Ternary M In 2 S 4 ( M = Mn, Fe, Co, Ni) Thiospinels – Crystal Structure and Thermoelectric Properties

A combined structural, magnetic and thermoelectric study of polycrystalline ternary M In 2 S 4 ( M = Mn, Fe, Co, Ni) thiospinels is presented. All compounds crystallize with MgAl 2 O 4 ‐type structure. Rietveld refinement analysis confirmed that the preferred crystallographic position of transition metal element changes from mainly tetrahedral 8 a for Mn to exclusively octahedral 16 d for Ni (i.e. increase of the inversion parameter). Magnetic susceptibility measurements revealed M ‐elements to possess 2+ oxidation state in M In 2 S 4 . All these compounds order antiferromagnetically with Néel temperatures T N ranging from 5–13 K. The studied thiospinels are n ‐type semiconductors with large values of electrical resistivity ρ > 0.6 Ω · m at room temperature. An increase of the inversion parameter leads to a reduction of the determined activation energies, as well as to a more disorder‐like behavior of thermal conductivity. The highest thermoelectric Figure of merit ZT was observed for M In 2 S 4 with M = Fe, Ni, which adopt inverse spinel structure.