroelectric and multiferroic memory elements to piezoelectric energy generators and high energy density storage devices.
10:45 AM - P10.4
Ferroelectric Cylindrical Nano-Shells: Materials, Properties and Devices.
Jonathan Spanier 1
1 Materials Science & Engineering, Drexel University, Philadelphia, Pennsylvania, United States
Show AbstractThe study of ferroic nanostructures is motivated in part by opportunities for manipulating functional phase stability and properties via finite size, shape, and surface chemical environment1. I shall present our recent work investigating the functional properties and their device functionalities in electrically-interfaced co-axial core-shell nanowires (NWs) consisting of a ferroelectric (FE) oxide shell surrounding a core composed of a normal1 or ferromagnetic metal, or a semiconductor. I shall discuss how polarization P oriented along the finite thickness direction in films possessing extreme curvature can be locally and controllably switched2. P is enhanced by extreme curvature, thereby suppressing the finite-size-driven evolution of the FE phase transition temperature Tc. Measured responses within individual nanoshells possess magnitudes ~3x their planar counterparts while exhibiting finite curvature-dependent offsets in FE hystereses. Landau-Ginzburg model calculations indicate geometric curvature-driven polarization gradients in ultrathin films result in significant increases in Tc3. I shall also highlight experimental characterizations of the electroresistive properties in, and gating by these nanoshells. In metal-FE core-shell NWs reversibility in conduction state following different stages of a redox anneal cycle provides evidence of an oxygen vacancy concentration-based conduction mechanism4, during which FE switching is also observed. In semiconductor-FE core-shell NWs, field-effect modulation of carrier transport is demonstrated5. The co-axial NW geometry also permits an unexpectedly large magnetoelectric coupling within individual NWs each consisting of a ferromagnetic metal core and a FE oxide shell. NWs exhibit a magnetic field-tunable piezoelectric response and FE switching owing to magnetoelastic coupling through the interfacial boundary6. These results provide insight into the design of integrated functional devices and magnetoelectric sensors. They are also relevant to magnetoelectric composites, where the potential benefit of maximizing interfacial area using nanostructured constituent ferroic components is typically offset by a suppression of functional properties at small scale. Work supported by ARO (W911NF-08-1-0067) and ONR (N00014-1-11-0370).1J. E. Spanier, A. Kolpak, I. Grinberg, J. J. Urban, L. Ouyang, W. S. Yun, A. M. Rappe and H. Park, Nano Lett. 6, 735-739 (2006). 2S. S. Nonnenmann, E. M. Gallo, M. T. Coster, G. R. Soja, C. L. Johnson, R. S. Joseph, and J. E. Spanier, Appl. Phys. Lett. 95, 232903 (2009). 3S. S. Nonnenmann, O. D. Leaffer, E. M. Gallo, M. T. Coster and J. E. Spanier, Nano Lett. 10, 542-546 (2010). 4S. S. Nonnenmann, E. M. Gallo and J. E. Spanier, Appl. Phys. Lett. 97, 102904 (2010). 5S. S. Nonnenmann, B. R. Beatty and J. E. Spanier, in preparation, (2011). 6S. H. Johnson, O. D. Leaffer, P. Finkel, S. S. Nonnenmann, K. Bussman, and J. E. Spanier, submitted, (2011).
P11: Electronic and Optical Properties of Ferroelectrics
Session Chairs
Wednesday PM, November 30, 2011
Room 302 (Hynes)
11:30 AM - **P11.1
Electrical Control of Magnetism.
R. Ramesh 1
1 , UCBerkeley, Berkeley, California, United States
Show AbstractComplex perovskite oxides exhibit a rich spectrum of functional responses, including magnetism, ferroelectricity, highly correlated electron behavior, superconductivity, etc. The basic materials physics of such materials provide the ideal playground for interdisciplinary scientific exploration. Over the past decade we have been exploring the science of such materials (for example, colossal magnetoresistance, ferroelectricity, etc) in thin film form by creating epitaxial heterostructures and nanostructures. Among the large number of materials systems, there exists a small set of materials which exhibit multiple order parameters; these are known as multiferroics. Using our work in the field of ferroelectric(FE) and ferromagnetic oxides as the background, we are now exploring such materials, as epitaxial thin films as well as nanostructures. Specifically, we are studying the role of thin film growth, heteroepitaxy and processing on the basic properties as well as magnitude of the coupling between the order parameters. In our work we are exploring the switchability of the antiferromagnetic order using this coupling. What is the importance of this work ? Antiferromagnets(AFM) are pervasive in the recording industry. They are used as exchange biasing layers in MTJ’s etc. However, to date there has been no antiferomagnet that is electrically tunable. We believe that the multiferroic BiFeO3 is one compound where this can be observed at room temperature. The next step is to explore the coupling of a ferromagnet to this antiferromagnet through the exchange biasing concept. Ultimately, this will give us the opportunity to switch the magnetic state in a ferromagnet( and therefore the spin polarization direction) by simply applying an electric field to the underlying antiferromagnetic ferroelectric. In this talk, I will describe our progress to date on this exciting possibility.
12:00 PM - P11.2
Dielectric Screening Enhanced Hall Mobility in Doped Ferroelectrics.
Wolter Siemons 1 , Michael McGuire 1 , Valentino Cooper 1 , Michael Biegalski 2 , Ilia Ivanov 2 , Gerald Jellison 1 , Lynn Boatner 1 , Brian Sales 1 , Hans Christen 1 2
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThe photovoltaic effect in ferroelectric perovskite oxides has recently reemerged as an area of intense research [1]. One limitation preventing device applications is a low carrier mobility in oxides, especially near room temperature. In contrast, at low temperatures some oxides, for example SrTiO3 and KTaO3, show mobilities in excess of 10,000 cm2 s-1 V-1. [2,3] Together with this dramatic increase in mobility as temperature is lowered, their dielectric constants also increase from a few hundred at room temperature to near 20,000 at low temperatures, suggesting a correlation between the dielectric constant and the mobility. In this presentation we show that the Hall mobility can be increased by a factor of 2-3 near a ferroelectric transition where the dielectric constant peaks. By using electron-doped ferroelectric crystals of composition KTa1-xNbxO3, where the ferroelectric transition temperature can be tuned by changing the Ta:Nb ratio, we demonstrate enhanced Hall mobility at the Curie temperature up to room temperature. We conclude that the mobility in these doped ferroelectrics peaks at the Curie temperature due to the increased dielectric constant, which reduces charge carrier scattering by impurities. Enhanced mobility could result in more efficient photovoltaic devices made from oxides.Research sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy (W.S., V.R.C., G.E.J., H.M.C.) and the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division (M.A.M., L.A.B., B.C.S.) and Scientific User Facilities Division (M.D.B., I.N.I).[1] T. Choi et al., Science 324, 63 (2009).[2] S.H. Wemple, Phys. Rev. 137, 1575-1582 (1965).[3] H.P. Frederikse, & W.R. Hosler, Phys. Rev. 161, 822-827 (1967).
12:15 PM - P11.3
Electrostatic Modulation of Sub-Bandgap Photovoltaic Properties in PbTiO3/Nb:SrTiO3 Heterostructures.
Ryota Takahashi 1 , Thomas Tybell 2 , Mikk Lippmaa 1
1 Institute for Solid State Physics, University of Tokyo, Chiba-ken Japan, 2 Department of Electronics and Telecommunications, Norwegian University of Science and Technology, Trondheim Norway
Show AbstractFerroelectric materials have a spontaneous polarization that can be reversed by applying an electric field. The internal polarization of a ferroelectric material results in an electric field that is accessible at surfaces and interfaces, and can be used in field-effect devices to modulate, for example, superconducting or magnetic properties of other materials [1]. One interesting possibility is to utilize the ferroelectric polarization field to tune the photovoltaic properties at interfaces between ferroelectrics and semiconductor materials. Here we present ferroelectric tuning of sub-bandgap photocurrents in the Pt/PbTiO3/Nb:SrTiO3 system. By relying on pyroelectric characterization [2], the photovoltaic properties were measured simultaneously with the ferroelectric signal dependent on the domain state at zero applied bias. Ferroelectric PbTiO3 films were prepared on Nb:SrTiO3(001) substrates by off-axis magnetron sputtering [3]. Typical PbTiO3 film thicknesses were 12 to 16 nm. For the electric contacts, 30 nm thick Pt top electrodes were deposited on the PbTiO3 surface by e-beam evaporation. Laser pulses (658 nm, 61 mW, 35 Hz) were directed onto the ferroelectric capacitors in order to modulate the temperature and to induce possible photocurrents. The resulting photo- and pyroelectric currents were evaluated at zero bias. Transient currents, originating from the pyroelectric effect, were dependent on the ferroelectric domain polarity. Furthermore, a positive offset current was obtained during light illumination for both polarization states, indicative of a photocurrent. The wavelength dependence of the photocurrent was investigated, and increased for photon energies larger than the 3.2 eV bandgap of SrTiO3. Sub-bandgap photovoltaic signals were also detected. Their magnitude was dependent on the ferroelectric domain state and displayed hysteretic behavior with poling bias, indicative of electrostatic control of the photovoltaic properties. [1] C. H. Ahn, et al. Nature, 424, 1015 (2003)[2] A. G. Chynoweth, J. Appl. Phys. 27, 78 (1956)[3] R. Takahashi et al. J. Appl. Phys. 104, 064109 (2008)
12:30 PM - P11.4
Ultrafast Electron Dynamics in PbTiO3 Probed via THz Emission.
John Goodfellow 1 2 , Dan Daranciang 3 2 , Aaron Lindenberg 1 2
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 2 PULSE/SIMES, SLAC National Accelerator Laboratory, Menlo Park, California, United States, 3 Chemistry, Stanford University, Stanford, California, United States
Show AbstractThe interaction of visible light with ferroelectics is generating recent interest due to the potential to extract above-bandgap voltages via the bulk photovoltaic response. While a growing body of work has characterized the effect under static conditions, time-resolved optical studies are needed to elucidate the intrinsically ultrafast electronic mechanisms. In recent measurements using femtosecond x-ray diffraction techniques to probe 20 nm monodomain PbTiO3 thin films, we have observed complex structural dynamics in the first 20 ps after photo-excitation with 400 nm light pulses. An initial decrease in the polarization occurs on an acoustically limited timescale of 5 ps. This can be attributed to a shift current response of the sample, a nonlinear optical effect associated with absorption in non-centrosymmetric media. The initial decrease is followed by a long-lived enhancement of the polarization by roughly 10% over its static value, explained by a dynamic screening of the depolarization field in the presence of excited carriers. As a further characterization of these processes we will report THz emission measurements from PbTiO3, in which the radiated THz field, collected via electro-optic sampling, directly reflects the photo-induced transient currents. With this technique we distinguish the shift current response from optical rectification and depolarization field screening. Detailed understanding of these ultrafast electronic dynamics is key to understanding the bulk photovoltaic response in these materials.
12:45 PM - P11.5
Understanding the Ultrafast Dynamics of the Electron-Phonon Interactions in BiFeO3 Thin Films.
Long-Yi Chen 1 , Jan-Chi Yang 2 , Chih-Wei Luo 1 , Ying-Hao Chu 2 3 , Takayoshi Kobayashi 1 4
1 Electrophysics, National Chiao Tung University, Hsinchu, Taiwan, Taiwan, 2 Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan, Taiwan, 3 Physics and Materials Science & Engineering, UC Berkeley, Berkeley, California, United States, 4 Engineering Science, The University of Electro-Communications, Tokyo Japan
Show AbstractMultiferroics, taking advantages of multiple coupled order parameters, have been a fascinating area for advanced condensed materials research and offered the exciting potentials for future device applications. Room-temperature multiferroic BiFeO3 has played a key role in rejuvenating the field after a report of large ferroelectric polarization combined with both a high ferroelectric Curie temperature and a high antiferromagnetic Néel temperature. In recent studies, several key discoveries, e.g. photovoltaic effect, photo-induced size change, etc., haven been explored based on the interaction between photon and BiFeO3 materials, which open new pathways to use multiferroic for optoelectronics. However, the mechanisms behind these phenomena are not carefully investigated and understood yet. In order to understand the electron-electron, electron-phonon and possible electron-magnon interactions, we have applied the femtosecond pump-probe spectroscopy to study BiFeO3 films, which is a powerful tool to study the fundamental microscopic dynamics for each order parameters as well as the coupling between them. In this study, as a function of film orientation, temperature, thickness, and light polarization, spectroscopy is performed and analyzed by the 400 nm (3.1 eV) pump pulses above BiFeO3 energy gap of 2.67 eV and the 800 nm (1.55 eV) probe pulses below the energy gap. A key feature that the ultrafast strain pulses in (110)-oriented BiFeO3 thin films was found. The propagation of strain pulse crossed the interface between film and substrate is intimately correlated to the marked discontinuity of the oscillation component in the transient reflectivity changes (ΔR/R). By doing the thickness-dependent measurements, the sound velocity of BiFeO3 can be extracted as 4.76 km/s. Moreover, the temperature-dependent variation in the oscillation period of ΔR/R exhibits an abrupt drop around 130 K, presumably due to the significant magnetoelastic coupling. This study provides a lot of detailed and fundamental insights on how electrons interact with (anti-)ferroic orders in BiFeO3 materials.
P12: Surface, Electronic, and Photovoltaic Properties
Session Chairs
Shiv Halasyamani
Sergei Kalinin
Wednesday PM, November 30, 2011
Room 302 (Hynes)
2:30 PM - **P12.1
Polarization-Dependence of Palladium Deposition on Ferroelectric Lithium Niobate (0001) Surfaces.
Seungchul Kim 1 , Michael Rutenberg Schoenberg 1 , Andrew Rappe 1
1 , University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractWe investigate the effect of ferroelectric polarization direction on the geometric properties of Pd deposited on the positive and negative surfaces of LiNbO3 (0001). We predict preferred geometries and diffusion properties of small Pd clusters using density functional theory, and use these calculations as the basis for kinetic Monte Carlo simulations of Pd deposition on a larger scale. Our results show that on the positive surface, Pd atoms favor a clustered configuration, while on the negative surface, Pd atoms are adsorbed in a more dispersed pattern due to suppression of diffusion and agglomeration. This suggests that the effect of LiNbO3 polarization direction on the catalytic activity of Pd [J. Phys. Chem. 88, 1148 (1984)] is due, at least in part, to differences in adsorption geometry. Further investigations using these methods can aid the search for catalysts whose activities switch reversibly with the polarization of their ferroelectric substrates.
3:00 PM - P12.2
Polarization Screening Mechanisms in Oxide Thin Films.
Nicholas Bristowe 1 2 , Massimiliano Stengel 3 , J. Pruneda 4 , P. Littlewood 5 2 , Emilio Artacho 1
1 Earth Sciences, University of Cambridge, Cambridge, CAMBS, United Kingdom, 2 Cavendish Laboratory, University of Cambridge, Cambridge, CAMBS, United Kingdom, 3 Institut de Ciéncia de Materials de Barcelona, Campus UAB, Bellaterra Spain, 4 Centre d’Investigación en Nanociéncia I Nanotecnologia, Campus UAB, Bellaterra Spain, 5 , Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractSince the discovery of the quasi two-dimensional electron gas (2DEG) at the interface between LaAlO3 (LAO) and SrTiO3 (STO) [1], the LAO/STO heterostructure has become a prototypical system for the understanding of polar discontinuities. One of the debated origins of the interface 2DEG, called the ‘polar-catastrophe’ [2], is based on the result that LAO has a fixed spontaneous, but non-switchable, polarization of precisely 0.5 electrons per surface unit cell [3,4], which requires screening charges at its surfaces via an electronic transfer from the LAO surface valence band to the interface STO Ti 3d conduction band. Recently it has been proposed that surface redox reactions (e.g. surface oxygen vacancies), which liberate free charges, are instead likely to be the source of the polarization screening and the interface carriers [5].We use the LAO/STO system as a starting point to understand more complex cases that include ferroelectric components, where the polarization is no longer fixed but switchable. We consider a system where robust switchable ferroelectricity has been recently observed under open-circuit electrical boundary conditions in nm thick ferroelectric films [6]. Based on first-principles calculations we show that the pristine system does not polarize and propose electrochemical ferroelectric switching as the phenomenon being observed. If not exceeding its bulk value, the ferroelectric polarization of the film adapts to the bound charge generated on its surface by redox processes when poling the film. The observed tunneling electro-resistance is explained, a magnetoelectric effect is predicted, and the whole is supported by the energetics calculated for varied electrochemical scenarios.1.A. Ohtomo and H. Hwang, Nature 427, 423 (2004)2.N. Nakagawa, H. Hwang and D. Muller, Nat. Mater. 5, 204 (2006)3.M. Stengel and D. Vanderbilt, Phys. Rev. B 80, 241103 (2009)4.N.C. Bristowe, P.B. Littlewood and E. Artacho, J. Phys.: Condens. Matter 23, 081001 (2011) 5.N.C. Bristowe, P.B. Littlewood and E. Artacho, Phys. Rev. B 83, 205405 (2011)6.V. Garcia et al., Nature 460, 81 (2009)
3:15 PM - P12.3
Oxygen Vacancy Ordering in Multiferroic Ca-Doped BiFeO3 Films.
Suresha S Jagannatha 1 , Jan Seidel 2 3 , Ying-Hao Chu 2 3 , Chan-Ho Yang 4 , R. Ramesh 2 3 5 , Ulrich Dahmen 1
1 National Center For Electron Microscopy, Lawrence Berkeley National Lab, Berkeley, California, United States, 2 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, Berkeley, California, United States, 3 Department of Physics, University of California, Berkeley, California, United States, 4 Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Yuseong-gu, Daejeon Korea (the Republic of), 5 Department of Materials Science and Engineering, University of California, Berkeley, California, United States
Show AbstractMultiferroic BiFeO3 (BFO) offers great potential applications in the nonvolatile random access memory and data storage due to its large room-temperature spontaneous polarization (~90 μC/cm2) and the coupling between the ferroelectric polarization and antiferromagnetism. Recent studies demonstrate the resistive switching in BFO. Such behavior is strongly related to the defects in BFO, in particular, oxygen vacancies. In this work we explore the mechanism of oxygen-vacancy ordering and melting of ordering under the influence of electric field in calcium-doped BFO films by High resolution TEM and aberration-corrected scanning transmission electron microscopy (STEM). 10 at.% and 20 at. % Ca doped BFO thin films of 100 nm thickness were grown epitaxially on strontium titanate (SrTiO3) substrates via pulsed laser deposition. In as-grown state of a sample containing 20 at.% Ca shows the oxygen vacancy order parallel to the sample surface with a period of 8 unit cells is seen and the application of an electric field does not yield changes in the oxygen vacancy ordering. HRTEM and STEM images reveals the presence of single perovskite-type dark layers appearing periodically every 8 perovskite blocks along the out-of plane direction, as confirmed by the occurrence of an incommensurate modulation along the [001] direction in the corresponding fast Fourier transformation (FFT). The as-grown sample containing 10 at.% Ca shows an oxygen vacancy ordering with a period of 2 to 3 unit cells at an angle of 45° to the sample surface. After the application of a bias of -12V in the c-AFM poling the oxygen vacancy ordering is completely melted. It is observed that the melting of the oxygen vacancy ordering and the associated redistribution of carriers will lead to an electrochromic effect in 10 at.% calcium-doped BFO thin films without the need for additional electrolytes that are needed in common electrochromic devices. The absorption change and coloration efficiency at the band edge are 4.8×106 m-1 and 190 cm2/C, respectively, which are among the highest reported values for inorganic electrochromes. This study provides fundamental understanding of oxygen vacancies in BFO and also opens the pathway to use BFO in RRAM and electrochromic application.
