WTh{sub 8}Zr{sub 18}F{sub 4}O{sub 53}: A new superstructure of fluorite type, associating anion-excess and anion-deficient blocks
- CNRS, Limoges (France)
The crystal structure of a new complex oxyfluoride WTh{sub 8}Zr{sub 18}F{sub 4}O{sub 53}, a member of a wide series MTh{sub 8}Zr{sub 18} (F, O){sub 57}, was solved on the basis of single-crystal data obtained on a four-circle diffractometer CAD-4 (R = 4.2%). The space group is Fm3m(Z = 4) and the lattice derives from fluorite-type one by the relationship a = 1578.5 pm = 3 a{sub F}. This structure is characterized by a fcc cationic array with full cationic ordering and by an ordered distribution of two kinds of structural units: (i) anion-excess fluorite units containing {open_quotes}cuboctahedral{close_quotes} clusters, similar to those observed in anion-excess fluorite phases, e.g., {beta}-U{sub 4}O{sub 9} and KY{sub 3}F{sub 10} (these units are composed of six ZrO{sub 8} square antiprisms, sharing edges with eight ThFO{sub 9} polyhedra, about a cuboctahedral anionic cavity occupied by an extra F anion); (ii) Anion-deficient fluorite units, based on the association, about a single WFO{sub 5} octahedron, of six ZrO{sub 7} and six ZrO{sub 8} polyhedra, in a similar way as in {open_quotes}stabilized{close_quotes} zirconia and L{sub n}O{sub 2n-2} rare earth oxides (e.g., Pr{sub 7}O{sub 12}). Then, WTh{sub 8}Zr{sub 18}F{sub 4}O{sub 53} is the first example of a fluorite superstructure composed of an ordered intergrowth of anion-excess Th{sub 8}Zr{sub 6}F{sub 3}O{sub 30} and anion-deficient WZr{sub 12}FO{sub 23} fluorite blocks. WTh{sub 8}Zr{sub 18}F{sub 4}O{sub 53} is the anion-excess fluorite superstructure the poorest in anions ever characterized: MX{sub 2.11}. The possibility, demonstrated for the first time, to associate in a fluorite structure anion-excess and anion-deficient parts constitutes a conceptual advance in the knowledge of nonstoichiometry.
- OSTI ID:
- 508686
- Journal Information:
- Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 1 Vol. 115; ISSN 0022-4596; ISSN JSSCBI
- Country of Publication:
- United States
- Language:
- English
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