RAMAN SCATTERING STUDY OF THE QUASI-ONE-DIMENSIONAL CONDUCTOR ZrTe_5 and HfTe_5(EXPERIMENTS ON MX_5 COMPOUNDS, International Symposium on NONLINEAR TRANSPORT AND RELATED PHENOMENA IN INORGANIC QUASI ONE DIMENSIONAL CONDUCTORS)

By Raman scattering, seven vibrational modes have been detected for ZrTe_5, whereas nine for HfTe_5. The application of a central force model reveals the characteristic vibrational-modes in the transition-metal pentatellurides. The comparison of the observed and calculated frequencies shows the reduction of the strength of the pairing interaction between the chalcogen atoms within the prismatic chain compared to ZrTe_3 and the weakness of the interaction in the tellurium zig-zag chain. The temperature dependence of the half widths shows an unusual increase of the spectral density at low temperatures. The obtained results suggest the existence of two structural distortions or transitions: one occurs above room temperature and the other is related with the reported resistivity anomaly at low temperatures.
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