Non-deterministic Dynamics in η-to-θ Phase Transition of Alumina Nanoparticles

Phase diagrams and crystallography are standard tools for studying structural phase transitions while acquiring kinetic information at the atomistic level has been considered essential but challenging. Here, we report a rare example of a statistical kinetics study, showing that the η-to-θ phase transition of alumina, unidirectional in bulk and retaining the crystal lattice orientation, occurs non-deterministically via an ergodic equilibrium via molten state, as observed for nanoparticles on bulk Al(OH)3 surface. The memory of the lattice orientation is lost. The rate of the interconversion was insensitive to the electron dose rate, and it is a thermal process with a small Gibbs free energy of activation. This non-deterministic kinetics should be a key feature of crystal nucleation occurring in high surface energy regions of bulk crystals.