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Electrets, 1991. (ISE 7) Proceedings., 7th International Symposium on (Cat. No.91CH3029-6)

Date 25-27 Sept. 1991

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  • 7th International Symposium on Electrets (ISE 7). Proceedings (Cat. No.91CH3029-6)

    Publication Year: 1991
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    Freely Available from IEEE
  • Study of space charge effects on electrical properties of polymers by direct probing

    Publication Year: 1991 , Page(s): 337 - 342
    Cited by:  Papers (1)
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    Direct and quantitative probing of space charge was carried out to study the effects of space charge on the dielectric breakdown of polymeric insulating materials. In poly-p-phenylene sulfide, in which dielectric-breakdown characteristics were explained in terms of space-charge formation, positive homo space charge was observed. The amount and the depth of space charge detected agreed well with those assumed from the breakdown characteristics. Similar results were also obtained for oxidized PE (polyethylene), where prominent electron injection and negative-homo-space-charge formation took place.<> View full abstract»

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  • Dynamics of poling PVDF between 250 degrees C and 120 degrees C

    Publication Year: 1991 , Page(s): 388 - 393
    Cited by:  Papers (3)
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    PVDF films with high beta -content are poled in an electric field of 60 MV/m at temperatures between 25 degrees C and 120 degrees C. At 25 degrees C the alignment of dipoles takes place in a central poling zone during several hours of poling. When the temperature is increased to 120 degrees C the poling time necessary to align the dipoles in this narrow zone is reduced to several seconds. In addition, at temperatures higher than 90 degrees C and increased poling times the central poling zone first increases but later decreases in its dielectric displacement. Simultaneously in a 10 mu m regime adjoining the positive electrode a secondary displacement zone starts to grow. The strong reduction of this peak under short circuit conditions indicates hetero-charge accumulation in front of an anode.<> View full abstract»

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  • Electrical conduction mechanism in zone refined acenaphthene

    Publication Year: 1991 , Page(s): 153 - 158
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    Electrical conductivity measurements of zone-refined acenaphthene were carried out as a function of temperature and field. The analysis of results in terms of I-V characteristics, log J vs. T, log σ vs. 1/T, Richardson plots Schottky plots, and Fowler-Nordheim plots reveals that the current density is predominantly temperature-dependent at higher temperatures and is temperature-independent (or less dependent) in the lower temperature range. This suggests that electrical conduction in acenaphthene takes place via Schottky emission and tunneling. Schottky emission operates at higher temperature, whereas the tunneling mechanism and hopping operate at lower temperature View full abstract»

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  • Influence of trap distributions on the surface potential kinetics in disordered materials

    Publication Year: 1991 , Page(s): 84 - 89
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    The surface potential kinetics for disordered materials described by Gaussian trap distributions was calculated on the basis of a stochastic hopping model. It is shown that an exact estimation of the transit time is possible only for narrow trap distributions. The transit time increases with the square of the standard deviation of the Gaussian trap distribution View full abstract»

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  • Triboelectret state of polymer composites

    Publication Year: 1991 , Page(s): 310 - 315
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    The influence of rubbing conditions, and of concentration and dispersity of fillers on the parameters of the triboelectret state in polymeric coatings containing particular electroconducting (graphite, nickel) or dielectric (Teflon) fillers has been studied. The residual charge, the activation energy, and the temperature of the injected and polarized components of the triboelectret charge were found to increase with the sliding velocity, when small quantities (1 to 3%) of particulate metals were added; the effect of the residual charge in the coating and its relaxation time increased with filler dispersity. Similar effects were detected when higher quantities (4 to 15 vol.%) of dielectric fillers were added to the polymer View full abstract»

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  • Polarization of VDF-TrFE copolymer films at elevated temperature

    Publication Year: 1991 , Page(s): 293 - 298
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    The build-up of the polarization of VDF-TrFE (vinylidene trifluorethylene) copolymer films at room temperature after various thermal treatment has been studied using the PWP (pressure wave propagation) method. This method allows for the nondestructive measurement of the homogeneity of the piezoelectric coefficient. The influence of different thermal treatments and of the insulator-electrode interfaces on the polarization at elevated temperature (100°C) is analyzed. The polarization which develops when the poling is performed at 100°C is very inhomogeneous and originates at the anode. The kinetics of the spreading of the polarized region towards the cathode depends on the applied field and on the thermal treatment applied to the samples. According to the history of the sample, the amount of the ferroelectric phase varies. This influence of the morphology of the samples and the role of charge injection at the cathode can explain the observed behavior View full abstract»

