Exploring structure and thermoelectric properties of p-type Ge1−xInxSb4Te7 compounds†

Abstract

Thermoelectric (TE) properties of layered Ge–Sb–Te compounds have received extensive attention owing to their decent TE performance with high electrical conductivity and low thermal conductivity. Here, we report the structure and TE properties of In-doped GeSb₄Te₇ compounds prepared by vacuum hot-pressing sintering. We determined that GeSb₄Te₇-based compounds exhibit site-occupational disorder due to Ge/Sb cation mixing and that In-doping in GeSb₄Te₇ compounds significantly lowers the thermal conductivity, enhances the Seebeck coefficient, and improves the power factor of pristine GeSb₄Te₇. Noticeably, the room-temperature power factor of the Ge_0.925In_0.075Sb₄Te₇ sample can be increased by 174% compared to that of the GeSb₄Te₇ sample. The optimized electrical properties and the suppressed thermal conductivity result in a maximal TE figure-of-merit of 0.62 achieved in Ge_0.925In_0.075Sb₄Te₇ at 750 K, which is about 41% higher than that of the pristine sample. Our theoretical calculations indicate that the band structure, the density of states, and the local crystal structure of GeSb₄Te₇ can be modified by the In-doping, which contributes to improving the TE properties of GeSb₄Te₇-based compounds. Our studies on the atomic-scale structure of GeSb₄Te₇ and the effect of In-doping on the TE performance are helpful to the configurational entropy design and the performance optimization of layered TE materials.