Thermoelectric properties of Fe 0.98Co 0.02Si 2 with ZrO 2 and rare-earth oxide dispersion by mechanical alloying

Abstract

The n-type Co-doped β-FeSi 2 (Fe 0.98Co 0.02Si 2) with dispersion of several oxides, such as ZrO 2 or several rare-earth oxides (Y 2O 3, Nd 2O 3, Sm 2O 3 and Gd 2O 3), was synthesized by mechanical alloying and subsequent hot pressing. The effects of these oxide dispersions on the thermoelectric properties of Fe 0.98Co 0.02Si 2 were investigated. ZrO 2 was decomposed in the β phase, and the ZrSi and ε-FeSi phases, which are metallic phases, were formed in the samples with ZrO 2 addition. The Seebeck coefficient and the electrical resistivity were significantly decreased with increasing amount of ZrO 2, indicating that a part of the Zr atoms was substituted for Fe atoms in the β phase. In the case of the samples with rare-earth oxide addition, a decomposition of a large amount of these added oxides did not occur. However, the rare-earth oxide addition caused a slight increase in the amount of the ε phase. The Seebeck coefficient was significantly enhanced by the rare-earth oxide addition especially in the low temperature range. These facts indicated that a small amount of rare-earth oxides was decomposed in the β phase, and rare-earth elements were substituted for Fe atoms as a p-type dopant, resulting in the decrease in the carrier concentration. The rare-earth oxide addition was also effective in reducing the thermal conductivity.