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.

Effect of iodine on depolarisation behaviour of polyvinyl fluoride (PVF) films

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.

http://iopscience.iop.org/article/10.1088/0022-3727/30/8/014/pdf

Space-charge distributed relaxations in vacuum-deposited polyvinyl fluoride films

Photopolarization process in orthorhombic lead monoxide

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).

https://ieeexplore.ieee.org/iel3/4293/12359/00578219.pdf

Thermally stimulated current and infrared studies of copolymer films of VDF and 5 mol.% TFE

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.

S. Radhakrishnan

Papers

Effect of injection contacts on depolarization behaviour of solution grown polyvinylfluoride films