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Please use this identifier to cite or link to this item: http://apo.ansto.gov.au/dspace/handle/10238/1087

Title: Structures of 6H perovskites Ba3CaSb2O9 and Ba3SrSb2O9 determined by synchrotron X-ray diffraction, neutron powder diffraction and ab initio calculations.
Authors: Rowda, B
Avdeev, M
Lee, PL
Henry, PF
Ling, CD
Keywords: Perovskites
Synchrotrons
Neutron Diffraction
Symmetry
Ionic Composition
Decomposition
Issue Date: Apr-2008
Publisher: International Union of Crystallography
Citation: Rowda, B., Avdeev, M., Lee, P. L., Henry, P. F., & Ling, C. D. (2008). Structures of 6H perovskites Ba3CaSb2O9 and Ba3SrSb2O9 determined by synchrotron X-ray diffraction, neutron powder diffraction and ab initio calculations. Acta Crystallographica Section B-Structural Science, 64, 154-159.
Abstract: The structures of the 6H perovskites Ba3 B 2+Sb5+ 2O9, B = Ca and Sr, have been solved and refined using synchrotron X-ray and neutron powder diffraction data. Ba3CaSb2O9 and Ba3SrSb2O9 have monoclinic C2/c and triclinic space-group symmetries, respectively, while Ba3MgSb2O9 has ideal hexagonal P63/mmc space-group symmetry. The symmetry-lowering distortions are a consequence of internal chemical pressure' owing to the increasing effective ionic radius of the alkaline-earth cation in the perovskite B site from Mg2+ (0.72 Å) to Ca2+ (1.00 Å) to Sr2+ (1.18 Å). Increasing the effective ionic radius further to Ba2+ (1.35 Å) leads to decomposition at room temperature. The driving force behind the transition from P63/mmc to C2/c is the need to alleviate underbonding of Ba2+ cations in the perovskite A site via octahedral rotations, while the transition from C2/c to is driven by the need to regularize the shape of the Sb2O9 face-sharing octahedral dimers. Ab initio geometry-optimization calculations were used to find a triclinic starting model for Ba3SrSb2O9. © 2008, International Union of Crystallography
URI: http://dx.doi.org/10.1107/S0108768108005041
http://apo.ansto.gov.au/dspace/handle/10238/1087
ISSN: 0108-7681
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