Amy Prieto, Colorado State University
Sarbajit Banerjee, The State University of New York
Matthew C. Beard, National Renewable Energy Laboratory
Claudia Felser, Max-Planck-Institut fuer Chemische Physik fester Stoffe
Claudia Felser, Johannes Gutenberg University of Mainz
Symposium Support National Science Foundation
Prieto Battery, Inc.
OO2: Novel Synthetic Approaches in Solid-State Chemistry
Monday PM, December 02, 2013
Hynes, Level 1, Room 102
2:30 AM - *OO2.01
Crystal Growth of Intermetallics with Competing Magnetic Behavior
Julia Chan 1
1University of Texas at Dallas Richardson USAShow Abstract
The search for materials with desired magnetic and electrical properties concomitantly relies on the discovery of new systems. To unequivocally determine the compounds&’ innate properties, large single crystals must be grown and characterized. In this talk, I will focus on the versatility and tunability of properties of intermetallics as it applies to the design and discovery of compounds with unusual magnetic and electrical properties. The challenges of phase stability, single crystal growth, structure determination, and physics of these materials will also be discussed.
3:00 AM - *OO2.02
Complex Intermetallic Phases Synthesized in Alkaline Earth-Rich Fluxes
Susan Latturner 1
1Florida State University Tallahassee USAShow Abstract
Alkaline earth metals such as calcium and magnesium are low-melting and reactive toward many elements in the periodic table; this makes them useful as solvents for metal flux reactions. Their melting points can be lowered further by mixing them with other elements; a 50/50 Ca/Li mixture melts at 300 C, and eutectic mixtures of Mg/Al and Ca/Mg both melt at ca. 450 C. Reactions of iron with rare earths and silicon in Mg/Al fluxes produce complex multinary phases including R5Mg5Fe4Al12Si6, R3FeAl4-xMgxSi2, and RFe2Al7-xMgx (R = rare earth). All of these structures feature a similar building block of chains of face-sharing aluminum trigonal prisms which are centered by iron. Pseudo-Zintl phases such as CaMgSi and EuMgSn can also be grown in this flux; these compounds are close to a metal-insulator transition and exhibit interesting properties such as magnetoresistance. Calcium-rich fluxes are excellent solvents for carbon and CaH2, enabling the formation of complex metal carbides and hydrides. These products range from charge-balanced salt-like Ca11Sn3C8 and LiCa2C3H to phases incorporating a range of hydride and/or carbide interstitials, such as Ca48In13C4-xH23+x.
3:30 AM - *OO2.03
Building Metal-Nonmetal Layers within Perovskite Hosts
Dariush Montasserasadi 1 Lea Gustin 1 Elisha Jospeha 1 John B Wiley 1
1University of New Orleans New Orleans USAShow Abstract
Topochemical reactions can be utilized to direct structure and properties in various compounds. Recent efforts in our group have involved the insertion of cation and/or anion species into layered perovskites via oxidative/reductive intercalation and/or ion exchange. In one case, we have found that the use of reductive intercalation with alkali metals, followed by oxidative intercalation with chalcogen hydride gases, allows for the construction of alkali-metal chalcogen hydride layers within Dion-Jacobson-type hosts; layered perovskites like RbLaNb2O7 can be manipulated to introduce Rb-ChH layers (ChH = OH, SH) within the interlayer. In other systems, two-for-one ion exchange reactions can be carried out on Ruddlesden-Popper perovskites; reactions of K2SrTa2O7 with divalent transition metal ions result in compounds of the form, MSrTa2O7 (M = Co, Zn). Details on the synthesis and characterization of these products will be presented with a discussion on the utility of these set of reactions for manipulations of other solids.
4:30 AM - *OO2.04
Facile Route to Novel Low Dimensional Fe-Based Magnetic Materials
Kirill Kovnir 1
1University of California, Davis Davis USAShow Abstract
Development of new routes to magnetic materials is a crucial step for the next generation of energy solutions. Besides the energy savings upon synthesis, low temperature methods significantly enhance the capabilities of fine tuning of the structure and properties of a magnetic material. A recent example is an intercalation of Li-ammonia or Li-pyridine into interlayer space of FeSe superconductor, which leads to the significant increase of the superconducting transition temperature. Products of the Li-amines intercalation into pre-synthesized FeSe are fine powders with low degree of crystallinity. Temperatures of conventional solid state synthesis of FeSe (> 1000 K) are not compatible with organic amines. We have developed low temperature (T < 500 K) synthetic route to iron chalcogenides, FeQ (Q = S, Se, Te). The developed method allows us to modify crystal structure of layered FeQ chalcogenides by means of the intercalation of iron-amino complexes. Unlike traditional intercalation techniques, high quality single crystals were obtained, thus facilitating determination of the crystal structure and evaluation of the properties of the synthesized compounds. Synthesis of new materials, their crystal and electronic structure as well as magnetic properties will be discussed.
