X-Ray Photoemission Spectroscopic Study on the Electronic States in the Mixed System between Charge-Transfer and Mott-Hubbard Type Metals: Co_0.91S and V_0.91S

In order to study the change of the electronic states from the charge-transfer(CT) type metal to the Mott-Hubbard(MH) one, X-ray photoemission spectra are measured on the NiAs-type (Co_1-xV_x)_0.91S (x ≤ 0.50) and V_0.91S. The asymmetry parameter α for S 2s and 2p core level spectra decrease with increasing x. This result indicates that the local density of states of S atoms at the Fermi level decreases as x increases; the system changes from the CT-type metal to the MH-one with x. The change in V 2p line shape with x suggests the possibility of the considerable hybridization between V 3d and S 3p in (Co_1-xV_x)_0.91S at lower x region. This feature would be related to the appearance of the extra peak at binding energy E_B = 2-3 eV in the valence band X-ray photoemission spectra.