Investigation of the Fe K-edge XANES Spectra from Fe_1−xGa_xSbO₄: Local versus Nonlocal Excitations

Abstract

The Fe K-edge X-ray absorption near-edge (XANES) spectra from Fe(1-x)Ga(x)SbO(4), having a rutile-like structure, have been investigated. Similar to the Ti K-edge XANES spectrum from TiO(2) (rutile), the low-energy pre-edge region observed in the Fe K-edge spectra is too broad to be representative of only a local, quadrupolar 1s → 3d excitation. The broadness of this peak results from the presence of a nonlocal transition, referred to as an intersite hybrid, which involves the excitation of 1s electrons to unoccupied 3d states of a next-nearest-neighbor Fe atom. (These 3d states overlap Fe 4p states of the absorbing atom through O 2p states.) With increasing Ga concentration, the intensity of the intersite hybrid peak decreases because of a deficiency of unoccupied next-nearest-neighbor 3d states. This observation provides important information on how the peak intensities of these nonlocal excitations are affected by substitution of the constituent elements.

An investigation of the electronic structure and structural stability of RE2Ti2O7 by glancing angle and total electron yield XANES

“…The intensity and absorption energy of the pre-edge (A) and main-edge features (B and C) in Ti K-edge XANES spectra change with changing CN [72][73][74][75][76][77][78][79]. The pre-edge features (A 1 and A 2 ) resulting from local excitations are very sensitive to changes in CN or a distortion of the local coordination environment [72][73][74][75][76][77].…”

“…The intensity of the main-edge feature (C) changes considerably because of variations in the chemical environment around the Ti atoms [72,73,78,79]. An increase in intensity of feature C can be a result of an increase in the number of Ti 4p final states (or Ti 4p-O 2p states) available for 1s electrons to be excited to.…”

An investigation of the Fe and Mo oxidation states in Sr2Fe2−xMoxO6 (0.25⩽x⩽1.0) double perovskites by X-ray absorption spectroscopy

“…The presence of Fe 2+ in these materials with varying x is further supported by the observed shifts in the main-edge energy of these spectra, which is defined as the inflection point of the main-edge (determined from the derivative spectrum by finding the peak maximum of the feature corresponding to the mainedge). The decrease in absorption energy with greater substitution of Fe for Mo (DE % 1.5 eV), is ascribed to the presence of lower-energy valence Fe 4p-O 2p states, caused by increased ground-state screening of the Fe nuclear charge that results from a reduction of Fe 3+ to Fe 2+ [54].…”

Seismic and Aseismic Fault Growth Lead to Different Fault Orientations

“…The Roscoe and Coulomb angles are upper and lower bounds, and the Arthur angle is defined as the mean of these two angles (Arthur et al, 1977). Despite the general agreement on these failure criteria, many natural faults deviate substantially from their predictions (Anderson, 1905;Fletcher et al, 2016;Hardebeck & Michael, 2004;Scholz et al, 2010;Sibson, 1990;Sibson et al, 2011;Townend & Zoback, 2004). One reason for this discrepancy might be a long-term rotation of the stress field surrounding the fault.…”