Ab-initio calculations of near-edge structures in electron-energy-loss spectra for metal-oxide ceramics
CHRISTIAN ELSAESSER and Sibylle Koestlmeier
Seestr. 92, D-70174 Stuttgart, Germany.

Ab-initio band-structure calculations were performed for main-group metal-oxide single crystals as model systems for ceramic materials, MgO, alpha-Al2O3, and MgAl2O4, in order to develop a theoretical scheme for a quantitative analysis and interpretation of experimentally recorded electron-energy-loss spectra (EELS). Site- and angular-momentum-projected densities of states (PDOS) of the conduction-electron bands, which can be related to measured energy-loss near-edge structures (ELNES), were obtained in the framework of the local density functional theory, employing norm-conserving pseudopotentials for core-valence interactions and a mixed basis of plane waves and localized functions for the representation of valence- and conduction-electron states. The approximations inherent to this approach and their consequences are discussed in detail. A "fingerprinting" scheme based on oxygen K edges is demonstrated to yield satisfactory results. The calculation of cation edge structures, however, was found to be more involved. For K edges an improved treatment of core relaxation processes is illustrated, and for L edges the role of the local symmetry around excited cations is analyzed.