The A-cation deficient perovskite series La2-xCoTiO6-delta (0 <= x <= 0.20): new components for potential SOFC composite cathodes

La2-xCoTiO6-delta/Ce0.9Gd0.1O2-delta composites are presented as promising new cathodes for solid oxide fuel cells. The B-site ordering characteristic of double perovskites is present in the whole series. Additionally, increasing amounts of La-vacancies give rise to ordering of alternating La-rich and square-rich (square = vacancy) Layers perpendicular to the c-axis. The introduction of La vacancies produces both oxidation of Co2+ to Co3+ and oxygen vacancies inducing a change of both electrical and electrochemical properties. The best electrochemical performances are obtained for Low x due to a compromise between sufficiently high amount of defects to provide electronic and ionic conductivities, but not so high to induce defect clustering. The material with x = 0.05 exhibits the best performances of the series. Symmetrical cells made of composites of this material and Ce0.9Gd0.1O2-delta deposited on pellets of this electrolyte show a polarization resistance of 0.39 Omega cm(2) at 1073 K.