The p–T phase diagram for new ferroelectric bis-thiourea pyridinium bromide

The effects of temperature and pressure on physical properties of the ferroelectric inclusion compound bis-thiourea pyridinium bromide were studied by dielectric spectroscopy, neutron and X-ray diffractometry and nuclear magnetic resonance (NMR). The results permitted a construction of the p–T phase diagram for this compound. At ambient pressure bis-thiourea pyridinium bromide exists in three phases and the ferro-ferroelectric phase transition observed at T2 = 150 K is discontinuous in contrast to the ferro-paraelectric phase transition observed at T1 = 180 K. The application of pressure of about 800 MPa at room temperature and then cooling of this compound to below T = 160 K induces the appearance of a new phase (IV).

► We used high pressure NMR and high pressure dielectric spectroscopy to obtain p–T phase diagram.
► The thermodynamics of the solid–solid phase transitions has been discussed.
► A pressure induced solid state phase has been discovered.