Soft X-ray photoemission study of thermoelectric alloys Fe 2 − x − yIr yV 1 + xAl and Fe 2 − xV 1 + x − yTi yAl

Abstract

The valence-band and core-level photoemission spectra of n-type thermoelectric Heusler( L2 1)-type alloys Fe 2 − x − y Ir y V 1 + x Al and p-type ones Fe 2 − x V 1 + x − y Ti y Al have been studied to clarify the origin of the enhancement of their thermoelectric power. It is found that the excess V content x (V-rich for x > 0 and Fe-rich for x < 0) causes the drastic change in the valence-band electronic structure within the binding energy of ∼0.7 eV near the Fermi level E F and the evolution of the satellite structures in the V 2 p core-level spectra with x increased. These spectral features are ascribed to the formation of the Fe or V anti-site defects in the off-stoichiometric alloys with non-zero x. The shift of the valence-band and core-levels towards the high (low) binding energy side is observed on partial substitution y of Ir (or Ti) for Fe (or V), which is attributed to the E F shift due to the common band formation with the Ir 5 d or Ti 3 d states incorporated into the main Fe–V 3 d bands. The enhancement of the thermoelectric power in those Heusler-type alloys can be explained in terms of the observed changes in the valence-band electronic structure near E F.