Effective medium theory for ionic conductivity of insulator dispersed composite electrolytes

The explanation for the enhancement of effective ionic conductivity (sigma*) of an ionic conductor dispersed with an insulator (Al2O3, SiO2 etc.) is a long standing problem. The enhancement has been suggested to be due to the presence of dislocations, grain boundaries, etc. In this paper we propose a theoretical model for such kind of composite and with the help of an effective medium theory we estimate sigma* of the composite as a function of insulator volume fraction and particle size for CaF2-Al2O3 for three different sizes of insulator grains. The results give a good qualitative fit of the experimental data and exhibits the charateristic experimental observations.