Solubility Phase Diagrams of ternary systems of CsCl–CdCl2–H2O and CsBr–CdBr2–H2O at T = 298.1 K and the thermodynamic properties of the new solid phase compounds

Abstract

Using an isothermal equilibrium method, thephaseequilibrium of the ternary systems CsCl–CdCl2–H2O and CsBr–CdBr2–H2O were studied at T = 298.1 K. In thephasediagram of the system CsCl–CdCl2–H2O, the solidphasesof CsCdCl3 and Cs2CdCl4, besides CsCl and CdCl2·2.5H2O, were discovered. Thephasediagramof the system CsBr–CdBr2–H2O contains five crystallization fields for the solidphases CdBr2·4H2O, CsCdBr3, Cs5Cd2Br9, Cs3CdBr5 and CsBr. The new solidphasesof CsCdCl3 and CsCdBr3 are congruently soluble, and Cs2CdCl4, Cs5Cd2Br9 and Cs3CdBr5 are incongruently soluble in the aqueous system. The experimental solubility data and phase diagrams for the ternary systems show more practical application for the obtained cadmium-based halide perovskite. The five new solid phase have been analyzed by X-ray diffraction and thermogravimetry/derivative thermogravimetry. By measuring the standard molar enthalpies of solution of the compounds, the standard molar enthalpies of formation of CsCdCl3, Cs2CdCl4, CsCdBr3, Cs5Cd2Br9, Cs3CdBr5 were determined to be –(873.3 ± 0.7) kJ·mol−1, –(1325.6 ± 0.9) kJ·mol−1, –(742.8 ± 0.7) kJ·mol−1, –(2710.0 ± 1.3) kJ·mol−1 and –(1558.1 ± 1.0) kJ·mol−1, respectively.