Alloys and Compounds for Thermoelectric and Solar Cell Applications IX: Session III
Sponsored by: TMS Functional Materials Division, TMS Structural Materials Division, TMS: Alloy Phases Committee
Program Organizers: Hsin-Jay Wu, National Chiao Tung University; Sinn-wen Chen, National Tsing Hua University; Franck Gascoin, CNRS Crismat Unicaen; Philippe Jund, Montpellier University; Yoshisato Kimura, Tokyo Institute of Technology; Lan Li, Boise State University; Takao Mori, National Institute For Materials Science; Tiejun Zhu, Zhejiang University; Alexandra Zevalkink, Michigan State University; Wan-Ting Chiu, Tokyo Institute of Technology
Tuesday 8:30 AM
March 16, 2021
Room: RM 21
Location: TMS2021 Virtual
Session Chair: Yoshisato Kimura, Tokyo Institute of Technology; Chenguang Fu, Zhejiang University
8:30 AM Invited
Mg3(Sb,Bi)2 Thermoelectric Single Crystals: From p-type to n-type: Chenguang Fu1; Yu Pan2; Kazuki Imasato3; Mengyu Yao2; Tiejun Zhu1; G. Jeffrey Snyder3; Claudia Felser2; 1Zhejiang University; 2Max Planck Institute for Chemical Physics of Solids; 3Northwestern University
The understanding of the intrinsic electronic structure and transport properties of solid-state materials lays the foundation for the optimization of their thermoelectric performance. Owing to the elimination of grain boundary effect, high-quality single crystals with fewer defects generally exhibit the up limit of the carrier mobility and lattice thermal conductivity of a material. In this talk, I will present our recent work on Mg3(Sb,Bi)2 thermoelectric single crystals. Started with the p-type crystals grown by the Sb flux method, we are now able to get n-type single crystals either by annealing the p-type crystals under Mg vapor or directly growing in the Mg flux method. These n-type single crystals enable the revelation of the intrinsic carrier scattering mechanism and demonstrate the enhancement of thermoelectric performance near room temperature owing to the eliminated grain boundary scattering. The electronic structure of Mg3(Sb,Bi)2 is also directly observed by performing the angle-resolved photoemission spectroscopy study.
8:50 AM Invited
Optimization of n- and p-type Mg2X (X: Si, Ge, Sn): Understanding the Impact of Mg on the Thermoelectric Performance and the Change of the Valence Bands Under Solid Solution Formation: Johannes De Boor1; Hasbuna Kamila1; Mohammad Yasseri1; Aryan Sankhla1; Eckhard Müller1; 1German Aerospace Center
Among the materials studied for thermoelectric applications, Mg2X (X: Si, Ge, Sn) and their solid solutions are of very high interest as their constitutive elements are abundant, non-toxic and mostly cheap. We have investigated the influence of excess or deficient Mg on the thermoelectric performance of n-type Mg2(Si,Sn) by in situ transport measurements and microstructural analysis of annealed samples. It will be shown that the Mg content has a strong impact on the demixing kinetics of the solid solutions. In-depth analysis of the transport data indicates an increased electron-phonon scattering for Mg-deficient samples as well as an increasing impact of grain boundary scattering.We will also show that the p-type material can be improved by solid solution formation of Mg2Ge with Mg2Si and Mg2Sn, making use of an advantageous, temperature dependent band structure of Mg2Ge and a thermal conductivity reduction due to alloying.
9:10 AM Invited
Phase Interface Formation Induced by Phase Separation Process in Thermoelectric Mg2(Si, Sn) Alloys and (Zr, Ti)NiSn Alloys: Yoshisato Kimura1; Yaw Wang Chai1; Manabu Watanabe1; Yonghoon Lee2; 1Tokyo Institute of Technology; 2KELK Ltd.
