Molecular dynamics simulation of oxygen ion diffusion in Ba₂In₂O₅

Molecular dynamics simulation was employed to study oxygen ion diffusion in Ba₂In₂O₅ with brownmillerite structure. When the system was heated, the original orthorhombic cell changed to a tetragonal cell at 2300 K. Inspection of the structure revealed that oxygen ions jump from their original sites to the nearest vacant sites. The diffusion was restricted for the sites around the tetrahedrally coordinated In ion, resulting in highly anisotropic diffusion on the ac plane. At 4600 K it further transformed to an oxygen disordered cubic perovskite structure, in which all oxygen ions contributed to diffusion. The predicted transition was consistent with the observed transition to a fast oxide-ion conductor for this compound, although predicted temperature was overestimated. The effect of composition on the transition was studied by simulating the A₂B₂O₅ (A²⁺ = Ba, Sr, Ca; B³⁺ = Al, Fe, In) systems. From these results, oxide-ion conductors with lower transition temperatures could be predicted.