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

Abstract

Glasses of the composition (100 − x) SrB4O7 (SBO)−x Bi2VO5.5 (BiV) (0 ≤ x ≤ 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 (Tg) and crystallization temperatures (Tcr). 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 (εr) 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 mixture 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 Pvs. E hysteresis loops exhibited by GNC samples at high temperatures (670–760 K) demonstrate their ferroelectric nature.