Crystallization of a highly viscous multicomponent silicate glass: Rigidity percolation and evidence of structural heterogeneity

A magnesium bearing multicomponent silicate glass was annealed at the temperature slightly above glass transition temperature (T-g) for various periods of time. The crystalline phase of fluorophlogopite with the chemical formula of NaMg3AlSi3O10F2 is precipitated in the floppy regions, which leads to the formation of a core-shell structure. Considering that there exists only four- or six-fold coordinated Mg2+ in the studied glass, the fraction of four-fold coordinated Mg2+ is determined by comparing the maximum size of the crystallite and the floppy region according to the percolation theory. In addition, a striking phenomenon of endotherm above glass transition in heat capacity (C-p) curve is observed for the first time when prolonging the annealing time, which is ascribed to the amorphous heterogeneous structure surrounding the crystallites. (C) 2016 Elsevier Ltd. All rights reserved.