Optical and dielectric properties of transparent glasses and nanocrystals of lithium niobate and lithium diborate in borate glasses

The glass composition 92.5 Li(2)B(4)O(7)-7.5Nb(2)O(5) (mol%) was prepared by the conventional melt quenching technique. The as-quenched sample, blue and transparent, was heat-treated at 550 and 650 C (HT). The glassy nature of the as-quenched sample was established by Differential scanning calorimetry (DSC). Lithium niobate LiNbO(3) and Li(2)B(4)O(7) nanocrystals were produced within the glass by heat-treating it at 550 and 650 degrees C/3. The amorphous nature of the as-quenched glasses and crystallinity of glass nanocrystal composites were confirmed by X-ray powder diffraction studies. Various optical parameters such as optical band gap (E(opr)) and Urbach energy (Delta E) of these transparent glass-ceramics have been found to be crystallite size dependent. The volume ratio of the particles increases with increase in heat-treatment temperature. The behavior of the sigma(ac), with the increase in the heat-treatment (HT) temperature, was related with the decrease in the free ions number in the glass matrix and consequent increase in the fraction of the crystallites LiNbO(3) phase to the crystallites Li(2)B(4)O(7) phase and the glass matrix. The dielectric constants of the glass-ceramics decrease with increase in the HT temperature and with increase in frequency (0.12-100 kHz). (C) 2010 Elsevier B.V. All rights reserved.