Electronic structure investigation of V1−xNbxO2 mixed oxide by XES and XPS

The mixed oxide system V_1−xNb_xO₂ (x ≦ 0.12) has been studied by X-ray and photo-emission spectroscopy as a function of the composition. The metal L valence band spectra (VL_III and NbLβ_2.15) with increasing Nb concentration change their width and relative band intensity substantially pointing to charge flow and hybridization effects. The XPS valence band for x ≧ 0.04 indicates a total d band shift of 0.4 eV relative to smaller Nb concentrations. The measured core level spectra at higher Nb doping x ≈︁ 0.10 support the expected existence of V³⁺-Nb⁵⁺ pairs. A comparison of different X-ray spectra and the XPS valence band spectrum for x = 0.08 exhibits a more stronger V3d localization relative to Nb4d, favouring charge transfer and bonding variations with Nb doping. Our spectroscopial data confirm the established ideas concerning the electronic structure of rutile-like compounds and its change at the phase transition point.