5:00 AM - *OO2.05
Novel Solvothermal Fluorination, Oxygen Deintercalation, and Multistep Soft Chemistry Techniques for Metastable Materials Synthesis
Viktor V. Poltavets 1 Shaun R. Bruno 1 Colin K. Blakely 1 Joshua D. Davis 1
1Michigan State University East Lansing USAShow Abstract
Our ability to design new materials with desired electrochemical, thermoelectric or strongly-correlated electron properties is limited by thermodynamic control over reaction products in traditional high-temperature synthetic procedures. On the contrary, topotactic reactions, where extensive parts of the original framework are retained, allow for greater control of the structure of the final products; therefore, a combination of desired structural features, spin and oxidation states can be produced in a final material in a predictable fashion.
A 'chimie douce' solvothermal reduction method was developed for topotactic oxygen deintercalation of complex metal oxides. The reduction of the Ruddlesden-Popper nickelate La4Ni3O10 was used as a test case to prove the validity of the method. The completely reduced phase La4Ni3O8 was produced via the solvothermal technique at 150°C - a lower temperature than by other more conventional solid state oxygen deintercalation methods. Unlike other techniques, a pure Ni1+ compound, LaNiO2, can be prepared by solvothermal reduction, demonstrating the advantages of the developed method for synthesis of highly metastable reduced compounds.
Metastable oxyfluorides SrFeO2F and La4Ni3O8F2 were prepared through a low temperature, multistep synthesis via fluorination of the infinite layer intermediate phases. Influence of the synthetic pathway on O/F short range ordering and physical properties will be discussed. Mossbauer spectroscopy measurements revealed the predominance of cis fluorine configuration in FeO4F2 polyhedra, confirming a difference in local Fe coordination in comparison with O/F disordered SrFeO2F.
When trying to achieve anion ordering during synthesis, it is important to perform anion intercalation at as low a temperature as possible to avoid thermal randomization of the anions. A low temperature solvothermal fluorination technique, which we developed, allows for fast and facile synthesis at lower temperatures than gas- solid fluorination by XeF2.
In all known compounds with the alpha-NaFeO2 structure transition metals oxidation states are either 3+ or 3+/4+. We have developed an “aliovalent exchange plus intercalation” multistep soft chemistry approach for the preparation of a series of new layered transition metal oxides. The synthetic procedure resulted in compounds with the alpha-NaFeO2 type structures and, uniquely, with transition metals in mixed valent 2+/3+ oxidation states. The oxidation state in the final compounds can be controlled by utilizing AxMO2 precursor phase with different x. Crystal structures and physical properties of these novel compounds will be presented.
5:30 AM - OO2.06
From Extended Solids to Molecular Clusters: Assembling Metal Cyanides from Square-Planar MII(CN)4 Units (M = Ni, Pd, Pt and Cu)
Ann Mary Chippindale 1 Simon John Hibble 1 Elena Marelli 1
1University of Reading Reading United KingdomShow Abstract
The structures of the metal-cyanide layers within the group 10 compounds Ni(CN)2, Pd(CN)2 and Pt(CN)2, which consist of vertex-sharing square-planar M(CN)4 units, have recently been determined in detail using total neutron diffraction and will be discussed. Moving to group 11, the binary cyanide, Cu(CN)2, is not known to exist. However, we show here that copper(II) can be stabilised in a cyanide-only environment in the stoichiometric, mixed copper-nickel cyanide, CuNi(CN)4, and in the solid-solution, Cu1-xNi1+x(CN)4 (½ le; x < 1).
