Enhanced ionic conduction in dispersed solid electrolyte systems CaF₂-Al₂O₃ and CaF₂-CeO₂

Abstract

Dispersions of Al₂O₃ as well as CeO₂ in CaF₂ are found to enhance the conductivity of CaF₂. 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 CaF₂-Al₂O₃ is by about two orders of magnitude in relation to the conductivity of the host electrolyte CaF₂, whereas for the CaF₂-CeO₂ system it is about three orders of magnitude. Some aspects of the increase in the ionic conductivities of CaF₂-Al₂O₃ and CaF₂-CeO₂ electrolytes can be explained by a recent theoretical model. It is proposed that a substantial enhancement in the vacancy concentration of CaF₂, brought about by the attraction of F^- ions to the surface of Al₂O₃ (or CeO₂), is responsible for the low temperature increase in the ionic conductivity of CaF₂.