Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session R47: Thermoelectrics -- Characterization and MetrologyFocus
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Sponsoring Units: DMP Chair: Marco Fornari, Central Michigan University Room: BCEC 213 |
Thursday, March 7, 2019 8:00AM - 8:12AM |
R47.00001: Mapping experimental electronic transport measurements on appropriate band structure models T. Ethan Stearns, Andrew R Supka, Nicholas A Mecholsky, Marco Buongiorno Nardelli, Stefano Curtarolo, Marco Fornari For several years, established guiding principles based on effective masses, carrier density, and constant relaxation time have been heuristically used to interpret trends in the power factor. In spite of many simplifying assumptions, the Sommerfeld model has became a standard for thermoelectricity. To verify and validate this interpretative approach we have developed a software tool that, using experimental electronic transport data, leads to band structure parameters that can then be compared with first principles calculations. We present our software tool by illustrating few specific examples for complex sulfides. |
Thursday, March 7, 2019 8:12AM - 8:24AM |
R47.00002: Selective breakdown of phonon quasiparticles across superionic transition in CuCrSe2 Olivier Delaire, Jennifer L Niedziela, Dipanshu Bansal, Andrew May, Jingxuan Ding, Tyson Lanigan-Atkins, Georg Ehlers, Douglas L Abernathy, Ayman Said Superionic crystals exhibit ionic mobilities comparable to liquids while maintaining a periodic crystalline lattice. The atomic dynamics leading to large ionic mobility have long been debated. A central question is whether phonon quasiparticles -which conduct heat in regular solids- survive in the superionic state, where a large fraction of the system exhibits liquid-like behaviour. Here we present the results of energy- and momentum-resolved scattering studies combined with first-principles calculations and show that in the superionic phase of CuCrSe2, long-wavelength acoustic phonons capable of heat conduction remain largely intact, whereas specific phonon quasiparticles dominated by the Cu ions break down as a result of anharmonicity and disorder. The weak bonding and large anharmonicity of the Cu sublattice are present already in the normal ordered state, resulting in low thermal conductivity even below the superionic transition. These results demonstrate that anharmonic phonon dynamics are at the origin of low thermal conductivity and superionicity in this class of materials. |
Thursday, March 7, 2019 8:24AM - 8:36AM |
R47.00003: Is AgCrSe2 really a phonon-liquid electron-crystal? Sercan Arslan, David Voneshen, Paul Steffens, Uthayakumar Sivaperumal, Robin S. Perry, Jon Goff The phonon liquid concept, in which superionic diffusion prevents the propagation of transverse acoustic phonons, has proved a popular view in the hunt for materials with ultra-low thermal conductivity. Recent inelastic neutron scattering results on AgCrSe2 have found a quasielastic signal (QENS) around 2 Å-1, and suppression of the transverse phonons above the superionic transition. The QENS scattering has been attributed to the melting of the Ag lattice and it is observed to increase dramatically above the superionic transition. Now, using polarised inelastic neutron scattering we determine the origin of this QENS below and above the superionic transition. The validity of a phonon-liquid in AgCrSe2 will be discussed in light of these results. |
Thursday, March 7, 2019 8:36AM - 9:12AM |
R47.00004: Nanoscale thermal metrology using SEM, TEM, and confocal microscopy Invited Speaker: Chris Dames Nanoscale thermal transport plays a fundamental role in several current research directions in thermoelectric materials, from nanocrystalline composites to transport in thin films and nanowires. However, experimental measurements of the thermal properties of such materials at the nanoscale is challenging. In this talk I will present several collaborative efforts to develop new non-contact methods for heating and thermometry at the nanometer scale, techniques which could eventually be applied to characterize thermoelectric materials. Examples to be discussed include methods based on SEM (e-beam as a point heater; secondary electron yield as a thermometer), TEM (thermometry using the Debye-Waller effect), and confocal microscopy (luminescence thermometry of individual nanoparticles). |
Thursday, March 7, 2019 9:12AM - 9:24AM |
