Preparation and electrochemical characterization of perovskite/YSZ ceramic films

Perovskite-type La0.8Sr0.2Co0.8Fe0.2O3-delta powders were prepared using a complex polymeric precursor method. Thermal analysis was carried out on the perovskite precursor to investigate the oxide-phase formation. The structural phase of the powders was determined by X-ray diffraction. These results showed that the decomposition of the precursors occurs in a two-step reaction and temperatures higher that 1000 degreesC are required for these decomposition reactions. For the electrochemical characterization, La0.8Sr0.2Co0.8Fe0.2O3-delta electrodes were deposited by a wet spray technique on dense yttria-stabilized zirconia (YSZ) layers. The morphology of the deposited perovskite thick films (similar to50 mum) was investigated by field emission scanning electron microscopy and showed a porous microstructure. Electrochemical impedance spectroscopy (EIS) measurements were carried out under synthetic air flux at temperatures ranging from 200-600degreesC in the 10 mHz-10 MHz frequency range showing an interfacial electrical resistance related to the La0.8Sr0.2Co0.8Fe0.2O3-delta electrodes. EIS measurements were also performed in the same frequency range at different oxygen partial pressures (10(-5)- 1 atm) at 600 degreesC. At this temperature and frequencies below 0.1 MHz, the electrical response to the applied signal of the electrode material is best fitted by two semicircles, which can be related to charge-transfer processes. The activation energy for the limiting step (adsorption/desorption) was found to be 1.6 eV. (C) 2004 The Electrochemical Society.