X-ray dichroism and polarized anomalous scattering of the uranyl ion

Templeton, David H.; Templeton, L. K.

doi:10.1107/s0567739482000114

Cited by 165 publications

(131 citation statements)

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“…Resonant x-ray diffraction occurs when a photon excites a core electron to empty states, and is subsequently reemitted when the electron and the core hole recombine. 46 anisotropic contributions to the x-ray susceptibility tensor, [49][50][51] the amplitude of which increases dramatically as the photon energy is tuned to an atomic absorption edge. In the presence of long-range magnetic order, or a spatially anisotropic electronic distribution, the interference of the anomalous scattering amplitudes may lead to Bragg peaks at positions forbidden by the crystallographic space group.…”

Section: Resultsmentioning

confidence: 99%

EuTiO3magnetic structure studied by neutron powder diffraction and resonant x-ray scattering

et al. 2012

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We combine neutron powder diffraction and x-ray single-crystal magnetic diffraction at the Eu L 2 edge to scrutinize the magnetic motif of the Eu ions in magnetoelectric EuTiO 3 . Our measurements are consistent with an antiferromagnetic G-type pattern with the Eu magnetic moments ordering along the a,b -plane diagonal. Recent reports of a novel transition at 2.75 K with a flop of magnetic moments upon poling the sample in an electric field cannot be confirmed for a nonpoled sample. Our neutron diffraction data do not show any significant change of the structure below the Néel temperature. Magnetoelastic coupling, if present, is therefore expected to be negligible.

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Section: Resultsmentioning

confidence: 99%

EuTiO3magnetic structure studied by neutron powder diffraction and resonant x-ray scattering

et al. 2012

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“…Post-edge features or multiple scattering resonance features (MSRs) in the U L 3 -edge XANES spectra have been associated with the bonding geometry and coordination of the central U atom (DENECKE et al, 1998;FARGES et al, 1992). One of these MSR features, a "shoulder", which is present on the high-energy side of the main absorption edge has been attributed to the presence of axial O bonds (TEMPLETON and TEMPLETON, 1982;HUDSON et al, 1995). At higher energy, the position of select post edge oscillations has also been used to extrapolate equatorial bond length values for U(VI) species (DENECKE et al, 1998).…”

Section: Uranium Xanes Studiesmentioning

confidence: 99%

Uranium co-precipitation with iron oxide minerals

Duff

Coughlin

Hunter

2002

Geochimica et Cosmochimica Acta

418

266

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ABSTRACT-In oxidizing environments, the toxic and radioactive element uranium (U) is most soluble and mobile in the hexavalent oxidation state. Sorption of U(VI) on Fe-oxides minerals [such as hematite (α-Fe 2 O 3 ) and goethite (α-FeOOH)] and occlusion of U(VI) by Feoxide coatings are processes that can retard U transport in environments. In aged Ucontaminated geologic materials, the transport and the biological availability of U toward reduction may be limited by co-precipitation with Fe-oxide minerals. These processes also affect the biological availability of U(VI) species toward reduction and precipitation as the less soluble U(IV) species by metal-reducing bacteria.To examine the dynamics of interactions between U(VI) and Fe oxides during crystallization, indicated that almost all of the Fe in these solids was crystalline and that most of the U was associated with these crystalline Fe oxides. X-ray diffraction and Fourier-transform infrared (FT-IR) spectroscopic studies indicate that hematite formation is preferred over that of goethite when the amount of U in the Fe-oxides exceeds 1 mol % U (~4 wt % U). FT-IR and room temperature continuous wave luminescence spectroscopic studies with unleached U/Fe solids indicate a relationship between the mol % U in the Fe oxide and the intensity or existence of the spectra features that can be assigned to UO 2 2+ species (such as the IR asymmetric υ 3 stretch for O=U=O for uranyl). These spectral features were undetectable in carbonate-or oxalate-leached Molecular modeling studies reveal that U 6+ species could bond with O atoms from distorted Fe octahedra in the hematite structure with an environment that is consistent with the results of the XAFS. The results provide compelling evidence of U incorporation within the hematite structure.

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“…The physics of this phenomenon is fairly clear: the incident waves 'see' symmetry-related but differently oriented ASF tensors giving rise to non-vanishing structure-factor tensors and violations of extinction rules owing to screw rotations and glide reflections. This effect may be considered an unwanted complication that can be circumvented by simply avoiding the say 50 eV wide region of resonance energies but, as immediately recognized by Templeton & Templeton (1982), 'where there is a complication there is also the opportunity of sharper, more penetrating methods for extracting information from diffraction experiments'. And indeed, while anisotropic resonant scattering principally affects all Bragg reflections, the 'forbidden' ones have attracted most attention in the past two decades, mainly because they are exclusively signals from the partial structure of the edge atom(s) and thus most sensitive element and sitespecific probes of the atomic local environments.…”

Section: Introductionmentioning

confidence: 99%

Polarization anisotropy of X-ray atomic factors and `forbidden' resonant reflections

et al. 2005

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Symmetry and physical aspects of 'forbidden' reflections excited by a local polarization anisotropy of the X-ray susceptibility are surveyed. Such reflections are observed near absorption edges where the anisotropy is caused by distortions of the atomic electronic states owing to interaction with neighbouring atoms. As a consequence, they allow for extracting nontrivial information about the resonant atom's local environment and their physical conditions. The unusual polarization properties of the considered reflections are helpful to distinguish them from other types of 'forbidden' reflections. When such reflections are excited, it is, for example, possible to determine not only the intrinsic anisotropy of an atomic form factor but also additional anisotropy induced by thermal motion, point defects and/or incommensurate modulations. Even the local 'chirality' of atoms in centrosymmetric crystals is accessible. Unsolved key problems and possible future developments are addressed.

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X-ray dichroism and polarized anomalous scattering of the uranyl ion

Cited by 165 publications

References 5 publications

EuTiO3magnetic structure studied by neutron powder diffraction and resonant x-ray scattering

EuTiO3magnetic structure studied by neutron powder diffraction and resonant x-ray scattering

Uranium co-precipitation with iron oxide minerals

Polarization anisotropy of X-ray atomic factors and `forbidden' resonant reflections

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