Enhanced thermoelectric performance of n-type TiCoSb half-Heusler by Ta doping and Hf alloying
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Enhanced thermoelectric performance of n-type TiCoSb halfHeusler by Ta doping and Hf alloying Rui-Fang Wang, Shan Li, Wen-Hua Xue, Chen Chen, Yu-Mei Wang, Xing-Jun Liu* , Qian Zhang*
Received: 20 June 2020 / Revised: 29 July 2020 / Accepted: 6 August 2020 Ó The Nonferrous Metals Society of China and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The p-type TiCoSb-based half-Heuslers are widely studied due to the good electrical transport properties after hole doping, while the pristine TiCoSb is intrinsically n-type. It is thus desired to obtain a comparable n-type counterpart through optimization of electron concentration. In this work, n-type Ti0.9-xHfxTa0.1CoSb half-Heuslers were fabricated by arc melting, ball milling, and spark plasma sintering. An optimized carrier concentration, together with a decreased lattice thermal conductivity, was obtained by Ta doping at the Ti site, leading to a peak figure of merit (ZT) of 0.7 at 973 K in Ti0.9Ta0.1CoSb. By further alloying Hf at the Ti site, the lattice thermal conductivity was significantly reduced without deteriorating the power factor. As a result, a peak ZT of 0.9 at 973 K and an average ZT of 0.54 in the temperature range of 300–973 K were achieved in Ti0.6Hf0.3Ti0.1CoSb. This work demonstrates that n-type TiCoSb-based halfHeuslers are promising thermoelectric materials. Keywords Thermoelectric; Half-Heusler; N-type; TiCoSb
Rui-Fang Wang and Shan Li have contributed equally to this work. R.-F. Wang, S. Li, C. Chen, X.-J. Liu*, Q. Zhang* School of Materials Science and Engineering, Institute of Materials Genome and Big Data, Harbin Institute of Technology, Shenzhen 518055, China e-mail: [email protected] Q. Zhang e-mail: [email protected] W.-H. Xue, Y.-M. Wang Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Science, Beijing 100190, China
1 Introduction The overexploitation of traditional fossil fuels has caused energy crisis and serious environmental pollution problems, which pushes the exploration of high-efficiency green renewable energy sources [1–4]. Thermoelectric (TE) materials can realize the direct conversion between thermal energy and electrical energy through the transport process of electrons and phonons within the material for the special applications in the waste heat recovery or accurate refrigeration [5–7]. The conversion efficiency is determined by the dimensionless figure of merit (ZT), which is defined as ZT = S2rT/j, where S, r, T, and j are Seebeck coefficient, electrical conductivity, absolute temperature, and total thermal conductivity, respectively [8]. A high ZT material should possess a high Seebeck coefficient, a high electrical conductivity, and a low thermal conductivity. However, all these physical parameters are interdependent via the carrier concentration [9–11]. Half-Heusler (HH) compounds have received significantly attention due to the merits of outstanding electrical properties, robust mechanical properties, and good the
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