POLARIZATION DYNAMICS OF VDF-TRFE COPOLYMERS

The polymer PVDF and its copolymers with TrFE show a strong piezoelectric effect after poling in high electric fields (100 MV/m). In order to study the dynamics of the poling process we have applied HV impulses of definite duration to the polymer. The dielectric displacement during the HV impulse is recorded. After the impulse the remanent polarization under short circuit condition is measured. Thus it is possible to obtain the minimum poling time dependent on the applied field strength necessary to stabilize the remanent polarization. By comparing the time development of the dielectric displacement with the corresponding remanent polarization we find a time delay between the orientation of the dipoles and their stabilization. Therefore we conclude that the process of orientation of the dipoles itself is not sufficient to lead to a remanent polarization. An additional interaction between trapped charges and the oriented dipoles can explain the stability of the remanent polarization and the observed time delay.