Neutron diffraction investigation of ordered oxygen vacancies in the defect pyrochlores, Pb2Ru2O6.5 and PbT1Nb2O6.5
| Autor: | R. A. Beyerlein, M.E. Leonowicz, John M. Longo, Harold S. Horowitz, James D. Jorgensen, Frank J. Rotella |
|---|---|
| Rok vydání: | 1984 |
| Předmět: |
Diffraction
Chemistry Neutron diffraction Pyrochlore Crystal structure engineering.material Condensed Matter Physics Electronic Optical and Magnetic Materials Inorganic Chemistry Crystallography Tetragonal crystal system Vacancy defect Materials Chemistry Ceramics and Composites engineering Frenkel defect Physical and Theoretical Chemistry Stoichiometry Nuclear chemistry |
| Zdroj: | Journal of Solid State Chemistry. 51:253-265 |
| ISSN: | 0022-4596 |
| DOI: | 10.1016/0022-4596(84)90341-4 |
| Popis: | Powder neutron diffraction has been used to investigate the structure of the defect pyrochlores Pb2Ru2O6.5 and PbT1Nb2O6.5. Both materials show evidence for oxygen vacancy ordering that is accompanied byA-site cation displacement. The diffraction data for Pb2Ru2O6.5 have been successfully fit in the cubic space groupF¯43m. The results confirm half occupancy of the defect site, demonstrate oxygen vacancy ordering, and show that each Pb atom is displaced by 0.040(4)A˚toward its associated vacancy. The diffraction data for PbT1Nb2O6.5 have been fit in the tetragonal space groupP¯4m2 using a model that allows ordering of Pb and T1 on theA site in concert with oxygen vacancy ordering. The fitting results specify a stoichiometry PbT10.90Nb2O6.45 for this material; the slight T1 deficiency is probably associated with some T1 loss to the vessel walls during the sealed tube synthesis at 600°C. The Rietveld structural refinement also shows that Pb is displaced slightly away from its associated vacancy while T1 is displaced significantly toward its associated vacancy with resulting T1 T1 separations similar to those found in T1 metal. It is suggested that theA-site cation ordering observed in each of these materials is a consequence ofA cation-oxygen bonding rather than the formation ofA Abonds through the oxygen vacancy despite the closeA Aseparations observed. These results are believed to provide the first examples of anion/vacancy ordering in a defect pyrochlore of the typeA2B2O7−y. |
| Databáze: | OpenAIRE |
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