Strong hybridization in vanadium oxides: evidence from photoemission and absorption spectroscopy

We present x-ray photoemission spectra of the vanadium oxides V2O5, VO2, and V2O3, and their analysis in terms of a simple cluster model based on the Anderson impurity Hamiltonian. The electronic structure of these materials is characterized by a strong V 3d-O 2p hybridization energy which exceeds the energy scales related to on-site Coulomb correlation and metal-ligand charge transfer. This result is at variance with the usual Mon-Hubbard picture, but agrees with recent studies of other early 3d transition metal compounds. The V 3d groundstate occupations obtained by the cluster-model analysis are considerably higher than the values derived from the formal valencies. Covalency also affects the exchange splitting observed in the V 3s core-hole spectra. X-ray absorption measurements and resonant photoemission spectroscopy at the V 2p-3d threshold provide further evidence for a strong V 3d-O 2p coupling.