Determination of critical nucleus radius in oxyfluoride glass via molecular dynamics simulations

Abstract

The critical nucleus radius is a fundamental parameter for understanding nucleation kinetics and crystallization behavior. However, in glass-forming oxides, direct observation of nucleation from melts or the growth of nuclei near the critical radius using the seeding approach has not been achieved in molecular dynamics (MD) simulations. In this study, we investigated BaF₂–ZnO–B₂O₃ glass, which exhibits an ultrafast nucleation rate. BaF₂ crystalline nuclei of varying radii were embedded within the glass composition, and their stability was monitored at different temperatures by determining whether they grew or dissolved. A linear relationship between temperature and the critical radius was observed, enabling the calculation of interfacial energy using the classical Gibbs approach. The interfacial energy was determined to be γ = 0.144 J/m², and the critical radius was evaluated to be r* = 0.48 nm at the crystallization onset temperature (823 K). The relatively low interfacial energy, comparable to metals but much lower than oxide glasses, is attributed to the structural affinity between fluoride-rich domains in the glass and the BaF₂ crystalline phase. This study demonstrates the applicability of the seeding approach to oxide-based glassy systems and provides one of the first direct computational validations of the critical radius in glasses.