Composition Dependence of the Atomic Structures and Properties of Sodium Aluminosilicate Glasses: Molecular Dynamics...

Understanding the composition-structure-property relations of glass materials is essential for their technological applications. In this study, the structures and properties of a series of sodium aluminosilicate glasses with varying Al₂O₃/Na₂O ratios ((35 - x)Na₂O-xAl₂O₃-65SiO₂, x = 0, 5, 10, 15, 17.5, 20) covering peralkaline to peraluminous compositions, have been studied by using molecular dynamics simulations with two types of interatomic potentials: a fixed partial charge pairwise potential (Teter) and a reactive diffusive charge reactive potential (DCRP). The short and medium structural features such as bond lengths, coordination numbers, Q distributions, and ring size distributions were obtained and compared with experimental data. It was found that silicon remained fourfold-coordinated throughout the compositional range, while a noticeable amount of fivefold-coordinated aluminum together with oxygen triclusters (TBO) are present in compositions with higher Al₂O₃ contents (R_Al/Na > 1). In addition, the simulation results from both potentials show a certain level of violation of the Al avoidance rule by exhibiting a non-negligible amount of [AlO]-[AlO] polyhedral connections. Neutron and X-ray diffraction structure factors of the simulated glasses were calculated and compared with available experimental data. The mechanical properties, including Bulk, Shear, and Young's modulus, were calculated and found to increase with increasing R_Al/Na, in good agreement with the experiments. Correlations of the properties with glass structures as a function of glass compositions and the advantages as well as potential issues of the two sets of potentials in modeling sodium aluminosilicate glasses are discussed in the context of features of glass structures and the prospect of future simulations of glass-water reactions.