Thermoelectric properties of β-FeSi2 with dispersion of SiC by mechanical alloying.

The thermoelectric properties of the hot-pressed n-type Fe0.98Co0.02Si2 and p-type Fe0.92Mn0.08Si2 mechanically alloyed with Si and carbon powders have been investigated. It has been found that MA even after a short period is very effective to form the beta-FeSi2 phase from the mixture of the alpha-Fe2Si5 and epsilon-FeSi phases during hot-pressing for 1 h. Both of the hot-pressed n-type and p-type samples are composed of mostly the beta-phase with dispersion of a small amount of epsilon-phase particles. The amount of the epsilon-phase decreases with increasing amount of (Si+C) addition. A lot of fine alpha-SiC particles around 20 nm forms in the samples mechanical alloyed for 20h and hot-pressed at 1173 K for 1 h. The addition of(Si+C) markedly increases the thermoelectric power of both n-type and p-type FeSi2 due to the decrease in the amount of metallic epsilon-phase and the thermoelectric power values are at maximum at 3-4 mass%(Si+C) for both cases. The electrical resistivity increases with increasing amount of (Si+C) addition for both n-type and p-type FeSi2 probably due to the decrease in the amount of metallic epsilon-phase with low resistivity and the increase in the amount of alpha-SiC with high electrical resistivity as well as grain refinement. The addition of(Si+C) markedly decreases the thermal conductivity of both n-type and p-type FeSi2 due to the dispersion of fine alpha-SIC particles, which results in the marked increase in the figure of merit. The figure of merit values are at maximum at 3-4 mass%(Si+C) for both n-type and p-type FeSi2.