Phase composition identification and microstructure of BaTiO3-containing sodium-aluminoborosilicate glass-ceramics

• Oxide glasses with high concentrations of TiO2, BaO and Fe2O3 were prepared.
• XPS shows mainly the presence of the oxidized species, Ti4+ and Fe3+ in glass.
• Temperature-dependent Raman spectroscopy verifies the presence of cubic BaTiO3.
• The BaTiO3 cell parameter increases with decreasing crystallite size.
• Phase separation and growth of interconnected globular BaTiO3 particles is observed.

Bulk glasses with a composition 20.1Na2O/23.1BaO/23.0TiO2/7.6B2O3/17.4SiO2/3Al2O3/5.8Fe2O3 containing less than 30 mol% glass-forming oxides are synthesized. Information on the valency of the glass constituents is obtained by x-ray photoelectron spectroscopy and it is concluded that all species are predominantly present in their oxidized state. Glassy samples are annealed above the glass transition temperature which leads to the crystallization of BaTiO3 for all time-temperature applied schedules. The phase composition of the glass-ceramics is studied by x-ray diffraction and the formation of cubic BaTiO3 is suggested. Temperature-dependent Raman spectroscopy confirms the presence of solely cubic BaTiO3. The microstructures of all annealed samples are similar and consist of globular interconnected particles in which nanosized BaTiO3 crystals grow randomly. The mean size of the spherical formations increases with the increasing annealing time from 200 to 600 nm. Electron microscopy suggests that during the annealing process first phase separation and then crystallization of BaTiO3 occurs.

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