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Title: Ion-transport phenomena and anomalous transformations in strontium uranium oxides
Authors: Murphy, GL
Zhang, Z
Avdeev, M
Wang, CH
Beridze, G
Kowalski, PM
Gu, QF
Kimpton, JA
Johannessen, B
Kennedy, BJ
Keywords: Uranium oxides
Spent fuel storage
X-ray diffraction
Crystal lattices
Issue Date: 28-Aug-2014
Publisher: International Union of Crystallography
Citation: Murphy, G. L., Zhang, Z., Avdeev, M., Wang, C.-H., Beridze, G., Kowalski, P., Gu, Q., Kimpton, J., Johannessen, B., & Kennedy, B. (2014). Ion-transport phenomena and anomalous transformations in strontium uranium oxides. Paper presented at XXIV IUCr Congress, Hyderabad, India, 21-28 August. In Acta Crystallographica Section A Foundations and advances A73 Supplement, C1450. doi:10.1107/S2053273317081487
Abstract: Structural-chemical elucidation of low dimensional ternary uranium oxide systems is considered an essential aspect of the nuclear fuel cycle since understanding of their physicochemical properties may guide the storage and disposal of spent nuclear fuel [1]. The study of these systems allows for further exploration of the peculiar, exotic and poorly known properties of materials containing, or which can access, 5f electrons. SrUO₄ exemplifies this, a potential waste form resulting from reaction between spent UO₂+x fuel and the fission daughter Sr-90. We have found, through a combination of in situ synchrotron X-ray powder diffraction and X-ray absorption spectroscopy, that during its first order rhombohedral-orthorhombic transition under oxidising conditions, the rhombohedral form of SrUO₄, α, undergoes a spontaneous reduction of the uranium valence state through oxygen vacancy formation [2]. The process is synergetic, as the triality of oxygen vacancy formation, subsequent ion diffusion and uranium reduction, seemingly reduces the activation energy barrier for the transformation to the thermodynamically favoured stoichiometric orthorhombic form, β-SrUO₄. However formation of the orthorhombic form is only possible if a source of oxygen is present, without this, the oxygen deficient α-SrUO₄-x remains rhombohedral as shown by in situ neutron powder diffraction measurements. These experimental observations are further supported by ab initio DFT+U calculations using the self consistently calculated Hubbard U parameter values and bond valence sums calculations [2-3]. These methods indicate the affinity for α-SrUO₄-x to retain oxygen vacancies as opposed to β-SrUO₄, a consequence of the crystal lattice’s ability to stabilise the coordination environment of the Sr²⁺ cation via the flexibility of uranium to undergo reduction through vacancy formation. © International Union of Crystallography
ISSN: 2053-2733
Appears in Collections:Conference Publications

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