Effect of the growth treatment on two-stage nucleation experiments

Numerical simulations are presented that document the strong effect of a pr eviously underappreciated portion of two-stage thermal treatments used in t he study of nucleation processes: the "heat-up'' process whereby samples ar e heated from ''nucleation" conditions to "growth" conditions. The simulati ons indicate that two limiting regimes exist, dependent on (a) the cluster size distribution of as-quenched glasses, (b) the temperatures used for nuc leation and growth, and (c) the rates of heating and cooling: (1) all clust ers larger than the critical size at growth conditions (n(g)*) will grow to macroscopic size (the "standard" case); and (2) all clusters larger than t he critical size at nucleation conditions (n(nuc)*) will grow to macroscopi c size. In addition, cases in which the "effective critical size" (n(eff)* is intermediate between n(gr)* and n(nuc)* can also occur. Cases in which n (eff)* < n(gr)* is manifested during nucleation experiments as an abrupt bo ost in crystal number density during the heat-up from nucleation to growth conditions, as all dusters larger than n(eff)* are rapidly "flushed" past n (gr)*. For the system studied herein, this can lead to a 10(6)-fold increas e in final number density within seconds to a few minutes. Finally, the imp ortance of structural relaxation for this process is demonstrated by examin ing a case in which the nucleation temperature is below the nominal glass t ransition temperature.