IMPROVED PREPARATION OF LA1-XMEXCOO3-DELTA (ME = SR, CA) AND ANALYSISOF OXIDE-ION CONDUCTIVITY WITH ION CONDUCTING MICROCONTACTS

Preparation and ionic conductivity of the mixed conducting perovskites La1-x,MexCoO3-delta with Me = Sr, Ca were investigated in the composi tion range x = 0.1-0.5. Two preparation methods, the first via metal c omplexes in aqueous solution and the second based on a spray-freezing/ freeze-drying process, were studied with an emphasis on lower reaction temperatures for the formation of perovskite type oxides. Oxygen ion conductivities were measured as a function of composition x and temper ature (550 degrees C-750 degrees C) using oxygen ion conducting microc ontacts (made of stabilised zirconia, contact radius in the range 10-8 0 mu m). Evaluation of the steady-state current voltage curves (slope, curvature) yields the oxygen ion conductivity as a function of the ox ygen partial pressure. For all investigated compositions of Sr and Ca substituted perovskites, oxygen transport occurs by a vacancy mechanis m. For instance, values of the ionic conductivities are 4.6 x 10(-5) ( Omega cm)(-1) for La0.8Sr0.2CoO3-delta and 2.8 x 10(-5) (Omega cm)(-1) for La-0.8, Ca-0.2, CoO3-delta at 700 degrees C in air increasing by nearly a factor of ten with increasing Sr or Ca concentration.