Coupled processes in nucleation

Coupled phase transitions are common, with amorphous phase separation preceding crystallization, for example. The coupling can be more complicated than this, however, such as when long-range diffusion becomes competitive with the interfacial attachment processes underlying nucleation in the classical theory, or when fluctuations in one order parameter catalyze the fluctuations underlying nucleation during glass crystallization. Three case studies are used for illustration, (i) phase separation or nano-scale precipitation followed by glass devitrification, (ii) time-dependent nucleation when the initial and final phases have a different composition, and (iii) structural fluctuations that catalyze the nucleation of particular phases. While these examples are drawn from crystallization processes in metallic glasses or liquids, as well as silicate glasses, they demonstrate general nucleation features that are relevant to all nucleation-based first order phase transitions.