Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session A21: Thermoelectrics IFocus
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Sponsoring Units: GERA DMP Chair: David Singh, University of Missouri Room: LACC 309 |
Monday, March 5, 2018 8:00AM - 8:36AM |
A21.00001: High Performance Thermoelectric Half-Heusler and Zintl Materials Invited Speaker: Zhifeng Ren In order to achieve high thermoelectric figure-of-merit, we have to obtain high power factor and low thermal conductivity simultaneously. In the past twenty years, significant progress has been made on either achieving high power factor or low thermal conductivity in a variety of thermoelectric materials, but rarely both. In this talk, I will present our effort on enhancing the power factor and reducing the thermal conductivity in both half-Heusler and Zintl materials, which eventually leads to high thermoelectric performance. |
Monday, March 5, 2018 8:36AM - 8:48AM |
A21.00002: Thermoelectric Properties of New As-based Compounds Ba1-xKxZn2As Kunihiro Kihou, Haruno Kunioka, H Nishiate, A Yamamoto, Chul-Ho Lee Sb-based 122-systems crystalized in the CaSi2Al2-type structure (space group: P-3m1) exhibit high thermoelectric properties. Examining Sb-based 122-systems is now one of hot topics in the development of thermoelectric materials. As-based 122-systems, on the other hand, were not reported as high thermoelectric materials. In this work, we examined thermoelectric properties of As-based Ba1-xKxZn2As2 compounds crystallized in the α-BaCu2S2-type structure (space group Pnma) for x ≤ 0.02 and the ThCr2Si2-type structure for x ≥ 0.04 [1]. The κL is independent on K concentration with relatively low values of 0.8 - 1.1 W/mK at 773 K. This is almost the same value as Sb based BaZn2Sb2 crystallized in the α-BaCu2S2-type structure, though Ba1-xKxZn2As2 consists of As atoms, which are lighter than Sb atoms. The obtained highest value of the dimensionless figure-of-merit ZT is 0.67 at T = 900 K for x = 0.02. The result opens a new class of thermoelectric materials with the As-based 122 Zintl compounds. |
Monday, March 5, 2018 8:48AM - 9:00AM |
A21.00003: Sublattice melting in Cu2-xSe investigated by single crystal diffuse scattering Stephan Rosenkranz, Matthew Krogstad, A. Rettie, Mercouri Kanatzidis, Raymond Osborn, Feng Ye Considerable improvements in the efficiency of thermoelectric materials have been achieved by a number of different approaches to reduce their thermal conductivity. This reduction has sometimes been achieved by incorporating complex nanoscale inhomogeneity or loosely bound ions into the crystal structure, which can scatter phonons without affecting their electronic transport, guided by the concept of the phonon-glass electron-crystal. A high thermoelectric figure-of-merit was however recently observed in a very simple crystal structure, the cubic anti-fluorite semiconductor Cu2-xSe. The very low thermal conductivity in these compounds have been attributed to a sublattice melting of the copper ions, which suppresses the shear modes that would persist even in a phonon glass. This material has thus been dubbed a phonon-liquid electron-crystal. We will present our detailed investigation of this postulated sublattice melting utilizing single-crystal diffuse neutron scattering and the three-dimensional pair-distribution-function analysis as a function of temperature across the structural transition. |
Monday, March 5, 2018 9:00AM - 9:12AM |
A21.00004: First Principles Studies of Electronic and Thermoelectric Properties of La3Te4 and Pr3Te4 Trinh Vo, Paul von Allmen, Sabah Bux, Jean-Pierre Fleurial, Dean Cheikh We present the results for the electronic structure and thermoelectric properties of La3Te4, Ce3Te4, and Pr3Te4, using first principles computation and Boltzmann’s transport equation. The effect of 4f electrons on the electronic and thermoelectric properties is investigated. We found that even though the presence of 4f electrons results in significant changes in the electronic structures, it does not always lead to an increase in thermoelectric properties as expected. The large increase in thermoelectric properties only occurs when the Fermi energy for the experimental value of the electron density is close enough to the resonance in the density of states such that band contributions to figure of merit ZT become dominant. |
Monday, March 5, 2018 9:12AM - 9:24AM |
