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

An unstretched alpha -form specimen of polarised PVDF shows four TSC peaks designated P 1 , P 2 , P 3 and P 4 in ascending order of temperature. The P 1 and P 2 peaks are associated with the dipolar depolarisation due to the alpha a and alpha e relaxations, respectively. The P 3 and P 4 peaks may both be attributed to interfacial polarisations formed by trapped carriers in the surface regions of PVDF crystals. The P 3 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 P 4 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 P 4 peak in the alpha -form specimen. Therefore, the P 3 and P 4 peaks may be associated with nonpolar and polar alpha -form crystals, respectively.