Enhanced thermoelectric properties of p-type argyrodites Cu8GeS6 through Cu vacancy

Abstract

Cu8GeS6 compound with room temperatures orthorhombic phase, high temperatures cubic phase and the low intrinsic lattice thermal conductivity is a potential thermoelectric material. However, its performance is limited by low electrical conductivity. In this study, p-type polycrystalline Cu8(1-x)GeS6 (x = 0.03, 0.05, 0.08, 0.10) are successfully synthesized through solid-phase reaction and hot pressing. The electrical conductivity of the wide band gap semiconductor Cu8GeS6 as verified by the density functional theory (DFT) calculation can be greatly enhanced by intentionally introduced Cu vacancy. Also, the calculation indicates that the top of valence band is mainly comprised of the Cu 3d orbitals. As a consequence, the Hall carrier concentrations are significantly enhanced to ∼1018 cm−3 with Cu vacancy. Owing to the improved electrical conductivity, the compound with nominal composition of Cu7.36GeS6 reaches a maximum zT ∼0.29 at 819 K.