Local ordering and interfacial structure between spinel crystal and aluminosilicate glasses from molecular dynamics simulations

Abstract

Molecular dynamics simulations were performed to investigate the interfaces of soda magnesia aluminosilicate glass and MgAl2O4 spinel crystals. The glass structures were first generated and characterized. It was found that the glass-forming network consists of fourfold coordinated [SiO4] and [AlO4] tetrahedra connected through corner sharing with Na+ and Ca2+ acting as modifiers or charge compensators. The glass and crystal interfaces were then constructed on low energy spinel surfaces with special measures to ensure two natural interfaces. The interfacial structures were characterized by z-density profile, pair distribution function and coordination number analysis. The results show that there exist local ordering on the glass side and preferential adsorption of specific cation near the interface. Cation coordination analyses showed that aluminum ions changed from mainly fourfold coordination in the glass to five and sixfold coordination near the interface suggesting a gradual change in structural role of aluminum from the glass to the crystal. The ordering and segregation of cations, as well as change in aluminum coordination, at the glass/crystal interface strongly suggest that the ordered crystal structure influence the atom distribution and local structure of the adjacent glasses and this ordering can be the initial stage of nucleation or crystal growth.