INFLUENCE OF OXYGEN VACANCIES ON THE ELECTRONIC-STRUCTURE OF YTTRIUM-OXIDE

The influence of oxygen vacancies on the electronic structure of yttrium oxide was investigated both experimentally and theoretically. By means of X-ray absorption spectroscopy, at the yttrium K and L(II) edges and at the oxygen K edge, information on the local densities of states of various orbital symmetries, around each type of atom, was obtained. The total density of states in the valence band was studied using X-ray photoelectron spectroscopy. Experimental results were compared with those obtained on stoichiometric yttria. The evolution of the densities of states is well reproduced by self-consistent, semiempirical tight-binding calculations applied to clusters of increasing size, in which oxygen vacancies are introduced. The charge transfer between oxygen and yttrium is modified, as experimentally observed from the study of the O KLL Auger line shape. The decrease of the local atomic charge on oxygen is theoretically confirmed by the tight-binding calculations, showing a tendency toward a more covalent bond in nonstoichiometric yttria.