Thermoelectric performance and electronic properties of transition metal monosilicides

Abstract

We have performed a comprehensive series of lattice structure, band structure, electrical transport, and thermoelectric performances measurements for MnSi, FeSi, and CoSi single crystals. The band structure of this family of compounds demonstrates significant changes across the Fermi level as the number of 3d-electron is increased with transition metal substitution. In particular, a crossover from metal to semiconductor and back to semimetal has been observed in this series of compounds. Practical measurements (electrical transport and thermoelectric performances) are combined with theoretical calculations to qualify the reliability of band structures. By means of standard thermal activation simulations of electrical resistivity for FeSi, we identify a narrow band gap ∼57 meV, which is well consistent with our band calculation result. A double sign reversal of the Seebeck coefficient for FeSi suggests that both electrons and holes are contributed to electrical transport, indicating that the electronic structure of FeSi is substantially influenced by hole-doped (MnSi) and electron-doped (CoSi) effects.