| 1. |
- Butorin, Sergei, et al.
(författare)
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Effect of Ag Doping on Electronic Structure of Cluster Compounds AgxMo9Se11 (x = 3.4, 3.9)
- 2018
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Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 1:8, s. 4032-4039
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of AgxMo9Se11 as a potential material for thermoelectric applications was studied using high-energy-resolution fluorescence-detection X-ray absorption spectroscopy (HERFD-XAS) and the resonant inelastic X-ray scattering (RIXS) technique. The experiments were supported by first-principle calculations using density functional theory (DFT). The analysis of obtained spectra indicate the presence of subvalent (less than 1+) Ag in AgxMo9Se11. The advanced HERFD-XAS measurements allowed us to resolve the contribution of the electronic states at the Fermi level of AgxMo9Se11 and to monitor its dependence on the x value. A comparison of the experimental data with the results of the DFT calculations suggests the importance of the Ag2-type sites with the shortest Ag–Se distance for affecting the properties of AgxMo9Se11.
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| 2. |
- Kapaklis, Vassilios, et al.
(författare)
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Temperature dependence of the electrical resistivity and electronic structure of amorphous Fe100-xZrx films and multilayers
- 2012
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 24:49, s. 495402-
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Tidskriftsartikel (refereegranskat)abstract
- The electrical resistivity of amorphous Fe100-xZrx metal alloy films and multilayers has been investigated in a wide temperature and composition range. The overall behavior of the resistivity is consistent with bulk measurements, exhibiting prominent semiconductor-like changes at low temperatures. The transition from positive (metallic) to negative temperature coefficient of resistivity behavior is accompanied by minute changes in magnetoresistance and we can therefore rule out magnetic phase changes as being the cause for the observed changes in the resistivity. Using x-ray absorption and emission spectroscopies we are able to probe the unoccupied and occupied electronic densities of states. The corresponding spectra are found to significantly overlap, as expected for a metallic-like electronic structure and the absence of a band gap. Besides a broadening of the x-ray emission lines expected from an amorphous material, remarkably small differences are observed in the electronic structures when changing the amount of Zr. The resistivity data were modeled and agreement with the Mott variable range hopping model was found, indicating localized electronic states due the disordered structure of the Fe100-xZrx alloys.
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| 3. |
- Vegelius, J. R., et al.
(författare)
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X-ray Spectroscopic Study of Cu2S, CuS, and Copper Films Exposed to Na2S Solutions
- 2012
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:42, s. 22293-22300
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of copper sulfides was studied using X-ray absorption at Cu K and L-2,L-3 and S L-2,L-3 edges and X-ray emission spectroscopy at S L-2,L-3 thresholds. The experimental data were compared with results of local density approximation calculations taking into account the calculated valence band contributions and core-level chemical shifts between inequivalent sites. The presence of divalent Cu was detected in CuS with X-ray absorption spectroscopy in the high-energy-resolution fluorescence detection (HERFD) mode. The S L-2,L-3 emission spectrum of CuS was found to be significantly broader than that of Cu2S due to contributions from inequivalent S sites. This difference in the spectral width was used to distinguish between sulfide species formed on the Cu foil exposed to Na2S solutions. The Cu-S interaction processes for Cu films of different thicknesses exposed to Na2S solutions were monitored in situ using X-ray absorption spectroscopy in the HERFD mode at the Cu K edge. It was found that Cu ions were diffusing in the sulfide and entering the solution. The rate at which Cu ions enter the solution via diffusion was estimated on the basis of the results for a 1000 angstrom thick film.
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| 4. |
- 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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| 5. |
- Butorin, Sergei M., et al.
(författare)
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Chemical Reduction of Actinides Probed by Resonant Inelastic X-ray Scattering
- 2013
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 85:23, s. 11196-11200
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Tidskriftsartikel (refereegranskat)abstract
- The study addresses the possibilities of immobilizing the mobile species of actinides in the geosphere using metallic iron. Sorption on corroding iron is well-known, but there have been uncertainties with regard to the possibilities of reducing the actinyl species to sparingly soluble oxides and, thereby, permanently immobilizing them. Resonant inelastic X-ray scattering (RIXS) measurements at the actinide 5d edges on Fe foils exposed to uranium(VI) and neptunium(V) solutions in groundwater unambigiously indicate reduction of actinides to, respectively, uranium(IV) and neptunium(IV) on iron surfaces. The reduction manifests itself in an appearance of distinct specific signatures of uranium(IV) and neptunium(IV) in the RIXS profile of 5f-5f excitations. Such signatures and RIXS intensity/cross-section behavior with varying energy of incident photons can be reproduced by model atomic-multiplet calculations of the RIXS spectra. By normalizing the RIXS signal of corresponding 5f-5f excitations to core-to-core 6p-to-5d characteristic fluorescence transitions of actinides, their reduction rates on Fe samples with different exposure to actinide solutions can be estimated. Observed reduction implies similar processes in the nuclear waste canister thus suggesting reduced probability of nuclear waste release with ground waters from the canister.
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| 6. |
- Butorin, Sergei M., et al.
