Ferroelectric Behavior in Thin Films of Polyurea-5

Thin polyurea-5 films were prepared by vapor-deposition polymerization of 1,5-diaminopentane and 1,5- diisocyanatepentane. In order to investigate the ferroelectric properties of polyurea-5, we used dielectric hysteresis measurements. Ferroelectric hysteresis loops were observed for the polymer thin film at room temperature. The dielectric hysteresis curve shows large polarization values above 70° C, which are much larger than the calculated value of the spontaneous polarization in the single crystal of polyurea-5. To evaluate the residual polarization, sinusoidal electric fields with varying frequency were applied at various temperatures and the time variation of the electric displacement was detected by a charge amplifier. As a result, we obtained a residual polarization of about 25 mC/m 2 at temperatures in the range of 20–70° C. This value is consistent with a polyurea-5 film crystallinity of 50%.