Enhanced figure of merit in antimony telluride thermoelectric materials by In–Ag co-alloying for mid-temperature power generation

V–VI compounds have been widely investigated as promising thermoelectric materials for room temperature refrigeration. In this paper, we report a systematic study of high performance p-type antimony–telluride-based thermoelectric alloys for mid-temperature power generation. Indium alloying is adopted as an effective approach to widen the band gap and suppress the detrimental bipolar conduction at elevated temperatures. The low Seebeck coefficient of binary antimony telluride, arising from high hole concentration generated by antisite defects, was enhanced by raising the antisite defect energy formation. Meanwhile, the induced alloying scattering significantly reduced the lattice thermal conductivity. Ag acceptor doping was used to further suppress the detrimental bipolar conduction and improve the figure of merit, zT. These combined effects resulted in a peak zT of ∼0.92 at 710 K for the hot-pressed Ag_0.01Sb_1.85In_0.15Te₃ alloy, whereas the average zT_av of 0.8 was obtained in the temperature range of 500–710 K, indicating a great potential of the alloy for application in mid-temperature thermoelectric power generation