Pressure Dependence of Raman Spectra of SiO2 Polymorphs: α-Quartz, Coesite, and Stishovite
- Murli H. Manghnani and
- Yasuhiko Syono
Published Online: 21 MAR 2013
Copyright © 1987 by Terra Scientific Publishing Company (TERRAPUB), Tokyo.
High-Pressure Research in Mineral Physics: A Volume in Honor of Syun-iti Akimoto
How to Cite
Hemley, R. J. (1987) Pressure Dependence of Raman Spectra of SiO2 Polymorphs: α-Quartz, Coesite, and Stishovite, in High-Pressure Research in Mineral Physics: A Volume in Honor of Syun-iti Akimoto (eds M. H. Manghnani and Y. Syono), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM039p0347
- Published Online: 21 MAR 2013
- Published Print: 1 JAN 1987
Print ISBN: 9780875900667
Online ISBN: 9781118664124
- Mineralogy and Crystal Chemistry;
- Phase transformations;
- High Pressure-High Temperature Research
The pressure dependence of the room-temperature Raman spectra of α-quartz, coesite, and stishovite is investigated to probe compression mechanisms, possible soft-mode transitions, and high pressure thermodynamic properties of these phases. The experiments are performed with a diamond-anvil cell that is optically interfaced with an Ar+ laser and a triple spectrograph equipped with an optical multichannel analyzer. The pressure dependences are found to be particularly large for the low-frequency modes in quartz and coesite, including the 206 cm−1 A 1 phonon in quartz which is associated with the α-β transition. A phase transition is found in coesite at 22–25 GPa, as evidenced by a splitting of the main Raman bands. Above ∼30 GPa the Raman bands in quartz and coesite decrease and broaden significantly with increasing pressure, and both spectra closely resemble that of silica glass under these conditions. For stishovite, soft-mode behavior of the B 1g optical phonon associated with a pressure-induced shear instability was investigated. The pressure shift of the B 1g mode is observed to be negative, whereas those of the other Raman-active bands are positive, in agreement with both crystal-chemical considerations and recent theoretical predictions. The pressure shift and mode-Grüneisen parameter γ l for the B 1g mode in stishovite is considerably smaller than that found for other rutile-type oxides. Implications for the thermodynamic properties of the silica phases at high pressure are examined with the mode-Grüneisen parameters determined from the Raman spectra.