Order-disorder phase transformations in quaternary pyrochlore oxide system: Investigated by X-ray diffraction, transmission electron microscopy and Raman spectroscopic techniques

Journal Article · Sat Aug 15 00:00:00 EDT 2009 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2009.06.016· OSTI ID:21370557

Radhakrishnan, A N ^[1]; Sibi, K S; Deepa, M; Koshy, Peter ^[1]

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1. Materials and Minerals Division, National Institute for Interdisciplinary Science and Technology (NIIST), Trivandrum 695 019 (India)

Order-disorder transformations in a quaternary pyrochlore oxide system, Ca-Y-Zr-Ta-O, were studied by powder X-ray diffraction (XRD) method, transmission electron microscope (TEM) and FT-NIR Raman spectroscopic techniques. The solid solutions in different ratios, 4:1, 2:1, 1:1, 1:2, 1:4, 1:6, of CaTaO{sub 3.5} and YZrO{sub 3.5} were prepared by the conventional high temperature ceramic route. The XRD results and Rietveld analysis revealed that the crystal structure changed from an ordered pyrochlore structure to a disordered defect fluorite structure as the ratios of the solid solutions of CaTaO{sub 3.5} and YZrO{sub 3.5} were changed from 4:1 to 1:4. This structural transformation in the present system is attributed to the lowering of the average cation radius ratio, r{sub A}/r{sub B} as a result of progressive and simultaneous substitution of larger cation Ca{sup 2+} for Y{sup 3+} at A sites and smaller cation Ta{sup 5+} for Zr{sup 4+} at B sites. Raman spectroscopy and TEM analysis corroborated the XRD results. - Graphical abstract: Selected area electron diffraction (SAED) patterns showed highly ordered diffraction maxima with characteristic superlattice weak diffraction spots of the pyrochlore structure for (a) Ca{sub 0.6}7Y{sub 1.33}Zr{sub 1.33}Ta{sub 0.33}O{sub 7} (C2YZT2) and bright diffraction maxima arranged in a ring pattern of the fluorite structure for (b) Ca{sub 0.29}7Y{sub 1.71}Zr{sub 1.71}Ta{sub 0.29}O{sub 7} (CY6Z6T).

• OSTI ID: 21370557
• Journal Information: Journal of Solid State Chemistry, Vol. 182, Issue 8; Other Information: DOI: 10.1016/j.jssc.2009.06.016; PII: S0022-4596(09)00266-7; Copyright (c) 2009 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CALCIUM COMPOUNDS
CATIONS
CERAMICS
CRYSTAL STRUCTURE
ELECTRON DIFFRACTION
ORDER-DISORDER TRANSFORMATIONS
OXIDES
PYROCHLORE
RAMAN SPECTRA
RAMAN SPECTROSCOPY
SUPERLATTICES
TANTALUM COMPOUNDS
TRANSMISSION ELECTRON MICROSCOPY
X-RAY DIFFRACTION
YTTRIUM COMPOUNDS
ZIRCONIUM COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
CHALCOGENIDES
CHARGED PARTICLES
COHERENT SCATTERING
DIFFRACTION
ELECTRON MICROSCOPY
IONS
LASER SPECTROSCOPY
MICROSCOPY
MINERALS
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
REFRACTORY METAL COMPOUNDS
SCATTERING
SPECTRA
SPECTROSCOPY
TRANSITION ELEMENT COMPOUNDS