Effect of powder oxidation on thermoelectric properties of Fe-Si alloys

Oxygen was incorporated into Fe-Si alloys sintered bodies by thermal oxidat ion of FeSi2, Fe0.95Mn0.05Si2 and Fe0.95Co0.05Si2 powders at 550 degreesC a nd 650 degreesC, in air. The Seebeck coefficient and electrical conductivit y were measured in the range of 100-600 degreesC and the effect of oxygen o n thermoelectricity was clarified. Oxygen gave rise to an increase of the f raction of a residual metallic epsilon -phase, lowering the Seebeck coeffic ient. Addition of oxygen to FeSi2 prevented both densification during sinte ring and transformation from metallic phases to semiconducting beta -phase during annealing treatment. Electrical conductivity of FeSi2 was dependent on the quantity of residual epsilon -phase, SiO2 and porosity in the sinter ed specimens. In an intermediate temperature range, polaron model could be applied to explain the variation of the Seebeck coefficient with temperatur e.