3:30 PM - P12.4
The Growth and Properties of Insulating and Ionically Conducting Overlayers in Ferroelectric Heterostructures.
Matthew Highland 1 , Stephan Hruszkewycz 1 , Seongkeun Kim 1 , Edith Perret 1 , Chad Folkman 1 , Danielle Proffit 1 2 , Carol Thompson 3 , Dillon Fong 1 , Jeffrey Eastman 1 , Paul Fuoss 1 , Stephen Streiffer 4 , Gregory Stephenson 1
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Department of Materials Science and Engineering , Northwestern University, Evanston, Illinois, United States, 3 Department of Physics , Northern Illinois University, DeKalb, Illinois, United States, 4 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractFerroelectric thin film heterostructures have been utilized in a variety of applications and have still further potential as tunable catalysts and enhanced ionic conductors. Many of these applications require the synthesis of heterostructures in which overlayers are grown on ferroelectric thin films, such that the ferroelectric polarization affects the behavior of the interface and overlayer. Our previous work has demonstrated that the gas environment in contact with a ferroelectric thin film can be used to modify ferroelectric switching behavior, through control of the supply of ions to the surface. Through the creation of ferroelectric / ionic conductor (Y2O3-stabilized ZrO2 (YSZ)) heterostructures, we are exploring whether ferroelectric switching behavior can also be modified by control of the diffusion of ions through a solid. We are also investigating whether changes to the polarization state of the ferroelectric film in such heterostructures can induce changes to the ionic conductivity of overlayer materials such as ZrO2. Such behavior would be extremely beneficial in synthesizing structures with electronically controllable ionic conductivity. However, dissimilarity in crystal structures and lattice parameters often makes controlling the epitaxial relation of these layers challenging. Here we discuss the growth and in-situ characterization of YSZ/PbTiO3/SrRuO3/SrTiO3 and ZrO2/PbTiO3/SrRuO3/SrTiO3 heterostructures. We find that YSZ overlayer can adopt either a cube-on-cube or a 45° rotated epitaxial relation to the PbTiO3 film. We have investigated the dependence of the epitaxy on the surface termination of the PbTiO3 film, i.e. whether the film is terminated with a PbO or TiO2 layer. These results suggest potential strategies for controlling crystal orientation in heterostructures and may lead to systems in which the properties of an overlayer material can be altered by changing the polarization state of the underlying ferroelectric film. Work supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract DE-AC02-06CH11357.
3:45 PM - P12.5
Enhanced Pyroelectric and Electrocaloric Response in Epitaxial Ferroelectric Thin Films.
Karthik Jambunathan 1 , Lane Martin 1
1 Materials Science and Engineering and Materials Research Laboratory, University of Illinois, Urbana-Champaign, Urbana, Illinois, United States
Show AbstractMotivated by the need to more efficiently utilize our energy resources, there has been much work on direct thermal-to-electrical energy conversion and low-power thermal management systems. Ferroelectric thin films offer an exciting potential to realize these applications since the properties of these materials can be varied with temperature and electric field to realize thermal energy conversion and solid state cooling through the pyroelectric and electrocaloric effects, respectively. Furthermore, the ferroelectric properties of thin films of these materials can be tuned with a wide variety of experimental parameters such as epitaxial strain, temperature, composition, domain structure, and more. In this presentation, we will investigate recent advances in the understanding of thermal properties and responses of complex oxide thin films, with special attention to how epitaxial constraints can enhance pyroelectric/electrocaloric responses in ferroelectric thin films. We will report on the study of dielectric, pyroelectric/electrocaloric, and ferroelectric properties of highly engineered ferroelectric thin films and multilayers using PbZr1-xTixO3 (PZT) as the model system. We study the temperature and electric field dependent properties of fully epitaxial, highly strain-engineered thin films produced on a wide range of single crystal substrates (i.e., LaAlO3, SrTiO3, DyScO3, TbScO3, GdScO3 and NdScO3) by pulsed laser deposition. X-ray diffraction reciprocal space mapping studies have revealed that the films are coherently strained to the substrate and atomic force microscopy studies reveal the ability to create atomically smooth films. Through a combination of classical thermodynamic analyses, Ginzburg-Landau-Devonshire phenomenological modeling, and low-noise electrical measurements, the potential of modern oxide materials for energy conversion and solid state cooling will be examined. Aided by theoretical modeling, we have optimized the experimental processing parameters and have obtained record-breaking pyroelectric coefficients of up to 0.1 μC/cm2K by making use of novel epitaxial strain and domain structure induced effects in PZT thin films. Additionally, our investigations suggest that traditional thermodynamic cycles designed to maximize efficiency in devices based on these materials have overlooked key aspects of material response. The combined experimental and theoretical approach provides fundamental insights into the temperature and electric field response in ferroelectric materials and we will provide a framework of the materials design paradigms with respect to achieving efficient energy conversion/solid state cooling with complex oxide materials.
4:30 PM - **P12.6
In Situ Studies on the Effect of Oxygen Partial Pressure on Ferroelectric Thin Films.
Dillon Fong 1 , Chad Folkman 1 , Matt Highland 1 , Tiffany Santos 1 , Seong Keun Kim 1 , Pete Baldo 1 , Paul Fuoss 1 , Carol Thompson 2 1 , Jeff Eastman 1 , Stephen Streiffer 1 , G. Stephenson 1
1 , Argonne National Laboratory, Argonne, Illinois, United States, 2 , Northern Illinois University, DeKalb, Illinois, United States
Show AbstractFrom our previous studies [1], it is known that the behavior of ferroelectric thin films can depend strongly on oxygen partial pressure (pO2) as well as temperature. This can have significant implications in understanding both ferroelectricity (e.g., switching without domain formation [2]) and the reactivity of oxide surfaces. Others have recently shown that polarization at BaTiO3 and LiNbO3 surfaces can affect adsorption behavior [3,4], suggesting that ferroelectricity may be a potential route for modulating surface catalytic properties.We use in situ synchrotron x-ray scattering to study the pO2 dependent properties of PbTiO3 and BaTiO3 films grown on 0.5 wt% Nb-doped SrTiO3 (001) substrates. In high pO2 conditions, PbTiO3 is in the "up" polarized state; the film forms 180° stripe domains at low pO2. A c(2×2) surface structure is observed under both conditions. Conversely, BaTiO3 is polarized down regardless of pO2; changes in pO2 result only in piezoelectric response from the lattice. The BaTiO3 surface shows a (3×n) surface structure that is also independent of pO2. Differences between the PbTiO3 and BaTiO3 behavior will be discussed in terms of oxygen surface reactivity. Recent results on the effect of a one-unit-cell capping layer of SrTiO3 on BaTiO3 will also be discussed.Work supported by the U. S. Department of Energy under Contract No. DE-AC02-06CH11357.[1] R.-V. Wang, D. D. Fong, F. Jiang, M. J. Highland, P. H. Fuoss, et al., Phys. Rev. Lett. 102, 047601 (2009).[2] M. J. Highland, T. T. Fister, M.-I. Richard, D. D. Fong, P. H. Fuoss, et al., Phys. Rev. Lett. 105, 167601 (2010).[3] D. Li, M. H. Zhao, J. Garra, A. M. Kolpak, A. M. Rappe et al., Nature Mater. 7, 473 (2008).[4] J. Garra, J. M. Vohs, and D. A. Bonnell, Surf. Sci. 603, 1106 (2009).
5:00 PM - P12.7
Rare-Earth Doping in BaTiO3 and Its Implications for the Ferroelectric Properties.
Colin Freeman 1 , James Dawson 1 , Julian Dean 1 , John Harding 1 , Ben-Liu Ben 1 , Derek Sinclair 1
1 Materials Science and Engineering, Univ Sheffield, Sheffield United Kingdom
Show AbstractBarium Titanate has a range of exciting properties such as piezo- and ferro-electricity and has a high dielectric constant that makes it a valuable commercial material for capacitor applications. The electrical properties of BaTiO3 are obviously crucial to its uses and much effort is placed in their modification via manipulation of its defect chemistry.Rare-earth dopants such as La and Gd are frequently used to modify the properties of BaTiO3; their influence, however, is not fully characterised [1]. This is partly due to disagreements over the compensation mechanisms with different dopants [2,3]. This has led to the question of whether La doping for Ba produces Ti vacancies or reduces the Ti cations (so called ‘donor doping’). We have analysed this system with a series of classical simulations [4] exploring a wide range of dopant concentrations which demonstrate Ti vacancies are always preferred.Unlike La, which exclusively dopes on the Ba, Gd is capable of substituting on both the Ba and Ti sites depending on the concentration and environment. Several different effects have been observed with Gd doping that have yet to be fully explained. These include a small decrease in the Curie temperature with increasing Gd concentration. This reduction is unexpectedly smaller than observed with larger dopants. In addition, the bulk conductivity of doped samples is found to decrease dramatically with a concentration in excess of 10% Gd. We explore these effects with a series of classical simulations using energy minimisation and molecular dynamics. Our simulations demonstrate how the local structure of the systems is vital to explaining the large-scale properties.[1] C. Metzmacher, K. Albertsen, J. Am. Ceram. Soc., 84 (2001) 821[2] D. Smyth Proc. of the 2001 12th IEEE Int. Symp. on Applications of Ferroelectrics Vols I and II, 345 (2001) 369[3] F. Morrison, D. Sinclair, A West J. Appl. Phys. 86 (1999) 6355[4] C.L. Freeman, J.A. Dawson, H.-R. Chen, J.H. Harding, L.-B. Ben, D.C. Sinclair, J. Mater. Chem., 21, (2010), 4861
5:15 PM - P12.8
Spatially Resolved Photovoltaics in Bismuth Ferrite.
Won-Mo Lee 1 , Ji Ho Sung 1 , Kanghyun Chu 3 , Xavier Moya 5 , Young-Jun Cho 1 , Cheol-Joo Kim 1 , Neil Mathur 5 , Sang-Wook Cheong 6 , Chan-Ho Yang 3 4 , Moon-Ho Jo 1 2
1 Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang Korea (the Republic of), 3 Department of Physics, Korea Advanced Institute of Science and Technology(KAIST), Daejeon Korea (the Republic of), 5 Department of Materials Science, University of Cambridge, Cambridge United Kingdom, 6 Department of Physics and Astronomy, Rutgers State University, Piscataway, New Jersey, United States, 4 KAIST Institute for the NanoCentury, Korea Advanced Institute of Science and Technology(KAIST), Daejeon Korea (the Republic of), 2 Division of Advanced Materials Science, Pohang University of Science and Technology (POSTECH), Pohang Korea (the Republic of)
Show AbstractLeaky ferroelectric oxides can serve as optoelectronic circuit elements in which potential gradients due to the spontaneous polarization yield asymmetric and nonlinear photocarrier dynamics. Ferroelectric domains and domain walls should each influence photocarrier generation, separation and transport differently, but the microscopic mechanisms are unknown. Here, we present scanning photocurrent images of epitaxial BiFeO3 thin films that reveal how the photoresponse depends on dynamic domain configurations. Locally, photocurrent direction is determined by local domain orientation, whereas magnitude is spectrally centred around charged domain walls that are associated with oxygen vacancy migration. Our observations demonstrate that photodetection can be electrically controlled by manipulating domains, which suggests non-volatile optoelectronic memory applications.
5:30 PM - P12.9
Photovoltaic Effect of BiFeO3 Thin Films with 109° Domains.
Rui Guo 1 , Lu You 1 , Lang Chen 1 , Junling Wang 1
1 , Nanyang Technological University, Singapore Singapore
Show AbstractDomain walls in BFO thin films have been reported to possess some unique functionalities. Recently, a new mechanism of photovoltaic charge separation which produces voltages that are significantly higher than the bandgap was reported in BFO thin films with 71° domains. It was proposed that the effect arises from the structurally driven steps of the electrostatic potential at the nanometer-scale domain walls. Since the potential drop at 109° domain walls is much higher than that at 71° domain walls, it was predicted that the photo-voltage of samples with 109° domain walls will be significantly higher than that of samples with 71° domain walls. However, PV measurement of the 109° domain sample is restricted due to the presence of a random distribution of the two in-plane structural variants (four polarization variants). In this paper, we report the photo-voltage of BFO thin film with 109° domain walls. We obtained 109° domains with mainly two polarization variants through using miscut DSO substrate or polarization switching. Much higher photo voltage was obtained in BFO thin film with 109 domains than that in BFO thin film with 71 domains. The mechanism of polarization switching of 109° domains in BFO thin films was also studied.
5:45 PM - P12.10
Visualization of Ferroelectric Domain Behavior Using Piezoresponse Force Microscopy.
Seungbum Hong 1 , Moonkyu Park 1 2 , Nishit Murari 1 3 , Hyunwoo Choi 1 2 , Miso Kim 1 4
1 Materials Science Division, Argonne Nat Lab, Lemont, Illinois, United States, 2 Department of Materials Science and Engineering, KAIST, Daejon Korea (the Republic of), 3 , University of Puerto-Rico, San Juan United States, 4 Department of Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractFerroelectric materials possess spontaneous polarization – net electric dipole moment per unit volume, of which magnitude and direction determine the surface charge density, and of which direction can be switched by electric field larger than a threshold called coercive field. As polycrystalline materials have grains with different crystallographic orientations and various grain boundaries dividing those grains, ferroelectric materials usually form domains with different polarizations and various domain boundaries dividing those domains. As such, ferroelectric domain structure and its dynamic behavior determine their macroscopic electric and piezoelectric properties. Furthermore, electric charges in various forms such as charged defects, electrons and ions interact with ferroelectric domains and their boundaries to influence the stability of domains and mobility of each domain boundary. Here we present our efforts to develop angle-resolved piezoresponse force microscopy (AR-PFM) to visualize ferroelectric domains with polarization variants in 3D and scanning resistive probe microscopy (SRPM) to map the surface charge density (~0.8 µC/cm2) with spatial resolution of 25 nm and temporal resolution of 125 µs, both of which are based on the system of atomic force microscopy (AFM). Furthermore, we demonstrate how we could address the origin of domain structure showing polarization variants deviating from ferroelectric easy axes and electrostatically unstable charged domain boundaries in conjunction with the crystal nucleation and growth model. Lastly, the impacts of such domain structures on the local polarization switching behaviors will be discussed with the future implications for energy harvesting and memory devices.
P13: Poster Session: Synthesis and Characterization of Ferroic Materials
Session Chairs
Thursday AM, December 01, 2011
Exhibition Hall C (Hynes)
9:00 PM - P13.1
Facile Mechanochemical Synthesis and Magnetic Properties of Pervoskite YFe1-xCrxO3, (0〈x〈1).
Vijayalaxmi Malagareddy 1 , Sanjay Mishra 1 , Sunil Karna 1 , C. Rong 2 , J. Liu 2 , E. Gunapala 3 , G. Marasinghe 3
1 Physics, The University of Memphis, Memphis, Tennessee, United States, 2 Physics, University of Texas, Arlington, Texas, United States, 3 Physics, University of North Dakota, GrandForks, North Dakota, United States
Show AbstractMultiferroic compounds such as YFeO3, YMnO3, and BiMnO3, show magnetoelectric properties, where magnetic and ferroelectric ordering coexist and are coupled. The subject of this paper is to present a low temperature mechanochemical synthesis method for mixed oxide YFe1-xCrxO3 and study the effect of Fe substitution by Cr in these compounds. The proposed low temperature synthesis method leads to the formation of pure phase orthoferrite which otherwise is difficult to prepare due to easy formation of the undesirable garnet composition Y3Fe12O15 and Fe3O4. Moreover, there have been few investigation on the mixed orthoferrite-orthochromite mixed pervoskites RE(CrFe)O3 system, primarily due to impediment in obtaining pure phase oxides.In a typical synthesis process, chloride salts of Yttrium (III), Iron (III), Chromium (III), and NaOH along with ethanol are blended in stoichiometric ratio in agate mortar and then ball milled for 2 hours to get a uniform mixture. The mixture is heated at 200oC for 10 min to complete the reaction. The dark brown slurry was washed with water to remove chloride salts. The resultant sample was calcined at 1000oC for 48 hours to obtain pure phase polycrystalline YFe1-xCrxO3 powder.The powders obtained were nanocrystalline nematic (cylindrical) in shape and crystallized in pure orthorhombic phase. TGA/DTA indicates crystallization of YFeO3 starts at 650oC and end at ~1000oC. This temperature is lower than the 1300oC used in solid state reactions for the synthesis of YFeO3. The magnetic properties of these compounds are temperature and concentration dependent. The magnetic hysteresis loops measured at 5 and 300 K indicate the typical ferromagnetic or ferrimagnetic character of the samples. The hysteresis loops for samples with Cr <0.5 are open at high fields (5T) with maximum Ms ~ 5.0 emu/g and Hc~100 Oe at 5K. It was found that Cr ion enhances the Ms of YFeO3 for x<0.33. Samples with Cr>0.5 show ferrimagnetic/antiferromagnetic behavior at 5K. One possible reason for Cr to increase the magnetization of YFCrO is the presence of strong ferromagnetic coupling between Fe3+ and Cr3+ under 180° superexchange interaction. The other possible reason is that the addition of Cr might increase the oxygen vacancies in YFCrO. The small magnetization of YFCrO observed in our work might also be attributed to the canting of the magnetic moments arising from oxygen vacancies. On the other hand YCrO3 (x=1) is a ferrimagnet with weak ferromagnetism (TN =140 K). Our magnetic measurements show an increase in the magnetization around 140 K and the presence of magnetic hysteresis below this temperature, Hc~10,000 Oe. Clearly,YCrO3 exhibits features similar to those of a ferrimagnetic system. In summary, the pure perovskite YFe1-xCrxO3 compounds were synthesized using a mechanochemical method. Hysteresis loops with small Ms and Hc were observed in these compounds, and the addition of Cr enhances the magnetization for Cr<0.33.
9:00 PM - P13.10
Deconvolution of Substrate Type and Film Texture to Extract True Young’s Modulus in PZT Films.
Dan Liu 1 , Seon-Bae Kim 1 , Hosang Ahn 1 , Barton Prorok 1 , Seung-Hyun Kim 2 , Dong-Joo Kim 1
1 Mechanical Engineering, Auburn University, Auburn, Alabama, United States, 2 Engineering, Brown University, Providence, Rhode Island, United States
Show AbstractPZT films are widely used in microelectromechanical systems (MEMS) due to their large piezoelectric coefficients, dielectric constants, and excellent electromechanical properties. Since the piezoelectric properties of PZT films are influenced by the mechanical coefficients, the designing MEMS devices should consider the scaling effects of mechanical properties of PZT films. However, the bulk properties are usually employed due to the lack of knowledge of mechanical and ferroelectric properties as well as coupled response of the PZT film structure, which may induce large variations in the design of MEMS structures and even FEM simulations. As such, research work relevant to the measuring mechanical properties of PZT films by nanoindentation, such as crystalline orientations dependence, electrode materials effects, annealing temperature influences have been conducted.However, the measurement of ‘film-only’ mechanical properties is not trivial due to multilayer structure of PZT films. Therefore, it is necessary to employ a combined experimental and analytical method. In this study, PZT films with SiO2 and SiNx-based MEMS structure were used since they are most common structures used in MEMS application. PZT films were deposited by the sol-gel method on platinized silicon substrates with either silicon nitride or silicon oxide structural layers. The crystalline orientations of the PZT films were controlled by a chelating agent and pyrolysis temperature. Nanoindentation was utilized to characterize the Young’s moduli of these films. The measured modului of PZT films on the two types of substrate structures showed similar orientation dependence (E(001)>E(111)>E(110,111)) but distinct values. A new model of film indentation based on discontinuous transfer of elastic strain was employed to assess properties. Furthermore, this model enables to decouple the effects of film orientation and structural layer type on the Young’s modulus.
