Atomistic computer simulation techniques were used to investigate defect structures and phase relationships in Ba hexa-aluminates. Equilibrated lattice energies were calculated for several structural models which had been proposed in order to explain the non-stoichiometry of such materials. This suggested that Ba hexa-aluminates with the magnetoplumbite structure were unstable when compared with non-stoichiometric -alumina structures. The lack of a superstructure in phase I was attributed to the very small difference in lattice energies between the structures in which defect complexes of this phase were arranged differently. The calculations also suggested that the most appropriate structural model(from the point of view of both energy and crystal symmetry) for phase II was one which included both triple Reidinger defects and Ba interstitials within the spinel blocks.

J.G.Park, A.N.Cormack: Journal of Solid State Chemistry, 1996, 121[2], 278-90