Cuboctahedral oxygen clusters in U3O7

Garrido, F.; Ibberson, R. M.; Nowicki, Ł.; Willis, B. T. M.

doi:10.1016/s0022-3115(03)00318-0

Cited by 50 publications

(81 citation statements)

References 11 publications

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“…2 (the peaks occur at shorter distances because the figure is not corrected for phase shift). These distances are in accordance with the recent description of the UO 2+x structure [12][13][14]. This description is based on the presence of cuboctahedral defects into the fluorite structure.…”

Section: Extended X-ray Absorption Fine Structure (Exafs)supporting

confidence: 90%

XAS study of (U1−yPuy)O2 solid solutions

Martin

Grandjean

Valot

et al. 2007

Journal of Alloys and Compounds

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Section: Extended X-ray Absorption Fine Structure (Exafs)supporting

confidence: 90%

XAS study of (U1−yPuy)O2 solid solutions

Martin

Grandjean

Valot

et al. 2007

Journal of Alloys and Compounds

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“…86 Such a comparison demonstrates that these novel states are not the postulated small polarons that reside in the slightly modified structures 78,99,100 found by neutron scattering [79][80][81][82][83][84] or the result of similar small compressions of the U-O bonds. Instead, given the correlations with our previous experiments, we conclude that these novel states are either the CPQP itself or its signature within these measurements that show the electronic structure.…”

Section: E Dos Of the Coherent Quantum Phase Of Photoinduced Polaronsmentioning

confidence: 90%

“…These defectstructures are very similar locally to the long-standing cuboctahedron model derived from extensive analysis of neutron diffraction. [79][80][81][82][83][84] In both descriptions adventitious O is added into the cubic hole sites accompanied by the displacement one or two neighboring cube vertex O atoms into adjacent cubic holes. U 3 O 7 uses the same motif, differing from U 4 O 9 in the longer range ordering of the cuboctahedron or alternative less ordered defect structures.…”

Section: A O Xas and Rixs Of Relevant Standard Compoundsmentioning

confidence: 99%

Closure of the Mott gap and formation of a superthermal metal in the Fröhlich-type nonequilibrium polaron Bose-Einstein condensate in UO2+x

Conradson¹,

Andersson²,

Boland³

et al. 2017

Phys. Rev. B

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with O XAS and NIXS and U M 5 RIXS shows that O-doping raises the peak of the U 5f states of the valence band by ~0.4 eV relative to a calculated value of 0.25 eV. However, it lowers the edge of the conduction band by 1.5 eV vs. the calculated 0.6 eV, a difference much larger than the experimental error. This 1.9 eV reduction in the gap width constitutes most of the 2-2.2 eV gap measured by optical absorption. In addition, the XAS spectra show a tail that will intersect the occupied U 5f states and give a continuous density-of-states that increases rapidly above its constricted intersection. Femtosecond-resolved photoemission measurements of UO 2 coincident with the excitation pulse with 4.7 eV excitation show the unoccupied 5f states of UO 2 and no hot electrons. 3.1 eV excitation, however, complements the Odoping results by giving a continuous population of electrons for several eV above the Fermi level. The CPQP in photoexcited UO 2 therefore fulfills the criteria prescribed for a non-equilibrium condensate. The electron distributions resulting from both excitations persist for 5-10 ps, indicating that they are the final state that therefore forms without passing through the initial continuous distribution of nonthermal electrons observed for other materials. Three exceptional findings are: 1) the direct formation of both of these long lived (>3-10 ps) excited states without the short lived nonthermal intermediate; 2) the superthermal metallic state is as or more stable than typical photoinduced metallic phases; and 3) the absence of hot electrons accompanying the insulating UO 2 excited state. This heterogeneous, non-equilibrium, Fröhlich BEC stabilized by a FanoFeshbach resonance therefore continues to exhibit unique properties.Closing the Mott gap in UO 2(+x) -2

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“…The fcc cubic fluorite-type crystal structure of UO2 can accommodate extra oxygen atoms and therefore is able to form the polymorphs U4O9 and U3O7. These are described as UO2 matrices enriched with oxygen atoms 20 . Solubility of oxygen in UO2+x depends on temperature 21 : above 773 K uranium oxides from UO2.26 -UO2.…”

Section: Introductionmentioning

confidence: 99%

Oxidation of UC: An in situ high temperature environmental scanning electron microscopy study

Gasparrini

Podor

Horlait

et al. 2017

Journal of Nuclear Materials

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Abstract. In situ HT-ESEM oxidation of sintered UC fragments revealed the morphological changes occurring during the transformation between UC to UO2 and UO2 to U3O8 at 723 to 848 K and in an atmosphere of 10 to 100 Pa O2. Two main oxidation pathways were revealed. Oxidation at 723 K in atmospheres ≤ 25 Pa O2 showed the transformation from UC to UO2+x, as confirmed by post mortem HRTEM analysis. This oxidation pathway was comprised of three steps: (i) an induction period, where only surface UC particles oxidised, (ii) a sample area expansion accompanied by crack formation and propagation, (iii) a stabilisation of the total crack length inferring that crack propagation had stopped. Samples oxidised under 50 Pa O2 at 723 K and at 773 -848 K for 10 to 100 Pa O2 showed an "explosive" oxidation pathway: (i) sample area expansion occurred as soon as oxygen was inserted into the chamber and crack propagation and crack length followed an exponential law; (ii) cracks propagated as a network and the oxide layer fragmented, (iii) an "explosion" occurred causing a popcorn-like transformation, typical for oxidation from UO2 to U3O8. HRTEM characterisation revealed U3O8 preferentially grow in the [001] direction. The explosive growth, triggered by ignition of UC, proceeded as a self-propagating high-temperature synthesis reaction, with a propagation speed of 150-500 ± 50 µm/s.

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Cuboctahedral oxygen clusters in U3O7

Cited by 50 publications

References 11 publications

XAS study of (U1−yPuy)O2 solid solutions

XAS study of (U1−yPuy)O2 solid solutions

Closure of the Mott gap and formation of a superthermal metal in the Fröhlich-type nonequilibrium polaron Bose-Einstein condensate in UO2+x

Oxidation of UC: An in situ high temperature environmental scanning electron microscopy study

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