Alloys and Compounds for Thermoelectric and Solar Cell Applications XI: Session II
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; Takao Mori, National Institute For Materials Science; Wan-Ting Chiu, Tokyo Institute of Technology; Chenguang Fu, Zhejiang University
Monday 2:00 PM
March 20, 2023
Room: Sapphire A
Location: Hilton
Session Chair: Yoshisato Kimura, Tokyo Institute of Technology; Hsin-Jay Wu, National Chiao Tung University
2:00 PM Invited
Mg2Sn Epitaxial Thin Film for Thermoelectric Application: Takeaki Sakurai1; Mariana Lima1; Takashi Aizawa2; Isao Ohkubo2; Takao Mori2; 1University of Tsukuba; 2National Institute for Materials Science
Mg2X (X=Si, Ge, Sn) is a promising material for thermoelectric thin films because of its excellent physical properties using elements abundant in the earth. However, studies have reported that the power factor of Mg2X thin films are one order lower than that of the bulk material. Typically, the point defects show strong influence on thermal conductivity by acting as a phonon scattering center. If an epitaxial thin film behaves similar to a single crystal, the combination of the epitaxial nature and the doping could improve the power factor of Mg2X thin films. In this study, molecular beam epitaxy (MBE) is used to explore thermoelectric properties of the Mg2Sn epitaxial thin film. The relationship between microstructure and thermoelectric properties was shown by introducing alloying and doping effects in epitaxial Mg2Sn thin film. A higher quality epitaxial Mg2Sn thin film was fabricated and can be used in future in micro thermoelectric devices.
2:20 PM
A Robust Thermoelectric Module Based on MgAgSb/Mg3(Sb,Bi)2 with a Conversion Efficiency of 8.5% and a Maximum Cooling of 72 K: Pingjun Ying1; Lennart Wilkens1; Heiko Reith1; Nicolas Rodriguez1; Xiaochen Hong1; Qiongqiong Lu1; Christian Hess1; Kornelius Nielsch1; Ran He1; 1Leibniz Institute of Solid State and Materials Science
The applications of thermoelectric technology around room temperature are monopolized by bismuth telluride. However, due to the toxicity and scarcity of tellurium (Te), it is vital to develop a next-generation technology to mitigate the potential bottleneck in raw material supply for a sustainable future. Hereby, we develop a Te-free n-type compound Mg3Sb0.6Bi1.4 for near-room-temperature applications. Together with the p-type MgAgSb, we demonstrate module-level conversion efficiencies of 3% and 8.5% under temperature differences of 75 K and 260 K, respectively, and concomitantly a maximum cooling of 72 K when the module is used as a cooler. Besides, the module displays exceptional thermal robustness with a < 10% loss of the output power after thermal cycling for ∼32000 times between 323 K and 500 K. These proof-of-principle demonstrations will pave the way for robust, high-performance, and sustainable solid-state power generation and cooling to substitute highly scarce and toxic Bi2Te3.
2:40 PM Invited
Effects of Doping Element Addition on Phase Equilibria and Mg2Si–Mg2Sn Two-phase Microstructure Formation in Thermoelectric Mg2(Si, Sn)-based Alloys: Yoshisato Kimura1; Naoki Ueda1; Yaw Wang Chai1; Manabu Watanabe1; Yonghoon Lee1; 1Tokyo Institute of Technology
Formation of solid solution Mg2(Si,Sn) is a dominant factor to effectively reduce the thermal conductivity, while introducing the phase interfaces according to the Mg2Si–Mg2Sn two-phase separation based on large lattice misfit can be an additional factor. The objective of the present work is to evaluate and to understand the effects of typical doping elements addition, n-type Al and p-type Ag, on the phase equilibria, two-phase Mg2Si–Mg2Sn microstructure formation, and thermoelectric properties. Since the solubility of Al is negligible small in both Mg2Si and Mg2Sn phases, solidification microstructure during furnace cooling after the induction heat melting is hardly affected by the Al addition. Contrary to this, Ag is preferably partitioned and soluble in the Mg2Sn phase with a small amount but in the Mg2Si phase, which causes drastic change of solidification path and resulting in Mg2Si phase grains coarsening, which is unfavorable to reduce thermal conductivity.
3:00 PM Invited
Thermoelectric Modules Based on Thin Films for Localized Heat Harvesting: Paolo Mele1; Giovanna Latronico1; Marco Fronzi1; Hiroki Shigemune1; Motoki Maeda1; Kimiyoshi Usami1; Cedric Bourges2; Takao Mori2; 1Shibaura Institute of Technology; 2NIMS
Compact, light thermoelectric modules based on thin film legs were prepared using different materials and techniques: (i) 5 Al-doped ZnO (n-type) legs alternated with 5 Ca3Co4O9 (p-type) legs deposited on Al2O3 and silica substrates by pulsed laser deposition (PLD); (ii) 5 n-type and 5 p-type skutterudite legs of the composition Smy(FexNi1-x)4Sb12 (n-type: x = 0.63 and y = 0.20; p-type: x = 0.70 and y = 0.40) deposited on silica substrate by PLD; (iii) 5 ink-jet printed n-type Ag legs alternated with 5 screen-printed p-type PEDOT-PSS legs on photopaper scaffold. Maximum output power of the modules was measured as 16 pW at 300 °C, 0.16 μW at 300 °C and 0.045 μW at 70 °C, respectively. These encouraging results suggest the feasibility of miniaturized thermoelectric modules for powering out-of-the-grid IoT devices in the μW range.International Research Center for Green Electronics (IRCGE), Shibaura IT is acknowledged for the financial support.
