The pressure influence on the incommensurate-commensurate ferroelectric phase transition in [4-NH2C5H4NH][SbCl4]

The dielectric properties of the [4-NH2C5H4NH] SbCl4 (abbreviated as 4-APCA) crystal were investigated under hydrostatic pressure up to 300Mpa. The pressure-temperature phase diagram was given. The paraelectric-ferroelectric phase transition (II -> III) temperature (T-c) increases linearly with increasing pressure with a slope dT(c)/dp=21X10(-) K-2/MPa. The pressure dependence of Curie-Weiss constants has been evaluated also. In the paraelectric phase (II) the Curie constant (C+) was pressure dependent whereas the C_ constant over the ferroelectric phase (III) was almost constant. The results are interpreted in terms of improper and displacive type phase transition model with a soft phonon at a zone boundary. (c) 2005 Elsevier Ltd. All rights reserved.