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Haüyne: phase transition and high-temperature structures obtained from synchrotron radiation and Rietveld refinements

Published online by Cambridge University Press:  05 July 2018

I. Hassan ,
S. M. Antao  and
J. B. Parise
I. Hassan*
Affiliation:
Department of Chemistry, University of the West Indies, Mona, Kingston 7, Jamaica
S. M. Antao
Affiliation:
Mineral Physics Institute & Department of Geosciences, State University of New York, Stony Brook, NY 11794-2100, USA
J. B. Parise
Affiliation:
Mineral Physics Institute & Department of Geosciences, State University of New York, Stony Brook, NY 11794-2100, USA
*
*E-mail: [email protected]
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Abstract

The structural behaviour of a haüyne with a chemical composition of Na4.35Ca2.28K0.95[Al6Si6O24]- (SO4)2.03, at room pressure and from 33 to 1035°C on heating, was determined by using in situ synchrotron X-ray powder diffraction data (λ = 0.92249(5) Å). The satellite reflections in haüyne are lost at ∼400°C and a true substructure results because of this phase transition. There is a discontinuity in the a unit-cell parameter at ∼585°C. The α parameter increases rapidly and non-linearly to 585°C, but above 585°C, the expansion rate decreases. The percent volume change between 33 and 576°C is 2.0(3)%, and 0.6(3)% between 593 and 1035°C. Between 33 and 1035°C, the Al–O, Si–O and S–O distances are constant. Between 33 and 576°C, the angle of rotation of the AlO4 tetrahedron, jAl, changesfrom 11.5 to 5.8°, while the angle of rotation of the SiO4 tetrahedron, φSi, changesfrom 12.4 to 6.3°. The Al–O–Si bridging angle changesfrom 150.05(2) to 153.08(1)° from 33 to 576°C. Beyond 585°C, φAl and φSi angles remain nearly constant even though the maximum rotation of the tetrahedra is not achieved. Moreover, the Al–O–Si angle continues to increase at a slower rate from 585 to 1035°C by 1.05(2)°. From 33 to ∼585°C, the K atom position migrates at a slower rate than the Na and Ca atoms, and the structure expands at a high rate. Beyond 585°C, all the atomic positions of the interstitial cations (Na+, K+, Ca2+) remain nearly constant and the expansion of the structure is retarded.

Keywords

haüynephase transitionhigh-temperature structuressynchrotron radiationRietveld refinement
Type
Research Article
Information
Mineralogical Magazine , Volume 68 , Issue 3 , June 2004 , pp. 499 - 513
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2004

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