title: Structure and thermodynamic stability of UTa3O10, a U(v)-bearing compound.
abstract: Heating a mixture of uranyl(vi) nitrate and tantalum(v) oxide in the molar ratio of 2 : 3 to 1400 °C resulted in the formation of a new compound, UTa3O10. The honey colored to yellow brown crystals of UTa3O10crystallize in an orthorhombic structure with the space group Fddd (no. 70), lattice parameters a = 7.3947(1), b = 12.7599(2), c = 15.8156(2) Å, and Z = 8. Vertex sharing [TaO6]7-octahedra of two crystallographically distinct Ta cations form a three dimensional tantalate framework. Within this framework, six membered rings of [TaO6]7-octahedra are formed within the (001) plane. The center of these rings is occupied by the uranyl cations [UO2]+, with an oxidation state of +5 for uranium. The pentavalence of U and Ta was confirmed by X-ray photoelectron spectroscopy and X-ray adsorption spectroscopy. The enthalpy of formation of UTa3O10from Ta2O5, β-U3O7, and U3O8has been determined to be 13.1 ± 18.1 kJ mol-1using high temperature oxide melt solution calorimetry with sodium molybdate as the solvent at 700 °C. The close to zero enthalpy of formation of UTa3O10can be explained by closely balanced structural stabilizing and destabilizing factors, which may also apply to other UM3O10compounds.
authors.affiliation: Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA and Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California, Davis, California 95616, USA. anavrotsky@ucdavis.edu.
authors.forename: Xiaofeng
authors.identifier: http://orcid.org/0000-0003-3129-493X
authors.initials: X
authors.lastname: Guo
authors.affiliation: Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, Indiana 46556, USA.
authors.forename: Christian
authors.initials: C
authors.lastname: Lipp
authors.affiliation: Nuclear Research Center - Negev Be'er-Sheva 84190, Israel Institution, Israel.
authors.forename: Eitan
authors.initials: E
authors.lastname: Tiferet
authors.affiliation: Center for Advanced Radiation Sources, University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Antonio
authors.initials: A
authors.lastname: Lanzirotti
authors.affiliation: Center for Advanced Radiation Sources, University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Newville
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99354, USA.
authors.forename: Mark H
authors.initials: MH
authors.lastname: Engelhard
authors.affiliation: The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington 99163, USA.
authors.forename: Di
authors.identifier: http://orcid.org/0000-0001-6879-321X
authors.initials: D
authors.lastname: Wu
authors.affiliation: Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
authors.forename: Eugene S
authors.initials: ES
authors.lastname: Ilton
authors.affiliation: Center for Advanced Radiation Sources, University of Chicago, Chicago, Illinois 60637, USA and Department of Geophysical Sciences, University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Sutton
authors.affiliation: Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: Hongwu
authors.initials: H
authors.lastname: Xu
authors.affiliation: Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, Indiana 46556, USA and Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Burns
authors.affiliation: Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California, Davis, California 95616, USA. anavrotsky@ucdavis.edu.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Navrotsky