Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session V47: Thermoelectrics -- Emerging Materials and DevicesFocus
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Sponsoring Units: DMP Chair: Daryoosh Vashaee, North Carolina State University Room: BCEC 213 |
Thursday, March 7, 2019 2:30PM - 2:42PM |
V47.00001: 2D Metal-Organic Frameworks as a New Class of Thermoelectric Material* Ryuichi Tsuchikawa, Nabajit Lahiri, Neda Lotfizadeh, Shuwan Liu, Mackenzie Lach, Celine Slam, Janis Louie, Vikram Deshpande Organic materials are desired in many fields of thermoelectric applications due to material abundance, light weight, and flexibility. Electrically conductive 2D metal-organic frameworks (MOFs) are a new class of organic material, and the two dimensionality and nanopores have a potential to realize a comparable thermoelectric figure of merit in 2D MOFs. As such, we measured thermal conductivity, electrical conductivity, and Seebeck coefficient of Copper Benzenehexathiol (Cu-BHT), an electrically conductive 2D MOF, in a mesoscopic device scale. We found that phonon mean free path is of the order of the length scale associated with nanopores and interlayer distance and it is responsible for the observed low thermal conductivity of 0.25 W/mK at room temperature. This result ensures low thermal conductivity in any 2D MOFs without artificially imposing nanostructures. Electronic transport and Seebeck coefficient measurements revealed that the charge carrier is n-type and the electronic transport is governed by the degree of polycrystallinity. However, unlike conductive polymers, each domain retains a definite crystal structure, resulting in an electronic band in each domain. This leads to a possibility of enhancing Seebeck coefficient by band engineering. |
Thursday, March 7, 2019 2:42PM - 2:54PM |
V47.00002: High thermoelectric properties of As-based 122-Zintl compounds Ba1-xKxCd2As2 Haruno Kunioka, Kunihiro Kihou, Hirotaka Nishiate, Hidetomo Usui, Kazuhiko Kuroki, Chul-Ho Lee, Atsushi Yamamoto, Tsutomu Iida, Haruhiko Obara 122-Zintl phase is well known as a high performance thermoelectric (TE) material. For the past decade, Sb-based 122-Zintl compounds have been found that the dimensionless figure-of-merit exceeds the value of 1. In contrast, there are only few studies on As-based Zintl compounds. Lighter atomic mass of As than Sb discourages exploring As-based compounds because the lattice thermal conductivity (kL) usually becomes higher with lighter atoms. Recently we have found that Ba1-xKxZn2As2 exhibits low kL of 0.8 W/mK and high ZT of 0.67 at 900 K [1]. This discovery demonstrates that the As-based 122-Zintl compounds also have a potential for a high performance TE material. |
Thursday, March 7, 2019 2:54PM - 3:06PM |
V47.00003: Cold Spray Additive Manufacturing of Thermoelectric Generators Harry Radousky, Alexander A. Baker, Richard Thuss, Elissaios Stavrou, Joseph Michael Zaug, Scott McCall Thermoelectric generators (TEGs) provide a pathway to recovering and converting thermal energy directly into electricity. Adoption of the technology has often been limited due to the difficulty of manufacturing TEGs that can be incorporated into industrial environments where waste heat is prevalent. To address this shortcoming an additive manufacturing technique has been developed for the fabrication of arbitrary shape Bi2Te3 based (and other semiconductors) thermoelectric generators, promising greater design flexibility to harvest low grade waste heat. We have demonstrated that cold-spraying of powdered material yields near-full density parts, without significant loss of thermoelectric properties in the operating window of ~100 C. A systematic study is presented of the structural characteristics for the deposited material, correlated with thermal and electrical transport measurements to allow further understanding of the thermoelectric efficiency in the cold-sprayed samples. In particular cold spraying allows deposition on curved geometries such as copper pipes, and produces thermoelectric materials with Seebeck coefficients comparable to the bulk starting material. |
Thursday, March 7, 2019 3:06PM - 3:18PM |
V47.00004: Interplay between flexoelectric and thermoelectric effects in bismuth telluride thin films Bruno Lorenzi, Svetlana Boriskina, Akihiro Kobayashi, Masayuki Takashiri, Gang Chen Flexoelectricity is a phenomena for which a strain gradient induces an internal polarization in semiconductor and dielectric materials. This effect can be used to enhance thermoelectric properties, and to enable the collection of photo-generated carriers without the need of a p-n junction. In this context, flexoelectricity was claimed to be the reason behind the variation of Seebeck coefficient in bismuth telluride (Bi2Te3) thin films deposited on different substrates, and was shown in many materials under illumination. However, a clear explanation of the relation between the applied strain and the detected signal is still missing, along with a comprehensive theoretical and experimental analysis. |
Thursday, March 7, 2019 3:18PM - 3:30PM |
