Composition-Dependent Dielectric Properties of Poly(vinylidene fluoride-trifluoroethylene)s Near the Morphotropic Phase Boundary

The discovery of relaxor behavior in poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymers plays a crucial role in driving the formation of a morphotropic phase boundary (MPB) near which large enhancements of dielectric and piezoelectric responses are achieved. Here we study the dielectric spectra of P(VDF-TrFE)s near MPB and analyze the relaxor behavior using two different theoretical models. We observe the largest dielectric constant of ∼76 at 1 kHz in morphotropic composition P(VDF-TrFE) 50/50 mol % at around 69 °C. We show that the compositional dependence of dielectric peak temperature changes dramatically in the vicinity of VDF = 49 mol %. Moreover, we find that the parameters (i.e., dielectric relaxation strength) deduced from the fit of the experimental data by different models also changes abruptly at VDF = 49 mol %. These findings clearly signify the destabilization of normal ferroelectric phase occurring at the critical VDF content of 49 mol % and explicitly mark one boundary of ...