Electron microscopy investigation of the microstructure and elemental composition of barium titanate precipitated in oxide glasses

The present work reports on the synthesis of glasses for two different ratios of alumina to sodium oxide in compositions of the system Na₂O/Al₂O₃/BaO/TiO₂/B2O₃/SiO₂ with addition of Fe₂O₃. Barium titanate-based glass-ceramics of different average crystallite sizes, depending on the ratio Na/Al-oxides, are precipitated after appropriate thermal treatment of the glasses prepared. The phase composition analyses performed by X-ray diffraction show the formation of cubic barium titanate, BaTiO₃ as a main phase and also, some BaTi_0.75Fe_0.25O_2.888. Additional crystalline phases, such as nepheline, NaAlSiO₄ appear in the course of thermal treatments at higher temperatures and longer anneal-ing times. The scanning electron micrographs of the prepared glass-ceramics verify the presence of interconnected spherulitic structures, which correspond to barium titanate crystals and which start to grow with crystallization time increase. The morphology of the spherulitic crystals is elucidated by means of transmission electron microscopy. The elemental analysis carried out by TEM verifies the precipitation of two main crystalline phases – barium titanate and barium titanium iron oxide. Keywords: barium titanate, controlled crystallization, glass-ceramics, microstructure.