BiO1.5–BO1.5–GeO2 glass system and crystallization of Bi4Ge3O12 phase

The BiO1.5–BO1.5–GeO2 ternary glass samples were prepared by fusion in a platinum crucible and cast in a brass mould. For each nominal composition a sample’s physical properties, such as glass transition (Tg), crystallization (Tx) temperatures and densities, were measured. The 45BiO1.5–40BO1.5–15GeO2 (mol%) glass sample with Tg=385±2°C, Tx=517±2°C presented a density of 6.94±0.02 g cm−3. A non-isothermal crystallization study of this glass by differential scanning calorimetry (DSC) showed that the directionality of crystal growth was equal to 1.1 and that the activation energy was approximately 54 kcal mol−1. The presence of two crystalline phases, Bi6B10O24 (surface) and Bi4Ge3O12 (BGO) (bulk), were detected by powder X-ray diffraction (XRD) and composition analysis. Experiments of isothermal crystallization showed that the crystal growth rate was ∼1.5 μm/min, at 520°C.