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Research Article | Open Access

Understanding secondary phase inclusion and composition variations in the microstructure design of n-type Bi2Te3 alloys via selective dissolution of KCl

Gwang Min Parka,b, Seunghyeok Leeb,c, Jun-Yun Kangd, Seung-Hyub Baekb, Heesuk Kime, Jin-Sang Kimf, Seong Keun Kima,b()
KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 02841, Republic of Korea
Electronic Materials Research Center, Korea Institute of Science and Technology, Seoul 02792, Republic of Korea
Department of Materials Science and Chemical Engineering, Hanyang University, Ansan 15588, Republic of Korea
Ferrous Alloy Department, Korea Institute of Materials Science, Changwon 51508, Republic of Korea
Soft Hybrid Materials Research Center, Korea Institute of Science and Technology, Seoul 02792, Republic of Korea
Institute of Advanced Composite Materials, Korea Institute of Science and Technology, Wanju 55324, Republic of Korea
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Abstract

This study investigated the effects of KCl treatment on microstructure and thermoelectric properties of n-type Bi2Te2.7Se0.3 (BTS) thermoelectric materials. The innovative KCl treatment was originally intended to introduce nanopores through selective dissolution of KCl from a mixture of thermoelectric materials and KCl. However, it unexpectedly induced substantial variations in material composition and microstructure during the subsequent spark plasma sintering (SPS) process. Hydroxyl groups adsorbed on the powder surface during the dissolution resulted in the emergence of a Bi2TeO5 secondary phase within the BTS matrix after the SPS process at 450 ℃. The concentration of Bi2TeO5 increased with an increase in the KCl content. Furthermore, a remarkable grain growth occurred at low KCl concentrations, likely due to the liquid-phase formation in a Te-rich composition during SPS. However, excessive Bi2TeO5 at higher KCl concentrations hindered grain growth. These variations in the microstructure had complex effects on electrical properties: The TeBi antisite defects increased the electron concentration, and Bi2TeO5 reduced electron mobility. Additionally, the lattice thermal conductivity decreased due to the presence of Bi2TeO5, from 0.8 W∙m−1∙K−1 at 298 K for the pristine BTS to 0.6 W∙m−1∙K−1 at 298 K for BTS treated with 1 wt% KCl. These insights allowed precise adjustments of the electrical and thermal conductivities, leading to an enhancement in the maximum value of figure-of-merit (ZT) from 0.76 to 0.96 through the selective dissolution of KCl approach. We believe that our observations potentially enable advances in thermoelectric materials by engineering microstructures.

Keywords

thermoelectric materialsBi2Te3Bi2TeO5grain growthn-typeKCl

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Journal of Advanced Ceramics
Volume 12 Issue 12,
December 2023
Pages 2360-2370
DOI: 10.26599/JAC.2023.9220825
Cite this article:
Park GM, Lee S, Kang J-Y, et al. Understanding secondary phase inclusion and composition variations in the microstructure design of n-type Bi2Te3 alloys via selective dissolution of KCl. Journal of Advanced Ceramics, 2023, 12(12): 2360-2370. https://doi.org/10.26599/JAC.2023.9220825
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