Nondeterministic dynamics in the η-to-θ phase transition of alumina nanoparticles

Phase diagrams and crystallography are standard tools for studying structural phase transitions, whereas acquiring kinetic information at the atomistic level has been considered essential but challenging. The η-to-θ phase transition of alumina is unidirectional in bulk and retains the crystal lattice orientation. We report a rare example of a statistical kinetics study showing that for nanoparticles on a bulk Al(OH)₃ surface, this phase transition occurs nondeterministically through an ergodic equilibrium through the molten state, and the memory of the lattice orientation is lost in this process. The rate of the interconversion was found to be insensitive to the electron dose rate, and this process had a small Gibbs free energy of activation. These nondeterministic kinetics should be a key feature of crystal nucleation occurring in high-surface-energy regions of bulk crystals.