Formation of solid solution of a compound phase is very effective to reduce the lattice thermal conductivity. In the case that a solid solution phase is formed having compositional difference (gradient) of solute atoms, phase separation with interface formation is induced in order to release the elastic energy due to a lattice misfit. As the objective of the present work, we focused on the formation mechanism of phase separation induced interfaces, and microstructure control based on phase separation process. We have observed and analyzed phase interfaces which are formed due to the phase separation in two alloy systems, one between Mg2Si–Mg2Sn phases during solidification process and the other between ZrNiSn–TiNiSn phases during heat treatments. We have determined the formation of sharp interfaces in the former alloys and quite diffuse interfaces in the latter alloys. The lattice thermal conduction can effectively be reduced in both alloys.
9:30 AM
Microstructure and Band Engineering for the High Performance of n-type Mg3Sb2-Mg3Bi2 Alloy: Kazuki Imasato1; G. Jeffrey Snyder1; 1Northwestern University
There has been significant interest in Mg3(Sb,Bi)2 since the recent demonstration of high zT in the n-type materials. In this study, we demonstrate that the Mg3Sb2-Mg3Bi2 alloy can overcome the performance of Bi2Te3 around room temperature. The main mechanisms of this improvement are optimization of the band structure and microstructure. Our annealing and grain size study shows, the reduction of low temperature electrical resistance leads to a multi-fold improvement in the thermoelectric performance zT at room temperature. By investigating the effect of Bi content on the effective mass and grain size, the optimized composition of the alloy, achieves comparable zT as commercialized Bi2Te3. The understanding of these mechanisms is crucial to the cooling and wasted heat recovery applications of Mg3Sb2-Mg3Bi2 alloy. Considering the limited number of state-of-art n-type thermoelectric materials, the further development of Mg3Sb2-Mg3Bi2 alloys is a significant step towards the commercial application of thermoelectric materials.
9:50 AM Invited
Self-tuning of Carrier Type and Improved Thermoelectric Performance in Skutterudite CoM1.5Te1.5 (M = Sn or Ge): Li-Chyong Chen1; Suneesh MV2; Ta-Lei Chou2; Kuei-Hsien Chen2; 1National Taiwan University; 2Academia Sinica
CoSb3-based skutterudites can realize the “phonon glass electron crystal” concept, capable of manipulating electrical and thermal transports independently. The skutterudite compounds possess caged structure in which a filler atom vibrates with large amplitude. The anharmonic vibration of the filler atom scatters the phonons effectively while maintaining relatively high carrier mobility through the caged network. Further reduction in thermal conductivity could be achieved by modifying the pnicogen Sb4 ring. In this present work, we iso-electronically replace the Sb4 ring with M2Te2 (M=Sn or Ge), by mechano-chemical ball-milling plus hot pressing and, as revealed by Seebeck coefficient, the sample can be either n- or p-type semiconductors, depending on the Te/Sn ratio. Meanwhile, this approach raises the carrier concentration, conductivity and thereby thermoelectric power factor. Eventually, with thermal conductivity as low as ~2 W/m-K, we boost the dimensionless figure of merit of CoM1.5Te1.5 50 times higher to 0.6 at 773 K.
10:10 AM Invited
The Doping Effects on the Thermal Conductivity of GeTe: Jie Ma1; Jiong Yang2; Yangzhong Pei3; Siqi Lin3; 1Shanghai Jiao Tong University; 2Shanghai University; 3Tongji University
GeTe is a thermoelectric material with the superior electronic performance and low thermal conductivity. The high electronic performance arises from the multiple valence bands and highly degenerated band at high symmetric points of Brillouin zone, while the origin of the low thermal conductivity has so far been elusive. As the other IV-monotellurides, PbTe and SnTe, a strong anharmonic coupling between the ferroelectric transverse optic mode and the longitudinal acoustic mode is believed to be existed in GeTe, which plays a central role in explaining the low thermal conductivity. Therefore, the signal of the acoustic-optical phonon coupling in GeTe should be strong around the ferroelectric transition temperature, around 700K, and is the indicator of low thermal conductivity. We conducted inelastic neutron scattering experiments with Ge0.9Bi0.1Te and GeTe0.9Sb0.1, to have a sight of the lattice dynamic of GeTe for further analysis of thermal conductivity.
