Symposium Organizers
Terry M. Tritt Clemson University
George S. Nolas University of South Florida
Yuri Grin Max-Planck Institute for Chemical Physics of Solids
Jeff Sharp Marlow Industries, Inc.
LL1: Thermoelectrics: General
Session Chairs
Monday PM, November 29, 2010
Commonwealth (Sheraton)
10:30 AM - **LL1.1
Structure and Aims of Recent Thermoelectric Programs in Germany.
Harald Boettner 1
1 TES, Fraunhofer IPM, Freiburg Germany
Show AbstractIt is obvious that worldwide activities in thermoelectrics do increase significantly. Thus J. Goldsmid (ICT 2010) expected an upcoming golden decade for thermoelectrics.In contrast to the consequent support for thermoelectrics in USA starting with the implementation of RTG's as power source for space research the activities in thermoelectrics in Germany were on a rather limited level.In recent years the situation did change completely driven by topics energy efficiency, waste heat recovery, miniaturized devices, stand alone sensor systems, and in particular nanoscale material science for thermoelectrics. To strengthen the basic physical and chemical knowledge on different nanoscale thermoelectric approaches the German DFG "German research society" is funding since middle 2009 a priority program "Nanoscale thermoelectrics". In addition, based on a proposal named HoTT (High Temperature Thermoelectrics) the BMBF (Federal Ministry of Education and Research) launched a program at the beginning of 2010 called "Thermopower", which acts as an umbrella for 11 applied oriented projects.Both programs cover different aspects from basic research, material science and industrial application.In this survey structure and content of the programs will be reported including interdependencies. Additional information on current EU-FP7 funded projects will be given.
11:00 AM - **LL1.2
The Department of Energy/National Science Foundation Partnership on Thermoelectric Devices for Vehicle Applications.
John Fairbanks 1 , C. Thomas Avedisian 2 , Theodore Bergman 3
1 Vehicle Technologies Program, US Department of Energy, Washington, District of Columbia, United States, 2 Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, New York, United States, 3 Department of Mechanical Engineering, University of Connecticut, Storrs, Connecticut, United States
Show AbstractThe Department of Energy's (DOE's) Vehicle Technologies Program (VTP) has a long history of supporting research and development to utilize thermoelectric generator (TEG) technology for waste heat recovery in automotive systems. Such devices might be installed within the exhaust system of a vehicle to convert the energy within the hot combustion products into high-grade electrical power. In this way thermoelectric devices could allow for smaller alternators and reduced engine load that would increase fuel economy.The long term goal is to improve fuel economy by 10 percent. The emphasis on DOE’s efforts to this end have been to fund development and manufacturing by industry-led teams through a number of Cooperative Agreements (e.g., with BSST, Ford, Visteon and BMW; GM, GE, Delphi, and Marlow; Michigan State University, NASA, JPL, and Cummins). Some of these efforts have led to production prototype TEGs for heavy duty diesel trucks and commercial transportation vehicles (i.e., the Ford Fusion and the BMW X-6 and Series 5 vehicles). The 1st generation TEG's developed by these teams are anticipated to provide a nominal 5 percent improvement of highway fuel economy, which would be achieved by reducing the alternator load by a third. The complete elimination of the alternator by converting waste heat to electricity through thermoelectric means calls for a more integrated approach that rests upon a highly-linked set of interdisciplinary challenges that involve not only materials development but bridging across system levels through interfaces, heat sink design and convective and radiative processes. To this end, the DOE and the National Science Foundation (NSF) have partnered to develop a jointly funded program at a level of $3M/year with equal shares from DOE and NSF. From 6 to 9 teams would be selected with university PIs as the lead. This partnership is intended to exploit the complementary missions of NSF and DOE to promote new discovery through research and development, and deployment and commercialization. The deliverables will include the critical understanding and technology improvements that are required to make viable the efficient conversion of waste heat in automotive exhaust systems to electricity. The intent is to ensure focus on commercially viable materials. The NSF procurement cycle began with a Letter of Intent (LOI) that led to selection of 6 to 9 proposals for funding. A brief summary of the selected projects will be presented. Also, the status of development of the 1st generation TEG's for Ford, BMW and GM will be presented.
11:30 AM - LL1.3
Progress on Thermoelectric Generator Development for Automotive Exhaust Gas Waste Heat Recovery.
Gregory Meisner 1
1 Chemical Sciences & Material Systems Lab, GM Global R&D, Warren, Michigan, United States
Show AbstractGeneral Motors Global R&D has an ongoing research program to develop advanced thermoelectric (TE) technology for automotive waste heat recovery, and we have made significant progress on constructing a working prototype automotive TE generator (TEG). The modeling for the design of our prototype TEG was based on exhaust gas characteristics of a GM production vehicle using the Federal Test Procedure for urban and highway drive cycles. The design was optimized by minimizing the cost per watt of electrical power generated averaged over the drive cycle using the properties of known state of the art TE materials and modules, estimates of the various material and fabrication costs, and the performance of the heat exchanger. The fabrication and assembly of the prototype has been completed, and it has been installed on a test vehicle, which included completion of all the exhaust system modifications, incorporation of a bypass valve system, and installation of the required controls and integration electronics. Data from the TEG sensors and TE module outputs have now provided important preliminary data for the operation of the mechanical, thermal, and electrical systems of the TEG in combination with the various vehicle systems; including exhaust bypass valve controls, thermocouples, gas and coolant flow and pressure sensors, and the TE output voltage and electrical power. Our recent results on this functioning TEG will be presented. Essential to the long term success of TEGs for production vehicles is continued new TE materials research and the development of those materials into robust and high performance TE modules. Our work in this area includes Skutterudite-type materials systems, and some of those results will also be presented. GM gratefully acknowledges funding from the U.S. Department of Energy in support of this work.
11:45 AM - LL1.4
Bottom-up Strategy Towards Thermoelectric Materials With Nano-scale Domains.
Anuja Datta 1 , J. Paul 1 , A. Popescu 1 , L. Woods 1 , G. Nolas 1
1 Department of Physics, University of South Florida, Tampa, Florida, United States
Show AbstractA two-step bottom-up strategy was implemented in preparing bulk thermoelectric nanocomposites. The approach involved composition and size controlled syntheses of thermoelectric materials as nanocrystals by facile solution based processes followed by densification into bulk pellets by Spark Plasma Sintering (SPS). Synthesis approaches were selected based on the effectiveness of yielding organics free nanocrystals in large quantity. Densification of nanocrystals by SPS contributed to the uniform distribution of nano-scale domains in the bulk matrix material that also preserved the nanostructures. Doping of the nanocrystals allowed for modifications of the bulk carrier concentrations. Electronic and thermal transport properties of the nanocomposites were evaluated and indicated enhancement in the thermoelectric properties as compared to that of bulk materials. The bottom-up strategy was investigated in the context of research into cost-effective, scalable, and reproducible materials preparation approaches towards improving the thermoelectric properties of existing materials.*This work is supported by the U.S. Army Medical Research and Materiel Command under Grant No. W81XWH-07-1-0708 and the National Science Foundation under Grant Nos. CBET-0932526 and CMMI-0927637.
12:00 PM - **LL1.5
Rapid Solidification Methods for Fabrication of Novel Thermoelectric Materials.
Xinfeng Tang 1 , Wenjie Xie 1 2 , Han Li 1 , Yonggao Yan 1 , Qingjie Zhang 1 , Ctirad Uher 3 , Terry Tritt 2
1 State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan, Hubei, China, 2 Department of Physics and Astronomy, Clemson University, Clemson, South Carolina, United States, 3 Department of Physics, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractThe development of novel preparation technique about high-performance thermoelectric materials with nanostructure is of great significance to the commercial applications. In this research, we developed a new synthesis route that is melt spinning combined with spark plasma sintering technique (MS-SPS) to rapidly prepare nanostructured thermoelectric materials. Using this synthesis route, we have prepared p-type Bi-Sb-Te bulk materials with some special nanostructures (such as amorphous structure, fine nano-crystalline, quasi-coherent structure and so on) by MS-SPS. This system show very low thermal conductivity while they possess good electrical transport properties, and therefore ZTmax reaches 1.56 at 300 K. The nanostructured Bi-Sb-Te bulk materials show a very high compressive strength which is double of zone-melting samples. Moreover, we also prepared nanostructured n-type Yb0.3Co4Sb12+y bulk materials and InxCeyCo4Sb12 compounds with evenly dispersed nano-InSb (10 ~ 80 nm) second phase on the boundaries. More importantly, compared with traditional method, the preparation time of filled Skutterudite by using MS-SPS can be notably reduced from 10 days to less than 40 hours. The ZTmax reaches 1.45 at 800 K for n-type In0.15Ce0.15Co4Sb12 compound prepared by MS-SPS technique.
12:30 PM - LL1.6
Quasi-ballistic Heat Transfer from Metal Nanostructures on Sapphire.
Austin Minnich 1 , Gang Chen 1
1 Mechanical Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractQuasi-ballistic phonon transport, where heat transfer is not diffusive and does not obey Fourier's law, has been theoretically predicted to occur when length or time scales become comparable to the phonon mean free path or relaxation time. Understanding this regime of heat transport is of fundamental interest, as the manner in which the heat transport deviates from Fourier's law reveals important information about the distribution of phonon mean free paths. This distribution is still not known with certainty even in crystalline silicon. Transient thermoreflectance is a common experimental technique to study heat transfer with sub-picosecond resolution using femtosecond laser pulses; however, the minimum size of the heated region is fundamentally restricted to the diffraction-limited spot size. In this work, we fabricate arrays of aluminum dots on sapphire with diameters as small as 50 nm to act as light absorbers rather than the usual continuous metal film. In this way, we obtain a spatial resolution far below the diffraction limit and comparable to the phonon mean free paths in sapphire. We show that ballistic phonons play a critical role in the heat transfer at these length and time scales. We expect this technique will prove useful to analyzing phonon mean free paths in bulk and nanostructured thermoelectric materials.
12:45 PM - LL1.7
High-performance Thermoelectric Cooling Modules Based on Advanced Bulk Nanostructured Materials.
Chris Caylor 1 , Jonathan D'Angelo 1 , Lon Bell 2 , Zhifeng Ren 3 , C. Chen 4
1 , GMZ Energy, Waltham, Massachusetts, United States, 2 , BSST, Irwindale, California, United States, 3 , Boston College, Chesnut Hill, Massachusetts, United States, 4 , Teledyne, Thousand Oaks, California, United States
Show AbstractThe development of nanostructured bulk bismuth telluride alloys, which exhibit high thermoelectric performance compared to state-of-the-art materials, will enable the fabrication of high heat flux cooling devices capable of operating with a coefficient of performance greater than two. GMZ Energy, Boston College, BSST and Teledyne are working to bring these devices to fruition based on increased materials performance, minimizing device parasitics (such as electrical and thermal contact resistances) and utilizing micro-machining device fabrication techniques. The status of these important aspects will be reported.
LL2: Skutterudites/Clathrates and Skutterudites
Session Chairs
George Nolas
James Salvador
Monday PM, November 29, 2010
Commonwealth (Sheraton)
2:45 PM - LL2.1
Mechanical and Elastic Property Evaluation of n and p-Type Skutterudites.
James Salvador 1 , Jung Cho 1 , Jihui Yang 2 , Andrew Wereszczak 3 , Hsin Wang 3
1 Chemical Sciences and Materials Systems Laboratory, GM Global Research, Warren, Michigan, United States, 2 Electrochemical Energy Research Laboratory, GM Global Research, Warren, Michigan, United States, 3 Materials Science and Technology Division, Oakridge National Lab, Oakridge, Tennessee, United States
Show AbstractSkutterudites have emerged as a front-runner for applications in medium to high temperature thermoelectric based waste heat recovery. Skutterudites offer a great compromise of good thermoelectric performance and mechanical and chemical stability as well as being composed of relatively abundant and benign starting materials. In this contributed talk we will discuss the mechanical and elastic properties of these compounds and the materials processing steps used to obtain them. Fracture strength was determined at room and elevated temperatures using a custom made three-point bend ceramic test fixture capable of rapid sample analysis at elevated temperatures while providing an environment isolated from ambient atmosphere. The results will be discussed in terms of module design and resulting durability under operating conditions.
3:00 PM - **LL2.3
Are Skutterudites Phonon Crystals or Phonon Glasses?
Jihui Yang 1 , Xun Shi 2 , Hsin Wang 4 , Miaofang Chi 4 , James Salvador 1 , Jiong Yang 2 , Shengqiang Bai 2 , Wenqing Zhang 2 , Lidong Chen 2 , John Copley 3 , Juscelino Leao 3 , John Rush 5
1 , GM R&D Center, Warren, Michigan, United States, 2 , Shanghai Institute of Ceramics, Shanghai China, 4 , Oak Ridge National Lab, Oak Ridge, Tennessee, United States, 3 NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 5 , University of Maryland, College Park, Maryland, United States
Show AbstractOver the past decade the Phonon-Glass-Electron-Crystal concept has played an important role in the understanding and design of highly efficient thermoelectric materials. Caged compounds such as skutterudites and clathrates, with occupied voids, have been assumed to be phonon-glasses with low lattice thermal conductivity but there has been no direct experimental evidence to confirm this hypothesis, and the idea has recently been challenged. In this presentation we present a combined inelastic neutron scattering, scanning transmission electron microscopy, and thermoelectric properties study of selected multiple-filled skutterudites with partial void occupancy. Our results unambiguously show that these materials exhibit phonon-glass behavior, due to the combined effects of sufficiently random spatial distribution and wide-spectrum phonon scattering by the filler atoms, which behave as phase-incoherent Einstein oscillators. These factors result in minimum lattice thermal conductivity and remarkable thermoelectric performance.
3:30 PM - LL2.4
Temperature-dependent Thermal Expansion and Elastic Moduli of Skutterudite Thermoelectric Materials.
Robert Schmidt 1 , Eldon Case 1 , Bradley Wing 1 , Rosa Trejo 2 , Edgar Lara-Curzio 2 , E. Payzant 2 , Roberta Peascoe-Meisner 2 , Edward Timm 3
1 Materials Science Engineering, Michigan State University, East Lansing, Michigan, United States, 2 High Temperature Materials Laboratory, Oak Ridge National Laboratory, Oak Ridge, Kentucky, United States, 3 Mechanical Engineering, Michigan State University, East Lansing, Michigan, United States
Show AbstractPowder processed specimens of antimony-based skutterudite thermoelectric material were hot pressed and cut into specimens by diamond saw. SEM micrographs of polished surface, thermally etched surface, and fractured surface were used to determine the microstructure of the densified specimens. The thermal expansion coefficient was determined from room temperature to 723K using a ThermoMechanical Analyzer (TMA) and by x-ray diffraction. The temperature dependent elastic moduli were measured by Resonant Ultrasound Spectroscopy (RUS) from room temperature to 773K. Using the elasticity and thermal expansion data, the thermally induced stresses may be estimated as a function of temperature.
4:15 PM - LL2.5
Electron-phonon Interactions in AE-Ga-(Ge,Si) Clathrates (AE=Sr and Ba).
Katsumi Tanigaki 1 2 , Jingtao Xu 1 , Jun Tang 1 , Khuong Huynh 2 , Yoichi Tanabe 1 , Satoshi Heguri 2
1 WPI, Tohoku University, Sendai Japan, 2 Physics, Graduate of Science, Tohoku University, Sendai Japan
Show AbstractRattling phonons have so far been the priority researches in clathrates as the issues of acoustic phonon scattering as well as electron-phonon interactions for enhancing effective mass of conduction electrons in controlling physical properties. The former can help for suppressing heat conductivity in keeping high electric conductivity and the latter contribute increasing Seebeck coefficient, and therefore these factors make clathrate compounds one of the very promising materials for high efficient thermoelectric conversion with a large dimension less figure of merit. These unique phonons are produced via anharmonic motions of the atomic elements endohedrally accommodated inside the polyhedra in clathrate structure, and therefore should be discussed in comparison with lattice phonons and intra-cluster phonons [1-3]. Among clathrate compounds, AE-Ga-Ge ternary system clathrates (AE=Sr, Ba, Eu) have been drawing much attention because the carrier concentration can be controlled nearly in the semiconducting regime and thus provide a relatively large S coefficient, and heat conductivity can be smaller by showing a glass-like behavior when the small elements are accommodated. In this talk we have elucidate how large the electron-phonon interactions when rattling anharmonic phonons are involved using single crystals with various carrier concentrations[4-5]. We will present the accurate effective masses for both SGG (AE=Sr) and BGG (AE=Ba) using heat capacity measurements in a wide range of energy scale. Our analyses ambiguously show that the electron-phonon interaction can be enhanced when the anharmonic rattling phonon is involved. In addition, we discuss the origin of glass-like behavior in AE-Ga-(Ge,Si) clathrates from the experiments obtained by core-level soft X ray spectroscopy in a high energy facility.[1] K. Tanigaki, et al., Nature Materials, 2, 653 (2004). [2] T. Rachi, K. Tanigaki et al., Chem. Phys. Letters, 409, 48 (2005). [3] T. Rachi, K. Tanigaki et al., Phys. Rev. B, 72, 144504 (2005). [4] J. Tang, T. Rachi, K. Tanigaki et al., Phys. Rev. B, 78, 085203 (2008).[5] J. Tang, K. Tanigaki et al., Chem. Phys. Lett. 472, 60 (2009).
4:30 PM - LL2.6
Thermal Transport in Cage-like Structures.
Mona Zebarjadi 1 , Keivan Esfarjani 1 , Boris Kozinsky 3 , Jian Yang 2 , Zhifeng Ren 2 , Gang Chen 1
1 Mechanical Engineering, MIT, Cambridge, Massachusetts, United States, 3 Research and Technology Center, Robert Bosch LLC, Cambridge, Massachusetts, United States, 2 Physics Department, Boston College, Chesnut Hill, Massachusetts, United States
Show AbstractThe relation between the thermal conductivity of cage like structures with crystal parameters are investigated using a two dimensional toy model. The model consists of host atoms on a rectangular lattice with fillers at the center of each rectangle. The thermal conductivity is calculated by using Green- Kubo equilibrium molecular dynamics simulations. It is generally believed that the smaller and the heavier the filler, the lower is the thermal conductivity. We show that the thermal conductivity decreases with atomic displacement parameter while it has local minima versus filler mass. Similar trends were observed in experiments on skutterudites. The trends are explained by analyzing the effect of the filler on the phonon dispersion and relaxation times of the host material. Our study shows that it is very important to include the correct band dispersion (group velocities) to get the right features of the thermal conductivity. To demonstrate this further, the mean free paths of real skutterudite materials are calculated and the results of the Debye+ Einstein model are compared with those of the first principle calculations and the experimental data.
4:45 PM - LL2.7
Multiple Filler Skutterudites: CezInxYbyCo4Sb12 Posses High Figure of Merit.
Jennifer Graff 1 , Song Zhu 2 , Timothy Holgate 1 , Jiangying Peng 3 , Jian He 2 , Terry Tritt 2
1 Material Science and Engineering, Clemson University, Clemson, South Carolina, United States, 2 Physics and Astronomy, Clemson University, Clemson, South Carolina, United States, 3 School of Mechanical Science & Engineering, Huazhong University of Science & Technology, Wuhan China
Show AbstractSkutterudites have been approached in the last decade as one of the future state of the art materials which have motivated research on the concept of energy conversion, or more specifically the field of thermoelectrics. The ability to tune a skutterudites electrical and thermal transport properties have been proven successful in single-filled, double-filled, and multiple-filled skutterudites. This article will focus on multiple-filled skutterudites, CezInxYbyCo4Sb12 (0 ≤ (x, y, z) ≤ 0.2). Indium was attempted to be inserted as a filler but results seem to indicate that it is substituting on the Sb sites. The samples were prepared via melt-annealing-sintering technique and were characterized by X-ray powder diffraction, thermal and electrical transport properties, specific heat, Hall coefficients, scanning electron microscopy within the temperature range of 10-800K. Results from the thermoelectric property measurements indicate a high ZT over a temperature regime of approximately 500-800K as well as a maximum ZT of 1.4 around 800K.
5:00 PM - LL2.8
Thermoelectric Properties of Double-filled Skutterudite Thin Films Grown by Pulsed Laser Deposition.
Sarath Kumar 1 , Ahmed Alyamani 2 , J. Graff 3 , Terry Tritt 3 , Husam Alshareef 1
1 Materials Science and Engineering, KAUST, Thuwal Saudi Arabia, 2 Nanotechnology Centre, King Abdul Aziz City for Science and Technology, Riyadh 11442 Saudi Arabia, 3 Department of Physics and Astronomy, Clemson University, South Carolina 29634, South Carolina, United States
Show AbstractIn the present work, we report the growth of In0.2Yb0.2Co4Sb12 double filled skutterudite thin films onto SiO2, MgO and Si/SiO2 substrates by pulsed laser deposition under different conditions. Grazing incidence X-ray diffraction of the films have revealed that single phase skutterudite films are formed only under optimized conditions of deposition, at a substrate temperature of 525 K. Raman spectroscopy studies have been performed to confirm the formation of the skutterudite phase. It has been observed that the presence of argon during deposition results in formation of predominant secondary phases. The surface morphology of the films has been analyzed using atomic force microscopy and transmission electron microscopy. The Seebeck coefficient and electrical resistivity of the films on different substrates have been measured in the temperature range 300-1200 K using the Ozawa Seebeck tester. The Seebeck coefficient of the films was negative indicating n-type conduction. It has been observed that the electrical conductivity and the absolute Seebeck coefficient of the films increase with increase in temperature. A respectable power factor of 4 µW/K2.cm has been obtained. Furthermore, strategies to enhance the power factor are discussed.
5:15 PM - LL2.9
Transport Properties of Partially-filled Single Crystal Type II Si Clathrates.
Stevce Stefanoski 1 , George Nolas 1
1 Physics, University of South Florida, Tampa, Florida, United States
Show AbstractInorganic clathrates are "open-structured" materials in which a covalently bonded frameworks enclose metal atoms in atomic cage-like polyhedra. Intermetallic clathrates are actively investigated because of their potential for thermoelectric applications. Thus far clathrates with the type I and VIII crystal structure have been investigated, while a more systematic investigation of the physical properties of type II clathrates has yet to be undertaken. Moreover, to get a better understanding of the intrinsic properties of these materials, investigations on single crystals is ideal. In this work we present structural and transport properties of single crystal type II "partially filled" Si clathrates. Whereas fully filled Na24Si136 clathrates show metallic behavior, a metal-to-insulator transition is expected upon reducing the Na content below 33 % of full filling. This approach may offer a potentially new direction in the search for novel materials for thermoelectric applications.
5:30 PM - LL2.10
Different Physical Properties in n/p-type Ba8Ga16Ge30.
Jingtao Xu 1 , Jun Tang 1 , Hitoshi Heguri 2 , Yoichi Tanabe 1 , Katsumi Tanigaki 1 2
1 WPI AIM-Research, Tohoku University, Sendai Japan, 2 Department of Physics, Tohoku University, Sendai, Miyagi, Japan
Show AbstractClathrate compounds have attracted much attention as potential thermoelectric materials because of the low thermal conductivity and the large thermopower. Among a large number of clathrate types, type I clathrates M8Ga16Ge30 (M = Ba, Sr, and Eu) have been most extensively explored. The unit cell consists of two Ga-Ge dedecahedra and six tetrakaidecahedra, which can accommodate two and six M guest atoms, respectively. When the size of guest atoms decrease from Ba to Eu, the thermal conductivity is greatly suppressed and changes from a crystal-like behavior to a glass-like behavior. So far, all samples of Eu8Ga16Ge30 (EGG) and Sr8Ga16Ge30 (SGG) are of n-type except for Ba8Ga16Ge30 (BGG). The change of carrier type in BGG results in completely different thermal conductivity. The thermal conductivity of the n-type sample has a pronounced peak at about 20 K, as in a typical crystalline material. On the other hand, the thermal conductivity of the p-type sample shows glass-like behavior, being similar to that for EGG and SGG. This glass-like behavior in EGG and SGG is believed to originate from the tunneling effect of the off-centered guest atoms. However, further neutron diffraction studies on n/p-type BGG single crystals showed that the differences in thermal conductivity do not result from different off-centered displacement of the guest atoms. Therefore, the reason for the different behaviors remains to be one of the most curious questions in clathrate compounds. In this presentation, we will discuss the important physical parameters useful for having reasonable explanations, based on our XPS, transport and susceptibility measurements. [1] J. Tang, R. Kumashiro, J. Ju, Z. Li, M. A. Avila, K. Suekuni, T. Takabatake, F. Guo, K. Kobayashi, K. Tanigaki, Chemical Physics Letters, 472, 2, 6-64, (2009).[2] J. Tang, T. Rachi, R. Kumashiro, M. A. Avila, K. Suekuni, T. Takabatake, FZ. Guo, K. Kobayashi, K. Aoki and K. Tanigaki, Phys. Rev. B, 78, 085203-085206 (2008).
5:45 PM - LL2.11
Lattice Thermal Transport from First-principles: Role of Higher Order Phonon Processes.
Dmitri Volja 1 , Boris Kozinsky 2 , Jivtesh Garg 1 , Nicola Marzari 1 , Marco Fornari 3
1 DMSE, MIT, Cambridge, Massachusetts, United States, 2 Research and Technology Center, ROBERT BOSCH LLC, Cambridge, Massachusetts, United States, 3 Department of Physics, Central Michigan University, Mount Pleasant, Michigan, United States
Show AbstractThermal transport is a fundamental quantity in the field of thermoelectricity. Accurate theoretical prediction of thermal conductivity is crucial for design of new highly efficient thermoelectric materials. In the most promising systems heat is primarily carried by the lattice vibrations, and anharmonicinteractions are responsible for the finite thermal conductivity. Within density-functional perturbation theory one can, in principle, evaluate completely ab-initio these phonon interactions. However, for most materials evaluation of such interactions from first-principles is currently a formidable task. In this work we analyze third order phonon-phonon scattering mechanisms that arise from the anharmonicity of interatomic interactions, and use a Boltzmann transport approach to estimate thermal conductivity. In our methodology we combine first-principles determination of interatomic force constants with empirical models potentials to calculate higher order response terms. The scheme is extended further within perturbation theory to evaluate numerically four-phonon processes. We validate this approach by testing the approximations in simple systems like silicon, where full evaluation of anharmonic force constants from first principles is possible. Finally, we apply the approach to optimize performance of complex thermoelectric materials, such as skutterudites.
Symposium Organizers
Terry M. Tritt Clemson University
George S. Nolas University of South Florida
Yuri Grin Max-Planck Institute for Chemical Physics of Solids
Jeff Sharp Marlow Industries, Inc.
LL3: Nano Thermoelectrics/Thermoelectrics Theory & Phenomenon
Session Chairs
Tuesday AM, November 30, 2010
Commonwealth (Sheraton)
9:30 AM - LL3.1
Simplified Thermoelectric Figure of Merit Calculations for Semiconducting Nanowires.
Jane Cornett 1 , Oded Rabin 1 2
1 Materials Science and Engineering, University of Maryland, College Park, Maryland, United States, 2 Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland, United States
Show AbstractBy confining a material to a one-dimensional nanowire, the resulting discretization of the density of states function and decreased lattice thermal conductivity due to increased phonon scattering leads to an increase in the thermoelectric figure of merit (ZT). In 1993, Hicks and Dresselhaus reported ZT calculations for one-dimensional Bi2Te3 assuming a one-subband model [1]. Here, we have developed a simplified model for calculating transport properties as a function of nanowire radius for a more realistic multiple-subband system. This method, which can be applied to any single-carrier materials system, requires little more than transport property calculations using a two-subband model. We have applied this model, which approximates both power factor (σS2) and ZT as the product of their single-subband value and the maximum Number of Nearly-Degenerate Subbands (NNDS), to room temperature n-type indium antimonide nanowires. For comparison, we also report calculations done assuming the full electronic band structure and find excellent agreement between the two models. Surprisingly, the power factor increases between the radii of 15 and 100nm due to the substantial increase in degeneracy of subbands with wire radius. We recover the expected monotonic increasing ZT with confinement due to a decrease in the lattice thermal conductivity. 1.Hicks, L.D. and Dresselhaus, M.S., Thermoelectric figure of merit of a one-dimensional conductor. Physical Review B, 1993. 47(24): p. 16631-16634.
9:45 AM - LL3.2
Analysis of Nanostructure Generation and Evolution in Thermoelectric PbTe - PbS.
Steven Girard 1 , Jiaqing He 2 , Jeffrey Doak 2 , Chris Wolverton 2 , Vinayak Dravid 2 , Mercouri Kanatzidis 1
1 Department of Chemistry, Northwestern University, Evanston, Illinois, United States, 2 Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractOf great importance in thermoelectric research is the synthesis of nanostructured materials in order to reduce lattice thermal conductivity and enhance thermoelectric figure-of-merit. The PbTe – PbS materials system has been demonstrated as a model nanostructured thermoelectric due to controllable phase separation that naturally produces kinetically- and thermodynamically- stable nanoscale precipitates. As a result, these materials exhibit low values of lattice thermal conductivity. However, previous reports show generation of a wide range of particle sizes as a result of the annealing conditions that allow coarsening of particles between 2 nm – 5 μm. Here, we will provide a detailed analysis of nanostructure generation and evolution in the PbTe – PbS system. Selective annealing studies will aim to pinpoint the onset of generation and coarsening of nanostructures. In conjunction with detailed properties measurements, microscopy, and first-principles modeling, we hope to address the effect of size and dispersion of PbS nanostructures within PbTe on thermoelectric properties.
10:00 AM - **LL3.3
Enhancing the Performance of Thermoelectrics by Nanostructures.
Mildred Dresselhaus 1 , Gang Chen 2 , Zhifeng Ren 3
1 EECS and Physics, MIT, Cambridge, Massachusetts, United States, 2 Mechanical Engineering, MIT, Cambridge, Massachusetts, United States, 3 Physics, Boston College, Chestnut Hill, Massachusetts, United States
Show AbstractThe performance of thermoelectric materials has been steadily improving through the incorporation of nanostructures into bulk samples. Strategies for carrying out this process together with strategies for controlling interfaces and dopants are discussed. Results of enhanced performance will also be presented.
10:30 AM - LL3.4
Novel Approaches in Thermionic Energy Conversion by Molecular Charge Transfer from Diamond Thin Films.