V47.00005: Superionic diffusion and anharmonic lattice dynamics in AgCrSe2 Jingxuan Ding, Jennifer L Niedziela, Dipanshu Bansal, Andrew May, Georg Ehlers, Douglas L Abernathy, Yang Ren, Ayman Said, Olivier Delaire Superionic conductors exhibit promising thermoelectric properties due to their ultralow thermal conductivity. The fundamental mechanisms have long been debated between the anharmonicity or the breakdown of transverse acoustic (TA) phonons, where the shearing vibrational degrees of freedom are lost, as in a liquid state. We report on neutron/x-ray scattering and first-principles studies on the lattice dynamics and ionic diffusion of AgCrSe2. Our momentum-resolved measurements on single-crystals clearly establish the persistence of long-wavelength TA phonons in the superionic phase, whereas the shorter wavelength, non-dispersive portions of the TA branches severely broaden reflecting extreme anharmonicity. Further, we find a strong repulsion between Ag neighbors, affecting the diffusion mechanism. Our studies of atomic dynamics and diffusion will help rationalize the emergence of ultralow thermal conductivity for thermoelectrics and facilitate the design of high-performance solid-state electrolytes. |
Thursday, March 7, 2019 3:30PM - 3:42PM |
V47.00006: Fabrication and Measurement of the Physical and Thermoelectric properties of Ca3-xDyxCo4-yFeyO9+ρ systems Ifeanyi Ifeduba, Robert M Catchings, David Mckeown, Winnie Wong-NG, Xueyan Song The properties and performance of Cobalt oxide material as a p-type semiconductor for commercial use depends on its stability at high temperature region and its excellent physical and thermoelectric properties. Here in, we substitute (dope) and study the effects of magnetic ions (Dy, Fe) for (Ca, Co) in polycrystalline Ca3Co4O9+ρ. A series of Ca3-xDyxCo4-yFeyO9+ρ samples was synthesized using the sol-gel combustion method. After preparations, the samples were subjected to heat treatment at different temperature. X-ray diffraction analysis indicates the partial substitution of Dy in the Ca site and Fe in the Co site. It also confirmed the formation of single phase compounds, as well as changes in the structure of the materials depending on the sintering temperature. The obtained values of the electrical resistivity for all samples falls within the range of a semiconductor. The thermopower values are all positive, indicating that the majority carrier are holes. |
Thursday, March 7, 2019 3:42PM - 3:54PM |
V47.00007: Axis Dependent Transport Properties of Single Crystal Re4Si7 Bin He, Mike Scudder, Yaxian Wang, Wolfgang E Windl, Joshua E. Goldberger, Joseph P C Heremans We measured the thermoelectric transport properties of Re4Si7 along different axis and prove Re4Si7 to have axis dependent carrier polarity. In the cryostat measurement, we observe electrical conductivity and thermopower both increasing with temperature. In-plane Hall effects shows the crystals we obtained has a carrier density around 2*1019/cm3, while the Hall coefficient in-plane and cross-plane have opposite signs. Thermal conductivity measurement shows an isotropic lattice thermal and Nernst measurement shows a small Nernst coefficient and eliminates the possibility of two carrier system. High temperature thermoelectric properties measurement shows the resistivity keeps decreasing at high temperature. The thermopower of the cross-plane direction reaches 300 µV/K and turns flat at high temperature, which may come from a thermal smearing effect. With an estimate of the thermal conductivity, we propose a promising ZT over unity for future optimization. |
Thursday, March 7, 2019 3:54PM - 4:06PM |
V47.00008: Spin Effects Making zT > 1 Daryoosh Vashaee, Md Mobarak Hossain Polash, Vladislav Perelygin, Morteza Rasoulianboroujeni, Yuanhua Zheng, Tianqi Lu, Ning Liu, Michael Manley, Raphael Hermann, Alex I Smirnov, Joseph P C Heremans, Huaizhou Zhao Recent studies of thermoelectric properties of the antiferromagnetic MnTe:Li have revealed the existence of a strong spin effect that extends across a broad range of temperature leading to zT>1 [1,2]. While carrier mobility and heat capacity were strongly affected by spin contributions near the Neel temperature, TN=307K, the thermopower demonstrated robust spin effects extending up to 900K. Spin contribution to those properties below TN has been attributed to the magnon-drag effect [3]. A recent study [2] attributed the thermopower enhancement to paramagnon-drag effect originated from the mid or short-range magnetic ordering above TN. Neutron scattering study showed an agreement to that theory to some extent while some competing theories such as the spin-fluctuations and spin entropy can also explain thermopower enhancement in magnetic materials [1,4]. The objective of this work is to show the agreements and disagreements of different spin-based theories in describing the transport properties of MnTe:Li and to compare similar material systems to gain better insight to the underlying physics. |
Thursday, March 7, 2019 4:06PM - 4:18PM |
V47.00009: Thermal transport and thermoelectric effects at solid-melt interfaces in semiconductors: Underlying physical phenomena that give rise to Thomson heat in semiconductors Sadid Muneer, Gokhan Bakan, Nathan Henry, Helena Silva, Ali Gokirmak Partial melting in self-heated nanocrystalline silicon microwires via fast pulses show a drastic asymmetry in melting profiles, where half of a wire may be melted and recrystallized while the other half remain in solid state. This asymmetry, in the direction of the electrical current, point to the significance of Thomson heat close to the solid-melt interfaces in semiconductors. The diffusion of the electron-hole pairs away from the melted regions increase thermal transport via (i) increased electronic convective heat flow and (ii) recombination of the excess carriers away from the melted region. In presence of an electric field a non-equilibrium non-isothermal condition is achieved. Generation (G) of electrons and holes, transport (T), and recombination (R) of the minority carriers downstream, GTR1, lead to a strong asymmetry in thermal profiles at melt-solid interfaces in semiconductors. |
