Density functional theory investigation of the layered uranium oxides U3O8 and U2O5

• Published in: Dalton transactions : an international journal of inorganic chemistry 2015-02, Vol.44 (6), p.2613-2622
• Main Authors: Brincat, Nicholas A, Parker, Stephen C, Molinari, Marco, Allen, Geoffrey C, Storr, Mark T
• Format: Article
• Language: English
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c4dt02493a

Oxidation of UO 2 in the nuclear fuel cycle leads to formation of the layered uranium oxides. Here we present DFT simulations of U 2 O 5 and U 3 O 8 using the PBE + U functional to examine their structural, electronic and mechanical properties. We build on previous simulation studies of Amm 2 α-U 3 O 8 , P 2 1 / m β-U 3 O 8 and P 6&cmb.macr;2 m γ-U 3 O 8 by including C 222 α-U 3 O 8 , Cmcm β-U 3 O 8 and Pnma δ-U 2 O 5 . All materials are predicted to be insulators with no preference for ferromagnetic or antiferromagnetic ordering. We predict δ-U 2 O 5 contains exclusively U 5+ ions in an even mixture of distorted octahedral and pentagonal bipyramidal coordination sites. In each U 3 O 8 polymorph modelled we predict U 5+ ions in pentagonal bipyramidal coordination and U 6+ in octahedral coordination, with no U 4+ present. The elastic constants of each phase have been calculated and the bulk modulus is found to be inversely proportional to the volume per uranium ion. Finally, a number of thermodynamic properties are estimated, showing general agreement with available experiments; for example α- and β-U 3 O 8 are predicted to be stable at low temperatures but β-U 3 O 8 and γ-U 3 O 8 dominate at high temperature and high pressure respectively. New predictions of structural, electronic and mechanical properties of layered uranium oxides using DFT + U calculations.