First principles calculations on the thermoelectric properties of bulk Au₂S with ultra-low lattice thermal conductivity

Sulfide nanocrystals and their composites have shown great potential in the thermoelectric (TE) field due to their extremely low thermal conductivity. Recently a solid and hollow metastable Au₂S nanocrystalline has been successfully synthesized. Herein, we study the TE properties of this bulk Au₂S by first-principles calculations and semiclassical Boltzmann transport theory, which provides the basis for its further experimental studies. Our results indicate that the highly twofold degeneracy of the bands appears at the Γ point in the Brillouin zone, resulting in a high Seebeck coefficient. Besides, Au₂S exhibits an ultra-low lattice thermal conductivity ( ~0.88 W·m^-1·K^-1 at 700 K). At 700 K, the thermoelectric figure of merit of the optimal p-type doping is close to 1.76, which is higher than 0.8 of ZrSb at 700 K and 1.4 of PtTe at 750 K. Our work clearly demonstrates the advantages of Au₂S as a TE material and would greatly inspire further experimental studies and verifications.