Atomistic simulation techniques were used to investigate crystal structures and defect energetics. An interatomic potential model was developed which reproduced the orthorhombic brownmillerite structure, with alternating layers of O octahedra and tetrahedra. Defect calculations showed that the most energetically favorable intrinsic defects were of Frenkel type, with an O vacancy on the O(1) site and an O ion in an interstitial position in the tetrahedral layer. The predicted formation energies of electronic defects suggested that this material would oxidize with the formation of positive holes which then contributed to the observed electronic conductivity. An analysis of the possible O-ion migration pathways suggested that the energy barriers to migration were lowest between the equatorial sites of O octahedra in the [001] direction.

C.A.J.Fisher, M.S.Islam, R.J.Brook: Journal of Solid State Chemistry, 1997, 128[1], 137-41