Symposium Organizers
Timothy P. Hogan Michigan State University
Jihui Yang General Motors R&D Center
Ryoji Funahashi National Institute of Advanced Industrial Science and Technology
Terry Tritt Clemson University
U1: Nanocomposites I
Session Chairs
Monday PM, November 26, 2007
Room 311 (Hynes)
11:15 AM - **U1.1
Low-dimensional and Nano-composite Thermoelectric Materials.
Lidong Chen 1
1 Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai China
Show AbstractRecent resurgence in thermoelectric (TE) materials research has led to a significant improvement of TE performance and development of some new TE materials designs and concepts. This review provides a summary of some effective techniques for improving TE performance through multi-level microstructure control. A proven approach to elevate figure of merit is via formation of nanocomposites, in which nanophases are dispersed at grain boundaries or within grain. Acting as energy filter or scattering center, nanophases contribute to the increase of Seebeck coefficient and the reduction of thermal conductivity without much degradation of electrical conductivity. For anisotropic TE materials, textured microstructure favors to enhance TE performance along the certain direction. In addition, TE thin film assembled from one-dimensional nanotructured materials is presented as a promising TE film.
11:45 AM - U1.2
Alkali Metal Hydrothermal Treatment ---- Fabricate a Beneficial Interface on p-type Bi2Te3 Thermoelectric Materials.
Xiaohua Ji 1 , Jian He 1 , Zhe Su 1 , Nick Gothard 1 , Terry Tritt 1
1 Department of Physics and Astronomy, Clemson University, Clemson, South Carolina, United States
Show AbstractBi2Te3 based alloys have been known as one of the best room-temperature thermoelectric (TE) materials for decades. However, the thermoelectric performance of Bi2Te3 based alloys is sensitive to the inherent microstructure of the material: the pulverized system often exhibits an inferior figure of merit than that of the aligned ingot, due primarily to the inter-grain boundary scattering. So an important question may arise as to whether one can somehow fabricate a beneficial inter-grain boundary. In order to address this question, p-type Bi2Te3 is employed as a test-system in present work. Pulverized Bi0.4Sb1.6Te3 (p-type) powders with selected sizes were put into the autoclave and then hydrothermally treated, where the solution of various alkali metal (Li, Na, K, Rb, Cs) compounds were being used as reaction medium. After the treatment, the as-processed powders were removed, washed and dried, followed by hot pressing into pellet for further TE property measurements. The TE properties were found to be significantly improved as compared to the untreated reference sample. Extensive characterizations including X-ray/electron diffraction, TGA analysis, Raman / Fourier Transform Infrared Spectroscopy, electron microscopy, Rutherford back-scattering and Energy dispersive X-ray analysis were performed on the treated sample. The results revealed that a surface layer (from 10 nm to up to micron in thickness) exhibiting a combined crystalline/amorphous feature was formed on the original bare particles. This layer is believed to be the key factor in the improvement of TE properties of the p-type Bi0.4Sb1.6Te3 material. The synthesis technique will be discussed in detail while some results on the microscopic analysis and TE properties will be presented briefly.
12:00 PM - U1.3
Synthesis and Characterization of Novel Thermoelectric Nanomaterials.
Xiaofeng Qiu 1 , Ian Steward 2 , Jeffrey Dyck 2 , Clemens Burda 1
1 Chemistry, Case Western Reserve University, Cleveland, Ohio, United States, 2 Physics , John Carroll University, University Heights, Ohio, United States
Show Abstract12:15 PM - U1.4
Thermoelectric Properties of Bi2Te3-based Nanocomposites.
Nick Gothard 1 , X. Ji 1 , J. He 1 , T. Tritt 1
1 , Clemson University, Clemson, South Carolina, United States
Show AbstractNanocomposites have been produced by incorporating thermoelectric nanoparticles into a matrix of bulk Bi2Te3 material via a hot pressing process. These nanocomposites have been examined by SEM and X-ray powder diffraction. The effects of the incorporation of a variety of nanoparticles upon the resulting thermoelectric properties such as the thermopower, electrical resistivity, thermal conductivity, etc., have been studied in these composites at room temperature and below. The details of the synthesis along with results of the microscopic analysis and thermoelectric properties will be discussed. The potential for improving the figure of merit within the Bi2Te3 system by this technique is considered.
12:30 PM - U1.5
Synthesis and Thermoelectric Properties of Lead Chalcogenide Nanocomposites.
Joshua Martin 1 , Stevce Stefanoski 1 , Lidong Chen 2 , George Nolas 1
1 Physics, University of South Florida, Tampa, Florida, United States, 2 , Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 China
Show AbstractLead chalcogenide dimensional nanocomposites were prepared by densifying nanocrystals synthesized employing an alkaline aqueous solution-phase reaction. The nanocrystal synthesis procedure resulted in high product yields of over 2 g per batch. These nanocrystals were then subjected to Spark Plasma Sintering (SPS) for densification. Transport properties were evaluated through temperature dependent resistivity, Hall, Seebeck coefficient, and thermal conductivity measurements, indicating a strong sensitivity to stoichiometry, surface oxygen adsorption, and porosity. The results for these lead chalcogenide nanocomposites were compared to bulk polycrystalline lead chalcogenides with similar carrier concentrations.
12:45 PM - U1.6
Thermoelectric Properties of Semiconducting Silicide Nanowires.
Song Jin 1 , Jeannine Szczezh 1 , Feng Zhou 2 , Li Shi 3 2
1 , University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 Materials Science and Engineering Program, Texas Materials Institute, , Materials Science and Engineering Program, Texas Materials Institute, , Austin, Texas, United States, 3 Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas, United States
Show AbstractSemiconducting silicides (e.g. CrSi2, β-FeSi2, MnSi1.8, Mg2Si) are promising thermoelectric materials. In addition to their respectable thermoelectric figure-of-merit (ZT up to 0.8), silicides have the advantages of low cost, excellent thermal stability and mechanical strength, and outstanding oxidation resistance, making them suitable for high temperature applications. We have developed general synthetic approaches to high quality single crystal nanowires of silicides to investigate their potential enhancement of thermoelectric properties due to the reduced nanoscale dimension and to explore their applications in thermoelectrics. We will specifically focus on the synthesis and structural characterization of nanowires of chromium disilicide (CrSi2) prepared via a chemical vapor transport (CVT) method. This method complements the more versatile chemical vapor deposition (CVD) of metal carbonyl-silyl single source organometallic precursors we have developed. Structural characterization using electron microscopy, powder X-ray diffraction, and energy dispersive spectroscopy shows that these nanowires are hexagonal CrSi2 single-crystal structures along the <001> growth axis, with diameters ranging from 20−300 nm and length up to 100 μm. The Seebeck coefficient, electrical conductivity, and thermal conductivity of individual CrSi2 nanowires were characterized using a suspended microdevice and correlated with the crystal structure and growth direction obtained by transmission electron microscopy on the same nanowires. The obtained thermoelectric figure of merit of the nanowires was close to 0.1 and comparable to the bulk values. This combined Seebeck coefficient and electrical conductivity measurements also provide an effective approach to probing the Fermi level, carrier concentration and mobility in nanowires. We will also discuss our recent results of silicide nanowires of complex Novotny chimney ladder phases and our progress in using individual nanostructures combined well-defined structural characterization to conclusively investigate the complex thermoelectric behaviors of these silicide materials.
U2: Nanocomposites II and Theory
Session Chairs
S.D. (Bhanu) Mahanti
Terry Tritt
Monday PM, November 26, 2007
Room 311 (Hynes)
2:30 PM - **U2.1
New Opportunities in Existing Thermoelectric Materials: Interface Engineering in Pulverized p-Bi2Te3 System.
Jian He 1 , Xiaohua Ji 1 , Zhe Su 1 , Nick Gothard 1 , Terry Tritt 1
1 Physics, Clemson University, Clemson, South Carolina, United States
Show AbstractGrain boundary scattering provides an avenue by which to effectively lower the thermal conductivity in pulverized thermoelectric materials, however, the “bare” inter-grain boundary often simultaneously degrades the electrical conductivity and thermopower. Thus a controlled inter-grain boundary would be very beneficial in order to improve the thermoelectric performance of the system. But the question is how to engineer such a boundary.In this talk we present a proof-of-principle investigation on the pulverized p-Bi2Te3 (Bi0.4Sb1.6Te3) system by means of electrical resistivity, thermopower, thermal conductivity, specific heat, Hall coefficient, Raman/Infrared spectroscopy, X-ray/electron diffraction, electron microscopy and compositional analysis. Utilizing the alkaline hydrothermal treatment and nano-coating techniques recently developed at Clemson, we fabricate a thin layer on the surface of fine p-Bi2Te3 grains. The interface layer, ~ few tens nm thick and formed right at the inter-grain boundary in a hotpress-densified sample, enabled us to “decouple” and individually optimize the various thermoelectric properties. As a result, the hydrothermally treated and pulverized sample possessed ZT values comparable to those of a commercial ingot but with a better so called “compatibility factor” as well as better mechanical properties. In view of the concept of material design, this process helps achieve a new level of control as a tuning parameter with which to optimize the figure of merit ZT and compatibility factor. In principle, this strategy can be readily applied to other existing thermoelectric materials. This presentation will focus on the resulting thermoelectric properties and microscopic analysis and the synthesis techniques will be discussed in detail elsewhere.
3:00 PM - U2.2
Effect of In-Situ Hydrogen Annealing on the Thermoelectric Properties of Individual Bismuth Telluride Nanowires.
Anastassios Mavrokefalos 1 , Michael Pettes 1 , Li Shi 1 , Wei Wang 2 , Xiaoguang Li 2
1 Mechanical Engineering, University of Texas at Austin, Austin, Texas, United States, 2 Department of Physics, University of Science and Technology of China, Hefei China
Show AbstractSeveral theoretical studies suggested that Bi-based and III-V nanowire structures may possess enhanced thermoelectric figure of merit, ZT. It was found in our earlier measurements employing a suspended microdevice that the thermoelectric properties of individual bismuth telluride, InSb, and CrSi2 nanowires are largely influenced by the crystalline quality, chemical composition and surface roughness of the nanowires. In addition, a major problem for thermoelectric measurements of individual nanowires especially bismuth telluride nanowires is the presence of a stable native oxide that prohibits electrical contact to be made directly to the nanowires. Focused electron or ion beam induced deposition of Pt on the nanowire was used in our previous work to make electrical contact to the nanowire. Care was needed to prevent the nanowire from being contaminated by ions present during the Pt deposition process. Furthermore, it has been suggested that the presence of the surface oxide or surface contamination can result in high surface charge state densities that can dominate the intrinsic transport properties of nanowire and thin film thermoelectric materials. In fact, it was found that annealing in a hydrogen environment can significantly enhance the thermoelectric properties of bismuth telluride films.In this work, we investigate the effect of in situ hydrogen annealing on the thermoelectric properties of individual bismuth telluride nanowires. The thermoelectric measurement method is based on an improved design of our microfabricated suspended device. The current measurement does not require Pt deposition on the nanowire for making electrical contact. Instead, it was found that ohmic contact between the nanowire and the underlying pre-patterned Pt electrodes on the suspended devices can be made by annealing the nanowire at about 480 K while hydrogen is flown into the evacuated sample space of a cryostat. Our measurement results show that that the thermal and electrical conductances and ZT of the nanowires are increased upon hydrogen annealing. In addition, both the contact thermal and electrical resistances are eliminated from the measured thermal conductivity, electrical conductivity, or Seebeck coefficient by using a unique four-probe thermoelectric measurement method. Transmission Electron Microscopy (TEM) and Energy Dispersion Spectroscopy (EDS) measurements are performed on the same nanowires assembled on the suspended device so as to correlate the structural characteristics to the measured thermoelectric properties of the nanowires. High resolution TEM results reveal highly crystalline structure of the hydrogen-annealed bismuth telluride nanowires.
