Dielectric properties of relaxor-like vinylidene fluoride-trifluoroethylene-based electroactive polymers

The dynamic processes in poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer, lead lanthanum zirconate titanate (PLZT)-P(VDF-TrFE) composite, electron-irradiated P(VDF-TrFE) copolymer, and poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) terpolymer have been studied by measurements of the temperature and frequency-dependent linear (ε₁) and third-order nonlinear (ε₃) dielectric constants. While a paraelectric-to-ferroelectric transition takes place in the crystalline region of the nonirradiated copolymer and composite, electron-irradiated P(VDF-TrFE) copolymer and P(VDF-TrFE-CFE) terpolymer show a significantly different dielectric response: a broad frequency dispersion in ε₁ and ε₃, asymmetric temperature evolution of the relaxation spectrum as the longest relaxation time diverges at a finite freezing temperature while the shortest relaxation times remain active down to the lowest temperatures, and a paraelectric-to-glass crossover in the temperature dependence of the dielectric nonlinearity α₃ = ε₃/ε₀³ ε₁⁴. All these properties, together with the temperature dependence of the static field cooled dielectric constant, are very similar to those observed in the classical relaxor systems and are reminiscent of the dynamic behavior observed in various spin glasses. Thus, additional confirmation that giant electrostrictive response of the electron-irradiated P(VDF-TrFE) copolymer and P(VDF-TrFE-CFE) terpolymer is the consequence of their relaxor-like structure is obtained.