Thermoelectric Properties of Chevrel-Phase Sulfides Mx Mo6S8 (M: Cr, Mn, Fe, Ni)

Chevrel-phase sulfides M (x) Mo6S8 (M, Cr, Mn, Fe, Ni; x: 1.3, 2.0) were prepared by reacting appropriate amounts of M, Mo, and MoS2 powders. The samples were then consolidated by pressure-assisted sintering to fabricate dense compacts. While Cr1.3Mo6S8 crystallized in a triclinic structure, Mn1.3Mo6S8, Fe1.3Mo6S8, and Ni2.0Mo6S8 crystallized in a hexagonal structure. The Seebeck coefficient, electrical resistivity, and thermal conductivity of the sintered samples were measured over the temperature range of 300 K to 973 K. All the samples exhibited a positive Seebeck coefficient. The Seebeck coefficient, electrical resistivity, and thermal conductivity of M1.3Mo6S8 (M: Cr, Mn, Fe) were almost identical and increased with temperature. However, the corresponding values and temperature dependent behavior of Ni2.0Mo6S8 were different from those of M1.3Mo6S8 (M: Cr, Mn, Fe). For Ni2.0Mo6S8, as temperature increased, the Seebeck coefficient and thermal conductivity increased while the electrical resistivity decreased. The highest value of the thermoelectric figure of merit (0.17) was observed in Cr1.3Mo6S8 at 973 K.