Thermoelectric properties of β-FeSi/sub 2/ with dispersion of SiC by mechanical alloying

Abstract

The thermoelectric properties of the hot-pressed n-type Fe/sub 0.98/Co/sub 0.02/Si/sub 2/ and p-type Fe/sub 0.92/Mn/sub 0.08/Si/sub 2/ 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 /spl beta/-FeSi/sub 2/ phase from the mixture of the /spl alpha/-Fe/sub 2/Si/sub 5/ and /spl epsi/-FeSi phases during hot-pressing for 1 h. Both of the hot-pressed n-type and p-type samples are composed of mostly the /spl beta/-phase with dispersion of a small amount of /spl epsiv/-phase particles. The amount of the /spl epsiv/-phase decreases with increasing amount of (Si+C) addition. A lot of fine /spl alpha/-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 FeSi/sub 2/ due to the decrease in the amount of metallic /spl epsi/-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 FeSi/sub 2/ probably due to the decrease in the amount of metallic /spl epsi/-phase with low resistivity and the increase in the amount of /spl 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 FeSi/sub 2/ due to the dispersion of fine /spl alpha/-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 FeSi/sub 2/.