Highly Converged Valence Bands and Ultralow Lattice Thermal Conductivity for High-Performance SnTe Thermoelectrics.

SnTe, an analogue of high-performance thermoelectric material PbTe, has recently attracted wide attention for thermoelectric energy conversion. However, large energy gap (DeltaEv) between the light and heavy hole valence bands, intrinsic Sn-vacancies and high thermal conductivity result in inferior thermoelectric performance in pristine SnTe. Here, we have demonstrated a two-step optimization strategy to improve the thermoelectric performance of SnTe via modulating the electronic structure and phonon transport. We have first optimized the electrical transport of self-compensated SnTe (i.e., Sn1.03Te) via Ag doping, which resulted in an optimized carrier concentration. Further, Mn doping in Sn1.03-xAgxTe resulted in highly converged valence bands, which improved the Seebeck coefficient markedly. DeltaEv decreases to 0.10 eV in Sn0.83Ag0.03Mn0.17Te compared to the value of 0.35 eV in pristine SnTe. As a result of optimized carrier concentration and highly converged valence bands, we obtained a high power factor ~24.8 mW/cmK2 at 816 K in Sn0.83Ag0.03Mn0.17Te. The lattice thermal conductivity of Sn0.83Ag0.03Mn0.17Te reached to an ultralow value ~0.3 W/mK at 865 K, which is one of lowest values reported so far in SnTe-based crystalline thermoelectrics, due to the formation of Ag7Te4 nanoprecipitates in SnTe matrix. As a result of the synergy among optimized carrier concentration, valence band convergence and ultralow lattice thermal conductivity, we obtained a high thermoelectric figure of merit, zT ~1.45 at 865 K in Sn0.83Ag0.03Mn0.17Te.