Ice I_c without stacking disorder by evacuating hydrogen from hydrogen hydrate.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Crystallography

Background:

• Water typically freezes into hexagonal ice (ice Ih) under ambient conditions.
• Cubic ice (ice Ic) with a cubic stacking sequence can form but ideal, stacking-disorder-free ice Ic has been elusive.
• Stacking disorder significantly influences the physical properties of ice polymorphs.

Purpose of the Study:

• To develop a method for synthesizing stacking-disorder-free cubic ice (ice Ic).
• To investigate the properties and stability of ideal ice Ic.
• To understand the role of stacking disorder in ice properties by comparing ideal ice Ic with ice Ih.

Main Methods:

• Synthesized ideal ice Ic by degassing hydrogen from the C2 phase of hydrogen hydrate.
• The C2 framework is isostructural with ice Ic.
• Observed formation via an intermediate amorphous or nano-crystalline phase during decompression.

Main Results:

• Successfully obtained stacking-disorder-free ice Ic.
• The synthesized ice Ic exhibits remarkable thermal stability.
• Phase transition to ice Ih observed at 250 K, attributed to the absence of dislocations.

Conclusions:

• Demonstrated a novel route to ideal ice Ic, overcoming previous limitations of stacking disorder.
• The high thermal stability of ideal ice Ic highlights the impact of structural perfection.
• This discovery provides a crucial end-member for studying the effects of stacking disorder on ice properties.