Structural phase transitions in pyridinium perrhenate at high pressure

The structure of the deuterated pyridinium perrhenate (d5PyH)ReO4 (C5D5NHReO4) was studied by means of powder X-ray diffraction at high pressures up to 3.5 GPa at room temperature and neutron diffraction at high pressures up to 2.0 GPa in the temperature range 10–300 K. At ambient conditions deuterated pyridinium perrhenate has orthorhombic structure of the Cmc21 symmetry (ferroelectric phase II). At T < 250 K a phase transition to the orthorhombic phase of the Pbca symmetry (paraelectric phase III) was observed. At P > 0.7 GPa the phase transition to orthorhombic phase with the Cmcm symmetry (paraelectric phase I) was observed at ambient temperature. At P = 2 GPa the phase I is stable in the temperature range 10–293 K, indicating a suppression of the ferroelectricity in (d5PyH)ReO4 by application of high pressure. P–T phase diagram of (d5PyH)ReO4 at high pressures up to 2 GPa is discussed.