Formation of spherulite and metastable phase in stoichiometric Ba ₂Si₃O₈ glass

We investigated the crystallization and resulting morphology of a stoichiometric barium-silicate glass Ba₂Si₃O₈ (B2S3) using TEM observation and Raman spectroscopy. Spherical crystal growth (i.e., spherulite) of stoichiometric B2S3 phase was observed in the heat-treated glass samples, and the size of the spherulites drastically increased as the temperature increased during the heat-treatment process. It was also found that an initial precipitating phase in the precursive stage of crystallization is neither the B2S3 phase nor other crystalline phases in the BaO-SiO₂ system. It was deduced that a metastable phase precipitates prior to the formation of spherulite and acts as nucleation site for the spherulite.