3:15 PM - U2.3
Synthesis and Thermoelectric Properties of High-purity Single-crystal InSb Nanowires.
Feng Zhou 1 , Jae Hun Seol 2 , Yong Lee 2 , Li Shi 2 1 , Qi Laura Ye 3
1 Texas Materials Institute, University of Texas at Austin, Austin, Texas, United States, 2 Mechanical Engineering, University of Texas at Austin, Austin, Texas, United States, 3 , NASA Ames Research Center, Moffett Field, California, United States
Show AbstractIndium antimonide (InSb) is a narrow bandgap semiconductor with one of the smallest effective mass values among semiconductors and very high mobility. It is commonly used in infrared detectors and magnetic field sensors. The thermoelectric properties of bulk InSb crystals have been characterized by Yamaguchi et al. in the 10-723 K temperature range, with highest figure of merit (ZT) of 0.6 found at 673 K [1]. A theoretical calculation by Mingo has predicted that quantum confinement of electrons and diffuse phonon-surface scattering in InSb nanowires can result in enhanced ZT compared to the bulk value [2, 3]. Ye et al. has developed a vapor-liquid-solid (VLS) method to synthesize single crystal InSb nanowires. In an previous measurement, we observed that the obtained VLS InSb nanowires possess higher electrical conductivity and lower Seebeck coefficient than bulk crystals, most probably due to tellurium or oxygen impurities in the nanowire [4]. In this work the impurity concentration in the VLS InSb nanowires is minimized by using pure InSb wafers as source materials for VLS growth in high vacuum environment. The crystal structure and chemical composition of the obtained nanowires are analyzed using High Resolution Transmission Electron Microscopy (HRTEM) and Energy Dispersive X-ray Spectroscopy (EDAX). Temperature-dependant thermopower and electrical conductance are probed using a nanofabricated device where a top gate and substrate back gate voltage can be used to tune the Fermi level of the system via the field effect. Experiments are conducted to investigate the effect of in situ hydrogen annealing and surface passivation on the thermoelectric properties of the InSb nanowires. [1]S. Yamaguchi, T. Matsumoto, J. Yamazaki, N. Kaiwa, and A. Yamamoto, "Thermoelectric properties and figure of merit of a Te-doped InSb bulk single crystal," Applied Physics Letters, vol. 87, Nov 2005.[2]N. Mingo, "Thermoelectric figure of merit and maximum power factor in III--V semiconductor nanowires," Applied Physics Letters, vol. 84, pp. 2652-2654, 2004.[3]N. Mingo, "Thermoelectric figure of merit and maximum power factor in III-V semiconductor nanowires (vol 84, pg 2652, 2004)," Applied Physics Letters, vol. 88, pp. -, Apr 3 2006.[4]J. H. Seol, A. L. Moore, S. K. Saha, F. Zhou, L. Shi, Q. L. Ye, R. Scheffler, N. Mingo, and T. Yamada, "Measurement and analysis of thermopower and electrical conductivity of an indium antimonide nanowire from a vapor-liquid-solid method," Journal of Applied Physics, vol. 101, pp. 023706-6, 2007.
3:30 PM - **U2.4
Using Nano-composites to Enhance ZT.
Mildred Dresselhaus 1
1 EECS and Physics, MIT, Cambridge, Massachusetts, United States
Show AbstractThe concept of using self assembled nano-composites to enhance the thermoelectric figure of merit relative to bulk materials is presented in general terms. Specific application is made to the Si-Ge system for use at high temperature for space vehicle propulsion applications. The scientific advantages of the nano-composite approachfor the simultaneous increase in the power factor and decrease of the thermal conductivity are emphasized along with the practical advantages of having bulk samples for property measurements and an easy method for the of scale-up of nanostructured building blocks into bulk quantities of material for device fabrication.
4:00 PM - U2:Nano2amp;Theory
BREAK
4:30 PM - **U2.5
Oxide Thermoelectrics.
David Singh 1
1 Materials Science and Technlogy Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractNaxCoO2 is a fascinating material displaying a complex phase diagram and showing unprecedented properties. These include superconductivity upon hydration, apparent proximity to magnetic quantum critical points and high thermoelectric performance at metallic carrier densities. This high thermoelectric performance is remarkable as it was long held that neither oxides nor high carrier density metals could be good thermoelectrics. Furthermore, since the discovery of the thermoelectric properties of NaxCoO2 a decade ago, there are still no other examples of high performance thermoelectric oxides. Here, the problem of oxide thermoelectricity is discussed starting with NaxCoO2 within the context of electronic structure calculations and Boltzmann transport theory. These calculations suggest that there may well be other oxide thermoelectrics and suggest directions for identifying them. Some candidate materials are discussed.
5:00 PM - U2.6
An Investigation of Sodium Ordering in NaxCoO2 (x ≧ 0.50) by Density Functional Theory.
Ying Meng 1 , Yoyo Hinuma 1 , Gerbrand Ceder 1
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractUnderstanding the remarkable thermoelectric properties and interesting electronic/magnetic phenomena in P2-NaxCoO2 requires a detailed understanding of the structures at various sodium concentrations where sodium and vacancy order at finite temperature, which can couple strongly with the electronic structure. Using first principles electronic structure methods within the GGA and GGA+U approximations we find that Na ordering is determined by a competition between Na site energies difference and Na-Na repulsion. In addition the Co-Na interlayer interaction when charge localization occurs can facilitate the lock-in of certain ordering patterns of Na-Vacancy at simple fraction fillings. We will compare and contrast the stable ordering schemes obtained in this work with available experimental observations. Our work shows excellent agreement with experiments, in contrast to the previous DFT studies, in addition we predict a series of new ground states at concentration 0.60 to 0.71.
5:15 PM - U2.7
Large Thermoelectric Power Generated by the van Hove Singularity of Two-dimensional Triangular Lattice.
Tsunehiro Takeuchi 1
1 EcoTopia Science Institute, Nagoya University, Nagoya Japan
Show AbstractRecently, layered cobalt oxides, such as NaxCoO2, Bi2Sr2Co2O9, and Ca3Co4O9, were found to simultaneously possess large thermoelectric power and metallic electrical conduction. Those properties are two of the three necessities of practical thermoelectric materials. The layered cobalt oxides, therefore, were widely considered as one of the promising candidates for the thermoelectric materials in the next generation. Surprisingly, the carrier concentration of these materials were distributed over 10^(21)~10^(22) cm^(-3), which values are considered as those of metallic phases which generally possess very small thermoelectric power less than 10 μV/K. Thus a large number of attentions have been focused on the mechanism leading to the large thermoelectric power exceeding 100 μV/K with the large carrier concentration. In our resent studies, we performed high-resolution angle resolved photoemission spectroscopy measurements on these layered cobalt oxides and investigated the energy-momentum dispersion near the Fermi level (EF) in detail. By using the experimentally determined electronic structure and the Bloch-Boltzmann theory, we found that the large thermoelectric power with metallic conduction of the layered cobalt oxides was brought about by the Boltzmann-type electrical conduction with a unique spectral conductivity characterized by the large peak just below EF in associated with the van Hove singularity (vHs) of the two-dimensional system. More recently, however, we realized that even though a large peak in the electronic density of states is generated by the vHs, the layered copper oxides of two-dimensionally spanned square lattice have a very small peak in the spectral conductivity and consequently possess relatively small magnitude in their thermoelectric power. In order to investigate the origin of the large vHs peak in the spectral conductivity of the layered cobalt oxides, we employed, in this study, simple tight-binding simulations for several systems of different symmetry and calculated spectral conductivity within the rough assumption of a constant mean free path. As a result of the simulations, the very important role of the two-dimensionally spanned triangular lattice leading to a large peak in the spectral conductivity and consequently to a large magnitude in thermoelectric power was clearly revealed. In the presentation, the results obtained by the simulations will be explained in detail together with some typical examples of the two-dimensional triangular lattice possessing a large thermoelectric power.
5:30 PM - U2.8
Defect Clustering and Nanostructure Formation in PbTe-based Bulk Thermoelectrics.
Khang Hoang 1 , Subhendra Mahanti 1
1 Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan, United States
Show AbstractLead chalcogenides (PbTe, PbSe, and PbS) are IV-VI narrow band-gap semiconductors whose studies over several decades has been motivated by their importance in infrared detectors, light-emitting devices, infrared lasers, photovoltaics, and high temperature thermoelectrics. PbTe in particular is the end-compound of several high performance high temperature thermoelectrics such as AgPbmSbTe2+m [1] and Na1-xPbmSbyTe2+m [2]. These quaternaries are found to have enhanced thermoelectric figure of merit (compared to PbTe), due to the nanostructuring, which helps in lowering the lattice thermal conductivity and possibly enhancing the thermopower [1-2]. In this work we systematically study defect clustering in PbTe using density functional theory and supercell models. The defects being considered are (but not limited to) Na, K, Ag, Sb, Bi, and vacancies. Our energetic studies show that many defect pairs are stabilized when the two defects in a pair are either the nearest or the next-nearest neighbors in the PbTe lattice, which can help explain the nanostructuring found in various PbTe-based systems. Comparisons with similar defect cluster calculations in SnTe and GeTe will be made. We also study the electronic structure as a function of the relative distance between the two defects in a pair. Work partially supported by ONR-MURI.1. K.-F. Hsu et al., Science 303, 818 (2004).2. P. Poudeu et al., Angew. Chem. Int. Ed. 45, 3835 (2006).
5:45 PM - U2.9
Disorder Creates Band Gap in (Pb,Sn)Te Alloys.
Xing Gao 1 , Murray Daw 1
1 Dept. of Physics & Astronomy, Clemson University, Clemson, South Carolina, United States
Show AbstractThe PbTe, SnTe and their alloys are one of the commercial thermoelectric materials nowadays. The efforts to enhance its figure of merit have been extensively undertaking by doping rare-earth atoms, creating nano-structures in it, and so on. Furthermore, the electronic structure of Sn-doped PbTe is fundamentally interesting because of the so-called band inversion in its two end members, PbTe and SnTe [1,2]. Although, the electronic structure of these two compounds and their analogies have been intensively studied by first-principles calculations, to our best knowledge, there are no direct first-principles calculations of the band gap evolution through the full range of alloying. We report a study of the electronic structure of this material through the full range of alloy content, combining SQS [3] and LDA. Our results show that disorder plays an important role in the electronic structure of this alloy. The calculated results by taking account of the short-range disorder are in good agreement with experimental results. [1] Dimmock, Melngailis, and Strauss, Phys. Rev. Lett. 16, 1193 (1966).[2] Tung, and Cohen, Phys. Rev. 180, 823 (1969).[3] Wei and Zunger, Phys. Rev. B 55, 13605 (1997).This work is supported by DOE-EPSCoR.
