Domain structure and structural transformation of melt alumina under compression: insight from visualization method and molecular dynamic simulation

Molecular dynamic simulation has been done to investigate the domain structure and structural transformation of liquid alumina at 3500 K and under different pressures ranging from 0 to 60 GPa. The simulation results show that there is structural transformation from a tetrahedral to an octahedral network, and that structural units AlOx (x = 4, 5, 6) distribute uniformly and tend to form domain Dx. Under compression, the structure of the melt undergoes through many structural domain Dx. The existence of one- or two-domain structure in the alumina structure describes the phenomenon of 'liquid polymorphism'. In the model, we always found large domains and several small ones, in which the largest domains spread over whole model; meanwhile, the domains with fewer atoms are uniform in all over the simulation model. Moreover, due to the change of tetrahedral to octahedral structure in the alumina coordination which is occurred parallelly with the process of merging and splitting of domain structure, the number of the boundaries between domains atoms (DB atoms) depends on pressure. The number of O456 which connects with three Al types reaches up to 4% of total at 10 GPa. The visualization method has described the domain structure and the change of largest domain Dx (x = 4, 5, 6) under pressure.