Structure and nature of ice XIX

Area of Science:

• Materials Science
• Physics
• Chemistry

Background:

• Ice exhibits diverse phases crucial for multiple scientific fields.
• Typically, high-temperature disordered ice phases transition to ordered states upon cooling.
• This study investigates an exception to this common phase transition behavior.

Purpose of the Study:

• To explore the phase transitions of hydrochloric acid-doped ice VI at high pressure.
• To characterize the structural and orientational properties of ice phases under specific conditions.
• To investigate an alternative phase transition pathway in ice VI.

Main Methods:

• In-situ neutron diffraction was employed to analyze the ice structure.
• High-pressure conditions were utilized to induce and observe phase transitions.
• Hydrochloric acid doping was used to modify the properties of ice VI.

Main Results:

• Hydrochloric acid-doped ice VI, upon cooling at high pressure, forms a novel phase, ice XIX.
• Unlike typical transitions, ice XIX remains orientationally disordered but undergoes significant structural distortions.
• The observed Pbcn-type distortion involves the tilting and squishing of hexameric clusters within the ice structure.

Conclusions:

• The formation of ice XIX represents a unique phase transition where disorder is maintained but structure is altered.
• This discovery may elucidate previously observed ferroelectric signatures in dielectric spectroscopy of ice VI.
• The findings have potential implications for understanding other icy materials and their phase behaviors.