Franz Koeck 1 , Jeff Sharp 2 , Robert Nemanich 1
1 Department of Physics, Arizona State University, Tempe, Arizona, United States, 2 , Marlow Industries, Dallas, Texas, United States
Show AbstractThermionic energy conversion relies on efficient electron sources which can sustain significant emission current densities at the operating temperature. Utilizing nanostructured diamond based electron emitters a low thermionic emission barrier can be engineered by introduction of dopants, control of surface band bending and negative electron affinity (NEA) surface characteristics. For NEA diamond emitters the vacuum level is located below the conduction band minimum, eliminating a surface barrier for emission. We have prepared nanostructured, nitrogen doped NEA diamond films by plasma assisted chemical vapor deposition. Thermionic emission from this material can be detected below 250 °C corresponding to a low effective work function of ~ 1.3 eV. Exposure of the film surface to suitable gaseous species can result in efficient charge transfer from emitter conduction band to the affinity level of the gas molecule through a tunneling process evidenced by a strong increase in electron emission current density. In a thermionic converter configuration enhancement of charge transfer from emitter to collector could thus significantly improve converter performance. We present results for thermionic energy conversion utilizing nanostructured, nitrogen doped diamond emitter and similar collector structures separated by a micron size gap. Operating the emitter at a temperature of 500 °C while maintaining a vacuum gap established an open circuit voltage of ~ 0.4 V. Introducing hydrogen between emitter and collector resulted in a increase in the open circuit voltage to ~ 0.5 V. In addition, a significant increase in power output was observed under hydrogen ambient with a concurrent shift of maximum power output toward lower load resistance. This research is supported by the Office of Naval Research.
11:15 AM - LL3.5
Which Phonon Mean Free Paths Carry the Heat in Bulk and Nanostructured Materials?
Fan Yang 1 , Chris Dames 1
1 Mechanical Engineering, University of California, Riverside, Riverside, California, United States
Show AbstractReducing the lattice thermal conductivity through boundary scattering requires nanostructures with characteristic lengths that are comparable to or smaller than the mean free paths (MFPs) of the phonons in a bulk sample. Thus it is essential to have good models for this distribution of bulk MFPs. Here we derive these MFP distributions for several well-established phonon models including Callaway1, Debye-Callaway-Morelli (DCM)2, Holland3, and Born von Karman (BvK)4. Given the distribution of MFPs for an arbitrary bulk model, the corresponding thermal conductivity of a nanostructure is obtained through a simple integral transformation. This transformation is also applied to bulk results obtained from molecular dynamics simulations5. Using silicon as an example, all of these models1-5 are in excellent agreement with bulk experiments, but most (particularly Holland and Callaway) show significantly worse agreement for nanostructures6. The most successful models for nanostructures are found to be the BvK, molecular dynamics, and DCM (above 200 K), because their dispersion and phonon-phonon scattering laws result in a broad distribution of bulk MFPs. These results highlight the importance of long phonon MFPs, and the potential for thermal conductivity reduction even in relatively large nanostructures. 1J. Callaway, Physical Review 113, 1046 (1959).2D. T. Morelli, J. P. Heremans, and G. A. Slack, Physical Review B 66, 195304 (2002).3M. G. Holland, Physical Review 132, 2461 (1963).4G. Chen, Journal of Heat Transfer 119, 220-229 (1997).5A. S. Henry and G. Chen, Journal of Computational and Theoretical Nanoscience 5, 141 (2008).6D. Li, Y. Wu, P. Kim, L. Shi, P. Yang, and A. Majumdar, Applied Physics Letters 83, 2934-2936 (2003).
11:30 AM - **LL3.6
Enhancing Thermoelectricity in Composites by Density of States Modifications and Nanostructuring.
Lilia Woods 1
1 Physics, University of South Florida, Tampa, Florida, United States
Show AbstractExploring different routes to enhance the thermoelectric performance of various materials is a quest that is being pursuit for applications in energy harvesting. I will present some results investigating the possibilities of improving the power factor by the combined effect from introducing additional carrier scattering mechanisms and modifications in the electronic structure. The additional carrier scattering will be due to nanostructuring from nanoinclusions or granular interfaces, while the electronic structure changes will be from localized distortions due to resonant impurities. Interesting relations between the interplay of the two effects and possibilities for optimizing the thermoelectric transport will be shown. Experimental results for transport properties of PbTe composites will also be presented and explained in terms of charge carrier characteristics. Acknowledgement: Supported by NSF-CBET-0932526. In collaboration with A. Popescu, A. Datta, and G.S. Nolas.
12:00 PM - LL3.7
Crystal and Electronic Structure of AgPbmSbTe2+m Type Nanocomposites: First-principles Study.
Yi Zhang 1 , Xuezhi Ke 2 , Changfeng Chen 1 , Jihui Yang 3 , Paul Kent 4
1 Physics Department, University of Nevada, Las Vegas, Las Vegas, Nevada, United States, 2 Physics Department, East China Normal Univeristy, Shanghai China, 3 Electrochemical Energy Research Lab, General Motors R&D Center, Warren, Michigan, United States, 4 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractWe study the crystal and electronic structure of nanocomposites AgPbmSbTe2+m (LAST), AgPbmBiTe2+m (LABT), NaPbmSbTe2+m (LNST), and NaPbmBiTe2+m (LNBT) using first-principles density function theory calculations. We examine the ground state structures of impurity and nanocluster models within 2x2x2, 3x3x3, and 5x5x5 supercells and determine the electronic band structures and density of states. We find that as the size of the supercell increases, the impurity states induced by paired monovalent and trivalent dopants in the band gap in the 2x2x2 supercell disappear in the 3x3x3 supercell. Moreover, when the supercell is increased to 5x5x5 with nanoclusters included, we obtain a new split state at the conduction band minimum while the valence band top is only slightly changed. As a result, the trivalent dopants (Sb,Bi) play a more important role in manipulating the band structure of the PbTe-type nanocomposites. Our results provide an explanation for measured electronic transport properties of the PbTe-based thermoelectric materials.
12:15 PM - LL3.8
Observation of the Spin-Seebeck Effect in a Semiconductor.
Christopher Jaworski 1 , Jing Yang 2 , Shawn Mack 3 , David Awschalom 3 , Joseph Heremans 1 4 , Roberto Myers 2
1 Department of Mechanical Engineering, The Ohio State University, Columbus, Ohio, United States, 2 Department of Material Science, The Ohio State University, Columbus, Ohio, United States, 3 Center for Spintronics and Quantum Computation, University of California, Santa Barbara, Santa Barbara, California, United States, 4 Department of Physics, The Ohio State University, Columbus, Ohio, United States
Show AbstractThe spin-Seebeck effect, recently discovered in the metallic ferromagnet permalloy1, consists of a thermally generated spin distribution that is experimentally realized by utilizing the inverse spin Hall effect (ISHE). We experimentally reproduced this effect in a ferromagnetic semiconductor, GaMnAs, which allows for greater experimental flexibility. In particular, we explore both the magnetic anisotropy and temperature dependence through the magnetic phase transition. Using the ISHE, we measure a transverse voltage that depends on longitudinal position, following approximately a sinh(x) relation. The spatial distribution of spin-currents is maintained across electrical breaks, highlighting the local nature of the effect, which is therefore ascribed to a change in the statistical distribution between the up and down polarized spin-carriers induced by the temperature gradient. This is the spin analog of the conventional thermoelectric power ("charge-Seebeck" effect), which is an electric field induced by a redistribution of the charge-carriers.1 Uchida, K., et al., Nature 455, p 778, (2008)
12:30 PM - LL3.9
Computational Design of Materials with Enhanced Thermoelectric Efficiencies.
Joo-Hyoung Lee 1 , Jeffrey Grossman 1
1 Materials Science and Engineering, MIT, Cambrdige, Massachusetts, United States
Show AbstractThe main goal in thermoelectric (TE) research is to increase the TE figure of merit, ZT, by which the efficiency of TE materials is described. Since ZT=S2σ/κ, where S is the Seebeck coefficient, σ and κ the electrical and thermal conductivity, respectively, ZT can be increased either by reducing κ or by enhancing S2σ. κ can be significantly reduced through nanostructuring of materials which increases phonon scattering, and considerable advances have been made along this direction using semiconductor nanostructures such as nanowires and superlattices. On the other hand, S2σ, power factor, can be enhanced by tailoring the density of states (DOS) such that it is rapidly varying near the Fermi level, but this approach is challenging due to the need to preferentially control the DOS. In this work, based on a combination of classical and quantum mechanical calculations we describe novel strategies to achieve these goals: specifically, we will discuss our work on the prediction of high ZT in nanoporous semiconductors [1,2] and highly mismatched alloys (HMAs) [3]. We show that nanometer-sized pores in semiconductors can greatly decrease κ arising from increased phonon scattering, leading to a sharp enhancement in ZT. A number of effects that play a role in such nanoporous mateirals, such as strain and defects, will be discussed. Regarding the power factor, we explore the use of HMAs for thermoelectric applications; HMAs are known to provide control over the DOS due to a mismatch in electronegativity between isoelectronic constituents, and have been studied for a number of optoelectronic applications. In this work, we will show that TE properties can be greatly improved in HMAs due to the DOS restructuring.[1] J.-H. Lee, J. C. Grossman and G. A. Galli, Nano Lett., 8, 3750 (2008).[2] J.-H. Lee and J. C. Grossman, Appl. Phys. Lett., 95, 013106 (2009).[3] J.-H. Lee, J. Wu and J. C. Grossman, Phys. Rev. Lett., 104, 016602 (2010).
12:45 PM - LL3.10
Core-shell Silicon Carbide-transition Metal Silicide Thermoelectric Ensembles.
Dieter Gruen 1 , Paola Bruno 1 , Marshall Mendelsohn 1 , Jules Routbort 2 , Dileep Singh 2 , Paul Redfern 1 , Larry Curtiss 1
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Energy Systems, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractAs part of an ongoing study of the thermoelectric properties (TEP) of transition metal silicide/silicon carbide ensembles, we have synthesized Ni2Si/6H SiC composites by compressing fine-grained powders into discs in a SPS apparatus. The mole fraction composition of the powders was: Ni2Si (11%), SiC (85%), B4C (3%), Al4C3 (1%). During compaction the pressure is held constant at 50MPa while the temperature is ramped from ambient to 1700K over a period of 20 minutes. Rapid densification begins at 1400K, at least 200 degrees lower than for pure SiC, presumably because of the presence of Ni2Si which melts congruently at 1582K. The discs must have considerable porosity since their density is 2.62 g/cm3 which is 72% of theoretical density calculated on the basis of the composition given above. Nevertheless, extensive covalent bonding between Ni2Si and SiC as a result of SPS processing appears to have taken place as evidenced by the fact that the discs require cutting by a diamond saw for fabrication into shapes appropriate for various measurements. This remarkable material has an electrical conductivity of 100 S/cm that decreases slowly with temperature while the thermopower is essentially temperature invariant at -25 microV/K in the range 500-1100K. XRD, Raman, SEM and EDAX data will be presented to show that no new phases have been created as a result of the processing even though the mechanical properties of the material point to the occurrence of interfacial reactions leading to liquid phase mediated sintering. Although not completely homogeneous, one may picture the ensemble as composed principally of particles of SiC surrounded by shells of Ni2Si. To gain insight into the origins of the TEP of the ensembles will require extensive experimental as well as theoretical work. The TEP of doped SiC and transition metal silicides have been extensively studied individually but, as far as we can determine, not in combination with each other. It is well known that Ni2Si forms ohmic contacts with 6HSiC. However, the degree to which the electronic structures of the two materials are modified by their mutual interactions or by individual dopant and dopant levels is not known. Such knowledge is a prerequisite to obtaining a full understanding of what one might call “quantum proximity effects” that could be crucial to determining the thermoelectric behavior of complex nanomaterials. Our approach to this problem has been to do density functional cluster calculations using methods described in our earlier publications. In that way we have shown that Al and B substitutions in SiC lead to very substantial lowering of HOMO-LUMO separations. Here we plan to present additional molecular cluster analogue calculations on mixed SiC-Ni2Si clusters aimed at investigating proximity effects. The overall goal of the theoretical work is to obtain insight to help guide the design of ensembles with optimized TEP.Work for USDOE/BES #DE-AC02-06CH11357
LL4: Lead Chalcogenides/Half-Huesler Alloys
Session Chairs
Tuesday PM, November 30, 2010
Commonwealth (Sheraton)
2:30 PM - LL4.1
Temperature-dependent Elastic Moduli of PbTe-PbS Thermoelectric Materials.
Jennifer Ni 1 , Eldon Case 1 , Ryan Stewart 1 , Rosa Trejo 2 , Edgar Lara-Curzio 2 , Edward Timm 3 , Chun-I Wu 4 , Timothy Hogan 4 , Steven Girard 5 , Mercouri Kanatzidis 5
1 Chemical and Material Science Engineering, Michigan State University, East Lansing, Michigan, United States, 2 High Temperature Materials Laboratory , Oak Ridge National Laboratory , Oak Ridge, Tennessee, United States, 3 Mechanical Engineering, Michigan State University, East Lansing, Michigan, United States, 4 Electrical Engineering, Michigan State University, East Lansing, Michigan, United States, 5 Chemistry, Northwestern University, Evanston, Illinois, United States
Show AbstractSpecimens of (Pb0.95Sn0.05Te)0.92(PbS)0.08-0.055% PbI2 were powder processed from ingots and densified by hot pressing and pulsed electric current sintering (PECS). The temperature dependent Young’s modulus, shear modulus, and Poisson’s ratio of the densified specimens were measured by resonant ultrasound spectroscopy (RUS) for temperatures from 293 K up to 663 K. While the Young’s modulus and shear modulus decrease monotonically with increasing temperature, the Poisson’s ratio was relatively constant over the entire temperature range. The implications of the temperature-dependence of elasticity on the stress analysis of thermoelectric modules fabricated from PbTe-PbS will be discussed.
2:45 PM - LL4.2
Simultaneously Optimizing the Independent Thermoelectric Properties in (Ti,Zr,Hf)(Co,Ni)Sb Alloy by In-situ Forming InSb Nanoinclusions.
Wenjie Xie 1 2 , Jian He 1 , Song Zhu 1 , Xianli Su 2 , Shanyu Wang 2 , Tim Holgate 1 , Jennifer Graff 1 , Joseph Poon 3 , Xinfeng Tang 2 , Qingjie Zhang 2 , Terry Tritt 1
1 Department of Physics & Astronomy, Clemson University, Clemson, South Carolina, United States, 2 State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan, Hubei, China, 3 Department of Physics, University of Virginia, Charlottesville, Virginia, United States
Show AbstractWe report an induction-melting spark-plasma-sintering synthesis process of the nanocomposite material composed of (TiZrHf)(CoNi)Sb coarse grains and in situ formed InSb nanoinclusions that occur primarily on the grain boundaries. We were able to qualitatively control the amount of InSb nanoinclusions by varying the In and Sb contents in the starting materials. The effects of the nanoinclusion formation and the matrix–nanoinclusion boundaries on the thermoelectric properties have been studied and correlated. In particular, the nanoinclusion-induced electron injection and electron filtering mechanisms helped to simultaneously decrease the resistivity, enhance the Seebeck coefficient and reduce the thermal conductivity of the nanocomposite. A figure of merit of ZT~0.5 was attained at 820 K for the sample containing 1 at.% InSb nanoinclusions, which is a 160% improvement over the sample containing no nanoinclusions. The experimental results are discussed in the context of the effective medium model formerly proposed by Bergman and Fel.
3:00 PM - LL4.3
Enhanced Thermoelectric Properties of In-situ Synthesized Half-Heusler/ HfO2 Nanocomposites.
Girija Chaubey 1 , Julien Makongo 1 , Yuan Yao 1 2 , Dinesh Misra 1 , Pierre Poudeu 1 2 , John Wiley 1 2
1 Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana, United States, 2 Department of Chemistry, University of New Orleans, New Orleans, Louisiana, United States
Show AbstractIntroducing nanoparticles into thermoelectric (TE) materials has a favorable effect on enhancing thermoelectric properties. Homogeneous dispersion of nanoparticles into the matrix, however, remains a challenge. We report a novel route for the introduction of nanoparticles into the bulk thermoelectric materials using solution phase chemistry. HfO2 nanoparticles of average size 5 nm were grown in the presence of micron size of half-Heusler Hf0.75Zr0.25NiSn. TEM images show homogeneous dispersion of HfO2 nanoparticles into the half-Heusler Hf0.75Zr0.25NiSn matrix. This method has advantage over conventional mechanical mixing since homogeneous dispersion of nanoparticles was obtained throughout the TE matrix. The amount of HfO2 nanoparticles can be varied by controlling the initial feeding ratio of Hf-precursor with the existing matrix. The thermoelectric properties of the Hf0.75Zr0.25NiSn /HfO2 nanocomposite with different amounts of HfO2 nanoparticles as dispersants were measured from 300 K to 775 K. The synthesis technique as well as the electronic and transport properties will be discussed.
3:15 PM - LL4.4
Morphological Evolution of Ag2Te Precipitates in Thermoelectric PbTe.
Jessica Lensch-Falk 1 , Joshua Sugar 1 , Michelle Hekmaty 1 , Douglas Medlin 1
1 Materials Physics, Sandia National Laboratories, Livermore, California, United States
Show AbstractNanostructuring of thermoelectric materials is expected to enhance thermoelectric properties by reducing the thermal conductivity and improving the power factor from that of homogeneous bulk materials. In multiphase, nanostructured thermoelectric materials, an understanding of precipitation mechanisms and phase stability is crucial for engineering systems with optimal thermoelectric performance. In this presentation we will discuss our investigations of the morphological evolution, orientation relationship, and composition of Ag2Te precipitates in PbTe using transmission electron microscopy (TEM) and atom probe tomography (APT). Annealing in the region of two phase equilibrium between Ag2Te and PbTe results in the formation of monoclinic β-Ag2Te precipitates as determined by x-ray and electron diffraction studies. These precipitates are aligned to the PbTe matrix with an orientation relationship that aligns the Te sub-lattices in the monoclinic and rock salt structures. This relationship is the same as we have reported earlier for β-Ag2Te precipitates in rocksalt AgSbTe2. Observations using TEM and APT suggest that the Ag2Te precipitates initially form as coherent spherical precipitates which upon coarsening evolve into flattened semi-coherent disks along the <100>PbTe directions which is consistent with theoretical predictions for elastically strained precipitates in a matrix. Our HRTEM observations show that sufficiently small precipitates are coherently embedded, while larger precipitates exhibit misfit dislocations and multiple monoclinic variants to relieve the elastic strain. Analysis of the composition of both precipitate groups using APT indicates that the larger precipitates exhibit compositions close to equilibrium while the smaller nanoscale precipitates exhibit enhanced Pb compositions. This detailed analysis of the orientation relationship, morphology, composition, and coarsening behavior of embedded Ag2Te precipitates may be helpful in understanding the precipitation mechanisms and microstructure of related thermoelectric materials, such as LAST.
3:30 PM - LL4.5
Efficient Thermoelectric Materials from PbS Composite Materials.
Simon Johnsen 1 , Mercouri Kanatzidis 1
1 Department of Chemistry, Northwestern University, Evanston, Illinois, United States
Show AbstractMany efficient thermoelectric materials are tellurium based. The scarcity of tellurium in the Earth’s upper crust can become problematic if thermoelectric materials were to reach mass markets. Hence there is a continuous need for research in new efficient thermoelectric materials made from abundant and cheap elements.PbS is a narrow band gap (~0.4 eV) semiconductor, which match these criteria. PbS show promising electronic properties, but high thermoelectric performance is inhibited by a significant lattice thermal conductivity.Recently it has been shown how precipitates of foreign phases in PbTe can dramatically reduce the lattice thermal conductivity at little cost to the electronic power factor, and consequently boost the thermoelectric figure of merit significantly.In this paper the addition of metal chalcogenides beyond their solubility limit in PbS are explored. Notably, the effect of the composite nature of these materials on the thermal and electronic transport is investigated.
4:15 PM - LL4.6
Simultaneous Reduction in Thermal Conductivity and Enhancement of Power Factor in High Performance n-type Zr0.25Hf0.75Ni1+xSn (0≤ x ≤0.1) Half-Heusler Alloys.
Julien Makongo 1 2 , James Salvador 3 , Dinesh Misra 1 2 , Pierre Poudeu Poudeu 1 2
1 Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana, United States, 2 Department of Chemistry, University of New Orleans, New Orleans, Kentucky, United States, 3 Chemical Sciences and Materials Systems Laboratory, General Motors R&D Center, Warren, Michigan, United States
Show AbstractRecently, we showed a change from semiconducting to semimetallic to metallic character upon partial filling vacant sites in bulk Zr0.25Hf0.75NiSn half-Heusler (HH) alloy with elemental Ni [1]. The optimum concentration of Ni inclusion necessary to achieve the highest power factor was located between ~3 to 4% and a strong reduction in the lattice thermal conductivity was observed for the composite with 10 wt.% Ni inclusion [1]. In this work, we explore the thermoelectric performance of “Ni-rich” half-Heusler alloys with general composition Zr0.25Hf0.75Ni1+xSn prepared by high temperature solid state reaction of the elements followed by spark plasma sintering. The electronic and thermal transport properties were measured in the temperature range from 300 to 775K. All Zr0.25Hf0.75Ni1+xSn (0≤ x ≤0.1) compositions show n-type semiconducting behavior. A marginal decrease in the electrical conductivity and drastic increase of the thermopower from -150 μV/K for x = 0 to -250 μV/K for x = 0.02 was observed at 300K. This results in a large increase in the power factor. Simultaneously, a sharp reduction of the total thermal conductivity from 5 W/mK (x = 0) to 4 W/mK (x = 0.02) was observed at 775K. The drop in the total thermal conductivity is attributed to the reduction of its lattice component due to nanostructuring in bulk Zr0.25Hf0.75Ni1.02Sn alloy. The simultaneous increase in power factor and drop in the total thermal conductivity results in a sharp increase of the figure of merit, ZT, from 0.2 (x = 0) to 0.7 (x = 0.02) at 775K. The effect of the nanostructuring on the thermoelectric performance of Zr0.25Hf0.75Ni1+xSn half-Heusler alloys will be discussed by combining transmission electron microscopy studies with electronic charge transport and thermal conductivity data. [1] J.P.A. Makongo, D. Misra, J. Salvador, N.J. Takas, K.L. Stokes, H. Gabrisch, P.F. P. Poudeu, Mat. Res. Soc. Symp. Proc., 1267-DD05-12, 2010.
4:30 PM - **LL4.7
Fabrication, Microstructure and Properties of Half-heusler Thermoelectric Materials.
Tie-Jun Zhu 2 1
2 State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou China, 1 Materials Science and Engineering, Zhejiang University, Hangzhou China
Show AbstractMNiSn(M = Ti, Zr, Hf) based half-Heusler alloys have recently been developed as novel high temperature thermoelectric materials with a maximum ZT value of ~0.8 at about 1000K. (Hf,Zr)NiSn based alloys are conventionally fabricated by arc melting followed by long time annealing for improved homogeneity. We applied a combination of levitation melting and spark plasma sintering processing to prepare a series of Hf1-xZrxNiSn1-ySby (x=0.00, 0.25, 0.40, 0.50) alloys. Single phased ingots were obtained after levitation melting for only a few minutes and good thermoelectric properties were achieved. To further reduce the thermal conductivity, melt spinning was applied to refine grain sizes. In addition, M site doping by Y element and Y/Sb co-doping were investigated because theoretical calculation predicted that Yb/Sb co-doping would result in the formation of YSb nanodots in the half-Heusler matrix and enhanced Seebeck coefficient. Our experimental results show that no significant Seebeck enhancement can be found for the Y/Sb co-doped alloys. Some detailed information will be provided in the paper.
5:00 PM - **LL4.8
Endotaxial Nanostructuring in Lead Chalcogenide-based Materials and Thermoelectric Energy Conversion.
Mercouri Kanatzidis 1
1 Chemistry, Northwestern University, Evanston, Illinois, United States
Show AbstractSeveral novel nanostructured PbTe materials are under investigation and are promising for enhanced power factor and greatly reduced thermal conductivity. Coherent nanometer sized inclusions in a PbTe matrix (endotaxy) can serve as sites for scattering of acoustic phonons to lower the thermal conductivity. Innovative, convenient synthetic approaches used to create specific crystal structures and nanostructures will be presented. A new class of nanostructured bulk p-type thermoelectric material, SrxPbTe1+x doped with Na2Te, will be presented where the endotaxial nanostructures are capable of scattering phonons without scattering carriers.
5:30 PM - LL4.9
ZT Enhancement of Half-Heuslers by Ball Milling and Hot Pressing.
Xiao Yan 1 , Yucheng Lan 1 , Xiaowei Wang 2 , Jack William Simonson 3 , Joseph Poon 3 , Terry M. Tritt 4 , Hui Wang 1 , Weishu Liu 1 , Bed Poudel 2 , Dezhi Wang 1 , Gang Chen 5 , Zhifeng Ren 1
1 Physics, Boston College, Chestnut Hill, Massachusetts, United States, 2 , GMZ energy, Inc, Waltham, Massachusetts, United States, 3 , University of Virginia, Charlottesville, Virginia, United States, 4 , Clemson Univeristy, Clemson, South Carolina, United States, 5 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThe dimensionless figure of merit (ZT) in p-type half-Heusler bulk alloys has remained around 0.5 until recently. By ball milling alloyed bulk ingots into nanopowders and hot pressing them, we achieved a 62-89% ZT enhancement for p-type half-Heuslers, which is mainly due to the boosted Seebeck coefficient and partially due to the moderate reduction in the thermal conductivity. Peak ZT reaches 0.8 at 700 oC, 62% higher than that of the ingot. The effect of different ball milling times on the microstructure and thus on the thermoelectric properties was investigated in detail. Both low and high magnification SEM images show the trend of decreasing average grain sizes with increasing ball milling time, leading to the trend of decreasing thermal conductivities with longer ball milling time. Further improvement in ZT can be expected if average grain sizes can be inhibited down below 100 nm during press.
5:45 PM - LL4.10
Laser-deposition and Characterization of Amorphous Thermoelectric Films.
Garth Wilks 1 2 , Terry Murray 1 3 , Steven Fairchild 1 , Nicholas Gothard 1 4 , Jonathan Spowart 1
1 AFRL/RX, Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States, 2 , General Dynamics Corp., Dayton, Ohio, United States, 3 , University of Dayton Research Institute, Dayton, Ohio, United States, 4 , National Research Council, Washington, District of Columbia, United States
Show AbstractFrom the Efficient Cluster Packing model describing the topology of metallic glasses, it is understood that certain compositions are favored for glass-formability based on the ratio of atomic sizes between constituents. In this regard, the half-Heusler composition Zr0.5Hf0.5NiSn is nearly ideal. Although the crystallized form of this material has been widely studied because of its high thermoelectric power factor, it has been suggested that partial vitrification may enhance the thermoelectric figure of merit by preserving the favorable aspects of electronic structure while significantly disrupting thermal transport. Capitalizing on the high quench rates possible during pulsed laser deposition, a spectrum of thin films including amorphous and partially-amorphous duplex microstructures has been grown under various conditions. Transport characteristics relevant to the thermoelectric effect are rationalized in light of accompanying microstructure characterization.
LL5: Poster Session
Session Chairs
Yuri Grin
George Nolas
Jeff Sharp
Terry Tritt
Wednesday AM, December 01, 2010
Exhibition Hall D (Hynes)
9:00 PM - LL5.1
Thermoelectric Properties of the PbTe-CaTe System.
Kanishka Biswas 1 , Jiaqing He 1 2 , Guoyu Wang 3 , Ctirad Uher 3 , Vinayak Dravid 2 , Mercouri Kanatzidis 1 4
1 Chemistry, Northwestern University, Evanston, Illinois, United States, 2 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States, 3 Department of Physics, University of Michigan, Ann Arbor, Michigan, United States, 4 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractPbTe-based materials are promising for efficient heat energy to electricity conversion. We present studies on the synthesis, characterization and thermoelectric properties of the PbTe-CaTe system. X-ray diffraction patterns reveal that all the samples crystallize in the NaCl-type structure without noticeable secondary phase while transmission electron microscopy investigation indicates the presence of nanoprecipitate in the PbTe matrix. Na2Te doping in the PbTe-CaTe materials resulting in a positive sign of the Hall coefficients as well as of the Seebeck coefficients indicating p-type conduction. Thermal conductivity results as a function of CaTe concentration will be presented.
9:00 PM - LL5.10
Thermoelectric Properties of Pd:TCO Nanocomposites.
Otto Gregory 1 , Matin Amani 1 , Gustave Fralick 2
1 Chemical Engineering, University of Rhode Island, Kingston, Rhode Island, United States, 2 Sensors and Electronics Branch, NASA Glen Research Center, Cleveland, Ohio, United States
Show AbstractWide band gap semiconducting oxides having relatively large Seebeck coefficients, were co-sputtered with palladium to form optimized thin film nanocomposites. Relative to NiCoCrAlY based nanocomposites, the palladium based nanocomposites significantly improved the electrical conductivity of the resulting films at high temperature. Combinatorial chemistry techniques were used for rapid screening of the thermoelectric response. Towards this end, libraries containing hundreds of micro-thermocouples were used to determine the optimal Seebeck coefficient, resistivity, and power factor in the systems Pd:In2O3, Pd:SnO2, Pd:ITO, and Pd:ZnO. Based on the combinatorial chemistry results, select thermocouples having the optimum composition were fabricated and tested over the range 20°C to 1000°C and the power output of the resulting thermoelectric devices was determined using impedance matching techniques. The observed thermoelectric powers of these thin film nanocomposites were significantly greater than those observed for the bulk oxides such as ITO, In2O3, SnO2, and ZnO. These devices have large enough power factors to be considered for energy harvesting applications. For example, in the gas turbine engine environment where large temperature gradients exists between the tip and the root of turbine blades, thermoelectric devices could potentially be used to power active wireless sensors.
9:00 PM - LL5.11
Role of Atomic Ordering on Phononic Transport in Binary Alloys.
John Duda 1
1 , University of Virginia, Charlottesville, Virginia, United States
Show AbstractSubstitutional solid solutions that exist in both atomically ordered and disordered states will exhibit markedly different thermophysical properties depending on their exact crystallographic configuration. The transition from a disordered crystalline state to an ordered crystalline state in a binary alloy is marked by three signatures which effect thermophysical properties: the association of more than one atom per lattice point, a possible reduction in crystallographic symmetry, and a reduction in the volume of the first Brillouin zone. To investigate these phenomena, the role of the order-disorder transition on phononic transport properties of Lennard-Jones type binary alloys is explored via non-equilibrium molecular dynamics simulations. Several different ordering configurations are considered, and anisotropy is studied by applying thermal gradients along different crystallographic orientations.
9:00 PM - LL5.12
Mechanical Properties of SnTe, CuAlO2, and Fe2VAlxSi(1-x) Thermoelectric Materials.
Robert Schmidt 1 , Eldon Case 1 , Andrew Morrison 1 , Alexander Baumann 1 , Bradley Wing 1 , Ryan Stewart 1 , Chang Liu 1 , Donald Morelli 1 , Rosa Trejo 2 , Edgar Lara-Curzio 2 , Christopher Stender 3 , Mercouri Kanatzidis 3
1 Materials Science Engineering, Michigan State University, East Lansing, Michigan, United States, 2 High Temperature Materials Laboratory, Oak Ridge National Laboratory, Oak Ridge, Kentucky, United States, 3 Chemistry, Northwestern University, Evanston, Illinois, United States
Show AbstractStresses induced by a variety of mechanical and thermal mechanisms pose a severe challenge to the mechanical integrity of brittle materials, including most thermoelectrics. The analysis of such stresses requires knowledge of the mechanical properties of the material. However, the database of mechanical properties is extremely limited for most thermoelectric materials. In this study, we determined the hardness, elastic moduli, and fracture toughness of SnTe, CuAlO2, and Fe2VAlxSi(1-x) thermoelectric materials, where x = 0.8, 0.9, 0.97 and 1. For powder processed specimens of SnTe and CuAlO2¬, and arc melted Fe2VAlxSi(1-x) compounds, the hardness was determined by Vickers and nano indentation. The Young’s modulus, shear modulus, and Poisson’s ratio were determined by Resonance Ultrasound Spectroscopy (RUS) for the same set of specimens.
