Internal charge generation in polyvinylidene fluoride films during poling

The stability of the piezoelectric and pyroelectric properties of PVDF depends on ionic charge injection and trapping at the surface of polarized crystallites. Poled samples in general show complete internal field neutralisation but agreement between the amount of injected charges per cm² and the polarisation value. This indicates that a large number of additional charges must be generated internally for neutralisation. Such internal charge generation is possible by electrical degradation during poling. Now, Raman spectroscopy indicates that unzipping chain reactions produce additional H⁺ and F ^- ions. This is evidenced by two new peaks at 1118 cm^-1 and 1515 cm^-1 corresponding to conjugated polyene sequences arising in the Raman spectrum after poling. This is also in agreement with our observation that a large amount of HF gas is formed during poling. Thus, these additional charges could lead to a complete internal polarisation neutralisation even if the amount of injected charges is too small for this