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XANES
About: XANES is a research topic. Over the lifetime, 7737 publications have been published within this topic receiving 188032 citations.
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TL;DR: A general procedure to analyse the pre-edges in 1s x-ray absorption near edge structure (XANES) of transition metal oxides and coordination complexes is developed and large cross section at the 3d-band region due to the strong metal-metal interactions, which are oxygen mediated.
Abstract: We develop a general procedure to analyse the pre-edges in 1s x-ray absorption near edge structure (XANES) of transition metal oxides and coordination complexes. Transition metal coordination complexes can be described from a local model with one metal ion. The 1s 3d quadrupole transitions are calculated with the charge-transfer multiplet program. Tetrahedral coordination complexes have more intense pre-edge structures due to the local mixing of 3d and 4p states, implying a combination of 1s 3d quadrupole and 1s 4p dipole transitions. Divalent transition metal oxides can be described similar to coordination complexes, but for trivalent and tetravalent oxides, additional structures are visible in the pre-edge region due to non-local dipole transitions. The 1s 4p dipole transitions have large cross section at the 3d-band region due to the strong metal-metal interactions, which are oxygen mediated. This yields large intensity in the 3d-band region but at a different energy than the local 1s 3d quadrupole transitions because of smaller core-hole effects due to the delocalization of the excited electron.
275 citations
TL;DR: The X-ray absorption near-edge spectra (XANES) of the L1 tungsten edge in WO3/Al2O3 samples indicate that the symmetry of the Tungsten environment depends on both the surface coverage and the presence of coordinated water as mentioned in this paper.
Abstract: The X-ray absorption near-edge spectra (XANES) of the L1 tungsten edge in WO3/Al2O3 samples indicate that the symmetry of the tungsten environment depends on both the surface coverage and the presence of coordinated water. At coverages of less than 1/3 monolayer, in the absence of coordinated water, the XANES spectrum indicates a distorted tetrahedral structure for the surface tungsten oxide species. Samples exposed to air at room temperature have water molecules coordinated to the surface tungsten oxide species and produce an octahedral site symmetry, but the water is removed by heating to 500 "C. The Raman spectra of the W03/A1203 samples are consistent with a distorted tetrahedral tungsten oxide environment and, in addition, show features due to W=O and W-0-W bonds. These results suggest that the surface tungsten oxide is present as both isolated and dimeric tetrahedra. At coverages approaching a monolayer, in the absence of coordinated water, a significant fraction of the surface tungsten oxide sites appears to have a distorted octahedral environment in the XANES spectra. At this high coverage the effect of coordinated water molecules is much less evident than at low coverage. The Raman results, however, only provide information about the tetrahedral component because the Raman cross section of the tetrahedral tungsten oxide is much higher than the octahedral tungsten oxide. The Raman spectra show features of W4 and W-0-W bonds in the tetrahedral fraction of the surface tungsten oxide monolayer on alumina. These observations are consistent with a surface complex where the supported tungsten oxide has formed a polymeric structure on the alumina support composed of W04 and W06 units jointed in infinite chains.
273 citations
TL;DR: In this article, a series of anorthite-diopside eutectic glasses containing 1 wt% 57 3+ /ΣFe ratios from X-ray absorption near edge structure spectra were investigated.
Abstract: Fe K-edge X-ray absorption near edge structure (XANES) spectra were recorded for a series of anorthite-diopside eutectic glasses containing 1 wt% 57 3+ /ΣFe ratios from XANES spec- tra were investigated. The energy of the 1s ∅ 3d pre-edge transition centroid was found to correlate linearly with the oxidation state. Correlations also exist with the energy of the K absorption edge and the area of peaks in the derivative spectrum associated with the 1s ∅ 4s and crest (1s ∅ 4p) transi- tions. The Fe 3+ /ΣFe ratios determined from linear combinations of end-member spectra (Fe 3+ /ΣFe ~0 and ~1) were found to deviate significantly from the Mossbauer values. This may indicate the sus- ceptibility of this method either to errors arising from the treatment of the background or to changes in Fe 2+ or Fe 3+ coordination with the Fe 3+ /ΣFe ratio. The general applicability of any XANES calibra- tion for determining oxidation states is limited by variations in the Fe coordination environment, which affects both the intensity and energy of spectral features. Thus previous calibrations based on mineral spectra are not applicable to silicate glasses. Nevertheless, systematic trends in spectral features suggest that Fe 3+ /ΣFe values may be obtained from XANES spectra, with an accuracy com- parable to Mossbauer spectroscopy, by reference to empirical calibration curves derived from com- positionally similar standards.
273 citations
TL;DR: In this article, a binder-free Li-ion deintercalated Li 1 - x CoO 2 film was made using the electrostatic spray deposition (ESD) technique.
Abstract: To investigate the electronic structure of the electrochemically Li-ion deintercalated Li 1 - x CoO 2 system, soft X-ray absorption spectroscopy (XAS) for the oxygen K-edge and the Co L I I , I I I -edge has been carried out intensively with compositional x value variation, compared with Co K-edge X-ray absorption near edge structure (XANES) spectroscopy. To get reasonably good XAS spectra for the electrochemically Li-ion deintercalated Li 1 - x CoO 2 system, we made a binder-free LiCoO 2 film electrode using the electrostatic spray deposition (ESD) technique. The oxygen K-edge XAS for Li 1 - x CoO 2 shows more effective spectral change with respect to Li-ion content than the Co L I I , I I I -edge XAS. The dependence of the absorption peak feature on the Li content is described in terms of the ground state of the Co and O atoms, showing the systematic variation of the hole-state site distribution between Co and oxygen atoms. From the Co L I I , I I I -edge XAS, it is found that the broad peak shift to higher energy with the Li-ion deintercalation is due to rehybridization between Co and O atoms under the local structural distortion of CoO 6 octahedra, which is also confirmed by the formation of two additional absorption peaks below the threshold energy corresponding to the oxygen 2p hole state hybridized with the 3d orbital of Co ion in the distorted CoO 6 octahedral site. In the O K-edge XAS spectra for the deintercalated Li 1 - x CoO 2 film, the shoulder absorption peak in the energy region higher than the threshold energy could be assigned to the higher oxidation state of the oxygen site on Li deintercalation. From the Co L I I , I I I -edge and O K-edge XAS results for the Li-ion deintercalated Li 1 - x CoO 2 film, it is concluded that the charge compensation for the Li-ion deintercalation process could be achieved mainly in the oxygen site and Co metal atomic site simultaneously. O K-edge and Co L I I , I I I -edge XAS results for cycled LiCoO 2 film show that the capacity fading of the LiCoO 2 system is related to the decrease of Co-O bond covalency by the local structural distortion of CoO 6 octahedra remaining in the cycled LiCoO 2 .
272 citations
TL;DR: In this article, the authors provide an overview of the state-of-the-art synchrotron-based tools for soft X-ray characterization and discuss a number of applications to exemplify their unique aspects.
270 citations