Ternary MIn2S4 (M = Mn, Fe, Co, Ni) thiospinels - crystal structure and thermoelectric properties

The combined structural, magnetic and thermoelectric study of polycrystalline ternary MIn2S4 (M = Mn, Fe, Co, Ni) thiospinels is presented. All compounds crystallize with MgAl2O4-type structure. Rietveld refinement analysis confirmed that the preferred crystallographic position of transition metal element changes from mainly tetrahedral 8a for Mn to exclusively octahedral 16d for Ni (i.e. increase of the inversion parameter). The magnetic susceptibility measurements revealed M-elements to possess 2+ oxidation state in MIn2S4. All these compounds order antiferromagnetic with Néel temperature TN ranging from 5–13 K. Studied thiospinels are n-type semiconductors with large values of electrical resistivity ρ > 0.6 Ω∙m at RT. An increase of inversion parameter leads to reduction of determined activation energies, as well as to the more disorder-like behavior of thermal conductivity. The highest thermoelectric figure of merit ZT was observed for MIn2S4 with M = Fe, Ni, which adopt inverse spinel structure.