Phase transitions in ferroelectric pyridinium periodide under high pressure

Abstract

The effect of temperature and pressure on physical properties of pyridinium periodide has been studied by dielectric spectroscopy, neutron spectroscopy and NMR. The results obtained by the above methods enable a construction of the p--T phase diagram for this compound. It has been established that the temperature of the non-ferroelectric phase transition increases linearly with pressure, while the temperature of the ferroelectric phase transition reaches a maximum at about 200 MPa. Neutron powder diffraction measurements versus temperature and pressure permitted determination of the thermal expansion coefficient α and isothermal compressibility coefficient β. The pressure dependence of NMR parameters permitted obtaining the activation volume in phases II and III.