5. Crystallization kinetics – Glass formation and stability

The stability of an amorphous compound and the formation of a glass are dependent on the ability of a metastable liquid to crystallize. If a thermodynamic transition driving force ΔG (T) is required for crystallization of the subcooled liquid to occur, it is not only the value of this that determines the onset of the phenomenon itself, as well as the crystallization rate. The simple fact that crystallization can be avoided and a deeply subcooled compound vitrified when ΔG is very large clearly suggests this. Many other factors also play an important role. In what follows, the combined effect of the three main factors that determine the crystallization kinetics of an undercooled liquid and, therefore, determine the effective lifetime of the metastable amorphous state will be discussed. In addition to the driving force for crystallization, these factors are molecular mobility and the degree...