Effect of Re Substitution on the Phase Stability of Complex MnSiγ

Abstract

The thermal stability of different higher manganese silicide (HMS, MnSiγ) phases were analyzed in order to understand the thermal degradation of thermoelectric properties, which is strongly correlated with the phase stability. Synchrotron diffraction experiments were performed at 27°C, 300°C, and 600°C to obtain good statistical data. The Rietveld refinements by using the 3-dimensional commensurate crystal structure approach revealed that a phase transition from Mn27Si47 (γ = 1.741) to Mn15Si26 (γ = 1.733) takes place in the case of non-doped HMS above 500°C accompanied by a small amount of MnSi precipitation. These γ values showed good consistency with 1.744 (300°C) to 1.732 (600°C) determined from (3 + 1)-dimensional incommensurate crystal analyses. Notably, this phase transition behavior or the temperature dependence of γ = cMn/cSi was not observed in Re-substituted HMS. A heavy element substitution proved to be one of the most efficient methods for HMS to become a practical thermoelectric material.