POLING AND PROPERTIES OF POLARIZATION OF FERROELECTRIC POLYMERS AND COMPOSITES

Poling of ferroelectric polymers and composites can be achieved with thermal, corona, electron-beam and other methods. The polarization is related to the applied field strength by hysteresis loops and can be switched by application of large de fields. Switching times in PVDF and P(VDF-TrFE) copolymer typically range from 1s down to 100 ns for field strengths of 50 to 400 MV/m. The remanent polarization builds up more slowly than the displacement; this and other observations suggest that charges, injected from the electrodes and eventually trapped at the crystallite surfaces, are required for the formation of a stable polarization. The distribution of the polarization over the sample thickness, detectable with a number of methods, depends critically on field strength, temperature, composition and other parameters and is also controlled by charge injection. Good thermal stability of the polarization is observed in copolymers with high VDF content which are poled during stretching.