Molecular dynamics simulations were used to study O ion diffusion in samples with the brownmillerite structure. When the material was heated, the original orthorhombic cell changed to a tetragonal one at 2300K. Inspection of the structure revealed that O ions jumped from their original sites to the nearest vacant sites. Diffusion was restricted to sites around the tetrahedrally coordinated In ion, and this led to highly anisotropic diffusion on the ac-plane. At 4600K, the material further transformed to an O-disordered cubic perovskite structure in which all of the O ions contributed to diffusion. It was concluded that the predicted transition was consistent with the observed transition of this compound to a fast oxide-ion conductor; although the predicted temperature was an over-estimate.

M.Kanzaki, A.Yamaji: Materials Science and Engineering B, 1996, 41[1], 46-9