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

A two-step optimization strategy is used to improve the thermoelectric performance of SnTe via modulating the electronic structure and phonon transport. The electrical transport of self-compensated SnTe (that is, Sn1.03 Te) was first optimized by Ag doping, which resulted in an optimized carrier concentration. Subsequently, Mn doping in Sn1.03-x Agx Te resulted in highly converged valence bands, which improved the Seebeck coefficient. The energy gap between the light and heavy hole bands, i.e. ΔEv decreases to 0.10 eV in Sn0.83 Ag0.03 Mn0.17 Te compared to the value of 0.35 eV in pristine SnTe. As a result, a high power factor of ca. 24.8 μW cm-1  K-2 at 816 K in Sn0.83 Ag0.03 Mn0.17 Te was attained. The lattice thermal conductivity of Sn0.83 Ag0.03 Mn0.17 Te reached to an ultralow value (ca. 0.3 W m-1  K-1 ) at 865 K, owing to the formation of Ag7 Te4 nanoprecipitates in SnTe matrix. A high thermoelectric figure of merit (z T≈1.45 at 865 K) was obtained in Sn0.83 Ag0.03 Mn0.17 Te.