Temperature- and Pressure-Induced Phase Transition in Tetrafluoro-1,4-benzoquinone Crystal

Abstract

Abstract The temperature and pressure effects on the Raman-active inter- and intramolecular vibrations of tetrafluoro-1,4-benzoquinone crystal were studied. The diffuse Raman bands observed in the intermolecular vibrational spectrum could be resolved with decreasing temperature or increasing pressure. The observed spectral structure due to the intermolecular vibrations changed as the temperature fell and also as the pressure increased. The vibrational frequencies of some intramolecular vibrational bands changed discontinuously under a certain pressure when the applied pressure was increased. The calculated pressure-induced frequency shifts for these vibrations deviate from the observed frequency shifts under high pressure. The DSC curve shows no distinct endothermic or exothermic peaks at temperatures between 77 and 520 K. These observations indicate that a displacive phase transition takes place at a temperature of around 180 K under 1 atm or under a pressure of 0.8 GPa at 300 K in a tetrafluoro-1,4-benzoquinone crystal.