Thermoelectric properties of /spl beta/-FeSi/sub 2/ single crystals prepared with 5N source material

Thermopower and electrical conductivity of undoped /spl beta/-FeSi/sub 2/ single crystals have been investigated between 4 K and 350 K in dependence on the deviation from strict stoichiometry within the homogeneity 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 homogeneity 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 /spl mu/V/K.