U3: Poster Session
Session Chairs
Tuesday AM, November 27, 2007
Exhibition Hall D (Hynes)
9:00 PM - U3.10
Lanthanum Telluride: A Refractory Thermoelectric Material by Mechanical Alloying.
Andrew May 1 , Jeffrey Snyder 1 , Jean-Pierre Fleurial 2
1 , California Institute of Technology, Pasadena, California, United States, 2 , Jet Propulsion Laboratory, Pasadena, California, United States
Show AbstractLanthanum telluride demonstrates significant potential as an n-type material for high temperature thermoelectric application. The phase of interest is the cubic Th3P4 structure, which exists for compositions La3-xTe4 with 0≤x≤⅓. Mechanical alloying is utilized to synthesize the refractory compound at room temperature. The TE properties of various compositions (0<x<0.3) are examined, and zT > 1 is obtained at 1000oC for several compositions. When x = ⅓, one-ninth of lanthanum atoms are vacant and the system is a charge balanced insulator. As lanthanum vacancies are filled, free electrons are introduced and a maximum carrier concentration of approximately 4.5*1021cm-3 is expected for x = 0. TE properties vary as expected with the change in carrier concentration. Rare-earth chalcogenides of the Th3P4 structure thus offer an interesting inspection of the carrier concentration dependence of key TE properties. A two-band model characterizes the carrier concentration dependence and allows the system to be optimized for TE application. This analysis also provides insights into why lanthanum telluride is a zT>1 material and provides a framework for predicting the behavior of this and other TE systems.
9:00 PM - U3.11
Thermoelectric Properties of the Pseudo-binary PbTe-Sb2Te3 Composites with Lamellar Structure at Nanometer Scale.
Teruyuki Ikeda 1 , Eric Toberer 1 , Vilupanur Ravi 2 , Sossina Haile 1 , G. Jeffrey Snyder 1
1 Materials Science, California Institute of Technology, Pasadena, California, United States, 2 Department of Chemical and Materials Engineering, California State Polytechnic University, Pomona, California, United States
Show Abstract9:00 PM - U3.12
Effects of Tellurium and Thallium Doping on the Thermoelectric Properties of InSb.
Zhe Su 1 , Jian He 1 , Daniel Thompson 1 , Xiaohua Ji 1 , Terry Tritt 1
1 Physics, Clemson University, Clemson, South Carolina, United States
Show AbstractInSb is a promising candidate for thermoelectric applications in the intermediate temperature regime (500 K - 700 K). Single crystalline and polycrystalline Tellurium- and Thallium-doped InSb have been grown and characterized by means of resistivity, thermopower, thermal conductivity, and Hall coefficient measurements. The effects of Tellurium- and Thallium doping on the thermoelectric properties have been investigated, with the focus on lowering the thermal conductivity while preserving the high power factor in the InSb material.
9:00 PM - U3.13
Elastic Moduli of Lead Telluride as a Function of Temperature.
Fei Ren 1 , Jennifer Ni 1 , Eldon Case 1 , Joe Sootsman 2 , Mercouri Kanatzidis 2 , Edgar Lara-curzio 3 , Rosa Trejo 3
1 Chem. Eng. and Materials Science, Michigan State University, East Lansing, Michigan, United States, 2 Department of Chemistry, Northwestern University, Evanston, Illinois, United States, 3 High Temperature Materials Laboratory, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show Abstract Lead telluride (PbTe) is one of the established thermoelectric (TE) materials. Some doped PbTe compounds show superior TE properties, which is of great interest in the TE community in recent years. Although the elastic moduli of single crystal PbTe were reported in 1960’s, these characterizations were limited to room temperatures or below. There is little mechanical property reported on PbTe at high temperatures except a recent study of internal friction and relative shear modulus as functions of temperature by torsion pendulum method. In our study, we utilize resonant ultrasound spectroscopy (RUS) to characterize the elastic moduli as a function of temperature for polycrystalline PbTe materials fabricated by both the Bridgman method and quenching method. Young’s modulus decreases with increasing temperature and exhibits a linear temperature dependence between room temperature and ~ 800 K. Our high temperature Young’s modulus shows an excellent agreement when compared to the aggregate Young’s modulus values in literature that were calculated from single crystal elastic constants for p-type PbTe single crystals. In addition to the Young’s modulus, we also report the temperature dependence for shear modulus and Poisson’s ratio.
9:00 PM - U3.14
Systematic Investigation of Thermoelectric Materials: Substitution effect of Bi on the AgxPb18MTe20 (M = Bi, Sb) (x = 1, 0.86, 0.7).
Mi-kyung Han 1 , Huijun Kong 2 , Ctirad Uher 2 , Daniel Bilc 4 , Mercouri Kanatzidis 1 , Subhendra Mahanti 3
1 Chemistry, Northwestern University, Evanston, Illinois, United States, 2 Department of Physics, University of Michigan, Ann Arbor, Michigan, United States, 4 Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan, United States
Show Abstract9:00 PM - U3.15
Thermoelectric Properties of Nanostructured (Pb1-mSnmTe)1-x(PbS)x with Pb and Sb Precipitates.
Steven Girard 1 , Joe Sootsman 1 , John Androulakis 2 , Chia-Her Lin 2 , Mercouri Kanatzidis 1
1 Chemistry, Northwestern University, Evanston, Illinois, United States, 2 Chemistry, Michigan State University, East Lansing, Michigan, United States
Show AbstractNanostructuring achieved through spinodal decomposition and nucleation and growth in the thermoelectric material (Pb1-mSnmTe)1-x(PbS)x at m=0.05, x=0.04, 0.08, 0.16 will be presented as a method to obtain enhanced figures of merit. These systems are not solid solutions, but rather phase separate into distinct nanoscale PbTe and PbS regions as revealed by HRTEM. These nanoscale features help scatter phonons while allowing unaltered flow of charge carriers. We will compare and contrast the effectiveness of spinodal decomposition versus nucleation and growth in acoustic phonon scattering. Recently it has been demonstrated that precipitates of Pb and Sb can significantly alter charge carrier dynamics in PbTe. In this work, we report the thermoelectric properties of the (Pb0.95Sn0.05Te)1-x(PbS)x system with excess concentrations of Pb and Sb. Electrical and thermal measurements will investigate transport properties. Scanning and high-resolution transmission electron microscopy will be used to determine the micro- and nanostructure of these new systems, and possibly understand the role of spinodal decomposition, nucleation and growth, and matrix encapsulation in achieving high efficiency thermoelectric materials.
9:00 PM - U3.16
Investigation of Cubic PbS/AgSbS2 System for Thermoelectric Applications.
Duck-Young Chung 1 , Iliya Todorov 1 , Mercouri Kanatzidis 1 2
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Department of Chemistry, Northwestern University, Evanston, Illinois, United States
Show Abstract9:00 PM - U3.17
Estimation of Thermoelectric Property of FeVAl using Bloch Boltzmann Equation Based on First Principle Band Calculation.
Hiroki Funashima 1 , Noriaki Hamada 1
1 Department of Physics, Tokyo University of Science, noda Japan
Show Abstract9:00 PM - U3.18
Modeling the Electrical and Thermal Properties of Thermoelectric Materials.
Austin Minnich 1 , Daryoosh Vashaee 1 , Gang Chen 1
1 Mechanical Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractIn recent years several new approaches to designing thermoelectric materials have caused researchers to reexamine other materials previously thought unsuitable for thermoelectrics. Materials such as GaAs and InSb, while not currently used as thermoelectrics, could prove to be efficient thermoelectrics if prepared properly. To aid in this materials search we have developed a code which numerically calculates the electrical and thermal properties of many non-standard materials using the Boltzmann equation under the relaxation time approximation. The code incorporates a variety of scattering mechanisms and is capable of calculating properties over a wide range of temperatures and doping concentrations. Since lattice thermal conductivity can be reduced using the nanocomposite approach, we focus on characterizing materials by their electrical properties. We show that several materials have promising power factors and could serve as efficient thermoelectrics.
9:00 PM - U3.19
The Electronic Structure Study of Sb2Te3 with Doping Elements from 1A to 7A by the Ab initio Method.
Ming-Hong Chiueh 1 , Shan-Haw Chiou 1
1 Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu Taiwan
Show AbstractWe investigated the influence of the doping elements from 1A to 7A on Sb2Te3 crystal with performing first-principles calculations with the projector-augmented wave method and plane wave basis set. The formation energy and DOS were studied by substituting Sb and Te sites of Sb2Te3 with 1A to 7A elements. The calculation results show Be, Ca, Sr, Ba, B, Al and 4A and 5A elements substitute Sb or Te site to form p-type while the F substitutes Te site to form n-type.
9:00 PM - U3.2
Thermal Conductivity Measurements of Epitaxially Grown Nanowire Arrays using TDTR.
Ann Persson 1 3 , Yee Koh 2 , Heiner Linke 1 , Lars Samuelson 3 , David Cahill 2
1 Physics Department/Materials Science Institute, University of Oregon, Eugene, Oregon, United States, 3 Solid State Physics, Lund University, Lund Sweden, 2 Department of Material Science and Engineering , University of Illinois, Urbana, Illinois, United States
Show AbstractNanowires are suggested to be suitable for high-efficiency thermoelectric materials. Their one-dimensional nature result in a sharply peaked electronic density of states, predicted to enhance the power factor, and in confinement effects on the phonon transport, predicted to lead to a lowered lattice thermal conductivity [1]. We have investigated the thermal conductivity of highly ordered InAs nanowire arrays embedded in PMMA (polymethyl methacrylate) and present here a new approach for measuring the thermal conductivity of the technologically relevant case of nanowire arrays, using time-domain thermoreflectance (TDTR) [2]. TDTR has proved to be a very powerful method for characterizing the thermal transport properties of a wide variety of materials and here we apply TDTR for the first time to vertically aligned nanowires. The nanowires are arranged in arrays, where each array contains nanowires uniform in diameter and length and positioned in an ordered pattern. This well-controlled structure therefore enables us to extract also the thermal conductivity of a single InAs nanowire. The nanowires are grown with chemical beam epitaxy (CBE) and are epitaxially nucleated and positioned using lithographically defined Au discs as seed particles. The nanowires grow in the (111) direction, perpendicular to the substrate surface, and their diameters are defined by the Au discs. The fabrication is described in more details in Jensen et al. [3]. By changing the lithography parameters both the size and the position of the Au discs can be altered, which allows us to create arrays with nanowires of different diameters and with different filling factor (fraction of the matrix that consists of nanowires, where the matrix in this case consists of PMMA and nanowires). We report the fabrication of uniform nanowire arrays and the use of TDTR to measure the thermal conductivity of vertically aligned nanowires. We also present results of measurements on arrays with different filling factors, containing nanowires with different diameter and different length, showing that the thermal conductivity of InAs nanowires is clearly suppressed relative to the bulk value. [1] L. D. Hicks, M. S. Dresselhaus, Phys. Rev. B 47 (2003) 16 631[2] R. M. Costescu, M. A. Wall, D. G. Cahill, Phys. Rev. B 67 (2003) 054302.[3] L. E. Jensen, M. T. Björk, S. Jeppesen, A. I. Persson, B. J. Ohlsson, L. Samuelson, Nano Letters 4 (2004) 1961.
