Crystallization behavior of PbF2-SiO2 based bulk xerogels

Transparent glass ceramics containing xErF(3)-10PbF(2)-90SiO(2) (mol%, x = 0, 1, 2) were prepared by the sol-gel method. The thermal behavior of the xerogels was investigated by TG-DTA. Through non-isothermal experiments, the apparent activation energy for the crystallization of beta-PbF2 phase was evaluated by the Kissinger method to be about 162 kJ/mol and 167 kJ/mol for xerogels with x = 0 and x = 1, respectively, and the Avrami exponents lied between 1.5-2.0 for both samples, suggesting that the crystallization of beta-PbF2 phase was a diffusion-controlled process of three-dimensional growth with decreasing nucleation. XRD, TEM and EDS were carried out to study the evolution of the structure. For sample doped with 1 mol% ErF3, it was revealed that few Er3+ ions contributed or were incorporated to the beta-PbF2 lattice. They seemed to segregate at the surface of the crystallites and hindered the growth of beta-PbF2 and thus postponed the crystallization. (C) 2004 Elsevier B.V. All rights reserved.