Alloys and Compounds for Thermoelectric and Solar Cell Applications VIII: Session I
Sponsored by: TMS Functional Materials Division, TMS: Alloy Phases Committee
Program Organizers: Sinn-wen Chen, National Tsing Hua University; Franck Gascoin, Ensicaen University of Caen; Philippe Jund, Montpellier University; Yoshisato Kimura, Tokyo Institute of Technology; Lan Li, Boise State University; Takao Mori, National Institute For Materials Science; Hsin-jay Wu, National Chiao-tung University; Tiejun Zhu, Zhejiang University

Tuesday 8:30 AM
February 25, 2020
Room: Miramar
Location: Marriott Marquis Hotel

Session Chair: Hsin-jay Wu, National Chiao-tung University; Sinn-wen Chen, National Tsing Hua University


8:30 AM Introductory Comments

8:35 AM  Cancelled
ZT Enhancement in Thermoelectric Nanowires: Yang-Yuan Chen1; 1Academia Sinica
     The enhancement of thermoelectric performance has been observed in low-dimensional systems such as nanowires and films. In the report, I will introduce the typical methods to fabricate and characterize thermoelectric nanowire specimens. Since the sample quality is closely associated to the properties of specimens, the structure, profile, crystalline and elemental composition will be analyzed using the spectroscopic tools of X-ray, SEM, TEM and EDX. For nanowires, the standard thermoelectric measurement tools for bulk specimens are no longer suitable, thus special sample templates for nanowire should be designed for carrying out the measurements of Seebeck coefficient, electrical conductivity and thermal conductivity to evaluate their thermoelectric performance. Nanowires such as Bi-Sb-Te-Se system will be used to illustrate the experimental details. References1. Chia-Hua Chien, Ping-Chung Lee, Wei-Han Tsai, Chien-Hung Lin, Chih-Hao Lee1 and Yang-Yuan Chen, Sci. Rep. 6, 23672 (2016).

8:55 AM  Invited
Novel Thermoelectric Materials for Power Generation: Yaniv Gelbstein1; 1Ben-Gurion University of Negev
     Nano-based thermoelectric converters exhibit a major stability advantage for long-term operation, compared to many other competing conversion methods. Yet, such converters usually operate under high temperatures and large temperature gradients conditions, which can affect the stability of the nano-features embedded in the bulk thermoelectric main phases. In the current research, the thermodynamic nano-features generation approach in bulk thermoelectric materials, was considered, using controlled phase separation conditions according to the relevant phase diagrams. Specific systems showing a miscibility gap, including the PbTe-GeTe and PbTe-PbS systems, were heat treated under various required conditions for promoting spinodal decomposition and nucleation and growth reactions. High ZT values of up to 2.2 were obtained due to combined optimal doping and sub-micron phases' decomposition features. Such features were found as thermodynamically stable under long-term investigation at temperatures up to 400oC, resulting in almost unchanged figure of merit values after the various investigated heat treatment durations.

9:15 AM  
Current Progress on Fabrication and Life Testing of Advanced Skutterudite Thermoelectric Materials in a Proposed Enhanced Multi-mission Radioisotope Thermoelectric Generator (eMMRTG) for Space Power Applications: Thierry Caillat1; Chen-Kuo Huang1; Jong-Ah Paik1; Ike Chi1; Stanley Pinkowski1; 1Jet Propulsion Laboratory
    NASA has used Radioisotope Thermoelectric Generators to power a variety of space missions over the past 50 years. In order to enhance the power and thermoelectric conversion efficiency of future RTGs, the Skutterudite Technology Maturation project at NASA’s Jet Propulsion Laboratory is working to mature advanced TE technology for use in a proposed enhanced Multi-Mission Radioisotope Thermoelectric Generator (eMMRTG). The eMMRTG would use advanced skutterudite (SKD) based thermoelectric unicouples to convert heat from the natural radioactive decay of plutonium-238 into electricity. In order to maintain the lifetime stability of eMMRTG unicouples, SKD thermoelectric materials need to be phase stable to sustain 17 years of operation at a maximum temperature of ~ 600 degree C in an inert gas atmosphere. Here, we will report on the latest progress for demonstrating manufacturability and validating lifetime performance of advanced SKD thermoelectric materials jointly developed and tested by JPL and Teledyne Energy Systems, Inc.

9:35 AM  Invited
Approaches to Manipulate p-n Conduction Transition and High Thermoelectric Performance in Ga-incorporated Bi2Te3: Hsin-Jay Wu1; Chun-han Lin1; Wan-ting Yen1; 1National Chiao Tung University
    Years of efforts have driven the research trend seeking for high-zT, cost-effective and thermally stable thermoelectric (TE) materials, attempting to assemble a high-performance TE device that composed of p- and n-type legs with high zTs. In this study, a thermodynamic approach is established under the support of phase diagram, which allows one to control the p-n conduction transition in the Bi2Te3-based materials via the changing Ga solubility. With the incorporation of single-dopant Gallium (Ga), the p-type Ga-substituted Bi2-bGabTe3 achieves the highest zT peak value of 1.2 while the Ga2Te5-alloyed (Bi2Te3)1-a(Ga2Te5)a reveals an outstanding zT peak value over 1.5 at 300 K, where both alloys present different phase features.