R47.00005: Thermoelectric Properties of Carbon-rich Boron Carbide Nanocomposites Yucheng Lan, Jesse Dampare, Mobolaji Zondode, Hua Deng, Sz-Chian Liou, Saroj Pramanik, Abdellah Lisfi, Chundong Wang, Yong-Le Pan, Winnie Wong-Ng Boron carbide is widely used in industry and military because of its low mass-density, super high hardness, good electric conductivity, and excellent mechanical properties. The material is also one high-temperature thermoelectric compound capable for applications above 1000 oC. However, its thermoelectric properties, such as Seebeck coefficient and figure-of-merit, are low and need to be enhanced significantly for high-efficiency energy applications. Nanostructuring is an effective approach to improve thermoelectric properties. Here boron carbide nanomaterials with various chemical composites are prepared and their physical properties (crystallinity, chemical composition, band-gap, defects etc) are characterized. The as-synthesized nanomaterials are then bottom-up-ed to bulk nanocomposites. Thermoelectric properties of the bulks are measured. Their microstructures are characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, Raman scattering, and UV-vis spectroscopy etc. The enhanced performances of the carbide nanocomposites are like a result of their unique nanostructures. |
Thursday, March 7, 2019 9:24AM - 9:36AM |
R47.00006: Resolving Thermal Conductivity Spectrums through Time-resolved Spatial-Temporal Imaging Ding Ding, Kedar Hippalgaonkar With the advent of nano-engineered and 2D materials, quasiballistic and anisotropic effects have become more commonplace in thermal properties of these material systems. However, current methods to measure these properties through thermal conductivity generally requires variation of spatial or temporal parameters, or measurement of multiple samples with tedious fabrication procedures. Here, we numerically propose an optical pump-probe technique that uses time-resolved spatial and temporal temperature profile to characterize both quasiballistic and anisotropic thermal transport with no variation of experimental parameters. By performing heat-flow analysis of the thermal profile with multi-parameter optimization, we are able to obtain the thermal conductivity spectrums of both the in-plane and cross-plane heat transport as a function of temporal and spatial frequencies, respectively. Such spectrums can then be used to derive the anisotropy in thermal conductivity and the phonon mean-free-path spectrums within a single experiment. We believe that this technique can enable high throughput screening of thermal properties for nano-engineered and 2D materials. |
Thursday, March 7, 2019 9:36AM - 9:48AM |
R47.00007: Right Definition of Thermoelectric Figure of Merit toward the Thermoelectric Efficiency Prediction for Segmented Devices Byungki Ryu, Jaywan Chung, SuDong Park The dimensionless figure of merit zT has been considered as a good metric for thermoelectric efficiency. But, due to the strong temperature dependence of material properties, the relation between the material properties and device performances is not clear. Here, we generalize the definition of device figure of merit ZgenT. Since the thermoelectric leg acts as a electric and a thermal circuit, the Zgen should be written as Zgen = (V/ΔT)2/RK, where V, R, and K are generated voltage, electric resistance, and the thermal conductance. Thus V, R, and 1/K should be computed as integrals of material properties (-α.gradT, ρ, κ) on position x, not on temperature T. Using the temperature approximation of zero-electric-current condition, the Zgen is simply approximated as Zgen(0)=<α>2/<ρκ>, where <> is a temperature average. Also we reveal that the Zgen(0) is a good rank-preserving-parameter for efficiency prediction even for the segmented devices. |
Thursday, March 7, 2019 9:48AM - 10:00AM |
R47.00008: NMR investigation of filled skutterudites BaxYbyCo4Sb12 and AxCo4Sb12 (A = Ba, Sr) Yefan Tian, Ali Sirusi, Sedat Ballikaya, Nader Ghassemi, Ctirad Uher, Joseph Hansbro Ross Considered as one of the most promising thermoelectric families, skutterudite CoSb3 shows a high ZT value when prepared with filler atoms such as Ba, Sr, Yb, etc. We report 59Co NMR and transport measurements on BaxYbyCo4Sb12 and AxCo4Sb12 (A = Ba, Sr) as promising thermoelectric candidates. To analyze the experimental results, we developed a formalism for the NMR shifts and T1, allowing for arbitrary carrier densities rather than treating the extreme metallic or non-degenerate limit. We find that a model in which a large density of defect states located just below the conduction band edge dominate the electrical behavior works very well, providing a consistent picture of both the NMR and transport results. The carrier effective masses and g-factors estimated from NMR fitting results are in close agreement with each other. Additional contributions observed in shift and 1/T1 measurements are shown to correspond to the susceptibility of electrons in localized states. |
Thursday, March 7, 2019 10:00AM - 10:12AM |