9:00 PM - LL5.13
CMOS(Complementary Metal Oxide Semiconductor)-compatibleSilicon Thermoelectric Device.
Young-Sam Park 1 , Moongyu Jang 1 , Myungsim Jun 1 , Younghoon Hyun 1 , Sung-Jin Choi 2 , Taehyoung Zyung 1 , Yil-Suk Yang 1 , Jong-Dae Kim 1
1 , ETRI, Daejeon Korea (the Republic of), 2 , KAIST, Daejeon Korea (the Republic of)
Show AbstractDue to energy shortage and climate crisis, thermoelectric devices have recently attracted much attention because they can convert waste heat energy into electrical energy without environmental pollution. Bi2Te3 is widely used as a thermoelectric material because of its high thermoelectric performance. As an indicator of the thermoelectric performance, ZT is used. The ZT value is directly proportional to electric conductivity and the square of Seebeck coefficient and is inversely proportional to thermal conductivity. Bi2Te3 has a ZT value of 0.7 at room temperature. However, thermoelectric devices based on Bi2Te3 are difficult to miniaturize. In addition, according to the late tendency of development and production of products employing Bi2Te3 thermoelectric devices, supplies of Bi2Te3 are predicted to face shortage, soon. On the contrary, silicon is easy to be miniaturized and has endless deposits. But, it has a very high thermal conductivity of about 150 W/mK and a ZT value of 0.01 at room temperature. Thus, silicon has been considered as improper material for thermoelectric applications. However, it has been reported that silicon nanowires grown by aqueous electroless etching method or superlattice nanowire pattern transfer method can reduce the thermal conductivity down to 0.01 times, thus giving ZT around 1. Therefore, silicon nanowires are expected as promising material for thermoelectric devices. However, difficulty and complexity in fabricating silicon nanowires hinder mass production in an actual production step.In this work, to solve the problems, silicon nanowire based thermoelectric devices were realized on 8-inch wafers using CMOS-compatible semiconductor processes. Silicon nanowires were patterned to be a minimum width of 50nm by using KrF lithography and O2 ashing technologies. Both N-type and P-type silicon nanowires were realized by ion implantation and thermal annealing processes. SIMS(secondary ion mass spectrometry) analysis was conducted to investigate the dopant concentration with silicon depth. Electrical conductivity of the silicon nanowires was obtained from I-V measurements.Because the resistance of platinum is well known to be directly proportional to temperature, platinum films were deposited on hot and cold sides as a heater and a temperature sensor. As an adhesion layer between the platinum and the silicon films, a titanium layer was added. The resistance of platinum was measured from room temperature to 200oC under high vacuum conditions (10-5 Torr). Temperature calibration was conducted to study the relationship between input and real temperatures. Temperature coefficient of resistance characteristics of platinum heaters was analyzed with heater thickness. Finally, thermal conductivity, Seebeck coefficient and ZT characteristics will be discussed in this presentation.
9:00 PM - LL5.14
Nanostructured Telluride Films on Macroporous Silicon for High Efficiency Thermoelectric Devices.
Hans Robinson 2 , Ofer Sneh 3 , Vladimir Kochergin 1
2 Physics, Virginia Tech, Blacksburg, Virginia, United States, 3 , Sendew Technologies, Boulder, Colorado, United States, 1 , MicroXact, Inc., Blacksburg, Virginia, United States
Show AbstractNanostructured thin films fabricated via MBE, sputtering or chemical vapor deposition techniques exhibit some of the largest values of the thermoelectric figures of merit (ZT) that have been reported to date. Unfortunately, these films are generally very costly to fabricate in sufficient thickness for practical devices, and in addition their integration and packaging pose significant challenges. We present a new device structure that overcomes these obstacles by growing the nanostructured films on the pore walls of macroporous silicon (MPSi). MPSi is fabricated by a non-lithographic process that gives rise to an extremely regular array of highly uniform pores, several microns across by up to several hundred microns deep, and with walls as thin as 100 nm. The MPSi structure provides a large vertically oriented surface area onto which thin films can be grown with a built-in substrate to provide mechanical stability. The silicon walls can also be made thin enough that their impact on device performance will be negligible.Modeling of these devices show that ZT as high as 2.2 is possible with a Bi2Te3/Sb2Te3 superlattice grown on MPSi walls, and as high as 4 in a Si/Ge quantum dot superlattice. We will also discuss initial experimental results from fabrication of ALD grown telluride films on MPSi as well as more detailed characterization of such films grown on flat substrates .
9:00 PM - LL5.15
Thermal Transport in Nanoporous Silicon and Nanoporous SiGe Alloys: Interplay Between Disorder at the Mesoscopic and the Atomic Scale.
Yuping He 1 , Davide Donadio 1 , Ivana Savic 1 , Giulia Galli 1 , Joo Hyoung Lee 2 , Jeffrey Grossman 2
1 , UC Davis, Davis, California, United States, 2 , MIT, Cambridge, Massachusetts, United States
Show AbstractWe present calculations of the thermal conductivity of nanoporous silicon (np-Si), and we show that it may attain values 10 to 20 times smaller than in bulk Si, for porosities and surface to volume ratios similar to those obtained in recently fabricated nanomeshes. Further reduction of almost an order of magnitude is abtained in thin film with thickness of 20 nanometers, in agreement with experiment. We find that in np-Si heat is mostly carried by non propagating, diffusive vibrational modes with mean free paths reduced by up to two orders of magnitude with respect to the bulk. Finally, we investigate how alloying effects may further decrease the thermal conductivity of group IV nanoporous materials. Work supported by DOE/SciDAC-DE-FC02-06ER25794
9:00 PM - LL5.16
Enhanced Thermoelectric Properties of Strongly Degenerate Polycrystalline Silicon upon Second Phase Segregation.
Dario Narducci 1 , Ekaterina Selezneva 1 , Gianfranco Cerofolini 1 , Elisabetta Romano 1 , Rita Tonini 2 , Gianpiero Ottaviani 2
1 Dept. of Materials Science, University of Milano Bicocca, Milano Italy, 2 Dept. of Physics, University of Modena and Reggio Emilia, Modena Italy
Show AbstractOver the last years, a research effort has been undertaken to qualify silicon for thermoelectric applications. Moving from the observation of the damping of phonon diffusivity in Si nanowires, investigations have addressed the possibility of increasing the thermoelectric figure of merit both by depressing the thermal conductivity through dimensional constraints and by enhancing the system power factor (PF) α2σ (where α is the Seebeck coefficient and σ is the electrical conductivity). Most of this research endeavour has been focused onto single-crystals. However, only high-demand critical applications such as electricity generation for the aerospace may directly benefit of devices based on single-crystal silicon. Instead, to recover waste energy Seebeck generators owe to be based on polycrystalline materials. The aim of this study was actually to verify whether polycrystalline Si films deposited on top of a SiO2 insulating layer can meet the requirements for thermoelectric generation. We focused on the analysis of factors controlling the PF in boron-doped polycrystalline thin films. Reliable polycrystalline material qualification is notoriously complicated by the moderate reproducibility of poly layers. To avoid such a shortcoming we prepared 450-nm thick heavily boron doped poly-Si layers, implanting boron in the film in excess of the boron kinetic solubility at 1000 °C. Isochronal thermal treatments were then used to modify the BSi content by precipitation. A concurrent increase of α and σ was observed for heat treatments above 850 °C. Upon annealing at 1000 °C a PF at 300 K of 0.13 mW K-2 cm-1 was obtained, almost a factor of two higher than previously reported PFs for heavily phosphorus-doped SOI. These results could be explained observing that in strongly degenerate polysilicon two effects concur. On one side, the formation of an impurity band, along with an increase of the BSi solubility threshold in poly-Si, shift the Fermi energy Ef in an energy range where the density of states g(E) displays abrupt changes, thus enhancing its log-derivative [dlog g(E)/dE]Ef. On the other side, segregation of boron-rich second phases triggers a mechanism of carrier filtering at borders controlling the energy-dependent carrier mobility μ(E). Thus, conditions are predictable under which both α, proportional to [dlog[μ(E)g(E)]/dE]Ef, and σ, proportional to μ(Ef)g(Ef), simultaneously increase – in accord with our experimental findings.We could therefore put forward evidence that poly-Si is not only of interest for the development of Seebeck and Peltier devices sharing low cost and relatively high efficiency – but that it also provides opportunities to test the role that grain borders can play in carrier filtering.
9:00 PM - LL5.17
Crystal Lattice Controlled SiGe Thermoelectric Materials with High Figure of Merit.
Hyun Jung Kim 1 , Yeonjoon Park 1 , Glen King 2 , Sang Choi 2
1 , National Institute of Aerospace, Hampton, Virginia, United States, 2 , NASA Langley Research Center, Hampton, Virginia, United States
Show AbstractThe Production of significant levels of electrical power via direct energy conversion cycles with an advanced Thermoelectric (TE) Power Generation System (TPGS) is desirable since thermoelectric power generation is applicable for both primary and waste heat sources. The energy harvesting system considered for TPGS is based on advanced thermoelectric (TE) materials with a targeted Figure of Merit (FoM) greater than can be achieved by state of the art superlattice SiGe structure. The development of a SiGe “twin lattice structure (TLS)” plays a key role in phonon scattering. In the case of a SiGe layer, the ability to control the epitaxial growth in order to make a [111]-oriented single crystalline SiGe layer or a [111]-oriented highly twinned SiGe layer (60°-rotated crystal) on c-plane sapphire was the key to lowering the thermal conductivity so that a higher figure of merit could be achieved. Several samples were fabricated varying the portion of single-crystalline phase such as 99%, 80%, 70%, 60%, and so on, which were analyzed by Electron backscatter diffraction (EBSD) and XRD. The characterization of microstructure and crystal orientation relationship of SiGe layers on c-plane sapphire were observed by cross-sectional Transmission Electron Microscopy (TEM) methods, such as Selected-Area-Electron Diffraction (SAED) patterns, High-Resolution TEM (HRTEM) and two-beam diffraction contrast imaging. The SiGe samples prepared for testing showed an electrical conductivity of 1140S/m at a temperature of 600°C and a charge mobility of 202cm2/V.s with p-type dopant such as boron of 5.6 x 1018cm-3 concentration. The thermal conductivity of the NASA-designed twin-lattice structured SiGe has not been measured yet, but can be lowered to 12mW/cm.K, due largely to the disordered stacking faults that impede and scatter phonon transmission. Therefore, an increased TE figure of merit may be achieved through the use of a SiGe twin lattice structure.
9:00 PM - LL5.18
Investigating the Coherent Phase Stability of the PbS-PbTe System Using First Principles Calculations.
William Counts 1 , Chris Wolverton 1
1 , Northwestern University, Evanston , Illinois, United States
Show AbstractNanoscale inhomogeneities in PbS-PbTe alloys may enhance thermoelectric properties of these materials. The phase diagram and coherent spinodal are key factors controlling these nanostructured morphologies. We study the coherent phase stability of PbS-PbTe using density functional theory based calculations, a mixed-space cluster expansion, and Monte Carlo simulations. (i) Our calculations correctly reproduce the phase separating tendency of the PbS-PbTe phase diagram. (ii) Strain energy calculations show that for this rocksalt-based system (100) is the elastically hardest direction and that (111) is the softest. (iii) The formation energies for the PbS-PbTe structures are of the same order as the strain energies suggesting that strain energy will significantly depress spinodal decomposition in this system.
9:00 PM - LL5.19
The Impact of Melt-spinning Process on the Microstructures and Thermoelectric Performance of (Bi,Sb)2Te3 : A Combined Neutron Scattering, Microscopy and Thermoelectrics Study.
Dale Hitchcock 1 , Wenjie Xie 1 2 , Mark Laver 3 , Hye-jung Kang 1 , Song Zhu 1 , Menghan Zhou 1 , Isaac Bredeson 1 , John R. D. Copley 4 , Craig Brown 4 , Xinfeng Tang 2 , Terry Tritt 1 , Jian He 1
1 Physics and Astronomy, Clemson University, Clemson, South Carolina, United States, 2 State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, Whuan, China, 3 Laboratory for Neutron Scattering, Paul Scherrer Institute, CH-5232, Villigen PSI, Switzerland, 4 Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractThe efforts of pursuing higher performance thermoelectric materials have culminated into a new paradigm, i.e., the nanocomposite materials (NTMs). In a number of occasions, the melt-spinning technique has proved very effective in generating rich multi-scaled nanostructures that are thermoelectrically favorable. Though it is widely accepted that the nanostructures cause the improved thermoelectric performance, to our best knowledge, it lacks a systematic study of the correlation between a specific type of nanostructure and a specific thermoelectric quantity. In this work, we have employed inelastic neutron scattering, small angle neutron scattering and electron microscopy in melt-spun-spark-plasma-sintered (MS-SPSed) (Bi,Sb)2Te3 samples prepared at different SPS temperatures. In particular, small angle neutron scattering has provided us with a needed tool to probe the global microstructural evolution in a bulk sample. A clear correlation has been established between the SPS temperatures, microstructural evolution and the change of thermoelectric properties. It was found that 10 - 20 nm nanocrystalline domains with coherent boundaries are the key constituents that account for the exceptionally low lattice thermal conductivity and minimal degradation of electrical properties. We note that the nanostructure of this kind has been formerly reported by several groups in the higher performance NTMs prepared by different methods.
9:00 PM - LL5.2
Artificially Structured ZnO/ZnO:Al and ZnS/ZnO Nanostructures as Model Systems for Thermoelectrics.
Peter Klar 1 , Gert Homm 1 , Florian Gather 1 , Steve Petznick 1 , Christian Heiliger 1 , Bruno Meyer 1
1 I. Physikalisches Institut, Justus-Liebig Universität, Giessen Germany
Show AbstractFrom a semiconductor perspective, the properties of ZnO and ZnS as II-VI semiconductors have been extensively studied. For example, the electronic band structures, the phonon structures and the band alignment in heterostructures are well understood, crystalline material can be grown by various methods on different substrates, methods for artificial structuring are well developed. This has motivated us to employ ZnO/ZnS and ZnO/ZnO:Al micro- and nanostructures as model systems for studying the effects of interface structures on the thermoelectric properties. Series of different bar-shaped samples consisting of lateral arrangements of either alternating ZnO:Al and ZnO stripes or ZnO and ZnS stripes were fabricated from rf-sputtered layers or epitaxial layers by microfabrication techniques followed by a second sputtering process. Throughout each series the number of interfaces between the two materials was varied whilst the material fractions within the bars were not altered. Lateral thermoelectric transport, i.e. Seebeck effect and electrical resistivity, were measured as a function of temperature for all series of samples and corresponding reference samples. The transport direction through the bar was perpendicular to the stripe direction, such that the electrons and phonons have to pass all interfaces. The transport coefficients of all series show a characteristic dependence on the number of interfaces between the materials. Such a characteristic dependence allows one to extract information about the extension of the interface region and the interface structure by modelling the dependence of the Seebeck coefficient and the resistivity of the series of samples on the basis of a network model.
9:00 PM - LL5.20
Predictive Model for the Seebeck Coefficient of Organic Materials.
Wijnand Germs 1 , Erik Roeling 1 , Michel van Maasakkers 1 , Barry Smalbrugge 2 , Rene Janssen 1 , Martijn Kemerink 1
1 Applied Physics, Eindhoven University of Technology, Eindhoven Netherlands, 2 COBRA Research Institute, Eindhoven University of Technology, Eindhoven Netherlands
Show AbstractThe use of inorganic materials for thermoelectric applications is clearly dominant over the use of organic materials for these applications. Though, the interesting feature of organic semiconductors is the high Seebeck coefficient and low thermal conductivity often found for these materials. So far, no consistent theory existed that describes both the charge transport and the Seebeck coefficient in organic materials. In addition to that, the measurement of the Seebeck coefficient on organic materials is complicated by the much higher sensitivity to leakage currents and contact resistances than the standard I-V measurements. By extending a variable range hopping model [1], we are able to predict the Seebeck coefficient from standard I-V measurements. This can be of great benefit in the search for suitable organic thermoelectric materials.In amorphous organic semiconductors the density of states can be described by localized states between which thermally assisted hopping takes place. The assumption of an exponential density of states in combination with percolation theory makes it possible to determine a transport level. Charge carriers have to use states close to this transport level in order to move through the material. We used the position of this transport level with respect to the Fermi level to predict the Seebeck coefficient. The measurements are performed on a pentacene thin film in a transistor configuration. To be able to measure the Seebeck coefficient directly, leakage currents were minimized by patterning the active material and the contact resistance was reduced by etching the adhesive Ti layer at the sides of the Au electrode. The Seebeck coefficient is determined by measuring the zero-current-potential difference between the source and drain electrodes at different temperature gradients. The gate electrode is used to vary the charge carrier density. We also developed an AC technique which uses a heating wire to apply an oscillating temperature gradient over the transistor. As a result the sinusoidal signal on the heating wire, the thermovoltage measured will also show a sinusoidal signal depending on the Seebeck coefficient.Measurements show a Seebeck coefficient for pentacene from 300 µV / K up to about 1000 µV / K, depending mainly on the charge carrier density. Both the values and trends are well described by the prediction made from the I-V measurements, the charge transport model and the resulting transport level. The above results suggest that this new technique can be used to look more easily for possible interesting organic thermoelectric materials.[1]Vissenberg and Matters, Phys Rev B 57, 12964 (1998).
9:00 PM - LL5.21
WITHDRAWN 12/21/10 Studies of Sputtered Metal Interlayers on Metallization of Bismuth Telluride Based Thermoelectric Materials.
Bo Yu 1 , Hui Wang 1 , Yucheng Lan 1 , Xiao Yan 1 , Bed Poudel 2 , James Caylor 2 , Shien-Ping Feng 3 , Gang Chen 3 , Zhifeng Ren 1
1 Physics, Boston College, Chestnut Hill, Massachusetts, United States, 2 , GMZ Energy Inc., Waltham, Massachusetts, United States, 3 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractNickel (Ni) has been conventionally used as the barrier layer between copper interconnects and both p- and n-type bismuth telluride based thermoelectric (TE) elements. However, when nickel barrier layer is deposited onto our nanostructured TE bulk materials prepared by ball milling and hot pressing, the adhesion becomes an issue probably because of small grain sizes. Sputtered metal interlayers were deposited here between the Ni barrier layer and TE materials to enhance the bonding strength. Furthermore, it was found that the rapid diffusion of Ni into TE materials which would degrade the performance of TE devices at elevated temperatures was slowed down by those interlayers. The diffusion depths of Ni under different interlayers were discussed in this study.
9:00 PM - LL5.22
Laser Sintering of High-temperature Silicon Germanium Thermoelectric Materials.
Tyson Baldridge 1 , Mool Gupta 1 2
1 Charles L. Brown Department of Electrical and Computer Engineering, University of Virginia, Charlottesville, Virginia, United States, 2 , National Institute of Aerospace , Hampton, Virginia, United States
Show AbstractSilicon germanium remains an important thermoelectric material for reliable high-temperature operation in an oxidative atmosphere, yet lower processing costs and improved thermoelectric efficiency are still desired. Powder sintering potentially reduces processing costs while also providing the capability to process large areas with few restrictions on shape. Further improvement in the figure of merit (ZT) results primarily from reducing the thermal conductivity of the Si-Ge material system. Thermal conductivity can be restricted by increasing phonon scattering such as occurs at grain boundaries. The relatively high processing temperature required for silicon germanium systems impedes slower sintering methods like hot pressing due to grain growth. Likewise, most methods for sintering Si-Ge require substrates that can withstand the high-temperature processing. Alternatively, lasers can sinter a variety of materials for diverse applications without excessively heating the substrate. Laser sintering enables control of both porosity and grain size to facilitate enhanced scattering of phonons and is therefore well-suited to achieving a low thermal conductivity. Furthermore, the use of powder metallurgy with laser sintering permits direct deposition even on curved surfaces.Laser sintering of mechanically alloyed nano- and micro-particles of Si and Ge allows minimal grain growth to attain lower thermal conductivity and improved ZT. The relatively short laser heating time and low substrate temperature prevent significant grain growth during processing. The high-purity powders are first passed through a 10 micron sieve and then ball milled to produce a homogenous mix of nanoparticles. Preheating with an induction heater permits the powders to be processed under high-intensity CW laser conditions without ablating the lower melting point germanium particles. This processing system enables direct production of thermoelectric films or bulk materials on complex components such as heat engines or exhaust components. Characterization of morphology, composition, grain size and structure is performed using SEM, EDS and XRD. Seebeck coefficient is obtained by measuring the potential difference over the temperature difference. Results of laser-sintered materials characterization and thermoelectric properties for silicon germanium alloys of various compositions will be presented.
9:00 PM - LL5.23
Understanding Thermoelectric Transport Across Nanoscale Interfaces.
Bhaskaran Muralidharan 1 , Gang Chen 1
1 , MIT, Cambridge, Massachusetts, United States
Show AbstractWe study local thermoelectric energy conversion across nanoscale interfaces by employing the Non-equilibrium Green’s function (NEGF) technique. A salient feature of this approach is that both tunneling and scattering effects are treated together in conjunction. By employing the concept of average energy carried by the transported electron calculated using the NEGF approach we calculate local transport properties of interest. Around the interface region we depict a detailed picture of the special regions where thermoelectric and Joule power is distributed. Using several typical interfaces, we point out how and why each type of nanoscale barrier manifests a different thermoelectric profile. We also calculate the local electron temperature to point out many non trivial aspects about how the Seebeck voltage drops across nanoscale interfaces. We also note that a cascade of barriers opens the possibility of increasing the thermoelectric energy conversion. This general framework opens the possibility to theoretically design a cascade of materials to achieve a higher power factor.
9:00 PM - LL5.24
Characterization Of Ballistic Bi-based Thermoelectric Coolers.
Eyal Shapira 1 , Yoram Selzer 1
1 Chemistry, Tel Aviv University, Tel Aviv Israel
Show AbstractHere we report on a first experimental observation of unusually high thermoelectric values of devices based on individual bismuth nanowires (NWs). A chemical method has been devised to establish ohmic contacts to Bismuth NWs, 30 nm in diameter. The morphology of the NWs is tuned by means of electro- migration to result in controllable constrictions smaller than the electron Fermi wavelength (26nm). Ballistic as well as sub-quantum conduction can be measured in these devices and correlated with their thermopower properties. The experimental approach brings us closer than ever to the goal of highly efficient nano-scale thermoelectric coolers
9:00 PM - LL5.25
Effect of Citrate Sol-gel and Autoclave Processing Methods on Thermoelectric Properties of Ca3Co4O9 Nanopowders.
Murat Gunes 1 , Mehmet Parlak 3 , Ahmet Ozenbas 2 1
1 Micro and Nanotechnology Program, Middle East Technical University, Ankara Turkey, 3 Dept. of Physics, Middle East Technical University, Ankara Turkey, 2 Metallurgical and Materials Engineering, Middle East Technical University, Ankara Turkey
Show AbstractConventional thermoelectric materials are not stable at high temperatures. However, thermoelectric oxides have been found to be stable at elevated temperatures but their efficiencies should be improved for commercial applications. For this purpose, a citrate sol-gel and autoclave methods have been applied to synthesize Ca3Co4O9 powders. The formation process of Ca3Co4O9 and the characterization of powders were investigated by BET, XRD and FE-SEM. Thermoelectric properties such as thermo-power and electrical resistivity of Ca3Co4O9 thermoelectric material have been studied to investigate the thermoelectric efficiency of these materials. Computer controlled Seebeck coefficient and resistivity measurement systems were established in our laboratory. In order to investigate the effect of processing parameters on microstructural and thermoelectric properties of Ca3Co4O9 thermoelectric material, amount of ethylene glycol (EG) and the value of pH have been changed in citrate sol-gel process and autoclave processing methods, respectively. The amount of EG used as a dispersant for the nitrate solution during the formation of sol precursor was changed as 0.5, 2.5, 5 ml during the process. The citrate sol-gel precursor was heated at 80°C for 6-7 h in order to obtain the gel followed by drying at 120°C for 12 h. The dried gel was ground and calcined at 550°C for 2 h. The calcined powders were ground and then sintered at 750°C for 2 h. Powders were then compressed into pellets with a diameter of 10 mm under a pressure of 10 MPa, and then these pellets were sintered at 750°C for 2 h. Autoclave processing method has been applied as second synthesis method. In this method, the nitrate solution was placed in a stainless steel autoclave using a teflon glass as a container. 1M HNO3 was slowly dropped into the teflon glass with steady stirring and the pH reached the values of 8 and 9.36. The autoclave was heated at 140°C for 14 h, and then cooled to room temperature naturally. Further treatments applied were the same as treatments used for citrate sol-gel processing method. The surface areas of powders varying from 5.98 m2g-1 to 9.90 m2g-1 were determined using BET analysis. The resistivities of pH:8, pH: 9.36, 5 ml EG, 2.5 ml EG and 0.5 ml EG samples were measured as 0.346, 0.349, 0.57, 0.465, 1.83 Ω. Although autoclave processed samples have smaller resistivity values, which could indicate higher value of ZT (figure of merit), 2.5 ml EG sample of citrate sol-gel processing method has higher Seebeck coefficient than the others with the value of 358 µV/K-1 at 455 K. The Seebeck coefficient of pH:8 value is slightly different from pH:9.36 value for autoclave processed samples. This means that resistivity affects the thermoelectric properties, but it cannot be evaluated as the main factor.
9:00 PM - LL5.26
The Cr Impurity in PbTe.
Michele Nielsen 1 , Christopher Jaworski 1 , Joseph Heremans 1 2
1 Department of Mechanical Engineering, The Ohio State University, Columbus, Ohio, United States, 2 Department of Physics, The Ohio State University, Columbus, Ohio, United States
Show AbstractAfter the recent observation that the Tl impurity increased the zT of p-type PbTe through distortions in the density of states1, we have started to investigate resonant impurities in the conduction band. To this end, we synthesize Pb1-xCrxTe (0.125% < x < 4%) and measure electrical resistivity, Seebeck, Nernst and Hall coefficients, and magnetization over temperature. Magnetization reveals a unique temperature dependence of the Cr ionization state; this combined with the electrical transport properties reveal that Cr is capable of Fermi level pinning. We report here on a complete galvanomagnetic and thermomagnetic study from 80-400K.1.Heremans, J.P., et al., Science, 321 554 (2008)
9:00 PM - LL5.27
Texture Development During Hot Deformation of Bismuth Telluride and Bismuth Telluride Based Composites.
Raghavan Srinivasan 1 , Nicholas Gothard 2 , Jonathan Spowart 2
1 Mechanical and Materials Engineering Dept., Wright State University, Dayton, Ohio, United States, 2 AFRL/RXLM, Air Force Research Laboratory, Wright Patterson AFB, Ohio, United States
Show AbstractBismuth telluride (BT) has the highest Seebeck coefficient near room temperature making it the best candidate for refrigeration and energy conversion processes near RT. The crystallographic structure of this material is stacked planes following the sequence –[-Te-Bi-Te-Bi-Te-]n– in the “c” direction. The Bi and Te layers are covalently bonded, and adjacent Te layers have weak secondary bonds. Basal cleavage and basal slip are the primary fracture and deformation modes. This paper presents development of texture during hot deformation of BT and BT-carbon composites with C60 and nano-graphene. A variety of processing techniques, including extrusion, rolling, and powder sintering will be examined with aim of producing bulk textured ultrafine grained materials.
9:00 PM - LL5.28
Novel Thermal-to-electrical Energy Conversion Using Pyroelectric Thin Films.
J. Karthik 1 , Lane Martin 1
1 Materials Science and Engineering and Materials Research Laboratory, University of Illinois, Urbana-Champaign, Urbana, Illinois, United States
Show AbstractAs we look to the near future and the need for rapid development of sustainable energy solutions, it has become clear that we must more efficiently utilize the energy we produce. As part of this, considerable work has and will be focused on harvesting waste heat for energy production. Over the last few decades, significant advances in the use of thermoelectrics to convert waste heat to electrical energy have been achieved and ongoing work promises to overcome low efficiencies, limits in operating temperatures, the need for relative large temperature gradients, and scalability issues. Motivated by the promise of thermoelectrics for waste heat energy conversion, we will discuss the development of an alternate scheme to convert waste heat to electrical energy through the use of the pyroelectric effect in ferroelectric materials. Such a process is complimentary to thermoelectrics in that it does not require large spatial temperature gradients and is optimized through the use of reversible thermodynamic cycles that harvest temporally oscillating temperature profiles. In this spirit, we will discuss the fundamentals of pyroelectric energy harvesting, including the importance of design and synthesis of new candidate pyroelectric materials – materials such as ferroelectrics where there is a change in polarization in response to a changing temperature that results in an electric current that flows in an external circuit and the production of useable electric energy. Using epitaxial thin film growth, electrical-thermal characterization, and Ginzbug-Landau phenomenological modeling, we show that thin film ferroelectrics can be controlled to produce highly efficient thermal energy harvesting systems. In the current study we will discuss results from films of Pb(Zrx,Ti1-x)O3, Ba1-xSrxTiO3, BiFeO3, and others grown via pulsed laser deposition on a wide range of single crystal substrates. The thin films are characterized with X-ray diffraction, atomic force microscopy, and piezoresponse force microscopy and are found to be single phase and possessing a high degree of crystallinity. Further electrical and thermal studies of these samples suggest our ability to tune and control polarization, pyroelectric effects, and more with thin film strain and processing. This ability allows us to optimize material response for a given waste heat stream. Finally, we will report on a combined theoretical and experimental investigation of energy harvesting efficiencies through the study of a variety of thermodynamic energy harvesting cycles in these model systems. These results represent a new direction in modern thermal-to-electrical energy conversion in systems that can be tuned to have strong responses over a large temperature range and offer an exciting complimentary response to existing and developing thermoelectric systems.
9:00 PM - LL5.29
Thermal Conductivity of Silicon-germanium Alloys and Superlattices from First-principles.
Jivtesh Garg 1 , Nicola Bonini 2 1 , Nicola Marzari 2 1
1 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Materials, University of Oxford, Oxford United Kingdom
Show AbstractThe thermal conductivity of SiGe alloys and superlattices is computed in the single mode relaxation time approximation and using force constants derived from density functional perturbation theory. No adjustable parameters are used. In alloys the net scattering rate of a phonon mode is taken to be the sum of harmonic scattering due to mass disorder and the scattering due to anharmonicity. The harmonic scattering rates are computed using the expression derived by Tamura [PRB 27, 858 (1983)] and the anharmonic scattering rates are computed based on the lowest order three phonon scattering processes. Effect of disorder on anharmonic scattering is also estimated. The approach yields excellent agreement with measured thermal conductivity for all compositions. At 300 K more than 50% of the heat is found to be conducted by phonons of mean freepath greater than 1 micron. In thermoelectrics where low thermal conductivity is desired, this provides avenues to further substantially reduce the thermal conductivity through nanostructuring. Also at 300 K, addition of only about 12% Ge is found sufficient to reduce the thermal conductivity to the minimum achievable value through alloying. Prediction of such optimum compositions holds great importance in the design of low cost thermoelectricmaterials. In superlattices the thermal conductivity is found to decrease sharply with increase in period thickness. Computed thermal conductivity is found to be larger than measured values, and discrepancy is believed to be due to the presence of roughness at the interfaces.
