Crystal-crystal phase transitions with liquid intermediate states

Single-particle-resolution video microscopy of colloidal films reveal that transitions two different colloidal crystals (square- and triangular-lattices) occur via a two-step nucleation pathway with liquid nuclei in the intermediate stage. The nucleation pathway is favored over the direct one-step nucleation because the energy of the solid/liquid interface is lower than that between solid phases.The findings suggest that an intermediate liquid could exist in the nucleation processes of solid–solid transitions of many metals and alloys, and provide guidance for better control of the kinetics of the transition and for future refinements of solid–solid transition theory.