Thermoelectric properties of hot-pressed β-FeSi2 with yttria dispersion by mechanical alloying

The β-FeSi2 (n-type Fe0.98Co0.02Si2) sintered bodies with dispersion of Y2O3 particles were synthesized by mechanical alloying of Fe–Si powder with Y2O3 powder and subsequent hot pressing. The effects of Y2O3 addition on the thermoelectric properties of the β-FeSi2 were investigated. The thermal conductivity of the β-FeSi2 was significantly reduced by dispersion of fine Y2O3 particles on the β phase matrix. On the other hand, the electrical resistivity increased with increasing amount of Y2O3. The Seebeck coefficient was enhanced by Y2O3 addition, especially below 800 K, corresponding to the extrinsic conductive region of the β-FeSi2. Consequently, the figure of merit was significantly improved by 2 mass% Y2O3 addition. The energy dispersive X-ray spectroscopy (EDX) analysis revealed that the added Y2O3 was partially decomposed and a small amount of Y was dissolved in the β phase matrix. Based on this fact, the enhancement of the Seebeck coefficient caused by Y2O3 addition is considered to be due to reduction in carrier concentration which resulted from this Y solution as a p-type dopant in the β phase matrix, and the behavior of the Seebeck coefficient was found to be well consistent with that of the Y-doped samples synthesized by Y powder addition.