Investigation of Cathode Behavior of Model Thin-Film SrTi[sub 1−x]Fe[sub x]O[sub 3−δ] (x=0.35 and 0.5) Mixed Ionic-Electronic Conducting Electrodes

(STF) model cathodes, with compositions and 0.5, prepared as dense films with a well-defined area and thickness on top of a single-crystal yttria stabilized zirconia substrate by pulsed layer deposition at were investigated by electrochemical impedance spectroscopy as a function of electrode geometry, temperature, and oxygen partial pressure. The STF cathode was observed to exhibit typical mixed ionic-electronic behavior with the electrode reaction occurring over the full electrode surface area rather than being limited to the triple-phase boundary. The electrode impedance was observed to be independent of electrode thickness and inversely proportional to the square of the electrode diameter pointing to surface exchange limited kinetics. Furthermore, a interlayer was found to have no effect on the electrode impedance. Values for the surface exchange coefficient, , were calculated and found to be comparable in magnitude to those exhibited by other popular mixed ionic-electronic conductors, such as , thereby, confirming the suitability of STF as a model-mixed conducting cathode material. The observed trends are discussed in relation to the known defect and transport properties of STF.