Ionic conductivity of fluorite type crystals CaF2, SrF2, BaF2, and SrCl2 at high temperatures

The ionic conductivity of fluorite-type crystals (CaF2, SrF2, BaF2, and SrC l2) has been studied at high temperatures including the melting points. Rep resented in detail, the technique of measurements is based on the use of a capillary-type cell made of hexagonal boron nitride. Measurements were carr ied out on polycrystalline specimens obtained by the solidification of corr esponding melts. A common feature of all fluorites is that the temperature dependences of conductivity in the superionic region are described by sigmo id-like curves in the Arrhenius plot. The behaviour of the apparent Arrheni us energy and molar conductivity in the superionic region as well as on mel ting crystals has been characterized. From comparative analysis of these da ta, it is suggested that the conductivity anomaly is mainly due to a non-un iform course of anion sublattice disordering in crystals up to melting poin ts. The variation of transport properties is well correlated with the relat ive sizes of cations and anions in the fluorite lattice, that assumes a reg ularity in the degree of sublattice disorder in these solids near the melti ng points. (C) 2001 Elsevier Science Ltd. All rights reserved.