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

Abstract The preferential reaction path for oxygen isotope exchange was investigated on a large-grained polycrystalline (La 0.6 Sr 0.4 )CoO 3 with (La,Sr) 2 CoO 4 grains dispersed as the secondary phase. The isotope exchange experiment was performed at 773 K in 18 O enriched oxygen of 0.2 × 10 5  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 (La 0.6 Sr 0.4 )CoO 3 / (La,Sr) 2 CoO 4 . The surface exchange coefficient, k for the heterophase boundary was roughly estimated by analyzing the depth profile of 18 O. The calculated k was 8 × 10 − 6  cm s − U1 , which is larger than the value of k for the surface of single phase La 0.6 Sr 0.4 CoO 3 by three orders of magnitude.