Structure of Ternary Alumino-Silicate Glasses: Conditions of the Existence of Triclusters

Ternary alumino-silicate glasses, SiO2-Al2O3-(MO, M2O), contain two network former species, Si and Al. The glass structure basically consists of Si-O-Si and Si-O-Al linkages because of thermodynamically unfavorable of Al-O-Al linkage. However, Al-O-Al linkage is detected to exist as triclusters. Although some conditions have been proposed to explain the existence of the triclusters, it seems to be insufficient. This work attempts to clarify the conditions of the existence of triclusters in ternary alumino-silicate glasses based on the molar ratio of [MO, M2O]/[Al2O3], [SiO2]/[Al2O3] and the NBO (non-bridging oxygen) in the network. The existence of the triclusters conditions could be defined, stoichiometrically, as either [MO, M2O]