9:00 PM - LL5.3
Thermoelectric Properties of Quasiperiodic Systems.
V. Sanchez 1 , Julio Cesar Hernandez 2 , Chumin Wang 2
1 Departamento de Fisica, Facultad de Ciencias, Universidad Nacional Autonoma de Mexico, Mexico D.F. Mexico, 2 Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Mexico D.F. Mexico
Show AbstractQuasicrystals possess a low thermal conductivity and its electrical conductivity owns an anomalous temperature and defect dependence, i.e., it grows with increasing temperature or defect content in contrast with most metallic alloys. In this work, thermoelectric behaviors of multidimensional macroscopic quasiperiodic systems are studied within the Kubo-Greenwood formalism by using a previously developed renormalization plus convolution method [1]. In addition, the interaction between electron and phonon is explicitly considered in the study of electronic transport at finite temperatures. Starting from the Holstein Hamiltonian, the transport of electrons dressed by lattice vibrational waves is analyzed by means of the small polaron approach [2]. In particular, we calculate the Seebeck and Peltier coefficients of quasiperiodic lattices including the electron-phonon interaction. The results of electrical conductivity reveal both metallic and anomalous temperature dependences, as a consequence of the Fermi energy position in the multifractal band structure. For periodic lattices, there are analytical solutions and they show a uniformly decreasing temperature dependence, where the power-law exponent is a function of the system dimensionality. Finally, the numerical results of the Seebeck coefficient and electrical conductance are compared with experimental data.[1] V. Sanchez and C. Wang, Phys. Rev. B 70, 144207 (2004). [2] G. D. Mahan, Many-Particle Physics, 2nd Ed. (Plenum Press, New York, 1990).
9:00 PM - LL5.31
Phonon Transport in Rough Multilayer Thin Films.
Huarui Sun 1 , Kevin Pipe 1
1 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractEngineering of phonon transport by the addition of interfaces has proven to be a useful tool in reducing thermal conductivity, with important implications for thermoelectric energy conversion. While the topic of thermal boundary resistance has been studied for some time, recent advances in microfabrication have led to the ability to form many interfaces within a small volume, as well as the ability to controllably tune the spacing and physical characteristics of these interfaces. However, models that relate the geometries and physical structure of buried interfaces to bulk thermal conductivity are not yet sufficiently sophisticated to accurately account for interface characteristics such as roughness, which can lead to a number of important effects such as phonon mode conversion, interface waves, and angle-dependent scattering. Such roughness can be introduced purposefully into interfaces to engineer thermal transport, or it can be an unavoidable consequence of interface fabrication.Prior models of heat transfer at rough solid-solid interfaces have (for example) approximated phonon transport as specular scattering off of a fractal pattern of interface facets [1] or considered the interface region to be a mixed layer with a modified phonon density of states [2]. Models of phonon transport in multilayer thin films have so far focused on interfaces that are perfectly flat [3].Here we present a model for phonon transport in multilayer structures that captures the effects of interface roughness. By applying a second-order boundary perturbation method for the first time to solid-solid interfaces, we relate the amplitude and correlation length of interface roughness to the fractions of energy transmitted and reflected into coherent and scattered fields, as well as the fractions of energy scattered into different polarizations and into interface wave modes. This model is then used for each of the interfaces within a multilayer thin film, and a ray-tracing approach is implemented to calculate the propagation of incident phonon energy at a particular frequency, angle, and polarization through the set of interfaces. By integrating over angles, polarizations, and phonon frequencies, the thermal conductivity of the multilayer is calculated at various temperatures as a function of the number of buried interfaces and the amplitude and correlation length of their roughness. This approach is applied to model thermal transport in common thermoelectric multilayer systems such as Si/SiGe and Bi2Te3/Sb2Te3 using roughness amplitude and correlation length values that are typical of existing deposition tools.[1] A. Majumdar, Journal of Heat Transfer 113, 797 (1991)[2] T. Beechem et. al, Journal of Applied Physics 106, 124301 (2009)[3] G. Chen, Journal of Heat Transfer 121, 945 (1999)
9:00 PM - LL5.32
Transmission Electron Microscopy of the Ubiquitous Natural Nanostructure in Double Pressed Bi2Te2.7Se0.3.
Christopher Carlton 1 , Zhifeng Ren 1 , Gang Chen 2 , Lawrence Allard 3 , Yang Shao-Horn 1
1 Department Mechanical Engineering, MIT, Cambridge, Massachusetts, United States, 2 Department Physics, Boston College, Chestnut Hill, Massachusetts, United States, 3 High Temperature Materials Laboratory, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractA great amount of interest has been focused on high figure of merit (ZT) thermoelectric materials for use in solar thermal power and waste heat reclamation. The Bi2Te3 system has long been very important in this regard and, although it has been studied extensively for several decades, some aspects of the material are still not well understood. TEM examination of a double-pressed Bi2Te2.7 Se0.3 specimen with a high ZT revealed the presence of a ubiquitous nanostructure with a spacing of 10nm. To understand the significance and the origins of this nanostructure, a combination of a wide variety of electron microscopy techniques including diffraction contrast imaging, aberration-corrected high-angle annular dark-field imaging with sub-Ångström resolution, and diffraction pattern analysis have been used to determine the nature of these interesting nanostructures. The TEM/STEM analyses show the nanostructure consists of rods of material that is disordered along significant crystallographic directions. The applications of this these finding to the thermoelectric properties of the material are also considered and discussed. This work was supported as part of the S3TEC center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.The aberration corrected microscopy at the Oak Ridge National Laboratory's High Temperature Materials Laboratory was sponsored by the U. S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program.
9:00 PM - LL5.33
Experimental Studies on Anisotropic Thermoelectric Properties and Structures of n-type Bi2Te2.7Se0.3
Xiao Yan 1 , Bed Poudel 2 , Yi Ma 2 , Weishu Liu 1 , Giri Joshi 1 , Hui Wang 1 , Yucheng Lan 1 , Dezhi Wang 1 , Gang Chen 3 , Zhifeng Ren 1
1 Physics, Boston College, Chestnut Hill, Massachusetts, United States, 2 , GMZ energy, Inc., Waltham, Massachusetts, United States, 3 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThe peak dimensionless thermoelectric figure-of-merit (ZT) of Bi2Te3-based n-type single crystals is about 0.85 in the ab plane at room temperature, which has not been improved over the last 50 years due to the high thermal conductivity of 1.65 Wm-1K-1 even though the power factor is 47 x 10-4 Wm-1K-2. In samples with random grain orientations, we found that the thermal conductivity can be decreased by making grain size smaller through ball milling and hot pressing, but the power factor decreased with a similar percentage, resulting in no gain in ZT. Reorienting the ab planes of the small crystals by re-pressing the as-pressed samples significantly enhanced the peak ZT from 0.85 to 1.04 at about 125 degrees, a 22% improvement, mainly due to the more increase on power factor than on thermal conductivity. Further improvement is expected when ab plane of most of the small crystals is reoriented to the direction perpendicular to the press direction and grains are made even smaller.
9:00 PM - LL5.34
Improvement of the Thermoelectric Properties of Substituted SrTiO3 by Synthesis Conditions.
Stanislaw Kolesnik 1 , Stephen Boona 1 , Bogdan Dabrowski 1 2
1 Department of Physics, Northern Illinois University, DeKalb, Illinois, United States, 2 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractComplex oxides are attractive for high temperature thermoelectric applications thanks to their resistance to oxidation. Several examples of complex oxides with promising thermoelectric properties are known, including p-type NaCo2O4 and Ca3Co4O9, and n-type Al-substituted ZnO and La- or Nb- substituted SrTiO3.We have synthesized polycrystalline Sr1-xLaxTiO3 and SrTi1-xNbxO3 (x=0.01-0.2) by a solid state synthesis method in a H2/Ar atmosphere. The incorporation of La and Nb into the crystal structure was confirmed up to x=0.08 by x-ray diffraction and energy dispersive x-ray spectroscopy. Thermoelectric properties were measured in the range 10-400 K in a Physical Property Measurement System (Quantum Design).By increasing the synthesis temperature (up to ~1570oC) and decreasing the partial pressure of oxygen, we were able to optimize the thermoelectric properties of the studied materials. The determined values of the thermoelectric figure of merit ZT~0.1 at 400 K and ~0.3 at 800 K are comparable to those of single crystals of La- and Nb- substituted compounds. Our results show that the synthesis conditions play a crucial role in tailoring of the thermoelectric properties of substituted strontium titanates.*Work at NIU was supported by the NSF (DMR-0706610) and at ANL by the U.S. DOE under contract No. DE-AC02-06CH11357.
9:00 PM - LL5.35
First Principles Study of Phase Stability in PbTe – PbS Alloys.
Jeffrey Doak 1 , Steven Girard 2 , Mercouri Kanatzidis 2 , Chris Wolverton 1
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States, 2 Chemistry, Northwestern University, Evanston, Illinois, United States
Show AbstractThe creation of nanoscale precipitates via phase separation provides a mechanism for decreasing the lattice thermal conductivity and increasing the figure of merit of some bulk thermoelectric materials. PbTe – PbS is a semiconductor materials system that can phase separate from a solid solution by either spinodal decomposition or nucleation and growth depending on composition and temperature. The details of phase separation play an important role in determining the thermoelectric properties of the material, and it has been shown that precipitates formed via nucleation and growth decrease the lattice thermal conductivity more than precipitates formed via spinodal decomposition. To better understand these phase transformations, we investigate the coherent and incoherent phase stability of PbTe – PbS with first-principles density functional theory (DFT) calculations. We use mixing enthalpies derived from calculations of special quasirandom structures (SQS), along with constituent strain energies to model the thermodynamic driving forces for incoherent and coherent phase separation. By fitting these inputs to a sub-regular mixing enthalpy model and including an ideal mixing entropy term, we calculate incoherent and coherent phase diagrams for PbTe – PbS. Our calculations predict an incoherent miscibility gap, in agreement with experiment. Further, the incorporation of constituent strain energy causes a large depression of the miscibility gap and spinodal. Finally, we make comparisons between our data and the experimentally observed nucleation of stable PbS particles in a PbTe matrix.
9:00 PM - LL5.36
Efficient Monte Carlo Simulations of Phonon Transport in Semiconducting Materials for Thermoelectric Applications.
Jean-Philippe Peraud 1 , Colin Landon 2 , Nicolas Hadjiconstantinou 2
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 2 Mechanical Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractWe present a variance-reduction methodology for decreasing the statistical uncertainty associated with Monte Carlo simulations of phonon transport in semiconducting materials. The lower statistical uncertainty reduces the cost associated with simulations of systems close to equilibrium, such as those simulated when calculating the thermal conductivity, which typically needs to be minimized for thermoelectric applications. Our method is validated using known analytical results, as well as newly-developed analytical solutions for the transient as well as the steady-state response of thin films subject to boundary-temperature perturbations in the ballistic limit. We use our methodology for investigating the effect of engineered porosity patterns on the thermal conductivity of silicon. Three-dimensional simulation results will be presented and discussed.
9:00 PM - LL5.38
Thermoelectric Properties of p-type BixSb2-xTe3 Preparedby Arc Melting and then Ball Milling and Hot Pressing.
Qian Zhang 1 , Weishu Liu 1 , Qinyong Zhang 1 , Giri Joshi 1 , Dezhi Wang 1 , Zhifeng Ren 1
1 Physics, Boston College, Chestnut Hill, Massachusetts, United States
Show AbstractWe employ arc melting to fabricate BixSb2-xTe3 ingots, which are then ball milled for decreasing grain size. The XRD analysis shows the single phase has been obtained after melting. The SEM/EDS are used to estimate the grain size and verify the composition. By direct current hot-pressing method, dense bulk BixSb2-xTe3 is sintered for the measurement of the thermoelectric properties. With increasing content of Bi, electrical conductivity decreases and Seebeck coefficient/lattice thermal conductivity increase. ZT values of higher than 1.3 are obtained at 373 K.
9:00 PM - LL5.39
Indium Doped n-type PbTe Thermoelectric Material.
Qinyong Zhang 1 2 , Bo Yu 1 , Weishu Liu 1 , Xiaowei Wang 1 , Hui Wang 1 , Gang Chen 3 , Zhifeng Ren 1
1 Physics, Boston College, Chestnut Hill, Massachusetts, United States, 2 Material Science and Engineering, Xihua University, Chengdu, Sichuan, China, 3 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractIn this talk, Indium doping to form n-type PbTe by ball milling and hot pressing will be presented. The structure was characterized by XRD, SEM, and TEM. The maximum ZT of 1 was achieved at 450 °C, benefitted from a large grain size reduction resulting a low thermal conductivity, indicating that PbTeInx is potentially a promising thermoelectric material for moderate temperature.
9:00 PM - LL5.4
Film Type La(Co, Ni)O3 and La(Ca, Mn)O3 Materials for Thermoelectric Application.
Wenyan Jiang 1 , Seung-Hyun Kim 1 , Angus Kingon 1
1 , School of Engineering, Brown University, Providence, Rhode Island, United States
Show AbstractThermal management has been a longstanding issue with the increase of inevitable dissipative heat from high performance processors. Thermoelectric devices based upon conventional alloy materials have some shortcomings, such as toxicity and lower stability at high temperatures and air environment. In contrast, oxide thermoelectric materials are attractive due to their chemical and thermal stability, and potentially low cost. Recently, large thermopower has been found in perovskite-structured materials, and in particular those containing transition metal-oxides. To achieve a complete functional thermoelectric devices, we studied two types of transition metal oxides, p-type La(Co,Ni)O3 and n-type La(Ca,Mn)O3 as promising candidates for oxide thermoelectric devices. Our metal salt precursors-based chemical solution preparation route has proved to be a reliable and low cost method for the thin film thermoelectric preparation. Additionally, as some applications yield better device performance at thicker film dimensions, we researched preparation methods for thick thermoelectric films, including a hybrid technique that utilizes sol-gel infiltration of screen-printed thick films. Successful film preparation with a wide thickness range offers the possibility to fabricate scalable thermoelectric devices.Research has been supported by NSF, ECS Division.
9:00 PM - LL5.40
Post-deposition, Low-temperature Saturation Annealing of Thermoelectric Thin Films.
Andrew Taylor 1 , Clay Mortensen 1 , Ngoc Nguyen 1 , Matt Beekman 1 , David Johnson 1
1 Department of Chemistry, University of Oregon, Eugene, Oregon, United States
Show AbstractPrecise control over composition and defect concentrations is often prerequisite for achieving optimal performance in thermoelectric materials. This is particularly true for Bi2Te3 and related solid solutions such as Bi2-xSbxTe3 and Bi2Te3-ySey, where appreciable phase widths can significantly affect the electrical and thermal transport properties of these materials. Exceptional advances have recently been made by application of nanostructured approaches to these materials, resulting in substantial improvements in thermoelectric properties. However, given the challenges in controlling composition in nanostructured materials, further improvements might be expected if post-processing approaches to controlling composition can be identified; such approaches can also benefit quality control at the application level. We report on the implementation of a relatively low temperature post-processing method based on equilibrium vapor annealing using the bulk material as a tellurium vapor source, applied here to Bi2Te3 and Bi2-xSbxTe3 thin films prepared by sputtering. The effects of specimen temperature, source temperature, annealing time, and initial thin film specimen and bulk source composition on film morphology, composition, and electrical transport properties were systematically studied. These results are interpreted within the context of the equilibrium condition achieved between source, specimen, and vapor phase. The post-deposition annealing is found to be effective in fixing film composition and therefore carrier properties. The implications for controlling composition in nanostructured thermoelectric materials will be discussed.
9:00 PM - LL5.41
The Effect of Nano and Micrometer Scale Structure on the Electrical and Thermal Conductivities of Thermoelectric Materials.
Martin Maldovan 1
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractMaterials that can simultaneously manage the flow of heat and electricity are of critical importance for the development of highly efficient thermoelectric materials. Recently, nanostructured materials such as superlattices, nanowires, and quantum dots have been suggested as candidate thermoelectric structures having increased figure of merit ZT. Currently there is no theoretical model capable of accurately describing the simultaneous flow of electrical and thermal energy in nanostructures and basic physical properties such as thermal conductivity can not be predicted. We introduce a multiscale theoretical description of electrical and thermal energy transport in composite structures with length scales ranging from nano to macro. We are able to accurately calculate the electrical and thermal conductivities of three-dimensional nanoparticles and nanostructures at different length scales. An important feature is that the constituent materials can be described by general frequency-dependent band structures and relaxation times. We study the physical mechanisms that determine the dependence of heat conduction on the length scale, temperature, and composition of macro, micro, and nano structures. This opens the opportunity for the rational design of nanostructured materials that can control heat and electricity in thermoelectric materials.
9:00 PM - LL5.6
Thermal Fatigue of Thermoelectric Materials Characterized by Elasticity Measurements.
Jennifer Ni 1 , Eldon Case 1 , Corey Anderson 1 , Alex Baumann 1 , Chun-I Wu 2 , Timothy Hogan 2
1 Chemical and Material Science Engineering, Michigan State University, East Lansing, Michigan, United States, 2 Electrical Engineering, Michigan State University, East Lansing, Michigan, United States
Show AbstractThe harvesting of waste heat by thermoelectric generators subjects thermoelectric components to stresses induced by thermal transients. In this study Co0.95Pd0.05Te0.05Sb3 and Ag0.86Pb19Sb1.0Te20 specimens were thermally fatigued by repeatedly down-quenching heated specimens in water or silicon oil. The resulting microcrack damage was monitored by elastic property measurements. Thermal fatigue damage behavior in the thermoelectric materials is discussed and compared to trends of thermal fatigue damage in other brittle materials.
9:00 PM - LL5.8
Ab-initio Investigation of the Zn4Sb3 Phase Diagram.
Gregory Pomrehn 1 , G. Snyder 1 , Axel van de Walle 1
1 Materials Science, California Institude of Techlology, Pasadena, California, United States
Show AbstractA binary phase diagram of Zn4Sb3 has been determined through ab initio calculations and statistical thermodynamics. This work expands on previous computational investigation by considering numerous possible defect structures resulting from the configurational disorder of the Zn sub-lattice. A cluster expansion is utilized to account for the energetics of non-dilute defects. The Zn4Sb3 phase is shown to be entropically stabilized at finite temperatures with both configurational and vibrational entropy having significant contributions to the free energy of formation. Zn4Sb3 is predicted to stabilize in a Zn-deficient composition with respect to valence precise composition Zn13Sb10 resulting in a p-doped semi-conductor. The entropic stabilization of Zn8Sb7, another complex semi-conducting phase, is also investigated.
9:00 PM - LL5.9
Computational Study of the Electronic Performance of Cross-plane Peltier Devices.
Changwook Jeong 1 , Gerhard Klimeck 1 , Mark Lundstrom 1
1 Network for Computational Nanotechnology, Purdue University, West Lafayette, Indiana, United States
Show AbstractThe use of superlattice (SL) devices to improve the performance of thermoelectric (TE) and thermionic (TI) devices has received considerable attention. Although there have been a number of studies, it is still not clear how a superlattice affects the electronic performance (i.e. the power factor (PF)). This work explores the physics of transport in SL TE devices using a sophisticated quantum transport model. The non-equilibrium Green’s function (NEGF) approach to quantum transport is used in the NEMO simulation tool which was developed for resonant tunneling diodes. NEMO permits studies using a continuum effective mass representation as well as an atomistic material representation, ballistic or dissipative transport, with or without electrostatic self-consistency. An AlAs/GaAs SL is considered as a model structure and the power factors of an optimized SL are compared with those for AlxGa(1-x)As alloys with the Al fraction varying from 0 to 1 (i.e. GaAs to AlAs). Specific results obtained so far can be summarized as follows. We use a sophisticated quantum transport simulation to address the device physics, design, optimization, and performance benchmarking of SL Peltier coolers. Initial findings suggest that the SL degrades the electrical performance. The performance of AlAs/GaAs SL Peltier cooler is lower than that of a comparable AlxGa(1-x)As device and also lower than that of a bulk AlAs and bulk GaAs device. In a SL, energy filtering occurs within the device continuously, while in a bulk Peltier cooler, it occurs at the contact. We find that a SL device has a conductivity vs. Seebeck coefficient tradeoff that is similar to that of a bulk device. The overall TE device performance is, therefore, a compromise. The improved thermal properties must be balanced against reduced electrical performance. We believe that the insights developed in this study will be helpful in optimizing the overall – electrical and thermal properties of SL TE/TI devices.
Symposium Organizers
Terry M. Tritt Clemson University
George S. Nolas University of South Florida
Yuri Grin Max-Planck Institute for Chemical Physics of Solids
Jeff Sharp Marlow Industries, Inc.
LL6: Bi<sub>2</sub>Te<sub>3</sub>/Oxides
Session Chairs
Husam Alshareef
Jeff Sharp
Wednesday AM, December 01, 2010
Commonwealth (Sheraton)
9:30 AM - LL6.1
Microstructure Modification by Nanoparticle Addition and its Effect Upon Transport Properties in Bismuth Telluride Alloys.
Nick Gothard 1 , Garth Wilks 1 , Terry Tritt 2 , Jonathan Spowart 1
1 Materials & Manufacturing, Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States, 2 Physics & Astronomy, Clemson University, Clemson, South Carolina, United States
Show AbstractResearch into thermoelectric materials has progressed along many paths over the past decade, with one direction focusing on developing nanocomposites that meet the specimen size, durability, and performance requirements of industry. In the low temperature regime, the state-of-the-art material has long been bismuth telluride, a system with a high degree of crystalline anisotropy and with mechanical properties that can present difficulties for industrial applications. Using bismuth telluride as a matrix, we investigate the effects of nanoparticle incorporation on both the evolution of the microstructure and the attendant transport properties. Multiple families of samples have been produced via ball milling and spark plasma sintering in order to cover a wide range of nanoparticle loadings and processing conditions. Thermoelectric transport data are presented with regard to the effects of nanoparticle loading and processing route on the grain size and crystallographic texture of these nanocomposites, and comparison is made between the transport properties and microstructures of the nanocomposites and state-of-the-art ingot material.
9:45 AM - LL6.2
Doped pnictogen Chalcogenide Nanoplate Crystals as a Basis for Pure and Alloy High Figure of Merit Bulk Nanostructured Thermoelectrics.
Rutvik Mehta 1 , C. Karthik 1 , Binay Singh 1 , Yanliang Zhang 2 , Eduardo Castillo 2 , Damien West 3 , Yiyang Sun 3 , Shengbai Zhang 3 , Theo Borca-Tasciuc 2 , Ganpati Ramanath 1
1 Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Mechanical Engineering Department, Rensselaer Polytechnic Institute, Troy, New York, United States, 3 Physics Department, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractNanostructured forms of V-VI semiconductors based on bismuth telluride alloys are attractive for realizing high thermoelectric figure of merit (ZT) materials for solid-state refrigeration and efficient harvesting of electrical power from waste heat. We report single-component bulk assemblies of sulfur-doped nanostructured pnictogen chalcogenides (e.g., Bi2Te3, Bi2Se3 and Sb2Te3) with 25% to 250% enhancement in the room temperature ZT, compared with their respective non-nanostructured bulk counterparts, and for the first time, a bulk n-type material with a room temperature ZT > 1. We show that multiple-component assemblies fabricated of the pnictogen chalcogenides nanocrystals enable ~40-50% enhancement over single-component bulk, yielding a p-type material with ZT > 1. We synthesized ~5- to 20-nm-thick single-crystal hexagonal sulfur-doped nanoplates of the pnictogen chalcogenides by a rapid (<~ 60 seconds), scalable surfactant-assisted microwave synthesis approach, followed by compaction and sintering to obtain bulk nanostructured pellets. We show that by tuning <1% sulfur doping from mercaptan-terminated surfactants used as a nanoplate-sculpting and surface-passivating agent, we can not only enhance the electrical conductivity σ and Seebeck coefficient α over undoped nanocrystals, but also reverse the majority carrier type in the bismuth chalcogenides. Hall effect measurements show that carrier-concentration modulation by varying the sulfur amounts in the single-component pellets underlies Seebeck coefficient tuning. Electron spectroscopy and X-ray absorption spectroscopy in conjunction with density functional theory calculations provide insights into the doping induced power factor enhancement mechanisms. The single-component nanostructured pellets exhibit 50% lower thermal conductivity κ and up to 5% higher power factor (α2σ) when compared with that of the state-of-the-art alloys, while the multiple-component nanostructured pellets show large α ~ 250-290 μV/K with κ ~45-55% lower than single-component bulk. The single-component bulk pellets exhibit increased ZT at high temperature ~15-25% higher than room temperature values with peak ZT at 400 K, while the multi-component pellets show higher ZT at temperatures <300K, allowing the creation of high ZT materials for a wide temperature range. Our electron microscopy analyses reveal that measured κ values as low as 0.5 – 1.4 W/mK are due to 50-100 nm grains with intragrain structural modulations with characteristic wavelengths between 3-10 nm. Such low κ values obtained in single-component bulk without alloying provide an attractive means to preserve high intrinsic α and σ, which collectively enables large increases in ZT. We thus demonstrate both p-type and n-type high ZT materials using our novel bottom-up technique. Our findings open up completely new possibilities for realizing novel high ZT thermoelectric materials through the assembly of doped single-crystal nanostructures.
10:00 AM - **LL6.3
Thermoelectric Properties of Transition Metal Clathrates.
Silke Paschen 1 , E. Bauer 1 , J. Custers 1 , M. Ikeda 1 , S. Laumann 1 , L. Nguyen 1 , A. Prokofiev 1 , F. Widder 1 , X. Yan 1 , P. Rogl 2 , U. Aydemir 3 , M. Baitinger 3 , H. Borrmann 3 , U. Burkhardt 3 , R. Cardoso-Gil 3 , V. Pacheco 3 , W. Schnelle 3 , Yu. Grin 3 , A. Haghighirad 4 , K. Luther 4 , F. Ritter 4 , W. Assmus 4
1 Institute of Solid State Physics, Vienna University of Technology, Vienna Austria, 2 Institute of Solid State Physics, University of Vienna, Vienna Austria, 3 , Max Planck Institute for Chemical Physics of Solids, Dresden Germany, 4 Institute of Physics, Goethe-Universitaet, Frankfurt am Main Germany
Show AbstractThe type-I clathrates Ba8Ga16Ge30 and Eu8Ga16Ge30 are known to have excellent thermoelectric properties at several hundred degrees above room temperature. However, it is not straightforward to tune the charge carrier concentration to the optimum value for both the n- and the p-type leg. This has led to a search for efficient thermoelectric materials containing transition metal (TM) elements. In many TM clathrates the charge carrier concentration can be systematically varied by changing the TM content, for both n- and p-type conduction. We present here results of both Ge and Si based type-I clathrates containing TM elements.
10:30 AM - LL6.4
Chemical Potential Effect on Thermoelectric Power.
Tsunehiro Takeuchi 1 2 , Akio Yamamoto 2
1 EcoTopia Science Institute, Nagoya University, Nagoya Japan, 2 Department of Crystalline Materials Science, Nagoya University, Nagoya, Aichi, Japan
Show AbstractIt is widely known that thermoelectric power is closely related to the temperature dependence of chemical potential, but the effects of chemical potential on thermoelectric power have not been well understood yet. In order to obtain the materials possessing a large magnitude of thermoelectric power, it is of great importance to know the relation between the chemical potential and thermoelectric power. The linear response theory suggests that the contribution of chemical potential to the thermoelectric power is not negligibly small but rather large exceeding a half of the total magnitude of thermoelectric power. The contribution of chemical potential is more enhanced in the materials possessing a larger magnitude of thermoelectric power. In order to quantitatively analyze the effect of chemical potential to the thermoelectric power, we experimentally determined temperature dependence of chemical potential by using the high-resolution angle resolved photoemission spectroscopy (ARPES) of typical thermoelectric materials; Bi2Te3 and Bi2Se3. The former possesses the n-type behavior and the large magnitude of thermoelectric power S = 200 μV/K at 200K, while the latter is assigned as p-type possessing -60 μV/K at 200K. The ARPES measurement was performed on the single grained samples prepared by the conventional Bridgman method over the temperature range from 6 K to 200 K. The momentum resolved electronic structure observed by the ARPES measurement allowed us to quantitatively determining the chemical potential, and the experimentally determined temperature dependence of chemical potential was compared with the temperature dependence of thermoelectric power. In the presentation, the relation between chemical potential and thermoelectric power of these materials will be discussed in detail on the basis of experimentally determined chemical potential and thermoelectric power.
10:45 AM - LL6.5
Promising Thermoelectric Properties of Commercial PEDOT: PSS Materials and Their Bi2Te3 Powder Composites.
Bo Zhang 1 , Jia Sun 1 , Howard Katz 1
1 Department of Material Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractNewly commercialized PEDOT:PSS products CLEVIOS PH1000 and FE-T, among the most conducting of polymers, show unexpectedly higher Seebeck coefficients than older CLEVIOS P products that were studied by other groups in the past, leading to promising thermoelectric (TE) power factors around 47 μW/mK2 and 30 μW/mK2 respectively. By incorporating both n and p type Bi2Te3 ball milled powders into these PEDOT:PSS products, power factor enhancements for both p and n polymer composite materials are achieved. The contact resistance between Bi2Te3 and PEDOT is identified as the limiting factor for further TE property improvement. These composites can be used for all-solution-processed TE devices on flexible substrates as a new fabrication option.
11:15 AM - LL6.6
Development of Off-diagonal Thermoelectric Effect in Inclinedly-oriented Epitaxial Thin Films of Layered Cobaltite CaxCoO2.
