The high-pressure effect on the phase transition in pyridinium hexafluorophosphate

The effect of hydrostatic pressure on the phase transition in pyridinium he xafluorophosphate was studied by the methods of pressure dilatometry, press ure dielectric spectroscopy and DSC. The nonlinear increase of the phase tr ansition temperature with increasing pressure was analysed. The phase trans ition was established as the order-disorder type and the change in entropy at this transition was related to the change in inequivalent positions of t he pyridinium cation. The change in the activation enthalpy under the effec t of pressure was derived and related to an increase in reorientation barri er heights.