Phase diagram and thermodynamic properties of the LaI₃-RbI binary system

Differential Scanning Calorimetry (DSC) method was used to determine phase equilibria in the LaI3-RbI binary system, and heat capacity of LaI3 and compounds existing in the system under investigation. Two compounds were identified in the solid phase of this system. First of them, Rb2LaI5, melts incongruently at 809 K. The second one, Rb3LaI6, forms at 686 K from Rb2LaI5 and RbI, undergoes a solid-solid transition at 706 K and melts congruently at 864 K. The compositions of RbI-Rb3LaI6 and Rb2LaI5-LaI3 eutectics corresponding to LaI3 mole fraction of x = 0.177 (T = 789 K) and x = 0.472 (T = 773 K), respectively were found from Tammann's diagrams. The LaI3-RbI pseudobinary system was also optimized by CAPLHAD method. Thermodynamic properties of the liquid phase were modelled using Associate Solution Model.