Fine-tuning of oxygen vacancy and interstitial concentrations in La^sub 1.85^Ce^sub 0.15^CuO^sub 4+d^ by electrical bias

Defects present in oxide materials are well known to strongly impact transport properties, as well as interfacial reaction kinetics, such as oxygen exchange with the atmosphere. Most commonly, oxygen defect concentrations, or equivalently oxygen nonstoichiometry, are set in a given material by controlling the external oxygen partial pressure and temperature. This approach, however, is limited by the range of oxygen partial pressures readily experimentally achievable and the time it takes to reach equilibrium. In this study, we instead rapidly fine-tune oxygen defect concentrations in promising rare earth cuprate (RE2CuO4: RE = rare earth) SOFC cathode materials by controlling the electrical potential applied across a YSZ supporting electrolyte. We then monitor the induced oxygen nonstoichiometry variations by in-situ measurement of chemical capacitance. These layered perovskites, that incorporate both oxygen interstitials and vacancies, show promise as SOFC cathodes. In this study, we attempt to correlate the changing defect and transport properties with the measured area-specific-resistance, or equivalently the surface oxygen exchange coefficient. Success is also demonstrated in measuring in-plane film conductivity over a wide range of effective oxygen partial pressure, with the results agreeing with predictions from appropriate defect models.