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Pressure-induced sharp coordination change in liquid germanate.
Osamu Ohtaka1, Hiroshi Arima, Hiroshi Fukui
1Department of Earth and Space Science, Osaka University, Toyonaka, Osaka 560-0043, Japan. ohtaka@ess.sci.osaka-u.ac.jp
Physical Review Letters
|June 1, 2004
Summary
High pressure transforms liquid germanate's local structure. Germanium coordination shifts from fourfold to sixfold around 3 GPa, forming a dense liquid with compressible GeO6 octahedra.
Area of Science:
- Geochemistry
- Materials Science
- High-Pressure Physics
Background:
- Understanding the behavior of geological materials under extreme conditions is crucial for planetary science.
- The local structure of germanate liquids influences their physical and chemical properties.
Purpose of the Study:
- To investigate the local structural evolution of liquid germanate under high pressure and temperature.
- To determine the coordination changes of germanium in liquid germanate up to 9 GPa.
Main Methods:
- In situ X-ray absorption measurements were performed on liquid germanate.
- Experiments were conducted at pressures up to 9 GPa and temperatures of 1273 K.
Main Results:
- Liquid germanate initially contracts with increasing pressure, maintaining tetrahedral coordination up to 2.5 GPa.
- An abrupt transition from fourfold to sixfold coordination around germanium occurs near 3 GPa.
- A high-density liquid with stable octahedral germanium coordination (GeO6) forms below 4 GPa, exhibiting higher compressibility than solid counterparts.
Conclusions:
- High pressure induces a significant coordination change in liquid germanate, leading to a denser phase.
- The GeO6 octahedron in the high-pressure liquid phase is more compressible than in solid germanates.
- These findings provide insights into the behavior of silicate melts under deep Earth conditions.