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  • Ferro- and piezoelectric properties of flexible ferroelectric and electret films

    Publication Year: 1991 , Page(s): 518 - 523
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    A new development in the field of flexible ferroelectric and electret films based on PVDF (polyvinylidene fluoride) copolymer and blend-polymer is described, along with its composite film technology. The significance and properties of PVDF, PVDF-PMMA (polymethyl methacrylate), PVDF-PVC (polyvinyl chloride), PVDF/BT, and PVDF-PZT are investigated. Their microstructure analysis and applications are discussed. There exist three possible polarization mechanisms for ferroelectricity and electret in flexible films: β-crystal type, C-F bond polymer molecular chain with orientation and ordered domain, and spontaneous polarization ferroelectric domain. Ferroelectric composite effects are also present View full abstract»

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  • Nonlinear conductive spectra of ion-conducting polymers

    Publication Year: 1991 , Page(s): 165 - 170
    Cited by:  Papers (1)
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    An ion-conducting polymer, tetraethylene oxide-organosiloxane (TEOS) copolymer, was synthesized and the linear and nonlinear complex conductivities were measured as a function of frequency. Observed spectra were reproduced by taking into account the interfacial and electrode polarizations. The most important findings are the very large dielectric relaxation strength and the very long hopping distance in noncrystalline ion-conductivity polymers. The large relaxation strength suggests that the TEOS Li- comprises an inhomogeneous system consisting of highly conductive and less conductive regions. It is speculated that such inhomogeneity governs the conduction mechanisms of the ionic conductor and results in a very long hopping distance. A combination of linear and nonlinear DC conductivities leads to a hopping distance of 200 nm View full abstract»

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  • Thermally stimulated currents in holmium oxide-based thin-film capacitors

    Publication Year: 1991 , Page(s): 675 - 680
    Cited by:  Papers (1)
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    Results of experimental examinations of vacuum-evaporated aluminum/holmium oxide/aluminum thin-film thermoelectrets by the method of thermally stimulated currents are presented. All measurements were carried out in the temperature region from 297 K to 500 K with the help of an automated microcomputer-based system. The TSD (thermally stimulated depolarization current) and TSP (thermally stimulated polarization current) curves obtained under different measurement conditions exhibit only a single peak for the temperatures between 380 K and 406 K. The trapping levels with the activation energy of 0.5-0.7 eV are responsible for the observed results View full abstract»

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  • High field conduction and space charge formation in ethylene-styrene copolymers

    Publication Year: 1991 , Page(s): 159 - 164
    Cited by:  Papers (1)
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    High field conduction and space charge formation in low-density polyethylene and ethylene-styrene copolymers were studied by measuring DC conduction and thermal pulse current at various temperatures. Conduction current is considered to be dominated by traps due to benzene rings introduced into copolymers. At room temperature, injected electrons and holes seem to be trapped near the cathode and anode, respectively. At 50°C, electrons are considered to be transported by overcoming the effect of traps, and holes seem to become mobile at 90°C. The number of mobile carriers is a function of styrene content and temperature View full abstract»

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  • A novel method for electret production using impulse voltages

    Publication Year: 1991 , Page(s): 267 - 271
    Cited by:  Papers (2)
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    A novel method for producing electrets is proposed in which an electric discharge is induced by a negative impulse voltage in a small air gap. The dielectric foil to be charged is placed between two planar electrodes, being in contact with one of them and separated from the other by the air gap. The electric discharge in the gap causes electric charges to deposit onto the dielectric surface where they are trapped, thus forming the electret. Measurements carried out with Teflon FEP (fluoroethylene propylene) show a very uniform deposition, and that the sample surface potential increases linearly with increasing impulse peak voltage. In principle, this method compares with the corona discharge for the production of electrets with regard to high turnout and low cost View full abstract»

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  • Structural orientation and electric polarization of polymers in stationary magnetic fields

    Publication Year: 1991 , Page(s): 316 - 321
    Cited by:  Papers (1)
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    Magnetic fields (MFs) of 100 to 500 kA/m were found to order magnetoanisotropic structural units in nonpolar polymer melts, e.g., polyethylene (PE). A temperature range and a threshold intensity of MF were observed when PE melt was partially ordered, i.e., when it was in a quasi-liquid-crystalline state. It is believed that thermomagnetic treatment of polymers in MFs can result in electrical polarization and formation of magnetoelectrets. A relationship is believed to exist between the polarization processes and the orientation of magnetoanisotropic macromolecules and aggregates in MFs View full abstract»

