Ferroelectric Phase Transition of VDF/TrFE Copolymer at High Pressures

Abstract

High pressure ultrasonic and D-E hystresis measurements were performed on a vinylidene fluoride-trifluoroethylene (VDF/TrFE) copolymer with 54 mol% VDF content to investigate the pressure effect on physical properties accompanying wiht a ferroelectric phase transition. Differing from the results at atmospheric pressure where the ferro-to-paraelectric phase transition proceeded simply in one-step, this copolymer exhibited at 350 MPa two-step temperature variations in ultrasonic velocity and absorption, and remanent polarization upon the ferroelectric phase transition. These results agree well with the previous results of DTA and X-ray diffraction experiments, suggesting that the changes in the nature of the ferroelectric phase transition is attributed to the pressure-induced structural transformation.

Pressure effect on phase transition in ferroelectic polymers

“…Nakanishi, Ohigashi and Minomura ( 1982) reported that the heat treatment at high pressures substantially improved the crystallinity and the piezoelectricity of the copolymer samples. Moreover the present author and his group have conducted DTA, ultrasonic, dilatometric and X-ray measurements on a copolymer sample, and have observed that the nature of the ferroelectric phase transition as well as the ferroelectric crystal structures were altered by the application of pressure Matsushige, Tagashira, Horiuchi, Taki and Takemura, 1985).…”

Ferroelectricity of polymers based on vinylidene fluoride

“…The effect of pressure on the 54/46 VDF/TrFE copolymer has been studied. 124,125 This was done using a set of methods including DSC, X-ray diffraction, D ± E hysteresis, and ultrasonic studies. The temperature dependences of a number of parameters determined by these methods are shown in Fig.…”

“…This unusual phenomenon can be interpreted based on the above hypothesis concerning the formation of two types of ferroelectric phase, LT and QL, in the copolymers considered. 124,126 It is assumed that under normal pressure, crystallisation proceeds in the QL phase, whereas at the Curie point, the QL phase transforms in one step into the paraelectric phase. As the pressure increases to 350 MPa at room temperature, the QL ferroelectric phase transforms into a more perfect phase, LT.…”

“…Figure 28. Temperature dependences of heat evolution (1, 1 H ), interplanar spacing (2, 2 H , 3, 3 H ), absorbance (4, 4 H ), sound velocity (5, 5 H and remanent polarisation (6, 6 H ) at a pressure of 0.1 (a) and 350 MPa (b) for the 54/46 VDF/TrFE copolymer 124. …”