11:30 AM - 11:45 AM
[MIS13-08] Molecular mechanism on the formation of pristine ice Ic from ice XVII
Keywords:ice, surface melting, solid-solid phase transition
About 400 years ago, Scheiner observed a 28-degree halo around the sun in the sky of ancient Rome. Since then, the presence of cubic ice (ice Ic) in the atmosphere has been suggested. However, it was only five years ago that humans were able to obtain pristine ice Ic. The difficulty in synthesizing the metastable phase of ice Ic from liquid water lies in the competitive formation of the stable hexagonal ice (ice Ih) and the stacking-disordered ice (ice Isd), which is a mixture of Ih and Ic. In 2020, methods were reported for creating pristine ice Ic through solid-solid phase transitions from ice XVII and C2 hydrogen hydrate. However, the molecular mechanisms behind those processes remain a mystery. In this study, using molecular dynamics (MD) simulations, we reveal the microscopic details through which ice Ic preferentially forms from ice XVII in a two-step process. First, ice Ic forms within the melt layer on the surface of ice XVII. Then, the stable Ic-XVII solid-solid coexistence interface propagates inward in a layer-by-layer manner. We demonstrate that the matching of lattice lengths and defect-free layer-by-layer crystal growth are essential for the formation of pure ice Ic. Crystal polymorphs are ubiquitous in nature. The results presented here provide valuable insights for precisely controlling the synthesis of target crystals from polymorph groups with balanced stability, not limited to ice.