9:00 PM - P13.11
Fabrication of Ultra Smooth Lead Zirconium Titanate (US-PZT) Thin Film.
Robert Ferris 1 , Byung Seok Kwon 1 , Stefan Zauscher 1 , Benjamin Yellen 1
1 Mechanical Engineering and Material Science, Duke University, Durham, North Carolina, United States
Show AbstractDevelopment of low mean-surface roughness ferroelectric thin films will enable integration with electrokinetic lab-on-chip (bio)molecular sensing devices. Previously published PZT thin film roughness values range between 20 and 30 nm. We have fabricated, for the first time, ultra-smooth lead zirconium titanate (US-PZT) thin films from a sol-gel precursor with a root mean square roughness of only 2 to 3 nm, without surface discontinuities. Our method is simple and allows for the low-cost fabrication of US-PZT thin films. The fine control over solvent evaporation, pyrolyzation, and annealing conditions are deciding factors of surface roughness and discontinuities of US-PZT thin films. In addition to processing, we report on film resistivity, coercive field, and remnant polarization of 52/48 US-PZT thin films with mixed crystallographic orientations between <100> and <110>.
9:00 PM - P13.12
Growth and Dielectric Characterization of Barium Strontium Titanate Films on Metal Foils by Pulsed Laser Deposition.
Shanshan Liu 1 , Beihai Ma 1 , Sheng Chao 1 , Manoj Narayanan 1 , Uthamalingam Balachandran 1
1 Energy Systems Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractHigh-dielectric constant and high breakdown strength ceramic thin films hold special promise for advanced power electronics applications. We have deposited Ba0.6Sr0.4TiO3 films directly on copper foil by pulsed laser deposition using a two-step process inside a vacuum chamber under controlled oxygen partial pressure. A dense film with columnar grains was observed from cross-sectional scanning electron microscopy. X-ray diffraction revealed that our BST films were completely crystallized in the absence of secondary phases or substrate oxidation. The films exhibit good ferroelectric behavior with a slim and well-defined hysteresis loop, remanent polarization of ≈2.5 µC/cm2, spontaneous polarization of ≈19.2 µC/cm2, and coercive field of ≈43 kV/cm. We also measured a relative permittivity of 700, dielectric loss of 0.013, and leakage current density of 4.4×10-9 A/cm2 at room temperature. Details of processing conditions and dielectric properties will be presented. The work was supported by the U.S. Department of Energy, Office of Vehicle Technologies Program, under Contract DE-AC02-06CH11357.
9:00 PM - P13.14
Templated Grain Growth and Enhanced Piezoelectric Properties in Lead-Free Piezoelectric Ceramics.
Yunfei Chang 1 , Stephen Poterala 1 , Gary Messing 1
1 Department of Materials Science and Engineering and Materials Research Institute , Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractCrystallographic texturing of polycrystalline ferroelectric ceramics by templated grain growth (TGG) or reactive template grain growth (RTGG) can lead to significantly enhanced piezoelectric properties similar to those of single crystals. In this work, we report recent developments in fiber textured, lead-free piezoelectric ceramics. Both (K0.5Na0.5)0.98Li0.02NbO3 (KNLN) perovskites and Sr0.61Ba0.39Nb2O6 (SBN61) tungsten bronze ceramics show high density and texture quality (F00l = 98% and F00l ≥ 95%, respectively). KNLN and SBN61 are textured by TGG and RTGG mechanisms, respectively, as shown by correlation of phase evolution, densification and texture development in these systems. From this work, a schematic is presented to illustrate key differences between TGG and RTGG processes. The piezoelectric properties of textured KNLN (d33 = 192 pC/N and kp = 0.63) are 40-70% higher than those of randomly oriented ceramics, and are not accompanied by a reduction in the PPT temperature (To-t = 155°C). In textured SBN61, piezoelectric properties are enhanced and reach 52-72% of single crystal values.
9:00 PM - P13.15
WITHDRAWN 11/24/11 Effect of Excess Alkaline on Ferroelectric and Piezoelectric Properties of Lead-Free NKN Thin Films Deposited by RF Magnetron Sputtering.
Hye Yeon Jeong 1 , Hyung-Won Kang 1 , Hak In Hwang 1 , Hyeung-Gyu Lee 1 , Chang Won Ahn 2 , Ill Won Kim 2 , Seung Ho Han 1
1 Electronic Materials & Device Research Center, Korea Electronics Technology Institute, Seongnam Korea (the Republic of), 2 Department of Physics, University of Ulsan, Ulsan Korea (the Republic of)
Show AbstractLead-free piezoelectric materials have been attracting great attention due to their eco-friendly nature as compared with PZT based toxic materials which have been used in many sensor and actuator applications. In particular, (Na0.5K0.5)NbO3 (NKN) is considered to be a more promising candidate because it has good ferroelectric and piezoelectric properties as well as a high Curie temperature. There have been several reports on NKN thin films fabricated by sol-gel process, pulsed laser deposition, and RF magnetron sputtering. Among them, NKN films fabricated by RF magnetron sputtering have been scarcely reported because it is difficult to form high quality thin film with highly preferred orientation on Pt coated Si substrate.In this study, lead-free piezoelectric NKN thin films were fabricated on Pt(111)/Ti/SiO2/Si substrate by RF magnetron sputtering at different working pressure and annealing temperature. As K and Na are very volatile during in-situ deposition process and annealing process, a target enriched with K2CO3 and Na2CO3 was prepared to compensate the volatilization of K and Na. The NKN thin film displayed enhanced ferroelectric and electrical properties as the amount of excess alkaline element was increased.
9:00 PM - P13.16
Synthesis of Thick Pure Quasi-Layered Multiferroic Films.
Chang-Su Woo 1 , Jin Hong Lee 1 , Kanghyun Chu 1 , Chan-Ho Yang 1
1 Physics, KAIST, Daejeon Korea (the Republic of)
Show AbstractBismuth ferrite (BiFeO3; BFO) has been extensively studied since it has exceptionally large order parameters at room temperature in terms of electric and magnetic degrees of freedom. Recently it has been reported that a highly-elongated phase of BiFeO3 (T-BFO) can be stabilized by heteroepitaxial misfit strain. [1] The physical properties of the T-BFO will be expected to have completely different from those of normal BiFeO3 (R-BFO) because the tetragonal-like elongation (c/a ~1.26) is very large. In order to unveil the physical properties of T-BFO including P-E hysteresis loop, it is necessary to grow very thick pure T-BFO films. However it is problematic that the R-BFO phase is parasitically produced when the thickness of the film is larger than ~30 nm as a result of strain relaxation. We have grown BFO films on various substrates and found that it is possible to grow pure T-BFO films up to at least 120 nm in thickness when an exactly matched substrate is employed. Here we will present systematic studies of crystal structure, surface morphology, and ferroelectric domain structure, with varying misfit strain and film thickness.
9:00 PM - P13.17
Low Temperature Integration of Ferroelectric Thin Films Using Excimer Laser for Silicon on-Chip Applications.
Bharadwaja Srowthi 1 , F. Griggio 1 , W. Qu 1 , J. Kulik 1 , T. Clark 1 , S. Trolier-McKinstry 1
1 Materials Research Institute, Penn State University, University Park, Pennsylvania, United States
Show AbstractLow thermal budgets for processing of ferroelectric films are important for nonvolatile memories, pyroelectric detectors, miniaturized piezoelectric transducers, and embedded dielectrics. Most complementary metal oxide semiconductor (CMOS) based read-out circuits can withstand processing temperatures less than 450 oC; however large thermal budgets (≥ 500 oC) are required to crystallize ferroelectric thin films such as Pb(Zr,Ti)O3 and BaTiO3. Using KrF excimer laser annealing and oxidation, the substrate temperatures can be reduced below 400 o C. In this presentation, three main topics will be discussed: (i) Orientation control in laser annealed Pb(Zr,Ti)O3 (52/48) thin films using a bottom template layers at substrate temperatures below 400 oC. Both {111} and {100} orientations were achieved in ~ 200-300 nm thick PZT layers on (111) Pt and {001} PbTiO3 surfaces. The measured average remanent polarization and coercive fields are 31 μC/cm2 and 86 kV/cm for (001) PZT films and 23.6 μC/cm2 and 64 kV/cm for (111) oriented PZT thin films respectively. The maximum in-plane piezoelectric charge coefficients are ~–9.0 C/m2 for {001} and ~ –8.5C/m2 for (111) PZT thin films respectively. (ii) Oxidation kinetics of ~ 200 nm thick BaTiO3 thin films on Ni foils in O2/O3 (90/10) at substrate temperature below 400 oC for base metal capacitor applications. The resultant films have small signal dielectric permittivities ~ 1100 with < 4% loss values between 0.1-1 kHz. Well-controlled interfaces between the BaTiO3 and the Ni foil, without indication of a NiO reaction layer are confirmed from electron energy loss spectroscopy (EELS) and high resolution transmission electron microscopy (HRTEM) studies.
9:00 PM - P13.18
Critical Slowing down Mechanism and Reentrant Dipole Glass Phenomena in (1-x)BaTiO3-xBiScO3 (0.1≤x≤0.4).
Bharadwaja Srowthi 1 , L. Cross 1 , S. Trolier-McKinstry 1 , C. Randall 1
1 Materials Research Institute, Penn State University, University Park, Pennsylvania, United States
Show AbstractThe dielectric and ferroelectric switching properties of high temperature-high energy density (1-x)BaTiO3-xBiScO3 (0.1≤x≤0.4) dielectrics were investigated over a broad temperature range. It was found that these ceramics possess dipole glass features such as critical slowing down of the dielectric relaxation, polarization hysteresis aging, rejuvenation, and hole like memory below the dipole glass transition temperature (TDG). The dielectric relaxation behavior is consistent with a three-dimensional Ising model with critical slowing exponents (zυ)=10±1 and composition-dependent glass transition temperatures. The electric field and temperature dependence of polarization freezing effects in (1-x)BaTiO3-xBiScO3 , 0.1≤x≤0.4 have been investigated by Positive-Up-Negative-Down (PUND) switchable polarization measurements. Upon cooling, these solid solutions undergo polarization freezing effect determined by the magnitude of the field level for a given “x” value under zero field cooled condition. Inherent reentrant temperatures as a function of composition is determined under zero field approximation. These field and temperature dependent features suggest that, at lower temperatures, (1-x)BaTiO3-xBiScO3 ceramics transform into a reentrant dipole glass state owing to the breakup of local polar ordering. A phase diagram is developed marking the paraelectric, ferroelectric, and dipole glass regimes as a function of composition with the reentrant features.
9:00 PM - P13.19
X-Rays and Magnetic Materials - A Perfect Match.
Hendrik Ohldag 1
1 Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Center, Menlo Park, California, United States
Show AbstractToday’s fundamental and applied magnetism research is particularly focused on magnetic materials that are suitable as magnetic sensors, spin valves, spin transistors or magnetic media consisting of complex magnetic multilayer structures. Scientific investigations in this area are concerned with the origin of magnetic coupling, spin transport across interfaces, magnetic properties of magnetic oxides and the complex magnetic structures which evolve when different kind of magnets for example antiferromagnets (AF) and ferromagnets (FM) are brought into contact. Dichroism x-ray absorption spectroscopy (XAS) using synchrotron radiation represents a unique tool to understand complex nanomagnetic samples. The power of XAS is that it provides a possibility to address individual magnetic properties of different elements in a sample and a way to distinguish between different magnetic order like AF and FM order at the same time. It can furthermore be used to study the magnetism of buried interfaces, diluted magnetic systems like FM semiconductors or other exotic new magnets. The pulsed nature of the synchrotron as x-ray source allows for studying the time dependent behavior of a sample with a temporal resolution of a few tens of picoseconds. Dichroism soft x-ray absorption spectroscopy can furthermore be used to obtain spatially resolved information with less than 50nm lateral resolution in a modern full field or scanning x-ray microscopes.
9:00 PM - P13.2
Nanocrystalline Ferroelectric BaTi0,80Zr0,20O3 Ceramic Prepared by Spark Plasma Sintering.
Valmor Mastelaro 1 , Higor Favarim 1 2 , Alain Michalowicz 2 , Claude Godart 2
1 Physics and Materials Science Department, IFSC - University of São Paulo, Sao Carlos, Sao Paulo, Brazil, 2 , Institut de Chimie et des Materiaux Paris-Est, CNRS, Université Paris Est, Thiais France, Thiais France
Show AbstractIn the last decades, several processing methods to synthesize materials in a nanometer scale were developed because these nanocrystalline materials presented novel properties which were not observed in conventional microcrystalline material. The particle size influence on the nanostructured ferroelectric materials properties has also attracted much attention and several studies have been reported because of their potential technological applications like ultrasonic transducers and pyroelectric infrared sensors. However, most of the studies which show the size influence on nanostructured ferroelectric materials involve the preparation of thin films. The development of new synthesis processes for nanocrystalline ceramics densification received much attention in last year’s and recently and spark plasma sintering (SPS) emerged as an interesting technique to this goal. In this work, nanocrystalline BaTi0,80Zr0,20O3 ceramic was prepared by the polymeric precursor method and sintered by using the spark plasma sintering technique, resulting in nanocrystalline dense ceramic. A relative decrease in the values of maximum permittivity that was observed when compared to same samples prepared by conventional methods was attributed to differences between the core grain and the grain boundaries. The results of impedance spectroscopy on these samples also show a small shift of the maximum temperature and a slight broadening of the permittivity curve with decreasing grain size. However, these results do not allowed classifying the samples as having a typical relaxor ferroelectric material behavior.
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Fabrication and Electrical Properties of 0.7BiFeO3-0.3PbTiO3 Films on Stainless Steel Substrates by a Modified Sol-Gel Method.
Chen Zhao 1 , Guiyang Shi 1 , Leiyang Feng 1 , Shengwen Yu 1 , Dengren Jin 1 , Jinrong Cheng 1
1 School of Materials Science and Engineering, Shanghai University, Shanghai China
Show AbstractFerroelectric 0.7BiFeO3-0.3PbTiO3 (BFPT) films with thickness of about 5 μm have been fabricated on stainless steel substrates by a modified sol-gel method. A thin layer of PbTiO3 (PT) was introduced between the substrates and BFPT films in order to decrease the annealing temperature. X-ray diffraction revealed that BFPT films could be well crystallized into the perovskite structure at about 550 oC, which is about 100 oC lower than the annealing temperature of BFPT films without using a PT seeding layer. The thickness of BFPT has great effects on the homogeneity, film orientation and electrical properties of BFPT films. With the increase of thickness, BFPT films revealed a (100) preferred orientation. Our results indicated BFPT films deposited on stainless steel substrates maintained the excellent dielectric and ferroelectric properties.
9:00 PM - P13.22
Size Effects in Ferroelectric Nanocrystals with Incommensurate Phases.
Kazimierz Plucinski 1 , I. Kityk 2
1 Electronics, Mil. Univ. of Technology, Warsaw Poland, 2 Electrical Engineering Department, Czestochowa University of Technology, Czestochowa Poland
Show AbstractWe have carried out experimental studies into the optical birefringence of a large group of A2BX4 (K2ZnCl4, Rb2ZnCl4, K2SeO4 et al.) over a wide range of temperatures, these including paraelectric, ferroelectric and incommensurate phases for the wavelength 633 nm. We found that with a decrease in the NC sizes the temperature range of the incommensurate phase was enhanced. At the same time the ferroelectricity disappeared at sizes below 8 nm. This is a consequence of nano-confined effects which change electron-phonon anharmonic interactions responsible for such kinds of phase transitions. Additional superposition of the external electric field leads to radical changes in the relative amount of the ferroelectrics and incommensurate phases. The principal role of the defect trapping levels changing the corresponding interaction may be caused by surface nano-trapping levels. The effect is explained within the Landau-Ginzburg phenomenological approach with Lifshitz invariant. During phase transitions from ferroelectric-incommensurate phase a long-range modulated structure with an effective period many times higher than the basic crystallographic units occurs. The spontaneous polarization during such kinds of transitions is seen in wave vectors which are twisted with respect to the crystallographical second order axes. Additional confirmation of the observed effect was obtained by optical second harmonic generation. Where nanocrystallite sizes fall below 12 nm there are some harmonic soliton waves which are propagated in several directions parallel to the crystallographic axes. So despite the absence of long-range disorder some non-centrosymmetry is seen. This experimental fact makes it possible to conclude that with nanocrystallites of under 12 nm some additional mechanism for long-range ordering occurs causing the corresponding non-centrosymmetry.
9:00 PM - P13.23
Preparation and Characterization of Pb(Zr,Ti)O3 Thick Films Prepared by the Sol-Gel Based 0-3 Composite Route onto Metal Substrates.
Dan Jiang 1 , Xuelian Zhao 1 , Guiyang Shi 1 , Jinrong Cheng 1
1 , Shanghai University, Shanghai China
Show AbstractUniform and crack-free Pb(Zr0.53Ti0.47)O3 thick films (5-20 μm ) were grown on LaNiO3 buffered stainless steel substrates by a sol-gel based 0-3 composite method. Pb(Zr0.53Ti0.47)O3 nanopowders were prepared via sol-gel, and then dispersed in Pb(Zr0.53Ti0.47)O3 sol to form homogeneous slurry. The effects of the adding amount of Pb(Zr0.53Ti0.47)O3 nanopowders, annealing temperature and the film thickness on the electric properties of Pb(Zr0.53Ti0.47)O3 thick films were investigated in this study. Scanning electron microscope was applied to characterize the microstructure of the films. X-ray diffraction results indicated that the PZT thick films could be well crystallized into the perovskite structure at about 700 oC. The typical ferroelectric hysteresis loops and the J-V curve were characterized by using Radiant Technology Ferroelectric tester. Our results show that the PZT thick films are promising materials for MEMS applications.
9:00 PM - P13.24
Structure and Physical Properties Fluctuations in BiFeO3 Thin Film with Giant c/a Ratio.
