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The polymer PVDF and ita copolymers with TrFE show a strong piesoelectric effect ane r poling in high e lectric ficldl ( 100 MV / m). In order to . tudy the dynamiu of the poling proce •• we have applied HV impubes of deftnite duration to the polymer. The dielectrie di.placement during the HV impul.e i. r e corded. Aner tbe impul.e tbe remanent pollll'iBation under . bo rt eircuit condit ion i. mea.ured. Thu. it i. po .. ible to obtain the minimum poling time dependent on the applied field strength nece .. ary to I tabilise the remanent polarillation. By comparing the time development of t he dielectric di.placement with the corre.ponding r emanent polaris.tion we find. time delay between the orientation o f the dipole. and their .tabili.ation. Therefore we conclude that the procell o f orientation of the dipole. ihelfi. not .uffteient to le ad to a r emane nt polarization. An additional interaction between trapped cblll'g"" and the orie nted dipoles can explain the . tability of the remanent pola risation and the ob.erved time d e lay. INTRODUCTI ON KAWAI di aeovered piuoelectricity in the polymer of polyvinylidenefluoride (PV OF) in 1969. Later it wu shown that the copoly m~rl of vi nyl idenefluoride (V OF) with trifluoroethylene (TrFE) alto ex hi bit piezoelect rici ty TlFE) the cry.taUite di poles can be permanently aligned. Unpoled filma .how no piesoeleetricity. The pieloeleetrie reapon ... can be deaeribed mainly by a ehange in the num· ber density or aligned crYltallite dipole moment. under strain. While PVDF crYl tallize8 in the unpolar o·phMe, the P (VOF / TrFE) copolymer cry. taUilu directly in the ,8-phase, if the TrFE portion i. greater than 15 mole% [6J. o·PVOF it Iran.rormed to the polar ,8·ph3le by stretch· ing the fi lma.[21· By poling with lower field strength spatial inhomoge_ neOUI polarilation distributions are found in PVDF. The invest igation of t he development of these inhomogeneous distributions during t he poling process gives strong evi_ dence that injee~ion and migration of lpace charges dete rmine the polarisation distribution [9].Another point is the surprising stability of the remanent polarisation in both polymers al room temperature for many year •. In addi tion, the cocrdtive field Ilrength is th ree orders of magnitude latger than in other ferroelt<:triel [3]. In Figure 2 the expected behavior il.ho",n for the case of polarisation rever .... l of pre polarised filma. At t.) the di· polel begin to invert under t he field and the displacement I t arts to grow as in the ease of unpoled films (compare Figure 1). At t\ all dipole. are inverted under the field and the displlLCement attain. itl maximum. For long er poling time. it remain. conltant. Under .hort circuit the remanent polari1ation in the original dir ection fi rst decreuel to ,eTO li nd then growl in the new, opposite direction. The remanent polatilation in the opposi te direetion latu ratu again o.t h.Since the values of the remanent polarization are the lame (but in oPP01lite direction) before the application ...

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In the present paper, heat wave (LIMM) and pressure step (PPS) measurements of the spatial polarization and electric field distributions in nonuniformly thermally poled a-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 z 2 p 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 N 1 pm. 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.