Phase Transition in CCl₄ under Pressure: a Raman Spectroscopic Study

High-pressure Raman studies at room temperature are performed on CCl₄ up to 13GPa. The Raman bands of the internal modes (v₂, v₄ and v₁) show entirely positive pressure dependence. The slopes dω/dP of the internal modes exhibit two sudden changes at 0.73GPa and 7.13GPa, respectively. A new lower frequency mode (225cm^-1) appears at 3.03GPa, and the splitting of v₂, ν₃ and v₄ occurs at about 7.13GPa. Moreover, Raman spectra of Fermi
resonance show that the relative position of the v₁ + v₄ combination and the ν₃ fundamental firstly interchanges corresponding to that at ambient pressure, then the v₁ +v₄ combination disappears in the gradual process of compression. It is indicated that the pressure-induced phase transition from CCl₄ II to CCl₄ III occurs at 0.73GPa, and CCl₄ III undergoes a transition to CCl₄ IV below 3.03GPa. Further CCl₄ IV transforms in a new high-pressure phase at about 7.13GPa, and the symmetry of the new high-pressure phase is lower than that of CCl₄ IV. All the transitions are reversible during decompression.