Thermoelectric Properties of β-FeSi<SUB>2</SUB> Mechanically Alloyed with Si and C

Abstract

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 β-FeSi2 phase from the mixture of the α-Fe2Si5 and ε-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 β-phase with a dispersion of a small amount of ε-phase particles. The amount of the ε-phase decreases with increasing amounts of (Si+C) addition. A lot of fine α-SiC particles around 20 nm 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 α-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.