Ionic conductivity of halide sodalites

Abstract

The ionic conductivities of halide sodalites, Na₈(AlSiO₄)₆X₂, where X₂= Cl₂, Br₂ or I₂, have been investigated over the temperature range 200–550 °C in order to study the effect of the anion size on the sodium ion conductivities. The activation energy for conduction was found to decrease over the range 96.6–71.7 kJ mol^–1 as the halide anion size increased and at all temperatures the sodium ion conductivity was highest where the framework dimensions had expanded with enlargement of the halide ion. Ionic conductivity in the sodalite structure is primarily influenced by the potential barrier of the intercage bottleneck which is controlled by the size of the six-membered window in relation to the dimension of the mobile cations. The size of this bottleneck may be easily controlled by the anion size.