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| 2. |
- Amidani, Lucia, et al.
(författare)
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Oxygen K-Edge X-ray Absorption Spectra of ThO2 and CeO2 : Experiment, Interpretation, and Structural Effects
- 2023
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 127:6, s. 3077-3084
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Tidskriftsartikel (refereegranskat)abstract
- Experimental oxygen K-edge spectra of ThO2 and CeO2 are presented and interpreted based on density functional theory (DFT). The contribution of d and f orbitals to the O Kedge spectrum is identified as well-distinguished peaks, the presence of which evidences the strong hybridization of Th and Ce metal centers with O orbitals. The sensitivity of the O K-edge to both f- and d-states in the absence of a core-hole on the metal ion results in an insightful overview of the electronic structure involved in the chemical bond. In particular, the large bandwidth of the Th 5f band as compared to the Ce 4f band is observed as a set of wider and more substantial set of peaks in the O K-edge, confirming the stronger hybridization of the former with O orbitals. The peak ascribed to the 5f band of ThO2 is found at higher energy than the 6d band, as predicted from DFT calculations on actinide dioxides. To highlight the sensitivity and the potential use of the O K-edge for the characterization of ThO2-based systems, the sensitivity of the spectrum to structural changes such as lattice expansion and size reduction are calculated and discussed.
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| 3. |
- Amidani, Lucia, et al.
(författare)
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Understanding the size effects on the electronic structure of ThO2 nanoparticles
- 2019
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 21:20, s. 10635-10643
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Tidskriftsartikel (refereegranskat)abstract
- Developing characterization techniques and analysis methods adapted to the investigation of nanoparticles (NPs) is of fundamental importance considering the role of these materials in many fields of research. The study of actinide based NPs, despite their environmental relevance, is still underdeveloped compared to that of NPs based on stable and lighter elements. We present here an investigation of ThO2 NPs performed with High-Energy Resolution Fluorescence Detected (HERFD) X-ray Absorption Near-Edge Structure (XANES) and with ab initio XANES simulations. The first post-edge feature of Th L-3 edge HERFD XANES disappears in small NPs and simulations considering non-relaxed structural models reproduce the trends observed in experimental data. Inspection of the simulations of Th atoms in the core and on the surface of the NP indeed demonstrates that the first post-edge feature is very sensitive to the lowering of the number of coordinating atoms and therefore to the more exposed Th atoms at the surface of the NP. The sensitivity of the L-3 edge HERFD XANES to low coordinated atoms at the surface stems from the hybridization of the d-Density of States (DOS) of Th with both O and Th neighboring atoms. This may be a common feature to other oxide systems that can be exploited to investigate surface interactions.
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| 7. |
- Bauters, Stephen, et al.
(författare)
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Signatures of technetium oxidation states : a new approach
- 2020
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Ingår i: Chemical Communications. - : ROYAL SOC CHEMISTRY. - 1359-7345 .- 1364-548X. ; 56:67, s. 9608-9611
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Tidskriftsartikel (refereegranskat)abstract
- A general strategy for the determination of Tc oxidation state by new approach involving X-ray absorption near edge spectroscopy (XANES) at the Tc L-3 edge is shown. A comprehensive series of Tc-99 compounds, ranging from oxidation states I to VII, was measured and subsequently simulated within the framework of crystal-field multiplet theory. The observable trends in the absorption edge energy shift in combination with the spectral shape allow for a deeper understanding of complicated Tc coordination chemistry. This approach can be extended to numerous studies of Tc systems as this method is one of the most sensitive methods for accurate Tc oxidation state and ligand characterization.
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| 8. |
- Bes, R., et al.
