Phase and valence transitions in Ba{sub 2}LnSn{sub x}Sb{sub 1-x}O{sub 6-{delta}} (Ln=Pr and Tb)

Journal Article · Sat Nov 15 04:00:00 EST 2008 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2008.07.007· OSTI ID:21212088

Saines, Paul J ^[1]; Elcombe, Margaret M ^[2]; Harris, Hugh H ^[3]; Lingyun, Jang ^[4]; Zhang, Zhaoming ^[5]

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1. School of Chemistry, University of Sydney, Sydney, New South Wales 2006 (Australia)
2. Bragg Institute, ANSTO, Private Mail Bag 1, Menai, New South Wales 2234 (Australia)
3. School of Chemistry and Physics, University of Adelaide, Adelaide, South Australia 5005 (Australia)
4. Research Division, National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan (China)
5. Institute of Materials Engineering, ANSTO, Private Mail Bag 1, Menai, New South Wales 2234 (Australia)

Compounds in the double perovskites series Ba{sub 2}LnSn{sub x}Sb{sub 1-x}O{sub 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 Ba{sub 2}PrSn{sub x}Sb{sub 1-x}O{sub 6-{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 Pr{sup 3+} to Pr{sup 4+} with increasing x and that this is likely to be the cause of the loss of B-site ordering. Similarly, both Ba{sub 2}TbSbO{sub 6} and Ba{sub 2}TbSnO{sub 6-{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 Tb{sup 3+} to Tb{sup 4+}. Multiple linear regression analysis of the Pr and Tb L{sub III}-edge XANES indicates that the rate of Ln{sup 3+} transforming to Ln{sup 4+} is such that there are no oxygen vacancies in Ba{sub 2}PrSn{sub x}Sb{sub 1-x}O{sub 6-{delta}} but in Ba{sub 2}TbSn{sub x}Sb{sub 1-x}O{sub 6-{delta}} there is a small amount of oxygen vacancies, with a maximum of {delta}{approx}0.05 present. - Graphical abstract: Powder diffraction and spectroscopic techniques have been used to investigate the series Ba{sub 2}LnSn{sub x}Sb{sub 1-x}O{sub 6-{delta}} (Ln=Pr or Tb). It was found that increased Sn{sup 4+} doping leads to oxidation of the Ln{sup 3+} cations to Ln{sup 4+}. The X-ray absorption near-edge structure of the Ln L{sub III}-edge indicates that this oxidation state change occurs gradually such that there are few oxygen vacancies present.

• OSTI ID: 21212088
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 11 Vol. 181; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ABSORPTION
ABSORPTION SPECTROSCOPY
CATIONS
INFRARED SPECTRA
NEUTRON DIFFRACTION
OXIDATION
PEROVSKITE
PHASE TRANSFORMATIONS
PRASEODYMIUM COMPOUNDS
PRASEODYMIUM IONS
REGRESSION ANALYSIS
STANNATES
TERBIUM COMPOUNDS
TERBIUM IONS
TIN IONS
VACANCIES
VALENCE
X-RAY SPECTROSCOPY