Ultrahigh Thermoelectric Figure of Merit and Enhanced Mechanical Stability of p-type AgSb1–xZnxTe2

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 AgSb1–xZnxTe2, which is the highest value measured among the p-type materials in the 450–650 K range. A high average thermoelectric figure of merit (zTavg) of 1.3 is achieved in AgSb0.96Zn0.04Te2. Moreover, the AgSb1–xZnxTe2 sample exhibits a hardness value of ∼6.3 GPa (nanoindentation), which is significantly higher than that of the pristine AgSbTe2. Substitution of Zn in AgSbTe2 suppresses the formation of intrinsic Ag2Te impurity phases, which indeed increases the thermal and mechanical stability. The lattice thermal conductivity for AgSb1–xZnxTe2 samples is reasonably reduced compared to that of the pristine AgSbTe2 because of the significant solid solution point defect phonon scattering. Aliovalent Zn2+ doping in Sb3+ sites in AgSbTe2 increases the p-type carrier concentration, which boosts the electrical conductivity of AgSb1–xZnxTe2.