Devitrification of fluorozirconate glasses: from nucleation to spinodal decomposition

The main families of zirconium based fluoride glasses have been shown to undergo an heterogeneous nucleation process forming a BaF2–ZrF4 crystal phase. Here, a new fluorozirconate glass, with composition (mol%) 68.6ZrF4,18.4LaF3,5AlF3,5GaF3,3ErF3, undergoing a spinodal decomposition is presented. The devitrification process of this glass is studied by means of X-ray diffraction, Raman measurements after different time of heat treatment. Spatial fluctuations of composition are measured by X-ray microanalysis before the observation of any crystallisation trace. The final morphology of the separated phases, observed on the micrographs, shows a mainly crystalline connected glass-ceramic. The instability against decomposition of this composition has been attributed to the lack of glass-modifier and divalent ion in the starting melt.