Halide-sodalites: thermal expansion, decomposition and the Lindemann criterion

Abstract Twelve cubic sodalites |Na8X2|[T1T2O4]6 (T1 = Al3+, Ga3+; T2 = Si4+, Ge4+; X = Cl−, Br−, I−) were examined using high-temperature (HT) X-ray diffraction experiments and TGA-DSC measurements. Temperature-dependent structure data was obtained by Rietveld refinements. Decomposition temperatures were determined using TGA-DSC data for all compounds. The temperature-dependent volume expansion was used to determine Debye and Einstein temperatures using DEA fits. Distinct relations between thermal expansion, bond lengths and the decomposition temperature could not be found. Determination of Lindemann constants of all compounds enables a classification of the sodalites in three groups.