Proton ordering dynamics of H2O ice

Area of Science:

• Physical Chemistry
• Materials Science
• Thermodynamics

Background:

• Understanding the phase transitions of water ice is crucial for various scientific disciplines.
• Ice XI is a low-temperature proton-ordered phase of ice Ih, and its formation and stability are of significant interest.
• Previous studies have indicated the existence of different ice phases, but precise transition temperatures and triple points require detailed investigation.

Purpose of the Study:

• To precisely determine the onset temperatures for the phase transitions between hexagonal ice (Ih) and proton-ordered ice XI for both H2O and D2O.
• To identify the triple points where ices Ih, II, and XI coexist for H2O and D2O.
• To investigate the nature of phase transitions, including potential kinetic broadening related to proton ordering.

Main Methods:

• High-precision measurements of the complex dielectric constant.
• Preparation of specialized H2O and D2O ice samples.
• Analysis of dielectric data to identify phase transition temperatures and triple points.

Main Results:

• For H2O, the transition from ice Ih to ice XI occurs at 58.9 K, and the transition from ice XI to ice Ih occurs at 73.4 K.
• For D2O, the transition from ice Ih to ice XI occurs at 63.7 K, and the transition from ice XI to ice Ih occurs at 78.2 K.
• A triple point was identified at 0.07 GPa and 73.4 K for H2O, and 0.08 GPa and 78.2 K for D2O, involving ices Ih, II, and XI.
• A first-order phase transition with kinetic broadening, linked to proton ordering dynamics, was observed at 100 K.

Conclusions:

• The precise transition temperatures and triple points for ice XI formation and coexistence with other ice phases (Ih, II) have been established for both H2O and D2O.
• The findings provide critical data for understanding the thermodynamics and kinetics of water ice phase transitions.
• The observation of kinetic broadening at 100 K highlights the importance of proton ordering dynamics in phase transitions.