The structure and mechanical properties in amorphous alumina under pressure

Molecular dynamics simulations of amorphous alumina with various densities ranged from 2.84 to 3.81 g cm−3 were carried out to investigate their local atomic configuration and mechanical properties. The local atomic structure was analyzed through the pair radial distribution functions, bond angle distributions and simplex statistics. The simulation reveals that a mathematic expression can be derived from a relationship between bond angle distribution and structural units AlOx (and linkages OAly). The density can be estimated through the fraction of structural units AlOx. Void volume and void radii decrease as the density increases. Based on the analysis of simplex statistics, the perfect tetrahedron AlO4 (PTE) was determined. These PTEs may connect to each other via common oxygen to create a large poly-PTE. The largest poly-PTE consists of 19.2% Al in the sample with the lowest density and 3.8% Al in one with the highest density. From deformation of samples, elastic moduli and Poisson ratio were determined. The Young's modulus and yield stress increase with the increasing density. The strain hardening becomes more pronounced as the density increases.