Crystallization, dielectric and optical studies on strontium tetraborate glasses containing bismuth titanate

Glass nanocomposites comprising nanocrystallites of bismuth titanate, Bi4Ti3O12 (BiT), dispersed in a glass matrix of strontium tetraborate SrB4O7 (SBO) were obtained by the controlled crystallization of glasses with the composition 2xBi2O3−3xTiO2−(100 − 5x)SBO, (10 ≤ x ≤ 15). Ultrasonic treatment (UST) of the glass samples with an aqueous suspension of BiT followed by conventional heat treatment (HT) readily yielded the desired crystalline phase, which was otherwise difficult to obtain by conventional heat treatment. The phase formation was confirmed by powder X-ray diffraction (XRD) studies. High-resolution transmission electron microscopy (HRTEM) was used to confirm the crystallinity, and the average size of the crystallites was found to vary from 60 to 70 nm. The dielectric constant (εr) of the glass samples was found to increase with increase in Bi2O3–TiO2 content, and the dielectric loss (tanδ) values were reasonably low (0.02 to 0.04) for all the compositions under study, in the 100 Hz to 100 kHz frequency range. The frequency response of εr and dielectric loss (tanδ) of the crystallized sample exhibited sharp piezoelectrically induced resonances in the 185 to 200 kHz range. The resonance peaks were found to shift towards lower frequencies with increasing temperature and higher frequencies with increasing pressure. The temperature dependence of the stiffness coefficient (C) was defined, using the resonance data. The refractive index of the glasses and the second harmonic generation (SHG) efficiency of the glass-ceramics were found to increase with increase in Bi2O3–TiO2 or crystalline BiT content.