Jerome Pacaud 1 , Frederic Pailloux 1 , Manuel Bibes 2 , Agnes Barthelemy 2
1 Institute Pprime, University of Poitiers, Chasseneuil France, 2 , Unité Mixte de Physique CNRS/Thales, Palaiseau France
Show AbstractWe study BiFeO3 (BFO) thin films deposited on LaAlO3 (LAO) substrate by pulsed laser deposition. Several questions remain concerning the structure of this material in the thin film geometry. We combine different approach simultaneously in the electron microscope: energy filtered electron diffraction, high resolution electron microscopy, high angle annular dark field STEM and electron energy loss spectroscopy in order to gain insight into the structure of our BFO film.We use a JEOL 2200 FS equipped with a field-emission gun for small probe formation and an in-column Omega energy filter allowing the use of several detector type (CCD, Imaging-plate) depending on the nature of the signal to be recorded. Energy filtered electron diffraction drastically improves signal-to-background ratio of diffraction pattern particularly on the weak diffuse features. An energy slit of 15 eV has been used to keep a large angle of observation in the diffraction pattern while removing the important inelastic contribution of the plasmon peak. EELS is carried out in the spectrum imaging mode: linescans are typically acquired with a 0.2nm probe size and 0.07eV energy dispersion; they are subsequently processed by MSA to remove statistical noise and to detect interfacial components.The indexation of the zone axis diffraction pattern gives a space group of Cm with 4 pseudo-cubic unit-cells close to the tetragonal-like phase previously observed on similar samples. In off-axis geometry, a strongly structured diffuse scattering can be observed in the high order Laue zone of the diffraction pattern. This diffuse intensity consists in a sharp streak modulated along the growth direction. Geometrical Phase Analysis of the HRTEM micrographs reveals this modulation of the monoclinic structure in the thin film and its spatial extension. Two different fingerprints can be identified on the oxygen-K edge of the Electron Energy Loss Spectra. Linescans performed across the interface and the BFO film and subsequent linear fit of the signal by the weighted fingerprints, shows that one particular signature is confined near the interface while the other only appears after 4nm of film thickness. Low loss spectra show an interfacial signal which cannot be explained by the superimposition of the LAO and BFO. This specific phase extends over a few nanometer and can be attributed either to a different BFO phase or to an interface plasmon.The coupling of the different techniques which can be applied in a single experiment in an electron microscope can give invaluable information on the structure of the crystal and on the chemical environment of each ion. In our film, the fluctuation of the structure which has been detected in diffraction and spatially characterized in image mode, follows the fluctuation of coordination of the oxygen ions in the growth direction even for the 8 nm film.
9:00 PM - P13.25
Low Pressure Growth and Fully Saturated Hysteresis Loops of Epitaxial BiFeO3 Thin Films Prepared by Dual Ion Beam Sputtering.
Seiji Nakashima 1 , Yosuke Tsujita 1 , Hironori Fujisawa 1 , Masafumi Kobune 2 , Hiroshi Nishioka 2 , JungMin Park 3 , Takeshi Kanashima 3 , Masanori Okuyama 4 , Masaru Shimizu 1
1 Grad. School of Engineering, Dept. of Electrical Engineering and Computer Sciences, University of Hyogo, Himeji Japan, 2 Grad. School of Engineering, Dept. of Department of Materials Science and Chemistry, University of Hyogo, Himeji Japan, 3 Grad. School of Engineering Science, Dept. of Systems Innovation, Osaka University, Toyonaka Japan, 4 Institute for NanoScience Design, Osaka University, Toyonaka Japan
Show AbstractBiFeO3 (BFO) thin film shows excellent ferroelectricity1), 2) and has attracted much attention. One of the most difficult problems for application to devices is its large leakage current. However, BFO is an insulator having a band gap (Eg) of ~2.7 eV.3) It is well known that deposition of high quality BFO thin film is difficult because high volatility of Bi. Generally, higher kinetic energies of incident particles and low pressure condition are suitable for crystalline thin film growth from the view point of migration of adsorbed particles on a substrate surface. However, BFO thin films have been grown in higher pressure of >0.1 Pa in previous reports. In this study, we have demonstrated low pressure (< 0.1 Pa) growth of pure BFO thin films on SrRuO3-buffered 0.5o off-cut SrTiO3 (001) single crystal by a dual ion beam sputtering (dual-IBS), and the fully saturated hysteresis loops have been obtained at room temperature.280-nm-thick BFO thin films were grown on SrRuO3 buffered 0.5o off-cut SrTiO3 (001) single crystal substrate at substrate temperature of 650 oC by dual-IBS using 3 cm φ Kaufman source. Bi2O3 and α-Fe2O3 powder (5 inch φ) were used as targets. Ar+ ion beam current of Bi2O3 and α-Fe2O3 side ion source were fixed at 20 and 30 mA, respectively. During growth, total pressure and oxygen partial pressure were fixed at 70 mPa and 36 mPa, respectively.X-ray diffraction pattern shows the BFO film is phase pure without any secondary phase. Ultra smooth surface with a roughness (Ra) of 0.8 nm is confirmed by atomic force microscope (AFM) image, and stripe morphologies assumed to be step and terrace structure originated from morphologies of SRO/STO substrate can be observed. Moreover, fully saturated D-E hysteresis loops with good squareness are observed at room temperature. Remanent polarization (2Pr) of 130 μC/cm2 and coercive field (2Ec) of 438 kV/cm can be evaluated from the D-E loops.References 1) J. Wang et al. Science 299, 1719 (2003).2) K. Y. Yun et al, Appl. Phys. Lett. 89, 192902 (2006).3) S. J. Clark et al, Appl. Phys. Lett., 90, 132903 (2007).
9:00 PM - P13.26
Influence of Thickness on Structure and Electric Properties of 0.7BiFeO3-0.3PbTiO3 Films Prepared by Sol-Gel Method.
Haibo Zhang 1 , Shengwen Yu 1
1 , School of Materials Science and Engineering, Shanghai University, Shanghai China
Show Abstract0.7BiFeO3-0.3PbTiO3 thin film has already been proved exhibiting optimized properties among the xBiFeO3-(1-x)PbTiO3 thin films in our previous work. The different thickness of 0.7BiFeO3-0.3PbTiO3 (BFPT) thin films varying from 20nm to 1μm were fabricated by sol-gel method on Pt/Ti/SiO2/Si(100) substrate .The BFPT film with thickness of 20nm show special electrical property for the influence of structure and substrate. With the thickness increasing, the structure and electric properties of these thin films transformed accordingly. The thickness dependence of BFPT thin films are discussed.
9:00 PM - P13.27
Impedance Spectroscopy Analysis of High-Temperature Phase Transitions in (PZT)0.25(PFN)0.25(PFT)0.25(PFW)0.25.
Ricardo Martinez 1 2 , Venkata Sreenivas Puli 1 2 , Ashok Kumar 1 2 , Ram S. Katiyar 1 2
1 Physics, University of Puerto Rico, San Juan PR, Puerto Rico, United States, 2 Institute for Functional Nanomaterials (IFN), , University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractLead based, 0.25 PbZr0.52Ti0.48O3+ 0.25 PbFe0.5Ta0.5O3 + 0.25 PbF2/3W1/3O3 + 0.25 PbFe0.5Nb0.5O3 (PZT-PFT-PFW-PFN) solid solution have been prepared by mechanosynthesis and mixed oxides methods. Impedance spectroscopy analysis was made in a bulk ceramic over a wide range of temperatures (400–650 K) and frequencies (100 Hz–1 MHz) showing the presence of both grain and grain boundary effects in the material. The role of the contribution of the grain and grain boundary to the impedance becomes more prominent around the phase transition (~ 420 K). Two thermally activated processes were found from the temperature dependence of the relaxation time (t). Activation energies of ~1.21 and ~1.84 eV were estimated at 400-490 K and 490-650 K respectively. The activation energy of the grain and the grain boundary are basically the same at 400-490 K (~ 067 eV) and at 490-650 K (~1.0 eV). A constant phase element (CPE) is used in the equivalent electrical circuits for fitting of experimental impedance data. The nature of variation of the grain and grain boundary resistance with temperature suggested NTCR behavior.
9:00 PM - P13.28
Preparation and Piezoelectric Properties of a Novel PZT Fiber Ceramic.
Caifeng Chen 1 2 , Andong Wang 1 , Chaoying Ni 2 , Jun Liu 1
1 , Jiangsu University, Zhenjiang, Jiangsu, China, 2 , University of Delaware, Newark, Delaware, United States
Show AbstractPZT nano piezoelectric fibers were prepared by hydrothermal-template method. The effects of some reaction conditions on preparation were investigated, such as PH value, reaction temperature and time. The optimal hydrothermal conditions for preparing PZT nano fibers were discovered. The pH value is from 10 to 13, reaction temperature is 190 degree Celsius , hydrothermal reactor filling degree is 60%-70%, reaction time is 10h, and the activated carbon is as the template. Based on the observation from scanning electron microscopy (SEM) show the diameter of PZT fibers is around 100nm with the length up to a few microns, and the fibers are arrange orderly in one direction. PZT fiber ceramic made of the fibers was obtained through pressing carefully the fibers along a direction as possible, then sintering at the temperatures of 1050 degree Celsius for 1.5 hour. Microstructure of the PZT fiber ceramic was analyzed using X-ray diffraction (XRD) and SEM techniques. The piezoelectric properties were determined by impedance analyzer. The results indicated that the PZT fiber ceramic has a high value of kt/ kp (1.02) comparing to the conventional PZT ceramic made of milled PZT powder(0.40). It means that the novel PZT ceramic shows very good anisotropic property and has potential application for a sensor or device with high direction sensitivity. More PZT fiber ceramic characterization results will be reported in the full paper.
9:00 PM - P13.3
Fabrication and Characteristics of Ferroelectric/Fluorescent Oxide Structures for Ferroelectrically Controlled Emission Devices.
Koji Aizawa 1 , Naoya Hashimoto 1 , Hiroyuki Inagaki 1 , Hironori Oshiro 1 , Hideo Horibe 1 , Yoshiaki Tokunaga 1
1 , Kanazawa Institute of Technology, Nonoich Japan
Show Abstract Up to now, we introduced the fabrication and characteristics of the ferroelectric/fluorescent oxide structures used in the light emission devices controlled by ferroelectricity [1]. In this study, crystallinity, electrical and luminescent properties of Eu-doped Sr0.8Bi2Ta2O9 (Eu-SBT) films and those of (Ba0.6Sr0.4)TiO3 (BST)/Eu-SBT structures grown on SrTiO3(STO) single crystalline substrates are investigated. Eu-SBT and BST are used as fluorescent and ferroelectric oxide material, respectively. BST and Eu-SBT films were deposited by using a spin-coating method. STO(110) and (100)-oriented wafers cut out by 10×10 mm2 were used as substrate, in which (110)-oriented substrate was used in order to obtain both an SBT film with small surface roughness and its spontaneous polarization along normal to the surface [2]. Pt(200nm)/Ti(5nm)/SiO2/Si as well as low resistive Nb-doped STO substrates were also used in the electrical measurements. In the fabrication of a BST/Eu-SBT structure, the Eu-SBT wet film coated on a substrate was calcined at 850oC for 5min in air after drying at 140oC. This procedure was repeated until the desired thickness was obtained. The deposited film was finally annealed at 850oC for 30min in air. Next, a BST film was formed on an Eu-SBT film under the same condition as an above process. The crystallinity of the fabricated sample was analyzed by X-ray diffraction (XRD) method. The ferroelectric properties and photoluminescent (PL) spectra were measured using a standard Sawyer-Tower circuit and a spectrofluorometer, respectively. From XRD analysis of a BST/Eu-SBT/STO(110) structure, BST(100) and SBT(116) orientations were preferentially grown. Furthermore, double residual polarization of a Pt/Eu-SBT(116)/Nb-STO(110) structure was about 3.7 μC/cm2. In addition, it was found from PL spectra of the Eu-SBT/STO structures that the emission peaks at 590 and 615nm were associated with the 5D0-7F1 and 5D0-7F2 transitions of Eu3+ ion, respectively. The electrical properties of BST(330nm)/Eu-SBT(370nm) structures grown on Pt/Ti/SiO2/Si substrate were also measured. A well-saturated hysteresis loop with 2.5 μC/cm2 as double residual polarization and 3.8 V as double coercive voltage was obtained when a 1kHz sinusoidal wave with an amplitude of 18V was applied. No degradation after 108 switching cycles at a frequency of 1kHz was also found out. From the leakage current density vs. bias voltage characteristics, the leakage current density was lower than 10-7 A/cm2 even when a bias voltage of 10 V was applied. We conclude from these experimental results that realization of ferroelectrically controlled emission devices are expected in future. This work was partly supported by a Grant-in-aid for Scientific Research (No. 21560338) from the Japan Society for the Promotion of Science. [1] K. Aizawa et al., Jpn. J. Appl. Phys. 48 (2009) 09KA11-1. [2] H.N.Lee et al., J. Appl. Phys. 88, pp.6658-6664 (2000).
9:00 PM - P13.30
In Situ Pulsed Laser Annealing during Growth of PZT Thin Films.
Adarsh Rajashekhar 1 , Bharadwaja Srowthi 1 , Susan Trolier-McKinstry 1
1 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractThe ability to process PbZrxTi1-xO3 (PZT) thin films below 400°C is the key to their integration directly over Integrated Circuits (ICs) or on polymeric substrates. However, in general, it takes temperatures above 650°C to achieve good quality morphotropic phase boundary PZT. Pulsed laser deposition (PLD) coupled with in situ laser annealing is being studied as a route to synthesize crystalline PZT thin films below 400°C substrate temperature. A custom-built PLD setup that utilizes the two components of a split beam from a pulsed KrF excimer laser (248nm, 20ns pulse, 400mJ maximum energy and 20Hz max repetition rate) is utilized to achieve simultaneous deposition and laser annealing. Using this setup, reasonable compositional homogeneity over ~15cm length scale was demonstrated across the substrate in a PLD grown film owing to the incorporation of substrate rotation. Typical growth rates are ~0.2Å per pulse, with a substrate rotation of 10rpm. PZT phase formation (with heterogeneous nucleation) on (111)Pt/Ti/SiO2/(100) Si substrates was achieved by sequential growth and laser annealing steps, without breaking vacuum. In situ annealing during growth at a substrate temperature of 320°C yielded (111) oriented PZT 52/48 on a 40nm thick (111) PZT 30/70 seed layer (deposited using sol-gel), with 20Hz laser frequency and an annealing laser energy density of ~60mJ/cm2. The relative permittivity of the crystallized PZT 52/48 layer at 10kHz is 850. Polarization-Electric Field (P-E) loop measurements yielded a remanent polarization (Pr) of 27μC/cm2 and a coercive field (Ec) of 100kV/cm. Results on in situ annealing without the seed layer will be presented in this paper.
9:00 PM - P13.31
Influence of Platinum Bottom Electrode on the Piezoelectric Performance of PZT Thin Films Hot Sputtered in a High Volume Production Tool.
Dirk Kaden 1 , Hans-Joachim Quenzer 1 , Martin Kratzer 2 , Lorenzo Castaldi 2 , Bernhard Wagner 1 , Robert Mamazza 2
1 MEMS Department, Fraunhofer Institute for Silicon Technology, 25524 Itzehoe Germany, 2 , OC Oerlikon Balzers AG, 9496 Balzers Liechtenstein
Show AbstractIn the field of MicroElectroMechanical Systems (MEMS) perovskite type ferroelectric thin films are of great and still growing interest. Although its deposition is still a challenge, the large electromechanical coupling coefficient of lead zirconate titanate (PZT) makes it highly attractive for the realization of microactuators with high speed and high force at low power consumption. In recent years much effort has been focused on the deposition of PZT thin films with optimized piezoelectric properties by a large number of research groups. However, the major obstacle for the industrialization of piezo-MEMS components is that the transfer of the PZT process to an industrial environment and the demonstration of its volume manufacturability is not yet been achieved.In the present study high quality PZT thin films are deposited by a RF magnetron sputtering process on 200 mm silicon wafers prepared with different types of evaporated and sputtered Pt electrodes. Their influence on chemical composition, crystallographic, ferroelectric and dielectric properties of the PZT thin films is investigated at chuck temperatures from 550 °C to 700 °C. It should be emphasized that the PZT films are sputtered in-situ, i.e. without any post-annealing treatment, on a high volume capable and commercially available cluster tool. Electron probe microanalysis (EPMA) determines a loss of the relative Pb content which strongly depends on type of electrode as well as deposition temperature. While PZT thin films deposited on sputtered Ti/TiO2/Pt and Ti/TiO2/Pt/TiO2 bottom layers are randomly oriented, XRD analysis for films grown on evaporated Ti/Pt electrodes show an extended presence of secondary non-piezoelectric phases in addition to a preferred (111) crystallographic orientation of the perovskite phase. As a result, the experiments proved that 1 µm thick PZT films in-situ deposited on sputtered Ti/TiO2/Pt bottom electrodes at a chuck temperature of 600 °C exhibit notable e31,f and d33,f coefficients of -13,8 C/m2 and 101 pm/V, respectively. For this PZT process a typical wafer to wafer reproducibility in the range of 11±2 C/m2 for the e31,f coefficient has been observed.
9:00 PM - P13.32
Understanding the Role of BiFeO3 Additions to (Na0.5,K0.5) NbO3 Thin Films for Piezoelectric MEMS Applications.
Lindsay Kuhn 1 , Seung-Hyun Kim 1 , Alice Leung 1 , Wenyan Jiang 1 , Chang Young Koo 2 , Angus Kingon 1
1 Materials Science, Brown University, Providence, Rhode Island, United States, 2 R&D Center, Inostek, Sangnok Ansan, Gyeonggi, Korea (the Democratic People's Republic of)
Show AbstractLead oxide (PbO) based ferroelectrics have been widely investigated because of their excellent electromechanical and piezoelectric properties. Among PbO based ferroelectrics, the lead zirconate titanate (PZT) system is most extensively used in applications. Recently, however, there has been an urgency to replace the PZT system because the toxicity of lead is a major concern. Among various lead-free piezoelectric materials, the alkaline niobate system including sodium potassium niobate ((Na,K)NbO3, NKN) is a strong candidate for replacing PbO based piezoelectrics due to its benign environmental impact in combination with adequate piezoelectric and ferroelectric properties. Our focus is on the development of thin films of the NKN system by chemical solution deposition (CSD) process methods for application in MEMS-based devices.It is difficult to prepare high quality NKN films for various reasons including the severe volatility of Na and K components, the difficulty in densifying the films, and their tendency towards inhomogeneous microstructures, all of which result in poor electrical properties such as high leakage current density and low dielectric and piezoelectric performance. It has been observed the incorporation of low concentrations of BiFeO3 into the solid solution has a dramatic impact on processing, microstructures and properties. In this work we demonstrate that BiFeO3 doped NKN films show uniform and dense microstructures with excellent electrical and piezoelectric properties, providing a viable approach to thin films of this system. In order to understand this phenomenon we have systematically investigated microstructural evolution along with the dielectric and piezoelectric properties of BiFeO3 -doped NKN thin films as a function of BiFeO3 concentration, using chemical solution deposition (CSD). These results indicate BiFeO3 doped NKN films might be a promising lead-free piezoelectric system for a wide range of MEMS applications.
9:00 PM - P13.33
Stability of Ultra-Smooth Lead Zirconium Titanate in Aqueous Environments.
