Polarization of VDF-TrFE copolymer films at elevated temperature

The build-up of the polarization of VDF-TrFE (vinylidene trifluorethylene) copolymer films at room temperature after various thermal treatment has been studied using the PWP (pressure wave propagation) method. This method allows for the nondestructive measurement of the homogeneity of the piezoelectric coefficient. The influence of different thermal treatments and of the insulator-electrode interfaces on the polarization at elevated temperature (100°C) is analyzed. The polarization which develops when the poling is performed at 100°C is very inhomogeneous and originates at the anode. The kinetics of the spreading of the polarized region towards the cathode depends on the applied field and on the thermal treatment applied to the samples. According to the history of the sample, the amount of the ferroelectric phase varies. This influence of the morphology of the samples and the role of charge injection at the cathode can explain the observed behavior