Size-scaling behavior of hydriding phase transformations in nanocrystals

By partnering data obtained from a novel in-situ luminescence-based probe with a statistical mechanical model we derive size-scaling laws for hydriding phase transformations relevant for hydrogen storage. We conclude that the observed experimental trends are consistent with thermally-driven nucleation, and derive scaling relations that reveal the fundamental size-dependence of nucleation barriers in nanocrystals for first-order phase transformations: near the critical point, the barrier to nucleation is controlled directly by the size of the nanocrystal. Consequently, phase transformation can occur in a nanocrystal even at the critical point, in stark contrast to the classical bulk scenario. Our results provide a detailed framework for understanding how nanoscale interfaces impact broad classes of thermally-driven solid-state phase transformations of relevance for hydrogen storage, catalysis, batteries, and fuel cells.