Kazuo Soda1, Shota Harada1, Toshimitsu Hayashi1, Masahiko Kato1, Fumihiro Ishikawa2, Yuh Yamada2, Shin-ichi Fujimori3 and Yuhji Saitoh3
1Department of Quantum Engineering, Graduate School of Engineering, Nagoya University, Nagoya 464-8603
The electronic states of Heusler(L21)-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 Γ-X direction and an almost dispersion-less one around 0.3 eV in a gap of dispersive bulk bands in the Γ-L direction, which is attributed to the anti-site Fe defect. At the Γ point, the bulk band does not appear to cross the Fermi level EF, consistent with the rigid band model for the excess Fe content bringing about the increase in the valence electrons, but no band crossing EF down is found at the X point. The anti-site Fe defect states near EF 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.
angle-resolved photoelectron spectroscopy, electronic structure, anti-site defect state, thermoelectric properties, off-stoichiometric iron-based Heulser-type alloys
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