Low temperature heat capacity and thermodynamic functions of anion bearing sodalites Na8Al6Si6O24X2 (X=SO4, ReO4, Cl, I)

•Heat capacities of sulfate, perrhenate, chloride, and iodide sodalites were measured from 2K to 300K.•Heat capacities were fitted to equations in three temperature ranges.•Standard entropies and Gibbs energies were calculated.•All four sodalites undergo a phase transition below room temperature for which thermodynamic parameters were determined.•This work is relevant to nuclear waste disposal. Heat capacities of sulfate, perrhenate, chloride, and iodide sodalites with the ideal formula Na8Al6Si6O24X2 (X=SO4, ReO4, Cl, I) were measured from 2K to 300K using a Quantum Design Physical Property Measurement System (PPMS). From the heat capacity data, the standard thermodynamic functions were determined. All four sodalites undergo a phase transition below room temperature for which thermodynamic parameters were determined. Additionally, the heat capacity of one of the constituent compounds (NaReO4) was measured.