The phase diagram of high-pressure superionic ice
Jiming Sun1, Bryan K Clark2, Salvatore Torquato1,3,4
1Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.
Nature Communications
|August 29, 2015
Summary
Superionic ice phases at extreme pressures reveal competing structures and a novel P2(1)/c phase. Higher pressures lead to lower transition temperatures and unique hydrogen behavior in these planetary ice models.
Area of Science:
- Planetary Science
- High-Pressure Physics
- Materials Science
Background:
- Superionic ice, characterized by liquid hydrogen coexisting with a crystalline oxygen sublattice, is crucial for understanding ice-rich planets and exoplanets.
- The behavior of superionic ice at pressures above 280 gigapascals (GPa) remains largely unexplored.
Purpose of the Study:
- To investigate the structural properties and phase transitions of superionic ice at ultra-high pressures (280 GPa to 1.3 terapascals).
- To characterize the behavior of hydrogen and oxygen sublattices under these extreme conditions.
Main Methods:
- High-pressure experimental techniques (details not specified in abstract).
- Analysis of structural changes and phase stability within the superionic ice system.
Main Results:
- Identification of several competing phases within a close-packed oxygen sublattice between 280 GPa and 1.3 TPa.
- Discovery of a new P2(1)/c superionic phase at higher pressures where the close-packed oxygen sublattice becomes unstable.
- Observation that higher pressure phases exhibit lower transition temperatures.
- Characterization of anisotropic, quasi-two-dimensional liquid hydrogen behavior in the P2(1)/c phase.
- Abrupt ionic conductivity change during the solid to close-packed superionic phase transition, contrasting with a continuous change during the solid to P2(1)/c transition.
Conclusions:
- The P2(1)/c phase represents a novel state of superionic ice under extreme pressure conditions.
- The pressure-dependent phase diagram of superionic ice is more complex than previously thought.
- Understanding these phases is critical for modeling the interiors of giant planets and exoplanets.
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