Understanding secondary phase inclusion and composition variations in the microstructure design of n-type Bi 2Te 3 alloys via selective dissolution of KCl
Gwang Min Park, Seunghyeok Lee, Jun-Yun Kang, Seung-Hyub Baek, Heesuk Kim, Jin-Sang Kim, Seong Keun Kim
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引用次数: 0
Abstract
This study investigated the effects of KCl treatment on the microstructure and thermoelectric properties of n-type Bi2Te2.7Se0.3 (BTS) thermoelectric materials. The innovative KCl treatment was originally intended to introduce nanopores through the selective dissolution of KCl from a mixture of thermoelectric materials and KCl. However, it unexpectedly induced substantial variations in the material composition and microstructure during the subsequent spark plasma sintering (SPS) process. The 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 °C. 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 the electrical properties: the TeBi antisite defects increased the electron concentration, and Bi2TeO5 reduced the electron mobility. Additionally, the lattice thermal conductivity decreased due to the presence of Bi2TeO5, from 0.8 Wm-1K-1 at 298 K for the pristine BTS to 0.6 Wm-1K-1 at 298 K for the BTS treated with 1 wt% KCl. These insights allowed precise adjustments of the electrical and thermal conductivities, leading to an enhancement in ZTmax 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.
期刊介绍:
Journal of Advanced Ceramics is a single-blind peer-reviewed, open access international journal published on behalf of the State Key Laboratory of New Ceramics and Fine Processing (Tsinghua University, China) and the Advanced Ceramics Division of the Chinese Ceramic Society.
Journal of Advanced Ceramics provides a forum for publishing original research papers, rapid communications, and commissioned reviews relating to advanced ceramic materials in the forms of particulates, dense or porous bodies, thin/thick films or coatings and laminated, graded and composite structures.