Phase Diagram of RbI-SmI_2 Binary System and Structural Investigation of RbSm_2I_5 and RbSmI_3

The RbI-SmI₂, binary system was studied with DTA and X-ray powder diffraction. Its phase diagram shows that it has a congruently melting compound,RbSm₂I₅, with a melting point 524℃; an incongru-ently melting compound, Rb₂SmI₄, with an inconsruently point 467℃ and two compounds, RbSmI₃, and Rb₃SmI₅, being decomposed at 433℃ and 460℃, respectively. The measured structure of RbSm₂I₅ shows that it is isomorphous with NH₄ Pb₂ Cl₅ space group P2₁/c, a=10 . 063(3)Å, b=9.003(3)Å. c =14 . 242(5)Å,β=90.23(3)°;z = 4, MV_x= 1 94 . 3cm³/mol;D=5.255g/cm³ and D_o=5. 334g/cm³ (25. 0℃).The structural, investigation of RbSmI₃ shows that it belongs to the orthorhombic system with a = 15.914(6)Å, b=8.898(3)Å c =12.193(5)Å; Z=8, MV_x =130.0cm³/mol, D_x =4 . 743g/cm³,D_o = 4.597g/cm³(25.0℃).