Influence of nitrogenizing and Al-doping on microstructures and thermoelectric properties of iron disilicide materials

Aluminium doped iron disilicide based thermoelectric materials FeAlxSi2 (x=0.05, 0.10) were prepared by rapid solidification, nitrogenizing treatment and hot uniaxial pressing. β-FeSi2 phase with dispersed silicon have been obtained for all the hot-pressed samples after annealing at 1073 K for 20 h. The Seebeck coefficient α, electrical conductivity σ and thermal conductivity κ were measured from room temperature to 973 K. It was found that the Seebeck coefficients were markedly enhanced by the nitrogenizing treatment, but they decreased with increasing aluminium concentration x. The nitrogenizing treatment also significantly decreased the thermal conductivities of the Al-doped samples, especially for the sample with higher aluminium concentration. The maximum figure of merit of Z=1.55×10−4 K−1 at 743 K was obtained for FeAl0.05Si2 without nitrogenizing. It is concluded that nitrogenizing treatment is promising to improve the thermoelectric properties for more heavily Al-doped FeSi2.