The atomic structure of the layers in CuNi(CN)4 and the stacking relationship between nearest-neighbour layers have been determined from total neutron diffraction studies at 10 and 300 K. The structure consists of flat layers of perfectly square-planar [Ni(CN)4] and [Cu(NC)4] units linked by shared cyanide groups i.e. both the metal and cyanide groups are perfectly ordered with Cu(II) coordinated to the nitrogen end of the cyanide group and Ni(II) to the carbon end. It is rather unusual to find Cu(II) in a square-planar environment within an extended solid. The layered structure of this new mixed-metal cyanide is closely related to those of Ni(CN)2, which forms more extended sheets, and Pd(CN)2.xNH3 and Pt(CN)2.xH2O, which form as nanocrystalline materials.
The overall appearance of the powder X-ray diffraction pattern of CuNi(CN)4, including the unusual peak shapes of the observed Bragg reflections, has been successfully explained using models incorporating stacking disorder between next nearest neighbour layers. CuNi(CN)4 shows similar thermal expansion behaviour to that observed previously for Ni(CN)2 [1,4] with negative thermal expansion within the layers (αa = -9.7 MK-1) and positive thermal expansion between the layers (αc = +89 MK-1) measured over the temperature range 200-540 K.
The stability of Cu(II) atoms in a cyanide-only environment has been investigated by varying the ratio of the Cu2+ and Ni2+ ions used in the synthesis. Using a Cu:Ni ratio of 1:1, the anhydrous phase, CuNi(CN)4, is precipitated directly. For Cu:Ni ratios less than one, hydrates of the form Cu1-xNi1+x(CN)4.yH2O (½ le; x < 1; y le; 6) are produced which can be dehydrated to form the corresponding anhydrous compounds, Cu1-xNi1+x(CN)4. These compounds readily rehydrate. Replacement of Cu2+ by Ni2+, which occurs when the Cu:Ni ratio is less than one, leads to the creation of [Ni(NC)4] units. These in turn readily hydrate to form six-coordinated [Ni(NC)4(H2O)2] groups similar to those found in nickel-cyanide hydrates, such as Ni(CN)2.3H2O. [Ni(CN)4] units do not hydrate; hence CuNi(CN)4, which contains such units, is not found in a hydrated form. With Cu:Ni ratios above one, partial reduction of the Cu(II) occurs to form LT-CuCN, in addition to CuNi(CN)4. This result further confirms that Cu(II) ions can only be stabilised when connected to the nitrogen ends of bridging cyanide
5:45 AM - OO2.07
Industrial Scale Production of MnFePSi-Based Magnetic Cooling Materials
Sumohan Misra 1 David van Asten 1 Lian Zhang 1 Markus Schwind 2 Fabian Seeler 2 Bennie Reesink 1
1BASF Nederland B.V. De Meern Netherlands2BASF SE Ludwigshafen GermanyShow Abstract
The discovery of giant magnetocaloric effect (MCE) in rare-earth and transition metal based materials and prototype equipment development has sparked great interest for magnetic cooling technology. This has also made it a promising alternative to the current vapor compression technology. However, significant synthetic challenges for industrial scale production of MCE materials exist for the successful commercialization of this technology.
We have focused our research activities on the MnxFe2minus;xPySi1-y family of magnetocaloric materials which shows great promise due to their large magnetocaloric properties as a result of being first-order phase transition materials (Tegus et al. 2002, Thanh et al. 2008). Additionally, they exhibit tunable Curie temperatures and earth abundant constituent raw materials. Moreover, they possess excellent long-term stability and their ability to be formed into complex shapes. In this presentation, we will discuss some of the challenges encountered during the up-scaled production of these materials, and how these have been overcome using industrial synthetic routes (for e.g. meltspinning and atomization) in addition to more traditional academic ball milling approach. We will also discuss the magnetocaloric properties of the obtained materials and the performance of these materials during magnetocaloric cycling.
Tegus, O.; Brück, E.; Buschow, K.; de Boer, F., Transition-metal-based magnetic refrigerants for room-temperature applications, Nature2002, 415, 150.
Thanh, D.; Brück, E.; Trung, N.; Klaasse, J.; Buschow, K.; Ou, Z.; Tegus, O.; Caron, L., Structure, magnetism and magnetocaloric properties of MnFeP1-xSix compounds, J. Appl. Phys.2008, 103, 07B318.
