Crystal domain growth driven by nanometric phase separation in perfect surface crystallization

Phase separation often makes glass structure inhomogeneous. Nevertheless, a uniform texture consisting of single-crystal domains has been found by crystallization in nonstoichiometric glass, i.e., perfect surface- crystallization (PSC). Although the PSC is probably caused by evolution of SiO₂-rich amorphous nanoparasites on the domain, its mechanism has not been understood yet. In this study, we examined an early-stage of PSC in a strontium-titanosilicate glass by means of nanoscopic observations. It was demonstrated that the binodal-like nanometric phase-separation and crystal-growth of fresnoite-type phase occur simultaneously at the crystal interface. It was strongly suggested that the PSC process is driven by the phase separation.