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Thermally Stimulated Depolarization Current and Dielectric Relaxation Spectroscopy in Poly(vinylidene fluoride) Samples

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Dielectric relaxation properties of solution grown foil samples of poly(v inylidene fluoride) (PVDF) of 20 urn thickness with similar (AI-AI) electrode combination have been studied in the low frequency range of 100 Hz to 10 kHz by varying the temperature from 30°C to 170°C. PVDF foil samples exhibit two dielectric loss maxima, one around 130±10°C and the other around 150±10°C. These peaks correspond to a- and aי-relaxation processes, respectively. The variation of permittivity with temperature is attributed to the thermal expansion, orientation of dipolar molecules and the chaotic random motion of molecules in the close vicinity of a and a י peaks , respectively. The thermally stimulated depolarization current (TSDC) spectra of PVDF foil sample are characterized by two current maximas, one at 70±1O°C ( ~-peak) and the other centered at 135±10oC (a-peak). The first peak attributed to ~ - re l a x a t i o n process was caused by local motions of side chain. However, a-relaxation peak appeared due to the format ion of space charge at metal polymer interface. The peak position and activation energy do not change with the poling field (Ep) , but it strongly depends upon the poling temperature (Tpl. The location of the TSDC a -peak is found to be comparable with the a -peak obtained by dielectric relaxation spectroscopy.

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