Structural, dielectric and optical properties of lithium borate–bismuth tungstate glass-ceramics

Abstract

Glasses in the system (1 − x)Li 2B 4O 7–xBi 2WO 6 (0.1 ≤ x ≤ 0.35) were prepared by splat quenching technique. Powder X-ray diffraction (XRD) and differential thermal analysis (DTA) were employed to characterize the as-quenched glasses. High-resolution transmission electron microscopy (HRTEM) revealed the presence of fine, nearly spherical crystallites of Bi 2WO 6 varying from 1.5 to 20 nm in size, depending on x in the as-quenched glasses. The glasses (corresponding to x = 0.3) heat-treated at 723 K for 6 h gave rise to a clear crystalline phase of Bi 2WO 6 embedded in the Li 2B 4O 7 glass matrix, as observed by X-ray studies. The dielectric constants of the as-quenched glasses as well as the glass-ceramics decreased with increase in frequency (40Hz–100 kHz) at 300 K, and the value obtained for the glass-ceramic (x = 0.2) is in agreement with the values predicted using Maxwell’s model and the logarithmic mixture rule. The dielectric constants for both the as-quenched glass and the glass-ceramic increased with increase in temperature (300–873 K) and exhibited anomalies close to the onset of the crystallization temperature of the host glass matrix. The optical transmission properties of these glass-ceramics were found to be compositional dependant.