Heats of solution/substitution in TlNO3 and CsNO3 crystals and in RbNO3 and CsNO3 crystals from heats of transition: the complete phase diagrams of TlNO3–CsNO3 and RbNO3–CsNO3 systems Original Research Article

From measurements of the decrease in the heat (enthalpy) of transition in the solid phase using differential scanning calorimetry, the apparent molar heats of solution, slope ΔHt/x, the partial molar heats of solution at infinite dilution, χ, and the heats of solution, ΔHs°, of Tl+ in CsNO3 crystal and Cs+ in TlNO3 crystal and Rb+ in CsNO3 crystal and Cs+ in RbNO3 crystal along with their recovered lattice energies, ΔHL°, are reported. ΔHs° of Tl+ and Rb+ in CsNO3 crystal are each found to be negligible or zero representing an ideal solid solution, i.e. ΔHmix=0. The complete phase diagrams of the TlNO3–CsNO3 and RbNO3–CsNO3 systems with details of the sub-solidus regions are included. The properties of Tl(1−x)CsxNO3 and Rb(1−x)CsxNO3 compositions are discussed in terms of a ‘mixed crystal’ or ‘crystalline solid solution’ in relation to parallel compositions of Tl(1−x)RbxNO3.