Ultrahigh Thermoelectric Figure of Merit and Enhanced Mechanical Stability of p-type AgSb_1–xZn_xTe₂

High-performance thermoelectric materials are desirable in the lower-medium temperature range (450–650 K) for low-grade waste heat recovery. We report a thermoelectric figure of merit (zT) of 1.9 at 585 K in p -type AgSb 1– x Zn x Te 2, which is the highest value measured among the p -type materials in the 450–650 K range. A high average thermoelectric figure of merit (zT avg ) of 1.3 is achieved in AgSb 0.96 Zn 0.04 Te 2 . Moreover, the AgSb 1– x Zn x Te 2 sample exhibits a hardness value of ∼6.3 GPa (nanoindentation), which is significantly higher than that of the pristine AgSbTe 2 . Substitution of Zn in AgSbTe 2 suppresses the formation of intrinsic Ag 2 Te impurity phases, which indeed increases the thermal and mechanical stability. The lattice thermal conductivity for AgSb 1– x Zn x Te 2 samples is reasonably reduced compared to that of the pristine AgSbTe 2 because of the significant solid solution point defect phonon scattering. Aliovalent Zn 2+ doping in Sb 3+ sites in AgSbTe 2 increases the p -type carrier concentration, which boosts the electrical conductivity of AgSb 1– x Zn x Te 2 .