Cation diffusion in La0.6Sr0.4CoO3−δ below 800 °C and its relevance for Sr segregation

Abstract

Cation diffusion was investigated in La_0.6Sr_0.4CoO_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.