0000000000015793
AUTHOR
Ph. Parent
Influence of the focusing effect on XAFS in ReO3, WO3−x and FeF3
Abstract The role of the focusing effect in the formation of X-ray absorption fine structure (XAFS) is considered for ReO3, non-stoichiometric tungsten oxides WO3−x and FeF3 having the perovskite-type structure. Two cases are mainly discussed: (1) an admixture of rhenium and tungsten L2-edge XAFS in ReO3 and WO3−x crystals to the one above rhenium and tungsten L1-edge and (2) high-order superfocusing effect in Fe0F1Fe2F3Fe4 atomic chain in iron K-edge XAFS of FeF3 which is analysed using an ab initio multiple-scattering approach.
XAFS study of short range order in the heavily disordered MoxW1−wO3 oxides
We have done comparative XAFS analysis on the MoK and WL 3 edges of polycrystalline Mo x W 1-x O 3 solid solutions. It was found that their structures are closely related to corner-shared WO 3 -type for x<0.9 while α-MoO 3 -type structure is present for x≥0.9. The obtained structural parameters for the first shell around metal ions allow to distinguish several structural phase transitions due to the change of composition. A set of subshells within the first shell was found, and they are in good agreement with Raman data
X-ray absorption study of the electronic structure of tungsten and molybdenum oxides on the O K-edge
Magnetron sputtered amorphous thin films a-WO3, a-MoO3 and doped a-WO3:Ir have been studied by X-ray absorption spectroscopy on the oxygen K-edge in comparison with crystalline oxides as monoclinic m-WO3, orthorhombic α-MoO3, cubic Na0.6WO3, layered-type hexagonal h-WO3 and WO3·H2O, having variable electronic and atomic structure. The changes in the XANES ranging 10–15 eV above the absorption edge are interpreted based on the known band-structure calculations. The high-energy features are related to the multiple-scattering processes (EXAFS) at the nearest atoms.
In situ XAFS study of phase transitions and hydrogen intercalation in WO3-MoO3 system
Abstract The WO 3 -MoO 3 system has several reconstructive and displacive phase transitions which can be induced by temperature and/or by change of stoichiometry or valence state of metal ions under hydrogen intercalation. We have studied in situ the local electronic and structural changes arising in WO 3 -MoO 3 system with hydrogen intercalation and temperature. In situ XAFS measurements at the Mo K and W L 3 edges in H y Mo x W 1− x O 3 compounds, performed at different hydrogen intercalation level and temperatures (from RT to 500°C), allowed us to determine the rearrangement in the first and second coordination shells of Mo and W cations during phase transitions. It was found that hydrog…
XAFS analysis of the low symmetry octahedral molybdenum and tungsten oxides
Abstract Comparative XAFS analysis of the main isostructural crystalline phases of W(Mo)O3 oxides and W(Mo)O3·nH2O hydrates has been done at the W L3 and Mo K edges. These compounds have (1) 3D perovskite-type (PT) structure (m-WO3); (2) 2D PT structure (WO3·H2O and MoO3·nH2O (n = 1,2)); (3) 2D hexagonal-type structure (WO3·1/3H2O) and (4) 2D double layered structure (α-MoO3). The detailed analysis of X-ray absorption fine structure (XAFS) in the low-symmetry structures shows that in order to simulate the experimental spectrum, it is sufficient to take into account single-scattering contributions in the range from 1.7 to ∼ 5.0 A and a number of multiple-scattering paths from nearly linear a…