Effects of ZnO on the stability of the SiO2-BaO-TiO2 system

Glasses in the SiO2-BaO-TiO2 system are known to exhibit high refractive indices and exceptional infrared transmission. However, their strong tendency towards crystallization limits their production and commercial applications. In this study, we substituted ZnO for SiO2, BaO and TiO2, respectively, in a baseline 20SiO2-30BaO-50TiO2 glass. These glasses were synthesized by a traditional melt-quench method. The crystalline nature of both quenched between two metallic plates and heat-treated samples were assessed using X-ray diffraction (XRD) analysis, while differential scanning calorimetry (DSC) was used to estimate △T (Tx-Tg), Kgl, activation energy (Ea), and the Avrami parameter (n). The structure of the SiO2-BaO-TiO2-ZnO glass system was characterized by Raman spectroscopy, while SEM was performed for microstructural characterization of glassy and crystalline phases. The results indicate that these glasses can incorporate between 10 and 20 mol% of ZnO before crystallization occurs, where the maximum ZnO concentration is highly dependent upon the oxide substitution method. The apparent activation energy (Ea) of 20SiO2-30BaO-50TiO2 and Zn-Ba-2.5 are 796 kJ/mol and 511 kJ/mol while Avrami parameters (n) are 2.02 and 3.04, respectively. SEM analysis demonstrates that both glasses undergo volume crystallization. Comparing with 20SiO2-30BaO-50TiO2 glass, ZnO promotes the formation of [TiO4] and “supertetrahedra” structures which can increase △T and Kgl to 110 °C and 0.30 respectively. ZnO additions to the SiO2-BaO-TiO2 glass system improves glass stability against crystallization.