Enhanced Ionic Conduction in Dispersed Solid Electrolyte Systems $CaF_2-Al_2O_3$ and $CaF_2-CeO_2$

Dispersions of $Al_2O_3$ as well as $CeO_2$ a in $CaF_2$ are found to enhance the conductivity of $CaF_2$ . Both these systems are biphasic and the electrical conduction in them is purely ionic in nature. At 650 K the increase in the ionic conductivity of the dispersed solid electrolyte system $CaF_2-Al_20_3$ a is by about two orders of magnitude in relation to the conductivity of the host electrolyte $CaF_2$, whereas for the $CaF_2-CeO_2$ system it is about three orders of magnitude. Some aspects of the increase in the ionic conductivities of $CaF_2-Al_20_ 3$ and $CaF_2-CeO_2$ electrolytes can be explained by a recent theoretical model. It is proposed that a substantial enhancement in the vacancy concentration of $CaF_2$, brought about by the attraction of $F^-$ ions to the surface of $Al_20_3$ (or $CeO_2$) , is responsible for the low temperature increase in the ionic conductivity of $CaF_2$