Dielectric, structural and ferroelectric properties of strontium borate glasses containing nanocrystalline bismuth vanadate

Glasses of the composition (100-x) SrB4O7 (SBO)-x Bi2VO5.5 (BiV) (0 less than or equal to x less than or equal to 70) were fabricated by the splat quenching technique. The evolution of nanocrystallization of bismuth vanadate in the system 50 SBO-50 BiV (in mol%) was accomplished via controlled heat-treatment (in the temperature range 470-820 K) of the as-quenched glasses. Differential thermal analyses were performed to assess the glass transition (T-g) and crystallization temperatures (T-cr). X-Ray powder diffraction studies (XRD) confirmed the as-quenched samples to be amorphous. High resolution transmission electron microscopic (HRTEM) studies corroborated the XRD studies and indicated the BiV crystallite size in 720 K heat-treated composites to be around 15 nm. The dielectric constant (epsilon (r)) and the dielectric loss (D) were measured in the frequency range 100 Hz-10 MHz at different temperatures (300-900 K). The dielectric constant of the glass nanocomposite (GNC) under study was predicted using various dielectric 2mixture formulae at 300 K and found to be in close agreement with that obtained using the Maxwell and logarithmic mixture rules. The samples that were heat-treated at two different temperatures, 720 and 820 K, exhibited broad dielectric anomalies in the vicinity of ferroelectric-to-paraelectric transition temperature of the parent BiV ceramics. Diffuseness of the observed transitions were estimated using Curie-Weiss formalism. The P vs. E hysteresis loops exhibited by GNC samples at high temperatures (670-760 K) demonstrate their ferroelectric nature.