Crystallization kinetics analysis of BaF2 and BaGdF5 nanocrystals precipitated from oxyfluoride glass systems: A comparative study

Analysis of crystallization kinetics in glasses is an essential tool to gain control over ceramization to achieve desired functionalities. Here, the non-isothermal kinetics of crystallization in two different oxyfluoride glasses have been analyzed using various well-established kinetic models. Activation energies (E-a) have been estimated using Kissinger, Augis-Bennett and Ozawa methods while both E-a and Avrami index (n) were predicted from the Matusita and Avrami-Erofeev models. The values of E-a and n as predicted using Avrami-Erofeev model are 285kJ/mol and 1.18, respectively for the oxyfluoride glass yielding BaF2 nanocrystals whereas 269 kJ/mol and 1.33 for the glass yielding BaGdF5 nanocrystals. The Avrami indices predict three dimensional diffusion controlled crystallization through bulk nucleation. Moreover, isothermal prediction facilitated to optimize the ceramization temperature and time for obtaining transparent oxyfluoride glass-ceramics. Furthermore, Model-free kinetics analysis demonstrates initial decrease followed by a subsequent rise in activation energy during crystallisation in both the glass systems. (C) 2015 Elsevier B.V. All rights reserved.