Influence of nitriding on thermoelectric properties of Al- and Mn- doped iron disilicides

Iron disilicide based thermoelectric materials with the designed compositions of FeSi₂, Fe_0.90Mn_0.06Al_0.04Si₂, and FeAl_0.05Si₂ were prepared by rapid solidification, nitriding treatment and hot uniaxial pressing. Samples with a dominant β-FeSi₂ phase and a small amount of residual α and ε phases were obtained after annealing at 800°C for 20 hours. Transport property measurements showed that the Seebeck coefficients were markedly enhanced by nitriding for all samples. Both the electrical and the thermal conductivities were decreased by nitriding, but more strongly for Al-doped samples than for the samples with Al and Mn double doping. As a total effect, the figure of merit was significantly increased by either Al single doping or Mn and Al double doping. It shows that nitriding is more effective for double doping. The maximum figure of merit of Z=1.63×10^-4K^-1 at 573°C was obtained for nitrided Fe_0.90Mn_0.06Al_0.04Si₂.