Browsing by Author "Womes, Manfred"

Now showing 1 - 2 of 2

Open Access
Dynamics of polarization growth and polarization reversal in PVDF films
(1988) Womes, Manfred; Bihler, Eckardt; Eisenmenger, Wolfgang
The authors present measurements of the maximum displacement at the end of a rectangular high-voltage pulse together with the remanent polarization after the pulse under short-circuit condition as a function of the polarizing pulse end length. The pulse length varied from 10 μs to 100 s, and the field strength ranged from 0.8 MV/cm to 2 MV/cm. The original samples were reversely polarized or unpolarized 12-μm-thick films containing 37% β-material. It is concluded that the cooperative model combined with six-site potential alone cannot explain the observed switching back of the remanent polarization, its delayed development, and the long times necessary for polarization reversal. The results are qualitatively consistent with a model of charge injection and charge trapping at polarized crystallites.
Open Access
Dynamics of polarization growth and reversal in PVDF films
(1989) Womes, Manfred; Bihler, Eckardt; Eisenmenger, Wolfgang
Measurements are presented of the time development of the dielectric displacement and the remanent polarization in polyvinylidene fluoride (PVDF) for poling times ranging from 1 μs to 1000 s and poling fields between 0.8 and 2.0 MV/cm. For longer times (0.1 to 1000 s), the time dependence of the polarization distribution across the film thickness is also determined. After application of a steep rectangular high-voltage pulse, the sample is shorted to zero voltage. The remanent polarization under the short-circuit conditions is compared to the maximum dielectric displacement under the external poling field. A significant time delay of the buildup of the remanent polarization was observed as compared to the dielectric displacement under field. This time delay depends significantly on the applied field strength and the crystallinity of the films. In the case of polarization reversal, a flipping back' of the polarization was observed for shorter poling times of up to 200 μs. Under these conditions, a large part of the polarization is reversed under the field, but after the removal of the field, most of the polarization returns to the original direction. The results can be explained by the ferroelectric cooperative coupling of oriented crystallite dipoles to charges trapped at the surface of polarized crystallites.