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 Cu 26 Tr 2 M 6 S 32 (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( t 2 ) and d( e ) orbitals of Tr interact with the valence band maxima at the Γ and M points, respectively. The hybridization between the Tr- t 2 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.