Angle-Resolved Photoemission Analysis on Electronic Structures and Thermoelectric Properties of Off-Stoichiometric Fe 2− x V 1+ x Al

The electronic states of Heusler(L2(1))-type off. stoichiometric Fe2-xV1+xAl have been investigated by soft X-ray angle-resolved photoelectron spectroscopy (ARPES) in order to clarify the origin of their large thermoelectric powers, which cannot be explained in terms of the rigid band model. In off-normal and normal ARPES, Fe2.05V0.95Al shows a weakly dispersive bulk band around the binding energy of 0.3 eV in the Gamma-X direction and an almost dispersion-less one around 0.3 eV in a gap of dispersive bulk bands in the Gamma-L direction, which is attributed to the anti-site Fe defect. At the Gamma point, the bulk band does not appear to cross the Fermi level E-F, consistent with the rigid band model for the excess Fe content bringing about the increase in the valence electrons, but no band crossing E-F down is found at the X point. The anti-site Fe defect states near E-F might push up the band at the X point and cause the p-type thermoelectric properties, unexpected with the rigid band picture. The change in the electronic structures and thermoelectric properties are discussed on the off-stoichiometry and substitution of the forth element.