Hydrogen bond symmetrisation in D₂O ice observed by neutron diffraction

Area of Science:

• High-pressure physics
• Materials science
• Solid-state chemistry

Background:

• Hydrogen bond symmetrisation is predicted in ice VII under high pressure.
• Previous experimental studies show inconsistent transition pressures.
• Nuclear quantum effects and isotope effects are crucial in this phenomenon.

Purpose of the Study:

• To determine the atomic distribution of deuterium in D2O ice at high pressures.
• To identify the pressure at which hydrogen bond symmetrisation occurs in D2O ice.
• To investigate the associated changes in elastic properties.

Main Methods:

• Neutron diffraction experiments were conducted on D2O ice at pressures exceeding 100 GPa.
• Analysis of deuterium atomic distribution from bimodal to unimodal.
• Observation of peak width changes in diffraction patterns.

Main Results:

• A transition from bimodal to unimodal deuterium distribution was observed around 80 GPa.
• Significant narrowing of the 110 peak widths at the transition pressure.
• Evidence of structural relaxation and changes in elastic properties.

Conclusions:

• The study provides experimental evidence for hydrogen bond symmetrisation in D2O ice at approximately 80 GPa.
• The observed changes in deuterium distribution and peak widths confirm structural relaxation and altered elastic properties.
• This finding contributes to understanding hydrogen bonding under extreme conditions.