Cation diffusion in La₀.₆Sr₀.₄CoO 3 - δ below 800 °C and its relevance for Sr segregation
Cation diffusion was investigated in la₀.₆Sr₀.₄CoO 3 - δ (LSC) thin films on (100) yttria stabilized zirconia in the temperature range 625-800 °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 ∼3.5 eV for bulk and ∼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.
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Financial support from Austrian Science Fund (FWF) project P 21960-N17 is gratefully acknowledged.