Oxygen stoichiometries in La1-xSrxCo1-yFeyO3-delta perovskites at reduced oxygen partial pressures

La1-xSrxCo1-yFeyO3-delta perovskite materials have been considered as poten tial cathodes for solid oxide fuel cells operating at intermediate temperat ures. The effect of temperature, ambient oxygen partial pressure and compos ition on the extent of oxygen deficiency was electrochemically investigated for various perovskites by means of solid electrolyte coulometry. Experime nts were performed at reduced oxygen partial pressures between 1.3 X 10(-3) and 6 X 10(-5) atm since in a real fuel cell under cathodic bias, the mate rial near the electrode/electrolyte interface is expected to be in a reduce d state. It was found that the degree of oxygen non-stoichiometry (delta) i ncreases with increasing temperature, decreasing oxygen partial pressure an d increasing Sr or Co content. Transient re-equilibration experiments were also performed in an attempt to investigate the oxygen transport characteri stics of the perovskite under various operating conditions. These experimen ts have shown that the time needed for re-equilibration increases with incr easing oxygen deficiency. (C) 2000 Elsevier Science BN. All rights reserved .