Crystallization of dense binary hard-sphere mixtures with marginal size ratio

Molecular dynamics simulations are performed for binary hard-sphere mixtures with a size ratio of gamma =0.9 and a volume fraction of phi=0.58 over a range of compositions. We show how, at this high volume fraction, crystallization depends sensitively on the composition. Evidence is presented that crystallization in these mixtures does not proceed by the standard nucleation and growth paradigm. Rather, some crystallite forms almost immediately and then an interplay between compositional fluctuations and crystal growth is able to dramatically extend the time scale on which further crystallization occurs. This can be seen as a form of geometric frustration.