Kouhei Takahashi 1 , Tsutomu Kanno 1 , Akihiro Sakai 1 , Hideaki Adachi 1 , Yuka Yamada 1
1 , Advanced Technology Research Laboratories, Panasonic Corporation, Soraku-gun, Kyoto, Japan
Show AbstractPreviously, large laser-induced transverse voltage signals have been reported in inclinedly oriented thin films of YBa2Cu3O7 and La1-xCaxMnO3. The origin of this effect was ascribed to the unconventional thermoelectric phenomenon termed the off-diagonal thermoelectric (ODTE) effect, where a temperature gradient established in the sample out-of-plane direction produces a voltage signal in the sample in-plane direction. The uniqueness of this effect lies in the fact that a large film in-plane voltage can be induced by a very small film out-of-plane temperature differential ΔT, i.e., typically exceeding several ten millivolts by a unit ΔT. Since laser heating can easily introduce ΔT of several ten kelvin, the resultant ODTE voltage exceeds a very large value of several volts. This feature indicates potential applications to various devices such as sensitive thermal sensors and thermoelectric generators. However, there are two strict requirements to develop this phenomenon, i.e., (i) the material needs to exhibit anisotropic Seebeck coefficient along two different principal crystal axes, and (ii) one of the principal crystal axes needs to be inclinedly oriented from the sample surface. These conditions cannot be achieved easily for many materials. Thus, the observation of the ODTE effect has so far been limited in few numbers of “non-thermoelectric” materials, which made this phenomenon less attractive.Here, we report the first observation of the ODTE effect in a thermoelectric CaxCoO2. This material belongs to a member of the layered cobaltites with CdI2-type CoO2 planes, which is regarded as potential candidate for future thermoelectric applications. The layered structure gives rise to a large anisotropy in the Seebeck coefficient, which makes this material suitable for development of the ODTE effect. The samples examined here are CaxCoO2 thin films grown on sapphire single crystal substrates, whose c-axis is inclinedly oriented from the film surface by an angle of 30°. Infrared lamp and Nd:YAG laser were used as the heat source to examine the steady-state response and the transient response, respectively. As expected from the theory, surface heating by both types of heat sources gave rise to development of voltage signal in the film in-plane direction. In particular, upon heating by Nd:YAG pulse laser, a gigantic transient voltage exceeding 60 V was observed. We identified several features manifesting that the large voltage indeed originates from the ODTE effect. The general formula suggests that CaxCoO2 films exhibits a potential to develop large voltage signal of 1 V by introducing ΔT of merely 1 K. This responsivity is about 6 times larger than that reported in the pioneering work on YBa2Cu3O7 thin films. The detailed ODTE characteristics of CaxCoO2 films will be further discussed at the meeting.
11:30 AM - **LL6.7
Routes to Thermoelectrics by Strongly Correlated Electrons.
Ichiro Terasaki 1 , Wataru Kobayashi 2 , Hidefumi Takahashi 1 , Yukio Yasui 1
1 Physics, Nagoya University, Nagoya Japan, 2 , Waseda University, Tokyo Japan
Show AbstractStrongly correlated electrons are systems that conduction electrons in solids interact via the Coulomb interaction to move in a correlated way in order that they are apart as far as possible from one another. Since the discovery of the good thermoelectric properties in the layered cobalt oxide Na_xCoO_2, we have searched for a possibility of thermoelectrics using strongly correlated electrons, because in such systems we may have properties much better than the predictions based on one-electron approximations. In this talk, we show that (i) thermopower enhanced by spin and orbital degrees of freedom in some cobalt oxides, (ii) largely enhanced mobility at the gap opening in FeSb_2, and (iii) the high-temperature thermoelectrics explained from the Heikes formula.
12:00 PM - LL6.8
Anisotropy and Reduced Thermal Conductivity in Oxygen Deficient Rutile TiO2 Single Crystals.
Jinke Tang 1 , Corin Chepko 1 , Wendong Wang 1 , Guang-Lin Zhao 2
1 Physics & Astronomy, University of Wyoming, Laramie, Wyoming, United States, 2 Physics, Southern University and A&M College, Baton Rouge, Louisiana, United States
Show Abstract We have investigated a series of single crystal rutile TiO2 samples that were annealed in hydrogen at different temperatures ranging from 750 to 1170 C. When we purposely induce the defect planes in the single crystal samples, it was found that the thermal conductivity κ gradually decreases with the degree of reduction, i.e., with the increased amount of oxygen vacancies and defect planes. It is as low as 0.83 W/Km for the heavily reduced sample at 390 K due to phonon scattering by the defects. At low temperatures κ follows a T^1.77 temperature dependence for the heavily reduced sample, which is closer to a T^2 than a T^3 dependence. Such a temperature dependence indicates that the dominant phonon scattering mechanism in the sample may be by dislocations rather than by defect planes, as the former is expected to exhibit T^2 dependence and the latter T^3 dependence. Further reduction of the samples may lead to more prominent role of phonon scattering by the defect planes. On the other hand, our study on the orientation dependence of the thermal transport has already shown significant role of the defect planes. κ was measured in two directions: a) mainly along the (101) planes and b) across the (101) planes at right angle. The (101) planes are known to be the defect planes in this material. κ along the (101) planes is much higher than that across the (101) planes over the temperature range measured, suggesting large phonon scattering by the (101) planes. At the lowest temperature of the measurement, the ratio of the two is 2.4. This difference is retained at high temperatures although at a smaller percentage value. At room temperature it is about 30%. This demonstrates the defect planes play a significant role in restricting the flow of phonons when they try to cross these planes. Detailed orientation dependent experiments and thorough analysis of the thermal transport data are necessary and will be carried out to fully understand the roles of the defect planes. In summary, limited reduction in S, and much reduced κ and ρ of the reduced rutile contribute to the overall improved performance of the ZT. Of particular importance is the role played by the defect planes in phonon blockade as evidenced by the anisotropy observed in the thermal conductivity in the directions parallel and perpendicular to the defect planes.
12:15 PM - LL6.9
Detailed Microstructure Analysis and Thermoelectric Behavior of BaZrO3-doped Ca3Co4O9 Films.
Evan Thomas 1 , Xueyan Song 2 , Song Chen 2 , Breanna Ruter-Schoppman 3 , Joshua Martin 4 , Winnie Wong-Ng 4 , Paul Barnes 3
1 Metals and Ceramics Division, University of Dayton Research Institute-AFRL, Dayton, Ohio, United States, 2 Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, West Virginia, United States, 3 Propulsion Directorate, Air Force Research Laboratory/RZPG, Wright-Patterson AFB, Ohio, United States, 4 Ceramics Division, Materials Science and Engineering Laboratory, NIST, Gaithersburg, Maryland, United States
Show AbstractThe thermoelectric material Ca3Co4O9 (CCO) is a misfit cobaltite with an enhanced Seebeck coefficient, low electrical resistivity and high thermal stability in air. Figure-of-merit (zT) increases have been realized through nanostructured approaches to forming nanocomposites within bulk materials, since the small dimensions of the nanostructures results in boundary/interface scattering of phonons. Here, high quality, uniform c-axis oriented thin films have been grown on various single crystal substrates by means of pulsed laser deposition (PLD), using composite and sectored targets consisting of CCO and cubic perovskite BaZrO3. PLD conditions used were 300 mTorr, 700 °C, 4 Hz and 1.7 J/cm2. Detailed structural and compositional analysis, have been performed using x-ray diffraction, scanning electron microscopy (SEM), conventional high-resolution transmission electron microscopy (TEM) and analytical scanning transmission electron microscopy (STEM). These analyses reveal the incorporation of the dopant elements into the CCO lattice, the formation of fiber-textured CCO films resulting from the stacking of slightly tilted grains, and the existence of a spurious intergrowth phase. High resolution STEM elemental mapping depict segregation of Ba at the CCO grain boundaries and within the secondary phase regions. Thermoelectric property behavior for the films was determined using a custom-built thermopower screening device at room temperature, a Quantum Design Physical Property Measurement System, and a thermal effusivity measurement system. A markedly enhanced power factor is obtained at room temperature. Comparisons of the effects of controlled second-phase additions on the microstructure and thermoelectric behavior of doped and pure CCO thin films will be presented.
12:30 PM - LL6.10
Thermoelectric and Structural Properties of the Cu Doped Ca3Co4O9 System.
Tao Wu 1 , Trevor Tyson 1 , Hsin Wang 2 , Haiyan Chen 1
1 Physics Department, New Jersey Institute of Technology, Newark, New Jersey, United States, 2 High Temperature Materials Laboratory, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThe Cu doped thermoelectric oxide system [Ca2Co1-xCuxO3][CoO2]1.61 (x=0, 0.1, 0.2 and 0.25) was prepared by solid state reaction followed by annealing under oxygen. Temperature dependent thermoelectric properties, resistivity (ρ), Seebeck coefficient (S) and thermal conductivity (κ), were measured. To understand to origin of the changes in figure of merit (ZT) with doping, local (XAFS) and long range (XRD) structural measurements as a function of doping were performed. Identification of the location of the doping sites and the impact on ZT will be discussed.
12:45 PM - LL6.11
Atomic-scale Characterization of Thermo-electric Ca3Co4O9 Using Z-contrast Imaging and Electron Energy-loss Spectroscopy.
Robert Klie 1
1 Department of Physics, University of Illinois at Chicago, Chicago, Illinois, United States
Show AbstractThe misfit-layered oxide Ca3Co4O9 exhibits outstanding physical properties including high thermoelectric power, low thermal conductivity, low resistivity and high thermal stability. It has been shown that changes in the local valence state of Co and interfacial strain can result in significant changes in the material’s Seebeck coefficient, S. Ca3Co4O9, an incommensurately layered oxide, can be best described as a monoclinic structure with two misfit-layered subsystems, a distorted rocksalt-type Ca2CoO3 layer sandwiched between two CdI2-typed CoO2 layers along the c-axis, which makes it an ideal system for studying effects such as charge transfer, strain and spin-state transitions on the material’s thermoelectric behavior. Both subsystems share the same lattice parameters with a=4.8339 Å, c=10.8436 Å and β=98.14°, but along b-axis the incommensurate structure results in b1= 2.8238 Å for the CoO2 subsystem and b2=4.5582 Å for the Ca2CoO3 subsystem. In this presentation, I will discuss how the combination of atomic-resolution Z-contrast imaging, annular bright field imaging and EELS spectrum imaging can be used to determine the effects of structural disorder, strain and charge transfer on the thermoelectric properties of Ca3Co4O9-based materials. Using atomic-column-resolved EELS and in-situ heating experiments, I will demonstrated that there is significant charge transfer between the Co-ions in the insulating rocksalt layers and the metallic CoO2-layers. In addition, I will show that at high temperature the Co-ion spin-states undergo a transition into a higher spin-state without any structural transition. Using annular bright field imaging, distortions in the oxygen sublattice will be characterized, and the effects on the thermo-electric properties will be discussed. Finally, I will discuss the effects of dopants and interfacial strain on the Seebeck-coefficients and discuss how a higher thermo-electric figure of merit can be achieved. This research is funded by an NSF CAREER Award (DMR-0846748).
LL7: Properties & Characterization/Chalcogenides I
Session Chairs
G. Jeffrey Snyder
Terry Tritt
Wednesday PM, December 01, 2010
Commonwealth (Sheraton)
2:30 PM - LL7.1
Complete Characterization of Thermoelectric Materials by a Combined Van der Pauw Approach.
Johannes de Boor 1 , Volker Schmidt 1
1 2, Max Planck Institute of Microstructure Physics, Halle Germany
Show AbstractIn order to increase the scope of thermoelectric applications immense effort has been undertaken to improve the efficiency of thermoelectric materials. This efficiency is governed by the figure of merit ZT, given by ZT=σS2T/k, where σ is the electrical conductivity, S the Seebeck coefficient and k the thermal conductivity of the sample.We present a new method for the thermoelectric characterization of bulk and nanostructured bulk samples. We employ the well-known van der Pauw method for the determination of σ. Due to the similarity of electrical and thermal problems, the measurement principle can be adopted such that the thermal conductivity can be measured as well. The Seebeck coefficient can be obtained by an intelligent combination of electrical and thermal measurements and thus ZT can be calculated. Finally, combining electrical AC/DC measurements ZT can also be measured directly by means of a modified Harman method. This allows checking the consistency of the measurement data and enhances the reliability of the method.We have successfully tested the measurement method on several materials. Here, we will discuss measurement routine, data analysis and measurement results. Furthermore, we will discuss limitations of the presented method, in particular the effect of thermal losses due to radiation.The method is easy to adopt and does not require extensive preparation or expensive instrumentation. It allows for a relatively fast evaluation of materials and may therefore be a valuable tool in the strive for improved thermoelectrica.
2:45 PM - LL7.2
Solution Synthesis of New Thermoelectric Antimonide Nanophases and Their Structure Determination Using Automated Electron Diffraction Tomography.
Wolfgang Tremel 1 , Christina Birkel 1 , Gregor Kieslich 1 , Martin Panthoefer 1 , Tatiana Gorelik 2 , Enrico Mugnaioli 2 , Ute Kolb 2 , Tania Claudio Weber 3 , Juergen Schmidt 4 , Raphael Hermann 3
1 Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universität, Mainz Germany, 2 Institut für Physikalische Chemie, Johannes Gutenberg-Universität, Mainz Germany, 3 Institut für Festkörperforschung, Forschungszentrum Jülich GmbH, Jülich Germany, 4 , Fraunhofer-Institut für Fertigungstechnik, Dresden Germany
Show AbstractEngineering materials with specific physical properties has recently focused on the effect of nanoscopic inhomogeneities at the 10 nm scale. Such features are expected to scatter medium and long-wavelength phonons lowering thereby the thermal conductivity of the system. Low thermal conductivity is a prerequisite for effective thermoelectric materials, and the challenge is to limit the transport of heat by phonons, without simultaneously decreasing charge transport. A solution-phase technique was devised for synthesis of thermoelectric “Zn4Sb3” nanocrystals as precursor for phase segregation into ZnSb and a new Zn-Sb intermetallic phase, Zn1+δSb, in a peritectoid reaction. Our approach uses activated metal nanoparticles as precursors for the synthesis of this intermetallic compound. The small particle size of the reactants ensures minimum diffusion paths, low activation barriers, and low reaction temperatures, thereby eliminating solid-solid diffusion as the rate-limiting step in conventional bulk-scale solid-state synthesis. In a related fashion, nanoparticles of at the iron antimonides Fe1+xSb and FeSb2 could be obtained as well.X-ray powder diffraction data could be fitted in a first step to the crystallographic phases Zn4Sb3 and ZnSb, while they do not allow the distinction between the Zn4Sb3 and Zn1+δSb phase due to the qualitity of the XRD data, the profile broadening and the complexity of the corresponding crystal structures. HRTEM showed immediately that most of the sample consisted of a new phase that cannot be fit inside the Zn-Sb system. This raises the fundamental question how powerful and reliable structure determinations based on X-ray powder diffraction for nanomaterials with complex structures and mixtures really are. A deeper insight was obtained using electron diffraction tomography of several single crystalline nanoparticles, obtaining cell parameters and space group of known ZnSb and a new Zn1+δSb. Ab initio structure solutions were performed for both phases on the basis of electron diffraction data obtained by automated diffraction tomography (ADT). Remarkably, the structure of this new Zn1+δSb phase was obtained by single crystal analysis of a 50 nm particle and the solution was achieved ab initio in one step with a fully kinematical approach. The correctness of the structure is supported by the reproducibility of the solution and the stability of Fourier and least-squares refinements. Electronic and thermal transport properties were on samples obtained by spark plasma sintering by a simultaneous measurement of the thermal and electronic conductivity and the Seebeck coefficient. In addition, the physical properties that dictate the thermal conductivity, specific heat and speed of sound, have been measured, in order to extract the phonon mean free path in the samples and correlate it with sample preparation methods.
3:00 PM - **LL7.3
Experimental and Computational Evaluation of Seebeck Coefficient Metrology Methods.
Joshua Martin 1
1 , NIST, Gaithersburg, Maryland, United States
Show AbstractThe Seebeck coefficient is an essential physical property in evaluating the potential performance of new thermoelectric materials. However, researchers employ a variety of techniques and probe arrangements, often resulting in conflicting materials data. This disparity between research data has further complicated the inter-laboratory confirmation of reported high efficiency thermoelectric materials. To address these challenges, we have developed a complimentary strategy to both evaluate and compare these different probe arrangements and measurement methodologies: first, through the design of an improved thermoelectric probe, and second, through computational metrology simulations. This talk will provide an overview of thermoelectric metrology, our apparatus design and instrumentation, and a discussion of both the experimental and metrology simulation results. We will further emphasize the techniques required to effectively manage uncertainty in high temperature Seebeck coefficient measurements.
3:30 PM - LL7.4
A Measurement of Thermal Diffusivity for Nanometer Scale Films.
Chih-chao Shih 1 , Wei-Chuan Fang 1 , Ming-Sheng Leu 1
1 Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu Taiwan
Show AbstractThis study demonstrates a traveling wave technique, which is one kind of thermal diffusivity measurement for nanometer scale films. Several dozen nanometers of silver, gold and bismuth antimony telluride thin films were prepared by sputtering or arc ion plating on silicon substrate. The crystalline of samples was charactered by X-ray diffraction (XRD). Thickness of thin films was observed using cross-section scanning electron microscopy (SEM). The surface roughness of thin films was measured by atomic force microscopy (AFM). The relationships between thermal diffusivity of thin films and film thickness, crystalline property, and surface roughness were discussed respectively.
4:15 PM - LL7.5
Design and Realization of Novel Nanostructured Intergrowth Chalcogenide Materials.
Matt Beekman 1 , Colby Heideman 1 , Michael Anderson 1 , Mary Smeller 1 , Ngoc Nguyen 1 , David Johnson 1
1 Department of Chemistry, University of Oregon, Eugene, Oregon, United States
Show AbstractRecent advances in the field of thermoelectric (TE) materials research have resulted in the proven ability to achieve unprecedented TE properties via nanostructured approaches, constituting significant progress toward the long-standing challenge of identifying more efficient TE materials. Ultimately, one desires material systems in which composition and nanostructure can be precisely controlled such that the mechanisms for TE enhancement can be studied, understood, and applied. Toward this aim, we have been developing new nanostructured multilayer and intergrowth compounds using the modulated elemental reactants synthesis approach. These include intergrowth compounds with extremely low thermal conductivities (< 0.1 W m-1 K-1 cross plane and ~ 0.5 W m-1 K-1 in plane at room temperature) based on group 14 and transition metal chalcogenides, which can be precisely interleaved by capitalizing on interface stability. The wide variety of chemical compositions that is accessible in these systems offers a platform for new materials discovery. This includes the synthesis of materials comprised of Earth abundant elements that are needed for greener thermoelectric materials design as well as more widespread use in waste heat recovery and cooling applications. A promising attribute of these new intergrowth compounds is the potential for influencing electrical transport through designed nanostructure. We present current understanding of the interplay between nanostructure and electrical transport properties in these materials. Potential systems of future interest will also be discussed.
4:30 PM - LL7.6
Atomic Structure of Twin Boundaries in Bismuth Telluride.
Douglas Medlin 1 , Quentin Ramasse 2 , Catalin Spataru 1 , Nancy Yang 1
1 Materials Physics, Sandia National Laboratories, Livermore, California, United States, 2 , SuperSTEM Laboratory, STFC Daresbury, Daresbury United Kingdom
Show AbstractTwin boundaries are of particular interest for engineering the grain structure of polycrystalline thermoelectric materials because their coherent structure and nearly bulk-like coordination give the possibility of scattering phonons while not severely degrading the electronic transport properties. In this presentation we analyze the atomic-scale structure of the basal twin boundary in bismuth telluride. Electron diffraction measurements show that this interface corresponds to a 180° rotation of the crystal about the [0001] axis, an alignment that reverses the stacking of the basal planes. The basal planes in the perfect bismuth telluride structure are arranged in a repeating sequence of 5-layer wide Te(1)-Bi-Te(2)-Bi-Te(1) packets. Thus, it is possible for the twin interface to be located at one of three distinct locations: at the Te(2) layer, the Bi layer, or the Te(1) layer. Using aberration-corrected high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM), we show that the twin boundary is terminated at the Te(1) layer, where the stacking forms a double-layer of Te. Our observations are consistent with ab initio calculations, which predict this twin termination to have the lowest interfacial energy of the three configurations we considered. Our calculations and observations also find a small expansion in the interplanar spacing at the interface. Finally, we discuss the mechanisms for twin boundary formation in bismuth telluride and related tetradymite-structured thermoelectric compounds, considering in detail the atomic rearrangements produced by interfacial steps and dislocations in these systems.
5:00 PM - LL7.8
Characterization of Mechanical Properties and Microstructure of Cu-Sb-Se Based Materials.
Paul Majsztrik 1 , Melanie Kirkham 1 , Eric Skoug 2 , Donald Morelli 2 , Edgar Lara-Curzio 1
1 Mat. Sci. & Tech. Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Dept. of Chem. Eng. and Mat. Sci. , Michigan State University, East Lansing, Michigan, United States
Show AbstractThermoelectric materials utilized in power generation devices are subjected to thermal and mechanical stresses that could limit their reliability and durability. These mechanical stresses arise from thermal gradients (both transient and steady-state) as well as from differences in thermal expansion between dissimilar interfacing materials. In many existing and proposed thermoelectric power generation applications, thermal cycling will regularly be encountered at system startup, shutdown, and with changes in operating conditions. Characterizing the mechanical properties of thermoelectric materials and understanding how thermal cycling affects microstructure is essential to developing improved materials, modeling material behavior, and designing devices. This work presents the results from the mechanical, thermomechanical, and microstructural characterization of novel thermoelectric materials based on Cu-Sb-Se. Characterization of microstructure and composition using scanning electron microscopy (SEM) and x-ray diffraction (XRD) indicated that materials with overall stoichiometry of Cu3SbSe3 phase-separate into three distinct regions and have a microstructure that depends on thermal history. Samples with overall stoichiometry of Cu3SbSe4 were capable of forming a single-phase material. Thermodilatometry analysis (TDA) was used to determine the thermal expansion behavior of these materials and their stability with thermal cycling. Materials with overall stoichiometry of Cu3SbSe3 and Cu3SbSe4 had non-linear thermal expansion between room temperature and 300°C and underwent non-reversible expansion with thermal cycling. Thermal cycling caused both reversible and non-reversible phase changes. Nanoindentation was used to determine the hardness and modulus of each phase. Acknowledgements: The work at Oak Ridge National Laboratory was sponsored by the U. S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program through the High Temperature Materials Laboratory User Program and by Center on Revolutionary Materials for Solid State Energy Conversion, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001054. Work at MSU was supported by the National Science Foundation under award number NSF-CBET-0754029.
5:15 PM - LL7.9
Order/Disorder Transition in Cu3SbSe3 Thermoelectric Material.
Melanie Kirkham 1 , Paul Majsztrik 1 , Eric Skoug 2 , Donald Morelli 2 , E. Andrew Payzant 1 , Edgar Lara-Curzio 1
1 High Temperature Materials Laboratory, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, United States
Show AbstractThermoelectric materials are the focus of intensive research and development efforts because of their potential to harvest waste heat from industrial processes and internal combustion engines. In this presentation we report the results from an investigation of the phase evolution of Cu3SbSe3 as a function of temperature. In situ X-ray diffraction data were collected while heating and cooling over several cycles, and the orthorhombic crystal structures were refined at each temperature. The refined lattice parameters change non-linearly, but continuously, with temperature. The rate of thermal expansion of the a and b lattice parameters increases from around 140°C until around 170°C, where it returns to a rate close to that below 140°C. Non-linearity in the thermal expansion of the c axis begins at a lower temperature, around 100°C, where it enters a region of negative thermal expansion. The thermal expansion of the c lattice parameter again turns positive around 170°C. Crystallographic charge flipping analysis shows an increase in the disorder of the copper cations with temperature. Results from dilatometry, which suggest a phase transition at around 170°C, will also be presented. The implications of this order/disorder phase transition in Cu3SbSe3 on its potential use in thermoelectric generators will be discussed. This research through the Oak Ridge National Laboratory's High Temperature Materials Laboratory User Program was sponsored by the U. S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program and by the Center on Revolutionary Materials for Solid State Energy Conversion, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001054. Work at MSU was supported by the National Science Foundation under award number NSF-CBET-0754029.
5:30 PM - LL7.10
The Effect of Doping on the Thermoelectric Properties of I2-IV-VI3 and I3-V-VI4 Ternary Semiconductors.
Eric Skoug 1 , Jeffrey Cain 1 , Donald Morelli 1
1 Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, United States
Show AbstractThermoelectric devices convert directly between thermal and electrical energy, and can be used for waste heat recovery and solid-state climate control. The current state of the art thermoelectric materials have modest efficiencies, and thus the search for better performing materials is ongoing. Here we present thermal and electrical transport data for ternary semiconductors of the type I2-IV-VI3 and I3-V-VI4 where I is Cu, IV is Sn or Ge, V is Sb, and VI is Se. These compounds can be considered as ternary derivatives of the II-VI semiconductors whereby two distinct atomic species occupy the metal sublattice, maintaining four valence electrons per atom and tetrahedral coordination. Recent work has shown that Cu-based ternary chalcogenides derived in this manner are potentially good thermoelectric materials, and we aim to elaborate on this work by studying the most promising compounds in detail. The compounds Cu3SbSe4, Cu2SnSe3 and Cu2GeSe3 all feature Seebeck coefficients in excess of 250 μV/K and thermal conductivities near 3 Wm-1K-1 at room temperature. These compounds tend to be nominally p-type, presumably due to large intrinsic defect densities. We have analyzed different p-type impurity dopants for Cu3SbSe4 and Cu2SnSe3 and their ability to offer control of the electronic properties of these materials. In addition, we have closely investigated the previously-reported ability of Cu2GeSe3 to accommodate as much as 14% excess Ge. This excess Ge raises the symmetry of the crystal structure from orthorhombic to cubic. We have studied the transport properties of Cu2Ge1+xSe3, and found that excess Ge decreases the thermal conductivity and has a doping effect on Cu2GeSe3.We acknowledge a grant from the National Science Foundation (NSF- CBET-0754029) for partial support of this work.
LL8: Poster Session
Session Chairs
Yuri Grin
George Nolas
Jeff Sharp
Terry Tritt
Thursday AM, December 02, 2010
Exhibition Hall D (Hynes)
9:00 PM - LL8.1
Thermoelectric Transport in Quantum Dot Nanocomposites.
Jun Zhou 1 , Ronggui Yang 1
1 Mechanical Engineering, U. Colorado at Boulder, Boulder, Colorado, United States
Show AbstractNanocomposite materials have been shown to greatly improve thermoelectric conversion efficiency due to the significant thermal conductivity reduction. Periodic interfaces in a quantum dot nanocomposite can also alter the density of states (DOS) of electrical carriers beyond the filtering effects of low-energy electrons in a nanocomposite with random distribution of nanoparticles. In this work, we study thermoelectric transport of quantum dot nanocomposite with an ordered array of nanoparticles in a matrix material. The periodic parabolic potential at the interface forms a series of minibands of electrical carriers. The energy spectra of these minibands are calculated using the tight-binding method and the thermoelectric transport properties are calculated using Boltzmann transport equation. Very sharp density of states due to the miniband formation can be tuned by the selection of the materials, the size and inter-dot distance of the quantum dots. High Seebeck coefficient can be obtained by tuning the distance of the Fermi level and the location of sharp DOS through proper carrier doping. Our model can be used to guide the design of nanocompsites with enhancements in thermoelectric figure of merit ZT.
9:00 PM - LL8.10
An Anisotropic Debye Model for Thermal Contact Resistance.
Zhen Chen 1 , Chris Dames 1
1 Mechanical Engineering, UC Riverside, Riverside, California, United States
Show AbstractThermoelectric devices involve multiple contacts between various dissimilar materials, so it is essential to understand and minimize the thermal contact resistance between these different materials pairs. Nearly all models for the thermal contact resistance require that both materials have isotropic properties. This isotropic restriction is built into such widely-used models as the Diffuse Mismatch Model (DMM) and Acoustic Mismatch Model (AMM) [1]. However, certain important materials are highly anisotropic, including for example graphite, Bi2Te3, and Sb2Te3. Recently an anisotropic DMM was developed for contacts involving graphite [2]. Here we present a general framework to incorporate anisotropic material properties into calculations of the thermal contact resistance. The model is built around a generalized, anisotropic form of the Debye dispersion relation. This model dispersion relation yields numerical and analytical results for the thermal contact resistance in the DMM and Maximum Transmission Model (MTM). These results give interesting and in some cases unexpected guidelines for materials engineering to reduce the thermal contact resistance. For example, in some cases the contact resistance can actually be reduced by reducing a phonon velocity, as long as it is the velocity component parallel to the plane of the interface. [1] E. T. Swartz and R. O. Pohl, Reviews of Modern Physics 61 (3), 605 (1989).[2] J. C. Duda, J. L. Smoyer, P. M. Norris, P. E. Hopkins, Applied Physics Letters 95, 031912 (2009).
9:00 PM - LL8.11
Device Testing and Characterization of a Mid-temperature Thermoelectric Pair and Potential Applications.
Andy Muto 1 , Jian Yang 2 , Zhifeng Ren 2 , Gang Chen 1
1 , MIT, Cambridge, Massachusetts, United States, 2 Physics, Boston College, Chestnut Hill, Massachusetts, United States
Show AbstractThe maximum device efficiency of a thermoelectric generator is determined by the materials' dimensionless figure of merit, ZT=S^2*T/(roe*k), where roe is the electrical conductivity, S is the Seebeck Coefficient, k is the thermal conductivity and T is the mean temperature. In this work we present an experimental system that measures the efficiency as well as the individual properties of a mid-temperature thermoelectric material. A number of experimental challenges need to be addressed in fabricating and testing a mid temperature device including radiation losses, sublimation of thermoelectric material, thermal stresses, and electrical contact resistance. Experimental results will be presented and compared to device performance modeling. Potential applications of such a generator will be discussed.
9:00 PM - LL8.12
Bulk Thermal Conductivity Calculation from a First-principles-based Interatomic Potential: Case Of Si.
Keivan Esfarjani 1 , Asegun Henry 2 , Nuo Yang 1 , Gang Chen 1
1 Mechanical Engineering, MIT, Cambridge, Massachusetts, United States, 2 , Oak Ridge National LAbs, Oak Ridge, Tennessee, United States
Show AbstractBased on first-principles density-functional calculations, we have developed and tested a force-field for Silicon, which can be used for Molecular dynamics simulations and the calculation of its thermal properties. This force field uses the Taylor expansion of the total energy about the equilibrium positions up to 4th order. In this sense, it becomes systematically exact for small enough displacements, and can reproduce the thermodynamic properties of Si with high fidelity. Having the harmonic force constants, one can easily calculate the phonon spectrum of this system. The cubic force constants, on the other hand, will allow us to compute phonon lifetimes and scattering rates.Results on equilibrium Green-Kubo molecular dynamics simulations of thermal conductivity of Si, as well as an alternative calculation of the latter based on the relaxation-time approximation will be reported. The accuracy and ease of computation of the lattice thermal conductivity using these methods will be compared. This approach paves the way for the construction of accurate bulk interatomic potentials database, from which lattice dynamics and thermal properties can be calculated and used in larger scale simulation methods such as Monte Carlo.
9:00 PM - LL8.13
Evaluation of Energy Moment in Non-diffusive Solid Systems.
