The β-FeSi₂ Formation and Thermoelectric Power of the FeSi₂+Co Base Alloys

Abstract

Temperature dependence of thermoelectric power and resistivity was measured for the β-FeSi₂ based cast alloys on which n-type Co doping was performed with or without Cu addition. The Cu-free alloy shows a homogeneous eutectic microstructure consisting of metallic phases α-FeSi₂ and ε-FeSi, while the Cu-doped alloy has a quite heterogeneous microstructure dominated by coarse ε-FeSi dendrites in the α-FeSi₂ matrix. Adequate heat treatment condition for the semiconductor β-FeSi₂ phase formation has been evaluated as annealing at 923 K for less than 50 h, which is lower in temperature and shorter in duration than previously reported for alloys prepared by powder metallurgy. The resistivity measurement with the aid of microstructure observation has revealed that the β-FeSi₂ formation takes place and almost finishes at very early stage of annealing process. Addition of Cu effectively promotes the β-FeSi₂ formation rate of the present cast alloys.