Angle-Resolved Photoemission Analysis of Electronic Structures for Thermoelectric Properties of Off-Stoichiometric Fe_2–xV_1+xAl Alloys

Abstract

The electronic states of Heusler (L2₁)-type off-stoichiometric Fe_2–xV_1+xAl alloys have been investigated by soft x-ray angle-resolved photoelectron spectroscopy (ARPES) to clarify the origin of the remarkable increase in thermoelectric power, which cannot be explained by the rigid-band model. In off-normal and normal ARPES, Fe_2.05V_0.95Al shows weakly dispersive bulk bands from the binding energy of 0.3 eV at the Γ point in the Γ–X and Γ–L directions, and an almost dispersionless one around 0.3 eV in the gap of dispersive bulk bands in the Γ–L direction, which is attributed to antisite Fe defects. At the Γ point, the bulk bands do not appear to cross the Fermi level E_F, which is consistent with the rigid-band model for excess Fe content, but no band crossing E_F is found at the X point. The antisite Fe defect states near E_F might push up the band at the X point and cause p-type thermoelectric properties, which is unexpected for the rigid-band model. The change in electronic structures and thermoelectric properties for the off-stoichiometry and substitution by a forth element is discussed.