Raman spectroscopic studies of MX2-type layered compounds

The Raman spectra of transition metal ditellurides (TiTe2, ZrTe2, HfTe2, NbTe2 and TaTe2) have been measured. The spectra of TiTe2, ZrTe2 and HfTe2 show two Raman lines, respectively, in accordance with the group theoretical prediction, whereas those of NbTe2 and TaTe2 show complicated structures due to the distorted octahedral crystal structure. These complicated sectra are explained by the folding of the phonon dispersion curves which is brought about by the enlarged unit cell compared with that of the normal octahedral (1T) structure. The Raman spectra of transition metal dichalcogenides (1T-TaS2, 2H-TaS2, -TaSe2, -NbS2 and -NbSe2) intercalated with organic molecules have also been measured to investigate the effect of the intercalation on the lattice dynamics and the phase transitions in these crystals.