Mixed-valence vanadium oxides studied by XPS

We have investigated several mixed-valence vanadium oxides, single-crystals by X-ray photoelectron spectroscopy (XPS). Many studies have been performed on V2O5, VO2 and V2O3. Less investigated are the mixed-valence compounds, as the V3O5, V4O7 and V6O13 systems, which are discussed here. They exhibit as a function of temperature metal-insulator transitions (MIT), A detailed analysis for these systems, above and below the MIT temperature is given. The core-level spectra for the mixed-valence compounds are compared with those of the related systems, V2O5, VO2 and V2O3 having V5+, V4+ and V3+ ions, respectively. The electronic structures for all investigated oxides are characterized by strong V 3d-O 2p hybridization and they are discussed in relation with similar studies. (C) 2000 Elsevier Science B.V. All rights reserved.