Influencing dielectric properties of relaxor polymer system by blending vinylidene fluoride-trifluoroethylene-based terpolymer with a ferroelectric copolymer

We report the influence of blending the poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer [P(VDF-TrFE-CFE), a member of the relaxor polymer family that exhibits fast response speeds, giant electrostriction, high electric energy density, and large electrocaloric effect] with the ferroelectric poly(vinylidene fluoride-trifluoroethylene) copolymer [P(VDF-TrFE)] on its dielectric response. Although both components form separate crystalline phases, at low copolymer content, the P(VDF-TrFE-CFE)/P(VDF-TrFE) blends entirely exhibit a relaxorlike linear dielectric response, since the interfacial couplings to the bulky defects in the terpolymer convert the normal ferroelectric copolymer into a relaxor. On the other hand, the linear and particularly nonlinear dielectric experiments, i.e., temperature dependences of the second and the third harmonic dielectric response, clearly evidence that in blends with 20-50 wt. % of P(VDF-TrFE), the ferroelectric and relaxor states coexist. The nonlinear dielectric response further reveals the onset of ferroelectric behavior also in blends with low copolymer amount, due to a high VDF content in the terpolymer, which increases the ferroelectric interactions: While in relaxor polymers with lower VDF content, the third order nonlinear dielectric constant, in accordance with the theoretical predictions, exhibits solely positive values, here it changes sign even in the pure P(VDF-TrFE-CFE).