From molten glass to crystallizable melt: The essence of structural evolution

Within the frames of our model concept an attempt is made to reveal the principal differences in the structural self-assembling of melts responsible for their crystallization or vitrification. Results of in situ synchrotron diffraction and Raman spectroscopic study of melts, NMR spectroscopy of glasses, and computer modeling of predominant arrangement of cation and anion components of melts with different compositions were used as an experimental basis. We introduce the notions of active crystal-forming part of melt, which is an assembly of cation-anion associative complexes and “free” structure-forming cations, and its passive part, which is fragments of polycondensed anion groupings of various scales. Crystallization is interpreted as cooperative interaction caused by the formation of coordination spheres of “free” cations inside precursor clusters resulting from the crystal-forming part of melt.