It was recalled that the cause of the enhanced effective ionic conductivity, in an ionic conductor with a dispersed insulator, was still unclear. The enhancement had been suggested to be due to the presence of dislocations, grain boundaries, and other defects. A theoretical model was proposed here for such composites. With the help of effective medium theory, the conductivity of the composite was estimated as a function of the Al2O3 volume fraction, for 3 particle sizes. It was found that the theoretical results gave good qualitative agreement with the experimental data, and reproduced typical experimentally observed characteristics. In the present model, the blocking of dislocation lines by insulator clusters, together with an enhancement that was due to the presence of an increased number of dislocation lines, could together explain the conductivity enhancement in solid electrolyte-insulator composites. A small discrepancy with respect to experimental data was attributed to the use of the single-cluster approximation.

A.J.Bhattacharyya, T.Dutta, S.Roy, S.Tarafdar, T.R.Middya: Materials Science Forum, 1996, 223-224, 279-82