title: Structural Phase Transitions and Water Dynamics in Uranyl Fluoride Hydrates.
abstract: We report a novel production method for uranium oxyfluoride [(UO2)7F14(H2O)7]·4H2O, referred to as structure D. Structure D is produced as a product of hydrating anhydrous uranyl fluoride, UO2F2, through the gas phase at ambient temperatures followed by desiccation by equilibration with a dry environment. We follow the structure of [(UO2)7F14(H2O)7]·4H2O through an intermediate, liquid-like phase, wherein the coordination number of the uranyl ion is reduced to 5 (from 6 in the anhydrous structure), and a water molecule binds as an equatorial ligand to the uranyl ion. Quasielastic neutron scattering results compare well with previous measurements of mineral hydrates. The two groups of structurally distinct water molecules in D perform restricted motion on a length scale commensurate with the O-H bond (r = 0.92 Å). The more tightly bound equatorial ligand waters rotate slower (Dr = 2.2 ps(-1)) than their hydrogen-bonded partners (Dr = 28.7 ps(-1)).
authors.affiliation: Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Andrew
authors.initials: A
authors.lastname: Miskowiec
authors.affiliation: Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.|University of Tennessee - Knoxville , Knoxville, Tennessee 37996, United States.
authors.forename: Marie C
authors.initials: MC
authors.lastname: Kirkegaard
authors.forename: Ashfia
authors.initials: A
authors.lastname: Huq
authors.forename: Eugene
authors.initials: E
authors.lastname: Mamontov
authors.forename: Kenneth W
authors.initials: KW
authors.lastname: Herwig
authors.affiliation: Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Lee
authors.initials: L
authors.lastname: Trowbridge
authors.forename: Adam
authors.initials: A
authors.lastname: Rondinone
authors.affiliation: Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Brian
authors.initials: B
authors.lastname: Anderson