title: A new look at the structural properties of trisodium uranate Na3UO4.
abstract: The crystal structure of trisodium uranate, which forms following the interaction between sodium and hyperstoichiometric urania, has been solved for the first time using powder X-ray and neutron diffraction, X-ray absorption near-edge structure spectroscopy, and solid-state (23)Na multiquantum magic angle spinning nuclear magnetic resonance. The compound, isostructural with Na3BiO4, has monoclinic symmetry, in space group P2/c. Moreover, it has been shown that this structure can accommodate some cationic disorder, with up to 16(2)% sodium on the uranium site, corresponding to the composition α-Na3(U1-x,Nax)O4 (0 < x < 0.18). The α phase adopts a mixed valence state with the presence of U(V) and U(VI). The two polymorphs of this compound described in the literature, m- and β-Na3(U1-x,Nax)O4, have also been investigated, and their relationship to the α phase has been established. The completely disordered low-temperature cubic phase corresponds to a metastable phase. The semiordered high-temperature β phase is cubic, in space group Fd3̅m.
authors: †European Commission, Joint Research Centre, Institute for Transuranium Elements, P.O. Box 2340, D-76125 Karlsruhe, Germany.|‡Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS, United Kingdom.
authors: Anna L
authors: AL
authors: Smith
authors: †European Commission, Joint Research Centre, Institute for Transuranium Elements, P.O. Box 2340, D-76125 Karlsruhe, Germany.
authors: Philippe E
authors: PE
authors: Raison
authors: †European Commission, Joint Research Centre, Institute for Transuranium Elements, P.O. Box 2340, D-76125 Karlsruhe, Germany.
authors: Laura
authors: L
authors: Martel
authors: †European Commission, Joint Research Centre, Institute for Transuranium Elements, P.O. Box 2340, D-76125 Karlsruhe, Germany.
authors: Damien
authors: D
authors: Prieur
authors: §UMR CEA/CNRS 3685 - NIMBE, 91191 Gif-sur-Yvette, France.
authors: Thibault
authors: T
authors: Charpentier
authors: ∥PSL Research University, Chimie ParisTech-CNRS, Institut de Recherche de Chimie Paris, 75005 Paris, France.|⊥Sorbonne University, UPMC Université Paris 06, 75005 Paris, France.
authors: Gilles
authors: G
authors: Wallez
authors: #Institut Laue Langevin, Rue Jules Horowitz, BP 156, 38042, Grenoble cedex 9, France.
authors: Emmanuelle
authors: E
authors: Suard
authors: ○Helmholtz Zentrum Dresden Rossendorf (HZDR), Institute of Resource Ecology, P.O. Box 10119, 01314 Dresden, Germany.
authors: Andreas C
authors: AC
authors: Scheinost
authors: ○Helmholtz Zentrum Dresden Rossendorf (HZDR), Institute of Resource Ecology, P.O. Box 10119, 01314 Dresden, Germany.
authors: Christoph
authors: C
authors: Hennig
authors: ∇CEA, DEN, DEC, CEN Cadarache, 13108 St. Paul Lez Durance, France.
authors: Philippe
authors: P
authors: Martin
authors: ◆European Synchrotron Radiation Facility, 6 rue Jules Horowitz, BP 220, 38043 Grenoble, France.
authors: Kristina O
authors: KO
authors: Kvashnina
authors: ‡Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS, United Kingdom.
authors: Anthony K
authors: AK
authors: Cheetham
authors: †European Commission, Joint Research Centre, Institute for Transuranium Elements, P.O. Box 2340, D-76125 Karlsruhe, Germany.
authors: Rudy J M
authors: RJ
authors: Konings