Neutron scattering studies of the ferroelectric transition in P (VDF-TrFE) copolymers

Abstract

In P(VDF-TrFE) random copolymers with compositions from 60/40 to 80/20 mol%, the ferroelectric phase transition exhibits a strong first order character and is accompanied by a large expansion of the crystal lattice. In the ferroelectric structure, the polymer chains have an all-trans conformation and are close-packed parallel to one another in a pseudo-hexagonal lattice. According to the m2m symmetry, the spontaneous polarization Py is perpendicular to the chain axis 2. In the paraelectric phase, the structure is disordered : the chains undergo continuous conformational changes, they have a statistical Cm symmetry and the expanded lattice is hexagonal (6/m point group)