Thermally stimulated currents in polyvinylidene fluoride. I. Unstretched alpha -form PVDF

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Abstract
An unstretched alpha -form specimen of polarised PVDF shows four TSC peaks designated P1, P2, P3 and P4 in ascending order of temperature. The P1 and P2 peaks are associated with the dipolar depolarisation due to the alpha a and alpha e relaxations, respectively. The P3 and P4 peaks may both be attributed to interfacial polarisations formed by trapped carriers in the surface regions of PVDF crystals. The P3 peak shows a tendency to saturation in magnitude and a shift in peak temperature with poling field. The latter can be explained by the field-lowering of trap depth (the Poole-Frenkel effect). The P4 peak appears only in the specimen polarised at high fields which is expected to cause the field-induced structure change from the nonpolar alpha -form to the polar alpha -form. The polar beta -form specimen also shows a large TSC peak corresponding to the P4 peak in the alpha -form specimen. Therefore, the P3 and P4 peaks may be associated with nonpolar and polar alpha -form crystals, respectively.