Browsing by Author "Dehlen, Bernhard"

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    Binding energies of trapped charges in PVDF and P(VDF/TrFE)
    (1994) Küssner, Bodo; Dehlen, Bernhard; Eberle, Gernot; Eisenmenger, Wolfgang
    The remanent polarization in PVDF and P(VDF/TrFE) is stabilized by trapped charges. We measured the remanent polarization P as function of temperature during heating from room temperature to 180°C. The discharge current is then computed as the first derivative -dP/dT. Assuming a Debye relaxation and a continuous distribution of binding energies g(E) of the trapped charges we can show that the discharge current I(T) is proportional to g(E=mT), with m=const. The constant m can either be calculated numerically or by analytical approximation, With this method the distribution g(E) can be determined. These data are consistent with the extraordinary long life time of the remanent polarisation in PVDF and P(VDF/TrFE) at room temperature.
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    Influence of solvents on the polarization distribution in PVDF
    (1992) Dehlen, Bernhard; Eberle, Gernot; Eisenmenger, Wolfgang
    The authors report on polarization reductions when poled PVDF films are immersed in polar solvents like acetone, propanol, ethanol, and methanol for a few minutes. Also, immersion in nonpolar solvents, like hexane or carbon tetrachloride for some hours results in a small reduction of polarization. The amount of the reduction depends on the dipole moment of the solvent molecules, the length of the influence of the solvent, and the poling parameters. The authors also observe an influence on the remanent polarization if the films have been immersed in a solvent for some minutes before poling. They find inhomogeneous polarization distributions in these films that are different from distributions in untreated films before poling. In the case of a polar solvent pretreatment, the development of polarization profiles with several maxima is observed.
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    Time development of multiple polarization zones in PVDF
    (1993) Eberle, Gernot; Dehlen, Bernhard; Eisenmenger, Wolfgang
    The polarization distribution in PVDF which causes the piezo- and pyroelectricity of this polymer depends strongly on the polarization distribution. Applying an electric field of E = 60M/m causes a ca. 10μm thick polarization zone in the middle of the sample. Applying the same field in opposite direction a bimorph structure results. If the same field is applied to a homogeneously prepolarized PVDF sample a trimorph structure is formed with three polarization zones under field. But under short circuit conditions the polarization zone in the new field direction vanishes. The polarization distribution is measured with the acoustic PPS method with a spatial resolution of about 2μm.