The ionic conductivity of these fluorite-type crystals was studied at high temperatures, including the melting points. The measurement technique was based upon the use of a capillary-type cell that was made of hexagonal BN. Measurements were carried out on polycrystalline specimens that were obtained by solidification of the corresponding melts. A common feature was that the temperature-dependence of the conductivity in the superionic region was described by sigmoidal curves in an Arrhenius plot. From a comparative analysis of these data, it was deduced that the conductivity anomaly was due mainly to non-uniform anion sub-lattice disordering in crystals at up to the melting point. The transport properties were well correlated with the relative sizes of cations and anions in the fluorite lattice. This required a regularity in the degree of sub-lattice disorder in the solids when near to the melting point.

Ionic Conductivity of Fluorite-Type Crystals CaF2, SrF2, BaF2 and SrCl2 at High Temperatures. B.M.Voronin, S.V.Volkov: Journal of Physics and Chemistry of Solids, 2001, 62[7], 1349-58