Phase and valence transitions in Ba{sub 2}LnSn{sub x}Nb{sub 1-x}O{sub 6-{delta}}

The structures of compounds in the perovskite series Ba{sub 2}LnSn{sub x}Nb{sub 1-x}O{sub 6-{delta}} (Ln=Pr and Tb and x=0, 0.1, 0.2, ..., 1.0) have been examined using synchrotron X-ray and neutron diffraction. It was found that niobate members of both series feature full B-site cation ordering but...

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Bibliographic Details
Published in:Journal of solid state chemistry 2008-11, Vol.181 (11)
Main Authors: Saines, Paul J., Kennedy, Brendan J., Johannessen, Bernt, Poulton, Sarah, Department of Materials and Engineering, University of Maryland, College Park, MD 20742
Format: Article
Language:English
Subjects:
ABSORPTION
ABSORPTION SPECTRA
ABSORPTION SPECTROSCOPY
ANTIMONY IONS
BARIUM COMPOUNDS
CATIONS
INFRARED SPECTRA
INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
LEAST SQUARE FIT
NEUTRON DIFFRACTION
NIOBATES
OXIDATION
PEROVSKITE
PHASE TRANSFORMATIONS
PRASEODYMIUM COMPOUNDS
TERBIUM COMPOUNDS
TIN COMPOUNDS
TIN IONS
VACANCIES
VALENCE
X-RAY DIFFRACTION
X-RAY SPECTROSCOPY
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Summary:The structures of compounds in the perovskite series Ba{sub 2}LnSn{sub x}Nb{sub 1-x}O{sub 6-{delta}} (Ln=Pr and Tb and x=0, 0.1, 0.2, ..., 1.0) have been examined using synchrotron X-ray and neutron diffraction. It was found that niobate members of both series feature full B-site cation ordering but that this order is lost with increasing x. X-ray absorption near-edge structure (XANES) and near-infrared spectroscopies indicate that the oxidation state of the lanthanide cations gradually changes from Ln{sup 3+} to Ln{sup 4+} with increased Sn{sup 4+} doping. This is believed to be the cause of the loss of B-site ordering. Least squares analysis of the XANES spectra suggests that the rate of the transformation of Ln{sup 3+} cations to the tetravalent state is such that the Pr series contains no oxygen vacancies while the Tb series may contain a very small amount of vacancies, with {delta}{approx}0.02. - Graphical abstract: The series Ba{sub 2}LnSn{sub x}Nb{sub 1-x}O{sub 6-{delta}} (Ln=Pr and Tb) has been investigated using powder diffraction and spectroscopic techniques. Similarly to the analogous Sb{sup 5+} containing compounds it was found that Sn{sup 4+} doping leads to the gradual oxidation of the Ln{sup 3+} cations to the Ln{sup 4+} state. Quantitative analysis of the Ln L{sub III}-edge absorption spectra indicates that few or no oxygen vacancies are present.
ISSN:0022-4596
1095-726X
DOI:10.1016/j.jssc.2008.07.021