Enhancing room-temperature thermoelectric performance of n-type Bi 2 Te 3 -based alloys via sulfur alloying
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ORIGINAL ARTICLE
Enhancing room-temperature thermoelectric performance of n-type Bi2Te3-based alloys via sulfur alloying Feng Liu, Ye-Hao Wu, Qi Zhang, Tie-Jun Zhu*
, Xin-Bing Zhao
Received: 15 August 2020 / Revised: 9 September 2020 / Accepted: 10 September 2020 Ó GRINM Bohan (Beijing) Publishing Co., Ltd 2020
Abstract Bismuth-telluride-based alloys are the best thermoelectric materials used in commercial solid-state refrigeration near room temperature. Nevertheless, for n-type polycrystalline alloys, their thermoelectric figure of merit (zT) values at room temperature are often less than 1.0, due to the high electron concentration originating from the donor-like effect induced by the mechanical deformation process. Herein, carrier concentration for better performance near room temperature was optimized through manipulating intrinsic point defects by sulfur alloying. Sulfur alloying significantly decreases antisite defects concentration and suppresses donor-like effect, resulting in optimized carrier concentration and reduced electronic thermal conductivity. The hot deformation process was also applied to improve carrier mobility due to the enhanced texture. As a result, a high zT value of 1 at 300 K and peak zT value of 1.1 at 350 K were obtained for the twice hot-deformed Bi2Te2.7Se0.21S0.09 sample, which verifies sulfur alloying is an effective method to improve thermoelectric performance of n-type polycrystalline Bi2Te3-based alloys near room temperature. Keywords Bismuth telluride; Thermoelectric; Point defect; Sulfur alloying; Hot deformation
F. Liu, Y.-H. Wu, Q. Zhang, T.-J. Zhu*, X.-B. Zhao State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China e-mail: [email protected]
1 Introduction Thermoelectric (TE) materials, which can realize direct interconversion between heat and electric energy, have been extensively studied for solid-state refrigeration in past decades [1, 2]. The energy conversion efficiency for TE device is determined by the materials’ dimensionless figure of merit zT = S2r/j, where S, r, j are the Seebeck coefficient, electrical conductivity, thermal conductivity (including carrier contribution je and phonon contribution jL) and absolute temperature, respectively. As S, r and j are strongly coupled with carrier concentration n, optimizing n is a foremost procedure to improve TE materials performance [3–5]. For decades, bismuth-telluride-based alloys with layered structure have been the only TE materials realizing widely commercial application [2]. Both n-type and p-type Bi2Te3-based quasi-single crystals are prepared by zone melting (ZM), which exhibit maximum zT (zTmax) of * 1.0 near room temperature [6, 7]. Nevertheless, owing to the van der Waals bonding, their easy-cleavage nature increases the expenditure for device fabrication and weakens reliability. To improve the mechanical properties, polycrystalline Bi2Te3-based alloys have been prepared by powder metallurgical methods, such as mechanical
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