The electronic structure of actinide dioxides

Goodman, G. L.

doi:10.1016/0925-8388(92)90295-k

Cited by 30 publications

(8 citation statements)

References 36 publications

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“…This is mainly due to the fact that the calculated band gap (1.1 eV) is highly underestimated in comparison to the experimental one (1.8 eV) [12]. The band-gap in UO 2 is of f -f nature and a strong U 5f -O 2p hybridization takes place [13]. This implies that one reason for the discrepancy between the experiment and the calculation is due to an underestimation of the Coulomb site interaction parameter U.…”

Section: Resultsmentioning

confidence: 81%

Uranium oxides investigated by X-ray absorption and emission spectroscopies

Magnuson

Butorin

Werme

et al. 2006

Applied Surface Science

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X-ray absorption and resonant X-ray emission measurements at the O 1s edge of the uranium oxides UO 2 , U 3 O 8 and UO 3 are presented. The spectral shapes of the O Kα X-ray emission spectra of UO 3 exhibit significant excitation energy dependence, from an asymmetric to a symmetric form, which differs from those of UO 2 and U 3 O 8 . This energy dependence is attributed to a significant difference in the oxygen-uranium hybridization between two different sites in the crystal structure of UO 3 . The spectral shapes of UO 2 and U 3 O 8 are also found to be different but without significant energy dependence. The experimental spectra of the valence and conduction bands of the uranium oxides are compared to the results of electronic structure calculations available in the literature.

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Section: Resultsmentioning

confidence: 81%

Uranium oxides investigated by X-ray absorption and emission spectroscopies

Magnuson

Butorin

Werme

et al. 2006

Applied Surface Science

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“…Such a ground state should have a zero magnetic moment, contrary to the large moment found in this work and in experimental observations. 46,47 Painstaking experiments by Morss et al 46 suggested that the magnetic moment in CmO 2 is not due to significant amounts of Cm 3+ impurities. 48 Morss et al 46 concluded that "a re-evaluation of the electronic ground states in the actinide dioxides may be needed."…”

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confidence: 98%

Covalency in the actinide dioxides: Systematic study of the electronic properties using screened hybrid density functional theory

2007

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We present the first systematic study of the electronic properties of the AnO 2 series, An= Th-Es, using screened hybrid density functional theory. In contrast to local or semilocal functionals, this approach has been demonstrated to capture the strong electron correlation and localized Mott-insulating behavior observed in early dioxides such as UO 2 . One might expect later members of the series to show even more localized character as the f orbital radial extent decreases with increasing Z. However, we find two interesting features in the calculations: a 5f -O 2p orbital energy degeneracy, which leads to significant orbital mixing and covalency in the intermediate region ͑PuO 2 -CmO 2 ͒, and a strong Hund's rule exchange opposing spin-orbit coupling, which yields an unexpected ground state in CmO 2 .

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“…The lower valence band (10 eV < E b < 50 eV) is defined by the U 6p 3/2,1/2 -O 2s (C 2s) electron region (lifetime broadening determines the U 6p line-shape) and the U 6s core-level. [20][21][22][23][24] For the oxidized surface, the U 6p 3/2,1/2 binding energies are 17.2 eV and 27.8 eV, respectively, and the spin-orbit splitting of the U 6p 3/2,1/2 doublet is 10.6 eV. These U [25] and noting that they overlap, the manifold peak intensity would be affected in the U-carbide layer thus explaining the changing branching ratio.…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Uranium passivation by C+ implantation: A photoemission and secondary ion mass spectrometry study

Nelson

Felter

et al. 2006

Surface Science

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Implantation of 33 keV C + ions into polycrystalline U 238 with a dose of 4.3 x 10 17 cm -2 produces a physically and chemically modified surface layer that prevents further air oxidation and corrosion. X-ray photoelectron spectroscopy and secondary ion mass spectrometry were used to investigate the surface chemistry and electronic structure of this C + ion implanted polycrystalline uranium and a non-implanted region of the sample, both regions exposed to air for more than a year. In addition, scanning electron microscopy was used to examine and compare the surface morphology of the two Researchers have recently used N 2 + and C + ion implantation to modify the near surface region chemistry and structure of uranium to affect the nucleation and growth kinetics of corrosion and to passivate the surface. [2-4] These researchers used Auger electron spectroscopy (AES) in conjunction with sputter depth profiling to show that the implanted surfaces had compositional gradients containing nitrides and carbides. Oxygen and molybdenum ion implantation has also been used to affect the hydriding properties and oxidation resistance of uranium. [5,6] In addition to chemical modification, ion implantation can create special reactive surface species that include defect structures that affect the initial adsorption and dissociation of molecules on the surface. Overall the modified surface layers provide mechanical stability and protection against further air corrosion.This paper presents the results from an investigation of the surface chemistry, surface morphology and electronic structure of air-exposed C + implanted U. Examination of the resultant surface morphology with scanning electron microscopy (SEM) allowed a qualitative comparison between the implanted and the oxidized surfaces. Furthermore, core-level and valence band photoelectron spectroscopy in combination with time-ofRevised SurfSci 05133 UCRL-JRNL-210877 3 flight secondary ion mass spectrometry (ToF-SIMS) depth profiling provide a comprehensive characterization of the ion-implanted surface. ExperimentalPrior to implantation, the polycrystalline U was prepared with a final mechanical polishing step using 0.5 um diamond paste that provided a near mirror finish. Initial oxidation of the U in laboratory air prior to introduction into the ion implanter vacuum chamber results in a ≤20 nm oxide. [7,8] The specimen was firmly clamped to a watercooled stainless steel block and sample heating during the implant was therefore minimal.The implantation was performed on the lightly oxidized U sample with a Varian 3000C ion implanter. The cryosorption pumps on the beamline and endstation maintained vacuum in the mid 10 -6 to mid 10 -7 Torr regime, respectively, during the implant. The implant was at normal incidence and CO 2 gas was used as the source material in the Freeman-type hot filament ionizer. The magnet separated the carbon +1 ions from the other ion species and the beam was rastered onto the surface in the standard fashion for ion implantation, and thus the dose is pure...

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The electronic structure of actinide dioxides

Cited by 30 publications

References 36 publications

Uranium oxides investigated by X-ray absorption and emission spectroscopies

Uranium oxides investigated by X-ray absorption and emission spectroscopies

Covalency in the actinide dioxides: Systematic study of the electronic properties using screened hybrid density functional theory

Uranium passivation by C+ implantation: A photoemission and secondary ion mass spectrometry study

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