Investigation of cathode behavior of model thin-film SrTi(1-x)Fe(x)O(3-delta) (x=0.35 and 0.5) mixed ionic-electronic conducting electrodes

SrTi(1-x)Fe(x)O(3-delta) (STF) model cathodes, with compositions x = 0.35 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 700 C 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 Ce(0.9)Gd(0.1)O(2-delta) interlayer was found to have no effect on the electrode impedance. Values for the surface exchange coefficient, k, were calculated and found to be comparable in magnitude to those exhibited by other popular mixed ionic-electronic conductors, such as (La, Sr)(Co, Fe)O(3), 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. (C) 2008 The Electrochemical Society.