Dielectric behaviour and polarization response of proton irradiated Ba0.65Sr0.35TiO3/P(VDF-TrFE) composites

Ba0.65Sr0.35TiO3/P(VDF-TrPE)70/30 composites have been prepared by dispersing Ba0.65Sr0.35TiO3 powder in a vinylidene fluoride-trifluoroethylene copolymer (with 70 mol% vinylidene fluoride) matrix. The effects of irradiation with 3 MeV protons on the dielectric properties and polarization response of the composites have been investigated. At a dosage of 100 Mrad, both the copolymer and the composites exhibit a broad peak in the relative permittivity whose location shifts upwards in temperature with increasing frequency. This result implies that the proton irradiation breaks up the coherent polarization domains in the normal ferroelectric copolymer phase into nanopolar regions, thereby converting the material to a relaxor ferroelectric. The polarization-electric field hysteresis loop becomes slimmer after irradiation, particularly for the composites with low ceramic volume fraction. For the unirrdiated samples, the slight increase of remnant polarization with ceramic volume fraction indicates that the remnant polarization of the ceramic phase is not much higher than that of the copolymer phase. After irradiation, the remnant polarization of the copolymer drops sharply. The remnant polarization of the irradiated composites rises steeply with increasing ceramic volume fraction and is only 20% lower than that of the unirradiated composites at a ceramic volume fraction of about 0.5.