Effect of injection contacts on depolarization behaviour of solution grown polyvinylfluoride films
TL;DR: In this article, the authors discuss the origin of relaxations in terms of trapping of charge carriers injected from the electrodes and discuss the nature of the electrodes, injecting as well as blocking types.
About: This article is published in Physics Letters A.The article was published on 1981-11-30. It has received 7 citations till now.
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TL;DR: In this article, the depolarisation behavior of PVF films doped with iodine (0-2.0% by weight) has been studied using the TSD technique.
Abstract: The depolarisation behaviour of PVF films doped with iodine (0-2.0% by weight) has been studied using the TSD technique. The TSD spectra of these films reveal two relaxation peaks. The peak positions, peak currents, charges and activation energies associated with the two peaks are strongly affected by the concentration of iodine and have been explained in terms of formation of charge transfer complexes and molecular aggregates.
10 citations
TL;DR: In this article, the thermally stimulated discharge behavior of vacuum-deposited polyvinyl fluoride films was studied as a function of polarization temperature (313 - 453 K) and polarization field (1 - ) with a single relaxation peak whose peak temperature, charge, activation energy and so on depend strongly on the polarization parameters.
Abstract: The thermally stimulated discharge behaviour of vacuum-deposited polyvinyl fluoride films (about thick) studied as a function of polarization temperature (313 - 453 K) and polarization field (1 - ) shows a single relaxation peak whose peak temperature, charge, activation energy and so on depend strongly on the polarization parameters. The peak has been attributed to space-charge distributed polarization due to the migration of the charge carriers, injected from the electrodes or present inherently, over macroscopic distances and their subsequent trapping; the trapping levels being distributed in the range of energies 0.55 - 0.69 eV.
5 citations
TL;DR: In this article, two peaks have been observed at 320 and 370 K in the TSD spectra corresponding to trapping levels at 0.3 and 0.5 eV, respectively.
3 citations
25 Sep 1996
TL;DR: In this article, a comparison of the IR spectra of uniaxially stretched copolymer films of VDF and 5 mol.% TFE showed the absence of bands attributed to the a phase in contrast to the respective spectras of the homopolymers.
Abstract: Copolymerization of vinylidenefluoride (VDF) with tetrafluoroethylene (TFE) leads to a considerably higher /spl beta/-phase content than the copolymerization with trifluoroethylene (TrFE). This is confirmed by comparison of the IR spectra of the copolymers and the homopolymers. The IR spectra of uniaxially stretched copolymer films of VDF and 5 mol.% TFE show the absence of bands attributed to the a phase in contrast to the respective spectra of the homopolymer. Two peaks are found in the curve of the thermally stimulated current for these polymers above room temperature. An analysis of these peaks allows us to obtain a two-dimensional distribution of relaxation times (energy and frequency factors).
1 citations
22 Sep 1999
TL;DR: In this article, the spontaneous depolarization current (SDC) was observed in VDF copolymers with different moles ratios of 56/44, 70/30 and 77/23.
Abstract: Vinylidene fluoride (VDF)/trifluoroethylene (TrFE) ferroelectric copolymer samples with different mole ratio of 56/44, 70/30 and 77/23 were fabricated by casting from methyl ethyl ketone and followed by slowly cooling from the melting state. Trapped delocalized charges during circulating thermo-stimulating have been observed as spontaneous depolarization current (SDC). For the VDF(56)/TrFE(44) copolymer, SDC spectra show a positive current peak at 72/spl deg/C during heating and a negative peak at 58/spl deg/C during cooling. For the VDF(70)/TrFE(30) copolymer, SDC spectra display a positive current peak at 114/spl deg/C during heating and present a negative peak at 58/spl deg/C and a positive one at 52/spl deg/C during cooling, respectively. As for the VDF(77)/TrFE(23) sample, SDC show a negative peak at 71/spl deg/C and a positive one at 63/spl deg/C during cooling. By comparison with DSC measurements, the peaks are ascribed to the conformation change during ferro-to-paraelectric or para-to-ferroelectric phase transition in heating or cooling processes. This is also an evidence of two coexistent ferroelectric phases in the VDF/TrFE copolymers.
1 citations
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424 citations
TL;DR: In this paper, microscopic displacement of ions with trapping is proposed as the heterocharge mechanism, which is consistent with the observed temperature dependence of the thermal currents, and does not appear to contradict any of the experimental facts.
Abstract: Thermal currents have been obtained from carnauba wax electrets using a linear heating rate for various polarization fields, temperatures, times, and thickness of samples. The polarization is shown to be uniform, and hence space charges, resulting from either charge injection from the electrodes or macroscopic ion displacement, are ruled out as possible causes of the heterocharge. The case for dipole orientation is examined and it is shown that far too many dipoles must be aligned to produce the observed effects. Microscopic displacement of ions with trapping is proposed as the heterocharge mechanism. This model is consistent with the observed temperature dependence of the thermal currents, and does not appear to contradict any of the experimental facts. The thermal‐current spectra consist of three overlapping peaks with activation energies of 1.7, 2.3, and 2.7 eV and temperature maxima of 47°, 59°, and 69°C, respectively. In the proposed model, these activation energies are to be associated with the ionic trap depths.
137 citations
TL;DR: In this paper, a method of evaluating experimentally determined thermally stimulated current curves by a process of successive approximation is described, which is essentially one of curve fitting and an excellent fit is eventually obtained between the theoretical and experimental curves.
Abstract: A method of evaluating experimentally determined thermally stimulated current curves by a process of successive approximation is described. The method is essentially one of curve fitting and an excellent fit is eventually obtained between the theoretical and experimental curves. The process of curve fitting serves to determine the electron-trapping parameters. The technique can be used for the two extreme cases of trap emptying: emptying with no retrapping and emptying with fast retrapping. The technique is illustrated by its application to some experimental results obtained from CdS crystals.
136 citations
TL;DR: In this article, the TSC peak is inhomogeneously broadened by a distribution in relaxation frequencies and the authors analyzed both Arrhenius and Williams-Landel-Ferry descriptions of the temperature dependence of the relaxation processes.
Abstract: The thermally stimulated current (TSC) from polarized polyvinylidene fluoride is studied below room temperature The experimental results indicate that the maximum of the TSC observed at ∼ −50°C is due to reorientation of dipoles in a process associated with the glass transition The TSC peak is inhomogeneously broadened by a distribution in relaxation frequencies The results are analyzed in terms of both Arrhenius, and Williams‐Landel‐Ferry descriptions of the temperature dependence of the relaxation processes and the distribution function for the relaxation frequencies is calculated from the temperature dependence of the TSC It is shown that a distribution in preexponential factors or in activation energies can account for the observed width of the TSC peak For the latter case a distribution varying exponentially with activation energy seems most likely From the data we obtain (36±04)×104 °K for the apparent activation energy and ∼2×10−3 sec−1 for the relaxation frequency of the dominant realignment process The glass transition temperature is determined as Tg ∼ −51°C
70 citations
41 citations