10:30 AM
High-performance GeTe-based Thermoelectric Materials via Carrier Optimization: Yi-Fen Tsai1; Hsin-Jay Wu1; 1National Chiao Tung University
In recent years, Germanium-tellurides (GeTe) alloys were viewed as promising thermoelectric materials. Due to the presence of Ge vacancies, GeTe featured with high carrier concentration, high electrical conductivity and high thermal conductivity. With the incorporation of minor amount of group-IB group-VA and elements, both the carrier concentration and thermal conductivity can be effectively reduced, yielding a high thermoelectric figure-of-merit zT. Specially, the optimization counts on an equilibrium phase diagram, which offers a new avenue toward high-performance TE materials.
10:50 AM
Phase Transition Behavior and Thermoelectric Property of Te doped Cu2Se: Wan-Ting Yen1; Hsin-jay Wu1; 1National Chiao Tung University
The Copper Selenide, which exhibits a liquid-like behavior, shows superior electrical property and low thermal conductivity. It has a high zT at a phase transition temperature of 400 K. Herein, we prepared two series of Te-doped Cu2Se crystals, whose nominal compositions are Cu2Se1-xTex and Cu2-ySeTey, and their thermoelectric properties and phase transition are discussed. An isothermal section at 573 K of the ternary Cu-Se-Te is constructed based on the microstructural and compositional analysis. We further found that two ternary compounds are thermally stablized at 573 K.
11:10 AM Invited
Functionalization of the Conductive Network and Structural Disorder Engineering: Two Strategies to Reach High ZT in Ternary and Quaternary Sulfides: Emmanuel Guilmeau1; 1Laboratoire CRISMAT
Among the various possibilities offered by the periodic table, copper-rich ternary and quaternary sulfides represent a formidable source for the discovery of low cost and environmentally benign thermoelectric materials. Copper-rich sulfides form an important class where univalent copper is the dominant element, giving the possibility of creating hole carriers in the conductive “Cu–S” network for the generation of p-type thermoelectrics. During this presentation, recent advances in synthetic colusites will be shown [1-4]. Some peculiar structural features in connection with chemical bonding, such as the existence of metal complexes within the structure and/or structural disorder, were carefully examined to establish rules and correlations between the crystal structures, electronic structures, vibrational and thermoelectric properties.[1] Angewandte Chemie Int. Ed. 58, 15455 (2019), [2] Adv. Energy Mater. 9, 1803249 (2019), [3] JACS 140, 2186 (2018), [4] PRM 4, 025404 (2020), [5] Chem. Mater. 32, 830 (2020), [6] Acta Mater. 195, 229 (2020).
11:30 AM
Effect of Structural Disorder on the Thermoelectric Properties of Kesterite (Cu2ZnSnS4): Eleonora Isotta1; Binayak Mukherjee1; Carlo Fanciulli2; Nicola M. Pugno1; Paolo Scardi1; 1University of Trento; 2CNR-ICMATE, Lecco Unit
The crystallographic complexity of quaternary chalcogenides provides an opportunity for engineering defects and disorder, to modify and possibly improve specific properties. Kesterite (Cu2ZnSnS4) seems particularly suited to explore these possibilities, as it presents several structural defects and polymorphic phase transformations. This leads to a wide spectrum of consequences on thermoelectric properties, the physical origin of which can be studied both experimentally and through ab initio simulations. A remarkable case is the order-disorder transition of tetragonal kesterite, which produces a sharp enhancement in the Seebeck coefficient due to a flattening and degeneracy of electronic bands. Whereas in the recently produced low-temperature cubic kesterite, the total cation disorder provides an uncommon occurrence in thermoelectricity: a concurrent optimization of Seebeck coefficient, electrical and thermal conductivity. These discoveries, besides providing new and general understanding of kesterite, cast light on profitable mechanisms to significantly and completely enhance the thermoelectric performance of semiconducting chalcogenides.