3:20 PM Break
3:40 PM Invited
Full-Heusler Compounds: Unconfined Prospects for Tuning Thermoelectricity: Ernst Bauer1; Alexander Riss1; Michael Parzer1; Fabian Garmroudi1; Takao Mori2; 1Technische Universität Wien; 2NIMS Tsukuba
Full-Heusler alloys based on Fe2VAl turn out to bear large potentials for being used in the 100°C temperature range for power generation, cooling, or wireless sensing. Superior power factors (pf) and excellent mechanical properties, the easy synthesis and the non-poisonous and reasonably priced constituting elements, as well as their respective abundance are essential assets in this respect.The present talk aims to focus on various mechanisms which have been employed in order to enhance the thermoelectric performance of such systems. We demonstrate that by modifications of the charge carrier effective mass and the width of the gap in the electronic density of states that pf around 100°C can become 3 times as large, as best performing state-of-the-art materials. A novel mechanism based on charge carrier localization is proposed, boosting the thermoelectric performance and off-stoichiometric sample preparation is employed as well. Our DFT calculations allow to perfectly guide experimental studies.
4:00 PM
Modulating Doping Concentration via Thermodynamic Approach for High-Performance p-type Bi2Te3 Thermoelectrics: Hung-Wei Chen1; Hsin-Jay Wu1; 1National Yang Ming Chiao Tung University
Thermoelectric (TE) materials have attracted significant interest in recent decades due to their outstanding capability in waste-heat recovery and spot cooling. Among various TE materials, Bismuth telluride (Bi2Te3) based alloys are the most promising candidate for near room-temperature applications. Herein, the TE performance of p-type Bi2Te3-based materials is enhanced using two different procedures: (i) introducing dilute doping in the single-phase Bi2Te3, and (ii) incorporating the liquid-like dopants into heavily-doped Bi2Te3. Our p-type Bi2Te3 crystals perform enhanced electrical conductivity as well as boosted thermal power (S). Compared to the state-of-the-art p-type Bi2Te3, the peak zT value at 300 K for our lightly-doped p-type Bi2Te3 is 130% higher while an enhanced average zT (zTavg~ 1.2) is reported in the temperature range of 323 K to 493 K for the heavily-doped Bi2Te3.
4:20 PM
Mixing Amorphous and Crystalline Structures for High Performance n-type Bi2Te3 Thermoelectrics: Wan-Ting Yen1; Hsin-jay Wu1; Kuang-Kuo Wang2; 1National Yang Ming Chiao Tung University; 2National Sun Yat-sen University
Bismuth telluride-based thermoelectric (TE) materials have been widely used in waste heat recovery and thermoelectric (TE) coolers. However, the peak zT of n-type Bi2Te3 is lower than the p-type counterparts, hindering the conversion efficiency for a Bi2Te3-based device. In this work, the TE performance of n-type Bi2Te3 is improved by doping a dilute amount of liquid-like copper chalcogenides Cu2X (X = S, Se, Te), yielding the ultrahigh carrier mobility as fluxes of the highly-mobile Cu ions are introduced. Meanwhile, the chalcogenide anions induce severe crystal imperfections, leading to the low κL that lay close to the amorphous limit of Bi2Te3. A hybrid of crystalline materials with liquid-like superionic conductors paves a new route for designing high-performance TE alloys.
4:40 PM
Effect of Interfacial Stability of Bi2Te3 Thin Film Modules on Thermoelectric Property: Kai-Wen Cheng1; Albert T. Wu1; 1National Central University
With decreasing in the dimension of thermoelectric modules, the interfacial stability between thermoelectric materials and metal electrode becomes crucial. Serious interfacial reaction at the interface affects the thermoelectric properties and the reliability. In this study, Bi2Te3 thermoelectric thin films with highly preferred orientation were fabricated by co-sputtering deposition method and annealing process. Cu was selected as the electrode due to its high electrical conductivity. The effect of Cu diffusion from the electrode into Bi2Te3 thin films was investigated through long-term heat treatment. The thermoelectric power shows a significant degradation when Cu atoms diffuse into Bi2Te3 thin films and react with Te to form CuTe compounds. Furthermore, contact resistivity at the interface between Cu electrode and Bi2Te3 thin films substantially increases with aging time. The results suggest that the reliability of the thin film thermoelectric module deteriorates after long-term heat treatment.
5:00 PM Invited
Thermoelectric Effect Under Photon Excitation: A Connector between Thermoelectrics and Photovoltaics: Heng Wang1; 1Illinois Institute of Technology
The physical origin of thermoelectric phenomena are well understood with quantum or semi-classic theories such as the Boltzmann transport theory. Carefully conducted experiments often reveal results as predicted by such theories. Nonetheless, carrier transport not only happens when system is near thermal equilibrium, but also happens in excited systems with electrons far from thermal equilibrium. And this draws our interest over the past a few years. In this talk we will discuss the characteristic, the physical origin, and measurement strategies of the thermoelectric effect under photon excitation. We will discuss a few case studies and what can these results tell us about the materials. There are still much to understand with this effect and we hope our study could stimulate more interest and applications as well.