The separability of inter- and intragranular resistivities in sodium beta-alumina type ceramics

The intergranular and intragranular resistivity components in β-alumina ceramics cannot be separated quantitatively by impedance analysis, it was concluded a few years ago in a previous article in this journal. This conclusion was based on use of the so-called parallel multi-element equivalent circuit to model the electrical properties of polycrystalline electrolytes. However, this model is shown to be inconsistent with the observation that the activation energy for the intergranular resistivity is independent of the size of that component for many compositions — both β- as well as β″-alumina. From this finding and others, the author infers that the separation of intra- and intergranular resistivities in sodium beta-alumina type ceramics is clean. Consideration of the separability question is greatly facilitated by an unconventional method of resistivity analysis. This alternative method involves essentially d.c. measurements on a set of specimens of the same composition but with different microstructures and resistivities. The method is described and its use illustrated.