Synthesis and Stabilization of Crystal Hydrate Modification SrSO4⋅0.5H2O

A method has been developed for the synthesis of the metastable trigonal modification SrSO4⋅0.5H2O, isostructural to the well-known CaSO4⋅0.5H2O modification (space group P3121). Frozen solutions of NaCl in water have been proposed as a precursor in the crystallization of SrSO4⋅0.5H2O. The SrSO4⋅0.5H2O structure can be stabilized by isovalent substitution of calcium ions for strontium ions or by aliovalent substitution of potassium and lanthanum ions for strontium ions. The compound of composition K0.25La0.25Sr0.5(SO4)⋅0.5H2O has been synthesized as an example of the stabilized SrSO4⋅0.5H2O modification. The unit cell parameters have been determined and refined. A model of the structure of SrSO4⋅0.5H2O with a statistical distribution of potassium, lanthanum, and strontium atoms over the positions of Ca atoms in the well-known СаSO4⋅0.5H2O structure has been proposed.