9:00 PM - U3.20
Temperature - Concentration Phase Diagram from First Principles Calculations in P2-NaxCoO2.
Yoyo Hinuma 1 , Ying Meng 1 , Gerbrand Ceder 1
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThe unusual electronic properties of NaxCoO2 are attracting considerable interest in recent years. At high sodium content, the system displays unusually strong thermoelectric effect and a low metallic resistance1. In this study, we present a temperature - concentration phase diagram for NaxCoO2 (0.5 <= x <= 1) obtained by combining Density Functional Theory (DFT) in the Generalized Gradient Approximation (GGA) with the cluster expansion technique and Monte Carlo simulation. In comparison we will also present the results obtained from the GGA with Hubbard U correction (GGA+U), which forces the charges on Co to completely localize, forming Co3+ and Co4+ cations unlike in the GGA in which no distinct Co3+ and Co4+ cations form. We will discuss the key interactions that determine the ground states and the order/disorder transition temperatures of these states, which may be important for understanding the thermoelectric properties of these mixed valence oxides. References:1I. Terasaki, Y. Sasago, and K. Uchinokura, Physical Review B 56, 12685 (1997).
9:00 PM - U3.21
Theoretical Study of Phase Diagrams in CoSb3-based Skutterudites.
Xun Shi 1 2 , Jihui Yang 2 , Wenqing Zhang 3 , Lidong Chen 3 , Ctirad Uher 1
1 Physics, University of Michigan, Ann Arbor, Michigan, United States, 2 Materials and Processes Laboratory, General Motors R&D Center, Warren, Michigan, United States, 3 State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Shanghai China
Show Abstract9:00 PM - U3.3
Sub 10 nm Diameter Bi Nanowires Grown in ALD Modified Alumina Membrane.
Lee Jongmin 1 , Ulrich Goesele 1 , Kornelius Nielsch 1
1 , Max-Planck Institute of Microstructurephysics, Halle Germany
Show AbstractThermoelectric effects involve the conversion between thermal and electrical energy and provide a method for heating and cooling materials. Thermoelectric bismuth nanowires were fabricated in a porous anodic alumina (PAA) membrane by pulsed electrodeposition. The self-organized PAA was prepared by 2nd step anodization process in 0.3M sulfuric acid and the pore diameter reached ca. 20 nm as-prepared. The pore diameter was reduced to sub 10 nm by using the Atomic Layer Deposition (ALD) in order to increase the thermoelectric figure of merit. Thermoelectric Figure of Merit (FOM) is strongly influenced by the diameter of nanowire, which was theoretically reported previously. FOM of Bi is increased significantly from 20 nm of diameter due to semimetal-semiconductor transition. After preparation the PAA in sulfuric acid, ALD was performed using Tri-methyl aluminum (TMA) and water (H2O) as precursors for the deposition of aluminum oxide (Al2O3) inside PAA. The pore diameter is varied at 20, 15, 10 and 5 nm depending on the number of ALD cycles. Bi nanowires were subsequently fabricated by pulsed electrodeposition in dimethylsulfoxide (DMSO) with bismuth chloride as an electrolyte under inert atmosphere. This process was performed at 130°C for the purpose of enhancing the Bi nanowire crystallinity as well as inhibiting the hydrogen evolution. Thermal conductivity and electrical conductivity are characterized with 3-omega system and 4-point probe system, where the metal wire is connected by e-beam lithography.
9:00 PM - U3.4
Study of Nanostructured Thermoelectric Materials Using Integrated TEM-STM System.
X. Jia 1 , Y. Lan 2 , Z. Ren 2 , G. Chen 3 , M. Dresselhaus 4
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Physics, Boston College, Chestnut Hill, Massachusetts, United States, 3 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 4 Department of Physics and Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractNanostructured thermoelectric materials – nanowires, nanobelts and bulk materials – have attracted lots of interest in recent years, due to their enhanced performance regarding their thermoelectric figure of merit. However, because of equipment limitations, little work has been done on combining the structural behavior with transport measurement of these materials simultaneously. With an integrated TEM-STM system, we studied the structural behavior and transport properties of various nanostructured thermoelectric materials. We present results of these measurements and the physical reasoning behind these effects on the thermoelectric figure of merit. These results have implications on further directions to be taken for improvement of these thermoelectric materials. *Support for this work was provided by NSF-NIRT Grant number CBET-05-06830.
9:00 PM - U3.5
Thermopower Measurements of Arrays of Small Diameter (13-60 nm) Bi Nanowires.
Tito Huber 1 , Ajibola Adeyeye 1 , Tosin Odunfa 1
1 Chemistry, Howard University , Washington, District of Columbia, United States
Show AbstractBecause of the increased density of states arising from quantum confinement, it is anticipated that quantum wires will exhibit superior thermoelectric properties and therefore high thermal-to-electric conversion efficiency. Bismuth is a model system for this study. Recently, angle-resolved photoemission spectroscopy (ARPES) studies have shown that Bi supports surface states that have not been considered in current models of quantum confinement. The surface states appear due to spin-orbit interaction, a feature of many thermoelectric materials. Studies of the Fermi surface, employing the Shubnikov-de Haas (SdH) method, in arrays of 30-nm to 80-nm bismuth nanowires partially corroborates ARPES findings. Measurements of the thermopower of nanowire array samples is challenging due to the small size of the samples. Still, our measurements of the thermopower of 60-nm Bi nanowires presented at the 2006 International Conference on Thermoelectrics indicate that n-type surface carriers dominate over the quantum-confined electrons and holes for T< 30 K. Assuming the model of diffusing thermopower, in smaller diameter nanowires the surface effects should be stronger and the temperature range over which the surface effects dominate should extend to higher temperatures. We report on measurements of the thermopower of arrays of 18-nm and 35-nm nanowires to test this model.
9:00 PM - U3.6
Laser-assisted Synthesis and Optical Properties of Bismuth Nanorods.
Jason Reppert 1 , Rahul Rao 1 , Malcolm Skove 1 , Jian He 1 , Terry Tritt 1 , Apparao Rao 1
1 , Clemson University, Clemson, South Carolina, United States
Show AbstractInfrared absorption, temperature-dependent electrical resistance and magneto-resistance measurements of Bi nanowires (diameter < 200 nm) prepared using the alumina-template method confirmed the existence of a semimetal-semiconductor phase transition. We report the synthesis of ~10 nm diameter Bi nanorods using a pulsed laser vaporization method. The high resolution transmission electron microscopy images of our Bi nanorods show a crystalline Bi core oriented along <012> direction, and coated with a thin amorphous Bi2O3 layer. The infrared absorption and the surface plasmon peaks in our Bi nanorods are blue-shifted in energy when compared to the corresponding spectra in bulk Bi.
9:00 PM - U3.7
Mechanical Alloying Synthesis of K2Bi8Se13 – type Solid Solutions
Nikolaos Toumpas 1 , Theodora Kyratsi 1 , Euripides Hatzikraniotis 2 , Andreas Tsiappos 1 , Eleni Pavlidou 2 , Konstantinos Paraskevopoulos 2 , Duck Young Chung 4 , Mercouri Kanatzidis 3 4
1 Mechanical & Manufacturing Engineering, University of Cyprus, Nicosia Cyprus, 2 Department of Physics, Aristotle University of Thessaloniki, 54124, Thessaloniki Greece, 4 Materials Science Division, Argonne National Laboratory, Argonne, 60439, Illinois, United States, 3 Department of Chemistry, Northwestern University, Evanston, 60208, Illinois, United States
Show AbstractSolid solutions of β-K2Bi8-xSbxSe13 are interesting series of materials for thermoelectric investigations due to their very low thermal conductivity and highly anisotropic electrical properties. On the other hand, powder technology is an advantageous approach on synthesis and processing of thermoelectric materials due to its features such as good mechanical properties, easy shaping, low temperatures, mass production, etcIn this work, we aimed to synthesize solid solutions of β-K2Bi8-xSbxSe13 type materials using powder techniques. The synthesis was based on mechanical alloying as well as sintering procedures. The products were studied in terms of structural features, composition and purity in order to find the conditions that lead to pure materials using powder x-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. Their thermoelectric properties (Seebeck coefficient, electrical conductivity) as well as IR reflectivity were also investigated. The results are compared with materials prepared from the melt.
9:00 PM - U3.8
Impact of Nanoscale Substructures on the Thermoelectric Properties of AgPbmSbTe2+m.
Qing Jie 1 , Juan Zhou 1 , Lijun Wu 1 , Jincheng Zheng 1 , Yimei Zhu 1 , Qiang Li 1 , Jihui Yang 2
1 Condensed Matter Physics and Materials Science, Brookhaven National Lab, Upton, New York, United States, 2 Materials and Processes Lab, GM R&D Center, Warren, Michigan, United States
Show AbstractWe report a coordinated study of the thermoelectric and structural properties of AgPbmSbTe2+m (LAST-m) compounds in both single crystals and polycrystalline samples, in order to understand the impact of nanoscale substructures on the thermoelectric properties of LAST-m system. Analytical transmission electron microscopy (TEM) was used to obtain the structure information, while quantitative electron diffraction was used to explore the charge distribution. The ability for quantitative electron diffraction to probe nm-scale area is particularly useful in the studies of electronic structure of LAST-m compounds. Bulk thermoelectric properties were studied by direct transport measurements, and were compared with the infrared optical spectroscopy measurements of the same samples probing the electron and phonon dynamics. Evolution of nanoscale substructure and matrix materials as a function of temperature up to the melting point was investigated by in-situ TEM. We will discuss in detail the correlation between the thermoelectric properties and nanostructure of this class of materials at various temperatures.
9:00 PM - U3.9
Structural Studies of GeTe-AgSbTe2 Alloys.
Claudia Rawn 1 , Bryan Chakoumakos 1 , Jeff Sharp 2 , Alan Thompson 2 , Pat Gilbert 2
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Materials R&D, Marlow Industries, Dallas, Texas, United States
Show AbstractGeTe, a small bandgap semiconductor that has native p-type defects due to Ge vacancies, is an important constituent in the thermoelectric material known as “TAGS” [1]. TAGS is an acronym for alloys of GeTe with AgSbTe2, and compositions are normally designated as TAGS-x, where x is the fraction of GeTe. TAGS-85 is the most important with regard to applications, and there also is commercial interest in TAGS-80. The crystal structure of GeTe1+δ has a composition-dependent phase transformation at a temperature ranging from 430 °C (δ = 0) to ~ 400 °C (δ = 0.02) [2]. The high temperature form is cubic. The low temperature form is rhombohedral for δ < 0.01, as is the case for good thermoelectric performance. Addition of AgSbTe2 shifts the phase transformation to lower temperatures, and one of the goals of this work is a systematic study of the dependence of transformation temperature on the parameter x. In addition to TAGS, there are other Ag-containing tellurides that are of interest as thermoelectric materials. These include LAST (PbTe + AgSbTe2), compositions in the Tl-Ag-Te ternary system, and Ag2Te. We present results on phase transformations and associated instabilities in TAGS compositions in the range of 60-85 at.% GeTe, and on the atomic displacement parameter of Ag in TAGS and other materials. [1]E. A. Skrabek and D. S. Trimmer, “Properties of the General TAGS System,” in CRC Handbook of Thermoelectrics, ed. D. M. Rowe (CRC Press, Boca Raton, FL, 1995), pp. 267-275.[2]Ge-Te phase diagram, in Moffatt’s Handbook of Binary Phase Diagrams, ed. J. H. Westbrook (Genium Publ. Corp., Schenectady, NY, 1995).
