High-pressure dielectric studies of a novel hydrogen-bonded ferroelectric (NH4)2H2P2O6

The hydrostatic pressure effect on the dielectric properties of (NH4)2H2P2O6 ferroelectric crystal was studied for pressures from 0.1 MPa to 360 MPa and for temperatures from 100 to 190 K. The pressure–temperature phase diagram obtained is linear with increasing pressure. The paraelectric–ferroelectric phase transition temperature decreases with increasing pressure with the pressure coefficient dTc/dp=−5.16×10−2 K MPa−1. Additionally, the pressure dependences of Curie–Weiss constants for the crystal in paraelectric (C+) and ferroelectric (C−) phases are evaluated and discussed. The possible mechanism of paraelectric–ferroelectric phase transition is also discussed.

► Pure continuous phase transition in hydrogen bonded ferroelectric (NH4)2P2O6. ► Order–disorder and displacive phase transition mechanism confirmed. ► Ferroelectric phase transition disclosed a significant negative pressure coefficient.