First-principles study of the vibrational characteristics of the heavy element substitution on Cu3SbSe3

Abstract

Understanding the thermal transport in solids has been an emerging topic since its importance in many fields, such as thermoelectrics. Some typical thermoelectric compounds which has unique vibrational characteristics have been investigated, such as Cu3SbSe3. Experiments have shown that Cu3SbSe3 exhibits abnormally low and nearly temperature-independent lattice thermal conductivity. In this work, we theoretically studied the vibrational characteristics of Ag3SbSe3, Cu3BiSe3 and Cu3SbTe3, which are the substitution of prototype Cu3SbSe3 with heavier elements on each atomic sites. These compounds all exhibit low bulk moduli and group velocities; Ag3SbSe3 and Cu3BiSe3 show larger atomic displacement parameters than Cu3SbSe3 and thus lower Debye temperatures. Both results lead to abnormally low lattice thermal conductivities of these compounds. Furthermore, heavier element substitutions Cu3BiSe3 and Cu3SbTe3 reduce the band gaps, which are expected to be beneficial to higher electrical conductivities than that of Cu3SbSe3. Therefore, due to the lower lattice thermal conductivities and favourable electrical transport properties, Ag3SbSe3 and Cu3BiSe3 are promising thermoelectric candidates.