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High-pressure infrared sepctra of alpha-quartz, coesite, stishovite and silica glassHigh-pressure infrared absorption spectra of alpha-quatz, coesite, stishovite, and SiO2 glass are consistent with the primary compression mechanism of the initially tetrahedrally bonded phases being the bending of the Si-O-Si angle at pressures less than 10-20 GPa. At higher pressures, up to 40 GPa, we observe a decline in the intensity of the infrared SiO4 asymmetric-stretching vibrations of all three phases, with an increase in the relative amplitude between 700 and 900/cm. This change in intensities is attributed to an increase in the average coordination number of silicon through extreme distortion of tetrahedra. At pressures above approximately 20 GPa, the low-pressure crystalline polymorphs gradually become amorphous, and the infrared spectra provide evidence for an increase in silicon coordination in these high-density amorphous phases. The pressure-amorphized samples prepared from quartz and coesite differ structurally both from each other and from silica glass that has been compressed, and the high pressure spectra indicate that these materials are considerably more disordered than stishovite under comparable pressure conditions. Average mode Grueneisen parameters calculated for quartz, stishovite and fused silica from both infrared and Raman spectra are compatible with the corresponding thermodynamic value of the Grueneisen parameter, however, that of coesite is significantly discrepant.
Document ID
19950046154
Document Type
Reprint (Version printed in journal)
Authors
Williams, Q.
(Univ. of California, Santa Cruz, CA United States)
Hemley, R. J.
(Carnegie Inst. of Washington, Washington, DC United States)
Kruger, M. B.
(Univ. of California, Berkeley, CA United States)
Jeanloz, R.
(Univ. of California, Berkeley, CA United States)
Date Acquired
August 16, 2013
Publication Date
December 10, 1993
Publication Information
Publication: Journal of Geophysical Research
Volume: 98
Issue: B12
ISSN: 0148-0227
Subject Category
Geophysics
Accession Number
95A77753
Distribution Limits
Public
Copyright
Other

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