A theoretical approach to La L1-edge XANES spectra of La complex oxides and their local configuration

Abstract

The characteristic peaks (pre-edge peaks) in the La L1-edge X-ray absorption near edge structure (XANES) of various La complex oxides were analyzed by both experimental and theoretical approaches. The pre-edge peak areas are correlated with the bond angle analysis (BAA) parameter, which we proposed as an indicator of the centrosymmetry or disorder of the local configuration of the La site. The origin of the pre-edge peak and the parameterization criteria of the BAA parameter were evaluated using theoretical calculations based on molecular orbital theory and multiple scattering theory. The theoretical calculations showed that the origin of the pre-edge peak at the La L1-edge is electric dipole transition from 2s to unoccupied states generated by p-d hybridization. Medium-scale theoretical simulations of the La L1-edge XANES spectra of thousands of virtual La aqueous complex models verified that the parameterization criteria of the BAA parameter are applicable to local configuration analysis of La.

Local Structure Study of Lanthanide Elements by X‐Ray Absorption Near Edge Structure Spectroscopy

“…Therefore, we performed feasibility tests of the BAA index for local structure analysis. We first computationally generated thousands of virtual aqueous La model complexes with different local structures, La(H 2 O) n (n=7, 8, 9, 10, 12) . Then, the relationship between the BAA indexes and pre‐edge peak areas of the model La complexes was evaluated.…”

“…We first computationally generated thousands of virtual aqueous La model complexes with different local structures, La(H 2 O) n (n = 7, 8, 9, 10, 12). [33] Then, the relationship between the BAA indexes and pre-edge peak areas of the model La complexes was evaluated. As shown in Figure 5, the pre-edge peak areas of simulated La L 1 -edge XANES spectra of virtual La complexes are correlated with the BAA indexes.…”

Utilization of La₂O₃ as a Support of Ga₂O₃ Photocatalyst to Enhance Activity on CO₂ Reduction with Water

“…Figure 5 shows La L1-edge and Ga K-edge XANES spectra. The former are clearly different before and after use, indicating the change of a bonding nature of La from the oxide (La2O3) to the carbonate [NaLa(CO3)2] [31]. On the other hand, the Ga K-edge XANES spectra did not show an appreciable change, indicating that most of Ga remained as the oxide.…”

Polarized High-Energy-Resolution Fluorescence Detection-X-ray Absorption Near-Edge Structure of the (La,Sr)(Al,Ta)O3 Single Crystal at the La L1-Edge

“…X-ray absorption spectroscopy (XAS) is a powerful analytical tool for analyzing the electronic and local geometric structures of virtually all elements in the periodic table. For lanthanide (Ln) elements, we investigated the characteristic features observed at the Ln L 1 and L 3 -edge XANES spectra in relation to their local structure/symmetry. − For example, the areas of the pre-edge peaks in the La L 1 -edge XANES spectra of La complex oxides systematically increased as the number of adjacent oxygen atoms coordinated to La decreased from 12 to 7 atoms. This phenomenon is derived from the d-p orbital hybridization at the unoccupied levels just below the absorption edge, which heavily depends on the ligand field environment.…”