(författare)
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New insight in the uranium valence state determination in UyNd1-yO2 +/- x
- 2018
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Ingår i: Journal of Nuclear Materials. - : ELSEVIER SCIENCE BV. - 0022-3115 .- 1873-4820. ; 507, s. 145-150
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Tidskriftsartikel (refereegranskat)abstract
- The charge compensation mechanisms in UyNd1-yO2 +/- x, and its consequence on the overall O stoichiometry (or O/M ratio where M = Nd + U) have been studied through the uranium valence state mixture evolution as a function of Nd content up to y = 0.62 by means of high energy resolution fluorescence detection X-ray absorption spectroscopy (HERFD-XAS) at the U M-4-edge. Our results clearly demonstrate the formation of U5+ at low Nd content (y < 0.15). Upon increasing the Nd content, oxygen vacancies and the formation of U6+ appear as competing mechanisms for intermediate Nd concentrations, leading to the co-existence of U4+/U5+/U6+ mixed valence and an overall hypostoichiometry (O/M < 2.00). Finally, the formation of U6+ associated with strongly distorted U local environment is observed for high Nd concentrations (y = 0.62), leading to an overall hyperstoichiometry (O/M < 2.00).
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| 9. |
- Butorin, Sergei
(författare)
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3d-4f Resonant Inelastic X-ray Scattering of Actinide Dioxides : Crystal-Field Multiplet Description
- 2020
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Ingår i: Inorganic Chemistry. - : AMER CHEMICAL SOC. - 0020-1669 .- 1520-510X. ; 59:22, s. 16251-16264
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical overview of the core-to-core (3d-4f) resonant inelastic X-ray scattering (RIXS) spectra of actinide dioxides AnO(2) (An = Th, U, Np, Pu, Am, Cu, Bk, Cf) is provided. The 3d-4f RIXS maps were calculated using crystal-field multiplet theory and turned out to be significantly different at the An M-5 vs M-4 edges, because of selection rules and final state effects. The results of the calculations allowed for a general analysis of so-called high-energy-resolution fluorescence-detected X-ray absorption (HERFD-XAS) spectra. The cuts of the calculated RIXS maps along the incident energy axis at the constant emitted energy, corresponding to the maximum of the RIXS intensity, represented the HERFD spectra and provided their comparison with calculated conventional X-ray absorption (XAS) spectra with a reduced corehole lifetime broadening at the An M-5 and M-4 edges. Although the An M-5 HERFD profiles were found to depart from the X-ray absorption cross-section, in terms of appearing additional transitions, the results of calculations for the An M-4 edges demonstrate overall better agreement between the HERFD and XAS spectra for most dioxides, keeping in mind a restricted HERFD resolution, because of the core-hole lifetime broadening in the final state. The results confirm the utility of HERFD for the An chemical state determination and indicate the importance of calculating the entire RIXS process in order to interpret the HERFD data correctly.
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| 10. |
- Butorin, Sergei
(författare)
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Advanced x-ray spectroscopy of actinide trichlorides
- 2021
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 155:16
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Tidskriftsartikel (refereegranskat)abstract
- The application of core-to-core (3d-to-4f) resonant inelastic x-ray scattering (RIXS) and high-energy-resolution fluorescence-detected x-ray absorption (HERFD-XAS) at actinide M-4,M-5 edges, as techniques with the enhanced sensitivity to changes in the chemical state, was analyzed for trivalent actinide compounds. As an example, a series of actinide chlorides AnCl(3) (An = U, Np, Pu, Am, Cm, Bk, and Cf) was used. The crystal-field multiplet formalism was applied to calculate the 3d-4f RIXS maps, and the HERFD-XAS spectra were extracted as cuts of these RIXS maps along the incident energy axis at the constant emitted energy, corresponding to the maximum of the RIXS intensity. A relation between HERFD and conventional XAS methods was also examined. Despite some differences between profiles of the An M-5 HERFD and conventional XAS spectra of trivalent actinides, the results of calculations indicate that the HERFD method can be used at the An M-5 edge for monitoring even small variations in the An chemical state. As a whole, better agreement between the HERFD and XAS spectra was found for the An M-4 edges as compared to the An M-5 edges. By using the point charge electrostatic model, the dependence of the An M-4,M-5 HERFD-XAS spectra on the An coordination number was studied, which indicates the significant sensitivity of the distribution of the An 5f states to the ligand structural arrangement around the An sites.
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