Relaxation effect on crystal nucleation in a glass unveiled by experimental, numerical, and analytical approaches

Abstract

In this work, we significantly extend our new approach for analyzing nucleation kinetics below the glass transition, Tg, which considers the structural relaxation effect. Using a 5BaO·8SiO2 (B5S8) glass, we showed a significant stepwise change in the nucleation relaxation time, τsr, with temperature in the Tg region, in contrast with the expected monotonous variation with temperature: τsr is four times shorter for the supercooled liquid than for the glass. Then, using a combination of new experimental data and theoretical (analytical and numerical) analyses, we advance an interpretation within the Classical Nucleation Theory (CNT) framework that brings together the nucleation rates in the T > Tg and T < Tg ranges. We show once more that the so-called “breakdown” of the CNT is merely the result of underestimated nucleation rates due to incomplete glass relaxation during limited experimental nucleation times, confirming our recent findings for Li2O·2SiO2 and 2Na2O·CaO·3SiO2. Finally, for the first time, we also show that due to the almost complete crystallization of the B5S8 glass, and likely of other glasses that exhibit sufficiently high nucleation and growth rates, the relaxation process cannot be finished in the low-temperature range and the ultimate steady-state nucleation regime cannot be reached. These combined results shed light on the complex nucleation behavior below Tg.