Chemical dependence of network topology of calcium aluminosilicate glasses: a computer simulation study

Molecular dynamics and reverse Monte Carlo simulations are used to investigate the structure of calcium aluminosilicate glasses with low silica content. The polymerized network is close to that expected from a random distribution for all compositions with important amount of Al–O–Al linkages. Minor species such as triclusters and free oxygen atoms are present. The main structural variations are the changes in the ring size distribution or the Qn distribution. The ring statistics indicate the presence of 4-membered rings, with larger rings at high silica content. We observe that Al enters preferentially the tetrahedral polymerized units with increasing SiO2. A noteworthy structural property of the structure of these glasses is the presence of a significant amount of non-bridging oxygens, even in the fully charge-compensated glasses. The Ca environment correspond to a distorted polyhedra with seven oxygen neighbors. The variation of the glass transition temperature of these glasses are explained based on the preference of Al for more polymerized sites and the structural role of Ca.