Robert Ferris 1 , Stefan Zauscher 1 , Benjamin Yellen 1 , Byung Seok Kwon 1
1 Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina, United States
Show AbstractWe propose that the high surface charge density expressed on the surface of polarized ferroelectric thin films(FETFs) is attractive for a variety of applications from biological sensing to lab-on-chip devices. Before such applications can be realized, however, one must understand how FETFs interact, or change, with exposure to aqueous environments. First, we discuss key parameters in the sol-gel fabrication process for ultra-smooth lead zirconium titanate (US-PZT) with RMS ~2.5 nm. These FETFs have a remnant polarization of 11µC cm-2 and a resistivity of 37 µΩ-cm. The effects of water exposure on these US-PZT FETFs are contrasted with those of standard sol-gel processed PZT thin films. While US-PZT is stable in liquid, significant film degradation occurred with rough PZT (RMS ~10 nm). Water exposure of rough PZT resulted in crack propagation and a decrease in film resistivity. Fractal analysis of water-exposed US-PZT surfaces shows a decrease in fractal dimension for length scales below 100 nm which suggests a selective etching of small surface domains with exposure to DI-Water.
9:00 PM - P13.34
Ferroelectric Domain Morphology, Electrical and Electromechanical Properties of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 Ceramics.
Cheuk Tai 1
1 Department of Materials and Environmental Chemistry, Stockholm University, Stockholm Sweden
Show AbstractPerovskite ferroelectric Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) ceramics were prepared by mixed-oxides routes. The selected compositions of the ceramics are in the vicinity of the morphotropic phase boundary (MPB). Dielectric constant and loss of the ceramics were measured at different frequencies from room temperature to 400 °C. The maximum value of the dielectric constant and tan δ is over 15000 and less than 0.2, respectively. The phase transition temperature of the ceramics is over 150 °C and increases as the amount of PIN. Small frequency-dispersion is found near the phase transition temperature. The heating and cooling curves give thermal hysteresis. Piezoelectric and electromechanical coefficient of the poled ceramics was measured at room temperature. In order to understanding the influence of microstructures and ferroelectric domain morphology on material performance, transmission electron microscopy was used. The configuration of the ferroelectric domain is neither simply rhombohedral nor tetragonal phase, and relates to the lower symmetry in MPB, which can be seen in electron diffraction patterns. Multiple cations occupy in the B-sites in perovskite structure. Long-range structural order was absence in the ceramics, similar to Pb(Zr, Ti)O3, though the influence on electromechanical properties is found in PIN-PMN ceramics.
9:00 PM - P13.35
Temperature Dependence of Ferroelectric and Piezoelectric Properties of (1-x)(Bi0.94La0.06)FeO3-xPb(Ti0.98Mn0.02)O3 Ceramics near Morphotropic Phase Boundary.
Feng Leiyang 1 , Shi Guiyang 1 , Yu Shengwen 1 , Cheng Jinrong 1
1 , Shanghai University, Shanghai, Shanghai, China
Show Abstract(1-x)(Bi0.94La0.06)FeO3-xPb(Ti0.98Mn0.02)O3 (BLF-PTM) ceramics near the morphotropic phase boundary (MPB) composition ( x=0.35,0.37.0.40.0.43,0.45) have been processed by the sol-gel method combined with solid reaction. Analysis of XRD patterns revealed that the crystal structure changed gradually from rhombohedral to tetragonal with increasing lead titanate content. BLF-PTM of x=0.37 exhibited maximum dielectric and piezoelectric constant at room temperature. The dielectric and piezoelectric properties of BLF-PTM were investigated at elevated temperature. The Curie temperature of all the compositions were about 550oC. The depolarization temperature of samples decreased with lead titanate content increasing. Before 256 oC, Tan δ of the ceramics for x=0.40 is lower than 0.2 and the piezoelectric properties decreased slightly, showing the best thermal stability. Temperature dependence of ferroelectric hysteresis loops obviously revealed that Ec of all the compositions decreased with increasing temperature.
9:00 PM - P13.36
Three-Step Deposition Method for Improvement of the Dielectric Properties of BST Thin Films.
Hongrui Liu 1 , Vitaliy Avrutin 1 , Congyong Zhu 1 , Jacob Leach 1 , Emmanuel Rowe 1 , Lin Zhou 2 , David Smith 2 , Umit Ozgur 1 , Hadis Morkoc 1
1 Department of Electrical and Computer Engineering, Virginia Commonwealth University, Richmond, Virginia, United States, 2 Physics Department, Arizona State University, Tempe, Arizona, United States
Show AbstractFerroelectric BaxSr1-xTiO3 (BST) films have attracted a considerable attention as a promising material for microwave passive component owing to its electric-field-dependent dielectric constant. Dielectric tunability and dielectric loss, which are the most important parameters for microwave applications, are primarily controlled by the crystal quality and strain state of the film. The effect of crystal quality is intuitive: an increase in the quantity of defects in a thin film would tend to yield more centers with which the electromagnetic field could interact, resulting in increased loss. To improve structural perfection, the use of nearly lattice-matched substrate seems desirable. However, the in-plane lattice parameters of the epitaxial BST films grown on nearly (but not perfectly) lattice-matched substrates tend to be “clamped” to the lattice parameters of the substrate, inducing a biaxial strain in the film, which has a strong effect on the dielectric constant and tunability as well as shifts the ferroelectric Curie temperature of the film[1]. In this work, we studied the possibility to tailor the biaxial strain and its effect on dielectric properties in BST thin films by three-step growth which introduces a low-temperature (300-500°C) “compliant” BST layer sandwiched between two high temperature (795°C) layers. Ba0.5Sr0.5TiO3 thin films were grown epitaxially by off-axis RF magnetron sputtering on SrTiO3 (STO) and DyScO3 substrates. Those substrates were chosen because of their similar crystal structure and small lattice thermal-expansion mismatch to Ba0.5Sr0.5TiO3. We found from X-ray diffraction measurements that, although the as-grown tri-layer structures were compressively strained, upon anneals in oxygen at 1000 °C, the strain relaxed faster than in the control single-layer film grown at 795 °C. Compared with the control film, the tri-layer grown BST film on STO substrate increased the dielectric constant from 1024 to 1631 and enhanced its tunability from 19.6% to 24.3% for an applied field of 40 kV/cm at 10 GHz. The three-step growth method also raised the dielectric constant from 1059 to 1392 and improved the tunability from 16.7% to 25.6% for the BST film grown on DyScO3 substrate in the same field and frequency. The loss tangent of BST film is 0.13 on STO and 0.17 on DyScO3 substrate. The quality factor is 282 on STO and 176 on DyScO3 at 10 GHz. The tri-layer BST film has better dielectric performance on STO substrate than on DyScO3.[1] N.A. Pertsev, A.G. Zembilgotov, and A.K. Tagantsev, “Effect of mechanical boundary conditions on phase diagrams of epitaxial ferroelectric thin films,” Phys. Rev. Lett. 80, 1988 (1998).
9:00 PM - P13.37
Dual-Laser Ablation for the Growth of Epitaxial Pb(Zr0.52Ti0.48)O3 Ultra-Thin Films.
Devajyoti Mukherjee 1 , Robert Hyde 1 , Pritish Mukherjee 1 , Sarath Witanachchi 1
1 Department of Physics and Center for Integrated Functional Materials, University of South Florida, Tampa, Florida, United States
Show AbstractThe recent theoretical demonstration by Sichuga and Bellaiche, of a novel phase in ultra-thin Pb(Zr0.52Ti0.48)O3 (PZT) films under epitaxial strain makes it a promising system for investigation. Here, the authors present a detailed study on the epitaxial growth of Pb(Zr0.52Ti0.48)O3 thin films with varying thicknesses using a dual-laser deposition (PLDDL) process that combines a pulsed excimer (KrF) and a CO2 laser outputs. In this process the target is initially heated by a pulsed CO2 laser (wavelength 10.6 μm) to produce a shallow transient molten layer, from which a slightly time-delayed pulsed KrF excimer laser (wavelength 248 nm) initiates the ablation. It has been shown in the past that ablation from a momentarily liquid target can result in minimizing the non-congruent ablation of PZT target due to the high volatility of Pb. As reported earlier, this leads to stoichiometric PZT film deposition with enhanced ferroelectric properties. Moreover, the efficient heating of the KrF excimer ablated plasma plume by the tail end of the CO2 pulse produces a higher excited plasma plume that has a broader angular distribution, compared to the plume generated by excimer pulse alone in single-laser deposition (PLDSL) (as observed in the ICCD imaging of the plume). The higher ionization of the ablated species (as observed in the optical emission spectra of the plume) leads to enhanced gas phase reaction and better film morphology and crystallinity. In particular, point defects such as oxygen vacancies that are inherent in PZT films are minimized due to the higher O ionization. PZT films were deposited on single crystal MgO (100) and SrTiO3 (STO) (100) substrates at 550 oC under 500 mT O2 ambient pressure using both PLDDL and PLDSL for comparison. The structural characterization using XRD revealed the high quality and single crystalline nature of the films. The surface morphologies analyzed used AFM revealed smooth surfaces with roughness values as low as 1.6 nm. The PZT capacitors were made in-situ using metallic oxide La0.7Sr0.3MnO3 (LSMO) and La0.5Ca0.5MnO3 (LCMO) top and bottom electrodes deposited using PLDSL. The PLDDL deposited PZT films showed huge enhancements in polarization in comparison to those deposited using PLDSL. The remanent polarization (Pr) values for PLDDL deposited films were 91 μC/cm2 and 77 μC/cm2 as compared to 34 μC/cm2 and 45 μC/cm2 for PLDSL deposited films under the same conditions, for STO and MgO substrates, respectively. The coercive fields did not show such changes and were about 40 kV/cm. To eliminate the effect of space charges in the polarization measurements, frequency and voltage dependent P-E loops were also measured. In addition, P-E, C-V characterization and leakage current densities for PZT films grown at various thicknesses will also be presented.
9:00 PM - P13.38
Controlled Synthesis and Structural Characterization of Ferroelectric BaTiO3 Colloidal Nanoparticles.
ShivaprasadReddy Adireddy 1 , Amin Yourdkhani 1 , Gabriel Caruntu 1
1 Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana, United States
Show AbstractFree-standing, monodisperse hydrophobic barium titanate (BaTiO3) nanocrystals have been synthesized by a simple solvothermal route. By varying the reaction parameters, the size of the nanocrystals can be tuned between 5 and 155 nm. It was found that the morphological control is a complex interplay between various experimental parameters, including the polarity and the coordinating ability of the solvent, its vapor pressure and viscosity, as well as the reaction temperature and time. A detailed characterization of BaTiO3 NPs was performed by powder X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM, HRTEM and SAED), piezoresponse force microscopy (PFM), thermogravimetric and differential thermal analysis (TG-DTA) and Fourier transform infrared spectroscopy (FT-IR). Raman spectroscopy has shown the presence of a local tetragonal distortion in the NPs due to the off-shift of the Ti4+ within the TiO6 octahedra of the perovskite-type lattice. This has been further confirmed by the observation of a piezoelectric response in individual with a size as small as 5 nm. These ferroelectric nanocrystals will be used as building blocks for the design of complex multifunctional architectures, such as multiferroic nanoparticulate nanocomposites and thin films.
9:00 PM - P13.39
Cross Sectional Ferroelectric Domain Evolution in Ferroelectric Thin Films by In Situ TEM.
Christopher Nelson 1 , Peng Gao 1 , Jacob Jokisaari 1 , Colin Heikes 2 , Carolina Adamo 2 , Alexander Melville 2 , Benjamin Winchester 3 , Yijia Gu 3 , Yuanming Liu 4 , Seung-Hyub Baek 5 , Chad Folkman 5 , Chang-Beom Eom 5 , Jiangyu Li 4 , Long-Qing Chen 3 , Darrell Schlom 2 , Xiaoqing Pan 1
1 , University of Michigan, Ann Arbor, Michigan, United States, 2 , Cornell University, Ithaca, New York, United States, 3 , Pennsylvania State University, University Park, Pennsylvania, United States, 4 , University of Washington, Seattle, Washington, United States, 5 , University of Wisconsin–Madison, Madison, Wisconsin, United States
Show AbstractThe reorientation of the spontaneous polarization vector under an applied bias underlies many of the prospective applications of ferroelectric materials such as non-volatile memory. The low nucleation bias and inhomogeneity observed in nucleation and growth of ferroelectric domains has long pointed to defects as the dominant influence on switching processes. To study switching at the scale of crystalline defects, we characterize a ferroelectric BiFeO3 thin film under electric bias using in-situ transmission electron microscopy (TEM). The resulting real-time domain structure demonstrates the strong influence of defects on the domain evolution along the cross sectional film axis. In this work epitaxial ferroelectric thin films of (001) BiFeO3 were locally switched in a surface probe/buffer electrode geometry. The BiFeO3 films, grown on La0.7Sr0.3MnO3 buffer layers atop (110)O TbScO3 substrates by molecular beam epitaxy, preferentially switch by a 71° out-of-plane rotation of the polarization vector. However, large regions of the interface with the LSMO electrode locally switch by a non-ferroelastic 180°. We observe significant contributions from built-in electric fields on the domain dynamics resulting in interface assisted nucleation, due to the formation of a Schottky junction, and disparities in domain wall velocities for opposite poling directions. Pinning of the propagating domain wall is frequently observed including during the initial forward growth stage. Such direct observations of local switching provide insight into the governing processes in low-dimensionality ferroelectric devices and surface probe ferroelectric measurement techniques.
9:00 PM - P13.4
Growth of Self-Assembled BaTiO3 Nanodots via Tensile Strain.
Timothy Morgan 1 2 , Zhaoquan Zeng 1 2 , Robert Sleezer 1 2 , Gregory Salamo 1 2
1 Department of Physics, University of Arkansas, Fayetteville, Arkansas, United States, 2 Arkansas Institute for Nanoscale Materials Science and Engineering, University of Arkansas, Fayetteville, Arkansas, United States
Show AbstractOver a long time, much attention is paid on ferroelectric films due to unique properties of spontaneous, switchable polarization, piezoelectricity, and pyroelectricity. Recently, epitaxial nanoferroelectric materials are receiving enormous interest for the potential application to nanodevices, especially ultradense memories, driven by the experimental observation and control of a polarization vortex in ferroelectric nanostructures. In this presentation, we report the use of tensile strain to grow self-assembled BaTiO3 nanodots on a MgO (001) substrate by oxygen plasma assisted molecular beam epitaxy. The typical Stranski–Krastanov growth mode of BaTiO3 film on MgO was determined by in-situ reflection high energy electron diffraction (RHEED). Atomic force microscopy (AFM) observations revealed the existence of BaTiO3 nanodots with an average height and diameter of 2 nm and 20 nm, respectively. The 1:1:3 stoichiometry (Ba:Ti:O) of barium titanate nanodots was confirmed by x-ray photoelectron spectroscopy (XPS). Further investigation will pursue the structure of the dots, particularly the c/a ratio, to examine if the tensile strain will encourage the formation of polarization vortexes to form.
9:00 PM - P13.40
Improvement of Leakage Current of the La Substituted Ba(Cu1/3,Ta2/3)O3-Sr(Cu1/3,Ta2/3)O3 Bulk Ceramics.
Bong-Yeon Lee 1 , Takashi Iijima 1 , Hiroshi Funakubo 2 , Hiroshi Uchida 3 , Soichiro Okamura 4
1 , Advanced Industrial Science and Technology, Tsukuba Japan, 2 , Tokyo Institute of Technology, Yokohama Japan, 3 , Sophia University, Tokyo Japan, 4 , Tokyo University of Science, Tokyo Japan
Show AbstractIn recent years, perovskite oxides of high phase transition temperature have attracted attention owing to the excellent and stable dielectric properties in wide temperature range. Moreover, Ba-based system oxides were also gathered attention as lead free ferroelectric materials such as Ba(Cu1/3,Nb2/3)O3 (BCN).1) We have reported that a Ba(Cu1/3,Ta2/3)O3 (BCT) sintered body showed perovskite structure such as BCN, but showed poor sintered density and leakage property.2) Therefore, we had tried to make Ba(Cu1/3,Ta2/3)O3-Sr(Cu1/3,Ta2/3)O3 (BCT-SCT) solid solution system and the BCT-SCT sintered bodies improved the density, dielectric loss tangent and leakage property.3) But the dielectric loss tangent and leakage current density was still relatively high.We have investigated the dielectric and leakage properties of the La substituted BCT-SCT system to decrease the leakage current. The La substituted for A site of the BCT-SCT solid solution ([xLa-(1-x)(0.3Ba-0.7Sr)](Cu1/3,Ta2/3)O3, x= 0 ~ 0.075) were obtained from solid state reactions with conventional method. The mixed powder of the raw materials (BaCO3, CuO, Ta2O5, SrCO3, La2O5) was calcined at 1000oC for 1 hour in air. The calcined powders were grinded with ethyl alcohol at 600 rpm for 2 hours by planetary mill. Cylindrical pellets were formed from the calcined powder with an organic binder (Polyvinyl butyral resin (PVB), 1 wt%). The pellets were removed the PVB at 500oC for 3 hours, and sintered at 1100 ~ 1300oC for 1 hour in air. Finally, the Pt electrode was deposited on polished ceramic disk surfaces by rf-sputtering method to evaluate the electric properties.In the result, the La substituted BCT-SCT bulk sintered at 1200oC showed the tetragonal structure for the La contents below x= 0.075. Relative density of the 1200oC sintered bulk was 98% at the La contents x= 0 ~ 0.05. But the density was sharply reduced to 75% at the La contents x= 0.075. Dielectric constant and loss tangent were increased with increasing the La contents. But the leakage current density decreased with increasing the La contents. In the [0.05La-0.95(0.3Ba-0.7Sr)](Cu1/3,Ta2/3)O3 bulk sintered at 1200oC, the dielectric constant, the dielectric loss tangent, and the leakage current showed εr= 30, tanδ= 0.25 at 100 kHz, and J= 6.40 x 10-9 A/cm2 at 2 kV/cm, respectively.
9:00 PM - P13.41
Ultrafast Synthesis of BiFeO3 Nanostructures by a Microwave-Assisted Hydrothermal Method.
Shun Li 1 , Riad Nechache 1 , Velasco Ivan Alejandro Davalos 1 , Andreas Ruediger 1 , Federico Rosei 1
1 , EMT-INRS, Varennes, Quebec, Canada
Show Abstract Among all multiferroics, BiFeO3 that exhibits coexistence of ferroelectric and antiferromagnetic orders has attracted considerable studies due to its relatively high Neel temperature and Curie temperature. In addition, recent studies show that BiFeO3 nonmaterial is also a good visible-light responsive photocatalyst due to its narrow band gap (∼2.2 eV) and excellent chemical stability. Therefore, the preparation of nanostructured multiferroic BiFeO3 is significant not only for designing new multifunctional materials combining magnetic, ferroelectric and optical properties but also for studying fundamental physics. Until now, researchers developed various techniques for successfully preparing BiFeO3 such as solid state reaction, rapid liquid phase sintering, sol-gel, co-precipitation, etc., but all these method need high calcination temperature, which means high energy consumption and cost. The hydrothermal process is an efficient low temperature technique that allows the formation of powders with high degree of crystallinity. In contrast, the main disadvantage of this method is the slow reaction kinetic at any given temperature. Therefore, all the reported preparation of BiFeO3 by conventional hydrothermal method need long reaction time (more than 6 h). The microwave-assisted hydrothermal (MH) method is one possible modification of the conventional hydrothermal technique. In MH processing, the kinetics of the reaction is enhanced by one to two orders of magnitude by high frequency electromagnetic radiation (2.45 GHz). The precipitate can be rapidly dissolved in aqueous solution to make a saturated solution, resulting fast rates of crystallization. Here, we report a successful ultrafast, facile, one-pot synthesis of BiFeO3 nanostructures under MH conditions within a very short reaction time (ca. 1~2 min). Various parameters influencing the final products such as reaction time, radiation power, and the concentration of NaOH were discussed in the present study. The resulting BiFeO3 nanomaterials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The magnetic and optical properties of the products were studied in detail. Our results show that through the use of a MH process, the BiFeO3 nanoparticles could be obtained with a shorter reaction time and lower thermal energy, in comparison to conventional hydrothermal methods. Therefore, this approach could considerably reduce the synthesis time, cost, and energy required, and it could be used in the large-scale fabrication of nanosized BiFeO3.
