Polarization profiles in fatigued ferroelectric polymers

When ferroelectric materials are subjected to repeated reversal of polarisation, the magnitude of the reversed polarisation is observed to decrease. This phenomenon is referred to as fatigue and is generally ascribed either to space charge effects or to the pinning of domain walls at defects. In recent times several techniques have been developed which allow the study of polarization profiles in thin, insulating films. In the present work, the polarization profiles in fatigued ferroelectric polymers were measured using the laser intensity modulation method (LIMM). The polymers studied were polyvinylidene fluoride (PVDF) and its copolymers with trifluoroethylene (TrFE). The polymers were fatigued by reversing the polarisation many times using a cyclic field with an amplitude above the coercive field. For some of the polymers, this leads to a decrease in the magnitude of the reversed polarization, while for others, the magnitude remained reasonably constant. It was found that those polymers which showed most fatigue in their hysteresis loops had a more symmetrical distribution of polarization after fatiguing. The lack of fatigue and asymmetrical polarization profiles seem to be associated with materials which contain the non-polar α crystal form