OO3: Poster Session I
Monday PM, December 02, 2013
Hynes, Level 1, Hall B
9:00 AM - OO3.02
Accommodation and Migration of Excess Oxygen in ThO2, CeO2 and UO2
Simon Charles Middleburgh 1 Greg R Lumpkin 1 Robin W Grimes 2
1ANSTO Lucas Heights Australia2Imperial College London London United KingdomShow Abstract
Accommodation of excess oxygen in CeO2, ThO2 and UO2 has been investigated using ab-initio modelling. Hyperstoichiometry was preferentially accommodated by the formation of peroxide species in CeO2, ThO2 but not in UO2, where oxygen interstitial defects are dominant. Migration of the excess oxygen defects was also studied; the peroxide ion in CeO2 and ThO2 is transported via a different mechanism to the oxygen interstitial in UO2. Formation of Frenkel defects was investigated to understand the eect of a peroxide formation on the drive for defect recombination. The presence of the Frenkel vacancy in proximity to the associated additional oxygen defect induces the oxygen to take up an interstitial site, similar to excess oxygen defects in UO2 rather than remain part of a peroxide molecule.
9:00 AM - OO3.03
Effects of pH in the Incorporation of Mn2+ in Ce1-xMnxO2-x (0.05 le; x le; 0.25) Solid Solutions Using Oxalate Co-Precipitation Technique and Its Characterizations
Poh Shing Ong 1 Yen Ping Tan 1 2 Yun Hin Taufiq-Yap 1 2 Zulkarnain Zainal 1 2
1Universiti Putra Malaysia UPM Serdang Malaysia2Universiti Putra Malaysia UPM Serdang MalaysiaShow Abstract
Mn-doped CeO2 electrolytes were prepared using a soft chemical technique which involved co-precipitation of Mn2+ and Ce4+ using oxalic acid as the precipitant. The incorporation of MnO into ceria lattice was found to be pH dependant. A wider solubility range of managanese dopant concentration into ceria lattice prepared via this method is highlighted. The resultant powders of Mn-doped CeO2 solid solutions, formulated as Ce1-xMnxO2-x, (0.05 le; x le; 0.25), were investigated thoroughly for the first time, from the aspect of synthesis where pH was precisely controlled and varied from 5 - 11. The optimized pH for a stable incorporation of Mn dopant into ceria was found to be pH = 10, in order to obtain the correct stoichiometric compound. The solubility limit of MnO in the CeO2 fluorite lattice structure was suggested to be x = 0.20. The phase composition, morphology properties and elemental analysis of the oxalate and derived-powder was characterized using X-ray diffraction, DTA/TG, SEM and X-ray fluorescence (XRF) respectively. The grain size decreases with increase of MnO content. The electrical conductivity of sintered samples of Mn-doped CeO2 ceramics were investigated in air as a function at 473 - 1073 K using AC impedance spectroscopy. The contributions of the bulk (grain interior), the grain boundary and the electrode polarization behaviour are well documented. The bulk conductivities of the Mn-doped CeO2 ceramics sintered at 1473 K at a test temperature of 1073 K were determined to be 4.223 x 10-4 S cm-1 for Mn content x = 0.10 with activation energy, Ea = 0.88 eV.
9:00 AM - OO3.07
Structure and Properties of Magnetic Ceramic Nanoparticles
Monica Sorescu 1 Tianhong Xu 1
1Duquesne University Pittsburgh USAShow Abstract
Magnetic ceramic nanoparticles of the type xIn2O3-(1-x)alpha-Fe2O3, xV2O5-(1-x)alpha-Fe2O3 and xZnO-(1-x)alpha-Fe2O3 (x=0.1-0.7) were synthesized from the mixed oxides using mechanochemical activation for 0-12 hours. X-ray diffraction was used to derive the phase content, lattice constants and particle size information as function of ball milling time. Mossbauer spectroscopy results correlated with In3+, V5+ and Zn2+ substitution of Fe3+ in the hematite lattice. SEM/EDS measurements revealed that the mechanochemical activation by ball milling produced systems with a wide range of particle size distribution, from nanometer particles to micrometer agglomerates, but with a uniform distribution of the elements. Simultaneous DSC-TGA investigations up to 800 degrees C provided information on the heat flow, weight loss and the enthalpy of transformation in the systems under investigation. This study demonstrates the formation of a nanostructured solid solution for the indium oxide, an iron vanadate (FeVO4) for the vanadium oxide, and of the zinc ferrite (ZnFe2O4) for the zinc oxide. The transformation pathway for each case can be related to the oxidation state of the metallic specie of the oxide used in connection with hematite.
