The Density–Structure Correlations in Al2O3Glasses: Insights from Molecular Dynamics Simulation

The relationship between structure and density in Al2O3 glass has been studied by mean of molecular dynamic simulation. Simulation results reveal that the structure of Al2O3 is formed by AlOx structural unit. Under densification, there is the transformation from tetrahedral to octahedral structure. The AlOx structural units tend to form the cluster of AlOx units. Alumina exhibits polymorphism and heterogeneous structure due to the presence of AlOx clusters and two-domain types (D4–D5 or D5–D6) in the intermediate density range. Moreover, a continuous random network of basic structural units linking to each other via with corner-sharing, edge-sharing, face-sharing bond. At low density region, the basic structural units are mainly linked via bridge oxygen and the connectivity between AlOx is mainly corner sharing bonds. The numbers of corner-sharing and edge-sharing bonds vary in opposite directions. The basic structural units are barely bonded to each other via face-sharing bond. In the model, there is the existence of the free volume region. The distribution of free volumes depends on density. It has the Gaussian form and the position of the peak tends to shift to the left under compression. As densnit increases, the void radius decreases rapidly.