RAMAN-SPECTRA OF THE RARE-EARTH DISULFIDES

Raman, IR and VIS-reflection spectra of a new group of layered compounds, LnS2, have been studied. All Ag and Bg modes in the orthorhombic and monoclinic structural modification were assigned and peculiarities of spectra were interpreted as resulting from three kinds of vibrations: cation sublattice (70-160 1/cm), S2- ions connected with Ln3+ in one layer (160-350 1/cm) and dumb-bell pairs S2(2-) related to the other layer of structure (380-420 1/cm). Series of the LnS2 spectra (La = La-Er) as a function of the rare earth elements ionic radius are given. Every variation in spectral features, beginning with SmS2, is attributed to the structural phase transition for the LnS2 compounds. Raman spectroscopy is shown to be a very usefull method for the characterization of unknown structures of heavy rare earth disulfides.