Alper Kinaci 1 , Justin Haskins 2 , Tahir Cagin 1 2
1 Materials Science and Engineering, Texas A&M University, College Station, Texas, United States, 2 Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractThe introduction of micro and nano-scale structures promises enhanced thermoelectric figure of merits. However, estimating the thermoelectric performance is challenging since the small scale measurement techniques are still in development. Especially, thermal conductivity measurements can be problematic due to non-uniform heating, heat losses and errors resulting from approximations that account for the sample size. In this sense, computational tools are increasingly employed in predicting thermal conductivity. In systems evolving under classical dynamics, using Einstein relation is one method to calculate lattice thermal conductivity. This method, in theory, is equivalent to Green-Kubo approach and it does not require a derivation of an analytical form for the heat current. However, in application of Einstein relation to molecular dynamics (MD), a discrepancy exists regarding the calculation of the energy moment (R). The classical definition for the energy moment for a single particle is the total energy of the particle multiplied by its unwrapped coordinate in simulation domain. The total energy moment of the system is then calculated by summation over all particles. With this formulation of R, Einstein relation gives incorrect thermal conductivity (i.e. zero) for non-diffusive solid systems in MD. In this paper, we propose a new formulation for R and apply it to a model pair potential. Resulting thermal conductivity values from Einstein relation are in agreement with those from Green-Kubo method. We further discuss the extension of this formulation to more sophisticated interatomic potentials.
9:00 PM - LL8.14
Atom-probe Tomographic Analyses of Nanometer-scale Precipitates in PbTe-SrTe Doped with Na2Te Thermoelectric Materials.
Kanishka Biswas 2 , Dieter Isheim 1 3 , Mercouri Kanatzidis 2 , David Seidman 1 3
2 Department of Chemistry, Northwestern University, Evanston, Illinois, United States, 1 Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States, 3 Northwestern University Center for Atom-Probe Tomography, Northwestern University, Evanston, Illinois, United States
Show AbstractPbTe-based materials are promising candidates for high-efficiency heat to electricity conversion. Nanoscale inclusions in PbTe can dramatically suppress the lattice thermal conductivity by scattering the longer wavelength heat-carrying phonons. Knowledge of the local concentrations and spatial distribution of nanoscale precipitates is crucial for understanding and designing improved thermoelectric materials. We utilize laser-assisted local-electrode atom-probe (LEAP) tomography to characterize nanometer-scale precipitates and dopant atom distribution in specimens of PbTe - 2 at.% SrTe doped with 1 at.% Na2Te. Micro-tips for LEAP tomography are prepared utilizing focused-ion beam milling. Pulsed evaporation of individual atoms on the LEAP is achieved employing picosecond ultraviolet (355 nm wavelength) laser pulses. LEAP tomography detects small Na-rich precipitates with an approximately 5 nm diameter, whose average composition is close to the Na2(Pb,Te) stoichiometry, with Pb and Te being in about equal proportion. The implications of this nanostructure on thermoelectric properties are discussed. This material is based upon work supported as part of the “Revolutionary Materials for Solid State Energy Conversion”, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001054. APT measurements were performed at the Northwestern University Center for Atom-Probe Tomography (NUCAPT). The LEAP tomograph was purchased and upgraded with funding from NSF-MRI (DMR-0420532) and ONR-DURIP (N00014-0400798, N00014-0610539, N00014-0910781) grants.
9:00 PM - LL8.15
Off-stoichiometry, Defect Thermodynamics, and Electronic Properties of AgSbTe2-based Thermoelectrics: A First Principles Study.
Sergey Barabash 1 , Vidvuds Ozolins 1
1 Materials Science and Engineering, UCLA, Los Angeles, California, United States
Show AbstractUsing first-principles density-functional theory calculations, we analyze the Fermi surface topology, the thermodynamics of various point defects, the composition, and the stability of AgSbTe2. We find that some defects, particularly Ag vacancies, may form in high concentrations even at low temperatures, leading to large deviations from the formal stoichiometry. The defect formation energy and the resulting composition of AgSbTe2 are largely unaffected by shifting the experimental conditions to favor Ag2Te or Sb2Te3, but depend critically upon relative changes in cation vs. anion chemical potential, which in turn are limited only by precipitation of elemental Ag or elemental Te phases. This is in contrast to the common practice of defining AgSbTe2 composition in terms of the isoplethal Ag2Te-Sb2Te3 phase diagram section, and may explain the contradictions in the low-temperature regions of such phase diagrams. We estimate the defect concentrations and the resulting intrinsic doping levels under various experimental conditions. We analyze the evolution of the Fermi surface topology at low hole dopings in D4-ordered AgSbTe2 and use it to refine the interpretation of the de Haas-van Alphen measurements on naturally doped AgSbTe2. Finally, we demonstrate that the stoichiometric AgSbTe2 is at the verge of a dynamical instability: the energies of acoustic phonons near the L point depend strongly on volume, changing sign if the local density approximation is improved with generalized gradient corrections. We analyze the implications of this instability on the accuracy of our defect calculations.This work has been supported the U.S. Department of Energy EFRC on "Revolutionary Materials for Solid State Energy Conversion", Grant No. DE-SC0001054.
9:00 PM - LL8.16
Optimization of Thermoelectric Properties by Locally Distorted Density of States and Nanostructure Integration.
Adrian Popescu 1 , Lilia Woods 1
1 Department of Physics, University of South Florida, Tampa, Florida, United States
Show AbstractNew ways for thermoelectric properties enhancement of composite materials are investigated. The material design can be optimized with the analytical formulas we have derived, which take into account the simultaneous effect of the bulk host with locally distorted density of states together with the characteristics of the nanostructure integration. We determine the best characteristics of the localized levels in the density of states in terms of their shapes and locations with respect to the Fermi level. Furthermore, the benefits of nanostructure integration in a material with already improved thermoelectric characteristics by proper impurity doping are explored. It is shown that composites with both locally distorted density of states and nanostructures are potential candidates for thermoelectric applications at room temperature. Acknowledgement: Supported by NSF-CBET-0932526.
9:00 PM - LL8.17
Size-dependent Microstructure Evolution and Thermoelectric Properties of Bi2Te3 Nanowires.
Ho Sun Shin 1 , Seong Gi Jeon 1 , Jin Yu 1 , Jae Yong Song 2 3 , Ho-Ki Lyeo 2 , Nguyen Thach 2 , Dongmin Kang 2 , Jinhee Kim 2 3 , Hyun Min Park 2
1 Dept. of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of), 2 , Korea Research Institute of Standards and Science, Daejeon Korea (the Republic of), 3 Dept. of Nano Science, University of Science and Technology, Daejeon Korea (the Republic of)
Show AbstractThermoelectric (TE) materials have attracted much attention as a potential candidate for clean and sustainable future energy sources. Bi2Te3 has been one of the most promising material for TE devices due to its high dimensionless figure of merit near room temperature. Since Hicks and Dresselhaus proposed that the size-effects and quantum confinement effects may play a major role of increasing the ZT value, there have been many efforts to increase ZT value using nanostructures, such as quantum dots, superlattices, and nanowires(NWs).In this work, we investigated the size-dependent TE properties of Bi2Te3 NWs. We deposited Bi2Te3 nanowires into AAO (anodic aluminum oxide) templates using the pulsed-electrochemical process. The diameter of NWs deposited in the AAO templates is relatively uniform and we have varied the diameter from 15 to 200nm. Cyclic voltammetry technique was used to determine the reduction potentials at which Bi and Te were simultaneously deposited into AAO templates. Electrodeposition parameters of reduction potential, pH, and electrolyte concentration were controlled to vary the composition of Bi-Te compound NWs. We analyzed the microstructure of NWs by using XRD, FESEM and TEM. The variations in electrical conductivity of Bi2Te3 NWs were measured using PPMS (physical property measuring system, QuantumDesign Inc.) in the temperature range of 2-300 K. The thermal conductivities of Bi2Te3 NWs within the templates were measured by TDTR (time domain thermoreflectance) analysis at room temperature; we measured the conductivity of AAO templates and AAO-NWs composites, respectively. Results showed that the grain size of polycrystalline Bi2Te3 NWs increased from the bottom to the top of the NWs depending on the wire radius. For the Bi2Te3 NW with a diameter of 65 nm, the temperature-dependent I-V curves showed typical semiconductor behavior with a narrow bandgap and the electrical resistivity was 72 μΩ-m at room temperature. The Bi2Te3 NWs array (65 nm in diameter) in AAO template had ~20 % smaller value of thermal conductivity than that of the bulk value; the conductivity corresponds to the upper bound value among previous reports for Bi2Te3 NWs with the diameter of 50 ~ 400nm.
9:00 PM - LL8.18
Thermoelectric Properties of Carbon Nanotubes Added n-type CoSb3 Compound.
Takashi Itoh 1 , Masashi Tachikawa 2
1 EcoTopia Science Institute, Nagoya University, Nagoya Japan, 2 Graduate School of Engineering, Nagoya University, Nagoya Japan
Show AbstractCobalt triantimonide compounds are well known as materials with good thermoelectric properties over temperature range of 550-850 K. For further improving thermoelectric performance, reduction of thermal conductivity is required. In this study, we attempted to disperse carbon nanotubes (CNTs) uniformly into the n-type CoSb3 compound for lowering lattice thermal conductivity by the phonon scattering. Powders of Co, Ni, Sb and Te were blended with molar ratios of n-type Co0.92Ni0.08Sb2.96Te0.04 compound, and the compound was synthesized through a pulse discharge sintering (PDS) process. After coarsely grinding the synthesized compound, CNTs were mixed with the compound powder at different mass% (0, 0.01, 0.05 and 0.1 mass%). Then, the mixture was mechanically ground with a planetary ball milling equipment. The ground composite powder was compacted and sintered by PDS. Thermoelectric properties (Seebeck coefficient, electrical resistivity and thermal conductivity) of the sintered samples were measured. It was confirmed that the fibrous CNTs existed uniformly in the compound matrix. The minimum thermal conductivity was obtained at addition of 0.01 mass% CNTs, and the electrical resistivity was a little increased with amount of CNTs. The maximum ZT of 0.56 was achieved at 800K in the 0.01 mass% CNTs added sample.
9:00 PM - LL8.19
Investigation of Thermoelectric Properties of Fe-based Filled Skutterudites on Incorporation of Co, Ni and In.
Pooja Puneet 1 , Jennifer Hubbard 1 , Jian He 1 , Terry Tritt 1
1 Department of Physics and Astronomy, Clemson University, Clemson, South Carolina, United States
Show AbstractWe present detailed synthesis and characterization of one of the most promising p-type Fe-based skutterudites (Fe4Sb12). Solid state reaction technique was employed to prepare various compositions of single and double filled Fe4Sb12 skutterudites along with Co/Ni substitution. Here, we analyze the effects of growth conditions and filling ratio on the thermoelectric performance of the single and double filled Fe4Sb12 skutterudites. Furthermore, we also show lowering of thermal conductivity on the incorporation of Indium in single filled samples.
9:00 PM - LL8.2
Optical Observations and Numerical Modeling of the Thermoelectric Thomson Effect on Self-heating Silicon Microwires.
Gokhan Bakan 1 , Niaz Khan 1 , Helena Silva 1 , Ali Gokirmak 1
1 Electrical and Computer Engineering, University of Connecticut, Storrs, Connecticut, United States
Show AbstractThermoelectric properties of a material can be characterized through three phenomena: Seebeck, Peltier, and Thomson effects. The Seebeck and Peltier effects are utilized in thermoelectric modules for power generation or cooling which require at least two different materials. The Thomson effect, however, can be observed on a current carrying homogeneous material under a temperature gradient as asymmetric self-heating of the material. The Thomson effect is typically very small in metals, however it has been shown that it can be significant in small-scale, self-heating semiconductors such as polycrystalline silicon (poly-Si) micro-lamps1, micro-heaters2, 3, and GeSb phase-change memory (PCM) elements4 due to large current densities and temperature gradients. We also have verified asymmetric self-heating of nanocrystalline silicon (nc-Si) microwires through analysis of light emission from the wires. The brightest (hottest) spot on self-heating n-type wires shifts towards the lower potential end , where it shifts towards higher potential end on p-type wires. The hottest spot moves away from the center by ~10 % of the wire length. These observations are in agreement with the previous reports. Only one work1 among the previous reports models thermoelectric transport in poly-Si micro-heaters, however thermoelectric effects in electrical conduction is ignored and thermoelectric parameters of poly-Si is mistakenly extrapolated up to 1100K assuming indefinitely increase Seebeck coefficient. A complete numerical modeling of an n-type silicon microwire is constructed including thermoelectric effects in both electrical conduction and thermal transport equations, and assuming decreasing Seebeck coefficient at high temperatures as literature Seebeck data on poly-Si suggest . The shift in the simulated temperature profile is towards lower potential end and increases with current, being consistent with experimental observations. The shift in the hottest spot location is as large ~7 % of the wire length for the peak temperature of 1570 K on the wire. A review of previous works, our experimental, and simulation results will be presented. References 1. C. H. Mastrangelo, J. H. J. Yeh and R. S. Muller, IEEE Trans. Electron Devices 39, 1363 (1992). 2. O. Englander, D. Christensen and L. Lin, Appl. Phys. Lett. 82, 4797 (2003). 3. A. Jungen, M. Pfenninger, M. Tonteling, C. Stampfer and C. Hierold, J Micromech Microengineering 16, 1633 (2006). 4. D. T. Castro, L. Goux, G. A. M. Hurkx, K. Attenborough, R. Delhougne, J. Lisoni, F. J. Jedema, M. A. A. in 't Zandt, R. A. M. Wolters, D. J. Gravesteijn, M. A. Verheijen, M. Kaise, R. G. R. Weemaes and D. J. Wouters, IEEE IEDM 315 (2007).
9:00 PM - LL8.20
Transmission Electron Microscopy Studies of Nanostructures in SrZnSb2.
Oystein Prytz 1 , Eric Toberer 3 , Andrew May 2 , Espen Flage-Larsen 1 , Johan Tafto 1
1 Department of Physics, University of Oslo, Oslo Norway, 3 Materials Science, California Institute of Technology, Pasadena, California, United States, 2 Chemical Engineering, California Institute of Technology,, Pasadena, California, United States
Show AbstractWe report on transmission electron microscopy studies of the orthorhombic SrZnSb2 compound, showing a high density of planar faults. The thermoelectric properties of this material were recently investigated [1], revealing a rather low thermal conductivity. The lattice contribution to the thermal conductivity approaches 1 W/Km at high temperatures, which is about half the value reported for filled Skutterudites.
While the previous study showed that the Seebeck coefficient and electric conductivity are too small for thermoelectric applications, it is still of interest to further investigate the source of the low thermal conductivity. The observed defects are rigid shifts of the unit cell, causing a change in the local structure that resembles the similar tetragonal SrZnBi2 structure. In areas with the highest density of defects, these shifts occur at every, or every other, unit cell. We discuss the effect of these defects on the observed lattice thermal conductivity.
[1] A. F. May et al. J. Appl. Phys. 106, 013706
9:00 PM - LL8.22
Electrical Characteristics and Thermal Stability of Metal Electrodes for n-type Mg2Si Prepared by Monobloc Plasma Activated Sintering Process.
Mitsuhiro Tada 1 , Tsutomu Iida 1 , Tatsuya Sakamoto 1 , Yasuhiko Honda 1 , Hirohisa Taguchi 1 , Yoshifumi Takanashi 1
1 Materials Science and Technology, Tokyo University of Science, Noda Chiba Japan
Show AbstractThe use of thermoelectric technology to convert waste heat energy directly into electrical energy has been proposed as a possible technology to reduce our dependence on fossil fuels and to reduce greenhouse gas emissions. Magnesium silicide (Mg2Si) has been identified as a promising advanced thermoelectric material operating in the temperature range from 600 to 900 K. Compared with other thermoelectric materials that operate in the same conversion temperature range, such as PbTe and skutterudite, some important characteristics of Mg2Si are that it has been identified as an environmentally-benign material, its constituent elements are abundant in the earth’s crust, and it is non-toxic. In order to realize thermoelectric devices that are based on Mg2Si, along with improvements in its thermoelectric properties, cost reductions of the source materials and manufacturing processes are also needed.Undoped and antimony (Sb) doped Mg2Si samples, using a plasma activated sintering (PAS) technique, exhibits n-type conductivity, and the value of dimensionless figure-of-merit, ZT, of 0.6~1.0 has been obtained at around 880 K. In order to fabricate Mg2Si TE power generation modules, metal electrode is indispensable to extract generated electricity efficiently. However, electrode materials, that exhibit stability at operating temperature, environmental friendliness and low production cost, have not yet been identified for n-type Mg2Si. Although silver brazing (Ag-Cu-Zn alloy) is widely used as a contact electrode to TE materials for practical operation temperatures < ~1000 K, the contact resistance to Mg2Si is not sufficiently low and the brazing process temperature is rather high. The electrical and thermoelectrical properties of n-type Mg2Si with Cu, Ti and Ni have already examined using a monobloc sintering method, which provides simultaneous formation of metal electrodes during sintering of Mg2Si. Cu and Ti electrodes were found to be unsuitable for the monobloc PAS process due to the evaporation and fusion during sintering, while Ni exhibited a stable boundary between the Mg2Si and Ni layers and its inter-layer adhesion properties were adequate at an elevated temperature of up to 900 K. In this report, in order to inquire electrode material possessing lower contact resistance, better interfacial junction to the n-type Mg2Si, and sufficient persistence at elevated temperatures, we examine the temperature-dependent electrical characteristics and durability of electrodes for Ni-related alloys and transition metal silicides on n-type Mg2Si. As for the formation of electrodes, we used the monobloc PAS process, thus, the difference of the thermal expansion between the Mg2Si and electrodes could affects to obtain a good interfacial conjugation between the electrodes and n-type Mg2Si. In order to obtain lower contact resistance and sufficient conjugation, some buffer layers have also studied between the electrodes and n-type Mg2Si.
9:00 PM - LL8.23
Thermoelectric Properties of Pseudobinary (GeTe)x(AgSbTe2)1-x Compounds Fabricated by Rapid Solidification Process.
Bong-seo Kim 1 , In-Hye Kim 2 , Jae-Ki Lee 2 , Bok-Ki Min 1 , Min-Wook Oh 1 , Su-Dong Park 1 , Hee-Woong Lee 1 , Myeong-Ho Kim 2
1 Advanced Maerials and Application Research Division, Korea Electrotechnology Research Institute, Changwon, Gyeongnam, Korea (the Republic of), 2 Department of Nano & New Materials Engineering, Changwon National University, Changwon, Gyeongnam, Korea (the Republic of)
Show AbstractThermoelectric conversion can directly convert from the thermal energy to electrical energy in solid state and vice versa. Thermoelectric conversion systems can be applied for power generation and thermoelectric cooling. It is characterized of silent (noise free), non-evolution of CO2 gas, maintenance free and long life, but low conversion efficiency due to the low figure of merit of materials. The performance of thermoelectric materials directly depend on the figure of merit, Z=α2σ/κ, here α is Seebeck coefficient, σ electrical conductivity and κ thermal conductivity. Good thermoelectric materials need a high Seebeck coefficient and electrical conductivity, and low thermal conductivity in material system. Recent trends in thermoelectric materials for medium temperature like GeTe and PbTe are focused in control of nanostructure like as nano-dot, nano-domain in matrix to reduce thermal conductivity. Ge-Te based compounds doped with Ag and Sb(TAGS) which is p-type semiconductor and pseudobinary (GeTe)x(AgSbTe2)1-x have a good figure of merit, Z=1.45 at 700K. TAGS compound which x is 80 has a good figure of merit but poor mechanical stability. To improve the mechanical stability TAGS-85 is proposed as a best compound which has both optimized thermoelectric and mechanical properties. In this study we fabricated the Ge-Te compounds doped with Ag and Sb (TAGS-85) by rapid solidification process (RSP) and sintered with Spark plasma sintering in Ar gas atmosphere.We measured the Seebeck coefficient, electrical conductivity, thermal conductivity and Hall coefficient for transport properties of electron and phonon And the nanostructure of TAGS compounds were investigated with high resolution transmission electron microscopy. Also we compared with thermoelectric properties between RSP-hot press and conventional melting-hot press.
9:00 PM - LL8.24
Thermoelectric Properties of Zn-Sn-Sb Based Alloys.
Motoki Ito 1 , Yuji Ohishi 1 , Hiroaki Muta 1 , Ken Kurosaki 1 , Shinsuke Yamanaka 1 2
1 Graduate School of Engineering, Osaka university, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan, 2 Research Institute of Nuclear Engineering, Fukui university, 3-9-1 Bunkyo, Fukui 910-8507, Japan
Show AbstractIn the Zn-Sn-Sb ternary system, Zn4Sb3, ZnSnSb2, and ZnSb have attracted attention as advanced thermoelectric materials. Especially, β-Zn4Sb3 is known as one of the most efficient materials in the temperature range of 150-400 deg C. In the present study, the Zn-Sn-Sb based alloys with various compositions were prepared and the thermoelectric properties were investigated. The alloys were prepared by melting in sealed quartz ampoules, and the obtained ingots were crushed into fine powders followed by spark plasma sintering to obtain the pellets for characterizations. From the X-ray diffraction analyses, the tin-rich (Zn,Sn)Sb alloys were identified as a single phase with a rhombohedral structure. The Seebeck coefficient S, the electrical conductivity σ, and thermal conductivity κ were evaluated in the temperature range from room temperature to 400 deg C. All the alloys indicated positive S with relatively low absolute values, e. g. 30 μV/K at room temperature. The temperature dependences of S, σ, and κ of the alloys will be discussed.
9:00 PM - LL8.25
Thermal Conductivity of Silver Ion Conductors.
Do-Young Jung 1 , Ken Kurosaki 1 , Masaaki Shuto 1 , Yuji Ohishi 1 , Hiroaki Muta 1 , Shinsuke Yamanaka 1 2
1 , Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka Japan, 2 , Research Institute of Nuclear Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui Japan
Show AbstractAgI, Ag2Te, and Ag2Se are well-known as silver ion conductors. In these compounds, a phase transition occurs at a specific temperature and silver ions will jump to interstitial sites repeatedly at the point of starting the phase transition. The active movement of silver ions would have an effect on not only the increase of the ionic conductivity but also the decrease of the lattice thermal conductivity through phonon scattering. In the present study, the thermal diffusivities and the Hall coefficients of AgI, Ag2Te, and Ag2Se were measured before and after the phase transitions. As for Ag2Te, the lattice thermal conductivity rapidly decreased after the phase transition. The effect of the silver ion movement on the lattice thermal conductivity as well as the carrier mobility will be discussed.
9:00 PM - LL8.26
Porous Silicon as Thermoelectric Material.
Johannes de Boor 1 , Dong Sik Kim 1 , Ala Cojocaru 2 , Nadine Geyer 1 , Helmut Foell 2 , Volker Schmidt 1
1 2, Max Planck Institute of Microstructure Physics, Halle Germany, 2 , Institute for Materials Science, University of Kiel, Kiel Germany
Show AbstractRecently, it has been shown that Si nanowires have a thermoelectric figure of merit ZT around unity, which is comparable to commercial state-of-the-art materials. The main reason for the improved thermoelectric properties compared to bulk Si was a dramatic reduction in thermal conductivity, presumably due to increased phonon scattering at the surface.However, Si nanowires may not be well-suited for applications in real, macroscopic devices. After all, an enormous amount of nanowires has to be fabricated and contacted successfully.We have focused on porous Si, which is in a way an inverted nanowire structure. Porous Si is sponge-like but still single-crystalline. The wall thickness of the individual elements of the Si matrix can be varied between a few and hundreds of nanometers by adjusting electrochemical etching parameters. And while the samples are nanostructured they possess macroscopic sizes: we have prepared homogeneous samples with a thickness of more than 0.1mm and a size of several square centimeters. For characterization we have investigated the dependence of the thermal conductivity on the wall thickness by means of the 3-omega method. The thermal conductivity decreases with smaller wall size, similar to what has been observed for Si nanowires. For a wall size of approx. 30 nm the thermal conductivity was measured to be around 4 Wm-1K-1 at 300 K. For good thermoelectric performance the porous Si samples have to be doped after fabrication. We have performed systematic investigation of the effect of doping time and temperature and prepared samples with resistivities ranging from 0.001 Ωcm to 1 Ωcm.
9:00 PM - LL8.28
Effects of Intercalation in Layered Transition Metal Dichacolgenides.
Tim Holgate 1 , Jian He 2 , Terry Tritt 2
1 MS&E, Clemson University, Clemson, South Carolina, United States, 2 Physics, Clemson University, Clemson, South Carolina, United States
Show AbstractTransition metal dichalcogenides form in a layered graphite-like structure with weak Van der Waals interactions between layers. Many works have shown the success of intercalating low mass elements between these layers thus changing the electronic properties. The single crystal electrical transport properties of many of these materials have been studied and are well known. However, previous to now there has been a lack of data on the thermal conductivity of needle like single crystals. This data may now be obtained through the use of a novel measurement method: parallel thermal conductance. Additionally, the advent of new processing techniques such as spark plasma sintering have given rise to the possibility of creating highly densified bulk samples for property measurements. Present work, presented herein, reveals the results of modern processing and measurement techniques performed on familiar materials to further complete our understanding.
9:00 PM - LL8.29
Thermoelectric Properties of MeV Si Ions Modified Sequentially Deposited SiO2/SiO2+Cu Nanolayered Multilayer Films.
John Chacha 1 , Satilmis Budak 1 , Cydale Smith 2 3 , Marcus Pugh 1 , Kaveh Heidary 1 , Barry Johnson 3 , Claudiu Muntele 3 , Daryush Ila 3
1 Electrical engineering, Alabama A&M University, Huntsville, Alabama, United States, 2 Physics, Alabama A&M University, Huntsville, Alabama, United States, 3 Center for Irradiation of Materials, Alabama A&M University, Huntsville, Alabama, United States
Show AbstractWe made 100 periodic nano-layers of SiO2/SiO2+Cu multilayer thin films using DC/RF sputtering. The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT = S2δT/k, where S is the Seebeck coefficient, δ is the electrical conductivity, T is the absolute temperature and k is the thermal conductivity. ZT can be increased by increasing S, increasing δ, or decreasing k. Rutherford Backscattering Spectrometry (RBS) and RUMP simulation software were used to determine the stoichiometry of SiO2, Cu in the multilayer films and the thickness of the grown multi-layer films. The 5 MeV Si ions bombardment was performed using the AAMU Pelletron ion beam accelerator, to make quantum clusters in the multi-layer superlattice thin films, to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity.
9:00 PM - LL8.3
Electrical Resistivity, Seebeck Coefficient and Crystal Structure of Mn-substituted Strontium Cobalt Lanthanum Oxides.
Julio E. Rodriguez 1
1 Department of Physics, Universidad Nacional de Colombia, Bogota Colombia
Show AbstractLa0.8Sr0.2Co1-xMnxO3 (0≤x≤0.06) perovskite oxides were synthesized by conventional ceramic route. The effect of Mn substitution for Co on transport properties and crystal structure was studied. The transport properties were studied from electrical resistivity and Seebeck coefficient measurements in the temperature range between 100 and 300 K. The magnitude of electrical resistivity and Seebeck coefficient increases with the manganese doping level. The temperature behavior of S(T) and ρ(T) was interpreted in terms of small-polaron doping mechanism. From electrical resistivity and Seebeck coefficient experimental data it was possible to calculate the thermoelectric power factor which reach maximum values around 25 μW/K2-cm in the temperature range between 200 and room temperature.
9:00 PM - LL8.30
Solid State NMR Studies of Thermoelectric Module Materials 29Si, 31P and, 11B Nuclei.
Rafael Vazquez-Reina 1 , Sohan De Silva 1 , Phillip Stallworth 1 , Steve Greenbaum 1 , Sabah Bux 2 , Richard Kaner 2
1 , Hunter College, New York, New York, United States, 2 , University of California at Los Angeles, Los Angeles, California, United States
Show AbstractThermoelectric conversion is one of the most viable technologies for small scale energy management. A thermoelectric device, which can produce an electric potential via temperature gradient, is constructed from materials that exhibit both high thermal resistance and high electrical conductivity [1]. To this end, ball-milled and doped (P, B) nano-silicon, which shows great promise towards higher Seebeck coefficients and higher efficiencies, is being developed for these applications. In order to better understand these materials, solid-state 29Si, 31P and 11B magic-angle spinning nuclear magnetic resonance (MAS NMR) has been carried out on ball milled nano-silicon samples and crystals (wafers) with increasing donor or acceptor impurity concentrations [2].
Five different ball milled nano-silicon samples were chosen where four were doped by phosphorus and boron (two samples each), whereas the fifth remained undoped. Doping levels were provided by the supplier. Also regular silicon wafers (undoped, p-type and n-type) were studied for comparison.
The behavior of the 29Si MAS NMR line center in a-Si (amorphous silicon) is significantly shifted (0.6 ppm) from the value in c-Si (silicon crystal). The observation of a comparable shift in various silicates by recent studies suggests that it is partially due to intermediate-range-order (IRO) effects [3]. In general, changes in the electronic states may arise from localization due to large density of localized occupied valance-band tail states, which are far fewer in c-Si. NMR studies also indicate that changes in IRO due to a dihedral bond angle distribution relative to c-Si may also contribute.
Two distinct sites 31P and 11B MAS NMR spectra taken for the doped a-Si. Where one resonance is due to the classic tetrahedral dopant site, the second resonance may be indicative of a different coordination about the dopant atom.
[1]Kanellos, M. (2008, November 24). Tapping America’s Secret Power Source. Retrieved from Greentech Media, October 30, 2009.
[2]E. O. Stejskal and J. D. Memory “High Resolution NMR in the Solid State: Fundamentals of CP/MAS”
[3]S. Sampath, C. J. Benmore, K. M. Lantzky, J. Neuefeind, K. Leinenweber, D. L. Price, and J. L. Yarger “Intermediate-Range Order in Permanently Densified GeO2 Glass”. Phys. Rev. Let. Vol.90, 11 (2003).
9:00 PM - LL8.31
Melt-spun Ribbon Characterization from a Thermoelectric Power Factor Screening Approach.
Yonggao Yan 1 2 , Xinfeng Tang 1 , Winnie Wong-Ng 2 , Jim Kaduk 3 , Brian Burke 1 , Gangjian Tan 1 , Wenjie Xie 1 4 , Martin Green 1 , Terry Tritt 4
1 , Wuhan University of Technology, Wuhan, Hubei, China, 2 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 3 , Poly Crystallography Inc., Naperville, Illinois, United States, 4 , Clemson University, Clemson, South Carolina, United States
Show AbstractWe demonstrated the gradient phase composition and microstructure variation inside melt-spun (MS) p-CeFe4Sb12, and p- and n-Bi2Te3 ribbons by using X-ray diffraction and a power factor screening tool previously developed at NIST. The spatial variation of thermoelectric (TE) properties has been observed and demonstrated to be correlated with phase composition and microstructure throughout the tapes. Unlike the Bi2Te3 ribbons, the CeFe4Sb12 ribbons show complex phase segregation as well as morphology variation. A versatile model has been established based on the results of property/microstructure relationships to describe the microstructure and phase evolution during the MS process and also to serve as a guide to optimize the MS process parameters.
9:00 PM - LL8.32
Thermoelectric Properties of BiTe-InSe Nano-composite Thin Film.
