Phase equilibria in the CeI3-CsI binary system

The phase equilibria in the cerium(III) iodide-cesium iodide pseudobinary system were established by differential scanning calorimetry. The system is characterized by existence of three compounds: Cs3CeI6, Cs3Ce2I9 and CsCe2I7. First one, namely Cs3CeI6, melts congruently at 823 K and undergoes two phase transitions at 658 and 762 K. Second compound, Cs3CeI6, decomposes in the solid state at 610 K. The last existing compound, CsCe2I7, melts incongruently at 826 K. The eutectics composition was found from Tammann plot, which predicts, through application of the lever rule, the variation of the enthalpy associated with eutectic melting as a function of composition. The composition of CsI-Cs3CeI6 and Cs3CeI6-CsCe2I7 eutectics corresponds to cerium(III) iodide mole fraction x = 0.127 (T = 823 K) and x = 0.485 (T = 737 K), respectively.