Symposium Organizers
Timothy P. Hogan Michigan State University
Jihui Yang General Motors R&D Center
Ryoji Funahashi National Institute of Advanced Industrial Science and Technology
Terry Tritt Clemson University
U4: Chalcogenides
Session Chairs
Tuesday AM, November 27, 2007
Room 311 (Hynes)
9:30 AM - U4.1
Melt Spinning Preparation of Bismuth Telluride and Partially Alloying with IV-VI Compounds for Thermoelectric Application.
Harald Boettner 1 , Dirk Ebling 1 , Alexandre Jacquot 1 , Uta Kuehn 2 , Juergen Schmidt 3
1 Thermoelectric Systems, Fraunhofer Institute for Physical Measuremnt Techniques, Freiburg Germany, 2 , Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden, Dresden Germany, 3 , Fraunhofer-Institut für Fertigungstechnik und Angewandte Materialforschung IFAM, Dresden Germany
Show AbstractBismuth telluride and its alloys is known as the best thermoelectric semiconductor for room temperature application.One promising approach to improve thermoelectrical properties are nanocomposite materials with lower thermal conductivities and therefore higher ZT-values. Melt spinning, originally developed for rapid cooling of metal liquids, is used to develop material, that requires extremely high cooling rates in order to form metallic glasses or nanocomposites. Here we will report on the evolution of the thermoelectric material parameters like thermal and electrical conductivity, and the Seebeck coefficient in dependence on the fabrication and doping of the base material comparing the properties as prepared to different post-annealing processes. As far as the melt spinning process is concerned parameters like the rotation speed, extrusion pressure, casting temperature, distance nozzle to cooling wheel, pressure and kind of gas were varied. Crystalline, textured flakes of some 10µm thickness and areas ~30mm2 were achieved. Before and after post-annealing processes the flakes were structurally characterized by SEM, XRD and TEM and they could also be analysed for the Seebeck-coefficient and Hall-effect properties. Beside the intrinsic p- and n-doping the material was alloyed with up to 0.5% lead telluride to influence the thermoelectric properties by a tentative nanocomposite, see also the phase diagram respectively. The resulting flakes were also structurally characterized and analysed to about 600 K for the thermoelectric properties. Melt spinning is only capable to produce small and thin ribbon shaped specimens. This limits melt spinning for V2-VI3-materials currently to the manufacturing of academic specimens. Therefore in addition the spark plasma sintering (SPS)-technique was used to compress a few grams of the flakes to specimens which were suitable to determine the thermal conductivity of the melt spinning material. In addition the influence of the SPS-procedure was studied with respect to the thermoelectric properties of the material.
9:45 AM - U4.2
Theory of Enhancement of Thermoelectric Properties of Materials with Nanoinclusions: Application to Pb_{1+x}Te.
Sergey Faleev 1
1 , Sandia National Laboratories, Livermore, California, United States
Show AbstractWe present a theoretical model, based on the Boltzmann Transport Equation in relaxation time approximation, for description of the Seebeck coefficient and electrical conductivity for a PbTe system with Pb nanoinclusions. The effect of nanoinclusions has been taken into account by considering the electron scattering on the Schottky potential of the metal-semiconductor boundary of Pb islands. Both Born approximation and exact solution of the Schrödinger equation have been applied to calculate the scattering probability and it was found that Born approximation is applicable for small island radiuses or large electron concentration. The model predicts an increase of the Seebeck coefficient because the relaxation time due to scattering on the Pb islands has stronger energy dependence compared to the relaxation time for bulk PbTe. We demonstrated that the model can be applied to maximize the power factor by choosing an optimal radius of the the Pb islands and/or optimal concentration of the islands. The results for electron mobility and Seebeck coefficient calculated by our model are in qualitative agreement with recent experimental data. Nevertheless the experiments with more control on the geometry of scattering centers should be performed in order to quantitatively verify the validity of present model.
10:00 AM - **U4.3
Nanostructured LAST and PbTe-based Thermoelectrics for Power Generation.
Mercouri Kanatzidis 1 , Tim Hogan 3 , Ctirad Uher 2 , Elson Case 4 , Harold Schock 5 , Pierre Poudeu 1 , Mi-Kyoung Han 1 , Hui-J. Kong 2 , Adam Downey 3 , Jonathan D'Angelo 3 , Chun-I Wu 3 , Rei Fen 4 , Edward Timm 5
1 Department of Chemistry, Northwestern University, Evanston, Illinois, United States, 3 Department of Electrical and Computer Engineering, Michigan State University, East Lansing, Michigan, United States, 2 Department of Physics, University of Michigan, Ann Arbor, Michigan, United States, 4 Department of Chemical Engineering, Michigan State University, East Lansing, Michigan, United States, 5 Department of Mechanical Engineering, Michigan State University, East Lansing, Michigan, United States
Show Abstract10:30 AM - U4.4
Mechanical Characterization of PbTe-based Thermoelectric Materials.
Fei Ren 1 , Bradley Hall 1 , Jennifer Ni 1 , Eldon Case 1 , Joe Sootsman 2 , Mercouri Kanatzidis 2 , Edgar Lara-curzio 3 , Rosa Trejo 3 , Edward Timm 4
1 Chem. Eng. and Materials Science, Michigan State University, East Lansing, Michigan, United States, 2 Department of Chemistry, Northwestern University, Evanston, Illinois, United States, 3 High Temperature Materials Laboratory, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 Department of Mechanical Engineering, Michigan State University, East Lansing, Michigan, United States
Show AbstractPbTe-based thermoelectric (TE) materials exhibit promising thermoelectric properties and have potential applications in waste heat recovery from sources such as truck engines and shipboard engines. TE components designed for these applications will be subject to mechanical/thermal loading and vibration as a result from in-service conditions, including mechanical vibration, mechanical and/or thermal cycling, and thermal shock.In the current study, we present and discuss the mechanical properties of several PbTe-based compositions with different dopants and processing methods, including n-type and p-type specimens fabricated both by casting and by powder processing. Room temperature hardness and Young’s modulus are studied by Vickers indentation and nanoindentation while fracture strength is obtained by biaxial flexure testing. Temperature dependent elastic moduli, including Young’s modulus and Poisson’s ratio are studied via resonant ultrasound spectroscopy (RUS).
10:45 AM - U4.5
Phase Separation in Bulk Thermoelectric Alloys based on AgPbmSbTe2+m.
Douglas Medlin 1 , M. Hekmaty 1 , A. Morales 1 , M. Homer 1 , M. Clift 1 , J. Sugar 1
1 , Sandia National Laboratories, Livermore, California, United States
Show AbstractRecent work in the literature has reported a high thermoelectric figure-of-merit for some compositions within the general formula of AgPbmSbTe2+m (e.g. Hsu et al, Science 2004). This high performance has been attributed to the formation of nanoscale clusters thought to be rich in Ag and Sb. To better understand how such a nanostructure forms, we have synthesized a series of alloys based on this general formula and have investigated the structural evolution of these materials using transmission electron microscopy (TEM), x-ray diffraction, and electron microprobe measurements. For sufficiently high Ag and Sb concentrations, we find a two-phase microstructure composed of both fine-scale (~10-20 nm diameter) precipitates, which are rich in Ag and Sb, and larger scale (~100 nm and larger) lamellae of alternating Pb-rich and Ag/Sb-rich material. Fine-scale energy dispersive x-ray spectroscopy (EDXS) measurements in the TEM and larger-scale electron microprobe measurements show that the Ag and Sb concentrations track each other and are anticorrelated with the Pb concentration while the Te concentration remains fixed. This result is consistent with the notion that, in these materials, silver and antimony substitute for Pb in the crystal structure and have a tendency to cluster. This idea is further supported by electron diffraction measurements showing that both phases are topotactically aligned and are consistent with a cubic, rock-salt-type structure. The Ag/Sb-rich phase possesses a 4% smaller lattice parameter than the Pb-rich phase--a somewhat smaller difference than that between pure PbTe and AgSbTe2 (6%). This misfit leads to dense arrays of dislocations at the lead-rich and antimony/silver-rich phase boundaries. We will discuss our microstructural results in the context of the existing body of literature on phase stability in the Pb-Te-Ag-Sb system with the goal of identifying the conditions for obtaining an optimal internal nanostructure and assessing the conditions under which this structure will remain stable.Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States DOE-NNSA under contract DE-AC04-94AL85000.
11:30 AM - **U4.6
Atomic Ordering, Electronic Structure, and Transport Properties of LAST-m Systems.
Subhendra Mahanti 1
1 Physics and Astronomy, Michigan State University, East Lansing, Michigan, United States
Show AbstractIn recent years, LAST-m (AgPb_mSbTe_m+2) and related materials have emerged as potential high performance high temperature thermoelectrics.[1] These compounds are obtained by starting from PbTe, a well-known high temperature thermoelectric, and replacing a pair of divalent Pb2+ ions by a combination of a monovalent (Ag1+, Na1+, K1+ etc) and a trivalent (Sb3+) ion. One example is LAST-18. When appropriately doped, it gives a value of the thermoelectric figure of merit, ZT~1.7 near T=600-700K. A major reason for this large ZT is the low lattice thermal conductivity caused by the presence of nanostructures associated with the ordering of Ag, Sb, and Pb ions. These nanostructures scatter phonons efficiently. It is also believed that nanostructures can lead to increased thermopower by manipulating the electronic density of states near the Fermi energy.[2,3]In this talk I will discuss the possible origin of this atomic ordering[4,5] and how the presence of these nanostructures can affect the electronic properties of LAST-m compounds[6]. The physics of gap/pseudogap formation in the end member of this series, AgSbTe2, itself an excellent thermoelectric, will be explained.[7] Finally, I will discuss the transport properties of PbTe and LAST-m systems, focusing on the energy and temperature dependence of the transport function and how they impact on the temperature dependence of the electrical conductivity, constant current and constant field electronic thermal conductivity and the Wedemann-Franz law, which is widely used to extract lattice thermal conductivity from the experimentally measured total thermal conductivity.[8]*Work partially supported by ONR MURI grant.+Work done in collaboration with Daniel Bilc, Khang Hoang, Salameh Ahmad, and M. G. Kanatzidis and his group.1. K. F. Hsu et. al. , Science 303, 818 (2004)2. D. Hicks and M. S. Dresselhaus, Phys. Rev. B 47, 12727 (1993).3. G. D. Mahan and J. O. Sofo, Proc. Natl. Acad. Sci. U.S.A 93, 7436 (1996).4. Khang Hoang, K. Desai, and S. D. Mahanti, Phys. Rev. B 72, 064102 (2005).5. H. Hazama et al., Phys. Rev. B 73, 115108 (2006); Khang Hoang, S. D. Mahanti, and P. Jena (submitted to Phys. Rev. B).6. D. Bilc et al. Phys. Rev. Lett. 93, 146403 (2004).7. Khang Hoang et al. (submitted to Phys. Rev. Letters).8. D. Bilc et al., Phys. Rev. B 74, 125202 (2006); S. Ahmad and S. D/ Mahanti (Unpublished)
12:00 PM - U4.7
Galvanomagnetic Measurements of Neodymium Doped Lead Telluride.
