Polythermal Section FeSb₂S₄–FeSm₂S₄ of the FeS–Sb₂S₃–Sm₂S₃ System

Abstract

Phase equilibria in the FeSb₂S₄–FeSm₂S₄ system were studied by physicochemical analysis methods (differential thermal and X-ray powder diffraction analyses and microhardness and density measurements), and the T–x phase diagram of the system was constructed. Intermediate phase FeSmSbS₄ melting congruently at 1255 K was found to form. According to the X-ray powder diffraction data, FeSmSbS₄ crystallizes in the orthorhombic system with the unit cell parameters a = 11.446 Å, b = 14.160 Å, c = 3.800 Å, Z = 4, space group Pnam, ρ_pycn = 4.96 g/cm³, and ρ_X-ray = 5.00 g/cm³. In the FeSb₂S₄–FeSmSbS₄ segment of the phase diagram of the FeSb₂S₄–FeSm₂S₄ system, an unlimited series of solid solutions with an orthorhombic unit cell forms. The isothermal section of the FeS–Sb₂S₃–Sm₂S₃ system at 298 K was constructed. The molar specific heat C_p (T) of FeSb₂S₄ was approximated within the range 300–800 K.