A comparative study of thermoelectric Cu2TrTi3S8 (Tr = Co and Sc) thiospinels: Enhanced Seebeck coefficient via electronic structure modification

We studied the electronic structures of Cu2TryTi4-yS8 (Tr = Sc, Co) thiospinels by combining thermoelectric measurements and first-principles calculations. The thiospinels showed n-type and metallic properties governed by a conductive network composed of edge-shared (Ti/Tr)S-6 octahedra. The substitutions of Sc and Co for Ti decreased the electron carrier concentration in a similar manner, leading to increases in both the electrical resistivity and Seebeck coefficient. Although the electrical resistivity was equivalent for Tr = Sc and Tr = Co, the Seebeck coefficient was remarkably enhanced for Tr = Co as compared to that for Tr = Sc. The enhanced Seebeck coefficient in the Co-substituted system was ascribed to the increased density of states of conduction band near the Fermi level due to the partial replacement of Ti-3d orbitals by Co-3d orbitals. Owing to the electronic structure modification, a higher dimensionless thermoelectric figure of merit (ZT= 0.2 at y = 1-1.5) was achieved for the Co-substituted samples at 673 K. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The electronic structures of Cu2TryTi4-yS8 thiospinels were studied using a combination of thermoelectric measurements and first-principles calculations. Substituting Sc and Co for Ti reduced electron carrier concentration, leading to increased electrical resistivity and Seebeck coefficient. Co-substituted samples showed remarkably enhanced Seebeck coefficient at 673 K, resulting in higher dimensionless thermoelectric figure of merit.