Vladimir Jovovic 1 , Joseph Heremans 2
1 Mechanical Engineering, The Ohio State University, Columbus, Ohio, United States, 2 Mechanical Engineering and Physics, The Ohio State University, Columbus, Ohio, United States
Show AbstractA systematic study of the thermoelectric properties of alloys of PbSe with rare earth elements (Ce, Pr, Nd, Eu, Gd and Yb)1 has shown an increase in thermopower perhaps due to a hybridization of 4f levels with the PbSe bands. As predicted by Mohan and Sofo2 theory these high-density-of-state levels, if at Fermi level, can result in significant improvement in thermoelectric properties. We have found that largest improvement in thermopower is observed in PbSeNd alloys where we measured doubling of thermopower at high carrier concentrations as compared to PbSe. Here we study telluride alloys: we analyze set of Pb1-xSnxTe:Nd with Nd concentrations up to 10% and x ranging from 0 to 1. Since Nd3+ is a donor in PbTe, we use counterdoping in two systems. The first system is PbTe + Nd2Te3 , which is electrically neural; the second system is the Pb1-xSnxTe + NdTe, where the Pb1-xSnxTe alloys are naturally heaviliy p-type. Galvanomagnetic measurements are performed in standard flow cryostat at temperatures ranging from 80 to 600K and in magnetic field from -2.5 to 2.5 T. Measurements of electrical resistivity, thermopower, Hall and transverse Nernst-Ettinghausen effect are used to deduce the fundamental properties: the carrier density, mobility, effective mass and scattering exponent. Results are analyzed to evaluate the possible hybridization of Nd levels in the Pb1-xSnxTe bands. [1] V. Jovovic, S. Joottu Thiagarajan, J. West, J. P. Heremans, T. Story, Z. Golacki, W. Paszkowicz and V. Osinniy, submitted to Journal of Applied Physics (2007)[2] G. D. Mahan and J. O. Sofo, Proc. Natl. Acad. Sci. USA 93 7436 (1996)
12:15 PM - U4.8
Optimization of High Thermoelectric Figure of Merit in p-type Ag1-x(Pb1-ySny)mSb1-zTem+2.
Kyunghan Ahn 1 , Mercouri Kanatzidis 1
1 Chemistry, Northwestern University, Evanston, Illinois, United States
Show AbstractThermoelectric (TE) power generation is the focus of considerable attention because of the potential for environmentally benign and cost-effective conversion of waste heat to electricity. The search for high TE efficiency materials is a quest to maximize the dimensionless figure of merit ZT = (σS2/κ)T, where σ is electrical conductivity, S is the TE power (Seebeck coefficient), and κ is thermal conductivity. Certain compositions of Ag(Pb1-ySny)mSbTe2+m (LASTT) series have been recently found to exhibit high performance p-type TE properties (ZT ~ 1.45 at 630 K). Varying the m and y values as well as the concentrations of Ag and Sb allows for control over carrier concentration, TE power, and thermal conductivity. We will present detailed investigations on the TE properties of p-type Ag1-x(Pb1-ySny)mSb1-zTem+2 (LASTT) series by tuning primarily through controlling m value and Pb/Sn ratio (y value) and secondarily the Ag and Sb concentrations (x and z values) because the LASTT system has not been optimized yet well. In addition we will present experimental evidence of the nanostructured nature of these materials which results in very low lattice thermal conductivity.
12:30 PM - U4.9
High-Temperature Thermoelectric Properties of Pb1-xSnxTe:In.
Suraj Joottu Thiagarajan 1 , Vladimir Jovovic 1 , Joseph West 1 , Joseph Heremans 1 , T. Komissarova 2 , Dmitriy Khokhlov 2 , A. Nicorici 3
1 , The Ohio State University, Columbus, Ohio, United States, 2 , Moscow State University, Moscow Russian Federation, 3 , Institute of Applied Physics, Moldova Academy of Sciences, Kishinev Moldova (the Republic of)
Show AbstractIndium in Pb1-xSnxTe alloys forms a narrow energy level which might hybridize with valence or conduction bands[a]. In this study we investigate interactions between Indium impurity levels and band at extended range of temperatures from 80 to 400K. In contrast to our previous work at 80 K[b], it turns out that the PbTe band structure is very temperature-dependent, and so is the location of the In level with respect to the conduction and valence band edge. Transport properties, measurements of electrical resistivity, thermopower, Hall and transverse Nernst-Ettingshausen effect are used to assess effective mass, and carrier mobility, Fermi energy level and scattering coefficient. Measurements are performed on a set of p and n type Pb1-xSnxTe indium doped alloys with Sn concentrations from 0 to 30% and In up to 3%. Using these measurements we evaluate the In level location in the bands at higher temperature. Hybridization at the Fermi levels can have positive effects on the thermoelectric properties of materials resulting from an increase in thermopower due to an increase in electron scattering exponent as predicted by Ravich, Nemov and Kaidanov. Our study evaluates possibility of increasing thermoelectric figure of merit of Pb1-xSnxTe:In alloys at operating temperatures. [a] K. Hoang et al., APS Meeting Abstracts, 40012 (2007)[b] V. Jovovic et al., Electronic Materials Conference, Notre Dame, June 20-22, 2007[c] V.I. Kaidanov et al., Sov. Phys. Semicond. 26, 113 (1992)
12:45 PM - U4.10
N-type Lead-Chalcogenide Thermoelectric Materials Alloyed with Tin.
Jan Koenig 1 , Alexandre Jacquot 1 , Harald Boettner 1
1 Thermoelectric Systems, Fraunhofer IPM, Freiburg, Baden-Württemberg, Germany
Show AbstractIV-VI materials, especially lead-chalcogenides are used until now for mid-temperature thermoelectric applications. Currently PbTe doped with PbI2 is used as n-type material and TAGS85 or (Pb,Sn)Te with a tin content above x=0.25 as p-type legs. To increase the thermoelectric efficiency it is worth to look for an alternative n-type material. This alternative material should be preferentially also be based on lead-tin chalcogenides. Therefore we studied the preparation and thermoelectrical properties of n-type alloys respectively as thin film and as bulk materials.To do this, single crystalline thin film samples and also bulk single crystals of (Pb,Sn)Te and (Pb,Sn)Se in the composition range of a tin content below x=0.25 were grown by molecular beam epitaxie and by the unseeded vapour growth technique respectively. Recent temperature dependent measurements of the thermoelectric transport properties of a series of n-type (Pb,Sn)Te and (Pb,Sn)Se are presented. The alloying with tin results in a multifunctional effect: With increasing tin content the band gap reduces towards ideal values for applications in the room- and mid-temperature range. The effects of the tin alloying on the overall power factor and figure-of-merit (ZT) will also be discussed. It was found, that the stable or increasing carrier mobility and the reduction of the lattice thermal conductivity due to alloy scattering is the main reason for the ZT enhancement with increasing tin content. Based on these investigations the currently used n-type material could be substituted by the material systems presented in this paper.
U5: Bulk Thermoelectrics I
Session Chairs
Tuesday PM, November 27, 2007
Room 311 (Hynes)
2:30 PM - **U5.1
Bulk Materials Research for Thermoelectric Power Generation Applications.
George Nolas 1 , Joshua Martin 1 , Matthew Beekman 1 , Xiumu Lin 1
1 Physics, University of South Florida, Tampa, Florida, United States
Show AbstractThere are a variety of material systems employing different strategies in an effort to establish a new paradigm for thermoelectric materials performance. One approach is the PGEC, or “phonon-glass electron crystal”, approach were research towards optimization of the electrical properties of very low thermal conductivity materials is key. Other efforts focus on materials that exhibit high power factors via quantum-confinement or nano-scale affects. Still others focus on “engineering” metastable phases that possess properties that are distinct, if not unique, to solid-state chemistry. All these approaches are valid and provide a fundamental knowledge base whereby present and future scientific materials discoveries will lead to new technological improvements. This talk will focus on bulk materials, in particular those material systems currently under investigation in our laboratory and the requirements and strategies for their optimization towards improved thermoelectric properties.
3:00 PM - U5.2
Thermoelectric Properties of Silicon and Germanium Network Polyhedra viewed from Physical Parameters.
Katsumi Tanigaki 1 , Takeshi Rachi 1 , Jun Tang 1 , Ryotaro Kumashiro 1 , Shoji Yamanaka 2 , Macros Avila 2 , Toshiro Takabatake 2
1 Physics, Tohoku University, Sendai Japan, 2 , Hiroshima University, Hiroshima Japan
Show Abstract When the special conditions are constrained to the network formation in IVth group of elements like silicon, germanium and tin, nano materials having network polyhedra are produced. Although the sp3-hybridized bonding is favored in silicon and germanium different from carbon where both sp2- and sp3- hybridization are realized in graphite and diamond, a new series of materials featured by the polyhedral cage frameworks with sp2-characters have been sought in these days and lots of such materials, so called clathrates, have been synthesized. In these nano materials, one of the important issues is phonons. Because of the cluster cages and their large inner spaces inside, the phonons different from the conventional lattice phonons should be taken into account. For instance, intra-cluster phonons are believed to play an important role for giving rise to unique electronic states through electron-phonon coupling and endohedral atomic phonons with showing time- and space-dependent anharmonic oscillations are also expected to provide exotic interactions with conduction electrons at the Fermi surfaces. The latter phonons have recently been drawing much attention in materials science and are called as rattling phonons. The rattling phonons have freedom in motion and will break the symmetry of crystals. In this sense, phonons are glass-like and the electrons spreading over the polyhedral networks are crystal-like in silicon and germanium clathrates. This intriguing concept of phonon-glass and electron-crystal (PGEC) shows lots of possibilities of creating novel materials like good thermoelectric compounds. Among the compounds showing such features as regulated nano spaces that make it possible to accommodate atomic elements, like clathrates, skutterdites, pyrochlores and fullerides, clathrates will be one of the most perspective candidates to be applied to thermopower materials with high conversion figure of merits.In this meeting, we would like to present our recent systematic experimental studies on type I silicon and germanium clathrates [1-3] with emphasis on the three component type I clathrates (Sr,Ba)8(Ga,Al,In)16(Si,Ge)30. Depending on the component ratios, carrier type can be controlled between p and n for single crystals in this system and some of them show high performances as thermoelectric power materials. We will provide all sets of experimental parameters and discuss their electronic states on a basis of the information.The work is supported by Grand-in-Aid for Science Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan as well as by the 21st Century Tohoku University COE program and the Center for Interdisciplinary Research Project in Tohoku University.[1] K. Tanigaki, et al, Nature Materials, 2, 653 (2004).[2] T. Rachi, K. Tanigaki et al., Phys. Rev. B, 72, 144504 (2005). [3] Takeshi Rachi , Katsumi Tanigaki et al., J. Physics and Chemistry of Solids 67, 1334–1337 (2006).
