Phase Transition of Cubic Ice to Hexagonal Ice during Growth and Decomposition

Ice, one of the most enigmatic materials on Earth, exhibits diverse polymorphism, with research mainly focusing on the most commonly observed phases: hexagonal ice (I_h), cubic ice (I_c), and stacking-disordered ice (I_sd). While their formation or structural changes are crucial for advancements in cloud science, climate modeling, and cryogenic technology, the molecular mechanisms driving these phenomena remain unexplored. Herein, utilizing cryogenic transmission electron microscopy, we investigate the formation of ice at two different temperatures, demonstrating a size-dependent phase shift from I_c to I_sd. Furthermore, a relatively metastable cubic phase in I_sd transitions to a hexagonal phase under electron beam radiation. This transition, facilitated by crystal defects, contrasts with perfect crystalline I_c, which maintains its original phase, emphasizing the importance of defects in polymorphic phase transitions. Our findings provide novel insights on phase control during the ice growth processes and polymorphic phase transitions from the cubic-to-hexagonal phases.