Absence of Amorphous Forms When Ice XIc Is Compressed at Low Temperature

Area of Science:

• Solid-state physics
• Materials science
• Computational chemistry

Background:

• Ice crystal transitions are generally thought to be impossible below the glass-transition temperature.
• Compression of ice I typically leads to a metastable state or collapse into high-density amorphous ice (HDA), not crystal-to-crystal transformation.

Purpose of the Study:

• To investigate the possibility of ice crystal-to-crystal transitions under compression.
• To explore the role of hydrogen ordering in ice polymorph transformations.
• To identify the thermodynamically most stable hydrogen-ordered ice IV configuration.

Main Methods:

• Molecular dynamics (MD) simulations were employed to model ice transformations.
• Density functional theory (DFT) calculations were used to assess the stability of different ice configurations.
• A comprehensive search for various configurations was performed.

Main Results:

• Demonstrated that hydrogen-ordered cubic ice (ice Ic) transforms into hydrogen-ordered ice IV without forming HDA.
• Identified the thermodynamically most stable configuration for hydrogen-ordered ice IV under compression.
• Predicted the phase boundary for the hydrogen order-disorder transition in ice IV.

Conclusions:

• Hydrogen ordering in ice facilitates direct transitions between polymorphs, contrary to previous assumptions.
• This finding suggests a new mechanism for ice phase transitions that bypasses amorphous states.
• The study provides insights into the behavior of water ice under pressure and the significance of hydrogen arrangement.