A First-Principles Theoretical Study on the Thermoelectric Properties of the Compound Cu₅AlSn₂S₈

A new compound of Cu₅AlSn₂S₈, which contained earth-abundant and environment-friendly elements and had a diamond-like crystal structure, was designed, and its electronic structure and thermoelectric transport properties from 300 K to 700 K were investigated by first-principles calculations, Boltzmann transport equations, and a modified Slack’s model. The largest power factors of Cu₅AlSn₂S₈ at 700 K were 47.5 × 10¹⁰ W m⁻¹ K⁻² s⁻¹ and 14.7 × 1010 W m⁻¹ K⁻² s⁻¹ for p- and n-type semiconductors, respectively. The lattice thermal conductivity of Cu₅AlSn₂S₈ was calculated with its shear modulus and isothermal bulk modulus, which were also obtained by first-principles calculations. The lattice thermal conductivity was 0.9–2.2 W m⁻¹ K⁻¹ from 300 K to 700 K, relatively low among thermoelectric compounds. This theoretical study showed that Cu₅AlSn₂S₈ could be a potential thermoelectric material.