Thermoelectric properties of β-FeSi2 mechanically alloyed with Si and C

The thermoelectric properties of the hot-pressed n-type Fe0.98Co0.02Si2 and p-type Fe0.92Mn0.08Si2 mechanically alloyed with Si and C powders have been investigated. It has been found that mechanical alloying (MA) even for a short period is very effective for forming the beta-FeSi2 phase from the mixture of the alpha-Fe2Si5 and epsilon-FeSi phases during hot-pressing at 1173 K for 1 h. Both of the hot-pressed n-type and p-type samples are composed of mostly the beta-phase with a dispersion of a small amount of epsilon-phase particles. The amount of the F-phase decreases with increasing amounts of (Si+C) addition. A lot of fine alpha-SiC particles around 20 nn form in the samples mechanically 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 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. 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 maxima at 3-4 mass%(Si+C) for both n-type and p-type FeSi2.