Kwang-Chon Kim 1 2 , Won Chel Choi 1 , Hyo-Jung Kim 1 3 , Kyooho Jung 1 , Hyun Jae Kim 2 , Jin-Sang Kim 1
1 Electronic materials center, Korea Institute of Science and Technology, Seoul, cheongryang, Korea (the Republic of), 2 School of Electrical and Electronic Engineering, Yonsei University, Seoul, Seodaemun-Gu, Korea (the Republic of), 3 Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show Abstract Thermoelectric materials based on bismuth telluride (Bi-Te) have been adapted to achieve a high figure of merit (ZT) at room temperature. However, it has a limit to get ZT value higher than 1. So some researchers are trying to enhance the ZT value through control of the grain size, because the grain boundary plays important role in the phonon scattering due to decreasing the thermal conductivity, which command the thermoelectric property of materials. In this work, we had tried to enhance the ZT value of Bi-Te thin film through nano-particlization and nano- composite with In-Se nano-particles. The BiTe-InSe compounded thin films were prepared by RF co-sputtering technique at room temperature and the nano-composite thin films were fabricated by sequential annealing, which was performed in Argon (99.999%) ambient with a temperature range of 150 – 500°C. Structural characterizations were done using X-ray diffraction (XRD, BRUKER, D8, 60kW) and transmission electron microscopy (TEM, FEI, Tecnai, F30 S-Twin), respectively. By addition of In-Se to Bi-Te thin film, we could achieve the average grain size of ~10 nm, which is smaller than that (~50 nm) of Bi-Te thin film. It was also confirmed that the grain size can be controlled by the post-annealing. The maximum value in Seebeck coefficient and power factor was -131 μV/K at 150°C and 1.15 μW/K^2cm at 400°C, respectively. The addition of In-Se contributed to the enhancement of Seebeck coefficient and the ZT of Bi-Te thin film.
9:00 PM - LL8.33
The Effect of Grain Size on the Thermoelectric Properties of BiTe-InSe Thin Film with Multi-layer Structure.
Hyo-Jung Kim 1 2 , Kwang-Chon Kim 1 3 , Won Chel Choi 1 , Chan Park 2 , Jin-Sang Kim 1
1 Electronic Materials Center, Korea Institute of Science and Technology (KIST), Seoul Korea (the Republic of), 2 Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of), 3 School of Electrical and Electronic Engineering, Yonsei University, Seoul Korea (the Republic of)
Show AbstractThe effect of grain size on the thermoelectric properties of BiTe thin film compounded with InSe was investigated. The grain sizes of BiTe and InSe were controlled by a multi-layer structure, which was fabricated by depositing alternate layers of indium selenide and bismuth telluride films which was followed by annealing. The structure of the multi-layer film was Bi-Te /In-Se/ Bi-Te/In-Se, and it was prepared on sapphire substrate by RF magnetron sputter using stoichiometric Bi2Te3 (99.9%) and In2Se3 (99.99%) target at room temperature. Then, it was annealed at temperature range of 150 – 500℃ in Ar ambient. Structural characterizations were carried out using X-ray diffraction (XRD, BRUKER, D8, 60kW) and transmission electron microscopy (TEM, FEI, Tecnai, F30 S-Twin). Cross-section of multi-layer structure was observed by Scanning electron microscopy (SEM). The resistivity and Seebeck coefficient of these samples were measured using conventional equipment at room temperature. The grain size of BiTe and InSe could be controlled via modulation of the each layer thickness and sequential annealing. The effect of grain size on the thermoelectric properties of BiTe - InSe multi-layer film was investigated, and the results and the causes of the change of the properties will be presented and discussed. This research was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (# 2009-0082026) and the Core Technology of Materials Research and Development Program of the Korea Ministry of Intelligence and Economy (# K0006007).
9:00 PM - LL8.34
Improved Thermoelectric Efficiency of Silicon Germanium Alloys at Moderate Temperatures by Nanostructuring.
Liang Yin 1 , Choongho Yu 1
1 MEEN, Texas A&M University, College station, Texas, United States
Show AbstractSilicon germanium alloys are high performance thermoelectric materials that have been used at high temperatures (above 1000 K). However, their performance at moderate temperatures is not competitive due to relatively high thermal conductivity with moderate electrical conductivity and thermopowers. This paper presents performance enhancement of silicon germanium alloys by making them into nanowire shapes at temperatures below 450 K. Particularly, thermal conductivity has been reduced significantly, which results in a large increase in the thermoelectric figures of merit. In order to characterize thermoelectric properties, nanowires were suspended between two membranes whose temperatures were measured by resistance sensors. Their thermal conductivities were measured to be ~1.4 W/m-K, which is ~5 times smaller than bulk alloys. Furthermore, the influence of oxide layers on thermoelectric properties is also discussed.
9:00 PM - LL8.35
Polymeric Materials for Exceptional Thermoelectric Properties.
Kyungwho Choi 1 , Jaime Grunlan 1 , Choongho Yu 1
1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractOrganic material based composites have been recently reported to be promising thermoelectric materials. Particularly, the thermoelectric properties of carbon nanotube (CNT) based nanocomposites can be manipulated by various methods including metal nanoparticle incorporation. This is because carriers transport occurs along the nanotubes, which makes it susceptible to impurity incorporation. Depending on reduction potential and intrinsic properties of incorporated metal nanoparticles, electrical transport has been dramatically changed. Furthermore, the large different in mass between metals and carbon plays a role in disrupting coherent phonon transport. For example, when gold particles were incorporated into the composites, electrical conductivity was increased to ~10^5 S/m without significant changing of thermopower (or Seebeck coefficient) and thermal conductivity. This study demonstrates that metal incorporated CNT/polymer nanocomposites could be viable approaches for improving thermoelectric transport properties in organic nanotube composites.
9:00 PM - LL8.36
Large Thermoelectric Voltage in Point Contacts of Ni Ferromagnetic Metals.
Kenji Kondo 1 , Hideo Kaiju 1 2 , Akira Ishibashi 1
1 , Research Institution for Electronic Science, Sapporo Japan, 2 , PRESTO, Japan Science and Technology Agency, Kawaguchi Japan
Show AbstractWe have theoretically investigated thermoelectric effects in point contacts (PCs) of Ni ferromagnetic metals using spin quantum cross structure (SQCS) devices, and we have verified the thermoelectric effects in PCs of Ni ferromagnetic metals experimentally. The SQCS device is one of the nanoscale junction devices, which consists of two ferromagnetic metal thin films with their edges crossing. The junction area made of two edges can be scaled down to nanometer size due to the good resolution in making films by the metal-deposition rate, ranging from 0.01 to 1 nm/s. We have analyzed the spin dependent thermoelectric characteristics within the framework of the Anderson Hamiltonian, taking into consideration the dimensionality of electrons in both electrodes. Then, we have obtained the theoretical results that a large thermoelectric voltage can emerge in PCs of Ni ferromagnetic thin films. In the calculation, we assumed that the gap of PCs was approximately ∼2 nm and there existed energy-states in the gap due to a parabolic confinement potential formed by surface states of two Ni electrodes. The energy-states, ε(1), ε(2), were set to be 10 meV, 20 meV, respectively. Also, we have calculated thermoelectric characteristics when two Ni electrodes have the parallel magnetic moment, and when two Ni electrodes have the antiparallel magnetic moment, respectively. As a result, the thermoelectric voltage Vq changes from 0.48 mV to 2.12 mV with the temperature difference of PCs increasing from 10 K to 50 K. Also, the magnitude of the thermoelectric voltage Vq is independent of spin direction and the thermopower is 42.4 μV/K for both spin directions. On the other hand, the power extracted from PCs of the devices is dependent on spin direction. We find that PCs of Ni SQCS devices can serve as spin dependent thermobatteries. You may think that the difference of the temperature 50 K is large. However, the difference can easily occur at the condition that the thermal conductivity of two electrodes differs from each other by one order of magnitude. The change of ambient temperature causes the thermal current between two electrodes so that the temperature of the two electrodes is approaching the same as the ambient one. This process is much longer than expected, and it takes about 5 minutes to be in equilibrium. Then, the thermal flow is disturbed at PCs of SQCS devices because the thermal conductance of PCs of SQCS devices is as small as 6.58x10-11 W/K. This causes the large temperature difference to make the same amount of the thermal flow through PCs. We also measured the experimental thermoelectric characteristics of PCs of Ni SQCS devices with the ambient temperature changing. The experimental thermoelectric voltage was as large as 2.2 mV with an ambient temperature change of 1 K. This large thermoelectric voltage shows good agreement with calculation results performed within the framework of the Anderson model.
9:00 PM - LL8.37
Period Control of InGaO3(ZnO)m Superlattice Thin Films for Thermoelectric Applications by the Thickness of ZnO Buffer Layers on Sapphire Substrate.
Dong Kyu Seo 1 , Cheol Hyoun Ahn 1 , Bo Hyun Kong 1 , Ho Seong Lee 2 , Hyung Koun Cho 1
1 School of Advanced Materials Science Engineering, Sungkyunkwan Univ., Suwon Korea (the Republic of), 2 Department of Materials Science and Metallurgy, Kyungpook University, Daegu Korea (the Republic of)
Show AbstractThermoelectric (TE) effect means that conversion between electric to heat energy and vice versa. It is noticed as a candidate of green alternative energy because of no generation of pollution or noise. Most of all, TE enable recycle wasted heat of device, vehicles or other generators so that allows enhancement of energy efficiency. Development of TE is mostly focused on investigation of materials with high TE properties which are evaluated by ‘thermoelectric figure of merit (ZT=S2σ/κ, S : Seebeck coefficient, σ : electrical conductivity, κ : thermal conductivity)’ The development of TE materials with low dimensional structures such as superlattice and nanowire suggests possibility of enhancement of the figures of merit of TE devices due to the quantum effect or reduction of κ. In particular, thin-film based superlattice structure has a merit to reduce thermal conductivity (κ) effectively, where the occurrence of phonon scattering is expected due to the formation of interfaces of superlattice. Representative TE material BiTe compound shows high ZT value, and application of nanostructure before-mentioned is widely investigated. However, BiTe exhibits demerits such as low stability at high temperature, low mechanical stability, and toxicity of Bi element also.On the other hand, oxide materials are chemically stable, nontoxic, cheap and easy to fabricate. They have received an attention as a candidate of high temperature TE materials. P-type cobalt oxide is a representative oxide TE material. However, n-type oxide shows relatively low ZT value.ZnO based oxide semiconductors are naturally n-type semiconductor and also have wide band gap and good electrical conductivity by incorporating dopants. In particular, multi-component InGaZnO naturally forms superlattice structure when crystallized so that is expected to be able to enhance ZT effectively by decreasing κ when fabricated into single crystal. Following the research of fabrication of single crystal InGaZnO with superlattice structure, the InGaZnO film requires high growth/annealing temperatures above 1400 oC. In our study, we successfully fabricated the InGaZnO thin films with perfect superlattice structure by introducing ZnO buffer layers and appropriate post-thermal treatment, which is expected to be a very useful method to decrease κ. To produce superlattice structure, the InGaZnO thin films with the stoichiometry of 1(Ga):1(In):1(Zn) were deposited on the ZnO buffer layers with various thicknesses by magnetron sputtering. Post-thermal treatment was provided in 900 oC, to prevent reaction between ZnO buffer and substrate. During post-thermal treatment, the InGaZnO film and ZnO buffer layer were intermixed with being crystallized. As a result, the final composition (In:Ga: Zn ratio) and superlattice period of the films were determined by the thickness of ZnO buffer layers.
9:00 PM - LL8.38
Structure and Thermoelectric Properties of La-doped Double-Perovskite Oxide Sr2CoTiO6.
Tohru Sugahara 1 , Michitaka Ohtaki 2 , Ken Kurosaki 1 , Hiroaki Muta 1 , Yuji Ohishi 1 , Shinsuke Yamanaka 1 3
1 Graduate School of Engineering, Osaka University, Suita Japan, 2 Interdiscipilnary Graduate School of Engineering Sciences, Kyushu University, Kasuga Japan, 3 Research Institute of Nuclear Engineering, Fukui University, Fukui Japan
Show AbstractThe search for new oxide thermoelectric materials is becoming more and more important for recovery and utilization of high temperature waste heat. It is important to develop new oxide materials with high thermoelectric efficiency. Recently, we investigated the thermoelectric properties of several double-perovskite oxides, Ca2-xSrxFeMoO6, Sr2-xBaxFeMoO6[1], Sr2-xLaxMnMoO6[1], Ba2-xLaxFeMoO6, etc. These oxides show relatively high thermoelectric performance as oxides, because the thermal conductivity of the double-perovskite oxides is much lower than those generally observed oxides. The objective of this study is to increase the thermopower of the double-perovskite oxides by introducing Ti with narrow 3d band, maintaining the low thermal conductivity of the oxides.The thermoelectric properties of La-doped double-perovskite oxides Sr2-xLaxCoTiO6 were investigated with respect to their crystal structure. The samples were prepared by conventional solid state reaction. The crystal structures of all the samples were refined by the Reitveld method, assuming I4/m and P21/n space groups. The electrical conductivity, Seebeck coefficient, and thermal conductivity of the oxides were measured by 4-wire method, steady state method, and laser flash technique, respectively.An XRD study indicated that all the samples are almost single phase. The samples at x = 0.0 - 0.8 crystallized in the tetragonal perovskite structure, and the sample at x = 2.0 showed a monoclinic structure. The oxides showed significantly low thermal conductivity values at around 1.5 W/mK. However, the electrical conductivity and the absolute values of the Seebeck coefficient of the oxides were lower than those of the other double-perovskite oxides we have reported previously [1].
[1] T. Sugahara, M. Ohtaki, T. Souma, J. Ceram. Soc. Jpn., 116 (12), 1278-1282 (2008).
9:00 PM - LL8.39
Incipient Wetness Preparation of Nanostructured Materials for Thermoelectrics.
Shreyashi Ganguly 1 , Kevin Zhou 2 , Donald Morelli 2 , Jeff Sakamoto 2 , Ctirad Uher 3 , Stephanie Brock 1
1 Chemistry, Wayne State University, Detroit, Michigan, United States, 2 Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, United States, 3 Physics, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractAn approach for the synthesis of compositionally heterogeneous and homogeneous nanostructures with potential for improved thermoelectric properties is presented. Better materials for interconversion of thermal and electrical energy, as assessed by figure of merit, ZT (ZT = (S2 σ) T / κ ; S = Seebeck coefficient, σ = electrical conductivity, κ = thermal conductivity), are needed if thermoelectric technologies are to become commercially viable for electrical energy generation or refrigeration (ZT > 3 from current ZT ~ 1). Improvements in ZT can potentially be achieved by the creation of nanostructures. This can be ascribed to a number of factors, among them (1) quantum confinement effects in nanostructured materials resulting in increased density of states at the Fermi level, which increases the thermopower (S2σ); and (2) reduction of thermal conductivity (κ) by the introduction of interfaces and pores in the material.In an effort to understand how nanoscale inclusions impact the thermoelectrically relevant properties of materials, we are developing routes that enable inclusion size to be sensitively tuned. This can be achieved by solution phase synthesis of quantum dots followed by their introduction into bulk matrices using incipient wetness techniques. In the present work, the preparation of nanostructures by incorporation of discrete PbTe and Bi2Te3 nanoparticles into a secondary bulk phase, Bi2Te3, will be reported. Additionally, preliminary measurements of relevant thermoelectric properties will be described and the suitability of these nanostructures for thermoelectric applications discussed.
9:00 PM - LL8.41
Thermoelectric Performance of the p-type Zr0.5Hf0.5Co0.4Rh0.6Sb1-xSnx (0 < x < 0.5) Half-Heusler Alloys.
Pramathesh Maji 1 2 , Julien Makongo 1 2 , Pierre Poudeu Poudeu 1 2
1 Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana, United States, 2 Department of Chemistry, University of New Orleans, New Orleans, Louisiana, United States
Show AbstractIn our previous work, we investigated the effect of rhodium substitution at the cobalt site on the thermoelectric properties of Zr0.5Hf0.5CoyRh1-ySb0.99Sn0.01 (0< y <1) alloys. The composition Zr0.5Hf0.5Co0.6Rh0.4Sb0.99Sn0.01 showed the highest thermoelectric performance among this series of alloys with lattice thermal conductivity as low as ~3.4 W/mK at 775K [1]. However, the ZT value remained very low (~0.03 at 775K). Here, we report large improvement in the thermoelectric figure of merit via Sn doping at the Sb site in Zr0.5Hf0.5Co0.4Rh0.6Sb1-xSnx alloys. Several compositions with various Sn concentrations were synthesized via mechanical alloying using hardened steel jar and balls. X-ray powder diffraction indicates the formation of single phase half-heusler alloys after 10hrs ball milling. High density pellets of the synthesized materials were obtained using a uniaxial hot-press system and their thermoelectric properties were measured in the temperature range from 300K to 775K. A ZT value as high as 0.2 was observed at 775K for the composition Zr0.5Hf0.5Co0.4Rh0.6Sb0.8Sn0.2 (x = 0.2). This is about seven times the value reported for the composition with x = 0.01 [1]. Although Sn doping at the Sb site was primarily intended to optimize the power factor, significant reduction of lattice thermal conductivity was also achieved for composition with high Sn (x > 0.3) content due to phonon scattering via mass fluctuation between tin and antimony. The effect of Sn doping on the thermoelectric performance of Zr0.5Hf0.5Co0.4Rh0.6Sb1-xSnx alloys will be discussed using transmission electron microscopy, Hall coefficients, electronic charge transport and thermal conductivity data.[1] Maji, P.; Takas, N. J.; Misra, D. K.; Gabrisch, H.; Stokes, K.; Poudeu, P. F. P.; J. Solid State Chem. 2010, 183, 1120 – 1126.
9:00 PM - LL8.5
Thermomechanical and Thermoelectric Properties of Porous Bi2Te3 Thin Films.
Jae Yong Song 1 3 , Seungmin Hyun 2 , Nguyen Thach 1 , Ho -Ki Lyeo 1
1 , Korea Research Institute of Standards and Science, Daejeon Korea (the Republic of), 3 Dept. of Nano Science, University of Science and Technology, Daejeon Korea (the Republic of), 2 , Korea Iintitute of Machinery and Materials, Daejeon Korea (the Republic of)
Show AbstractBismuth telluride (Bi2Te3) has attracted much attention on its high efficiency in thermoelectric energy conversion near room temperature. Since the works of Hicks and Dresselhaus [1], recently, there have been many efforts to enhance the figure of merit (FOM) by controlling the thermal conductivity of the thermoelectric materials. In this study, Bi2Te3 thin films with n-type carriers were prepared by magnetron cosputtering method. We investigated the thermo-mechanical behaviors of Bi2Te3 thin films during the thermal annealing process up to 773 K using the in-situ wafer curvature measurements (K-Space Associates, MOS) and then measured the thermoelectric properties of Seebeck coefficient (Fraunhofer IPM), electrical conductivity (van der Pauw method, Ecopia Inc, HMS-5000) and thermal conductivity (time-domain thermo-reflectance method) after the thermal annealing processes. Results showed that the electrical conductivity decreased from 1224 to 781 /(Ωcm) with the annealing temperature above 573 K, which was due to the decrease of carrier concentration. Interestingly, the Seebeck coefficient abruptly increased up to 81 from 221 μV/K with the annealing temperature increasing above 573 K. The change in the thermal conductivity was relatively small. We discuss that the microstructure changes in the Bi2Te3 thin films are responsible for the evolution of high tensile stress (about 200 MPa) as well as the improvement of thermoelectric properties. [1] L.D. Hicks and M.S. Dresselhaus, Phys. Rev. B47, 12727 (1993)
9:00 PM - LL8.7
Process Repeatability and Thermoelectric Property Studies on n-type Bi2Te2.7Se0.3 by Addition of Copper.
Weishu Liu 1 , Qinyong Zhang 1 , Yucheng Lan 1 , Giri Joshi 1 , Hui Wang 1 , Zhifeng Ren 1 , Gang Chen 2
1 Department of Physics, Boston College, Chestnut Hill, Massachusetts, United States, 2 Department of Mechanical Engineering, Massachusetts Institute of technology, Newton, Massachusetts, United States
Show AbstractA significant enhancement has been reported in p-type Bi0.4Sb1.6Te3 nanocomposite by combining high energy ball milling and hot pressing. The same technique has been applied to the n-type Bi2Te2.7Se0.3, but without any improvement on ZT since the benefit from the decreased lattice thermal conductivity is off set by the decreased power factor and increased carrier thermal conductivity due to the higher carrier concentration and carrier mobility, and the worst is that the process is very unrepeatable. Here, we show that an improved repeatability has been achieved by introducing a very low concentration of copper. The peak ZT values are 0.94 and 0.99 when measured in the in-plane and out-of-plane direction, respectively. This is higher than the peak ZT of 0.85 for the pure Bi2Te2.7Se0.3. The impact of Cu concentration on thermoelectric transport properties was also investigated.
9:00 PM - LL8.8
Comparison of Thermoelectric Performance in Nanodot Nanocomposites and Nanograined Nanocomposites.
Chanyoung Kang 1 , Hyoungjoon Kim 1 , Sung-geun Park 1 , Kangmin Kim 1 , Buyoung Jung 1 , Woochul Kim 1
1 School of Mechanical engineering, Yonsei university, Seoul Korea (the Republic of)
Show AbstractMost recent increases in thermoelectric performance have come by reducing thermal conductivity through nanostructuring. Interfaces in the nanostructures scatter phonons much more effectively than electrons. As a result of this, research efforts are mainly focused on bulk nanocomposites which have huge surface area-to-volume ratio. We simulated the thermal conductivities of two types of nanocomposites. We nanostructured Tl0.02Pb0.98Te1 by (i) embedding InSb nanodots in it, creating a nanodot nanocomposite, and (ii) polycrystallizing it, creating a nanograined nanocomposite. The thermal conductivity of phonons is predicted using Callaway’s model2. And we need to fix power factor, so we assumed minimum nanograin or inter-nanodots distance is larger than electron mean free path of Tl0.02Pb0.98Te. The nanograined nanocomposite achieved lower thermal conductivity than did the nanodot nanocomposite due to the ability of the nanosized grains in nanograined nanocomposites to effectively scatter phonons over a wide range of frequencies, as long as the nanograined nanocomposite has sufficiently small grain size. We also developed a rule-of-thumb expression for when thermal conductivities of those two composites are the same.
9:00 PM - LL8.9
Effects of Group III Element Doping on Thermoelectric Properties of PbTe.
Shuang Tang 1 , Keivan Esfarjani 4 , Tomasz Radzynski 6 , Andrzej Lusakowski 6 , Zhifeng Ren 5 , Gang Chen 4 , Mildred Dresselhaus 2 3
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 4 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 6 Institute of Physics, Polish Academy of Sciences, Warsaw Poland, 5 Department of Physics, Boston University, Chestnut Hill, Massachusetts, United States, 2 Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThe basic physics of group III element (In, Tl)-doped PbTe is of great interest for its potential application in thermoelectrics. The doping effects on the band structure are significant aspects of understanding how the doping defects influence the thermoelectric transport properties of the material. Here, we investigate the possibilities of different doping mechanisms and the associated changes expected in the electronic band structure. In this work, the density functional theory (DFT) method has been employed with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional and the inclusion of spin-orbit interaction. The effect of the latter, as well as the type of doping on the electronic structure has been studied, and in each case, the nature of the doping (n or p) has been elucidated. The concentration effect is taken into account by performing calculations using a super-cell. The density of states is further obtained, which can lead to the calculation of the Seebeck coefficient using the relaxation time approximation and compared to recent experiments.
Symposium Organizers
Terry M. Tritt Clemson University
George S. Nolas University of South Florida
Yuri Grin Max-Planck Institute for Chemical Physics of Solids
Jeff Sharp Marlow Industries, Inc.
LL9: Thermoelectric Materials/Chalcogenides II
Session Chairs
Harald Boettner
Yuri Grin
Thursday AM, December 02, 2010
Commonwealth (Sheraton)
9:30 AM - LL9.1
Thermoelectric Characterization of Single Phase MnSi1.75-x Grown from Solution.
Haruhiko Udono 1 , Yoshiyuki Takahashi 1 , Yusuke Ujiie 1 , Isao Ohsugi 2 , Tsutomu Iida 3
1 Electrical and Electronic Engineering, Ibaraki University, Hitachi Japan, 2 , Salesio Polytechnic, Machida Japan, 3 , Tokyo University of Science, Noda Japan
Show AbstractHigher manganese silicides (HMSs) with a formula of MnSi1.75-x are one of the attractive thermoelectric materials because they have relatively high figure of merit ZT ~0.7 and high oxidation resistance in an intermediate temperature range (~ 800K) [1]. Natural abundance of the constituent elements and their low-toxicity are suitable for use in a large-scale thermoelectric power generation and also a human-friendly thermoelectric power source in consumer use. Since energy gaps of HMSs (0.6-0.8eV) are close to that of Mg2Si (0.66eV) and their Fermi levels lie near the valence band, the HMSs are preferable to use as a p-leg combined with the magnesium silicide n-leg in thermoelectric energy conversion. There are several reports concerning four different tetragonal phases within MnSi1.75-x formula such as Mn4Si7, Mn11Si19, and Mn15Si26 and Mn27Si47. However, investigations on the thermoelectric property of single phase HMSs are limited, so far. Recently, we have obtained single phase Mn11Si19 crystals by temperature gradient solution growth (TGSG) method using Ga solvent and reported their thermoelectric property at low temperatures. Here, we report precise thermoelectric properties of single phase Mn11Si19 crystals above room temperature. The bulk single phase Mn11Si19 crystals with size of 11mm in diameter and 2-4mm in thickness were grown by the TGSG method. Seebeck coefficient and resisitivity were evaluated using ZEM-2 between 330K and 850K. Thermal conductivity was also determined by static measurement or laser flash measurement. Powdered X-ray diffraction measurement confirmed that the crystals are single phase Mn11Si19. Electrical conductivity of the typical crystal was 0.0015 Ωcm at 330K and increased up to 0.0025 Ωcm at 850K. The values are lower than that of melt grown poly phase MnSi1.7 crystals. Seebeck coefficient of the crystal was 150μV/K at 330K and 204μV/K at 850K.
9:45 AM - LL9.2
Thermoelectric Properties of Zinc Oxide Nanowires Embedded in Aerogel.
Jing Xie 2 , Bruce White 1 2
2 Materials Science Program, Binghamton University, Binghamton, New York, United States, 1 Physics, Binghamton University, Binghamton, New York, United States
Show AbstractThe development of efficient and sustainable thermoelectric materials is required for widespread adoption of this technology in waste heat energy scavenging. Due to the ability to form nanocomposite materials with characteristic dimensions smaller than the dominant phonon mean free path, the engineered scattering of phonons opens up the possibility of independent optimization of the electrical and thermal properties of these solids - an artificial means to creating the highly desired electron crystal-phonon glass thermoelectric material. In this work we report on the thermoelectric properties of zinc oxide embedded in silica aerogels. Well arrayed zinc oxide nanowires are grown on a sputtered zinc oxide thin film by the thermal decomposition of hexamine and zinc nitrate in aqueous solution. The nanowires are suspended in silica gel prior to the supercritical drying required to form the highly porous, low thermal conductivity aerogel. Thin films are characterized structurally using x-ray diffraction, scanning electron microscopy, and energy dispersive x-ray spectroscopy. Thermal conductivity measurements are carried out using the well known 3 omega technique.
10:00 AM - LL9.3
Atomistic Modeling of Thermal Transport in SiGe Alloys: Green's Function and Molecular Dynamics Approaches.
Ivana Savic 1 , Davide Donadio 2 , Giulia Galli 1 3
1 Department of Chemistry, UC Davis, Davis, California, United States, 2 , Max Planck Institute for Polymer Research, Mainz Germany, 3 Department of Physics, UC Davis, Davis, California, United States
Show AbstractIt has been suggested that SiGe based nanostructured materials may have considerably lower thermal conductivity than that of their bulk counterparts, and thus a significantly improved thermoelectric figure of merit [1]. Atomistic-level theories are expected to play an important role in understanding the physical processes responsible for heat transport in alloys, in interpreting recent measurements and guiding new experiments. However, several conceptual and computational issues related to modeling of thermal transport in alloys at the microscopic scale are yet unsolved [2]; in particular,an assessment of the regime of validity of the different techniques commonly used to model heat transport, such as Green's function (GF) and molecular dynamics (MD) methods, is still missing. In this work, we compare the results obtained for the thermal conductivity of SiGe alloysusing GF techniques [3] with those of equilibrium MD [4], we identify the strengths and weaknesses of the two approaches and discuss their suitability to describe nanostructured alloys. Work supported by DOE-SciDAC, DE-FC02-06ER25794. [1] M. S. Dresselhaus, G. Chen, M. Tang, R. Yang, H. Lee, D. Wang, Z. Ren, J.-P. Fleurial, and P. Gogna, Adv. Mater. 19, 1043 (2007). [2] A. Skye and P. K. Schelling, J. Appl. Phys. 103, 113524 (2008). [3] I. Savic, N. Mingo, and D. A. Stewart, Phys. Rev. Lett. 101, 165502 (2008). [4] D. Donadio and G. Galli, Phys. Rev. Lett. 99, 255502 (2007).
10:15 AM - LL9.4
High Seebeck Coefficient in ScB~30, a Boron-rich Boride.
Frederick Stober 1 , Joachim Barth 2 , Claudia Felser 2 , Barbara Albert 1
1 Eduard-Zintl-Institute of Inorganic and Physical Chemistry, Technische Universität Darmstadt, Darmstadt Germany, 2 Institut für Anorganische und Analytische Chemie, Johannes-Gutenberg-Universität Mainz, Mainz Germany
Show AbstractBoron-rich borides are promising materials for thermoelectrics, due to their extreme thermal stability, semiconducting properties and good Seebeck coefficients. Boron in its β-rhombohedral modification is a semiconductor with low thermal conductivity and remarkable thermal stability. Its Seebeck coefficient has been described to be up to 800 µV/K at room temperature, but decreases at increasing temperatures. The electrical conductivity is too low to make it an interesting material for thermoelectrics. It is possible to introduce metal and halfmetal atoms into the boron atom framework (Y, Mn, Ni, Sc, Si), thus forming metal borides with β-B structure with possibly higher electrical conductivities.Boron-rich scandium boride ScB~30 was obtained by heating the elements in an induction furnace or an electric arc at temperatures of 2000 K and approx. 3000 K, respectively. In both cases, the sample obtained consisted of very hard agglomerates of crystalline material. Electrical and thermal conductivities as well as Seebeck coefficients were measured using a PPMS (Quantum Design) for low and LSR3 (Linseis) for high temperatures. With a Seebeck coefficient ranging from 50 µV/K at 50 K up to 400 µV/K at 1450 K and still rising the Seebeck coefficient of this ScB~30 is larger than that of all other boron-rich borides with β-B structure that have been investigated so far. The electrical conductivity was raised several magnitudes in comparison to pure β-B Boron up to 1700 S/m at 1450 K, whilst still keeping the thermal conductivity at 4 W/(Km) as it is typical for boron rich borides.
10:30 AM - LL9.5
Preparation and Thermoelectric Properties of Polycrystalline Nonstoichiometric Yb14MnSb11 Zintl Compound and Lu Doping Effect Study.
