A novel high-temperature commensurate superstructure in a natural bariopyrochlore: A structural study by means of a multiphase crystal structure refinement
- Dipartimento di Scienze della Terra, Universita degli Studi di Firenze, Via La Pira 4, I-50121 Florence (Italy)
- Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague (Czech Republic)
- Research School of Chemistry, Australian National University, GPO Box 4, Canberra ACT 0200 (Australia)
Additional X-ray diffraction effects yielding an eightfold commensurate superstructure [a=20.974(5)A] of the ideal pyrochlore structure were observed after annealing at 873K of a thallium-doped bariopyrochlore single crystal. Electron diffraction indicated the coexistence of two cubic phases, the pyrochlore structure and a new F-centred, cubic phase. The superstructure was solved and refined in the space group F4-bar 3m. The two phases were combined together and refined as independently diffracting to R=0.0628. The resulting unit-cell content is (A,-bar ){sub 20}Nb{sub 16}Ti{sub 2}O{sub 53}(Z=8), with A=Ba, Tl, Ce, Th. For some atomic positions of the superstructure, third- and fourth-order anharmonic ADP's were used to account for the specific density shape having a continuous character as typical for ionic conductors. There are three distinct clusters in the superstructure, leading to a new structure type no longer strictly of pyrochlore-structure type.
- OSTI ID:
- 20784916
- Journal Information:
- Journal of Solid State Chemistry, Vol. 179, Issue 3; Other Information: DOI: 10.1016/j.jssc.2005.11.031; PII: S0022-4596(05)00569-4; Copyright (c) 2005 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
- Country of Publication:
- United States
- Language:
- English
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