Controlling the Size of Nanodomains in Calcium Aluminosilicate Glasses

Transparent nanostructured glasses show interesting properties for optical fibers or laser beam applications. Binary calcium silicate glasses are known to undergo phase separation in silica-rich compositions. However, adding up to a few mole percent of alumina seems to inhibit the phase separation. By adjusting the amount of alumina added to demixing calcium silicate glasses, we managed to obtain transparent, but nanostructured, glasses with either silica-rich or calcium aluminosilicate-rich nanodomains of a controlled size down to 5 nm for compositions beyond the limits of the immiscibility domain. Therefore, the limits of the immiscibility domain of the SiO(2)-Al(2)O(3)-CaO ternary diagram must be extended to consider the presence of nanosized domains. An atomic-scale analysis of these glasses was performed using (29)Si and (27)Al nuclear magnetic resonance (NMR) experiments, showing that, as the size of the domains decreased, repolymerization of the silicon network and formation of aluminum-rich dusters were observed.