First principles calculations on the thermoelectric properties of bulk Au2S with ultra-low lattice thermal conductivity**Project supported by the National Natural Science Foundation of China (Grant Nos. 11504312, 11775102, and 11805088), the National Basic Research Program of China (Grant No. 2015CB921103), China Postdoctoral Science Foundation (Grant No. 2018M641477), Guangdong Provincial Department of Science and Technology, China (Grant No. 2018A0303100013), and the

Abstract

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.