A21.00005: Ultralow and Anisotropic Thermal Conductivity in Crystalline As2Se3 Robert González-Romero, Alex Antonelli, Anderson Chaves, Juan Meléndez Among renewable sources of energy, thermoelectricity has been in recent years the subject of intensive research. Thermoelectric applications depend fundamentally on materials. Therefore, research on thermoelectricity has been, to a large extent, the search for or development of materials for that purpose. In this work we studied the lattice thermal conductivity of crystalline As2Se3, through state-of-the-art calculations that combine density functional theory and semi-classical Boltzmann transport equation. This chalcogenide compound is a semiconductor that crystallizes in a layered monoclinic structure. The calculations show an ultralow lattice thermal conductivity of 0.14 W m−1 K−1 along the b axis at 300 K. The origin of this ultralow thermal conductivity arises from a cascade-like fall of the low-lying optical modes and from the avoided crossing of these with acoustic modes. These results, whose validity has been addressed by comparison with the compound SnSe, for which excellent agreement between the theoretical predictions and the experiments is achieved, point out that As2Se3 could exhibit improved thermoelectric properties. |
Monday, March 5, 2018 9:24AM - 9:36AM |
A21.00006: Counter-ion and dopant effects on the electronic structure and thermoelectric properties of intrinsically conductive polymers Jonathan Ogle, Mandefro Yehulie, Christoph Boehme, Luisa Whittaker-Brooks Conductive organic polymers have seen increased interest in the field of thermoelectrics, in part due to their high electrical conductivity (≈ 103 S cm-1) and intrinsically low thermal conductivity (<1 W m-1K-1). These properties are highly tunable through optimization of their chemical structure and polymerization methods. It is well documented that modifications to the counter-ion present in conductive polymers as well as any alteration done to the polymerization process will change their thermoelectric properties significantly. Such variations yield an extremely broad range of reported thermoelectric figure of merit (ZT) values (0.1-0.42) for conductive polymers. While charge carriers at lower conductivities have been identified as polarons, an understanding of the electronic structure of conductive polymers as their conductivity increases is not well understood. We have investigated the electronic and thermoelectric properties of conductive polymers to provide insight into how their electronic structure and the type of charge carriers present change with different counter-ions as well as different polymerization processes. We believe the fundamental insights developed in this study might be beneficial in the development of emerging polymers for thermoelectric applications. |
Monday, March 5, 2018 9:36AM - 9:48AM |
A21.00007: Magnetic field dependent Dirac point in Bi1-xSbx alloys: magnetoresistance and thermoelectric properties. Dung Vu, Koen Vandaele, Bin He, Joseph P Heremans Bi1-xSbx alloys with varying Sb concentration have bands that at x≈5 have a Dirac dispersion with the Dirac point at the L-point of the Brillouin zone. In strong magnetic fields, this Dirac point is theoretically expected to split into two Weyl points. This talk will present experimental magnetic field dependent transport properties of Bi1-xSbx alloys with varying Sb concentration. Field-dependence of thermoelectric properties, including thermopower, Nernst effect, Hall effect, resistivity, and thermal conductivity, at different Sb concentrations will be presented. Interestingly, a strong negative longitudinal magnetoresistance is observed at the composition and field where the Weyl points are expected to appear. |
Monday, March 5, 2018 9:48AM - 10:00AM |
A21.00008: NMR study of local structures and anharmonic phonon behavior in tetrahedrite thermoelectrics. Nader Ghassemi, Xu Lu, Joseph Ross We report Cu NMR studies of tetrahedrites, including Cu12Sb4S13 as well as substituted materials, which have been of considerable interest as thermoelectric materials as well as due to the metal-insulator transition present at low temperatures. NMR lineshapes show a splitting of the Cu(1) site at room temperature, a result which is consistent with a split atomic configuration. The results indicate that this behavior is static in pure materials, rather than a dynamical effect. NMR T1 relaxation data for Cu12Sb4S13 also are shown to be dominated by an electric quadrupole mechanism for the entire range 4 K to room temperature, indicating an anomalous vibrational contribution. We have fitted to a model based on quasi-localized rattling-type motion, with fitting parameters giving an approximate measure of the anharmonic potential. Samples with substitution by Zn and Ni show increasing paramagnetic Cu NMR shifts, with the largest (2000 ppm) in Cu12Sb4S13. We have analyzed the data in terms of changes in the metallic shift contribution, and also compare to ab initio calculations of the NMR shifts. |
Monday, March 5, 2018 10:00AM - 10:12AM |
