Thermal analysis and X-ray crystal structural studies on phase transitions in (NH4)3Na(SO4)2

Tri-ammonium sodium di-sulphate (NH4)3Na(SO4)2 was crystallized by evaporating the aqueous solution at room temperature. The phase transition and the crystal structure at room temperature were studied by means of differential scanning calorimetry (DSC) and single-crystal X-ray diffraction, respectively. As a result, thermal anomalies relating to phase transitions were observed at 224.4 K. At room temperature, (NH4)3Na(SO4)2 belonged to the monoclinic space group P21 (Z = 2) and had lattice constants of a = 5.9991 (4) Å, b = 7.7851 (5) Å, c = 10.6528 (8) Å and β = 90.0000 °. The R factor converged to 0.0488.