ИСТИНА

One of key problems limiting practical applications of high-conductivity solid oxide electrolytes based on lanthanum gallate is their chemical reactivity with most promising electrode materials. This makes it necessary to introduce protective sub-layers between the electrolyte and electrodes, blocking cation interdiffusion between the cell components and increasing electrochemical activity of the electrodes. The materials of the multifunctional interlayers should possess mixed ionic-electronic conductivity, fast kinetics of the interfacial oxygen exchange, a high thermodynamic stability, and thermomechanical compatibility with respect to the electrodes and solid electrolyte. These requirements can be partly satisfied using ceria-based solid solutions, particularly Ce0.6La0.4O2-δ. However, the latter composition and its derivatives only exhibit mixed conductivity under reducing conditions, such as anodic environments in solid oxide fuel cells (SOFCs), and are solid electrolytes with moderate level of the oxygen ionic transport in oxidizing atmospheres. The present work was centered on the analysis of defect formation and transport mechanisms in Pr-codoped Ce(La)O2-δ, where the partial substitution of Pr4+/3+ cations for cerium increases p-type electronic conduction and electrochemical activity in the reactions involving molecular oxygen. Fluorite-type Ce1-x-yLaxPryO2-δ (x=0.29-0.40, y=0-0.20) were synthesized by the glycine-nitrate technique and characterized employing X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The total electrical conductivity and Seebeck coefficient of dense ceramic materials, measured in the oxygen partial pressure range from 10-19 to 0.5 atm at 973-1223 К, were analyzed and used to model point-defect formation, association and migration processes in the crystal lattice. The chemical stability with respect to the gallate-based solid electrolyte was studied using long-term annealings of the powder mixtures with subsequent XRD analysis, and also by SEM/EDS studies of the model electrochemical cells. Finally, model SOFCs with the new interlayer compositions, fabricated by screen-printing, were evaluated by electrochemical and microscopic techniques.