Oxygen Diffusion in Ceramic Mixed Conducting La0.6Sr0.4Co0.2Fe0.8O3−δ : The Role of Grain and Twin Boundaries

Measurements of the oxygen diffusivity of ceramic samples of the mixed ionic electronic conductor La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3− δ (LSCF6428) have shown the appearance of grain boundary tails in diffusion profiles at temperatures below 600 °C. Analysis of the tails yields values of the grain boundary diffusion products ( D g b δ ). The activation enthalpies for the grain boundary and lattice diffusion are very close at 1.69 eV and 1.61 eV respectively, suggesting a common diffusion mechanism. Comparison with literature values on both lattice and grain boundary diffusion products have shown that values of D g b δ obtained for LSCF6428 are the highest yet recorded for any oxide material. The reasons for this high value are discussed, including the degree of nonstoichiometry of the parent lattice and the possible involvement of the twin boundaries found in these ceramic samples.