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

The thermoelectric properties of the hot-pressed n-type Fe_0.98Co_0.02Si₂ and p-type Fe_0.92 Mn_0.08Si₂ 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 β-FeSi₂ phase from the mixture of the α-Fe₂Si₅ and ε-FeSi phases during hot-pressing for 1 h. Both of the hot-pressed n-type and p-type samples are composed of mostly the β-phase with dispersion of a small amount of ε-phase particles. The amount of the ε-phase decreases with increasing amount of (Si+C) addition. A lot of fine α-SiC particles around 20 nm form in the samples mechanical alloyed for 20 h 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 ε-phase and the thermoelectric power values are at a 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 ε-phase with low resistivity and the increase in the amount of α-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 α-SiC particles, which results in the marked increase in the figure of merit. The figure of merit values are at a maximum at 3-4 mass% (Si+C) for both n-type and p-type FeSi₂