New Piezoelectric Polymers

Four kinds of piezoelectric polymers are introduced. Submicron thin films of polyurea are prepared by vapor deposition polymerization. Poled films of aromatic polyurea exhibit the piezoelectric constant d 31 =20 pC/N, which is almost independent of temperature in the range of 100 to 200°C. Aliphatic polyureas show a ferroelectric hysteresis with a coercive field of about 100 MV/m. Single crystalline films of a copolymer of vinylidene fluoride and trifluoroethylene were prepared by annealing elongated films at a paraelectric temperature range avoiding the side surface contacts. No lamella structures were present and the crystallinity was near 100%. The large electromechanical coupling factors k 33 =0.3 and k 31 =0.1 were observed. A large electrostrictive constant R =2.6×10 -17 m 2 /V 2 was observed for polyurethane. With a dc bias field of 15 MV/m, a piezoelectric constant of d 33 =600 pC/N was obtained, which was larger than that of PZT. A shear piezoelectric constant d 14 =-10 pC/N was obtained for oriented films of poly-L-lactic acid, which were optically active and biodegradable. After poling, this polymer showed the tensile piezoelectricity and pyroelectricity.