Persistent non-switchable polarization in P(VDF TrFE) films

Poling experiments were performed on as-prepared and on annealed polyvinylidene fluoride/trifluoroethylene (P(VDF-TrFE)) copolymer films. The polarization of the samples was recorded as a function of temperature by the measurement of the second order dielectric permittivity. The polarization of samples annealed before the first poling completely vanishes in the paraelectric phase. However, in samples poled before the first annealing a persistent polarization is detected that remains stable in the paraelectric phase. It is unchanged after several heating and cooling cycles and even after poling the sample in the opposite direction. This constant polarization can be explained by non switchable dipoles which form an intermediate phase between the crystalline and the amorphous phase. The polarization state of the film before the first annealing is permanently stored in this intermediate phase.