Electron-energy-loss near edge structures of six-fold-coordinated Zn in MgO.

Electron-energy-loss near edge structures (ELNES) at the Zn-L(2,3) edge and the O-K edge have been measured for 10 mol% ZnO-doped MgO, and were compared with spectra from reference materials. In order to interpret the spectra, first principles molecular orbital calculations were made using model clusters composed of 125 and 153 atoms. Photoabsorption cross sections (PACS) were computed at the Slater's transition state in which a half-filled core hole was included in the self-consistent calculations. The difference in the coordination numbers of Zn was found well distinguishable by the Zn-L(2,3)-edge ELNES. The experimental spectra in the first 25 eV were well reproduced by the theoretical PACS. In this energy region, the Zn-L(2,3)-edge ELNES from four-fold coordinated Zn showed four sets of peaks, whereas the six-fold coordinated Zn exhibits three sets of peaks. The origin of these peaks can be explained by the point symmetry within the first coordination unit. A small shift toward the lower energy side was observed in the O-K edge ELNES of the ZnO-doped MgO as compared with pure MgO. This can be ascribed to the lower energy of the Zn-4s orbital as compared with the Mg-3s orbital, which is the common mechanism to the difference in the band gap between MgO and ZnO.