Soft X-ray Photoelectron Spectroscopy of Heusler-type Thermoelectric Alloys Fe_2-x-yIr_yV_1+xAl

Abstract

The valence-band and core-level electronic structures of Heusler-type alloys Fe_2-x-yIr_yV_1+xAl have been investigated by soft X-ray photoelectron spectroscopy, which shows that the valence-band structure near the Fermi level E_F is drastically altered by the off-stoichiometric concentration change x, while the position of E_F is moderately tuned by the Ir substitution y in a rigid-band-like manner. These changes in the electronic structure lead to the remarkable enhancement of their thermoelectric power. For x > 0, the V 2p core level spectra also show the appearance of new chemically shifted components in the low binding energy side of the main line, which may be attributed mainly to the excess V occupying the Fe site (the anti-site V) as well as V in the surface layer. The present results suggest that the drastic and moderate changes in the electronic structure may be caused by the emergence of such anti-site defects in the off-stoichiometric Fe and V concentrations and by the common band formation between the Fe 3d bands and the substituted Ir 5d states, respectively.