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Structural changes of filled ice Ic structure for hydrogen hydrate under high pressure
Shin-ichi Machida1, Hisako Hirai, Taro Kawamura
1Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan. m417shin@geol.tsukuba.ac.jp
The Journal of Chemical Physics
|December 17, 2008
Summary
High-pressure experiments reveal structural changes in hydrogen hydrate at 40 and 60 GPa. A denser phase than filled ice Ic may exist at extreme pressures.
Area of Science:
- Materials Science
- High-Pressure Physics
- Chemistry
Background:
- Hydrogen hydrate, a filled ice Ic structure, is studied under extreme conditions.
- Understanding its behavior at high pressures is crucial for materials science.
Purpose of the Study:
- To investigate the structural evolution of hydrogen hydrate under high pressure.
- To identify phase transitions and structural changes within the material.
Main Methods:
- Experiments were conducted using a diamond-anvil cell up to 80.3 GPa at room temperature.
- In situ X-ray diffractometry (XRD) and Raman spectroscopy were employed to analyze structural and vibrational changes.
Main Results:
- Structural changes were observed at approximately 35-40 GPa and 55-60 GPa.
- Raman spectroscopy confirmed vibrational mode changes at 40 and 60 GPa, consistent with XRD findings.
- Hydrogen bond symmetrization in water molecules occurred around 40 GPa, potentially altering the filled ice Ic structure.
- A high-pressure phase, denser than filled ice Ic, was indicated above 55-60 GPa.
Conclusions:
- High-pressure conditions induce significant structural transformations in hydrogen hydrate.
- The study suggests the existence of a novel, denser phase of hydrogen hydrate at extreme pressures.
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