Electronic structure of niobium oxides

Abstract

The results of X-ray fluorescence measurements of niobium metal and its oxides (NbO, NbO 2 and Nb 2O 5) are presented. Non-resonant Nb M 4,5 and O Kα X-ray emission spectra (XES) have been measured at the Advanced Light Source (ALS, Berkeley). The experiments are compared with self-consistent band structure calculations of niobium metal and niobium oxides. We find the experimental spectra are consistent with band structure calculations of niobium metal and the oxides NbO 2 and Nb 2O 5. The difference between experimentally determined Nb M 4,5 XES of NbO and the calculated spectrum of Nb 1.0O 1.0 is understood on the basis of vacancies. We have mimicked the natural structure of NbO, which contains vacancies amounting to 25% in both sublattices. The electronic DOS of Nb 0.75O 75 is characterised by the formation of additional subbands connected with vacancy states. The calculated electronic structure based on this model is consistent with the XES measurements.