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

Abstract

We have used phonon Raman spectrophotometry as a rapid and convenient tool, complimentary to X-ray diffraction, for investigating the polymorphism of TbCl 3. In the literature one finds references to the polymorphism of TbCl 3, but there is some confusion regarding the structural identity and temperature relationship of the different phases reported. In the present work TbCl 3 was prepared via reaction of Tb 4O 7 and anhydrous HCl gas. Its Raman spectrum was acquired at room temperature and pressure (RTP) and correlated with the results of X-ray diffraction analysis to confirm the PuBr 3-type orthorhombic structure. This TbCl 3 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 RTP form. No evidence for a UCl 3-type hexagonal or AlCl 3-type monoclinic structure was found in this work, though they are common forms of other lanthanide trichlorides.