Kinetic and structural analyses for the formation of anatase nanocrystals in barium titanoborate glasses

Abstract Transparent barium titanoborate glass-ceramics bearing TiO₂ (anantase) nanocrystals were prepared by the conventional melt-quenching and subsequent heat treatment of 35BaO-xTiO₂-110B₂O₃ (in mol) (x = 20, 25, and 30) glasses. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) results clearly reveal the formation of highly-crystalline anatase nanocrystals in glass matrices. The average crystal size ranges from ∼10 to 20 nm according to TiO₂ contents. Non-isothermal kinetic analyses were performed to understand the crystallization behavior of each glass using differential scanning calorimetry (DSC) scan curves. With the increase of TiO₂ contents in the glass, the crystallization peak temperature of TiO₂ decreases, while the activation energy for crystallization increases. We propose a possible mechanism for the formation of TiO₂ nanocrystals based upon kinetic analysis results and structural changes in barium titanoborate glass matrices according to TiO₂ contents. The nanocrystalline glass-ceramics show ∼60-75% visible light transmittance and sharp UV-light absorption edges at ∼387 nm, corresponding to the energy band gap of anatase (3.2 eV). They show apparent photocatalytic properties and ∼70% of methylene blue solution was decomposed within 180 min.