9:00 AM - OO3.08
Modulated Synthesis of Mesoporous Zirconium Metal-Organic Frameworks with Large Cavity, High Stablity and New Topology
Muwei Zhang 1 Ying-Pin Chen 1 2 Hong-Cai Zhou 1 2
1Texas Aamp;M University College Station USA2Texas Aamp;M University College Station USAShow Abstract
Metal-Organic Frameworks (MOFs) have gained a tremendous amount of attention in the past few decades. Due to the tunable nature of their ligand geometry, their enormous surface area and their large gas uptake capacities, MOFs are widely applied in many areas such as gas storage, gas separation, CO2 capture, catalysis, drug delivery, sensors, photosensitive materials and magnetic materials. However; it is still problematic to construct MOFs with large porosity, high stability and good crystal quality, while many potential MOF applications require them to possess those properties simultaneously. Typically, in order to attain larger pore sizes and surface areas, researchers attempt elongation of MOF constructional units. However, this will often inherently undermine the framework stability and crystallinity and increase the possibility of framework interpenetration. Additionally, recent research indicates that the crystal size, quality and morphology can largely affect the surface area of the resulting MOFs.
The MOFs based on the ultrastable zirconium polyoxo clusters have demonstrated their excellent stability toward air, water, or even concentrated acid. Even though a limited number of Zr MOFs were published, many of them suffer from a low crystallinity and limited pore sizes. In this work, a series of non-interpenetrated zirconium MOFs were synthesized from a group of tetrahedral ligands via a modulated synthesis strategy. All of them possess new MOF topologies, large cavities and high crystal quality. Two categories of polymorphic MOFs can be identified and their isostructural MOFs were obtained by using elongated analogous ligands. Remarkably, PCN-525 has largest surface area, pore size (up to 25Å) and solvent accessible volume (up to 84.10%) among all the MOFs constructed from tetrahedral ligands. It is one of the rare examples of mesoporous Zr MOFs with three dimensional channels. PCN-522 is the first MOF that contains two distinctive Zr-based clusters, which has an unprecedented 4, 12, 12-connected topology that incorporates tetrahedra, cuboctahedra and icosahedra in the same network. This work provides both insights into novel framework topologies with tetrahedral building units and a practical method of constructing MOFs with large pore size and high stability.
9:00 AM - OO3.10
Multifuncitonal GdPO:Ln3+ (Ln = Ce3+, Pr3+) Nanocrystals with UV Emission and Magnetic Properties
Junsang Cho 1
1Korea Research Institute of Chemical Technology Daejeon Republic of KoreaShow Abstract
Multifunctional materials combine more than one imaging modality such as optical imaging, X-ray computed tomography (CT), positron emission tomography (PET), and magnetic resonance (MR) imaging contained in single vehicle. In particular, optical imaging provides its high resolution in bio-imaging and MR imaging offers excellent anatomical depth, non-invasive, and real time monitoring. Thus, a lot of attentions had been paid to the development for the multifunctional nanomaterials combining the two representative modalities such as optical and MR imaging, especially for application in biomedical applications.
It is worth noting that lanthanide-doped (Ln3+) nanoparticles serves as an alternative to conventional luminescent labels such as organic dye, QDs for application in biological medical imaging due to its advantageous characteristics such as low toxicity, high resistance to photo-bleaching and photochemical degradation. Moreover, the luminescence features of lanthanide ions also include high quantum yield, large stoke shift, abundant energy level transitions, narrow emission band width, and long fluorescent life time.
In recent, Gd3+-based inorganic nanomaterials has attracted much interest because they could be used as potential multifunctional platform. It was well known that a paramagnetic nature of Gd3+ ion arising from seven unpaired electrons in 4f electron shell could be utilized as contrast agents for T1-enhanced MR imaging owing to their enhancement of relaxation of the neighboring protons. In addition, by doping light-emitting various lanthanide ions (Ln3+) into a Gd3+-containing host matrix, novel materials possessing both advantages of fluorescent and magnetic properties could be achievable for multimodal imaging. For the research of optical imaging on the multifunctional GdPO4 nanoparticles, the research has been extensively studied only in visible range. There have been no reports on multifunctional GdPO4 nanoparticles having both UV emission and MR properties, which could be potentially used as alternative multifunctional nanoprobes. The understanding of optical properties of Ce3+, Pr3+ and Gd3+, having electronic configuration in UV spectral domain in inorganic compounds is of great important due to the potential technological applications as imaging, lithography, and optical data recording. Thus, nanoparticles with both UV emission and magnetic resonance properties could open new area of biomedical technology.
