Composition and temperature induced changes on the structure of molten ScCl3–CsCl mixtures

Abstract

Raman spectroscopy has been used to elucidate the structure of ScCl₃–CsCl molten mixtures in the complete composition range and at temperatures up to 1000 °C. The variation of temperature and composition reflected systematic changes in the spectra which were interpreted in terms of structural changes in the melts. In mixtures with ScCl₃ mole fractions below 0.5 the melt structure was predominated by a series of ionic species ScCl₇⁴⁻, ScCl₆³⁻, Sc₂Cl₉³⁻ and ScCl₄⁻ which established different chemical equilibria. At melt compositions rich in ScCl₃ the isotropic Raman spectra are characterized by two bands P₁ and P₂. The position and relative intensities of these bands change with composition in a similar way as observed previously in studies of other rare earth halide systems. Furthermore, the continuous shift of the P₂ band with composition is in accordance with the recent computer simulations [P. A. Madden, M. Wilson and F. Hutchinson, J. Chem. Phys., 2004, 120, 6609] which give an understanding of the origin of this band. A cluster-like model is proposed for the structure of molten ScCl₃ where fragments of scandium “octahedra” bridged by chlorides are terminated with scandium “tetrahedra” having terminal chlorides.