Phase and valence transitions in Ba₂LnSnₓSb₁−xO₆−δ (Ln=Pr and Tb) | Phase and valence transitions in Ba(2)LnSn(x)Sb(1-x)O(6-delta) (Ln = Pr and Tb)
2008
Saines, P. | Kennedy, B. | Elcombe, M. | Harris, H. | Jang, L. | Zhang, Z.
Compounds in the double perovskites series Ba<inf>2</inf>LnSn<inf>x</inf>Sb<inf>1-x</inf>O<inf>6-δ</inf> (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 Ba<inf>2</inf>PrSn<inf>x</inf>Sb<inf>1-x</inf>O<inf>6-δ</inf> 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 Pr<sup>3+</sup> to Pr<sup>4+</sup> with increasing x and that this is likely to be the cause of the loss of B-site ordering. Similarly, both Ba<inf>2</inf>TbSbO<inf>6</inf> and Ba<inf>2</inf>TbSnO<inf>6-δ</inf> 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 Tb<sup>3+</sup> to Tb<sup>4+</sup>. Multiple linear regression analysis of the Pr and Tb L<inf>III</inf>-edge XANES indicates that the rate of Ln<sup>3+</sup> transforming to Ln<sup>4+</sup> is such that there are no oxygen vacancies in Ba<inf>2</inf>PrSn<inf>x</inf>Sb<inf>1-x</inf>O<inf>6-δ</inf> but in Ba<inf>2</inf>TbSn<inf>x</inf>Sb<inf>1-x</inf>O<inf>6-δ</inf> there is a small amount of oxygen vacancies, with a maximum of δ≈0.05 present. Crown Copyright © 2008.
Show more [+] Less [-]Paul J. Saines, Brendan J. Kennedy, Margaret M. Elcombe, Hugh H. Harris, Ling-Yun Jang and Zhaoming Zhang
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