Miscibility Gap in the Phase Diagrams of Thermoelectric Half-Heusler Materials CoTi $$_{1-x}Y_x$$ 1 - x Y x Sb (Y = Sc, V, Mn, Fe)

Abstract

The half-Heusler system CoTi $${_{1-x}Y_x}$$ Sb (Y = Sc, V, Mn, Fe) has been investigated by means of an ab initio-based mean-field model which provides phase diagrams of alloys. Co(Ti,Y)Sb materials show a miscibility gap, which leads to spontaneous demixing within a spinodal region. The results are compared with experimental investigations of microstructure and transport properties of the alloys. The thermoelectric properties of the solid solution were investigated comprehensively by measuring the temperature dependence of the Seebeck coefficient as well as electrical and thermal conductivity. Compared with pure CoTiSb, the thermal conductivity of substituted CoTi $${_{0.9}Y_{0.1}}$$ Sb was significantly reduced by approximately 53% for Y = V. Here, we report on the effect of phase separation in the Co(Ti,Y)Sb system and its consequences for the thermoelectric figure or merit.