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Glasses with the composition 51.9 SiO2 21.2 MgO 21.2 Al2O3 5.7 ZrO2 (in mol%) are transformed into high- and low-quartz solid solution glass ceramics, by a heat treatment at 950 °C for different periods of time. X-ray absorption near edge structure (XANES) studies at the Zr L2,3 edge show a transition of the Zr coordination number from approximately 6 in the base glass to 8 after completion of crystallization. Scanning transmission electron microscopy in combination with energy dispersive X-ray spectroscopy element mapping shows that this coordination change is linked to structural alterations that occur in the samples upon annealing: in the base glass, Zr is evenly distributed, whereas in the crystalline samples, it occurs as nanocrystalline ZrO2. A comparison of the Zr L2,3 spectra of the glass ceramic samples with spectra of tetragonal ZrO2 reference samples also indicates that the ZrO2 nanocrystals in the samples are of tetragonal nature, a finding that is also backed by a comparison of the spectra with ab initio multiplet calculations of the Zr L2,3 edges from ZrO2 in different modifications.

Transition-metal L-2,L-3 XANES spectra are widely used to determine coordination and valence of the target ion. For decades, experimental fingerprinting, i.e., the comparison with spectra obtained from known reference compounds was the way to interpret spectral features. This approach was based on the common understanding that only anions in the first coordination sphere would determine the near-edge structure, and crystalline references were selected accordingly. Using ab initio charge-transfer multiplet calculations, we demonstrate that there is also a significant impact on spectral features from the second-nearest neighbor cations. This finding is exemplified for three fresnoite-type vanadates, namely Ba2VSi2O8 (BVS), K2VV2O8 (KVV), and Rb2VV2O8 (RVV). The theoretical treatment provides evidence that for the three compounds studied it is not variable bond lengths or bond angles between vanadium and oxygen that make the V-L-2,L-3 XANES spectra different, but the interaction of the target vanadium ions with its neighboring cations (Si for BVS, V for KVV and RVV), which dominates. Therefore, we conclude that simple fingerprinting can result in misleading interpretations when interactions with second-nearest neighboring cations are not taken into account. Ab initio charge-transfer multiplet calculations of spectral shapes (theoretical fingerprinting) should be employed instead to get a deeper understanding of structure-spectra relationships, or the choice of reference spectra should take into account second-nearest neighbors. Our findings are similarly important for the interpretation of electron energy-loss near-edge (ELNES) spectra.

Zr-L2,3 XANESs of tetravalent zirconium oxides with different coordination numbers and local symmetries are systematically investigated by ab initio multiplet calculations using fully relativistic molecular spinors for model clusters. Experimental Zr-L2,3 XANESs are obtained for SrZrO3, m-ZrO2 (monoclinic) and t-ZrO2 (tetragonal). The theoretical spectra are in good agreement with the experimental data. The multiplet effects are found to play essential roles in determining the peak shape. The shapes of L3- and L2-edges are systematically different. The intensity ratios of the doublet peaks at both L3- and L2-edges are found to be sensitive to the coordination number of Zr. The ratio can therefore be used to estimate the coordination number of Zr in such oxides.

The effect of oxygen vacancy on Ti-L_[2, 3] electron energy-loss near-edge structures (ELNES) of BaTiO_3 was theoretically investigated through ab initio multiplet calculation. The presence of an oxygen vacancy influences spectral features not only at the nearest neighbor Ti site but also at Ti sites further from the oxygen vacancy. The effects of different oxygen vacancy concentrations were also investigated. Based on this study, it was concluded that the detection limit for oxygen vacancy with Ti-L_[2, 3] ELNES is approximately 1%.

First principles calculations are performed for the interpretation of the L-2,L-3 x-ray absorption spectrum of calcium oxide and calcium fluoride. The first principles calculations are based on configuration interaction (CI) calculations using fully relativistic molecular spinors. The first principles results are compared to experimental data and also to calculations based on a semi-empirical crystal field multiplet model and also on a multichannel multiple scattering method. We show that the CI calculations show good agreement with experiment, both for bulk and for surface experiments. The remaining differences with experiment and between the theoretical models are discussed in detail.

The purpose of this work is to compare the two different procedures to calculate the L2,3 x-ray absorption spectra of transition-metal compounds: (1) the semi-empirical charge transfer multiplet (CTM) approach and (2) the ab initio configuration-interaction (CI) method based on molecular orbitals. We mainly focused on the difference in the treatment of ligand field effects and the charge transfer effects in the two methods. The reduction of multiplet interactions due to the solid state effects has been found by the ab initio CI approach. We have also found that the mixing between the original and the charge transferred configurations obtained by the ab initio CI approach is smaller than that obtained by the CTM approach, since charge transfer through the covalent bonding between metal and ligand atoms has been included by taking the molecular orbitals as the basis functions.

X-ray-absorption near-edge structures (XANES) at the transition metal (TM) L2,3-edge of TiCl4 and VOCl3 are calculated by the all-electron configuration interaction (CI) method using fully-relativistic molecular spinors with density functional theory (DFT). The electronic excitation from molecular spinors mainly composed of ligand p atomic spinors to those of TM-3d spinors, i.e., the charge transfer, is included by taking additional electronic configurations in the CI. The effects of the ligand field and the charge transfer on the TM-L2,3 XANES are investigated by an ab-intio method. The reduction of inter-electron interaction due to the covalent bonding between TM and ligand atoms has been found. The contribution of charge transferred configuration is small at the initial state of TM-L2,3 XANES while the significant amount of charge transferred configuration is found at the final states. The spectral shapes of TM-L2,3 XANES of both TiCl4 and VOCl3 are strongly modified by the charge transfer effects.