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Published on: June 18, 2020
High pressure partially ionic phase of water ice
Yanchao Wang1, Hanyu Liu, Jian Lv
1State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China.
Nature Communications
|December 1, 2011
Summary
Under extreme pressure, water ice transforms into a novel partially ionic phase. This high-pressure ice structure features alternating layers of hydroxide and hydronium ions, challenging previous low-temperature expectations.
Area of Science:
- Condensed Matter Physics
- Materials Science
- High-Pressure Physics
Background:
- Water ice typically exists in molecular or symmetric atomic phases.
- Dissociation into ionic forms (hydronium and hydroxide) at low temperatures is energetically unfavorable due to high proton transfer costs.
- Superionic ice forms at high temperatures (>2,000 K) and pressures, with distinct lattice and diffusion properties.
Purpose of the Study:
- To investigate the potential formation of ionic water ice phases at low temperatures under extreme pressures.
- To explore novel structural phases of water ice beyond known molecular and symmetric atomic forms.
- To understand the pressure-induced structural transitions in water ice.
Main Methods:
- Computational structural search using particle-swarm optimization.
- Simulations conducted at zero temperature and pressures exceeding 14 Mbar.
- Analysis of atomic bonding and structural packing under high-pressure conditions.
Main Results:
- Predicted the formation of a partially ionic water ice phase with a monoclinic P2(1) structure.
- This phase consists of coupled, alternating layers of hydroxide (OH)(δ-) and hydronium (H(3)O)(δ+) ions (δ=0.62).
- The ionic phase formation is linked to the breakdown of O-H covalent bonds and denser packing under extreme pressure.
Conclusions:
- Extreme pressure can induce a partially ionic phase in water ice at low temperatures, contrary to previous expectations.
- This discovery reveals a new structural motif for water ice under high-pressure conditions.
- The findings highlight the complex phase diagram of water and the influence of pressure on chemical bonding.
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