| 1. |
- Butorin, Sergei, et al.
(författare)
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Effect of carbon content on electronic structure of uranium carbides
- 2023
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of UCx (x = 0.9, 1.0, 1.1, 2.0) was studied by means of x-ray absorption spectroscopy (XAS) at the CK edge and measurements in the high energy resolution fluorescence detection (HERFD) mode at the U M-4 and L-3 edges. The full-relativistic density functional theory calculations taking into account the 5f - 5f Coulomb interaction U and spin-orbit coupling (DFT+U+SOC) were also performed for UCand UC2. While the U L-3 HERFD-XAS spectra of the studied samples reveal little difference, the U M-4 HERFD-XAS spectra show certain sensitivity to the varying carbon content in uranium carbides. The observed gradual changes in the U M-4 HERFD spectra suggest an increase in the C2p-U 5f charge transfer, which is supported by the orbital population analysis in the DFT+U+ SOC calculations, indicating an increase in the U 5f occupancy in UC2 as compared to that in UC. On the other hand, the density of states at the Fermi level were found to be significantly lower in UC2, thus affecting the thermodynamic properties. Both the x-ray spectroscopic data (in particular, the CK XAS measurements) and results of the DFT+U+SOC calculations indicate the importance of taking into account U and SOC for the description of the electronic structure of actinide carbides.
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| 2. |
- Butorin, Sergei, et al.
(författare)
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X-ray spectroscopic study of chemical state in uranium carbides
- 2022
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Ingår i: Journal of Synchrotron Radiation. - : International Union of Crystallography (IUCr). - 0909-0495 .- 1600-5775. ; 29, s. 295-302
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Tidskriftsartikel (refereegranskat)abstract
- UC and UMeC2 (Me = Fe, Zr, Mo) carbides were studied by the high-energyresolution fluorescence-detected X-ray absorption (HERFD-XAS) technique at the U M-4 and L-3 edges. Both U M-4 and L-3 HERFD-XAS reveal some differences between UMeC2 and UC; there are differences also between the M-4 and L-3 edge results for both types of carbide in terms of the spectral width and energy position. The observed differences are attributed to the consequences of the U 5f, 6d-4d(3d) hybridization in UMeC2. Calculations of the U M-4 HERFD-XAS spectra were also performed using the Anderson impurity model (AIM). Based on the analysis of the data, the 5f occupancy in the ground state of UC was estimated to be 3.05 electrons. This finding is also supported by the analysis of U N-4,N-5 XAS of UC and by the results of the AIM calculations of the U 4f X-ray photoelectron spectrum of UC.
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| 3. |
- Gerber, Evgeny, et al.
(författare)
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Insight into the structure-property relationship of UO2 nanoparticles
- 2021
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Ingår i: Inorganic Chemistry Frontiers. - : Royal Society of Chemistry (RSC). - 2052-1545 .- 2052-1553. ; 8:4, s. 1102-1110
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Tidskriftsartikel (refereegranskat)abstract
- Highly crystalline UO2 nanoparticles (NPs) with sizes of 2–3 nm were produced by fast chemical deposition of uranium(IV) under reducing conditions at pH 8–11. The particles were then characterized by microscopy and spectroscopy techniques including high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), high-energy resolution fluorescence detection (HERFD) X-ray absorption spectroscopy at the U M4 edge and extended X-ray absorption fine structure (EXAFS) spectroscopy at the U L3 edge. The results of this investigation show that despite U(IV) being the dominant oxidation state of the freshly prepared UO2 NPs, they oxidize to U4O9 with time and under the X-ray beam, indicating the high reactivity of U(IV) under these conditions. Moreover, it was found that the oxidation process of NPs is accompanied by their growth in size to 6 nm. We highlight here the major differences and similarities of the UO2 NP properties to PuO2, ThO2 and CeO2 NPs.
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| 4. |
- Koehler, Luisa, et al.
(författare)
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Insights into the Electronic Structure of a U(IV) Amido and U(V) Imido Complex
- 2022
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Ingår i: Chemistry - A European Journal. - : Wiley-VCH Verlagsgesellschaft. - 0947-6539 .- 1521-3765. ; 28:21
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Tidskriftsartikel (refereegranskat)abstract
- Reaction of the N-heterocylic carbene ligand (i)PrIm (L-1) and lithium bis(trimethylsilyl)amide (TMSA) as a base with UCl4 resulted in U(IV) and U(V) complexes. Uranium's +V oxidation state in (HL1)(2)[U(V)(TMSI)Cl-5] (TMSI=trimethylsilylimido) (2) was confirmed by HERFD-XANES measurements. Solid state characterization by SC-XRD and geometry optimisation of [U(IV)(L-1)(2)(TMSA)Cl-3] (1) indicated a silylamido ligand mediated inverse trans influence (ITI). The ITI was examined regarding different metal oxidation states and was compared to transition metal analogues by theoretical calculations.
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| 5. |
- Suksi, Juhani, et al.
(författare)
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Uranium remobilisation in anoxic deep rock-groundwater system in response to late Quaternary climate changes - Results from Forsmark, Sweden
- 2021
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Ingår i: Chemical Geology. - : Elsevier. - 0009-2541 .- 1872-6836. ; 584
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Tidskriftsartikel (refereegranskat)abstract
- Unusually high uranium (U) concentrations (up to 175 mu g/L) have been measured in groundwater at depths between 400 and 650 m at the Forsmark site, eastern Sweden. Since it is unlikely that such high concentrations formed under the stagnant and low redox groundwater conditions that currently prevail, this study employs Useries isotopes to understand how the recent evolution (<1 Ma) of the flow system has influenced the observed U distribution. Material from fractures as deep as 700 m along the assumed flow route was subject to U-series disequilibrium (USD) measurements, as well as sequential extractions (SE) and U redox-state analyses that revealed the U-series activity ratios in the bulk and soluble fraction of the fracture precipitates. Uranium isotope data collected over several years of annual groundwater monitoring were scrutinized to evaluate the U sources and U exchange in fractures located in high-U groundwater sections. Numerical simulations with the experimental data were used to study evolution of U-series isotope composition in a fracture in the highest U section at similar to 500 m depth under various U mobility scenarios. The results show that U redistribution in fractures with certain dissolution/deposition flux ratios during periodic water intrusions, driven by glaciation and deglaciation events during the last 120 ka, can explain the U anomaly in the groundwater.
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