Study of the structure and electrostrictive property of proton-irradiated P(VDF-TrFE) 56/44 mol% copolymer

High-energy proton (3 MeV) irradiation with dosages ranging from 43 to 200 Mrad have been carried out to investigate the potential for modifying both the structure and property of vinylidene fluoride-trifluoroethylene 56/44 mol% copolymer. The structural and transitional behavior of the irradiated copolymer was studied by X-ray diffraction and differential scanning calorimetry. The polarization hysteresis, relative permittivity properties and electrostrictive strain response of these copolymers were also measured. It was found that the ferroelectric copolymer could be successfully converted to a relaxor at a low proton dosage of about 75 Mrad at ambient temperature. A slim polarization hysteresis loop and a frequency dispersion of the relative permittivity observed in the irradiated copolymer imply that the high-energy protons break up the coherent polarization domains in the ferroelectric copolymer into nanosized regions. In addition, the irradiation leads to a significant change in the ferroelectric-to-paraelectric phase transition behavior. X-ray diffraction measurements show that the crystalline region in the copolymer is converted into a nonpolar phase upon irradiation, and the lattice spacing increases significantly. The electric field induced phase transformation of the nanosized regions between the nonpolar and polar phase leads to a high electrostrictive strain observed in the irradiated copolymer.