Microstructure and thermoelectric properties of SiGe-added higher manganese silicides

Polycrystalline higher manganese silicides (HMS) with SiGe-additions were synthesized and their microstructure and thermoelectric properties were investigated. The SiGe-addition was found to have introduced dual effects, namely the substitution of Ge and the precipitation of Si–Ge phases. The volume ratio of MnSi striations in HMS was decreased by increasing amount of SiGe-addition, while the Si–Ge precipitations with various Si/Ge ratios were simultaneously formed. The electrical conductivity and the electronic contribution of the thermal conductivity were increased by SiGe-addition. However, the Seebeck coefficient showed insignificant change and the phonon thermal conductivity was effectively reduced, which was attributed to the enhanced scattering of phonons resulted by the substitution of Ge atoms for Si. The maximum ZT of 0.5 was achieved in polycrystalline MnSi1.733–2%SiGe at 550 °C showing 25% improvement compared to the pure HMS.