Nonlinear Dielectric Investigation of Trifluoroethylene-Rich Copolymers of Vinylidene Fluoride

Abstract

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 β n (n = 1, 2, 3) with those of P F and P A revealed that β2 is proportional to P F whereas β1 and β3 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.