Soft-x-ray emission and the localp-type partial density of electronic states inY2O3: Experiment and theory

Photon-excited yttrium $M_{\mathrm{I}\mathrm{V},\mathrm{V}}$, and electron-excited oxygen $K$ x-ray emission spectra for yttrium oxide are presented. It is shown that, as in the case of yttrium metal, the decay of $M_{\mathrm{IV}}$ vacancies does not contribute substantially to the oxide $M_{\mathrm{I}\mathrm{V},\mathrm{V}}$ emission. The valence emission is interpreted in a one-electron picture as a measure of the local $p$-type partial density of states. The yttrium and oxygen valence emission bands are very similar and strongly resemble published photoelectron spectra. Using local-density approximation electronic structure calculations, we show that the broadening of the Y-$4p$ signal in yttrium oxide relative to Y metal are due to two inequivalent yttrium sites in ${\mathrm{Y}}_2$ ${\mathrm{O}}_3$. Features present in the oxide, but not the metal spectrum, are the result of overlap (hybridization) between the Y-$4p$ wave function and states in the oxygen $2s$ subband.