08 Fakultät Mathematik und Physik

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/9

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Institute: search.filters.UBSInstitut.Sonstige EinrichtungAuthor: search.filters.author.Eisenmenger, Wolfgang

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    Piezo and pyroelectricity in electrets : caused by charges, dipoles, or both?
    (1992) Sessler, Gerhard M.; Das-Gupta, Dilip K.; deReggi, Aimé S.; Eisenmenger, Wolfgang; Furukawa, Takeo; Giacometti, José A.; Gerhard-Multhaupt, Reimund
    In a homogeneous medium space charges cannot cause piezo or pyroeiectricity. If stressed, there will be affine geometrical changes throughout the medium, and therefore the induction charges on the electrodes will remain the same, and piezoelectricity cannot be generated. However, if dipoles are present in such a homogeneous dielectric, then piezoelectricity is possible. In an inhomogeneous medium such as a semicrystalline polymer, charges and dipoles can cause piezoelectricity. If you have, for instance, a semicrystalline polymer then the crystalline and the amorphous parts are, upon compression, subjected to different degrees of deformation; and for this reason, a piezoelectric effect can be generated.
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    Phonon absorption-spectroscopy in the presence of strong elastic phonon scattering
    (1986) Mebert, Joachim; Koblinger, Otto; Döttinger, Siegfried; Eisenmenger, Wolfgang
    In this work we show that in the presence of a strong phonon scattering background absorption structures can only be well resolved by reducing sample thickness to the phonon mean free path. This mean free path can be determined by analyzing the pulse shape of 285 GHz phonons. By reducing sample thickness to the appropriate value of 0,3mm the 21,2 cm -1 crystalline field transition in CaF 2:Er 3+ could be evaluated with the very high resolution of 5 GHz. In experiments performed on a 1mm thick LaF 3 Er 3+ sample we observed an absoption line at 14,2 cm -1 not visible in FIR absorption measurements.
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    Electric-field profiles in corona- or electron-beam-charged and thermally treated Teflon PTFE, FEP, and PFA films
    (1992) Gerhard-Multhaupt, Reimund; Eberle, Gernot; Xia, Zhongfou; Yang, Guomao; Eisenmenger, Wolfgang
    Charge spreading in three different types of Teflon electrets was studied by means of piezoelectrically generated pressure steps, FEP and PFA samples corona-charged at room temperature usually exhibited only a surface charge layer. Uniform charge spreading throughout the bulk was found in FEP charged at or heated to high temperatures. Charge spreading was much less prominent in PFA because of a smaller retrapping efficiency. In PTFE (polytetrafluorethylene), charges from the surface and the rear electrode were injected into the bulk during charging at any temperature. Electron-beam-deposited charge layers broadened significantly upon heating.
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    Polarization profiles of electron-beam polarized VDF-TrFE copolymer films
    (1990) Schilling, Doris; Glatz-Reichenbach, Joachim; Dransfeld, Klaus; Bihler, Eckardt; Eisenmenger, Wolfgang
    In order to understand more clearly the poling mechanism in ferroelectric polymers, the PPS-technique was applied to copolymer films of vinylidenefluoride with trifluoroethylene P(VDF-TrFE), poled by a focused monoenergetic electron beam. Charges were injected in a well-defined way into the polymer films and thus provided information on the influence of externally introduced electrical charges on the poling process in ferroelectric polymers. The electron beam poling of P(VDF-TrFE) films is shown to produce very high values of polarization up to 180 mC/m2, which exceeds those produced in β-PVDF by electron irradiation by a factor of three. The distribution of the polarization across the film thickness is rather asymmetric, especially for samples irradiated with 20- and 30-KeV electrons. This may be caused by the rising electrical conductivity in samples with increasing electron energy. The annealing of the copolymer films before the poling procedure leads to a systematic increase of the polarization, with T a having its steepest rise around Tc.