Contrasting oxide crystal chemistry of Nb and Ta:
Journal Article
·
· Journal of Solid State Chemistry
- CSIRO Minerals, Box 312, Clayton South, Vic. 3169 (Australia)
- National Institute of Standards and Technology, Materials Science and Engineering Laboratory, Gaithersburg, MD 20899 (United States)
The high-temperature hexagonal forms of BaTa{sub 2}O{sub 6} and Ba{sub 0.93}Nb{sub 2.03}O{sub 6} have P6/mmm symmetry with unit-cell parameters a=21.116(1) A, c=3.9157(2) A and a=21.0174(3) A, c=3.9732(1) A, respectively. Single crystal X-ray structure refinements for both phases are generally consistent with a previously proposed model, except for displacements of some Ba atoms from high-symmetry positions. The structures are based on a framework of corner- and edge-connected Nb/Ta-centred octahedra, with barium atoms occupying sites in four different types of [0 0 1] channels with hexagonal, triangular, rectangular and pentagonal cross-sections. The refinements showed that the non-stoichiometry in the niobate phase is due to barium atom vacancies in the pentagonal channels and to extra niobium atoms occupying interstitial sites with tri-capped trigonal prismatic coordination. The origin of the non-stoichiometry is attributed to minimisation of non-bonded Ba-Ba repulsions. The hexagonal structure is related to the structures of the low-temperature forms of BaNb{sub 2}O{sub 6} and BaTa{sub 2}O{sub 6}, through a 30{sup o} rotation of the hexagonal rings of octahedra centred at the origin. - Graphical abstract: Polyhedral representation of the structure of BaM{sub 2}O{sub 6} projected along [0 0 1].
- OSTI ID:
- 21043824
- Journal Information:
- Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 9 Vol. 180; ISSN 0022-4596; ISSN JSSCBI
- Country of Publication:
- United States
- Language:
- English
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