Thursday, March 7, 2019 4:18PM - 4:54PM |
V47.00010: Integrated Device gets a Little Cooler based on Quantum Materials Invited Speaker: Kornelius Nielsch Micro-thermoelectric modules are of potential use in fields such as energy harvesting, thermal management, thermal imaging and high spatial-resolution temperature sensing. In particular, micro-thermoelectric coolers (μ-TECs) – in which the application of an electric current cools the device based on the Peltier effect – can be used to manage heat locally on a micrometer spot in microelectronic circuits, optoelectronic devices and microfluidic channels. However, a cost-effective μ-TEC device that is compatible with the modern semiconductor fabrication industry has been developed. N-type BiTeSe and p-type pure Te were electrochemically deposited at room temperature into microstructured photoresist patterns. A comprehensive study the electrochemically synthesis if thermoelectric chalcogenide materials is presented [1]. The material quality is every high, that even fundamental aspect like topological surface states can be demonstrated in these chalcogenide film by transport measurements. |
Thursday, March 7, 2019 4:54PM - 5:06PM |
V47.00011: Thermodynamics of atom motion and metal deposition in mixed ionic electronic conductors Matthias Agne, Pengfei Qiu, Xun Shi, Jeff Snyder The possibility of decomposition in superionic mixed ionic-electronic conductors (MIEC) has limited their engineering applications. Specifically, high efficiency MIEC thermoelectric materials have not been utilized due to decomposition under large electronic currents and large temperature gradients. Herein, we derive the critical condition for decomposition, which corresponds to a critical chemical potential difference defined from linear non-equilibrium thermodynamics. This analysis leads to the conclusion that voltage, not current density, is the relevant design parameter. Consequently, the decomposition condition is independent of the geometry of the device; whereby, a strategy is presented for improving stability in devices subjected to electrical and temperature gradients. By using a series of electronically conducting, but ion-blocking barriers to reset the chemical potential it is possible to keep the material below the threshold for decomposition. Experimentally, the thermodynamic theory is validated in the Cu2-dSe MIEC system. |
Thursday, March 7, 2019 5:06PM - 5:18PM |
V47.00012: High Thermoelectric Performance in n-doped Silicon-Based Chalcogenide Si2Te3 Rinkle Juneja, Tribhuwan Pandey, Abhishek Singh Silicon-based thermoelectric materials would be of great significance due to the huge dependence of electronic industry on silicon. Bulk silicon is not a good thermoelectric material due to its very high thermal conductivity, thereby limiting its thermoelectric efficiency. Nanostructuring and alloying are alternative solutions to reduce thermal conductivity, but the techniques involved are complex and costly. Recently, a silicon-based chalcogenide Si2Te3 has been experimentally synthesized. Si2Te3 exhibits layered structure, in which Te atoms form hexagonal sub-lattice and Si atoms can occupy any of the octahedral voids. Due to uncertainty in Si positions, previously unknown ground state structure of Si2Te3 was obtained using the Wyckoff positions of space group P-31c. The minimum energy configuration exhibits combination of desirable electronic and transport properties. In particular, n-doped Si2Te3 has an unprecedented figure of merit of 1.86 at 1000 K, which is comparable to some of the best state-of-the-art thermoelectric materials. Hence, n-doped Si2Te3 can be a long-sought silicon-based thermoelectric material which could be integrated to the existing electronic devices. |
Thursday, March 7, 2019 5:18PM - 5:30PM |
V47.00013: Enhanced Cross-plane Thermoelectric Transport of Rotationally-disordered SnSe2 via Se Vapor Annealing Jihan Chen, Danielle Hamann, David Choi, Nirakar Poudel, Lang Shen, Li Shi, David Johnson, Steve Cronin In this talk I will review our recent progress in cross-plane thermoelectric measurements of SnSe and SnSe2 films grown by the modulated element reactant (MER) approach. The initially grown SnSe films have relatively low cross-plane Seebeck coefficients due to significant unintentional doping originating from Se vacancies. By performing post-growth annealing at a fixed Se partial pressure, a transition from SnSe to SnSe2 is induced. This results in a 16-fold increase in the cross-plane Seebeck coefficient (from -38.6 to -631μV/K) after Se annealing due to both the SnSe to SnSe2 transition and the mitigation of unintentional doping by Se vacancies. The power factor S2σ increased by 44X after Se annealing. We believe that these results demonstrate a robust method for mitigating unintentional doping in a promising class of materials for thermoelectric applications.1 |
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