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 with the ideal formula Na₈Al₆Si₆O₂₄X₂ (X = SO₄, ReO₄, Cl, I) were measured from 2 K to 300 K 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.