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  • Electret measurements with ionic charge technique

    Publication Year: 1991 , Page(s): 299 - 304
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    A number of novel techniques for the investigation of thin electret films are proposed. These techniques employ ionic charge deposition on the external surface of thin films by using an original scanning mercury probe. The value and the spatial distribution of the deposited charge were monitored with the help of the same mercury probe. These techniques make it possible to monitor the conductivity of the electret layers, to study processes of charge accumulation in the volume of thin films, and to measure the trap parameters. These techniques are a good tool for studying the migration of ions along the electret film surfaces and for monitoring the processes of equilibrium establishment between these surfaces and the surrounding medium View full abstract»

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  • Piezo and pyroelectric radiation dosimetry

    Publication Year: 1991 , Page(s): 759 - 764
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    The use of photoacoustic, piezoelectric, and pyroelectric radiation dosimeters is presented. New results with photoacoustic, pulsed photoacoustic, piezoelectric, and pyroelectric systems are discussed. The characteristics of the new dosimeters developed are compared. A theoretical model to explain the results obtained with the pulsed pyroelectric radiation dosimeter is presented and compared with experimental results. The use of such dosimeters as calorimeters for measuring energy fluence rate is also presented View full abstract»

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  • Pyroelectric and piezoelectric studies on BaTiO3: silica glass composites

    Publication Year: 1991 , Page(s): 524 - 529
    Cited by:  Papers (1)
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    BaTiO3:silica-glass composites were prepared in different weight ratios and their dielectric constant was studied over a wide temperature and frequency range. The results indicated that with increasing amounts of silica the dielectric constant of the composite goes on decreasing, while their Curie temperature increases. Pyroelectric current and charge field hysteresis effects were also studied in these composites. It was observed that the pyroelectric coefficient decreases from 238 μC/m2K to 200 μC/m2 K as the percentage of glass in the composite is increased. The piezocoefficient d33 also shows a decrease with increasing glass percentage but the piezovoltage coefficient peaks at 1% glass content View full abstract»

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  • Measurement of the isothermal and adiabatic dielectric constant of TGS

    Publication Year: 1991 , Page(s): 681 - 686
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    With a high-precision digital lock-in amplifier with digital drift correction, spectra of the dielectric constant of TGS have been measured. With a digital realization of a lock-in amplifier, measurements of the dielectric constant can be performed down to frequencies of 10-3 Hz. The dielectric constant is usually measured at frequencies above the thermal relaxation frequency too, thus realizing isothermal conditions. To separate the influence of domain and conductivity effects, the thermal time constant of the sample has been varied. Spectra of the dielectric constant are measured with variable coupling of the sample to a heat sink of liquid paraffin. The influence of the entropic contribution to the dielectric constant is directly determined from these spectra View full abstract»

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  • TSDC study on VDF/TrFE copolymers

    Publication Year: 1991 , Page(s): 483 - 488
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    TSDC measurements were carried out with samples of 60:40 and 70:30 molar ratios of VDF/TrFE (vinylidene fluoride-trifluoroethylene) copolymers. The 60(VDF):40(TrFE) copolymer presented a current peak around 90°C, associated with its ferroelectric-to-paraelectric (F-P) transition. The 70:30 copolymer also presented the F-P peak and, in addition, another peak at a lower temperature, identified as a phase transition between two ferroelectric phases. A model combining fast and slow polarization processes was developed to explain the TSDC curves. The fast process was connected to the phase transition, and the slow one was composed of the thermal depolarization of dipolar units of the β-phase crystallites and the variation of the pyroelectric current View full abstract»

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  • Electrical charge transport in partial crystalline and amorphous polymer structures

    Publication Year: 1991 , Page(s): 189 - 192
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    The influence of static and dynamic structures on mechanisms of charge transport was investigated by means of isothermal current-voltage dependence for various polymeric materials systems based on poly(vinylchloride) and polyethylene. Poly(vinylchloride) was chemically dehydrochlorinated, thereby creating polyacetylene structures. These samples showed ten-decades-at-best higher conductivity than the precursor polymer in dependence on the concentration of double bonds. Electron spin resonance measurements supported the interpretation of electrical conduction by a hopping transport of electrons. The results obtained for dehydrochlorinated poly(vinylchloride) are compared with model mechanisms of charge transport in polyethylene and partial crystalline polyethylenes as borderline cases View full abstract»

