SOFT-X-RAY ABSORPTION-SPECTROSCOPY OF VANADIUM-OXIDES

We present the V2p and O1s X-ray absorption spectra of V2O3, VO2 and V2O5. The V2p spectra show strong multiplet effects caused by large 2p-3d and 3d-3d Coulomb and exchange interactions. The spectra exhibit noticeable chemical shifts and completely different multiplets. The shapes of the multiplet are related to the symmetry and spin of the ground state. The V2p spectrum of V2O3 can be simulated by an atomic-multiplet calculation projected in the appropriate crystal field. The O1s spectra are related to unoccupied Op character mixed in the conduction band. The spectra reflect V3d bands near the edge and V4sp bands at higher energies. The V3d bands are split by crystal field effects. Changes in the relative intensities are related to differences in the metal-ligand hybridization. The extra dispersion of the V3d bands in V2O3 is attributed to larger metal-metal interactions. The O1s spectrum of VO, compares favorably to a symmetry-projected band structure calculation. Finally, the O1s spectra of VO, taken at room temperature (insulator phase) and at T almost-equal-to 120-degrees-C (metallic phase) show clearly the splitting of the V3d(parallel-to) band across the metal-insulator transition.