title: Structure and Properties of Some Layered U2O5Phases: A Density Functional Theory Study.
abstract: U2O5is the boundary composition between the fluorite and the layered structures of the UO2→3system and the least studied oxide in the group. δ-U2O5is the only layered structure proposed so far experimentally, although evidence of fluorite-based phases has also been reported. Our DFT work explores possible structures of U2O5stoichiometry by starting from existing M2O5structures (where M is an actinide or transition metal) and replacing the M ions with uranium ions. For all structures, we predicted structural and electronic properties including bulk moduli and band gaps. The majority of structures were found to be less stable than δ-U2O5. U2O5in the R-Nb2O5structure was found to be a competitive structure in terms of stability, whereas U2O5in the Np2O5structure was found to be the most stable overall. Indeed, by including the vibrational contribution to the free energy using the frequencies obtained from the optimized unit cells we predict that Np2O5structured U2O5is the most thermodynamically stable under ambient conditions. δ-U2O5only becomes more stable at high temperatures and/or pressures. This suggests that a low-temperature synthesis route should be tested and so potentially opens a new avenue of research for pentavalent uranium oxides.
authors.affiliation: Department of Chemistry, University of Bath , Claverton Down, Bath BA2 7AY, United Kingdom.|Department of Chemistry, University of Huddersfield , Queensgate, Huddersfield HD1 3DH, United Kingdom.
authors.forename: Marco
authors.identifier: http://orcid.org/0000-0001-7144-6075
authors.initials: M
authors.lastname: Molinari
authors.affiliation: Department of Chemistry, University of Bath , Claverton Down, Bath BA2 7AY, United Kingdom.|AWE Public Limited Company, Aldermaston, Reading RG7 4PR, United Kingdom.
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Brincat
authors.affiliation: AWE Public Limited Company, Aldermaston, Reading RG7 4PR, United Kingdom.|Interface Analysis Center, University of Bristol , Bristol, United Kingdom.
authors.forename: Geoffrey C
authors.initials: GC
authors.lastname: Allen
authors.affiliation: Department of Chemistry, University of Bath , Claverton Down, Bath BA2 7AY, United Kingdom.
authors.forename: Stephen C
authors.identifier: http://orcid.org/0000-0003-3804-0975
authors.initials: SC
authors.lastname: Parker