Electrical and thermal properties of vinylidene fluoride-trifluoroethylene- based polymer system with coexisting ferroelectric and relaxor states

Dielectric, thermal, and electrocaloric investigations of poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) copolymer, irradiated with high-energy electrons, are reported. While the ferroelectric copolymer is transformed into a relaxor system at high irradiation doses, dielectric investigations, particularly nonlinear dielectric experiments, i.e., temperature dependences of the second and the third harmonic dielectric response, clearly evidence that at lower doses ferroelectric and relaxor states coexist in the P(VDF-TrFE). This is confirmed by the differential scanning calorimetry, which further reveals the influence of irradiation on the copolymer crystallinity and melting point. Finally, it is shown that large electrocaloric response of VDF-TrFE-based polymers is further enhanced in systems with coexisting relaxor and normal ferroelectric states.