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.