Preparation of SiC dispersed Fe0.98Co0.02Si2 by pressureless sintering with Cu and Si addition and its thermoelectric performance

The SiC-dispersed beta -FeSi2 compounds were synthesized by pressureless sintering with Cu and Si addition without a subsequent heat treatment for phase beta formation. The effects of Cu and Si addition on the phase transformation, sintering behavior, and thermoelectric performance of these samples were investigated. Cu addition significantly accelerated the beta phase formation during the pressureless sintering, and the samples with Cu were mostly composed of the beta phase with a small amount of the residual alpha and epsilon phases. Cu addition was effective for densification; Cu-Si liquid phase formation resulted in a high relative density of over 90%. The thermoelectric power and thermal conductivity of the pressurelessly sintered samples with Cu addition were quite lower and higher, respectively, than those of the hot-pressed sample. The differences were caused by a larger amount of metallic phases, such as the epsilon and Cu-Si phases. The figure of merit of these samples was about 1/3 of that of the hot-pressed sample, indicating that Cu addition completely ruined the enhancement of thermoelectric performance obtained by SiC dispersion. The addition of Si to the samples with Cu decreased the amount of the metallic epsilon phase and increased the amount of the semiconducting phase beta through the reaction epsilon + Si --> beta. The thermoelectric power and thermal conductivity of the samples with Cu were markedly improved by Si addition, which resulted in a significant increase in the figure of merit. The values of the figure of merit for the samples with Cu and Si addition were almost the same as that of the hot-pressed sample with SiC dispersion.