High-resolution Al L_2,3-edge x-ray absorption near edge structure spectra of Al-containing crystals and glasses: coordination number and bonding information from edge components

Abstract

High-resolution Al L 2,3 -edge x-ray absorption near edge structure (XANES) spectra have been measured in selected materials containing aluminium in 4-, 5-and 6-coordination. A shift of 1.5 eV is observed between the onset of [4] Al and [6] Al L 2,3 -edge XANES, in agreement with the magnitude of the shift observed at the Al K-edge. The differences in the position and shape of low-energy components of Al L 2,3 -edge XANES spectra provide a unique fingerprint of the geometry of the Al site and of the nature of Al-O chemical bond. The high resolution allows the calculation of electronic parameters such as the spin-orbit coupling and exchange energy using intermediate coupling theory. The electron-hole exchange energy decreases in tetrahedral as compared to octahedral symmetry, in relation with the increased screening of the core hole in the former. Al L 2,3 -edge XANES spectra confirm a major structural difference between glassy and crystalline NaAlSi 2 O 6 , with Al in 4-and 6-coordination, respectively, Al coordination remaining unchanged in NaAl 1−x Fe x Si 2 O 6 glasses, as Fe is substituted for Al.

Investigation of acidic dissolution of mixed clays between pH 1.0 and −3.0 using Si and Al X-ray absorption near edge structure

“…Relatively little information exists on the Al L 2,3 -edge XANES of minerals; however, two recent studies have utilized high resolution XANES spectroscopy at the Al L 2,3 -edge (Hu et al, 2008;Weigel et al, 2008). These studies provide some fundamental explanations for the shape and position of features in Al L 2,3 -edge XANES spectra that are consistent with the current study.…”

“…In general, the L 2,3 -edge spectra in the 76-84 eV range is dominated by two separate regions, which are termed peak A and peak B in this study (Fig. 5b) following the convention set by Weigel et al (2008) and other researchers (Mo and Ching, 2001). The peak A region was often split into two or three distinct peaks (A 0 , A 00 , A 000 ; Fig.…”

“…5a). Several previous studies attribute this shift to a change in the average Al-O bond length, from 1.9 Å for 6 Al phases to 1.7 Å for 4 Al phases (Kato et al, 2001;Weigel et al, 2008).…”

“…Only the Al K-edge TEY spectra were presented as the corresponding FY spectra were nearly identical to the TEY results. The Al L 2,3 -edge TEY spectra were significantly affected by surface charging, as was observed by Weigel et al (2008); therefore, only the Al L 2,3 -edge FY spectra were presented. The Al K-edge onset energy (peak A 0 or A) result from electron transitions from the 1s to 3p Al orbitals (Cabaret et al, 1996).…”

“…Additionally, Cabaret et al (1996) and Wu et al (1999) demonstrate that major peak features above the initial peak result from multiple scattering and medium-range Al order. In the Al L 2,3 -edge spectra, peak A results from the excitation of Al 2p electrons to Al 3s and 3d orbitals (Hu et al, 2008;Weigel et al, 2008). Weigel et al (2008) indicate that, similar to the Si L 2,3 -edge spectra, the onset edge is split by spin-orbit coupling, which results in the separation of the 2p core state into 2p 1/2 (L 2 -edge; A 0 ) and 2p 3/2 levels (L 3 -edge; A 00 ), which comprise the peak A region (Fig.…”