Raman Scattering Investigations of Adamantane under High Pressure

Results of Raman scattering measurements under pressure up to 25 GPa on adamantane (C₁₀H₁₆) carried out at room temperature are reported. The analysis of Raman data indicated four phase transitions. The ambient pressure disordered Fm3m structure ($\alpha$-C₁₀H₁₆) transformed to a high pressure ordered phase at 0.6 GPa. Continue to pressurize to 1.7 GPa, the second structure phase transition began, and completely accomplished until 3.2 GPa. The third transition began at 6.3 GPa, ended at 7.7 GPa. C₁₀H₁₆ transformed to a new phase at 22.9 GPa. Because of the new lattice peak occurred during the third transition, it was defined to a first-order transition.