Interaction between Cu-S-Based Sphalerite-like Frameworks and Interstitial Cations in Colusite-Based Thermoelectric Materials

Cu-S-based multicomponent compounds with sphalerite-like frameworks have garnered attention as midtemperature p-type thermoelectric (TE) materials. Their valence bands, primarily comprising Cu-S hybridized orbitals, control electronic properties. Herein, for colusites Cu₂₆Tr₂M₆S₃₂ (Tr = V, Nb, and Ta; M = Ge and Sn), we investigate the distinctive interaction between the Cu-S-based sphalerite-like framework and Tr at the interstitial tetrahedral sites to improve the Seebeck coefficient (S). According to ab initio calculations, the d(t₂) and d(e) orbitals of Tr interact with the valence band maxima at the Γ and M points, respectively. The hybridization between the Tr-t₂ and S orbitals (under the presence of Tr), along with structural modifications, reduces the energy of the Γ band maximum toward the Fermi level, thereby increasing S. This understanding is expected to be a foundation for further advancements in the TE properties of Cu-S-based compounds.