Crystallization behavior of PbF2–SiO2 based bulk xerogels

Transparent glass ceramics containing xErF3–10PbF2–90SiO2 (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 β-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 β-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 β-PbF2 lattice. They seemed to segregate at the surface of the crystallites and hindered the growth of β-PbF2 and thus postponed the crystallization.