Enhancement of oxygen exchange at the hetero interface of (La,Sr)CoO3/(La,Sr)2CoO4 in composite ceramics

The preferential reaction path for oxygen isotope exchange was investigated on a large-grained polycrystalline (La0.6Sr0.4)CoO3 with (La,Sr)2CoO4 grains dispersed as the secondary phase. The isotope exchange experiment was performed at 773 K in 18O enriched oxygen of 0.2 × 105 Pa. Three-dimensional imaging of Secondary Ion Mass Spectrometry (SIMS) was carried out to visualize the isotope distribution. The SIMS image suggested that there are fast oxygen-incorporation paths along the heterophase boundary of (La0.6Sr0.4)CoO3 / (La,Sr)2CoO4. The surface exchange coefficient, k for the heterophase boundary was roughly estimated by analyzing the depth profile of 18O. The calculated k was 8 × 10− 6 cm s− U1, which is larger than the value of k for the surface of single phase La0.6Sr0.4CoO3 by three orders of magnitude.