9:00 PM - P13.42
Sintering and Dielectric Properties of SrTiO3-Based Ceramics.
Juan Li 1 2 , Dengren Jin 1 2 , Lixin Zhou 1 2 , Jinrong Cheng 1
1 Materials Science, ShangHai university, ShangHai, ShangHai, China, 2 State Key Lab of Silicon Materials, Zhejiang University, Hangzhou, Zhejiang, China
Show AbstractHigh dielectric tunability, low dielectric loss tangent and appropriate level of dielectric constant are the basic requirements for applications as electrically tunable dielectric microwave devices. In our experiment, the SrTiO3 green compacts made of the powder mixtures with different particle sizes were infiltrated with a BaTiO3 sol and sintered at the temperature from 1280o C /2h to 1350oC/6h. The sintering, microstructural and dielectric properties were investigated. Results showed that the relative density of SrTiO3 ceramics reached 93% when sintered at 1280oC/2h, the dielectric constant of SrTiO3 ceramics still remain moderate level of 900 at 1MHz frequency at the room temperature and had god temperature stability within a wide temperature range. The reason of the lower sintering temperature for the dense SrTiO3 ceramics and the effects of sintering scheme on the dielectric properties from 100K to 500K were discussed in this paper. These performances make the SrTiO3 ceramics a promising candidate as an electrically tunable dielectric material.
9:00 PM - P13.43
Changes in Oxygen Stoichiometry and Magnetic Properties of (La,Sr)CoO3-δ Thin Films Driven by Substrate Symmetry.
Young-Min Kim 1 , Michael Biegalski 2 , Jun He 1 3 , Hans Christen 2 , H. Ambaye 4 , V. Lauter 4 , Sokrates Pantelides 3 1 , Stephen Pennycook 1 , Albina Borisevich 1
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Physics and Astronomy, Vanderbilt University, Nashville, Tennessee, United States, 4 Neutron Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractEpitaxial thin films present multiple opportunities for tailoring physical properties of ferroelectric, multiferroic, and other functional oxides via substrate-imposed constraints. While the influence of the epitaxial strain and chemical composition of the substrate on the film behavior have been demonstrated for many systems, it is only recently that the “symmetry effect,” imposed in particular by different degree or pattern of the octahedral tilts in the substrate, is also being considered as a new tool for property manipulation.To test this idea, lantanum/strontium cobaltite (LSCO) thin films were grown by Pulsed Laser Deposition in identical conditions on two different substrates, La0.3Sr0.7Al0.65Ta0.35O3 (LSAT, cubic) and NdGaO3 (NGO, orthorhombic). These substrates have nearly identical lattice parameters (less than 0.05% different), but very different symmetry of the oxygen octahedral network. Indeed, measurements by polarized neutron reflectometry reveal different magnetic moments of Co for the two LSCO films deposited on the respective substrates.Using aberration-corrected scanning transmission electron microscopy (STEM), combined with electron energy loss spectroscopy (EELS), we have studied the atomic-scale mechanism of this difference. From observations of the ion-thinned samples we found that both films have oxygen-deficient structures with manifest vacancy ordering. However, the two films differ in the types of observed lattice distortions, as well as in the overall oxygen stoichiometry. The structure of the interface is also different in the two cases, with evidence for different electronic/magnetic states of Co at the LSCO/NGO interface. Thus, the result implies that the substrate symmetry can influence defect structure and even oxygen stoichiometry/valence state of the transition metal. Explanation of the results using first-principles calculations will also be presented.* This research is sponsored by the Materials Sciences and Engineering Division (YMK, JH, SJP, AYB) and Scientific User Facilities Division (MDB, HMC, HA, VL), Office of BES of the U.S. DOE, and by appointment (YMK) to the ORNL Postoctoral Research Program administered jointly by ORNL and ORISE.
9:00 PM - P13.44
Growth of Epitaxial Oxide Heterostructures by Sputtering with In Situ High Pressure RHEED.
Jacob Podkaminer 1 , K. Cho 1 , C. Folkman 1 , S. Baek 1 , C. Bark 1 , C. Eom 1
1 Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractIn situ monitoring by high pressure reflection high energy electron diffraction (RHEED) during pulsed laser deposition offers atomic layer controlled growth of epitaxial oxide thin film heterostructures such as ferroelectric superlattices and oxide heterointerfaces. We have employed in situ high pressure RHEED with sputter deposition of various epitaxial oxide thin films with a digital control. Sputtering has been used for the growth of very high quality films with smooth surfaces and uniform thicknesses over a large area. Previously, in situ RHEED was not possible with magnetron sputtering due to the challenges of large magnetic fields in close proximity to the electron beam of RHEED. We have observed RHEED intensity oscillations and diffraction patterns during layer-by-layer growth. We will discuss properties of various epitaxial oxide thin films including LaAlO3/SrTiO3 heterostructures grown by sputtering with in situ high pressure RHEED.
9:00 PM - P13.45
Preparation of Pb(Zr, Ti)O3 Film for MEMS Devices on Large Area Substrates by Sputtering Method.
HIroki Kobayashi 1 , Kazuya Tsukagoshi 1 , Youhei Ohnishi 1 , Youhei Endou 1 , Isao Kimura 1 , Takehito Jimbo 1 , Koukou Suu 1
1 , ULVAC Institute of Semiconductor and Electronic Technology, Susono Japan
Show Abstract Pb(Zr,Ti)O3 (PZT) film have been used for Micro Electro Mechanical Systems (MEMS) devices such as actuators and sensors, because of their excellent piezoelectric property.PZT film fabricated by SME-200(ULVAC) module manufactured planner magnetron RF sputtering systems. PZT(Zr/Ti=52/48) Ceramics target was used for high-rate-sputtering (>3 µm/h). In this study, we will report the high-rate deposition technology, and the crystalline, electrical and piezoelectric properties of PZT films on large area substrate(φ8inch) deposited by sputtering method.
9:00 PM - P13.5
Effects of Surface Morphology on Retention Loss of Ferroelectric Domains in Poly(vinylidenefluoride-co-trifluoroethylene) Thin Films.
Hyunwoo Choi 1 2 , Seungbum Hong 2 , Kwangsoo No 1
1 Department of Material Science and Engineering, KAIST, Daejeon Korea (the Republic of), 2 Materials Science Division, Argonne National Laboratory, Lemont, Illinois, United States
Show AbstractEffects of surface morphology on the retention loss of ferroelectric domains of poly(vinylidenefluoride-co-trifluoroethylene) thin films were investigated using piezoresponse force microscopy. We found that the retention loss occurred by nucleation of opposite domains at the regions with morphological gradients between 0.079 and 0.146. In addition, we observed collective decreases in piezoresponse amplitude of the opposite domains after 0.8×10^6 sec although each reversed domain showed different growth rate as evidenced by different threshold time for phase reversal. These results suggest that the surface morphology has a strong influence in determining the nucleation and growth kinetics by which the retention loss occurs.
9:00 PM - P13.6
Direct Room-Temperature Synthesis of BaTiO3 Nanoparticles Using an Organosol Crystallization Process.
Yanling Gao 1 , Doru Lupascu 1
1 Institute for Materials Science, University of Duisburg-Essen, Essen Germany
Show AbstractWe synthesized uniformly sized nanocrystallites showing comparatively high dielectric permittivity using a hydrophobic organic solution based synthesis process for nanocrystalline BaTiO3. We have succeeded in a room temperature synthesis of pseudo-cubic and hydrophobic BaTiO3 nanocrystallites with a size below 30 nm by the organosol-crystallization process using the water-insoluble titanium (IV) isopropoxide oleate (Ti(OiPr)4−x(RCOO)x) precursor in a high concentration aqueous sodium hydroxide (NaOH) solution. Non-aqueous solution routes to BaTiO3 nanoparticles are a valuable alternative to the well known aqueous sol-gel processes, offering advantages such as high crystallinity at low temperatures and better control of the crystal growth. In our non-aqueous solution synthesis approach, the organic solvent oleic acid plays the role of the reactant that controls the crystal growth and influences particle shape. The key process of crystallization of BaTiO3 was vacuum dry-ageing of the as-precipitates under alkaline conditions. The crystal structure, structural phase transition, microstructure and dielectric properties of the nanoparticles were characterized by powder X-ray Diffraction spectrometry (XRD), Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and impedance analysis. The XRD pattern of as-precipitated nanopowders showed reflections characteristic of crystalline BaTiO3 with evidence of the presence of barium carbonate (BaCO3). These crystallites can be dispersed in a variety of organic solvents forming highly stable dispersions. Moreover, they exhibit different morphology, depending on heat treatment and operating temperature. We observed that besides spherical nanoparticles, significant amounts of one-dimensional nanostructures (including nanosheets, nanorods, and nanowires) were formed as intermediate phases in the temperature range from 450 to 750°C. Furthermore, exaggerated grain-growth in the specimens sintered at 950°C with rapid heating rates occurred and particles had grown from 20 nm to 1-2 µm in cubic and tetragonal shapes.
9:00 PM - P13.7
The Oxidant Peroxo Method (OPM) to Obtain Lead-Based Ferroelectric Ceramics with Superior Properties.
Emerson Camargo 1
1 Chemistry, Federal University of São Carlos, São Carlos, São Paulo, Brazil
Show AbstractSince the discovery of ferroelectricity in single crystals and subsequent research on polycrystalline ceramics, ferroelectric materials with a perovskite structure have been studied extensively due to their technological importance and versatile properties. Several authors have reported the synthesis of ferroelectric materials using numerous techniques, including solid-state reaction, sol-gel, polymeric precursor and hydrothermal methods. One of the most interesting wet-chemical methods for the synthesis of lead-based nanometric materials was developed by Camargo and Kakihana [1], which they called the oxidant peroxo method, referred to simply as OPM. This wet-chemical method is characterized by the fundamental oxy-reduction reaction between lead (II) ions and several water-soluble titanium peroxo complexes, leading to the formation of an amorphous and reactive precipitate free of all the contaminants commonly found in materials synthesized by other chemical routes.[2] To date, a large series of nanometric oxide powders were synthesized by our group using the OPM route, and we demonstrated that solid solutions of lead-based perovskites with different rare-earth elements can also be obtained successfully. Although powders synthesized by the OPM route show evident advantages in terms of purity, reactivity, and control of particle size and size distribution, little attention has focused on the properties of these superior ceramics.[3,4] Here, we presenting the synthesis of several lead-based perovskites synthesized by the OPM route, such as lead titanate, pure PZT including compositions near to MPB, and rare-earth modified PZT, and the electrical characterization of their sintered dense ceramic bodies. These materials were characterized by X-ray diffraction, Raman spectroscopy and electron transmission microscopy (TEM). Particles of 50 nm in average with sharp size distribution could be obtained and single-phase ceramics with densities of 98 % or higher were obtained by conventional and microwave sintering. High dielectric constants, usually higher than that reported for materials synthesized by different techniques, were observed. This special characteristic resulted from the oxidant environment of synthesis that uses hydrogen peroxide to obtain the reactive precursor, which maintain the electrical neutrality of ceramics mainly because of vacancies in the cation site than because of the presence of oxygen vacancies.
9:00 PM - P13.8
Ferroelectric Nanocrystals: From Synthesis to Nanodevices.
Xiang Yang Kong 1
1 materials science and engineering, shanghai jiao tong university, shanghai China
Show AbstractFerroelectric materials exhibit a wide spectrum of functional properties which are ideal for use in electronic devices such as sensors, actuators, transducers, and nonvolatile memories, etc.. However, the ferroelectric nanocrystals perform the distinct behaviors from bulk ceramics. In this talk, we report some typical ferroelectric nanocrystals, such as BaTiO3, (Na0.5Bi0.5)TiO3 (NBT) and LiNbO3, were syntehsized via hydrothermal method. All these nanocrystals exhibit the uniform cubic shape and unisize typically in 200 nm. With respect to nanoscale ferroelectric behaviors, we managed to assmeble the unisized cubic nanocrystals into order array on conducting substrate, and employed the piezoresponse force microscopy to image the domain structures in these ferroelectric nanocrystals with high resolution as well as to examine the dynamic switching behavior and ferroelectric relaxation at the nanoscale. The assembly of nanocrystals into monolayer array can be tailored into the desired electrical and mechanical properties by controlling the low-dimensional ferroelectric structures and the coupling between the ferroelectric domains for prototype nanodevices.
9:00 PM - P13.9
Fabrication and Properties of 0.25Bi(Zn1/2,Ti1/2)O3-0.75PbTiO3 Thin Films on Pt/Ti/SiO2/Si Substrates with Different Conductive Oxide Buffer Layers.
Guangheng Wu 1 , Ni Qin 1 , Dinghua Bao 1
1 , Sun Yat-Sen University, Guangzhou China
Show AbstractRecently, xBi(Zn1/2,Ti1/2)O3-(1-x)PbTiO3 (xBZnT-PT) solid solutions have drawn an increasing interest due to enhanced spontaneous polarization and high Curie temperature. However, most studies have concerned polycrystalline BZnT-PT ceramics rather than the counterpart thin films. On the other hand, ferroelectric thin films deposited directly on Pt electrodes usually suffer from fatigue problems, which can be solved by using a conductive oxide electrode. In the present study, we report on the fabrication and properties of 0.25BiZnT-PT thin films on Pt/Ti/SiO2/Si substrates with different conductive oxide buffer layers by pulsed laser deposition. SrRuO3 (SRO), LaNiO3 (LNO) and (In0.9Sn0.1)2O3 (ITO) were chosen as the buffer layers, since they are frequently used as electrode materials for electronic devices. The thin film deposited directly on Pt/Ti/SiO2/Si substrate and annealed at 700 oC showed a dielectric constant (at 1 kHz) and a remanent polarization (2Pr) of 360 and 79 µC/cm2, respectively. Without a buffer layer, the switchable polarization reduced by 63 % after 109 fatigue cycles. On the contrary, the films with a buffer layer showed better fatigue properties. The switchable polarization reduced by 21 %, 37 % and 14 % in the films with SRO, LNO and ITO buffer layer, respectively. Although ITO can greatly improve the fatigue endurance, it reduced the dielectric constant and remanent polarization of the films to about 89 and 16 µC/cm2. The films with SRO buffer layers can retain high dielectric constant and large remanent polarization of 300 and 76 µC/cm2. The films with LNO buffer layers showed lower dielectric constant and smaller remanent polarization of 230 and 52 µC/cm2. The results suggest that the 0.25BZnT-PT films with SRO buffer layer can be applied in high temperature devices.
Symposium Organizers
Craig J. Fennie Cornell University
Lane W. Martin University of Illinois, Urbana-Champaign
Beatriz Noheda University of Groningen
Tsuyoshi Kimura Osaka University
Manuel Bibes Thales Research and Technology/CNRS
P14: Local Probes of (Photo)Conductivity
Session Chairs
Thursday AM, December 01, 2011
Room 302 (Hynes)
9:30 AM - **P14.1
Probing Oxygen Vacancy Dynamics and Ordering on the Nanoscale – from Fuel Cells to Ferroelectrics.
Sergei Kalinin 1 , Stephen Jesse 1 , Amit Kumar 1 , Donovan Leonard 1 , Albina Borisevich 1
1 , ORNL, Oak Ridge, Tennessee, United States
Show AbstractThe coupling between lattice, polarization, and spins order parameters underpins multiple existing and perspective applications of transition metal oxides, resulting in tremendous interest to these systems in the last two decades. However, a characteristic aspect of oxides compared to semiconductors or metals is the tendency for oxygen vacancy motion in response to electric, mechanical, and chemical stimuli. While extensively explored in the context of electrochemical energy sources, these effects were largely overlooked in condensed matter physics studies. In many oxides, defects such as oxygen vacancies are mobile at RT, and hence can segregate at topological and structural defects and internal interfaces to compensate for built-in electrostatic and strain fields. Vacancy dynamics can affect e.g. interfacial conductivity and polarization profiles at heterointerfaces, surface layers on oxides, or polarization-mediated tunneling transport through thin films. In this presentation, I will summarize recent results on the studies of bias-controlled oxygen vacancy dynamics using combination of electrochemical strain microscopy (ESM), and ex-situ aberration corrected scanning transmission electron microscopy. The ionically-controlled electromechanical coupling is demonstrated on a model non-ferroelectric centrosymmetric yttria stabilized zirconia and Gd-doped ceria. For these systems, we demonstrate ~10 nanometer local strain measurements of vacancy dynamics at room temperature. In mixed electronic-ionic conductors such as lanthanum-strontium cobaltite and manganite, mapping reversible vacancy motion and vacancy ordering and static deformation is possible. The associated mechanisms are established using ex-situ STEM/EELS studies of FIB-milled cross-sections, demonstrating the surprisingly broad range of bias-induced electrochemical transformations ranging from vacancy ordering to amorphization and cation demixing. Finally, we extend these studies towards classical ferroelectrics such as bismuth ferrite and barium titanate, and illustrate separating ferroelectric and ionic contributions to the electroresistance in these materials.This research was sponsored by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy. Part of this research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Division of Scientific User Facilities, U.S. Department of Energy.
10:00 AM - P14.2
Photogeneration of Surface Charges in Multiferroic BiFeO3 Films via Kelvin Probe Force Microscopy.
Feng Yan 1 2 , Guannan Chen 1 , Li Lu 2 , Jonathan Spanier 1
1 Materials Science & Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 2 Mechanical Engineering, National University of Singapore, Singapore Singapore
Show AbstractThe photovoltaic properties of multiferroic BiFeO3 (BFO) continue to attract considerable interest due to potential application of BFO and related photo-ferroelectric materials in solar cell and other optoelectronic devices. Recent investigations of photovoltaic charge separation in the vicinity of ferroelectric domain walls in BFO and its correlation with ferroelectric polarization have been reported, where the underlying mechanism for such effect was seen to be related to the distribution of defects, space charges and polarization in BFO1. Here, we report on the results of a study using Kelvin probe force microscopy (KPFM) of mesoscopic BFO films to provide, with nanoscale lateral resolution, spatial correlation of photovoltaic activity with surface potential variations and ferroelectric domain structure. Our results provide new insight into the role of surface potential in photo-ferroelectrics on charge transport and exciton separation. Work at Drexel supported by ARO under W911NF-08-1-0067 and in part by NSF under DMR-0907381.[1] S. Y. Yang, et al. Nature Nanotech. 5, 143 (2010).
10:15 AM - P14.3
Conduction through 71o Domain Walls in BiFeO3 Thin Films.
