Conductivity of composite calcium fluoride-silica solid electrolytes

Calcium fluoride based composites containing 1 to 15m/o SiO2 disperse phase were prepared. The electrical conductivity of the samples was measured in the temperature range 40-700 degrees C by both the d.c, four-probe and the impedance spectroscopy method. The conductivity values for the samples with SiO2 in the range 1 to 10 m/o were significantly higher than those of pure CaF2 and they were dependent on the preparation method of the sample. The maximum conductivity values were observed for 5.0m/o SiO2 content. The (CaF 2 + SiO2) composites appeared to be purely ionic conductors. The materials prepared were applied as electrolytes in solid-state oxide galvanic cells. In this way the Gibbs free energy of formation of calcium silicates, CaSiO3 and Ca2SiO4 at 700 degrees C was determined. (C) 1999 Elsevier Science Ltd and Techna S.r.l. All rights reserved.