3:15 PM - U5.3
Thermoelectric Properties of Silicon and Germanium Type III Clathrates Ba24IV100 (IV=Si and Ge).
Takeshi Rachi 1 , Harukazu Yoshino 2 , Ryotaro Kumashiro 1 , Hiroshi Fukuoka 3 , Shoji Yamanaka 3 , Keizo Murata 2 , Katsumi Tanigaki 1
1 Physics, Tohoku University, Sendai Japan, 2 Physics, Osaka City University, Osaka Japan, 3 Applied Chemistry, Hiroshima University, Higashi-Hiroshima Japan
Show Abstract3:30 PM - U5.4
High Temperature Thermoelectric Efficiency in Ba8Ga16Ge30.
Eric Toberer 1 , Mogens Christensen 2 , Bo Iversen 2 , Jeffrey Snyder 1
1 Materials Science, California Institute of Technology, Pasadena, California, United States, 2 Department of Chemistry, University of Aarhus, Langelandsgade Denmark
Show Abstract3:45 PM - U5.5
Synthesis and Characterization of Inorganic Clathrate-II Materials.
Matt Beekman 1 , George Nolas 1
1 Department of Physics, University of South Florida, Tampa, Florida, United States
Show AbstractInorganic clathrate materials are characterized by a covalently bonded framework, typically of Si, Ge, or Sn, which can encapsulate guest species inside polyhedral cages formed by the framework. Compounds with the clathrate-I crystal structure have been extensively investigated, and continue to generate much interest due to their promising thermoelectric properties. Phases with the clathrate-II crystal structure, however, still remain to be well characterized. Inorganic clathrate-II materials offer the unique ability to vary the guest concentration, which has significant implications for the control of their electrical and thermal transport properties. We present here recent results on the synthesis and characterization of silicon and germanium clathrate-II materials. The transport properties of NaxSi136 clathrates show strong dependence upon the guest content x, indicating a potential route for transport property “tuning.” We present results from an investigation into the possible “phase space” of inorganic clathrate-II phases, an exploration of new clathrate-II compositions including framework substitution by elements of Group III, as well as transition metals in clathrate-II compounds. The potential inorganic clathrate-II materials hold for thermoelectric applications will be discussed.
4:00 PM - U5:BulkThermo
BREAK
4:30 PM - U5.6
Thermoelectric Properties of InxCo4-yNiySb12 Skutterudite Compounds.
Veronique Da Ros 1 , Juliusz Leszczynski 1 , Bertrand Lenoir 1 , Anne Dauscher 1 , Christophe Candolfi 1 , Philippe Masschelein 1 , Christine Bellouard 2 , Christian Stiewe 3 , Eckard Müller 3 , Jiri Hejtmanek 4
1 Laboratoire de Physique des Materiaux, Ecole Nationale Superieure des Mines de Nancy, Nancy France, 2 Laboratoire de Physique des Matériaux, Université Henri Poincaré, Nancy France, 3 Institute of Materials Research, German Aerospace Center DLR e.V, Köln Germany, 4 Institute of Physics, Academy of Sciences of the Czech Republic, Praha Czech Republic
Show AbstractThe preparation of partially filled n-type InxCo4Sb12 skutterudite compounds has been recently reported. The results were particularly promising, the materials exhibiting a ZT value far higher than one at moderated temperature. An even higher value has been achieved by modulating the void filling by two different elements (In and Ce). In this paper, we propose to investigate another way to tune the electrical and thermal properties by substituting Co atoms by Ni atoms in InxCo4Sb12.InxCo4-yNiySb12 polycrystalline samples have been prepared by a conventional metallurgical route. Structural analyses have been carried out by X-ray diffraction. The chemical composition and micro-homogeneity have been checked by electron probe microanalysis. Measurements of the electrical resistivity, thermoelectric power, thermal conductivity and Hall coefficient have been performed between 4 and 800 K. The influence of the presence of Ni on the thermoelectric properties of InxCo4Sb12 compounds will be presented and discussed.
4:45 PM - U5.7
Dual-Frequency Resonant Phonon Scattering in BaxRyCo4Sb12 (R = La, Ce, and Sr).
Jihui Yang 1 , Wenqing Zhang 2 , Shengqiang Bai 2 , Zhigang Mei 2 , Lidong Chen 2
1 R&D Center, General Motors Corp., Warren, Michigan, United States, 2 State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 China
Show AbstractLow temperature transport properties of polycrystalline dual-element-filled skutterudites BaxRyCo4Sb12 (R=La, Ce, and Sr) are reported. Remarkably the combination of Ba and La, or Ba and Ce is much more effective in reducing lattice thermal conductivity than Ba and Sr, in spite of the much higher total void filling fraction in BaxSryCo4Sb12. Our density functional theory calculations and experimental data suggest that multiple-filled skutterudites using filler elements of different chemical nature, such as the rare-earths, the alkaline-earths, or the alkalines provide a broader range of resonant phonon scattering. The thermoelectric figure of merit of filled skutterudites can likely be improved by means of such multiple-element void filling.
5:00 PM - U5.8
Ternary Skutterudites: Anion Ordering and Thermoelectric Properties.
Paz Vaqueiro 1 , Gerard Sobany 1
1 , Heriot-Watt University, Edinburgh United Kingdom
Show AbstractMaterials with the skutterudite structure, MX3 (M = Co, Rh or Ir and X = P, As or Sb) possess attractive thermal and electrical transport properties for thermoelectric applications at temperatures over the range 650-900K. While binary skutterudites, MX3, have been widely investigated, little is known about the related ternary skutterudites, which can be prepared by isoelectronic substitution at the anion or cation sites. Our recent research efforts have been centered on the synthesis and characterisation of ternary skutterudites obtained by substitution at the anion site, X, by a pair of elements from groups 14 and 16.The skutterudite-related materials AB1.5Q1.5 (A = Co, Rh, Ir, B =Ge, Sn, Q = S, Te) have been synthesized and structurally characterised by high-resolution X-ray and neutron powder diffraction. Diffraction data are consistent with the presence of anion ordering, which results in a lowering of the symmetry from cubic to rhombohedral. Measurements of the resistivity, Seebeck coefficient and thermal conductivity have been carried out. The electrical transport properties of these materials are consistent with semiconducting behaviour, and large values of the Seebeck coefficient have been observed for several of these phases. In addition, these materials exhibit significantly lower thermal conductivities than their binary counterparts.
5:15 PM - U5.9
Enhanced Thermoelectric Figure of Merit in BaxYbyCo4Sb12 Skutterudites.
Ctirad Uher 1 , Xun Shi 1 , Huijun Kong 1
1 Physics, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractSkutterudites are among a handful of novel materials that are being intensely pursued in hope of developing more efficient thermoelectrics for power generation applications at temperatures between 500K – 850K. Filling the voids in the skutterudite structure by different fillers is an effective way of reducing thermal conductivity because a broader range of phonons is scattered. This approach is particularly effective when fillers with different phonon contrast (different masses and resonant frequencies) are used. We prepared double-filled skutterudites (BaxYbyCo4Sb12)using a melting method and studied their high temperature thermoelectric properties from 300K to 800K. The double-filled materials show a very low lattice thermal conductivity yet maintain good electrical transport properties. The highest ZT achieved in BaxYbyCo4Sb12 is 1.36 at 800K.
5:30 PM - U5.10
Complex Zintl Phases for Thermoelectric Power Generation.
Jeff Snyder 1
1 , California Institute of Technology, Pasadena, California, United States
Show AbstractComplex Zintl phases and polar intermetallics make ideal candidates for thermoelectric materials because the necessary “electron-crystal, phonon-glass” properties can be engineered with an understanding of the Zintl chemistry [1]. Zn4Sb3 achieves high thermoelectric figure of merit by having extraordinarily low lattice thermal conductivity that can be attributed to the presence of disorderd interstitial zinc atoms and nanometer sized domains. The Clathrate Zintl Phase Ba6Ga16Ge30 has low thermal lattice thermal conductivity due to the complex cage-host structure and high thermoelectric efficiency due to the good compatibility with Pbte. A recent example is the discovery that Yb14MnSb11, a transition metal Zintl compound, has twice the zT as the SiGe based material currently in use at NASA. This talk will outline a strategy to discover new high zT materials in Zintl phases, and presents results pointing towards the success of this approach.1.Susan M. Kauzlarich, Shawna R. Brown and G. Jeffrey Snyder "Zintl phases for thermoelectric devices" Dalton Trans. p. 2099 (2007).
5:45 PM - U5.11
Synthesis and Thermoelectric Properties of M3Ni3Sb4 (M=Zr or Hf).
James Salvador 1 , Jihui Yang 1 , Hsin Wang 2
1 R&D and Planning, General Motors, Warren, Michigan, United States, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThe Seebeck coefficient, electrical resistivity, thermal conductivity and Hall-effect for the cubic “Zintl” phases M3Ni3Sb4 (M= Zr or Hf) were measured. These materials were synthesized by induction melting of the elements. Powder X-ray diffraction and electron probe microanalysis reveal that a single phase of the Y3Au3Sb4 structure type was obtained. The Y3Au3Sb4 structure is a stuffed variant of the Th3P4 structure and the compounds presented are isostructural to Ce3Pt3Bi4, a known Kondo insulator and RE3Au3Sb4( RE = Gd, Nd, Ho, and Sm) which have been shown to posses good thermoelectric properties. Ab initio calculations demonstrate that a hybrization gap is present in M3Ni3Sb4 (M= Zr or Hf) in an analogous manner to the half-Huesler compound ZrNiSn, and may lead to interesting transport properties in these systems. The Seebeck coefficient of the Zr analog was found to change sign from negative to positive at 150 K and return to a negative value above 650 K; while Hf3Ni3Sb4 showed similar behavior becoming positive at 140 K. Hf3Ni3Sb4 with significant Sb vacancies was found to have a positive Seebeck coefficient above 2 K attaining a maximum value of 0.202 mV/K at 560 K. Hall measurements were performed to investigate this phenomenon. Both compounds exhibit low thermal conductivity with values of 4.35 W/m-K and 2.66 W/m-K at room temperature for The Zr and Hf analogs respectively. The low thermal conductivities and large Seebeck coefficients make these materials interesting for intermediate to high temperature thermoelectric applications. The effects of Sn doping and Co alloying were also explored. This work was supported by GM and by DOE under corporate agreement DE-FC26-04NT42278
U6: Poster Session
Session Chairs
Wednesday AM, November 28, 2007
Exhibition Hall D (Hynes)
9:00 PM - U6.1
Zintl Phase as Thermoelectric Materials: Synthesis, Structure and Properties of Yb5Al2Sb6.
Iliya Todorov 1 , Duck-Young Chung 1 , Mercouri Kanatzidis 2 1
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Department of Chemistry, Northwestern University, Evanston, Illinois, United States
Show Abstract9:00 PM - U6.10
Synthesis and High Temperature Thermoelectric Properties of Nano Bulk Silicon and Silicon-Germanium Semiconductors.