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  • Electric volume charging during radiation oxidation of polyethylene

    Publication Year: 1991 , Page(s): 366 - 370
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    The acoustic probe method was used for the study of the electric space charge dynamics in polyethylene irradiated by electrons. The samples investigated contained diffusion-introduced oxygen in volume. The results obtained point to the existence of a clear relation between the spatial distribution of the charge and the material oxidation degree. The major practical conclusion of the present study is the possibility of acting upon the process of volume charge formation under irradiation by changing the surrounding medium. In addition, direct control of the space charge distribution during irradiation may also serve as control of the radiation-chemical processes View full abstract»

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  • Phase transition in corona charged α-PVDF samples in dry air

    Publication Year: 1991 , Page(s): 432 - 437
    Cited by:  Papers (4)
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    The constant current corona triode has been used to charge and monitor the surface potential buildup of α-PVDF (polyvinylidene fluoride) samples. Under dry conditions it is possible to pole the samples to sufficiently high electric fields so as to cause a phase change from the nonpolar α form to the polar αp form. This phase transition is identified in the surface potential buildup by a plateau in which dipole orientation occurs, and can also be confirmed by X-ray diffractograms. A tentative theoretical model which takes into account ferroelectric polarization is developed to explain quantitatively the experimental results obtained for αp-PVDF View full abstract»

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  • Dielectric behavior of 0-3 type piezoelectric composites

    Publication Year: 1991 , Page(s): 407 - 414
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    Dielectric absorption and thermally stimulated current measurements were performed for PPN-P(VDF/TFE) (polyvinylidene fluoride/tetrafluoroethylene) composites obtained by hot-pressing of PPN ceramic and PVDF powder. Dielectric dispersion was observed in the composites with the maximum of absorption in the range of ~10 MHz at room temperature. The dispersion is characterized by a broad relaxation-time distribution. Electrical transport in the composite at temperatures below ~370 K is influenced by relaxation processes of the polymer View full abstract»

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  • Effect of dye-doping on photo-induced pyroelectric response in thin films of vinylidene fluoride/trifluorethylene copolymers

    Publication Year: 1991 , Page(s): 460 - 465
    Cited by:  Patents (1)
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    The time dependence of the current response induced by a chopped laser beam was measured for dye-doped vinylidene fluoride/trifluoroethylene copolymers spin-coated on an ITO coated glass substrate. In addition to conventional pyroelectric response, an anomalous current was observed in the high dye concentration region. This effect was explained by the photoconductivity of dye molecules densely dispersed in the noncrystalline regions of the polymer matrix View full abstract»

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  • Effect of the air humidity on the corona polarization of β-PVDF films

    Publication Year: 1991 , Page(s): 322 - 327
    Cited by:  Papers (4)
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    The corona triode making it possible to charge polymeric foils with a constant current has proved to be a powerful method for studying charge storage and transport. For ferroelectric polymers it allows one to determine the coercive field and the remanent polarization. A special version of such a triode was developed for poling samples in a controlled atmosphere. The results show that for β-PVDF (polyvinylidenefluoride) samples the surface potential build-up is dependent on the air humidity. For a dry air atmosphere, the polarization clearly shows the ferroelectric behavior of the PVDF sample. A tentative explanation for the saturation of the potential build-up dependence on the humidity takes into account the increase in conductivity due to the water in the bulk of the polymer View full abstract»

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  • On the equivalence of the mechanisms governing switching and hysteresis phenomena

    Publication Year: 1991 , Page(s): 454 - 459
    Cited by:  Papers (2)
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    The nucleation and growth model, which is usually applied to switching phenomena, is adapted for explaining surface potential measurements on the P(VDF-TrFE) (polyvinylidene fluoride-trifluoroethylene) copolymer obtained in a constant current corona triode. It is shown that the growth is one-dimensional and that the nucleation rate is unimportant, probably because surface potential measurements take much longer than the switching ones. The surface potential data can therefore be accounted for by a growth model in which the velocity of growth varies exponentially with the electric field. Since hysteresis loops can be obtained from surface potential measurements, it is suggested that similar mechanisms can be used when treating switching and hysteresis phenomena, provided that account is taken of the difference in the time scale of the measurements View full abstract»

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