Raman and X-ray diffraction studies of terbium trichloride: Phase characterization and temperature relationship

We have used phonon Raman spectrophotometry as a rapid and convenient tool, complimentary to X-ray diffraction, for investigating the polymorphism of TbCl3. In the literature one finds references to the polymorphism of TbCl3, but there is some confusion regarding the structural identity and temperature relationship of the different phases reported. In the present work TbCl3 was prepared via reaction of Tb4O7 and anhydrous HCl gas. Its Raman spectrum was acquired at room temperature and pressure (RTF) and correlated with the results of X-ray diffraction analysis to confirm the PuBr3-type orthorhombic structure. This TbCl3 structure was then monitored as a function of temperature, including after being quenched from the molten state. From our Raman and X-ray results, a phase transition occurred at about 510°C to a tentatively assigned tetragonal structure, which appeared stable up to the melting point (582°C). Additional annealing studies down to about 250°C resulted in the observation of only the RTF form. No evidence for a UCl3-type hexagonal or AlCl3-type monoclinic structure was found in this work, though they are common forms of other lanthanide trichlorides. © 2000 Elsevier Science S.A. All rights reserved.