Phase diagram of NdI3–RbI pseudo-binary system. Thermodynamic properties of solid compounds

• The phase diagram of NdI3–RbI system was measured.
• The heat capacity of NdI3 and Rb3NdI6 were measured.
• The thermodynamic properties of the phases were calculated.

Phase equilibria in the NdI3–RbI binary system were established from differential scanning calorimetry (DSC) measurements. This system exhibits three compounds, namely Rb3NdI6, Rb2NdI5 and RbNd2I7, and two eutectics located at NdI3 molar fractions x = 0.177 (T = 810 K) and x = 0.421 (T = 706 K), respectively. Rb3NdI6 undergoes a solid–solid phase transition at 718 K and melts congruently at 905 K. Rb2NdI5 and RbNd2I7 melt incongruently at 711 K and 737 K, respectively. The heat capacity of solid and liquid Rb3NdI6 has been measured in temperature range 298–1006 K. The all of accessible data were used for optimization of phase diagram by the CALPHAD method. Liquid model of associated solution with one associate has been used for description of the liquid phase. The dependence of mixing entropy on composition were determined and interpreted. For the pseudo-binary compounds, existing in investigated system, dependence of Gibbs energies of formation on temperature were calculated.

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