A21.00009: Toward establishing self-dopant design principles in n-type organic thermoelectrics Daniel Powell, Luisa Whittaker-Brooks Doping methods in n-type organic materials heavily rely on the addition of extrinsic compounds with relatively small ionization potentials. The introduction of dopants modifies the density of states near the Fermi-energy such that populated states now exist at some energy relative to the LUMO of the organic semiconductor. Upon charge transfer the energies of these states distort in ways that may be very difficult to predict, leading to a broader density of states. Furthermore, dopants can disrupt the packing structure of organic films and hinder charge mobility. The dopants may also aggregate during film casting, decreasing the number of charge carriers available to the system and creating additional grain boundaries. These challenges may be mitigated by intrinsically doping the n-type organic semiconductor via a process dubbed self-doping. Presently, the relationship between self-dopant structure and doping efficiency remains unknown. We have investigated the effect of dopant structure on the doping efficiency in a variety of perylene diimides. We believe our findings provide fundamental design principles for the fabrication of effective self-dopants geared toward increasing the thermoelectric properties of n-type organic semiconductors. |
Monday, March 5, 2018 10:12AM - 10:24AM |
A21.00010: Development of High Efficiency Segmented Thermoelectric Couples for Space Applications Fivos Drymiotis, Jean-Pierre Fleurial, Sabah Bux, Samad Firdosy, Kurt Star, Ike Chi, Vilupanur Ravi, Billy Chun-Yip Li, Sevan Chanakian, Dean Cheikh, Kathy Lee, Kevin Yu, Obed Villalpando, Kevin Smith, David Uhl, Chen-Kuo Huang, Jong-Ah Paik, Zi-Kui Liu, Jorge Paz Soldan Palma, Yi Wang, XiaoYu Chong Radioisotope Thermoelectric Generators (RTG) have been used by NASA to reliably power spacecraft for deep space exploration for over 40 years. Current state of the practice systems are limited to device-level efficiencies of 7.5% or less and system level specific powers of 2.8 to 5.1 W/Kg. NASA’s Radioisotope Power Systems Thermoelectric Technology Development Program (TTDP) is pursuing development of more efficient thermoelectric technologies that could increase performance by a factor of 2 to 4x over these state of the practice systems. NASA’s TTDP is developing high-efficiency segmented couples/modules with the following design goals: a) system conversion efficiency ≥ 11% (≥ 60% improvement over MMRTG at BOL) and b) ≥ 6-8.5 We/kg specific power (2-3 x improvement over MMRTG), for a temperature gradient ΔT = 800 K (TH=1273 K and TC = 473 K). We will be discussing the state of development of the aforementioned couples and the tools that we use to guide this development. |
Monday, March 5, 2018 10:24AM - 10:36AM |
A21.00011: Thermoelectric properties of functionalized MXene structures Sevil Sarikurt, Deniz Cakir, Murat Keceli, Cem Sevik In this study, we have investigated the electronic and lattice thermal transport properties of oxygen terminated M2CO2 (where M=Ti, Zr, Hf, Sc) MXenes in two different functional configurations (Model-II and Model-III), in order to assess their thermoelectric potentials. We determined that the model-III (MD-III) configuration of Ti2CO2 and Zr2CO2 has the lowest thermal conductivity as compared to Hf2CO2 and Sc2CO2 with the same configuration. The model-II (MD-II) configuration of Hf2CO2 has the highest thermal conductivity value. We revealed that the absorption site of oxygen atom has a large impact on the electronic and thermal transport properties of MXenes. The thermal conductivity, Seebeck coefficient and zT coefficient may vary 40% depending on the structural model. For instance, the thermal conductivity is 40.58 W/(mK) for MD-II and 18.42 W/(mK) for MD-III of Ti2CO2 at T=300 K. This structural variety provides us an additional degree of freedom for modulating physical and chemical properties of MXenes, that can be exploited to design efficient thermoelectric devices. Among the considered MXenes, Ti2CO2 and Zr2CO2 in MD-III configuration were found to have much lower thermal conductivity. |
Monday, March 5, 2018 10:36AM - 10:48AM |
A21.00012: Method of four coefficients in the presence of multiple carrier scattering mechanisms Thomas Linker, Matthew Beekman In the “method of four coefficients,” experimental electrical resistivity, Seebeck coefficient, Hall coefficient and Nernst coefficient of a material are fitted within Boltzmann transport theory at temperature T to extract four material parameters, e.g. the charge carrier mobility, carrier concentration, density of states effective mass, and scattering exponent λ. In the present work, we evaluated the practice of modeling the relaxation time energy dependence using a single effective scattering exponent λeff when multiple scattering mechanisms are present. Since the use of a single λeff is not directly justified by Mattheisen’s rule for scattering rates when multiple scattering mechanisms are present, the interpretation of the obtained λeff is not entirely well-defined. We therefore performed an evaluation to determine what information on individual scattering mechanisms and their relative contributions to the overall relaxation time might be extracted from λeff. Alternative approaches to fitting the experimental data by including the temperature dependence of the transport coefficients will also be discussed. |
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