Phase and valence transitions in Ba(2)LnSn(x)Sb(1-x)O(6-delta) (Ln = Pr and Tb)
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Date
2008-11
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Publisher
Elsevier
Abstract
Compounds in the double perovskites series Ba(2)LnSn(x)Sb(1-x)O(6-delta) (Ln = Pr and Tb) have been synthesised and structurally characterised using synchrotron X-ray and neutron powder diffraction. It was found that the two end-members of the Ba2PrSnxSb1-xO6-delta series both adopt rhombohedral symmetry but the antimonate is a fully ordered double perovskite while the stannate has no B-site cation ordering. X-ray absorption near-edge structure (XANES) and near-infrared spectroscopy indicate that the Pr cations gradually change oxidation state from Pr3+ to Pr4+ with increasing x and that this is likely to be the cause of the loss of B-site ordering. Similarly, both Ba2TbSbO6 and Ba2TbSnO6-delta are cubic with B-site ordering present in the former but absent in the latter due to the oxidation state change of the Tb from Tb3+ to Tb4+. Multiple linear regression analysis of the Pr and Tb L-III-edge XANES indicates that the rate of Ln(3+) transforming to Ln(4+) is such that there are no oxygen vacancies in Ba2PrSnxSb1-xO6-delta but in Ba2TbSnxSb1-xO6-delta there is a small amount of oxygen vacancies, with a maximum of delta approximate to 0.05 present. © 2008, Elsevier Ltd.
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Keywords
Perovskite, Phase transformations, Valence, X-ray diffraction, Oxygen, Rare earths
Citation
Saines, P. J., Kennedy, B. J., Elcombe, M. M., Harris, H. H., Jang, L. Y., & Zhang, Z. (2008). Phase and valence transitions in Ba(2)LnSn(x)Sb(1-x)O(6-delta) (Ln = Pr and Tb). Journal of Solid State Chemistry, 181(11), 2941-2952. doi:10.1016/j.jssc.2008.07.007