Thermoelectric properties of β-FeSi2 single crystals prepared with 5N source material

Thermopower and electrical conductivity of undoped beta-FeSi2 single crystals have been investigated between 4K and 350K in dependence on the deviation from strict stoichiometry within the homogeinity range. The crystals have been prepared by chemical transport reaction in a closed system with iodine as transport agent using high purity source material. Both electrical conductivity and thermopower depend on the composition within the homogeinity range which is explained by different intrinsic defect concentrations at the Si-rich and Fe-rich phase boundaries. Low ohmic material was only obtained by additional doping. At the Si-rich phase boundary the thermopower shows at low temperatures a significant phonon drag contribution with /S/>1000 mu V/K.