Nonlinear dielectric investigation of trifluoroethylene rich copolymers of vinylidene fluoride

Phase transition behavior in trifluoroethylene (TrFE)-rich copolymers of vinylidene fluoride (VDF) has been investigated by means of nonlinear dielectric spectroscopy. Unlike VDF-rich copolymers showing a single ferroelectric-to-paraelectric transition, TrFE-rich copolymers undergo two-stage transitions, loss of ferroelectric polarization at a temperature T-A and transition into a paraelectric motional phase at a temperature T-C. Between T-A and T-C, they exhibit the D-E double hysteresis loop characteristic of an antiferroelectric. Analysis of such a double loop allowed the estimation of antiferroelectric polarization P-A as well as ferroelectric polarization P-F. A comparison of the temperature dependences of reciprocal polarizabilities beta(n)(n = 1, 2, 3) with those of P-F and P-A revealed that beta(2) is proportional to P-F whereas beta(1) and beta(3) are proportional to P-F(2) + P-A(2). These results are consistent with phenomenological prediction for an antiferroelectric. It was concluded that TrFE-rich copolymers of VDF have an antiferroelectric-like phase consisting of all-trans molecules packed in a disordered manner.