X-ray spectra and electronic structure of Li x NbO2 superconductor and other niobium oxide compounds

X-ray emission Nb and OK spectra and O1s total photoelectron yield spectra for superconductor Li_0.71NbO₂ and other niobium oxide compounds NbO, BaNb₄O₆, Ba₂Nb₅O₉, BaNb₅O₈. LiNbO₂, NbO₂, LiNbO₃ were investigated. It was found that in stoichiometric LiNbO₂, niobium oxidation degree is 3+. Under the lithium deintercalation down to Li_0.71NbO₂ composition, the niobium ions oxidation degree increases up to 3.3+. As more electrons are supplied by Nb to fill the O2p band, the degree of O2p-Nb4d hybridization is increased. Using the full-potential linear muffin-tin orbital method, the self-consistent band structure calculations of Li _x NbO₂ (x=1.0; 0.7; 0.5) compounds were carried out. Agreement between partial Nb4d and O2p densities of states and corresponding X-ray spectra was observed. For thex=0.7; 0.5 the Fermi level is placed on the slope of sharp density of states peak formed mostly by the Nb4d states. With the decrease ofx thep-d hybridization becomes stronger, although remains well below the values typical for the high-temperature superconductors.