Raman study of plastic crystal phase of cyclooctanol under high pressure with different compression rate

• Compression rate plays one important role in phase transition of cyclooctanol.
• Plastic crystal phase and crystalline phase present with lower compression rate.
• Superpressuring liquid present with higher compression rate.

The cyclooctanol (C8H16O) has been investigated under high pressure with different compression rate using Raman spectroscopy. With lower compression rate, two-phase transformations are observed at around 0.4 and 1.1 GPa respectively. At around 0.4 GPa, solidification was observed while no any change presents in the Raman spectra, indicating plastic crystal phase formed. Further compressing to 1.1 GPa, most Raman peaks become sharper and more intense. Additionally, several new peaks present, meaning one ordered crystal phase occur at this pressure. While with higher compression rate, cyclooctanol maintains the liquid state during compression, indicating superpressuring liquid present. The result indicates compression rate plays one important role in phase transition of cyclooctanol. Finally, the phase transitions under high pressure are reversible. After depressurization to the ambient condition, the vibration spectra will return back to the original structure.