Scattering Mechanisms and Compositional Optimization of High‐Performance Elemental Te as a Thermoelectric Material

Abstract

Abstractp‐Type elemental tellurium (Te) has been found to be a promising thermoelectric (TE) material due to its high band degeneracy near the valence band maximum, and has exhibited a high zT ≈ 1.0 above 600 K. However, when forming Te1−xSex solid solutions, the maximal zTs are reduced because of the severely decreased carrier concentration. It is demonstrated that Se alloying is beneficial for enhancing TE performance of elemental Te provided the carrier concentration is optimized. Through Se alloying, the lattice thermal conductivity is remarkably suppressed by the induced large mass and strain field fluctuation, while the power factor can be maintained at a relatively high value as a result of the moderate alloying scattering potential, the unchanged density‐of‐state effective mass, and the optimized carrier concentration in Te1−xSex alloys. Notably, a positive temperature dependence of carrier mobility is observed near room temperature in Te1−xSex, which is proven to be caused by grain boundary scattering. A maximal zT ≈ 1.05 at 625 K is realized in Te0.93Se0.04As0.03 alloys, about 9% higher than the Se‐free Te. The conversion efficiency between 300 and 625 K is also improved ≈18% via Se alloying.