Dielectric Relaxation and Ferroelectric Imprint

The term imprint is generally used for a special kind of a reversible change in the ferroelectric state. It refers to a time dependent development of the material's resistance against polarization reversal. At the example of P(VDF-TrFE) it is shown that if polarized to the remanent polarization and under a switched off external field the coercive field of the sample's hysteresis loop increases in time, the ferroelectric switching time increases as well, the remanent polarization decreases, and the small signal ac capacitance decreases also. All four effects exhibit a linear behavior on a logarithmic time scale, i.e. they are proportional to log t
_w
, with t
_w
as the waiting time after switching off the external field. A model is developed which relates the four observations. The model is based on a feedback effect between a crystalline phase where the ferroelectric switching takes place and an amorphous or disordered phase with a relaxational polarization response.