Simulation of pressure-induced phase transition in liquid and amorphous Al₂O₃

We investigated the pressure-induced structural transformation in liquid and amorphous Al₂O₃ by the molecular dynamics (MD) method. Simulations were done in the basic cube under periodic boundary conditions containing 3000 ions with Born-Mayer type pair potentials. The structure of the amorphous Al₂O₃ model with real density at ambient pressure is in good agreement with Lamparter’s experiment. In order to study the amorphous-amorphous phase transition, 23 models of amorphous alumina at the temperature of 350 K and at densities ranging from 2.83 to 5.0 g cm⁻³ had been built. The microstructure of the Al₂O₃ systems had been analyzed through pair radial distribution functions, coordination number distributions, interatomic distances, and bond-angle distributions. Here we found clear evidence of a structural transition in amorphous alumina from a tetrahedral to an octahedral network upon compression. According to our results, this transformation occurred at densities ranging from 3.6 to 4.05 g cm⁻³. We also presented the amorphous-amorphous phase transition from an octahedral to a tetrahedral network structure upon decompression at densities ranging from 5.00 to 2.83 g cm⁻³. Also, the same study was carried out for the liquid state of the system at the temperature of 3500 K, and the liquid-liquid phase transition had been discussed.