9:55 AM Break

10:15 AM  Cancelled
Intrinsic Cu Vacancy Leading to High Thermoelectric Performance in CuBi3Se5: Jian Wang1; 1Wichita State University
     Thermoelectric materials can directly convert waste heat into electrical power and vice versa, which exhibit high potential in improving our society energy efficiency. The selenide compounds have attracted continual interests due to their excellent balance between electrical conductivity and thermal conductivity originating from their unique crystal structures and chemical bonds. In this work, we focus on the synthesis, crystal structure, and thermoelectric properties of CuBi3Se5. The crystal structure of CuBi3Se5 was determined by synchrotron powder X-ray diffraction and single crystal X-ray diffraction. Intrinsic Cu defects were detected at various atom positions, which were manipulated to enhance thermoelectric efficiency. Through controlling Cu contents, CuBi3Se5 was demonstrated to be a good thermoelectric material.Keywords: Thermoelectric materials; selenides; defects; crystal structure

10:35 AM  
Enhanced Averaged zT in n-type Bi2Te3 via Solubility Control: Wan-Ting Yen1; Hsin-jay Wu1; Pai-chun Wei2; 1National Chiao Tung University; 2King Abdullah University of Science and Technology
    Bismuth telluride (Bi2Te3) has been the most well-established room-temperature thermoelectric material since 1960s. In spite of countless efforts, there is still room for improvement, especially for the n-type counterpart. In this study, we introduced the electron-donor dopants (e.g., Cu, Se, etc.) into the Bi2Te3 alloys whose compositions are guided by a phase diagram that acts like a map navigating toward the n-type conduction zones. The presence of secondary phases in those (Cu,Se)-Bi2Te3 are likely responsible for the n-type conduction, whereas the concentration could be controlled via the dopant solubility. Notably, the power factor is significantly boosted to above 10.6 (mW/mK2) while the thermal conductivity remain unaffected low (κ~2.0-1.6 (W/mK)), leading to an enhanced average zT of 1.1 within 300 K – 550 K.

10:55 AM  Cancelled
Improving the Thermoelectric Properties of Atomized BiSbTe Alloy by Electroless Copper Coating: Pathan Sharief1; Madavali Babu1; Youhan Sohn2; Jun-Hyun Han2; Soon-Jik Hong1; 1Kongju National University; 2Chungnam National University
    The global warming causes human life survival difficult for future in which green technology, thermoelectrics attracts great attention for it’s capable of converting abundant waste heat energy into electrical energy. In here, we report high production (2kg/min) of BiSbTe thermoelectric material using powder metallurgy and enhancing its properties by electroless plating copper coating on powder surface. The copper was homogeneously distributed on the powder surface observed through SEM-EDS analysis. Compared to bare sample, the power factor greatly improved from 2.7 W/m-K2 to 3.9 W/m-K2 for copper coated samples. The improvement in power factor was related to high electrical conductivity from its high carrier concentration and mobility. The Cu-coated samples obtained high thermal conductivity than bare samples due to their higher carrier density. Overall, there was a significantly improvement in figure of merit (ZT) from 0.76 to 1.17 was achieved through facile Cu-coating on BiSbTe powder.

11:15 AM  
Minor Ga Addition in β-Zn4Sb3 Leads to Major Enhancement in Thermoelectric Performance: I-Lun Jen1; Hsin-Jay Wu1; 1National Chiao Tung University
    In order to cope with the energy shortage issue, the thermoelectric (TE) materials has attracted growing attention in recent years. The p-type β-Zn4Sb3 has been an ideal candidate for mid-temperature TE generator, as it composes of cost-effective and environmental-friend elements. Nevertheless, its moderate TE conversion efficiency and deficient high-temperature thermal stability have been the major roadblock for the development. Herein, we introduced the IIIA-group (Gallium) dopant into the Zn4Sb3, aiming to improve the TE performance. Meanwhile, the addition of Ga is effective in stabilizing the Zn4Sb3, providing eligible thermal stability at high temperature. The doping strategy is guided by the experimental-determined phase diagram. At 623 K, the maximum solubility of Ga in Zn4Sb3 is less than 4 at.%Ga. Consequently, the Ga-substituted (Zn1-xGax)4Sb3 achieves high figure of merit zT of 1.36 at 673 K, resulting from the reduced κ~0.70 (W/mK) and enhanced PF~1.3 (mW/mk2).