非化学量論組成 Fe₂VAl 合金の熱電特性に及ぼす遷移元素置換の効果

抄録

  We report on the thermoelectric properties of (Fe_2-x-yM_y)V_1+xAl alloys (M=Ir and Rh) with compositions x=0, 0.02 and 0.05, and y=0-0.10. While a small deviation from the stoichiometric Fe₂VAl composition causes an enhancement in the Seebeck coefficient, a slight substitution of Ir or Rh for Fe leads to a further increase in the Seebeck coefficient, reaching -170 μV/K at 300 K for x=0.05 and y=0.03, which is larger than that of the stoichiometric Fe₂VAl-based alloys so far reported. Substantial enhancements in the Seebeck coefficient of the off-stoichiometric Fe₂VAl-based alloys could be due to a modification in the band structure on the conduction band side around the Fermi level. The doping of heavier atoms such as Ir reduces more effectively the thermal conductivity, while retaining the low electrical resistivity as well as the large Seebeck coefficient, thus resulting in an increased figure of merit of 8.6×10^-4 K^-1 at 300 K.