The polymorphic phase transformations in resorcinol at high pressure

Measurements of spin-lattice relaxation time T1 for resorcinol have been made by the proton NMR technique using the saturation method in the temperature range 280–380 K and pressure up to 800 MPa. The pressure-induced α–β transition evolved through two phase coexistence range was observed. The crystal structure and vibrational spectra of the resorcinol have also been studied by means of X-ray diffraction and Raman spectroscopy at pressures up to 19 GPa in temperature range 290–380 K. In experiments with a rapid pressurization rate, suppression of α–β polymorphic transition in resorcinol occurs. In experiments with a slow pressurization rate, two structural phase transitions, between orthorhombic α and β phases at P = 0.4 GPa and from β to another orthorhombic γ phase at P = 5.6 GPa, were observed. At pressures above 12.5 GPa, a gradual transformation to the amorphous phase was revealed. The lattice parameters, unit cell volumes and vibration modes as functions of pressure and temperature were obtained for the different polymorphic modifications of resorcinol.