The crystal structure of β-U4O9−y

Bevan, D. J. M.; Grey, Ian E.; Willis, B. T. M.

doi:10.1016/0022-4596(86)90002-2

Cited by 134 publications

(141 citation statements)

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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: 76%

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: 76%

XAS study of (U1−yPuy)O2 solid solutions

Martin

Grandjean

Valot

et al. 2007

Journal of Alloys and Compounds

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“…The approximate structure of the phase of U 4 O 9 was determined by Bevan et al (1986), who showed that the U atoms occupy positions close to those in the¯uorite structure of UO 2 and that the additional O atoms are accommodated in cuboctahedral clusters centred on the 12(b) positions of the cubic space group I " 43d. Re®nement of this model has shown that the most signi®cant change concerns the centres of the clusters.…”

Section: Discussionmentioning

confidence: 99%

“…The structure of -U 4 O 9 was described by Bevan et al (1986) as an anion-excess¯uorite-related oxide phase, with the excess anions accommodated in cuboctahedral clusters centred on the 12-fold sites of the cubic space group I " 43d. In this paper, we shall re®ne the same neutron data set measured at 503 K, together with an additional data set measured at 773 K, taking into account the fact that the re¯ection conditions of the special positions 12(b) are obeyed by all the atoms, even though most of them occupy general 48(e) sites.…”

Section: Introductionmentioning

confidence: 99%

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Refinement of the structure of β-U₄O₉

Cooper

Willis

2004

Acta Cryst Sect A

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β‐U4O9 is a superlattice structure based on the fluorite arrangement of UO2. The U atoms occupy positions close to those in UO2 and the additional O atoms are accommodated in cuboctahedral clusters of 3m symmetry, which are centred on the special 12‐fold sites of the cubic space group I3d. The structure has been refined from single‐crystal neutron data in accordance with the procedure described in the previous paper [Popa & Willis (2004). http://scripts.iucr.org/cgi-bin/paper?lc0065].

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“…The three peaks also appear in the spectrum of U 4 O 9 , although some peaks have much stronger intensities than those in the irradiated UO 2 . U 4 O 9 contains some cuboctahedral oxygen interstitial clusters that have been identified in neutron diffraction experiments previously, 1 and the charge state of some uranium ions is found to change from 4+ to 5+. 2 Accordingly, the coordination polyhedrons of uranium ions change from a cube for U 4+ to a square antiprism for U 5+ , which can lead to high U2 and U3 peaks.…”

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confidence: 99%

Recent Progress in Using Advanced Characterization and Modeling Approaches to Study Radiation Effects in Oxide Ceramics

Bai

2014

JOM

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Oxide ceramics play a critical role in nuclear energy applications. For example, uranium dioxide (UO 2 ) and uranium-plutonium mixed oxide (MOX) are widely used as nuclear fuels in light water reactors (LWRs) to produce about 15% of the electricity in the world. Other oxide ceramics such as pyrochlores have been extensively studied as waste forms for the immobilization of nuclear waste. Similar to other materials, radiation induces complex microstructural evolution in oxide ceramics. In nuclear fuels, nuclear fission produces not only point defects and defect clusters but also many fission products such as xenon (Xe) and krypton (Kr). The evolution of these defects and fission products can form many extended defects such as dislocation loops, gas bubbles, and metallic precipitates. In turn, many physical properties such as thermal conductivity and mechanical strength degrade significantly. Pyrochlores are complex oxides and usually contain more than two types of cations (e.g., A and B cations in A 2 B 2 O 7 ). Under radiation, not only interstitials and vacancies are produced, but also cation antisite defects, in which some A and B cations exchange their positions. The accumulation of antisite defects can lead to amorphization and eventually degradation of the structural stability. Therefore, understanding the detailed information of radiation effects in these oxides is important for improving their performance for nuclear applications.Radiation damage is a multi-timescale and multilengthscale problem. The timescale spans from picosecond to year, and the lengthscale spans from angstrom to meter. Therefore, understanding the radiation effects requires a multiscale approach, both experimentally and computationally. In particular, the information at the atomistic and mesoscale levels is crucial for us to understand the detailed defect and microstructural evolution under radiation. In this topic, five articles have been selected to show some recent progress in using advanced characterization and modeling approaches to understand the complex radiation effects in oxide ceramics with atomistic-and meso-scale resolution.In the article by Desgranges et al., the authors used Raman spectroscopy to try to understand the defect structures in alpha particle irradiated UO 2 . Compared with pristine UO 2 , three new peaks, namely U1, U2, and U3, appeared in the Raman spectrum of the irradiated UO 2 . The appearance of new Raman peaks could be induced by resonant Raman, formation of new molecular entities, or breakdown in symmetry. The authors argued that the last one could be the predominant mechanism for inducing these new Raman peaks. To support this argument, the authors compared the Raman spectrum of irradiated UO 2 with that of U 4 O 9 , which has a known crystal structure. The three peaks also appear in the spectrum of U 4 O 9 , although some peaks have much stronger intensities than those in the irradiated UO 2 . U 4 O 9 contains some cuboctahedral oxygen interstitial clusters that have been identified in neutron diffrac...

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The crystal structure of β-U4O9−y

Cited by 134 publications

References 10 publications

XAS study of (U1−yPuy)O2 solid solutions

XAS study of (U1−yPuy)O2 solid solutions

Refinement of the structure of β-U₄O₉

Recent Progress in Using Advanced Characterization and Modeling Approaches to Study Radiation Effects in Oxide Ceramics

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The crystal structure of β-U4O9−y

Cited by 134 publications

References 10 publications

XAS study of (U1−yPuy)O2 solid solutions

XAS study of (U1−yPuy)O2 solid solutions

Refinement of the structure of β-U4O9

Recent Progress in Using Advanced Characterization and Modeling Approaches to Study Radiation Effects in Oxide Ceramics

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Product

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Refinement of the structure of β-U₄O₉