The effect of elastic stresses on the thermodynamic barrier for crystal nucleation

• An unusual increase the thermodynamic barrier for homogeneous crystal nucleation with a decrease in temperature below the maximum nucleation rate is analyzed.
• The interplay between stress development and relaxation is accounted for.
• The possibility of precipitation of the stable and different metastable crystal phases are taken into account.
• Several experimental results on nucleation are given an interpretation.

For a variety of oxide glass-forming liquids, the thermodynamic barrier for homogeneous crystal nucleation, Wc, exhibits an unusual increase with a decrease in temperature below the maximum nucleation rate. Such behavior differs from the predictions made using the classical nucleation theory. In this article, we seek possible explanations for the increasing Wc by analyzing whether it is caused by internal elastic stresses that arise due to density misfits between the crystal and liquid phases. For this purpose, crystal nucleation rates and induction time data for two glasses that display significantly different density misfits, lithium and barium disilicates, are employed to determine the work of critical cluster formation. To explain the results, quantitative estimates of the effect of the elastic strain energy on the work required to form a critical nucleus are performed for both glasses. The interplay between stress development and relaxation is accounted for. The computations were performed, taking into account not only the possibility of precipitation of the most stable crystal phase but also that different metastable phases may form during the early stages of nucleation. We show that elastic stresses do indeed reduce the thermodynamic driving force for crystallization, and thus increase the barrier to nucleation. However, the sole effect of elastic strain energy cannot explain the aforementioned unusual behavior of the thermodynamic barrier. Hence, a comprehensive explanation to this phenomenon remains an open issue.