Thermal Expansion of the AgBr–CuBr System

Abstract

The investigations of dilatometry and X-ray diffraction for the polycrystalline of (Ag_xCu_1−x)Br in the composition range 0.3≤x≤1.0 have been carried out. An abrupt increase of lattice constant a₀ was observed at about 230°C and the composition dependence of a₀’s showed considerable deviations from the Vegard’s law. The observed anomalous expansion of the lattice was caused due to the occupation of Cu⁺ ions at the interstitial sites which possess relatively small cavity. It is considered that the lattice expansion enables even Ag⁺ ions having larger ionic radius to migrate to the interstitial sites. The disordered distribution of cations is the reason of high ionic conductivity in the mixed crystals of silver and cuprous bromides.