In this report, we present a general strategy for the synthesis of GdPO4 nanorods and nanoparticles doped with Ln3+ (Ln3+ = Ce3+, Pr3+) having strong UV emission and magnetic property. We explain multifunctional property change when crystal phase and structure change from hexagonal GdPO4 nanorods to monoclinic GdPO4 nanoparticle after calcination at 900 degrees Celcius , which could be potentially applied as MR imaging contrast agent.
9:00 AM - OO3.11
The Preparation of Metal-Doped Monoclinic VO2 Nanoparticles in NIR Blocking Thermochromic Film with Enhanced Transparency
Ba Ryong An 1 Seung Yup Jeon 2 Gun-Dae Lee 1 Seong Soo Park 1
1Pukyong National University Busan Republic of Korea2CFC Teramate Busan Republic of KoreaShow Abstract
Thermochromic smart film, typically based on VO2 nanoparticles, has received particular interest because it can intelligently modulate the amount of near-infrared ray by changing from transparent state at low temperature to reflective state at high temperature, while maintaining visible transmittance. This film is promising for application in building and automotive glasses to increase energy efficiency.
In this study, we demonstrated that hydrothermal process used to prepare metal-doped VO2(M) nanopowder with a special emphasis on calcination condition and novel solution process used to prepare transparent, stable and flexible VO2(M) based film. Monoclinic VO2(M) nanopowder was obtained from vanadium pentoxide and oxalic acid by controlling hydrothermal and calcination conditions. By further increasing calcinations temperature to about 700°C for 2 h with N2 gas during calcinations step, VO2(A) was transformed only to VO2(M). Due to the small band gap between VO2(A) and rutile-type VO2(M), VO2(A) would directly be transferred to stable VO2(M). Metal doping led to decrease phase-transition temperature from 68°C to 35°C. Metal-doped VO2(M) nanoparticles based film could exhibit a large change of NIR transmittance for phase-transition temperature than bare VO2 based film.
9:00 AM - OO3.13
Atomic Structure of Decagonal Al-Cu-Me (Me = Co, Rh, Ir) Quasicrystals
Pawel Kuczera 1 2 Janusz Wolny 2 Walter Steurer 1
1ETH Zurich Zurich Switzerland2AGH - University of Science and Technology Krakow PolandShow Abstract
The structure refinement of three decagonal phases: Al-Cu-Co, Al-Cu-Rh, Al-Cu-Ir will be presented . The synchrotron diffraction experiments were performed at the Swiss - Norwegian beam line at ESRF, Grenoble, France. All three decagonal phases show ~4 Å periodicity (two atomic layers per period). A computer program SUPERFLIP , based on the charge-flipping algorithm, was used for the initial phasing of the data and obtaining the electron density maps. These maps were used for deriving a Rhombic Penrose Tiling (RPT) model with a tiling edge-length of ~17 Å. The decoration of the unit tiles is based on the ~33 Å cluster proposed by Hiraga & Oshuna . The decoration of RPT with Hiraga clusters is such, that the cluster centers form the Pentagonal Penrose Tiling of an edge-length of ~20 Å. The Hiraga cluster can be considered as a supercluster built of 5 clusters proposed by Deloudi et al. . Such a structure explains well the strong Patterson peaks of ~ 12 Å, ~20 Å, and ~32 Å occurring for all three phases. The structure refinement was performed in the real space using the so-called Average Unit Cell approach. This method allows a purely 3D optimization of a quasicrystalline structure and has been previously used for a variety of decagonal pahses in the Al-Ni-Co system [5-7]. Our work shows the first solution of a quasicrystal as a ternary alloy (Rh and Ir phases). The final R-values are reasonable, the structure is consistent with TEM images and the chemical composition agrees well with the EDX measurements.
