Structural Characterization of the High-Temperature Phase Transitions in Ca8[Al12O24](MoO4)2Aluminate Sodalite Using X-ray Powder Diffraction

van Smaalen, Sander, Dinnebier, Robert, Katzke, Hannelore and Depmeier, Wulf (1997) Structural Characterization of the High-Temperature Phase Transitions in Ca8[Al12O24](MoO4)2Aluminate Sodalite Using X-ray Powder Diffraction Journal of Solid State Chemistry, 129 (1). pp. 130-143. DOI 10.1006/jssc.1996.7251.

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Abstract

The structures are reported of the room-temperature and the three high-temperature phases of Ca8[Al12O24](MoO4)2aluminate sodalite CAM. Structure refinements have been performed with the Rietveld method using synchrotron radiation X-ray powder diffraction data. The cubic phase has symmetryI3mwitha=9.29377(4) Å. The tetragonal phases have symmetryPc2, and their unit cells corresponds to asupercell of the cubic phase. The second tetragonal phase (T2) exists for 614<T<624 K and has lattice parametersa=13.14536(6) Å andc=9.29224(8) Å. The first tetragonal (T1) phase is stable for 590<T<614 K and has lattice parametersa=13.12263(5) Å andc=9.32081(5) Å, The orthorhombic phase has symmetryAba2 witha=26.14683(8) Å,b=13.07061 Å, andc=9.31413(2) Å. The transition (on decreasing temperatures) atTc[approximate]624 K, from the cubic to the T2 phase, is of second order and is found to be related to change in the orientational order of the cage anions MoO2-4. The T2 to T1 transition atTc[approximate]614 K is of first order, and it corresponds to a displacement of the cage anions to an off-center position in the cages, while keeping orientational disorder over at least two orientations. The transition atTc[approximate]590 K, from the T1 phase to the orthorhombic phase, is again a first-order transition, and it is related to a complete ordering of the cage anions. A detailed description is given of the structural distortions of the framework, accompanying the phase transitions.

Document Type: Article
Research affiliation: Kiel University
Refereed: No
DOI etc.: 10.1006/jssc.1996.7251
ISSN: 0022-4596
Date Deposited: 02 Feb 2012 09:19
Last Modified: 08 Oct 2012 07:33
URI: http://eprints.uni-kiel.de/id/eprint/15552

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