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

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 (zTs) 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 (000l) 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 zT 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.