EFFECTIVE-MEDIUM THEORY FOR IONIC-CONDUCTIVITY IN POLYCRYSTALLINE SOLID ELECTROLYTES

It is usually found that for the relatively poor ion conducting solids , the ionic conductivity for the pure polycrystalline sample is higher than that of the single crystal. The difference has been suggested to be due to the presence of dislocations, grain boundaries etc. in the polycrystal. In this paper we propose a theoretical model for the poly crystal including these defects. A quantitative estimate of the grain boundary contribution to conductivity is made using an effective mediu m theory and it is found to exhibit an Arrhenius behaviour. The result s for calcium fluoride, thallium chloride and cuprous chloride show th at the grain boundary conductivity is approximate to 10(5) times that of the single crystal. The ratio of activation energy for grain bounda ry conduction to that of the single crystal is found to be 0.5-0.6 whi ch is consistent with results obtained from other sources.