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Sixfold-coordinated amorphous polymorph of SiO2 under high pressure
Tomoko Sato1, Nobumasa Funamori
1Department of Earth and Planetary Science, University of Tokyo, Tokyo 113-0033, Japan.
Physical Review Letters
|December 31, 2008
Summary
High-pressure studies reveal SiO2 glass forms a stable sixfold-coordinated structure above 40 GPa. Synchrotron techniques measured its density, coordination, and bond length, confirming its behavior as a single amorphous polymorph.
Area of Science:
- Materials Science
- Geophysics
- Condensed Matter Physics
Background:
- Understanding the behavior of amorphous silica (SiO2) under extreme pressure is crucial for geological and materials science applications.
- Previous studies have indicated potential structural transitions in SiO2 glass at high pressures, but direct measurements are limited.
Purpose of the Study:
- To develop and apply advanced synchrotron X-ray techniques for in-situ measurement of noncrystalline material properties at high pressures.
- To investigate the structural evolution and physical properties of SiO2 glass up to 50 GPa and beyond.
Main Methods:
- Utilized synchrotron X-ray absorption and diffraction techniques.
- Measured density, coordination number, and Si-O bond length of SiO2 glass at high pressure.
- Combined experimental density data with literature sound velocity data to estimate bulk modulus.
Main Results:
- At 50 GPa, SiO2 glass exhibits a density of 4.63 g/cm³, a coordination number of 6.3, and a Si-O bond length of 1.71 Å.
- The estimated bulk modulus at 50 GPa is 390 GPa, consistent with observed density changes.
- Evidence suggests SiO2 glass exists as a single amorphous polymorph with sixfold coordination from 40-45 GPa to at least 100 GPa.
Conclusions:
- Synchrotron X-ray techniques are effective for probing noncrystalline materials under extreme conditions.
- SiO2 glass maintains a stable, sixfold-coordinated amorphous structure over a wide range of high pressures.
- This finding has implications for understanding Earth's deep mantle composition and the properties of advanced glass materials.
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