Thermoelectric properties of chevrel-type sulfides AMo₆S₈ (A=Fe, Ni, Ag, Zn, Sn, Pb, Cu)

Thermoelectric properties of Chevrel-type sulfides AMo₆S₈ (A=Fe, Ni, Ag, Zn, Sn, Pb, Cu) were investigated with respect to many advantageous characteristics of the Chevrel compounds for thermoelectric applications. The electrical conductivity, σ, was 10^2.5 S·cm^-1<σ<10³ S·cm^-1 for most of the samples from room temperature to 1000°C; AgMo₆S₈ gave the largest σ up to 250°C. The Seebeck coefficient, S, was positive for all the samples, indicating the p-type conduction. All the S values were 10 μV·K^-1<S<80 μV· K^-1, and AgMo₆S₈ showed the smallest S, probably owing to the higher hole concentration for A=Ag compared to other samples. The maximum S²σ value was attained by SnMo₆S₈, reaching ca. 1.7 × 10^-4 W·m^-1· K^-2 at 800°C. All the κ values were 1 W·m^-1·K^-1<κ<3 W·m^-1·K^-1 from room temperature to 1000°C. The maximum Z value was ca. 0.07 × 10^-3 K^-1 attained by SnMo₆S₈ at 800°C.