Electronic signature of the vacancy ordering in NbO(Nb3O3)

Abstract

We investigated the electronic structure of the vacancy-ordered $4d$-transition-metal monoxide $\mathrm{NbO}\phantom{\rule{0.28em}{0ex}}({\mathrm{Nb}}_{3}{\mathrm{O}}_{3})$ using angle-integrated soft- and hard-x-ray photoelectron spectroscopies as well as ultraviolet angle-resolved photoelectron spectroscopy. We found that density-functional-based band-structure calculations can describe the spectral features accurately provided that self-interaction effects are taken into account. In the angle-resolved spectra we were able to identify the so-called `vacancy' band that characterizes the ordering of the vacancies. This together with the band-structure results indicate the important role of the very large inter-Nb-$4d$ hybridization for the formation of the ordered vacancies and the high thermal stability of the ordered structure of niobium monoxide.