Feature articleCrystallization 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 (Tg) 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 (Cp) curve is observed for the first time when prolonging the annealing time, which is ascribed to the amorphous heterogeneous structure surrounding the crystallites.