Crystallization of bismuth oxide nano-crystallites in a SiO2–PbO–Bi2O3 glass matrix

Abstract

SiO2–PbO–Bi2O3 glasses having the composition of 35SiO2–xPbO–(65−x)Bi2O3 (where x=5, 20 and 45; in mol%) have been prepared using the conventional melting and annealing method. Differential scanning calorimetry (DSC) was employed to characterize the thermal behavior of the prepared glasses in order to determine their crystallization temperatures (Tcr). It has been found that Tcr decreases with the decrease of Bi2O3 content. The amorphous nature of the prepared glasses as well as the crystallinity of the produced glass–ceramics were confirmed by X-ray powder diffraction (XRD) analysis. SiPbBi2O6 glass nano-composites, comprising bismuth oxides nano-crystallites, were obtained by controlled heat-treatment of the glasses at their (Tcr) for 10h. Transmission electron microscopy (TEM) of the glass nano-crystal composites demonstrates the presence of cubic Bi2O3 nano-crystallites in the SiPbBi2O6 glass matrix. Nano-crystallites mean size has been determined from XRD line width analysis using Scherrer's equation as well as from TEM; and the sizes obtained from both analyses are in good agreement. These sizes varied from about 15 to 170nm depending on the chemical compositions of parent glasses and, consequently, their structure. Interestingly, replacement of the Bi2O3 by PbO in the glass compositions has pronounced effect on the nature, morphology and size of the formed nano-crystallites. Decrease of the Bi2O3 content increases the size of the nano-crystallites, and at the lowest Bi2O3 extreme, namely 20mol%, introduces minority of the monoclinic Bi2O4 in addition to the cubic Bi2O3. The crystallization mechanism is suggested to involve a diffusion controlled growth of the bismuth oxide nano-crystallites in the SiPbBi2O6 glass matrix with the zero nucleation rate.