Lattice vibrational study of the phase transition in the plastic crystal adamantane (C10H16)

Using the Raman technique we have studied the lattice vibrations of the prototype plastic crystal adamantane (C₁₀H₁₆). The measurements, as a function of temperature through the phase transition (208K), show splittings in certain lines. At room temperature using hydrostatic pressure, we also induced a phase transition. The transition is detected by Raman measurements, and we observe splittings of the very same vibrational lines. This indicates that the pressure induced phase transition yields the same crystal structure as the low temperature structure. Some analysis of the pressure and temperature derivatives of the vibrational modes is presented.