Liquid‐Phase Hot Deformation to Enhance Thermoelectric Performance of n‐type Bismuth‐Telluride‐Based Solid Solutions

Abstract

Bismuth-telluride-based solid solutions are the best commercial thermoelectric materials near room temperature. For their n-type polycrystalline compounds, the maximum figures of merit (<i>zT</i>s) are often less than 1.0 due to the degraded carrier mobility resulting from the loss of texture. Herein, a liquid-phase hot deformation procedure, during which the Bi₂(Te,Se)₃ ingots are directly hot deformed with the extrusion of liquid eutectic phase, is performed to enhance the thermoelectric performance of n-type Bi₂(Te,Se)₃ alloys. The deformation-induced dynamic recrystallization is remarkably suppressed due to the reduction of nucleation sites and the release of deformation stress by liquid phase, contributing to a weakened carrier scattering and enhanced carrier mobility. The liquid eutectic phase also facilitates the rotation of grains and enhanced (000<i>l</i>) texture, further improving carrier mobility. In addition, the dense dislocations and lattice distortion introduced into the matrix reduce the lattice thermal conductivity. As a result, a high <i>zT</i> value of 1.1 at 400 K is obtained, about 75% increment over the normal one-step hot deformed alloys. This work not only demonstrates a simple and efficient technique for achieving superior n-type Bi₂Te₃-based materials, but also elucidates the important role of liquid eutectic phase in hot deformation.