Heats of solution/substitution in TlNO3 and RbNO3 crystals from heats of transition. The complete phase diagram of the TlNO3–RbNO3 system

Abstract

From measurements of the decrease in the heat (enthalpy) of transition in the solid phase by differential scanning calorimetry, the partial molar heats of solution at infinite dilution, χ, and the heats of solution or substitution, ΔH_s^°, of Tl⁺ in RbNO₃ crystal and Rb⁺ in TlNO₃ crystal along with their recovered lattice energies, ΔH_L^°, are reported. The complete phase diagram of the TlNO₃–RbNO₃ system with details of the sub-solidus regions is reported. The properties of a “mixed crystal’' or “crystalline solid solution’' of Tl_(1-x)Rb_xNO₃, viz., structure, transition temperatures, melting temperature, etc., are presented and discussed.