Electron microscopy investigation of the microstructure and elemental composition of barium titanate precipitated in oxide glasses
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2018-01-01
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Abstract
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 BaTi0.75Fe0.25O2.888. Additional crystalline phases, such as nepheline, NaAlSiO4 appear in the course of thermal treatments at higher temperatures and longer annealing 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.