Cation diffusion in La0.6Sr0.4CoO3-delta below 800 degrees C and its relevance for Sr segregation

Cation diffusion was investigated in La0.6Sr0.4CoO3-delta (LSC) thin films on (100) yttria stabilized zirconia in the temperature range 625-800 degrees C. Isotopic (86Sr) and elemental tracers (Fe, Sm) were used to establish diffusion profiles of the cations in bi- and multi-layered thin films. The profiles were analyzed by time of flight-secondary ion mass spectrometry (ToF-SIMS). Grain and grain boundary diffusion coefficients of the cations were determined for LSC thin films with columnar grains - diffusion along grain boundaries is shown to be about three orders of magnitude faster than in grains. This could be verified for thin films with different grain size. A- and B-site cations showed very similar temperature dependencies with activation energies of similar to 3.5 eV for bulk and similar to 4.1 eV for grain boundary diffusion. The importance of cation diffusivities for surface segregation of Sr and thus for a major degradation mechanism of LSC cathodes in solid oxide fuel cells is discussed.