Electronic structure of yttrium oxide

The electronic structure of stoichiometric ${\mathrm{Y}}_2$ ${\mathrm{O}}_3$ is studied both theoretically and experimentally. X-ray absorption, performed through total-yield measurements at the K and ${\mathit{L}}_{\mathrm{II}}$ edges of yttrium atoms and the K edge of oxygen atoms, through total-yield measurements has given access to empty states of various orbital characters in the conduction band. The shape of the valence band was obtained by means of photoemission spectroscopy. These results are compared with self-consistent, semiempirical tight-binding calculations applied to clusters of increasing sizes, which lead to local densities of states. We show that the quasi-octahedral local environment of the yttrium atoms is responsible for the splitting of their d levels. However, this ligand-field approach is not sufficient to account for the yttrium and oxygen K thresholds, nor for the shape of the valence band for which band effects are important. The two-peak structure of the oxygen K edge results from the hybridization of the O p orbitals with the ${\mathit{e}}_{\mathit{g}}$ and ${\mathit{t}}_{1\mathit{u}}$ states on the yttrium atoms. Three peaks are detected in the valence band: We show that they suggest the existence of direct-hopping terms between neighboring oxygen atoms. Finally, the various calculations have given an estimate of the degree of covalency of the Y-O bond.