Raman scattering in the IVB transition-metal trichalcogenides: ZrS3, ZrSe3, ZrTe3and HfSe3

Phonons in the quasi-one-dimensional compounds ZrS 3 , ZrSe 3 , ZrTe 3 and HfSe 3 have been investigated by Raman spectroscopy. Most of the structures observed have been assigned to Raman active zone centre phonons. Although twelve such k=0 optical phonons are theoretically predicted, some of them are still missing; particularly, the authors failed to excite most of the B g modes (which involve atomic motions along the b axis of the crystal) even with different laser frequencies. The more complete A g spectra are characterised by two sets of three major lines, well separated in frequency except for ZrTe 3 . The low-frequency set is attributed to scattering by rigid chain modes while the upper-frequency set is assigned to intrachain modes. The close relationship between analogous spectra from the different compounds suggests the establishment of one-to-one correspondence between the phonons and their wavenumbers by simple scaling relations. The A g spectra from HfSe 3 exhibit a strong dependence upon laser frequency in the range 1.83-2.73 eV.