Oxygen grain-boundary diffusion in (La,Sr)FeO3−δ perovskite-oxides probed by molecular-dynamics simulations†

Faster grain-boundary diffusion of oxygen has been observed experimentally in polycrystalline samples of Fe-based perovskite oxides at low temperatures, but this behaviour is at present not well understood. In our study, the influence of grain boundaries on oxygen diffusion is studied by means of classical atomistic simulation techniques. Oxygen tracer diffusion coefficients are determined for monocrystalline and polycrystalline simulation cells of orthorhombic La_0.9Sr_0.1FeO_3−δ and cubic La_0.6Sr_0.4FeO_3−δ by molecular-dynamics simulations at temperatures in the range 1000 ≤ T/K ≤ 2000. In particular, the effects of different oxygen nonstoichiometries δ and of equilibrium (as opposed to random) defect distributions were examined. Our results indicate, that the disrupted structures of the grain boundaries hinder oxygen diffusion; that Sr accumulation within grain-boundary regions does not produce faster diffusion; but that faster grain-boundary diffusion is observed when δ is decreased substantially with a consequent decrease in the rate of lattice diffusion.