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 clust ers composed of 125 and 153 atoms. Photoabsorption cross sections (PACS) we re computed at the Slater's transition state in which a half-filled core ho le 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-e dge 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 fr om 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 s mall 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, whic h is the common mechanism to the difference in the band gap between MgO and ZnO. (C) 2001 Elsevier Science B.V. All rights reserved.