MICROSTRUCTURE - IONIC-CONDUCTIVITY RELATIONSHIPS IN CERIA-GADOLINIA ELECTROLYTES

Impedance spectroscopy has been used to separate grain interior and gr ain boundary conductivities in a series of measurements on thin Ce0.8G d0.2O2-delta ceramic electrolytes with a range of different grain size distributions. The ''brick layer'' microstructural model has been use d to provide an estimate of a true grain boundary conductivity and to relate the electrical properties of the ceramic to microstructural par ameters. High resolution electron microscopy images show that insulati ng intergranular phases do not necessarily have to be present in order to cause a large grain boundary resistance, A clear relationship betw een grain boundary resistance and the number of grain boundaries was o bserved for samples of mean grain size of 3 mu m or larger. For sample s of sub-micron average grain sizes, measured grain boundary conductiv ities were inconsistent with model predictions, being significantly hi gher than predicted.