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Influence of phase separation on the crystallization behavior of glass-ceramics in the BaO-TiO2-SiO2 system

par Boulay, Emilie ;Ragoen, Céline ;Godet, Stéphane
Référence Crystallization 2012(2012: Goslar, germany), Influence of amorphous phase separation on the crystallization behavior of glass-ceramics in the BaO-TiO2-SiO2 system
Publication Publié, 2012

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Résumé :

Glass ceramics are of growing interest due to their enhanced properties comparing to the base glasses. The control of microstructures is consequently a major challenge in those systems. Even if it has been the topic of vigorous debates over the last decades, the possible role of a prior amorphous phase separation (APS) on the subsequent crystallization has not yet been clarified. This study focuses on the interplay between amorphous phase separation and the crystallization of fresnoite in glasses pertaining to the BaO-TiO2-SiO2 system. These glasses are known to undergo subliquidus phase separation via binodal or spinodal mechanisms for specific composition ranges in the ternary phase diagram. This process eventually leads to a final microstructure consisting of silica-rich droplets within a glassy matrix. The prior amorphous phase separation may have a significant effect on the subsequent nucleation and growth of crystals and furthermore on their morphology. Indeed, glasses with compositions falling outside the immiscibility gap have been reported to crystallize as strongly oriented crystals whereas glasses undergoing a prior APS lead to finer and randomly oriented crystals. This could be considered as an elegant way to improve optical properties such as the blue photoluminescence of fresnoite, particularly interesting for plasma screen applications. The aim of this work is to compare the crystallization behavior of glasses (i) with and (ii) without prior amorphous phase separation and also (iii) with the stoichiometric composition of fresnoite. This particular glass composition is well-known to bulk crystallize and to show high photoluminescence. The prior amorphous phase separation is shown to have a major influence for the glass compositions investigated. The microstructures of bulk samples are investigated using Scanning and Transmission Electron Microscopy. Differential Scanning Calorimetry and X-Ray Diffraction are also used to characterize the crystallization process on powder samples. The possible influence of the various interfaces present within the microstructure is investigated. In particular, the role of free surfaces or of droplets/matrix interfaces is scrutinized. Their respective influence on the nucleation and growth of fresnoite crystals is discussed in detail.