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Subject: search.filters.subject.530Author: search.filters.author.Eisenmenger, WolfgangAuthor: search.filters.author.Bihler, EckardtAuthor: search.filters.author.Eberle, Gernot

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    Polarization distribution in PVDF obtained by poling under constant current condition
    (1990) Neumann, Guido; Bihler, Eckardt; Eberle, Gernot; Eisenmenger, Wolfgang
    Since the resistivity of PVDE films increases when the films are poled, the voltage across the samples must be increased during the poling process in order to keep the current constant. Under these conditions, the formation of a polarization zone in the center of the film depth is observed. The thickness of the polarization-free zone close to the film surfaces is found to decrease with larger current densities. The results are consistent with a model assuming charge trapping in deep traps associated with the orientation of polar crystallites.
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    ItemOpen Access
    Polarization dynamics of VDF-TrFE copolymers
    (1991) Eberle, Gernot; Bihler, Eckardt; Eisenmenger, Wolfgang
    The polymer polyvinylidenefluoride (PVDF) and its copolymers with trifluoroethylene (TrFE) exhibit a strong piezoelectric effect after poling in high electric fields (100 MV/m). HV impulses of definite duration have been applied to the polymer in order to study the dynamics of the poling process. The dielectric displacement during the HV impulse was recorded. After the impulse, the remanent polarization under short-circuit conditions was also measured. It was thus possible to obtain the minimum poling time dependent on the applied field strength necessary to stabilize the remanent polarization. Comparing the time development of the dielectric displacement with the corresponding remanent polarization revealed a time delay between the orientation of the dipoles and their stabilization. It is concluded that the process of orientation of the dipoles itself is not sufficient to lead to a remanent polarization and that an additional interaction between the trapped charges and the oriented dipoles can explain the stability of the remanent polarization and the observed time delay.
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    ItemOpen Access
    Influence of charge injection on the formation of remanent polarization in P(VDF-TrFE) copolymers
    (1990) Bihler, Eckardt; Neumann, Guido; Eberle, Gernot; Eisenmenger, Wolfgang
    The influence of charge injection on the formation of remanent polarization of P(VDF-TrFE) copolymers was studied by inserting an insulating barrier between the metal electrodes and the P(VDF-TrFE) copolymer during the poling process. The resulting remanent polarization is significantly smaller than that of identically poled samples for the same field strength and time duration, but with directly contacting metal electrodes. This shows that the orientation of the dipoles alone is not a sufficient condition for the formation of remanent polarization in PVDF and its copolymers. The experiments indicate that the stabilization of the polarization is mediated by charge injection and charge trapping at polarized crystallite surfaces.