Evidence for high-pressure polymorphism in resorcinol

Abstract

Results of high-pressure Raman-scattering measurements carried out on resorcinol up to pressures of 14.5 GPa are reported. Changes observed in the Raman spectra suggest transition to a new phase $\ensuremath{\gamma}$ around $5.6\ifmmode\pm\else\textpm\fi{}0.2 \mathrm{GPa}$ besides the well-known isosymmetric $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\alpha}}\ensuremath{\beta}$ transition at 0.5 GPa. The $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\beta}}\ensuremath{\gamma}$ transition is found to be reversible with hysteresis when released from peak pressures of about 11 GPa. Raman line shapes at high-pressures suggest that the new phase $\ensuremath{\gamma}$ is disordered. Rapid pressurization of $\ensuremath{\alpha}$-resorcinol, with the suppression of $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\alpha}}\ensuremath{\beta}$ transition, leads to a new phase $\ensuremath{\delta}$ above 3 GPa which turns out to be more ordered, unlike the $\ensuremath{\gamma}$ phase, at comparable pressures. A luminescence peak centered around 2.25 eV is observed in the high pressure phase $\ensuremath{\gamma}$ as well as $\ensuremath{\delta}$ above 6 GPa. Above 11 GPa, intensity of the Raman bands weaken drastically and submerge in the luminescence background. The ambient pressure Raman spectrum of resorcinol is not recovered when released from pressures above 11 GPa.