High-pressure and high-temperature equation of state and phase diagram of solid benzene

The high-pressure structural properties of benzene have been investigated up to the occurrence of the chemical reaction by means of x-ray diffraction and infrared absorption techniques. The infrared spectra show that sample annealing above 500 K produces pure phase-II crystals. X-ray diffraction patterns collected at 540 K on these crystals allowed the equation of state of benzene to be obtained. These results indicate the stability of phase II up to the pressure where benzene reacts and no evidence of the III and III(') crystal structures is gained. On these bases the existing phase diagram of benzene is discussed and a simplified one is proposed.