Composite (CaF2+α-Al2O3) solid electrolytes:: Preparation, properties and application to the solid oxide galvanic cells

Calcium fluoride based composites containing up to 25 mol.% alpha-Al2O3 disperse phase were prepared. Electrical conductivities of the samples were measured in the temperature range 400-700 degrees C by the d.c. four-probe method. Dispersions of alpha-Al2O3 up to 5 m/o were found to enhance the conductivity of pure CaF2. The conductivity Values were increased two orders of magnitude higher than those of pure CaF2 and they were dependent on the preparation method of the sample. The maximum conductivity values were observed for 2.5 m/o alpha-Al2O3 content. The (CaF2 + alpha-Al2O3) composites appeared to be purely ionic conductors. The materials prepared were applied as electrolytes in solid-state oxide galvanic cells. The Gibbs free energy of formation at 700 degrees C for calcium metasilicate was determined from electromotive force (emf) measurements in this way. (C) 1997 Elsevier Science Limited and Techna S.r.l.