Compression mechanisms of coesite |
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| Authors: | R J Angel C S J Shaw G V Gibbs |
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| Institution: | (1) Crystallography Laboratory, Dept. Geological Sciences, Virginia Tech, Blacksburg, Virginia 24060, USA e-mail: rangel@vt.edu Tel.: +540-231-7974 Fax: +540-231-3386, US;(2) Department of Geology, University of New Brunswick, 2 Bailey Drive, Fredericton, New Brunswick, E3B 5A3, Canada, CA |
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| Abstract: | The structure of coesite has been determined at ten pressures up to a maximum of 8.68 GPa by single-crystal X-ray diffraction.
The dominant mechanism of compression is the reduction of four of the five independent Si–O–Si angles within the structure.
There is no evidence of the fifth linkage, Si1–O1–Si1, deviating from 180°. Some Si–O bond distances also decrease by up to
1.6% over the pressure range studied. The pattern of Si–O–Si angle reduction amounts to a rotation of the Si2 tetrahedron
around the 001] direction. This rotation induces significant internal deformation of the Si1 tetrahedron. Comparison of the
experimental data with rigid-unit distance least-squares simulations of coesite suggests that this pattern of compression,
the anomalous positive values of both s23 and K′′ in the equation of state of coesite, its high elastic anisotropy and the unusual straight Si1–O1–Si1 linkage within
the structure are all consequences of the connectivity of the tetrahedral framework.
Received: 11 July 2002 / Accepted: 14 January 2003
Acknowledgements The help of Christian Baerlocher of ETH Zurich in providing both the DLS-76 software and advice in its use is gratefully
acknowledged, as are discussions with Paul Ribbe of Virginia Tech and the comments of two anonymous reviewers. The data analysis
was supported by the National Science Foundation under grant EAR-0105864 to N.L. Ross and R.J. Angel. |
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| Keywords: | Coesite Structure High pressure Compression mechanisms |
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