Thermoelectric properties of β-FeSi2 with Si dispersoids formed by decomposition of α-Fe2Si5 based alloys

The microstructures of Fe2Si5 based alloys fabricated by spark plasma sintering and the subsequent heat treatment were investigated by X-ray diffraction (XRD) analysis and scanning electron microscope (SEM). The results showed that a two-phase structure consisting of β-FeSi2 and Si dispersoids was obtained by the eutectoid decomposition of α-Fe2Si5 phase during annealing. The thermoelectric properties of Fe2Si5 based alloys were also investigated as compared with the stoichiometric FeSi2 based alloys. It was found that Fe2Si5 based alloys have the same conduction mechanism with stoichiometric FeSi2 alloys doped with Mn and Co, respectively. An increase in carrier scattering caused by Si particles was observed in both Mn- and Co-doped alloys. The effect of Si dispersoids on Seebeck coefficient and electrical resistivity was discussed. Results show that the excessive Si dispersoids in Fe2Si5 based alloys could improve the transport properties of the material, especially for the Co-doped alloys.