Achieving a High Average Thermoelectric Figure of Merit (ZT) in Medium-Entropy SnTe Alloys

Entropy engineering is becoming a crucial strategy for enhancing the performance of thermoelectric materials, as increasing configurational entropy can influence the phase structure and localized microstructure profoundly. SnTe, as a lead-free alternative to PbTe, has drawn intensive attention for decades. Despite the outstanding maximal figures of merit have been reported in SnTe-based alloys, the average figure of merit across the working temperature range still stays at quite a low level as compared to PbTe-based materials. In this work, based on the SnTe-based Sn_1-xGe_xTe solid solution, we increased its configurational entropy to the medium-entropy range (1.0R < ΔS < 1.5 R) by Sb₂Te₃ alloying and Pb doping. Increasing configurational entropy substantially enlarged the effective mass of charge carriers while significantly reducing the lattice thermal conductivity, thereby realizing effective decoupling between electrical and thermal transports. As a result, we achieved a maximal ZT value of 1.31 at 723 K with an impressively high average ZT value of 0.89 across 323-773 K in the sample (Sn_0.5Ge_0.425Pb_0.075Te)₁₀Sb₂Te₃. This work offers a generalizable methodology for designing high-performance thermoelectric materials.