 P. Kuczera, J. Wolny, W. Steurer, Acta Crystallogr. B 68 (2012) 578.
 L. Palatinus, G. Chapuis, J. Appl. Crystallogr. 40 (2007), 786.
 K. Hiraga, T. Ohsuna, K.T. Park, Phil. Mag. Lett. 81 (2001), 117.
 S. Deloudi, F. Fleischer, W. Steurer, Acta. Crystallogr. B 67 (2011), 1.
 P. Kuczera, J. Wolny, F. Fleischer, W. Steurer, Philos. Mag. 91 (2011), 2500.
 P. Kuczera, B. Kozakowski, J. Wolny, W. Steurer, J. Phys. Conf. Ser. 226 (2010), 012001.
 J. Wolny, B. Kozakowski, P. Kuczera, H. Takakura, Z. Kristallogr. 223 (2008), 847.
9:00 AM - OO3.14
Polarization Rotation in a Monoclinic Perovskite BiCo1-xFexO3
Kengo Oka 1 Tsukasa Koyama 2 Tomoatsu Ozaki 2 Shigeo Mori 2 Yuichi Shimakawa 3 Masaki Azuma 1
1Tokyo Institute of Technology Yokohama Japan2Osaka Prefecture University Osaka Japan3Kyoto University Uji JapanShow Abstract
A piezoelectric ceramic Pb(Ti1-xZrx)O3 (PZT) is widely used for various applications such as transducer and sensors. PZT shows a maximum piezoelectric property at composition around x = 0.5, the boundary separating the tetragonal (Ti-rich) and the rhombohedral (Zr-rich) phases in the phase diagram. This boundary is known as a morphotropic phase boundary (MPB). The origin of the enhanced piezoelectric property at MPB is explained as follows. There exist a monoclinic phase with a radic;2a × radic;2a × a unit cell where a was the cubic perovskite lattice parameter, and Cm symmetry at MPB composition at low temperature. The lack of symmetry axis in the monoclinic structure allows the rotation of the ferroelectric polarization vector between the polar axes of the tetragonal and the rhombohedral phases. Such a polarization rotation is induced by application of electric filed leading to the enhancement of the piezoelectric constant. However, the polarization rotation has never been observed experimentally.
In this study, we show the presence of polarization rotation in BiCo1-xFexO3 (x ~ 0.7). BiCoO3-BiFeO3 system attracts attention as a candidate lead-free piezoelectric material because of the similarity of the phase diagram to that of PZT. The crystal structure as determined by powder synchrotron X-ray diffraction (SXRD) was the same as that of the low temperature phase of PZT at the MPB. Composition and temperature induced second order structural transition from tetragonal to monoclinic structures was observed. The structural change was accompanied by a rotation of the polarization vector from  to  directions of a pseudo cubic cell. This is the first observation of the polarization rotation in a monoclinic perovskite.
9:00 AM - OO3.15
Pb-Cr Charge Transfer in Pb1-xSrxCrO3
Runze Yu 1 Kengo Oka 1 Hajime Hojo 1 Masaichiro Mizumaki 2 Akane Agui 3 Daisuke Mori 4 Yoshiyuki Inaguma 4 Masaki Azuma 1
1Tokyo Institute of Technology Yokohama Japan2Japan Synchrotron Radiation Research Institute Sayo Japan3Japan Atomic Energy Agency Sayo Japan4Gakushuin University Toshima JapanShow Abstract
PbCrO3 had long been considered as a boring antiferromagnetic cubic perovskite. However, the lattice constant of 4.01Å is considerably larger than that of Sr2+Cr4+O3 and Cr3+ is expected from bond valence sum. Furthermore, pressure induced volume collapse of 9% was recently found. To clarify its mysterious nature we prepared pure PbCrO3 and Pb1-xSrxCrO3 samples, and systemically studied their physical properties. The temperature dependence of paramagnetic susceptibility indicated that the actual valence of Cr is +3 for pure PbCrO3, contrarily to +4 for Cr of the previous reports . Meanwhile a pressure induced insulator to metal phase transition was observed for PbCrO3 around 3GPa, which should be attributed to the electronic configuration change of Cr from t2g3 to t2g2. We thus proposed a new oxidation state of Pb2+0.5Pb4+0.5CrO3 like Bi3+0.5Bi5+0.5NiO3  with disordered arrangement of Pb2+ and Pb4+ which was confirmed by X-ray photoelectron spectroscopy (XPS). An intermetallic charge transfer between Pb4+ and Cr3+ leads to the Pb2+Cr4+O3 state under pressure. A distinct volume drop was found for Pb1-xSrxCrO3 at around x=0.3 where insulator to metal phase transition was also observed, suggesting the valence change of Cr ion from 3+ to 4+ which was confirmed by O-K edge X-ray absorption spectroscopy(XAS). Based on the above result