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

• Published in: Journal of alloys and compounds 2021-08, Vol.871, p.159548, Article 159548
• Main Authors: Hashikuni, Katsuaki, Suekuni, Koichiro, Usui, Hidetomo, Chetty, Raju, Ohta, Michihiro, Takabatake, Toshiro, Ohtaki, Michitaka
• Format: Article
• Language: English
• Subjects: Carrier density; Comparative studies; Conduction bands; Electrical resistivity; Electronic structure; Electrons; Figure of merit; First principles; Orbitals; Seebeck coefficient; Seebeck effect; Spinel; Substitutes; Sulfide; Thermoelectric materials; Thermoelectricity; Titanium
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2021.159548

•Thermoelectric properties and electronic structures of Cu2TryTi4−yS8 (Tr = Sc, Co) thiospinels were investigated.•The thiospinels exhibit n-type degenerate semiconducting electronic properties.•The Sc and Co substitutions for Ti decrease the electron carrier concentration in a same manner.•Seebeck coefficient for Tr = Co is remarkably larger than that for Tr = Sc.•The Co substitution leads to the increased electronic density of states to boost the Seebeck coefficient. [Display omitted] 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)S6 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.