(författare)
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High-resolution X-ray absorption spectroscopy as a probe of crystal-field and covalency effects in actinide compounds
- 2016
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 113:29, s. 8093-8097
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Tidskriftsartikel (refereegranskat)abstract
- Applying the high-energy resolution fluorescence-detection (HERFD) mode of X-ray absorption spectroscopy (XAS), we were able to probe, for the first time to our knowledge, the crystalline electric field (CEF) splittings of the 5f shell directly in the HERFD-XAS spectra of actinides. Using ThO2 as an example, data measured at the Th 3d edge were interpreted within the framework of the Anderson impurity model. Because the charge-transfer satellites were also resolved in the HERFD-XAS spectra, the analysis of these satellites revealed that ThO2 is not an ionic compound as previously believed. The Th 6d occupancy in the ground state was estimated to be twice that of the Th 5f states. We demonstrate that HERFD-XAS allows for characterization of the CEF interaction and degree of covalency in the ground state of actinide compounds as it is extensively done for 3d transition metal systems.
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| 7. |
- Butorin, Sergei. M., et al.
(författare)
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Probing Chemical Bonding in Uranium Dioxide by Means of High- Resolution X-ray Absorption Spectroscopy
- 2016
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:51, s. 29397-29404
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Tidskriftsartikel (refereegranskat)abstract
- A systematic X-ray absorption study at the U 3d, 4d, and 4f edges of UO2 was performed, and the data were analyzed within framework of the Anderson impurity model. By applying the high-energy-resolution fluorescence-detection (HERFD) mode of X-ray absorption spectroscopy (XAS) at the U 3d(3/2) edge and conducting the XAS measurements at the shallower U 4f levels, fine details of the XAS spectra were resolved resulting from reduced core-hole lifetime broadening. This multiedge study enabled a far more effective analysis of the electronic structure at the U sites and characterization of the chemical bonding and degree of the 5f localization in UO2. The results support the covalent character of UO2 and do not agree with the suggestions of rather ionic bonding in this compound as expressed in some publications.
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| 8. |
- Kotani, A., et al.
(författare)
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Spectator and participator processes in the resonant photon-in and photon-out spectra at the Ce L-3 edge of CeO2
- 2012
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Ingår i: European Physical Journal B. - : Springer Science and Business Media LLC. - 1434-6028 .- 1434-6036. ; 85:8, s. 257-
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Tidskriftsartikel (refereegranskat)abstract
- We study both theoretically and experimentally the photon-in and photon-out spectra of CeO2, which are caused by the Ce 2p to Ce 5d excitation followed by the three different de-excitation channels: (i) Ce 3d to Ce 2p (denoted by 3d-RXES), (ii) O 2p to Ce 2p (v-RXES), and (iii) Ce 5d to Ce 2p (RIXS). In 3d- and v-RXES, the 5d electron plays a role of a spectator, but in RIXS it is a participator. By extending our single impurity Anderson model (SIAM), which was used recently for our calculations of v-and 3d-RXES spectra of CeO2, we study the polarization dependence in the spectator and participator spectra, and we perform more detailed calculations for 3d- and v-RXES spectral features, as well as new calculations for the RIXS spectrum with charge transfer excitations. The polarization dependence is different for the spectator and participator spectra; we have no polarization correlation between the incident and emitted photons for the spectator spectra but a strong polarization correlation for the participator spectrum. The theoretical calculations predict that the charge transfer excitations in RIXS occur in the transfer-energy range overlapped with v-RXES, but the RIXS and v-RXES spectra can be discriminated by taking advantage of the different polarization dependence. The overlapped RIXS and v-RXES spectra are observed successfully by our experiments and well reproduced by our SIAM calculations.
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| 9. |
- Kuzenkova, Anastasiia S., et al.
(författare)
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New insights into the mechanism of graphene oxide and radionuclideinteraction
- 2020
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Ingår i: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 158, s. 291-302
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Tidskriftsartikel (refereegranskat)abstract
- The sorption of U(VI), Am(III)/Eu(III) and Cs(I) radionuclides by graphene oxides (GOs) synthesized byHummers’s, Brodie’s and Tour’s methods was studied through a combination of batch experiments withcharacterization by microscopic and spectroscopic techniques such as X-ray photoelectron spectroscopy(XPS), attenuated total reflection fourier-transform infrared spectroscopy (ATR-FTIR), high-energy resolutionfluorescence detected X-Ray absorption spectroscopy (HERFD-XANES), extended X-ray absorptionfine structure (EXAFS) and high resolution transmission electron microscopy (HRTEM). Remarkablydifferent sorption capacity and affinity of radionuclides was found towards GOs synthesized by Hummers’sand Brodie’s methods reflecting different structure and oxidation state of these materials.Mechanism underlying GO e radionuclide interaction is determined using variety of experimentaltechniques. For the first time it is shown here that GO - radionuclides interaction takes place on the smallholes or vacancy defects in the GO sheets. Mechanism of GO’s interaction with radionuclides wasanalyzed and specific functional groups responsible for this interaction were identified. Therefore, a newstrategy to produce improved materials with high capacity for radionuclides suggests the use perforatedand highly defected GO with a larger proportion of carboxylic functional groups.
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| 10. |
- Kvashnina, K. O., et al.
(författare)
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Chemical State of Complex Uranium Oxides
- 2013
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 111:25, s. 253002-
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Tidskriftsartikel (refereegranskat)abstract
- We report here the first direct observation of U(V) in uranium binary oxides and analyze the gradual conversion of the U oxidation state in the mixed uranium systems. Our finding clarifies previous contradicting results and provides important input for the geological disposal of spent fuel, recycling applications, and chemistry of uranium species.
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