Saeedeh Farokhipoor 1 , Beatriz Noheda 1
1 , Zernike Institute for Advanced Materials, Groningen Netherlands
Show AbstractBiFeO3 (BFO) is a rhombohedrally distorted, ferroelectric, antiferromagnetic perovskite and the only known room temperature, single phase multiferroic. Recent works have shown that the domain walls of BFO can display promising functionalities different from those of the domains, generating photocurrents[1], inducing exchange bias[2] and displaying conductivity at room temperature[3]. It was proposed that the reduction of the band gap at domain walls, associated with the suppression of ferroelectric distortions, was responsible for the observed conduction[3]. On the other hand, it has also been shown that control of the local defect chemistry largely affects conduction at domain walls[4], showing that a clear picture on the mechanisms underlying this phenomenon does not exist yet. Using conducting atomic force microscopy at high temperatures, we have investigated the mechanisms of conduction at 71o domain walls of BiFeO3 thin films on SrTiO3 substrates. We have observed a selective decrease of the Schottky barrier height (at the interface with the metallic tip) by ~ 2 eV at the domain walls, which clearly enhances the electronic conduction through the walls[5]. This understanding provides the key to control conductivity in these samples. The main experimental parameters that enable manipulating conduction through the domain walls are investigated and discussed.[1] S.Y. Yang. et al. Nature Nanotech. 5, 143 (2010).[2] L.W. Martin. et al. Nano Letters 8, 2050 (2008).[3] J. Seidel et al. Nature Mat. 8, 229 (2009).[4] J. Seidel et al. Phys. Rev. Lett. 105, 197603 (2010).[5] S. Farokhipoor and B. Noheda, arXiv:1104.3267v1 (submitted)
10:30 AM - P14.4
Orientation-Dependent Conductivity of Ferroelectric Domain Walls.
Dennis Meier 1 2 , Jan Seidel 2 3 , Andres Cano 4 , Kris Delaney 5 , Yu Kumagai 6 , Maxim Mostovoy 7 , Nicola Spaldin 6 , Manfred Fiebig 8 , Ramamoorthy Ramesh 1 2 3
1 Materials Science and Engineering, UC Berkeley, Berkeley, California, United States, 2 Department of Physics, UC Berkeley, Berkeley, California, United States, 3 Materials Science Devision, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 4 , European Synchrotron Radiation Facility, Grenoble France, 5 Materials Research Laboratory, UC Santa Barbara, Santa Barbara, California, United States, 6 Materials Theory, ETH Zürich, Zürich Switzerland, 7 Zernike Institute for Advanced Materials, University of Groningen, Groningen Netherlands, 8 HISKP, University of Bonn, Bonn Germany
Show AbstractInterfaces between transition-metal oxides reveal striking phenomena such as insulator-metal transitions, magnetism, and superconductivity. Such oxide interfaces are usually produced by sophisticated layer-by-layer growth techniques, which can yield high quality, epitaxial interfaces with almost monolayer control of atomic positions. The resulting interfaces, however, are fixed in space by the arrangement of atoms and rigid boundary conditions have to be obeyed in order to obtain the desired functionality. In consequence, the interfacial properties are irrevocably fixed after fabrication.Here we introduce a new route to overcoming this fundamental limitation by resorting to ferroelectric domain walls. In hexagonal ErMnO3 the primary symmetry-breaking order parameter is a unit-cell-tripling distortive mode that presets the orientation of the subsequent ferroelectric polarization. As a consequence, an unusual distribution of ferroelectric domains evolves. Using piezoforce-response microscopy (PFM) and conductive atomic force microscopy (c-AFM) we reveal that the electronic conductivity of the associated ferroelectric domain walls is a continuous function of the domain wall orientation, with a range of an order of magnitude. The experimental observations are explained using first-principle density functional and phenomenological theories.Since ferroelectric domain walls are tunable by external electric fields, our findings open a new degree of freedom in modifying the electronic performance that is not accessible to spatially fixed interfaces.
10:45 AM - P14.5
Tunable Metallic Conductivity in Ferroelectric Nanodomains.
Petro Maksymovych 1 , Anna Morozovska 2 3 , Pu Yu 4 , Eugene Eliseev 3 , Ying-Hao Chu 5 4 , Ramamoorthy Ramesh 4 , Arthur Baddorf 1 , Sergei Kalinin 1
1 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Institute of Semiconductor Physics, National Academy of Science of Ukraine, Kiev Ukraine, 3 Institute for Problems of Materials Science, National Academy of Science of Ukraine, Kiev Ukraine, 4 Department of Materials Sciences and Engineering and Department of Physics, University of California Berkeley, Berkeley, California, United States, 5 Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan
Show AbstractPerovskite oxides exhibit a notoriously rich gamut of electronic behaviors including metal-insulator transitions, CMR and superconductivity. Many of these properties can be initiated or controlled by tuning the carrier density through either doping or electrostatic gating across a surface or interface. Both approaches are inherently macroscopic, modifying either the bulk or an extended interface of the material. However, if an oxide is ferroelectric, tuning of the carrier density may be achievable on a local scale down to several nanometers by appropriate control of the domain structure. We will present a detailed analysis of the polarization-controlled electron transport in comparatively thick ferroelectric films of Pb(Zr0.2Ti0.8)O3 (PZT). Following our earlier finding that polarization switching in this material significantly enhances local tunneling conductivity [1,2], we explored the electronic signatures of the polarization-switching event itself. This regime has been previously unaccessible because of the overwhelming contribution of the capacitive displacement current and the complexity of ferroelectric switching in mesoscopic capacitors. The corresponding I-V curves exhibited complex hysteretic shape, which we traced to tunable, size-dependent conductance of ferroelectric nanodomains formed by localized polarization reversal. But the most suprising finding was metallic conductivity in ferroelectric nanodomains, in stark contrast to thermally activated conductivity of extended domains and equilibrium domain walls in the same material [3]. Based on analytical modeling, we suggest that metallic conductance arises from localized carrier accumulation that compensates the bound charge at curved domain walls decorating nanodomains. Though conceptually similar to theoretical proposals dating back to the early 70’s, to our knowledge we are the first to experimentally demonstrate this pathway to metallic conductance in ferroelectrics and reveal its tunability. We will further discuss the feasibility of finding this intriguing behavior in other ferroelectrics.Research was conducted at the Center for Nanophase Materials Sciences and sponsored by the Division of Scientific User Facilities, U.S. Department of Energy. Material synthesis at Berkeley was partially supported by the SRC-NRI-WINS program as well as by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences Division of the U. S. Department of Energy under contract No. DE-AC02-05CH1123.[1] P. Maksymovych et. al, Science 324 (1421) 2009.[2] P. Maksymovych et. al Nanotechnology 22 (254031) 2011.[3] P. Maksymovych et al, submitted (2011)
P15: Local Studies of Piezoelectricity
Session Chairs
Thursday PM, December 01, 2011
Room 302 (Hynes)
11:30 AM - **P15.1
Effect of Mechanical Clamping on Local Piezoelectric Nonlinearity in Lead Zirconate Titanate Thin Films.
Flavio Griggio 1 , Stephen Jesse 2 , Amit Kumar 2 , Oleg Ovchinnikov 2 , Hyunsoo Kim 1 , Thomas Jackson 1 , Sergei Kalinin 2 , Susan Trolier-McKinstry 1
1 , Penn State, University Park, Pennsylvania, United States, 2 The Center for Nanophase Materials Science and Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThe properties of a broad range of functional thin film materials, including ferroelectric films, are a function of the dynamics of domain boundary motion. In this work, changes in the dielectric and piezoelectric properties of PbZr0.52Ti0.48O3 (PZT) films were studied over a range of length scales. It was found that both the local stresses associated with pinning the film to the substrate, and global stresses associated with thermal mismatch influence domain wall motion in these materials. For example, when PZT thin films are relieved of in-plane tensile stresses and local mechanical pinning to the substrate, a dramatic increase in the dielectric nonlinearity is observed, and bulk-like response is achieved. Maps of the local piezoelectric nonlinearity showed a distinct increase in the correlation length associated with the coupled domain wall motion in PZT diaphragms that are released from the Si substrate (changing the local mechanical boundary conditions, while leaving the average in-plane tensile stress largely unchanged), with respect to clamped regions. This suggests that the local mechanical boundary conditions strongly influence the domain wall dynamics.
12:00 PM - P15.2
Proving of the Ferroelectric and Piezoelectric Properties of Pb(Zr, Ti)O3 Films by Raman Spectroscopy.
Hiroshi Funakubo 1 , Mitsumasa Nakajima 1 , Yoshitaka Ehara 1 , Ayumi Wada 1 , Tomoaki Yamada 1 2 3 , Nobuyasu Mizutani 1 , Takashi Iijima 4 , Hiroki Taniguchi 1 , Mitsuru Itoh 1 , Ken Nishida 5 , Takashi Yamamoto 5 , Minoru Osada 6
1 , Tokyo Institute of Technology, Yokohama Japan, 2 , Nagoya University, Nagoya Japan, 3 , PRESTO, Japan Science and Technology Agency, Tokyo Japan, 4 , National Institute of Advanced Industrial, Tsukuba Japan, 5 , National Defense Academy,, Yokosuka Japan, 6 , National Institute for Materials Science (NIMS), Tsukuba Japan
Show AbstractFilms of Pb(Zr, Ti)O3 has been widely investigated for MEMS applications due to their superior properties. Investigation of ferroelectric and piezoelectric properties without proving is the very useful for the mass production point of view. We can get various information from Raman spectroscopy, such as the spontaneous polarization, strain state of the films and the volume fraction of the non 180o domains. In the present study, we investigated the ferroelectric property, crystal structure, and A1(1TO) soft mode of almost strain-free epitaxial polar axis-oriented tetragonal Pb(Zr, Ti)O3 thick films grown on CaF2 substrates by changing the Zr/(Zr+Ti) ratio and the temperature. The relationships of Ps2, (c/a−1), and ω2[A1(1TO)] were experimentally obtained, which confirmed the Ps value obtained from (c/a−1) and ω[A1(1TO)] without direct polarization measurements.In addition, we employed in situ Raman spectroscopy under electric field for (100)/(001) -oriented tetragonal Pb(Ti0.61Zr0.39)O3 films. The increase in Vc was revealed above 200 kV/cm, which resulted in the larger remanent polarization. In addition, the application of high enough field also brings a feature, i.e., large reversible change in Vc with/without electric field that can quantitatively explain the enhanced piezoelectric response. These demonstrate the usefulness of ex situ and in situ Raman observations to probe the ferroelectric and piezoelectric properties including domain contributions to the electrical and piezoelectric responses.
12:15 PM - P15.3
Nanoscale Studies of Elastic Relaxation and Correlation of Local Strain Gradients with Ferroelectric Domains in (001) BiFeO3 Nanostructures.
Orlando Auciello 1 2 , Martin Holt 2 , Jeffrey Klug 1 3 , Ramesh Premnath 1 4 , Alexandra Joshi-Imre 2 , Seungbum Hong 1 , Ram Katiyar 4 , Michael Bedzyk 3 5 1
1 Materials Science, Argonne National Laboratory, Argonne, Illinois, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, 3 Physics and Astronomy, Northwestern University, Evanston, Illinois, United States, 4 Physics and Institute for Functional Materials, University of Puerto Rico, San Juan, Puerto Rico, United States, 5 Materials Science and Engineering , Northwestern University, Evanston, Illinois, United States
Show AbstractWe report an elastic relaxation and increase in local strain variation correlated with ferroelectric domains within epitaxial BiFeO3 thin film nanostructures fabricated by combined electron-beam and focused ion-beam nanolithography. Nano-focused x-ray diffraction microscopy, performed with the unique nanoprobe (Φ= 50 nm) X-ray beam at the Advanced Photon Source in Argonne National Laboratory, provided new insights into the relationship between film strain and ferroelectric domains in nanostructures, namely: i) an out-of-plane (C-axis) elastic relaxation of as much as -1.8% Δc/c in a BFO film-based nanostructure relative to the planar film lattice constant; ii) an out-of-plane rotation trending from the center towards all released edges of the nanostructure; and iii) an increase of inter-domain strain variation within the nanostructure of approximately 10 times the inter-domain variation found within the planar film, correlated with ferroelectric domain boundaries as confirmed by piezoresponse-force microscopy (PFM). These results indicate that the release of in-plane BFO/SRO mismatch strain in a planar film is taken up by the local ferroelectric domain structure after patterning, resulting in greatly increased mechanical strain gradients within the structure. The results obtained in this research indicate that direct manipulation of both local ferroelectric polarizability and local inter-domain mechanical energy is feasible via nanoscale patterning of multiferroic BFO thin films. These results may have significant implications for future use of sub-micron lateral scale multiferroic heterostructures in the fabrication of high-density FeRAMs and other micro- and nanoelectronic devices exploiting the multiferroic properties of BFO films.This work was supported by US Department of Energy, Office of Science, Office of Basic Energy Sciences-Materials Science, under contract DE-AC02-06CH11357. Use of the Center for Nanoscale Materials was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
12:30 PM - P15.4
Nanosecond Structural Response of Ferroelectric/Dielectric Superlattices to Applied Electric Fields.
Pice Chen 1 , Ji Young Jo 2 , Rebecca Sichel 1 , Sara Callori 3 , John Sinsheimer 3 , Eric Dufresne 4 , Matthew Dawber 3 , Paul Evans 1
1 Department of Materials Science and Engineering and Materials Science Program, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 School of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of), 3 Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York, United States, 4 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractFerroelectric/dielectric superlattices provide the means to manipulate the properties of complex oxide materials at the fundamental atomic scale. Among the intriguing properties of these materials is the formation of nanoscale 180° striped polarization domains within superlattice thin films. In contrast to the polarization switching process in a ferroelectric layer with an initially uniform polarization, the dynamics of the transition from striped domains to a homogeneous polarization state under applied electric fields has to date been far less well understood. Theoretical calculations have provided a range of intriguing predictions, but experiments probing the structural response of ferroelectric/dielectric superlattice have been limited to slow timescales from milliseconds to seconds.A time-resolved x-ray microdiffraction study was carried on a PbTiO3/SrTiO3 superlattice under applied electric fields with nanosecond time resolution. The dynamics of the superlattice as a whole is closely linked to the structural evolution of the striped domains. The rate of transition from striped domain into a homogeneous polarization state depends on the magnitude of the electric field, as indicated by the decay of intensities of domain satellite x-ray reflections. Regions of superlattice that have been switched into a uniform polarization state show lattice expansion as a consequence of the piezoelectricity. The piezoelectric response of the volume of the superlattice associated with stripe domains, however, is effectively suppressed due to electromechanical clamping between adjacent regions with opposite polarizations. We therefore propose that the transition of striped domains into a homogeneous polarization state occurs heterogeneously under electric fields.
12:45 PM - P15.5
Tip-Enhanced Piezoelectricity in Ultrathin Ferroelectrics.
Haidong Lu 1 , D. Wu 1 , A. Stamm 1 , C. Bark 2 , C. Eom 2 , E. Tsymbal 1 , X. Marti 3 , P. Zubko 4 , G. Catalan 5 , A. Gruverman 1
1 Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 2 Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 3 Department of Physics, Charles University, Prague Czechia, 4 Department of Physics, University of Geneva, Geneva Switzerland, 5 ICREA and CIN2, Campus Universitat Autonoma de Barcelona, Barcelona Spain
Show AbstractOne of the most distinctive features of ferroelectrics is a strong coupling between the external electric field, polarization and mechanical strain which gives rise to a range of electromechanical phenomena in these materials including piezoelectric, electrostrictive and flexoelectric effects. We report the unusual coupling effect in ultrathin BaTiO3 hetrostructures resulting in mechanically-induced polarization reversal and enhancement of piezoelectricity. It is observed that, in the absence of external bias or force, the piezoelectric response of the SrRuO3/BaTiO3/SrRuO3 capacitors behave as if they were paraelectric, due to the complete compensation of polarization by the formation of antiparallel domains. Applying a vertical uniaxial compression through a probing tip leads to a recovery of the polarization and an enhancement of the piezoelectric response. Moreover, polarization could be reversed by applying a mechanical stress on bare BaTiO3 films. We explain this result by the combination of flexoelectricity induced by the inhomogeneous stress field under the tip, plus a renormalization of the ferroelectric coefficients caused by the tip-induced vertical compression.
P16: Local Probes of Polar Domains
Session Chairs
Thursday PM, December 01, 2011
Room 302 (Hynes)
2:30 PM - **P16.1
Switching and Electronic Properties of Nanoscale Ferroelectric Structures.
Alexei Gruverman 1 , Haidong Lu 1 , X. Liu 1 , John D. Burton 1 , Chung Wung Bark 2 , Chang-Beom Eom 2 , Evgeny Tsymbal 1
1 Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 2 Department of Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin, United States
Show AbstractMaintaining and controlling a stable electrical polarization at room temperature in ferroelectric perovskite oxide thin films is essential for exploiting the functionality of these materials for nanoscale applications. We report on the investigation of polarization dynamics and related electronic transport behavior in high-quality single-crystalline ultrathin (in the range from 2 to 20 nm) BaTiO3 capacitors by means of piezoresponse force microscopy (PFM) and pulsed switching current measurements (PUND). It is shown that although polarization is stable in ultrathin BaTiO3 films with no top electrodes, deposition of top electrodes (SrRuO3 or La0.7Sr0.3MnO3) results in severe polarization relaxation. This effect is a consequence of strong effective depolarizing fields due to unfavorable interface terminations with the deposited electrodes, as opposed to more complete screening in the films by adsorbed charges on the free surface. These interface effects can smear out the ferroelectric transition and can even make the ferroelectricity unstable at room temperature. Several approaches to enhance polarization retention in the case of a deposited electrode, including strain engineering and control of electrically boundary conditions, were explored. In particular, first-principle calculations based on density functional theory show that engineering of the atomic termination at the electrode interface with BaTiO3 by insertion of ultrathin dielectric layers of SrTiO3 can alleviate stability issues in the case of SrRuO3 electrodes. This approach is confirmed by PFM observations showing spatially resolved dynamics of relaxation, local PFM spectroscopy and determination of the characteristic relaxation times by PUND.
3:00 PM - P16.2
Nanoscaled Domain Structures around the MPB Region in PMN-PT.
Shigeo Mori 1 , Kousuke Kurushima 2
1 Dept. of Material Sceince, Osaka Prefecture University, Sakai, Osaka, Japan, 2 , Toray Research Center, Ohtsu, Shiga Japan
Show AbstractFerroelectric relaxors have generated considerable interest because of their promising application as piezoelectric devices. Enhanced piezoelectric properties appear near the morphotropic phase boundary (MPB) in Pb(Zr,Ti)O3 (PZT) and (1-x)Pb(Mg1/3Nb2/3)O3- xPbTiO3 ((1-x)PMN-xPT). To understand the mechanism of the enhanced piezoelectric properties around MPB, several models have been proposed.[1,2] On the other hand, the existence of the low-symmetry monoclinic phase were found in between the rhombohedral and tetragonal phases by X-ray and neutron diffraction experiments [3]. In this work, in order to verify the proposed mechanisms of the enhanced piezoelectric properties and the existence of the low-symmetry monoclinic phase in (1-x)PMN-xPT, nanoscaled domain structures of (1-x)PMN-xPT single crystals in the range of the MPB were carefully examined by a transmission electron microscopy (TEM) and determined directions of the polarization vectors in the nanoscaled domains. We found domain structures with multiple inhomogeneities in the low-symmetry phase of x~0.32 at 298 K. In addition to the large plate-shaped tetragonal domains with the 100~200 nm width, fine lamella-type domain structures with ~10 nm width were found inside the large lamella-type tetragonal domains in the low-symmetry phase To determine directions of polarization vectors in fine lamella-type domain structures, we thoroughly examined the g-vector dependence of the domain contrast in the dark-field images, where g-vector means the reciprocal lattice vector. It is revealed that the directions of the polarization vectors in fine lamella-type domain structures are in between [111] and [112] directions. In-situ TEM observation of changes of the domain structures as a function of the temperature revealed that the domain configuration with multiple inhomogeneities is inherent to the low-symmetry phase in the MPB region. Our experimental results are in good accord with the proposed theoretical models [2,3]. [1] H. Fu and R. E. Cohen, Nature 403, 281 (2000) [2] G. A. Rossetti et al., J. Appl. Phys. 103, 114113 (2008). [3] B. Noheda, et al, Phys. Rev. B66, 054104 (2002).