Sabah Bux 1 2 , Richard Blair 3 , Chen-Kuo Huang 2 , Pawan Gogna 2 , Richard Kaner 1 , Jean-Pierre Fleurial 2
1 Chemistry and Biochemistry and California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California, United States, 2 Power and Sensors Systems Group, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, United States, 3 Chemistry, University of Central Florida, Orlando, Florida, United States
Show AbstractPrevious work in the 1960s demonstrated the use of solid solutions as a way to reduce the lattice thermal conductivity using point defect phonon scattering which significantly increased ZT values. It has been theorized that much larger reductions could be achieved through boundary scattering by engineering materials with a very high density of interfaces. Current research is focused on achieving such effects in 3-dimensional bulk semiconductors through high pressure sintering of Si and Si1-xGex nanoparticles. The unfunctionalized Si and Si1-xGex nanoparticles were synthesized using the technique of high-energy ball milling and mechanical alloying from the elements. Doped and undoped samples were characterized by powder X-ray diffraction and transmission electron microscopy. Thermal conductivity measurements on the densified pellets show a drastic reduction in the lattice thermal conductivity by up to a factor of 30 at room temperature compared to that of single crystalline samples. However, charge carrier mobility values remained fairly high, and the combination of the low thermal conductivity and relatively high power factor leads to an unprecedented increase in the ZT of pure heavily doped “nano bulk” Si by almost a factor of 3.5 over single crystal Si. Kinetic studies for optimization of the synthesis of the nanoparticles via mechanical alloying as a function of thermal conductivity, Hall mobility, carrier concentration, resistivity, crystallite size and nanoparticle distribution are presented and discussed.
9:00 PM - U6.11
Synthesis and Thermoelectric Properties of Y Doped SrTiO3 by Modified Pechini's Method.
Hirohumi Takenouchi 1 , Tomohiro Imai 2 , Hideo Mae 5 , Masakatsu Fujimoto 5 , Tohru Kineri 4 , Tsutomu Iida 1 , Noriaki Hamada 2 , Tsuneo Watanabe 3 , Keishi Nishio 1
1 Department of Materials Science and Technology, Tokyo University of Science, Noda-shi, Chiba, Japan, 2 Department of Physics, Tokyo University of Science, Noda-shi, Chiba, Japan, 5 , Yamaguchi Prefectural Industrial Technology Institute, Ube-shi , Yamaguchi, Japan, 4 Department of Materials Science and Environmental Engineering , Tokyo University of Science, Yamaguchi, Sanyoonoda-shi, Yamaguchi, Japan, 3 Department of Applied Electronics , Tokyo University of Science, Noda-shi, Chiba, Japan
Show Abstract Oxide thermoelectric materials are thermal stability and harmless in comparison with intermetallic compounds such as Bi2Te3. Mainly, cobalt oxide compounds including NaxCoO2 and Ca3Co4O9 have high thermoelectric properties. But they are p-type thermoelectric materials. High-performance n-type oxide materials are desired for p-n junction of thermoelectric device. One of high-performance n-type thermoelectric materials is SrTiO3. However SrTiO3 is a dielectric material, oxygen-deficient SrTiO3, Nb-doped SrTiO3, La-doped SrTiO3 and Y-doped SrTiO3 have been found to show electrical conduction. Particularly, Y-doped SrTiO3 shows high electrical conductivity in contrast to the other trivalent cation doped SrTiO3. In addition, it is reported that Y-doping reduces the thermal conductivity. In this study, we tried to prepare Sr1-xYxTiO3 ceramics having highly thermoelectric properties. At the same time, thermoelectric properties (Sr1-xYxTiO3 x=0-0.10) were calculated by the virtual crystal method. The Sr1-xYxTiO3(x=0 to 0.06) precursor powder was prepared using a modified Pechini’s method and the powder was sintered by hot press (HP) process. Precursor solution was prepared with metal salts (Sr(OCOCH3)2 and Y(OCOCH3)3), metal alcoxide (Ti[OCH(CH3)2]4), citric acid, ethanol, acetic acid and H2O. The precursor solution was heated at 823K for 5h after drying at 353K for 8h to obtain the precursor powder. It is confirmed that SrTiO3 single phase was obtained without residue organics or creation of SrCO3 by heat treatment above 823 K. In this method, pure SrTiO3 could be obtained by lower temperature compared with normal solid-state reaction method. To obtain the ceramics, the precursor powder was placed in a graphite die and heated to 1673 K and then kept at that temperature for 1h under a pressure of 31MPa. The obtained ceramics had high bulk densities larger than 99% of the theoretical density. Those samples of the Seebeck coefficient and electrical conductivity were measured by the standard four-probe method in flowing He gas atmosphere in the temperature range from 323 to 923 K. The conductivity of SrTiO3, Sr0.97Y0.03TiO3 and Sr0.94Y0.06TiO3 was 6.61×102, 5.61×103 and 1.58×104 S/m at room temperature, respectively. The Seebeck coefficient of SrTiO3, Sr0.97Y0.03TiO3 and Sr0.94Y0.06TiO3 was -548, -264 and -196μV/K at room temperature, respectively.
9:00 PM - U6.12
Thermoelectric Properties of La-doped BaSi2 and (Ba,Sr)Si2 Solid Solutions.
Kohsuke Hashimoto 1 , Ken Kurosaki 1 , Hiroaki Muta 1 , Shinsuke Yamanaka 1
1 Division of Sustainable Energy and Environmental Engineering, Graduate School of Engineering, Osaka University, Suita Japan
Show AbstractMetal silicides have attracted attention as new thermoelectric materials because they are environmentally-friendly. For example, the thermoelectric properties of FeSi2 and Mg2Si have been widely studied, and an excellent thermoelectric figure of merit (ZT = 1.1) was achieved in the n-type Mg2(Si,Sn) system [1]. In our previous study [2], it was found that BaSi2 indicated quite low thermal conductivity, which is comparable to or less than those of typical thermoelectric materials such as Bi2Te3. However, BaSi2 indicated very high electrical resistivity due to the low carrier concentration. Consequently, the dimensionless figure of merit (ZT) of BaSi2 is not so high: 0.01 at 954 K. In the present study, we have tried to improve the thermoelectric properties of BaSi2 by controlling the carrier concentration. We prepared polycrystalline samples of La-doped BaSi2 and (Ba,Sr)Si2 solid solutions. The electrical resistivity (ρ), Seebeck coefficient (S) and thermal conductivity (κ) were evaluated from room temperature to 973 K, and the ZT (= S2T/ρ/κ) was calculated. 3 at.% La doing increased the carrier concentration, leading to enhancement of ZT (0.07 at 970 K). [1] V. K. Zaitsev, M. I. Fedorov, E. A. Gurieva, I. S. Eremin, P. P. Konstantinov, A. Yu. Samunin, and M. V. Vedernikov, Phys. Rev. B 74 (2006) 045207. [2] K. Hashimoto, K. Kurosaki, Y. Imamura, H. Muta, and S. Yamanaka, Proceedings of the 26th International Conference on thermoelectric, (2007), submitted.
9:00 PM - U6.13
Crystal Growth of Mg2Si by the Vertical Bridgman Method and the Doping Effect of Bi and Al on Thermoelectric Characteristics.
Masataka Fukano 1 , Tsutomu Iida 1 , Masayasu Akasaka 1 , Noriaki Kato 1 , Yohei Oguni 1 , Yoshifumi Takanashi 1
1 Materials Science and Technology, Tokyo University of Science, Noda-shi, Chiba Japan
Show AbstractMagnesium silicide (Mg2Si) has been regarded as a candidate for advanced thermoelectric materials, for use in the temperature range from 500 to 800 K, corresponding to the temperature of vehicle exhaust emissions. In addition, the constituents of Mg2Si have the benefits of being abundant in the earth’s crust and are non-toxic, compared with other thermoelectric materials that operate in the above conversion temperature range, such as PbTe and CoSb3. The efficiency of a thermoelectric device is characterized by the dimensionless figure of merit, ZT=S2sT/k, of its constituent thermoelectric material, where S is the Seebeck coefficient, s is the electrical conductivity, k is the thermal conductivity, and T is the absolute temperature. For thermoelectric device operation, the use of a material with ZT greater than unity is needed to realize a conversion efficiency of ~10 %. The optimization of the doping carriers in Mg2Si is required in order to realize unity of ZT. In this manner, we have grown Mg2Si crystals, doped with Bi and Al, using the vertical Bridgman method.Mg (99.99 %) and Si (99.99999 %) with a stoichiometric Mg : Si ratio of 67 : 33 were mixed and melted into Mg2Si. Prior to the growth, Bi (99.999 %) powder, at the ratio from 0.5 to 3 at. % with Mg2Si and a pre-synthesized polycrystalline Mg2Si powder were mixed. Mg2Si crystals were then grown at a rate of 3 mm/h using the vertical Bridgman method. Grown samples were characterized by x-ray diffraction (XRD) patterns and electron-prove microanalysis (EPMA), and the results indicated that Mg2Si crystals were successfully grown through their use of polycrystalline Mg2Si as a growth source material. Hall carrier concentrations were evaluated at room temperature. The electrical conductivity, the Seebeck coefficient, and the thermal conductivity were estimated in the temperature range from RT to 850 K. The grown crystals exhibited n-type conductivity in undoped and all Bi doped conditions. All the Bi doped crystals showed high electrical conductivity and high carrier concentration than seen in the undoped crystals. On the other hand, the thermal conductivity was lowered in proportion to the concentration of Bi. Consequently, the thermal conductivity of the crystals, Bi doped at 3 at. %, was 0.021 W/cmK at 842K, with a ZT attaining 0.99 at 842 K, close to the unity value of ZT that is regarded as a standard for practical use of thermoelectric materials. The solid solubility limit of Bi in Mg2Si was assumed to be around 3 at. % from our findings, and thus Al was co-doped with Bi in order to further improve the thermoelectric properties.
9:00 PM - U6.14
Doping Characteristics of Silver in Mg2Si(1-x)Gex Prepared by Plasma Activated Sintering.
Junichi Sato 1 , Takashi Nemoto 1 , Tsutomu Iida 2 , Masayasu Akasaka 2 , Atsunobu Matsumoto 2 , Tadao Nakajima 1 , Keishi Nishio 2 , Yoshifumi Takanashi 2
1 , Nippon Thermostat Co., Ltd., Kiyose-shi Tokyo Japan, 2 Department of Materials Science and Technology, Tokyo University of Science, Noda-shi Chiba Japan
Show AbstractAs one of relevant solutions to remedying the Greenhouse effect, demands to reduce the usage of fossil fuels have been increasing. Since the immediate abstaining from the use of fossil fuels is impossible to attain in the near future, a remarkable increase in the energy conversion efficiency of combustible power generators is required. Mg2Si and Mg2Si1-xGex are promising candidates as thermal-to-electric energy-conversion materials, at operating temperatures ranging from 500 to 800 K. One important aspect of Mg2Si and Mg2Si1-xGex is the non-toxicity of source materials and processing by-products, which provides safe handling with no concerns regarding potential extended restrictions on hazardous substances. With Bi-doped n-type Mg2Si, we have achieved a maximum value of dimensionless figure-of-merit, ZT, of ~1.0 at ~ 850 K. In order to realize a Mg2Si thermoelectric power generator, a combination structure, consisting of n- and p-type Mg2Si, would appear to be more efficient in terms of space utility and output power density. Ho