title: Chemical ordering in substituted fluorite oxides: a computational investigation of Ho2Zr2O7and RE2Th2O7(RE=Ho, Y, Gd, Nd, La).
abstract: Fluorite-structured oxides find widespread use for applications spanning nuclear energy and waste containment, energy conversion, and sensing. In such applications the host tetravalent cation is often partially substituted by trivalent cations, with an associated formation of charge-compensating oxygen vacancies. The stability and properties of such materials are known to be influenced strongly by chemical ordering of the cations and vacancies, and the nature of such ordering and associated energetics are thus of considerable interest. Here we employ density-functional theory (DFT) calculations to study the structure and energetics of cation and oxygen-vacancy ordering in Ho2Zr2O7. In a recent neutron total scattering study, solid solutions in this system were reported to feature local chemical ordering based on the fluorite-derivative weberite structure. The calculations show a preferred chemical ordering qualitatively consistent with these findings, and yield values for the ordering energy of 9.5 kJ/mol-cation. Similar DFT calculations are applied to additional RE2Th2O7fluorite compounds, spanning a range of values for the ratio of the tetravalent and trivalent (RE) cation radii. The results demonstrate that weberite-type order becomes destabilized with increasing values of this size ratio, consistent with an increasing energetic preference for the tetravalent cations to have higher oxygen coordination.
authors.affiliation: Department of Materials Science and Engineering, University of California Berkeley, Berkeley, CA 94720, United States.
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Solomon
authors.affiliation: Department of Nuclear Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States.|Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, United States.
authors.forename: Jacob
authors.initials: J
authors.lastname: Shamblin
authors.affiliation: Department of Nuclear Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States.
authors.forename: Maik
authors.initials: M
authors.lastname: Lang
authors.affiliation: Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California Davis, Davis, CA 95616, United States.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Navrotsky
authors.affiliation: Department of Materials Science and Engineering, University of California Berkeley, Berkeley, CA 94720, United States.
authors.forename: Mark
authors.initials: M
authors.lastname: Asta