3:15 PM - P16.3
Direct Observation of Polarization Loss in Ferroelectric PbZr0.2Ti0.8O3 Thin Films.
Peng Gao 1 , Christopher Nelson 1 , Jacob Jokisaari 1 , Seung-Hyub Baek 2 , Chung Wung Bark 2 , Yi Zhang 3 , Yuanming Liu 4 , Jiangyu Li 4 , Enge Wang 5 , Chang-Beom Eom 2 , Xiaoqing Pan 1
1 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin, United States, 3 Materials Science and Engineering, Nanjing University, Nanjing China, 4 Mechanical Engineering, University of Washington, Seattle, Washington, United States, 5 School of Physics, Peking University, Beijing China
Show AbstractThe relaxation of an induced polarization state in the absence of an external electrical field causes data retention loss in ferroelectric memories. In this work, we studied polarization relaxation behavior in ferroelectric PbZr0.2Ti0.8O3thin films grown on (110) DyScO3 with SrRuO3 bottom electrodes, using a real-time in situ transmission electron microscopy. It was found that the retention behavior in such heterostructures depends on the magnitude and duration of the switching voltage: small and short voltage pulses created small triangular domains which showed poor retention.In contrast, larger and longer voltage pulses generated larger trapezoidal-shaped domains which exhibited excellent stability after relaxation. The instability of the small switched domains is attributed to their inclined, charged domain walls resultingfrom the built-in electrical field at the PbZr0.2Ti0.8O3/SrRuO3 interface. The triangular domains spontaneously and completely switched back to the original polarization state when voltage was removed. Meanwhile, trapezoidal-shaped domains transformed to rectangular domains when their inclined domain walls relaxed to vertical walls, which have no charge and are stable.Our results indicate that induceddomains are subject to retention loss even in thermodynamically favored orientations, which must be mitigated by overcoming a critical domain size.
3:30 PM - P16.4
Nonlinearity of Single Grain Boundaries in Thin Film Ferroelectrics.
Daniel Marincel 1 , Amit Kumar 2 , Sergei Kalinin 2 , Susan Trolier-McKinstry 1
1 Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 2 The Center for Nanophase Materials Science and Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractUnderstanding the influence of crystallographic defects on the dielectric and piezoelectric properties of ferroelectric materials becomes crucial as the size of piezoelectric devices is scaled down. Defects have been shown to act as pinning sites for domain wall motion and can impact the dielectric and piezoelectric response of the device. Polarization nonlinearity and hysteresis develop when domain walls move across pinning sites at sub-switching applied electric fields, resulting in a field dependent response. However, the quantitative influence of specific pinning sites on the measured dielectric and piezoelectric nonlinearities is currently unknown. In this work, epitaxial rhombohedral lead zirconate titanate (PZT) with a dielectric constant of 750 and remanent polarization of 38 μC/cm2 and tetragonal PZT with a dielectric constant of 610 and remanent polarization of 45 μC/cm2 were deposited on strontium titanate twist and tilt bi-crystals by pulsed laser deposition. Deposition on bi-crystal substrates creates a single grain boundary of a well-defined angle of incidence in the PZT film. The dielectric nonlinearity developed across such grain boundaries was analyzed using the Rayleigh and Preisach models. The influence of specific grain boundaries on the first order reversal curves describing the dielectric hysteresis will also be presented. Piezoresponse force microscopy was also used to analyze the nonlinearity across the grain boundary as an electric field was applied perpendicular to the boundary. A comparison of the nonlinearities and the resulting influence of a single grain boundary on the dielectric and piezoelectric nonlinearities will be given.
3:45 PM - P16.5
X-Ray Reflectometry of Complex Oxide Thin Films.
Alexei Grigoriev 1 , Ho Nyung Lee 2 , Donald Walko 3
1 Physics and Engineering Physics, The University of Tulsa, Tulsa, Oklahoma, United States, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractFerroelectric properties of thin film oxide materials such as electric polarization, piezoelectric response, and dielectric constant depend on the local properties of interfaces between oxide layers. The physical properties of a ferroelectric material can be locally modified in the vicinity of the interface and thus the interface is of the major importance for studying and using ferroelectric properties of nanometer-thick oxide films. For example, a layer with a low dielectric constant near the interface of a ferroelectric oxide with a conducting oxide can affect the stability of a ferroelectric phase and the dielectric properties of the material. The presence of such a non-ferroelectric “dead” layer has been confirmed indirectly by electrical measurements. The direct observations of the interfacial layer and probing its local properties in ferroelectric multilayer systems can be done by using such techniques as high-resolution transmission electron microscopy or x-ray scattering.In this work, we present our results of high-resolution synchrotron x-ray reflectometry of an ultrathin complex oxide system. The analysis of reflectivity data allowed us to reconstruct the electron density profile through the depth of the multilayer oxide system consisting of a 4-nm PbZr0.2Ti0.8O3 ferroelectric film on a 4-nm SrRuO3 conducting oxide film on a SrTiO3. The density profile reveals a ~1.5 nm-thick low density layer at the interface between PbZr0.2Ti0.8O3 and SrRuO3 films. The width of this interfacial layer is consistent with the transition region widths predicted for ferroelectric/electrode interfaces by M. Stengel, D. Vanderbilt, and N. Spaldin (Nat. Mater. 8, 392 (2009)). In addition to this important result, we will discuss the use of time-resolved x-ray reflectometry for probing electric-field driven transient changes in oxide layers and oxide interfaces.
4:00 PM - P16.6
Domain Studies in K0.5Na0.5NbO3 (KNN) Single Crystals Grown by a High Temperature Self Flux Method.
Paula Vilarinho 1 , Muhammad Rafiq 1 , Maria Costa 1
1 , University of Aveiro, CICECO, Aveiro Portugal
Show AbstractDue to environmental protection and related legislations, a lot more research is being conducted and required to produce lead free piezoelectrics and ferroelectrics which may have properties comparable to lead based compositions, such as Pb(Zrx,Ti1-x)O3 (PZT), currently the most widely used due to its remarkable properties. Undoped K0.5Na0.5NbO3 (KNN) has inferior electromechanical response as compared to PZT and thus various approaches for improving the properties of KNN based polycrystals have been attempted. On the other hand it is well known that single crystal usually exhibit enhanced performance when compared to counter polycrystalline parts. Comprehensive studies on the physical properties of single crystals will contribute to optimise the response of KNN polycrystals. There are only a few reports on KNN single crystals properties. The high temperatures used to synthesise KNN hampers the stoichiometry control. In the present work KNN single crystals have been grown by an alternative high temperature flux solution that uses a potassium carbonate (K2CO3) flux modified with boron oxide (B2O3). The addition of B2O3, related to its low melting temperature (450 °C), is crucial to decrease the mass losses during the growth of KNN crystals allowing the control of the stoichiometry during crystal growth. Different temperature profiles were used and the obtained single crystals characterised from the structural and electromechanical point of view, with a particular emphasis on the ferroelectric domain structure. The obtained KNN single crystals are orthorhombic with slight monoclinic distortion. Higher dielectric constants were attained for single crystals as compared to the bulk counterpart. Ferroelectric and electromechanical responses were macroscopically characterized by P-E hysteresis loops and d33 coefficient. Local domain structure was assessed by Electron Transmission Microscopy (TEM) and Piezoforce Response Microscopy (PFM). Piezoforce microscopy (PFM) was used to analyse the evolution of domain populations as a function of growth conditions. Domain structures of poled crystals, local piezoelectric properties of individual domains and piezoelectric histograms were studied. The obtained information is compared with domain imaging by TEM. Results are discussed in the framework of KNN single crystal growth conditions. The differences between the macroscopic and microscopic ferroelectric and piezoelectric parameters of KNN single crystals and polycrystals are described.
4:15 PM - P16: Domains
Break
P17: Lead Free Piezoelectrics and Thin Films
Session Chairs
Thursday PM, December 01, 2011
Room 302 (Hynes)
4:30 PM - P17.1
In Situ Transmission Electron Microscopy Study on the Electric-Field-Induced Phase Transitions in Lead-Free (Bi1/2Na1/2)TiO3–BaTiO3 Piezoelectric Ceramics.
Cheng Ma 1 , Xiaoli Tan 1
1 Materials Science and Engineering, Iowa State University, Ames, Iowa, United States
Show AbstractThe microstructural mechanism for the high piezoelectric performance in lead-free (Bi1/2Na1/2)TiO3–BaTiO3 (BNT–BT) ceramics was investigated using electric-field in-situ transmission electron microscopy (TEM) for the first time. The study was focused on compositions across the morphotropic phase boundary (MPB), which separates a R3c ferroelectric phase and a P4bm antiferroelectric phase at virgin state. These MPB compositions have been known to exhibit optimal piezoelectric properties after poling. The present in situ TEM study revealed the evolution of domain morphology and crystal structure during the poling process. It was found that, under applied electric fields, the short-range-ordered uncompensated antiferroelectric phase with P4bm nanodomains transformed into two different long-range-ordered ferroelectric phases with R3c complex domains and P4mm lamellar domains, respectively. After the phase transition, the switching of the induced ferroelectric domains was also observed. The results suggest that electric-field-induced phase transitions took place during the poling process of the lead-free BNT–BT ceramics, which is in sharp contrast to the widely used Pb(Zr1-xTix)O3 ceramics where only domain switching occurs during poling. The responses of microstructures of BNT–BT ceramics under electric fields with reversed polarity was also investigated in detail.
4:45 PM - P17.2
Origin and Stability of the Dipolar Response in a Family of Tetragonal Tungsten Bronze Relaxors.
Donna Arnold 1 , Andrei Rotaru 2 , Finlay Morrison 2
1 School of Physical Sciences, University of Kent, Canterbury, Kent, United Kingdom, 2 School of Chemistry, University of St Andrews, St Andrews, Fife, United Kingdom
Show AbstractThe combination of the requirement for Pb-free replacements for PbZrxTi1-xO3 (PZT)[1] and the recent renaissance in multiferroics[2] has re-invigorated the investigation of ferroelectric systems. To date the main focus has been on perovskite (ABO3) based materials such as K1-xNaxNbO3 (as a Pb-free piezoelectric)[3] and BiFeO3 (best-known room temperature multiferroic)[4] due to both their compositional flexibility and also our ability to tune properties in this structure type. The tetragonal tungsten bronze (TTB) structure, A12A24B12B28O30, is closely related to the perovskite structure and offers a similar degree of compositional flexibility, however, the presence of crystallographically non-equivalent A- and B-sites provides extra degrees of freedom for structural manipulation. Whilst ferroelectric TTBs were widely studied in the 1960’s-70’s our understanding of this structure-type is still poor.We recently reported a series of relaxor TTBs, based on Ba6MNb9O30 (M3+ = Ga3+, Sc3+ or In3+).[5,6] Here we present dielectric spectroscopy and variable temperature powder neutron diffraction data to discuss the correlation between the TTB structure and relaxor behaviour. We show that the real part of dielectric permittivity follows the Volger-Fulcher[7] model and that the dipole freezing temperature, Tf, increases with increasing ionic radii of the M3+ species. We also demonstrate that fitting of the dielectric loss to Jonscher’s universal law of dielectric relaxation[8] yields comparable Tf values. Furthermore, variable temperature powder neutron diffraction data indicates a strong anisotropy in the crystal lattice at Tf which is associated with stiffening of the dipoles along the c-axis of the unit cell. Crystallographic data further suggests that displacement of the Nb5+ ions in the c-direction is limited to the B1 crystallographic site suggesting these materials exhibit a ‘dipole glass’ –type model.1. T. R. Shrout & S. J. Zhang (2007) J. Electroceram. 19, 1112. N. A. Spaldin & M. Fiebig (2005) Science 309, 3913. Y. Salto et al (2004) Nature 432, 844. M. Bibes & A. Barthelemy (2008) Nature Materials 7, 4255. D. C. Arnold & F. D. Morrison (2009) J. Mater. Chem. 19, 6486. A. Rotaru, D. C. Arnold, A. Dauod-Aladine, F. D. Morrison (2011) Phys. Rev. B. 83, 184302 7. D. Viehland, S. J. Jang, L. E. Cross & M. Wuttig (1990) J. Appl. Phys. 68, 29168. A. K. Jonscher, (1983) ‘Dielectric Relaxation in Solids’, Chelsea Dielectrics Press, London
5:00 PM - P17.3
Origin and Role of Hierarchal Domain Structure in (Na1/2Bi1/2)TiO3-xBaTiO3 Single Crystals.
Deepam Maurya 1 , Shashank Priya 1
1 CEHMS, Department of Materials Science and Engineering, Virginia Tech, Blacksburg, Virginia, United States
Show AbstractThe environmental concern has propelled research on development of high piezoelectric lead-free piezoelectric materials. Present work addresses the synthesis and domain structure characterization of lead-free (1-x)(Na1/2Bi1/2)TiO3-xBaTiO3 (NBTBT) single crystals. The crystals were grown using flux method with composition in the vicinity of morphotropic phase boundary (MPB). Room temperature (RT) XRD-spectra measured on powdered single crystal was found to exhibit perovskite phase. In order to confirm crystallographic orientation, electron back scattered diffraction (EBSD) mapping was performed. Also, EBSD orientation mapping and transmission electron microscopy (TEM) were used to investigate hierarchal domain structure of NBTBT. TEM imaged revealed the presence of needle shaped and herringbone type domain structure. The domain size was observed to be around ~ 100 nm. Moreover, the temperature dependence of dielectric response for <001>pc oriented crystal was studied as a function of temperature in range of 20 - 500 oC. P-E hysteresis measurement was performed to investigate the variation of polarization below and above the coercive field. The longitudinal piezoelectric constant was measured to be 300 pC/N. Using all these measurements, an attempt was made to develop comprehensive structure - property - performance relationship for MPB composition NBTBT. We believe our study provides important insight towards modulating the magnitude of piezoelectric coefficient by tuning the size and structure of domains in this system.*
[email protected]5:15 PM - P17.4
Growth of Ruddlesden-Popper Can+1TinO3n+1 Thin Films.
Arsen Sukiasyan 1 , Julia Mundy 2 , Yongsam Kim 2 , Eftihia Vlahos 3 , Michael Biegalski 4 , Venkatraman Gopalan 3 , Dmitri Tenne 5 , Joel Brock 2 , David Muller 2 , Darrell Schlom 1
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Shool of Applied Science and Engineering, Cornell University, Ithaca, New York, United States, 3 Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 4 Center for Nanophase Materials Science, Oak Ridge National Lab, Oak Ridge, Tennessee, United States, 5 Physics, Boise State University, Boise, Idaho, United States
Show AbstractWe report for the first time the growth of Ruddlesden-Popper homologous series of epitaxial Can+1TinO3n+1 thin films (where n = 2, 3, 4, 5, and n = ∞ is CaTiO3) on (100) LSAT and (110) NdGaO3 substrates. Four-circle x-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to probe the structure of the Can+1TinO3n+1 thin films. Our results demonstrate that epitaxial Can+1TinO3n+1 thin films (except for n = 1) can be successfully grown by molecular beam epitaxy (MBE). We paid particular attention to the growth of (n = 2) Ca3Ti2O7 thin films, which was recently predicted to become ferroelectric. Measurements of the dielectric properties and lattice dynamics of Ca3Ti2O7 thin films will be reported.
5:30 PM - P17.5
Effect of Tensile Strain on Ferroelectric Polarization of (Ba,Sr)TiO3 Epitaxial Films on MgAl2O4 Substrates.
Xiaolan Zhou 1 , Ludi Miao 1 , Punam Silwal 1 , Ilan Stern 1 , Dae Ho Kim 1
1 Physics and Engineering Physics, Tulane University, New Orleans, Louisiana, United States
Show AbstractExtensive investigations on the effects of compressive strain on ferroelectric polarization in epitaxial films of oxide perovskites have greatly improved our understanding of ferroelectricity. On the other hand, lack of readily available substrates having larger lattice constants than important oxide ferroelectrics, such as (Ba,Sr)TiO3, Pb(Ti,Zr)O3, and BiFeO3 hindered studies on the effects of tensile strain. Such studies will effectively compensate current understandings. Spinel MgAl2O4 provides superb opportunity for studying tensile strain with a slightly larger lattice constant and an excellent crystalline quality. However, the incompatible atomic arrangement at the interface between spinel and perovskite generates lots of defects and relaxes the strain immediately. We introduce a high quality buffer layer, Ni0.6Al0.4O1+δ allowing coherent growth of (Ba,Sr)TiO3 films on MgAl2O4 (001) substrates. Ni0.6Al0.4O1+δ inherits a rock-salt structure of NiO. Added Al reduces the lattice constant to match that of MgAl2O4 stabilizing the structure. Ferroelectric properties of (Ba,Sr)TiO3 films show drastic change when Ni0.6Al0.4O1+δ buffer layers are introduced on the spinel substrates. In-plane polarization measurements reveal that the polarization of fully strained films with the buffer layer points along the out-of-plane direction, while that of relaxed ones lies along the in-plane directions. A detailed analysis on the relationship between the structural and ferroelectric properties of the films will be presented.
5:45 PM - P17.6
Nanoscale PFM Imaging of Intrinsic Domains in PbTiO3 Ultrathin Films.
Celine Lichtensteiger 1 , Pavlo Zubko 1 , Jean-Marc Triscone 1
1 DPMC, University of Geneva, Geneva 4 Switzerland
Show AbstractIn ferroelectric ultrathin films, the depolarization field arising from unscreened bound charges on the surface of the film and on the interface with the substrate is generally strong enough to suppress the polarization completely. The screening can be obtained by free charges from metallic electrodes, ions from the atmosphere, or mobile charges from within the semiconducting ferroelectric itself. Even in structurally perfect metallic electrodes, the screening charges will spread over a small but finite length, giving rise to a nonzero effective screening length that will dramatically alter the properties of an ultrathin film. In the absence of sufficient free charges, a ferroelectric has several other ways of minimizing its energy while preserving its polar state, e.g., by forming domains of opposite polarization, or rotating the polarization into the plane of a thin ferroelectric slab [Ferroelectricity in ultrathin-film capacitors, C. Lichtensteiger et al, to be published in Oxide Ultrathin Films, Science and Technology, Wiley].Using piezo-force microscopy (PFM), we investigate the intrinsic nanodomain pattern of PbTiO3 ultrathin films at room temperature, focusing on the effect of the film thickness and on the effective screening length.