R47.00009: Rattling dynamics under a planar coordination in tetrahedrites Chul-Ho Lee, Koichiro Suekuni, Eiji Nishibori, Hitoshi Mori, Hidetomo Usui, Masayuki Ochi, Takumi Hasegawa, Mitsutaka Nakamura, Seiko Ohira-Kawamura, Koji Kaneko, Katsuaki Hashikuni, Kazuhiko Kuroki, Toshiro Takabatake Suppressing lattice thermal conductivity (kL) as low as possible is essential to achieve high thermoelectric performance. One of effective methods is to use the rattling which is large anharmonic vibration of atoms. Typically, rattling atoms locate in oversized atomic cages of caged compounds. Recently, we found several new thermoelectric materials that contain rattling atoms without oversized cages. in LaOBiSSe and tetrahedrites, Bi and Cu atoms having a planar coordination vibrate largely toward out of plane [1-3]. We investigated crystal structures and phonon dynamics of tetrahedrites to clarify the driving force for the occurrence of rattling in a planar coordination. We found that the amplitude of Cu rattling increases with decreasing S3-triangle area. The rattling energy observed by inelastic neutron scattering decreases with decreasing the S3-triangle area and finally damped demonstrating an enhancement of anharmonicity. The results suggest that chemical pressure is essential for the appearance of planar rattling in contrast to caged compounds where free space is essential. |
Thursday, March 7, 2019 10:12AM - 10:24AM |
R47.00010: Enhancement of thermoelectric figure of merit by pressure-driven electronic topological transition Liucheng Chen, Pei-Qi Chen, Viktor V Struzhkin, Alexander Goncharov, Qian Zhang, Zhifeng Ren, Xiao-Jia Chen The world is currently facing a state of energy shortage, and thus the alternative green energy is ultimately in demand. Thermoelectric generators, which can generate electricity directly from waste heat with the advantages of reliability and compactness, are considered as potential devices for waste heat recovery. The thermoelectric performance is usually evaluated by a parameter named as the figure of merit zT. So far, the maximum zT at room temperature has remained around 1.0 over sixty years. For practical technological applications, it is highly desired to break this barrier. Here, we choose a Cr doped PbSe with the maximum zT less than 1.0 at high temperature of about 700 K. By simply applying external pressure, we obtain the record high zT value of 1.74 at room temperature. Pressure-driven electronic topological transition is proposed to account for such a huge enhancement. These results and findings point to a new direction in the improvement of zT in the existing thermoelectric materials through the lattice compression. |
Thursday, March 7, 2019 10:24AM - 10:36AM |
R47.00011: Impressive enhancement of thermoelectric performance in CuInTe2 upon compression Hao Yu, Liucheng Chen, Hongjie Pang, Xiaoying Qin, Pengfei Qiu, Xun Shi, Lidong Chen, Xiao-Jia Chen Thermoelectric materials can directly generate electric power by converting waste heat, and the efficiency is appraised by the figure of merit zT. A high zT value larger than 3 is required to achieve comparable efficiency of the traditional heat engines. Despite great efforts over a century, the desired value of 3 is seemingly an upper limit and many existing thermoelectric materials have the zT values less than 1. If their zT values can be improved for several times to break through the upper limit, the energy revolution could be expected. Here, a p-type CuInTe2 is chosen as an example to show the extremely important role of pressure played in enhancing the thermoelectric performance. Over 5 times increase of the zT value is realized by the application of pressure. Both the enhancement of the power factor and the reduction of the thermal conductivity account for this impressive enhancement. The former is due to the optimization of the carrier concentration and band structure, and the latter is attributed to the enhanced phonon anharmonicity. Our results offer an effective method to improve zT of the existing materials for the future technological applications. |
Thursday, March 7, 2019 10:36AM - 10:48AM |
R47.00012: Thermoelectric sulfides with the colusite structure: theory and experiments Ventrapati Pavan Kumar, Andrew R Supka, Pierrric Lemoine, Oleg I. Lebedev, Bernard Raveau, Koichiro Suekuni, Vivian Nassif, Rabih Al Rahal Al Orabi, Marco Fornari, Emmanuel Guilmeau We have achieved extraordinary power factors in bulk thermoelectric sulfides with the colusite structure without compromising the low lattice thermal conductivity. Using a synergy between high-throughput calculations and experiments we learned a possible strategy to engineer the electron relaxation time. The protocol is based on the “conductive network paradigm”, it has been applied to a variety of compositions and lead to power factors up to 1.86 mW m-1 K-2 at 700K and ZT=0.86 before any optimization procedure. |
Thursday, March 7, 2019 10:48AM - 11:00AM |
R47.00013: Thermoelectric transport properties with non-parabolicity, degeneracy and multiplicity of band edges: The case of anisotropic p-type SnSe Anderson Chaves, Juan J Melendez, Robert L Gonzalez-Romero, Alex Antonelli Efficient ab initio computational methods for the evaluation of transport |
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