Phase diagram of poly(VDF-ter-TrFE-ter-CTFE) copolymers: Relationship between crystalline structure and material properties

Abstract

Depending on their CTFE content (from 0 to 10 mol %), poly(VDF-ter-TrFE-ter-CTFE), poly(vinylidene fluoride-ter-trifluoroethylene-ter-chlorotrifluoroethylene) copolymers, exhibit ferroelectric (FE) or relaxor ferroelectric (RFE) properties at room temperature. Solvent cast films of these terpolymers can crystallize in three orthorhombic phases: FE, DFE (Defective Ferroelectric) or RFE according to their amount of CTFE. The relative amount of each crystalline phase depends on the amount of CTFE and evolves after annealing. We study the dependence of the electric displacement−electric field (D−E) loop with the amount of CTFE and with annealing step. We observed a closely link between the remnant polarization, PR, and the fraction of (FE + DFE) crystalline phase. Macroscopic properties, studied using thermo-mechanical experiments (DSC and DMA) and dielectric spectroscopy, evolve continuously with the CTFE amount and are well correlated with the structural properties. Finally, a temperature versus mol% CTFE phase diagram is established and discussed in relation-ship with material properties.