A New Perspective on Crystal Nucleation: A Classical View on Non-Classical Nucleation

Nucleation is the key step of crystallization and is also the most difficult part to observe, as it evolves in very short temporal and spatial resolution. Conflicts between the features of classical nucleation theory and the observed nucleation behaviors inspire hypotheses of nonclassical nucleation mechanisms. In this Review, experimental evidence and molecular dynamics simulations involving the structure and formation mechanisms of a series of precursors and intermediate species, such as prenucleation clusters, liquid precursors, and amorphous precursors that in some cases coexist in a single system and successively transform into one another, are summarized to advance the understanding on the nucleation mechanisms of crystalline phases. What's more, recent progress of building two-dimensional materials avoiding the nucleation barrier and accommodating nonclassical nucleation within the classical nucleation framework is outlined, which provides a new perspective on crystal nucleation: a classical view on nonclassical nucleation.