Cui Yu 1 , Tiejun Zhu 1 , Xinbing Zhao 1
1 , Zhejiang University, Hangzhou, Zhejiang, China
Show AbstractPolycrystalline nonstoichiometric Yb14MnSb11 compounds have been successfully prepared by modified induction melting and spark plasma sintering. The carrier concentration was finely tuned by changing the elemental ratio of Mn to Sb. Excess Mn decreases the electrical conductivity and increases the Seebeck coefficient. The thermal conductivity of all samples was less than 1.0 Wm-1K-1. A maximum ZT value is 0.35 at 673K for Yb14Mn1.05Sb11, significantly higher than that of stoichiometric Yb14MnSb11 polycrystalline sample. On this basis, Lu doping effect on the Yb site was studied.
10:45 AM - LL9.6
Interplay of Electron Correlation, Indium Doping and Nanostructuring Process in Thermoelectric Study of FeSb2.
Song Zhu 1 , Wenjie Xie 1 , Menghan Zhou 1 , Jian He 1 , Terry Tritt 1
1 Physics & Astronomy, Clemson University, Clemson, South Carolina, United States
Show AbstractAs a narrow-gap strongly correlated semiconductor, FeSb2 exhibits a huge thermopower and a relatively high lattice thermal conductivity at low temperatures. This material has attracted considerable interest recently due to its potential for thermoelectric applications. We herein report a novel doping-nanostructuring approach. In this work, a series of Indium-doped FeSb2 samples were prepared using a quench-and-anneal method followed by melt-spin and spark plasma sintering procedure. The X-ray diffraction, electron microscopy and elemental analysis corroborated that the InSb nanodots were formed in situ on the boundaries of FeSb2 coarse grains and the amount of nanodots was systematically increased with the increasing Indium content in the starting material. The presence of such nanoinclusions and other as-formed multi-scaled microstructures dramatically reduced the lattice thermal conductivity without significantly degrading the electrical properties. The impact of In-doping and nanostructuring on the thermoelectric properties of FeSb2 has been investigated by means of resistivity, Seebeck coefficient, thermal conductivity, Hall coefficient, Mossbauer spectroscopy and specific heat measurements in a wide range below and above room temperature. The impact of electron correlations, Fe:Sb non-stoichiometry, and melt-spin process has been discussed in view of the variation of thermoelectric performance. Overall, FeSb2-based materials have showed a promising potential for thermoelectric cooling applications at cryogenic temperatures.
11:30 AM - LL9.7
High Thermoelectric Performance in PbTe due to Large Nanoscale Ag2Te Precipitates.
Jeff Snyder 1
1 G Jeffrey Snyder, Caltech, Pasadena, California, United States
Show AbstractPbTe-based materials with small (< 20nm) nanoscale features have been previously shown to have high thermoelectric figure-of-merit, zT, largely arising from low lattice thermal conductivity particularly at low temperatures. Separating the various phonon scattering mechanisms and the electronic contribution to the thermal conductivity is a serious challenge to understanding, and further optimizing, these nanocomposites. Here we show that relatively large nanometer-scale (50-200nm) Ag2Te precipitates in PbTe can be controlled according to the equilibrium phase diagram and these materials show intrinsic semiconductor behavior with high electrical resistivity, enabling direct measurement of the phonon thermal conductivity. This study provides direct evidence that even large nanometer-scale microstructures reduce thermal conductivity below that of a macro-scale composite of saturated alloys with Kapitza-type interfacial thermal resistance at the same overall composition. Carrier concentration control is achieved with lanthanum doping, enabling independent control of the electronic properties and microstructure. These materials exhibit lattice thermal conductivity which approaches the theoretical minimum above ~650K, even lower than that found with small nanoparticles. Optimally La-doped n-type PbTe-Ag2Te nanocomposites exhibit zT > 1.5 at 775 K.
11:45 AM - **LL9.8
Reduction of Lattice Thermal Conductivity by Controlling Distribution of Structural Vacancies.
Shinsuke Yamanaka 1 2 , Ken Kurosaki 1 , Chang-eun Kim 1 , Yuji Ohishi 1 , Hiroaki Muta 1 , Manabu Ishimaru 3
1 Graduate School of Engineering, Osaka University, Suita Japan, 2 Research Institute of Nuclear Engineering, University of Fukui, Fukui Japan, 3 Institute of Scientific and Industrial Research, Osaka University, Ibaraki Japan
Show AbstractGa2Te3 and Ga2Se3 have the same crystal structure: a defect zinc-blende cubic crystal. Due to the valence mismatch between the cation and anion, one-third of the cation sites are structural vacancies in both Ga2Te3 and Ga2Se3; i.e., the chemical formula of Ga2M3 (M = Te or Se) can be described as Ga2VA1M3, where VA means vacancy. It has been expected that Ga2Te3 has a mesoscopic super-structured phase, having vacancy planes. We hypothesized that if we could create such vacancy planes in bulk Ga2Te3 and Ga2Se3 and control their size and periodicity, we could achieve a low lattice thermal conductivity, due to the effective phonon scattering by the vacancy planes. We have tried to control the vacancy distribution in Ga2Te3 and Ga2Se3 by changing the annealing conditions and investigated their thermoelectric properties. In addition, solid solutions of GaSb-Ga2Te3 and InSb-In2Te3 have been prepared and the thermoelectric properties were examined. Effect of the distribution of the structural vacancies on the thermoelectric properties will be discussed.
12:15 PM - LL9.9
Thermoelectric Properties of N-type PbSe Doped with Pb, In and Ga.
Iliya Todorov 1 , John Androulakis 1 , Yeseul Lee 1 , Duck-Young Chung 2 , Mercouri Kanatzidis 1 2
1 Chemistry, Northwestern University, Evanston, Illinois, United States, 2 Materials Science Division, Argonne National Laboratory, Lemont, Illinois, United States
Show AbstractPbSe combines a number of attractive features for potential thermoelectric applications like a highly symmetric cubic structure, favorable electronic band structure similar to that of PbTe. PbSe is much less studied compared to PbTe and we have initiated an investigation of the fundamental physical properties of PbSe-based systems as candidates for high ZT thermoelectric materials for solar thermal power generation. We present a systematic study with respect to the synthesis, characterization, and thermoelectric donor effects of In, Ga and excess Pb in the lattice of PbSe. The electrical conductivity, thermoelectric power, thermal conductivity, Hall effect and optical reflectivity properties will be reported. The experimental data indicate that the donor action of In, Ga and Pb is very effective and electron densities up to 8-9x1019 cm-3 can be generated routinely. The thermoelectric power values of all samples at room temperature are in agreement with the Pisarenko relation assuming only acoustical phonon scattering in PbSe. The observed substantial differences between the Hall mobilities indicate that the electronic effective mass is crucially affected by the type of the donor.
12:30 PM - LL9.10
Electronic Structure of PbTe/Si Interface.
Celine Hin 1 , Mildred Dresselhaus 2 , Qinyong Zhang 3 , Zhifeng Ren 3 , Gang Chen 1
1 Department of Mechanical Engineering, MIT, Cambridge, Massachusetts, United States, 2 Department of Physics, MIT, Cambridge, Massachusetts, United States, 3 Department of Physics, Boston College, Boston, Massachusetts, United States
Show AbstractEfforts to improve ZT have focused on preparing nanostructured materials to reduce the thermal conductivity by boundary scattering. Another way to enhance ZT is to increase the power factor and therefore to enhance the transport properties. PbTe seems to be a very promising semi-conducting material for creating efficient thermoelectrics that need to be very good at conducting electricity, but do not conduct heat. To investigate the effects of adding Si on the thermoelectric properties of PbTe, the electronic structures of PbTe and PbTe-Si bulk materials were calculated by using the linearized augmented plane wave based on the density functional theory of the first principles. We will compare the differences in the band structure, the partial density of states, and the electron density difference for PbTe and PbTe-Si. In addition, since Si is able to form Si precipitates in PbTe matrix, we have calculated the Si/PbTe interface electronic structure and evaluated their impact on thermoelectric properties.The authors gratefully acknowledge the financial support of the Department of Energy under grant DE-FG02-08ER46516.
12:45 PM - LL9.11
Thermoelectric Properties of Diamond-like Compounds Cu2GaxGe1-xSe3 (x = 0 ~ 0.1).
Jung Young Cho 1 , James Salvador 1 , Jihui Yang 2 , Hsin Wang 3 , Andrew Wereszczak 3 , Miaofang Chi 3
1 Chemical Sciences and Materials Systems Lab, GM Global Research & Development, Warren, Michigan, United States, 2 Electrochemical Energy Research Lab, GM Global Research & Development, Warren, Michigan, United States, 3 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractZincblende-type semiconductors have shown versatility of their structural and physical properties depending on the tetrahedrally coordinated atoms, with applications ranging from photovoltaics to thermoelectrics. Here the orthorhombic Cu2GeSe3 and Ga-doped derivatives of it have been synthesized by direct-melting of the constituent elements and their Hall coefficients and thermoelectric properties evaluated. All samples show positive Hall coefficients (RH) for the entire temperature range studied; the highest Seebeck coefficient of 446 μVK–1 was observed at 745 K for the undoped Cu2GeSe3 sample. Low thermal conductivities were observed for all samples resulting in a ZT ~ 0.77 for Cu2Ga0.1Ga0.9Se3 at 745 K. Interestingly, as the Ga concentration increases, an additional reflection, which is indexable to a related cubic phase, was observed in the powder x-ray diffraction patterns. To elucidate the microstructure of the Ga-doped samples TEM was performed to determine what potential role this may play in the thermal conductivity suppression. Coefficients of thermal expansion and elastic properties were also measured to better understand the low thermal conductivities of this class of materials.
LL10: Thermoelectric Materials II/Thermoelectric Materials III
Session Chairs
Thursday PM, December 02, 2010
Commonwealth (Sheraton)
2:30 PM - LL10.1
Thermoelectric Properties of Spark Plasma Sintered Mg- and Mn-silicides.
Juergen Schmidt 1 , Jan Koenig 2 , Conrad Zurbuchen 3 , Thomas Weissgaerber 1
1 Sintering and Composite Materials, Fraunhofer Institute for Manufactoring and Material Science, Dresden Germany, 2 , Fraunhofer Institute for Physical Measuring Techniques, Freiburg Germany, 3 Materials Science, Technical University Dresden, Dresden Germany
Show AbstractMagnesium silicide based alloys and higher Manganese silicdes are widely known as potential p- and n-type materials for thermoelectric high temperature applications. Due to the large differences in the melting points of Magnesium and silicon, the high melting point of the binary phase and the miscibility gap of the ternary phases, in addition with the volatility of the magnesium, the phase pure synthesis of these alloys is difficult. With the use of a precursor based on the decomposable magnesium hydride, the solid state synthesis can be can be done by the use of the spark plasma sintering technique (SPS). The result is a full dense sinterbody with a high degree on chemical and physical homogeneity and relatively high mechanical strength.Also, Mn11Si19 crystal structure is very complex and phase pure synthesis is very difficult. By the use of the SPS technique in combination with mechanical alloying, sinterbodies with good thermoelectrical properties can be made.This paper will report on the preparation and the influence of the SPS process on the thermoelectric and mechanical properties of the polycrystalline material.
2:45 PM - LL10.2
Size Effects in Bi-Sb Solid Solutions Thin Films.
Elena Rogacheva 1 , Dar'ya Orlova 1 , Mildred Dresselhaus 2 , Shuang Tang 2
1 Theretical&experimental physics, National technical university "Kharkov polytechnic institute", Kharkov Ukraine, 2 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractBi-Sb solid solutions attract attention of researchers as promising low-temperature thermoelectric materials and as convenient models for studying a number of physical phenomena. The objects of the present study are thin films of Bi-Sb solid solutions (0 – 10 at.% Sb) with thicknesses d=5–400 nm obtained by thermal evaporation in vacuum and subsequent deposition onto mica substrates at the substrate temperature ~ 380 K. The d-dependences of the electrical conductivity, Hall coefficient, and Seebeck coefficient were obtained in the temperature range 77-300 K. It was established that at a fixed Sb concentration in the charge (4.5 and 9 at.%) at room temperature, a distinct manifestation of the classical size effect is observed, i.e. an increase in the film thickness up to ~ 200 nm leads to an increase in electrical conductivity, Seebeck coefficient, charge carrier mobility and to a decrease in the Hall coefficient, whereas at larger film thicknesses the kinetic properties do not practically change. It was shown that the experimental data can be satisfactorily approximated by theoretical calculations based on the classical Fuchs - Sondheimer theory. At room temperature, in the thickness dependences of the kinetic properties of Bi-Sb films quantum oscillations were registered. The theoretically estimated period of oscillations and behavior of the monotonic component of the dependences are in good agreement with the experimentally observed results. It was shown that in the films of bismuth-antimony solid solutions with Sb concentrations 4.5 and 9 at.%, thermoelectric power factor P is 4-5 times higher than that in Bi films. It was established that values of P for “thick” films (d>200nm) of Bi-Sb solid solutions are practically equal to those for bulk samples after long-term annealing. The temperature dependences of the kinetic coefficients of Bi-Sb thin films with different thicknesses and with the antimony concentrations corresponding to semimetallic and semiconducting regions (4.5 and 9.0 %) were obtained. It was found that in contrast to bulk crystals, in thin films, the electrical conductivity increases with increasing temperature but the behavior of the temperature dependences of the Seebeck coefficient, charge carrier mobility, Hall coefficient, and magnetoresistance do not differ from that in crystals. For Bi-Sb films with smaller thicknesses d = 25-80 nm, in the temperature dependences of the Hall coefficient and magnetoresistance, maxima were observed. The maxima shifted to higher temperatures as the film thickness decreased and the antimony concentration in the solid solution increased.
3:00 PM - LL10.3
Non-thermal Plasma Created Silicon and Germanium Nanocrystals for Thermoelectric Nanocomposites.
Ariel Chatman Kleczewski 1 , Uwe Kortshagen 1 , Amanda Dillman 3 , David Kohlstedt 3 , Lee Wienkes 2 , Yves Adjallah 2 , Jim Kakalios 2
1 Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota, United States, 3 Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota, United States, 2 Physics, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractNanocomposite materials, consisting of densely compressed mixtures of nanocrystals, are of increasing interest in thermoelectric materials research. Interface scattering of phonons in nanocomposites reduces the thermal conductivity below the alloy limit while possibly improving the electrical conductivity and Seebeck coefficient through quantum confinement effects. In addition, nanocomposites are larger scale, dense materials, and can easily be integrated into practical device designs. A plasma based, bottom-up synthesis method is employed to create silicon and germanium nanocrystals while a variety of hot pressing and sintering methods are explored to create a high density composite. This method yields a controlled design of materials with smaller and more uniform grain sizes for study. A radiofrequency argon plasma reactor is used to dissociate the Si or Ge atoms from the precursor gases. The free atoms are then available to combine, forming nanocrystals in an aerosolized flow at a rate of approximately 5 mg/min. A sufficient sample for compression and testing of thermoelectric properties can be prepared in one hour which is a significant advantage over ball milling methods that can take up to 60 hours. Nanocrystal size is characterized by TEM to be monodisperse with an average size controllable down to 2-3 nm. This system allows the synthesis of n-type or p-type doped nanocrystals. Mixing techniques for combinations of silicon and germanium nanocrystals using a high energy beads mill or ultrasonication are compared using TEM and elemental analysis.Densification results for the collected particles are compared using a traditional hot press with a graphite die and a Patterson Vessel technique. The density and final grain size of Si nanocomposites are studied as a function of the pressure and duration of the hot press using geometric and mass measurements and wide angle x-ray diffraction. Final grain sizes are seen down to approximately 10 nm. Internal structure of the samples polished cross-section is studied using SEM. Measurements of the thermal conductivity down to 1.2 W/m*K are obtained using a modified micro-Raman method. Measurements of the Seebeck coefficient and electrical conductivity are taken in a heated vacuum system over a range of ΔT values and average temperatures. The hot-pressing of nanocomposites including both Si and Ge nanocrystals as well as the effects of dopants will be described.This work was supported partially by the MRSEC Program of the National Science Foundation under Award Number DMR-0819885. A. Chatman Kleczewski is supported through the NSF Graduate Research Fellowship Program.
3:15 PM - LL10.4
Surface Roughness Effects on Thermal Conductivities of SixGe1-x Nanowires.
Hyoungjoon Kim 1 , Yong-Hee Park 2 , Heon-jin Choi 2 , Woochul Kim 1
1 School of Mechanical Engineering, Yonsei Univ., Seoul Korea (the Republic of), 2 Department of Materials Science and Engineering, Yonsei Univ., Seoul Korea (the Republic of)
Show AbstractA. Hochbaum et al. (Nature, 451, 163 (2008)) showed that rough Si nanowires (NWs) have a way lower thermal conductivity than that of smooth Si NWs. This usually low thermal conductivity of rough Si nanowire could not be explained by existing theories, so a burst of theoretical papers(A. Moore et al. Appl. Phys. Lett. 93, 083112(2008), D. Donadio et al. Phys. Rev. Lett. 102, 195901(2009), P.Martin et al. Nano Lett. 10, 1120(2010)) came out to explain this. However, none of them are yet accepted as an established theory because of lack of experimental data on thermal conductivity of rough nanowires. We grew rough Si NWs with various surface roughnesses and measured thermal conductivities of those. Our results indicated that as the surface roughness increases, thermal conductivity decreases. We also grew rough SixGe1-x. Thermal conductivity of rough SixGe1-x NWs was compared with that of smooth SixGe1-x NWs as well. These results provide useful information for increasing ZT by using the surface roughness engineering.
3:30 PM - LL10.5
Self-assembled Mg2 (Si,Sn) Thermoelectric Nanocomposites: Microstructure Control and La-doping Optimization.
Jian He 1 , Qian Zhang 2 , Shengnan Zhang 1 , Tiejun Zhu 2 , Xinbing Zhao 2 , Terry Tritt 1
1 Physics and Astronomy, Clemson University, Clemson, South Carolina, United States, 2 Materials Science and Engineering, Zhejiang University, Hangzhou, Zhejiang, China
Show AbstractA good thermoelectric (TE) material should have high figure of merit (ZT) and be made of eco-friendly elements, Mg2(Si1-xSnx) compounds hence have attracted considerable interest. The pseudo-binary phase diagram of Mg2Si and Mg2Sn is featured by a peritectic point, and a miscibility gap between x = 0.2 and 0.4. It has been found that the Mg2(Si1-xSnx) compounds exhibit the highest ZT near the edges of the miscibility gap. In this work, we utilized these specific features of phase diagram to fabricate self-assembled Mg2(Si1-xSnx) TE nanocomposites with starting compositions barely inside the miscibility gap. We was able to control the micro-morphology of the as-formed composites by adjusting the starting compositions, cooling rates and La-doping ratio. The results of TE properties, especially the possible contributions from the interface between the Mg2Sn-rich and Mg2Sn-rich phases, have been discussed in view of a simplified Hashin-Shtrikman model. A ZT ~ 0.8 has been attained at 810 K in the composite in which the Mg2Si0.77Sn0.23 bulk grain coated by a thin layer of Mg1.98La0.02Si0.27Sn0.73.
3:45 PM - LL10.6
Benedicks Effect on Multi-contact Nanocrystalline Microstructures Heated Through Alternating Electrical Signals.
Nicholas Williams 1 , Ali Gokirmak 1 , Helena Silva 1
1 Electrical and Computer Engineering, University of Connecticut, Storrs, Connecticut, United States
Show AbstractThermoelectric effects in large temperature gradients are an important aspect to the understanding and optimization of thermal-to-electric energy conversion. We have observed considerable DC offsets due to large, asymmetric temperature gradients on multi-contact nanocrystalline microstructures where all the contacts remain at room temperature. this is interpreted as experimental observation of Benedicks effect [1].The microstructures used in the experiments are ~6–7 µm in length and ~300-600 nm in width with five contacts, two at each end of the wire and three distributed along the length of the wire with equal spacing, formed on a Boron doped nc-Si film that is deposited on SiO2 in a low-pressure chemical vapor deposition system.Self-heating of the structure was induced using two square waves, 180° out of phase with each other, applied to contacts at one end of the five contact structure. Thus, an AC current flows between the sections bridging the first and second contacts, where the narrowest segment is ~300-600 nm in width . This produces high density currents leading to significant local self heating reaching temperature > 1000 K (temperature gradients are ~1K/nm), which are observed as light emission from the heated region. While the amplitude of square waves is ramped, an open-circuit DC voltage is measured at a 3rd contact far away from the heated region. Experimental results show a sharp, exponential rise in DC offset when the amplitude of the applied square waves reach ~6 - 7 V peak to peak. DC offset peaks around ~150 mV before wire breaks due to melting. The metal contacts made at large contact regions all remain at approximately room temperature. Hence, the measured DC offset is due to non-linear thermoelectric effects (Benedicks effect) [1] which become appreciable at these asymmetric temperature gradients. The details of the experiments, the effect of large temperature gradients created by the self-heating will be presented.[1] G. Mahan, "The Benedicks effect: Nonlocal electron transport in metals," Physical Review B, vol. 43, pp. 3945-3951, 1991.
4:30 PM - LL10.7
Thermoelectric and Structural Properties of High-performance In-based Skutterudites for High-temperature Energy Recovery.
Terry Hendricks 1 , Mas Subramanian 3 , Krishnendu Biswas 3 , Morris Good 2
1 Microproducts Breakthrough Institute, Pacific Northwest National Laboratory, Corvallis, Oregon, United States, 3 Chemistry, Oregon State University, Corvallis, Oregon, United States, 2 Applied Physics & Materials Characterization Sciences, Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractThe Department of Energy (DOE) Transportation Energy Data Book: Edition 24 shows that in 2002 approximately 130 billion gallons of gasoline was used nationwide by light-duty passenger cars, vans and the sport-utility vehicle (SUV) segment. Some estimates indicate that approximately 4-5 Quads (1 Quad = 1015 Btus) of the energy in this fuel ended up as waste thermal energy in vehicle exhaust streams. The same reference indicates another approximately 30 billion gallons of diesel fuel was used nationwide by heavy-duty vehicles, in 2002, of which approximately 1.4 Quads of the energy in this fuel ended up as waste thermal energy in heavy-vehicle exhaust streams. In 2008, approximately 4.7 Quads (~20%) of transportation sector fuel energy was used to operate heavy-duty, Class 8 vehicles; approximately 1.6 Quads of this energy ended up in heavy vehicle high-temperature exhaust flows. The DOE Office of Vehicle Technologies is sponsoring research to develop advanced, high-temperature n-type and p-type skutterudite thermoelectric (TE) materials to harness this exhaust flow energy enabling higher energy efficiency in heavy-duty and light-duty vehicle engines. New n-type (In,Ce)-based “dual-rattler” skutterudite compositions (i.e., In0.2 Ce0.15 Co4 Sb12) have been developed and characterized that show ZT ~ 1.5 – 1.6 @ 475 K using one processing method and ZT ~ 1.45@ 625 K using a second processing method. We synthesized the composition In0.2Ce0.15Co4Sb12 by simple gas-solid reaction methods by varying the sequence of adding the void-filling atoms. We find that the sequence of adding filler atoms plays an important role governing the magnitude of TE transport properties. It is recognized that TE properties (Seebeck coefficient, electrical resistivity, and thermal conductivity) and structural properties (Young’s modulus, Poisson’s ratio, Coefficient of Thermal Expansion) are critical to transitioning these promising materials into operating devices. Consequently, this work has characterized simultaneously the TE and structural properties for these new (In,Ce)-based skutterudite materials. In addition to the new structural property data on these materials, this work has also characterized the thermal cycling behavior of these new materials from 313 K to 673 K for the first time. This paper will present and discuss the temperature-dependent TE and structural properties showing comparisons with other TE materials being considered for transportation energy recovery applications. In addition to their very good TE properties, these bulk materials are exhibiting good structural properties and stable thermal cycling characteristics, which will allow effective transition into operating TE devices. The paper will also briefly discuss the results of TE energy recovery systems analyses predicting how these new (In,Ce) skutterudite materials would perform in actual operating TE systems in typical transportation energy recovery applications.
5:00 PM - LL10.9
Novel Lead Telluride Based Thermoelectric Materials.
Chun-I Wu 1 , Steven Girard 2 , Joseph Sootsman 2 , Edward Timm 3 , Eldon Case 4 , Mercouri Kanatzidis 2 5 , Harold Schock 3 , Duck Young Chung 5 , Timothy Hogan 1 4
1 Electrical and Computer Engineering, Michigan State University, East Lansing, Michigan, United States, 2 Chemistry, Northwestern University, Evanston, Illinois, United States, 3 Mechanical Engineering, Michigan State University, East Lansing, Michigan, United States, 4 Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, United States, 5 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractPbTe-PbS materials are promising for thermoelectric power generation applications. For the composition of (Pb0.95Sn0.05Te)0.92(PbS)0.08 nanostructuring from nucleation and growth and spinodal decomposition has been reported along with thermal conductivity of approximately 1.1 W/mK at 650 K. Based on temperature-dependent measurements of electrical conductivity, thermopower, and thermal conductivity, the thermoelectric figure of merit, ZT, are 1.1 - 1.4 at 650 K for cast ingots. To develop larger quantities of material for device fabrication, advancement in the synthesis, processing and production of this material is necessary.Powder processing of samples is a well known technique for increasing sample strength, and uniformity. In this presentation, we show sample fabrication and processing details of pulsed electric current sintering (PECS) processed (Pb0.95Sn0.05Te)0.92(PbS)0.08 materials and their thermoelectric properties along with the latest advancements in the preparation of these materials.
5:15 PM - LL10.10
Intriguing Electrical Properties and Mechanism of ElectronScattering in Co-nanostructured Lead Telluride.
Jiaqing He 1 2 , S. Girard 2 , L. Xu 3 , J. Sootsman 2 , J. Zheng 3 , Mercouri Kanatzidis 2 4 , Vinayak Dravid 1
1 Department of Materials Science and Engineering , Northwestern University, Evanston, Illinois, United States, 2 Department of Chemistry , Nothwestern University, Evanston, Illinois, United States, 3 Department of Physics , Xiamen University, Xiamen China, 4 Materials Science Division, Argonne National Laboratory , Argonne , Illinois, United States
Show AbstractThermoelectric materials, which can convert heat energy into electrical power, will play an important role in energy community if their efficiencies can be enhanced. An efficient thermoelectric material must exhibit a high thermoelectric figure of merit, ZT, at a certain operational temperature. The figure of merit is related to the transport properties of a material through ZT=S2σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the total thermal conductivity. Usually, there are two ways to improve ZT of the thermal materials: one is to lower the thermal conductivity and other is to enhance power factor (S2σ). For example, nanostructured materials can achieve a high figure of merit by lowing thermal conductivity resulting from phonon scattering at the interfaces of nanoscale features but no altering or small reducing electron conductivity.[1] Approaches to increase the power factor were also paid extensively attention, such as changing the density of state by introducing a resonance level in valence band [2]. Recently, we also reported the synthesis and thermoelectric properties of PbTe nanostructured with precipitates of Pb and Sb [3]. These synergistic nano-precipitates profoundly impact the temperature dependence of the mobility. In some samples the mobility actually increases before it falls at high temperature. This behavior is tuned by the Pb/Sb ratio. This is an intriguing phenomenon in nanostructuring thermoelectric materials and as of yet is not fully understood. Here we investigated these materials by in situ transmission electron microscopy (TEM) results that add to our understanding of the novel behavior of these materials. Using in situ TEM techniques, we directly image the nanostructures as a function of temperature. We found the Pb nano-precipitates highly inter-diffuse into Sb precipitates when they separate out as one particle. Within the energy filtering model, our theoretical calculations of electrical conductivity are in agreement with experimental measurements, highlighting the important role of inter-diffusion play in electron scattering. We further propose that such tunable co-nanostructures can increase power factor and therefore enhance the overall figure of merit.[1] Hsu, K. F.; et al Science 2004, 303, 818-821.[2] Heremans, J. P.; et al. Science 2008, 321, 554-557.[3] Sootsman, J. R.; et al Angew. Chem., Int. Ed. 2008, 47, 1-6.
5:30 PM - LL10.11
Nano-layer Superlattices of Na0.7CoO2.
Mahmut Aksit 1 , Richard Robinson 1
1 Material Science and Engineering, Cornell University, Ithaca, New York, United States
Show AbstractNano-layer superlattices with extremely large aspect ratios (more than 1:500) of thermoelectric Na0.7CoO2 have been synthesized using the Pechini sol-gel process, kinetic demixing, and a high temperature diffusion treatment. The thickness of the layers ranges from 3 nm to 300 nm while the lengths of the layers can be varied between 10 µm and 4 mm, resulting in an aspect ratio of 1:500 at minimum. XRD indicates a single phase of Na0.7CoO2. The thickness and the length of the nano-layers were characterized with rocking curve x-ray diffraction measurements and scanning electron microscopy (SEM) images. Thin sheets of multiple layers (~200 nm total = ~10 layers) have been delaminated and characterized. Thermoelectric characterization of samples with tilted multiple-grains along the measurement axis and shorter layers indicate a thermoelectric efficiency on par with current results in the literature for polycrystalline samples. Due to phonon confinement in nano-structures, it is expected that a thermoelectric efficiency much higher than that of single crystalline Na0.7CoO2 will be obtained from future samples with single-grains along the measurement axis and longer layers.
5:45 PM - LL10.12
Ultralow Lattice Thermal Conductivity in Nanostructured Bulk Chalcogenides with Enhanced Thermoelectric Figure of Merit.
Yanliang Zhang 1 , Theodorian Borca-Tasciuc 1 , Rutvik Mehta 2 , Ganpati Ramanath 2
1 Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractThermal and thermoelectric transport investigations are reported in a novel class of nanostructured (NS) bulk chalcogenides of ultralow thermal conductivity and high thermoelectric figure of merit (ZT). The NS bulk materials were formed by compacting and sintering Bi2Te3 and Sb2Te3 single crystal nanoplates synthesized by a rapid, scalable surfactant-assisted microwave synthesis approach. The lattice component of thermal conductivity (κL) of NS-Bi2Te3 was obtained experimentally by measuring the thermal and electrical conductivity of a series of samples with the same stoichiometry and different carrier concentration and extracting the Lorenz number. The κL as low as 0.5 W/mK at room temperature was obtained in NS-Bi2Te3, presenting a 60-70% reduction compared with single-crystal bulk Bi2Te3. Moreover, a NS bulk mixture of Bi2Te3 and Sb2Te3 nanoplates leads to further reductions in κL by a factor a 2 at room temperature. The responsible mechanisms for κL reduction were quantitatively studied by employing a modified Debye-Callaway model, which infers that the nanograins and point defects play the major roles in the thermal conductivity reduction. To assess the effect of nanostructuring on charge transport, the carrier concentration and electron mobility were determined in these materials via Hall effect measurement. Our bottom-up approach yields electron-transmitting and phonon-blocking structures with electron mobility similar to the single crystals and a remarkable reduction in lattice thermal conductivity. These findings lead to room temperature ZT surpassing 1 in Bi2Te3/Sb2Te3 mixture, a 20% improvement vs the bulk alloy structure.