Non-uniform polarization profiles in P(VDF-TrFE) copolymer films after cyclical poling

Poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymers, probably the most often used electro-active polymers, are rendered ferro-, pyro-, and piezoelectric via poling under high electric fields. Uniform polarization profiles across the sample thickness are advantageous or even necessary for most device applications. Here, we attempted to obtain spatially uniform polarization profiles in commercial P(VDF-TrFE) copolymer films with 50/50, 72/28 and 75/25 mol% of VDF/TrFE by means of cyclical hysteresis poling. The polarization profiles were mapped with Piezoelectrically generated Pressure Steps (PPSs), and the resulting depth profiles were correlated with the corresponding hysteresis curves. In addition, Fourier-Transform Infrared (FTIR) spectroscopy was used to identify the β-phase fractions in the P(VDF-TrFE) compositions. 75/25 mol% copolymer samples show the most uniform polarization profiles and the highest remanent polarization of 70 mC/m
²
(as seen from the hysteresis curves) - corresponding to the highest β-phase fraction in comparison (as observed in FTIR measurements).