Transport properties of rocksalt-type cluster sulfides V4GeS8 and Mn substitution effect

Abstract

We experimentally and theoretically investigated the electronic and thermoelectric properties of rocksalt-type cluster sulfides V4-xMnxGeS8 (x = 0, 0.02, 0.05). For a polycrystalline sample of V4GeS8, the lnρ-T−1 curve shows good linearity over 250 K. On the other hand, the lnρ-T−1/4 curve shows linearity at less than 250 K. This result indicates that the Arrhenius type is dominant over 250 K and the 3D variable range hopping is dominant in the low-temperature region. For the Mn substitution V4-xMnxGeS8 (x = 0.02, 0.05), the absolute value of ρ and S decreases with increasing x. This result indicates that the hole doping occurred by the substitution of V3+ to Mn2+. The calculated HOMO of V4GeS8 using density functional theory calculation shows that the V-3d orbital in the V4S4 cluster is dominant. This result indicates that the conduction holes pass through V4S4 to other V4S4.