Polarization and electric field distribution in thermally poled PVDF and FEP

In the present paper, heat wave (LIMM) and pressure step (PPS) measurements of the spatial polarization and electric field distributions in nonuniformly thermally poled alpha-PVDF and Teflon FEP films are reported. The spatial distributions obtained by the two methods are compared over the entire thickness range, and a satisfactory agreement is found. For PVDF the results of both methods are in accordance with literature data for similarly poled specimens of similar material, the so-called 'thermal profile', a polarization peak near the anode. Furthermore, in the LIMM experiments we found a small peak near the cathode, which can be explained by a positive compensation charge layer extending approximate to 2 mu m in depth. For the first time, LIMM spectra of FEP are published. The space charge distribution in the FEP sample is nearly homogeneous inside the sample. Near the anode side an accumulation of negative charges appear. Near both surfaces a positive compensation charge was found with a thickness of similar to 1 mu m. It is demonstrated that by means of our deconvolution the spatial distribution can be determined simultaneously with two thermal parameters, the diffusivity of the sample material and the heat transfer coefficient between sample and sample holder.