title: Probing disorder in isometric pyrochlore and related complex oxides.
abstract: There has been an increased focus on understanding the energetics of structures with unconventional ordering (for example, correlated disorder that is heterogeneous across different length scales). In particular, compounds with the isometric pyrochlore structure, A2B2O7, can adopt a disordered, isometric fluorite-type structure, (A, B)4O7, under extreme conditions. Despite the importance of the disordering process there exists only a limited understanding of the role of local ordering on the energy landscape. We have used neutron total scattering to show that disordered fluorite (induced intrinsically by composition/stoichiometry or at far-from-equilibrium conditions produced by high-energy radiation) consists of a local orthorhombic structural unit that is repeated by a pseudo-translational symmetry, such that orthorhombic and isometric arrays coexist at different length scales. We also show that inversion in isometric spinel occurs by a similar process. This insight provides a new basis for understanding order-to-disorder transformations important for applications such as plutonium immobilization, fast ion conduction, and thermal barrier coatings.
authors.affiliation: Department of Nuclear Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA.|Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA.
authors.forename: Jacob
authors.initials: J
authors.lastname: Shamblin
authors.affiliation: Chemical and Engineering Materials Division, Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: Mikhail
authors.initials: M
authors.lastname: Feygenson
authors.affiliation: Chemical and Engineering Materials Division, Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: Joerg
authors.initials: J
authors.lastname: Neuefeind
authors.affiliation: Department of Geological Sciences, Stanford University, Stanford, California 94305-2115, USA.
authors.forename: Cameron L
authors.initials: CL
authors.lastname: Tracy
authors.affiliation: Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Fuxiang
authors.initials: F
authors.lastname: Zhang
authors.affiliation: Forschungszentrum Jülich, Institute of Energy and Climate Research, IEK-6: Nuclear Waste Management and Reactor Safety, 52425 Jülich, Germany.
authors.forename: Sarah
authors.initials: S
authors.lastname: Finkeldei
authors.affiliation: Forschungszentrum Jülich, Institute of Energy and Climate Research, IEK-6: Nuclear Waste Management and Reactor Safety, 52425 Jülich, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Bosbach
authors.affiliation: Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA.
authors.forename: Haidong
authors.initials: H
authors.lastname: Zhou
authors.affiliation: Department of Geological Sciences, Stanford University, Stanford, California 94305-2115, USA.
authors.forename: Rodney C
authors.initials: RC
authors.lastname: Ewing
authors.affiliation: Department of Nuclear Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA.
authors.forename: Maik
authors.initials: M
authors.lastname: Lang
mesh_terms: D008956:Models, Chemical; D015336:Molecular Probe Techniques; D033363:Neutron Diffraction / Q000379:methods*; D009556:Niobium / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D010087:Oxides; D009556:Niobium; C016709:pyrochlore