Piezoelectricity is observed in films of poly (vinylidene fluoride) (PVF
2), poly (vinyl fluoride), poly (vinyl chloride), polycarbonate and nylon 11 when they are elongated and polarized by a static field. The largest value of
g31, and
d31 found in PVF
2 films were 150 millivolts/gram cm and 20×10
-8cgs esu respectively. The piezoelectricity of the polymer films is caused by the electrostriction and the spontaneous polarization due to the poling effect. By a newly developed apparatus, electrostrictive constants, inverse piezoelectric constants and their temperature dependence were measured for the polymer films. The electrostrictive constant
γ31T of PVF2 film is about 3.5×10
-11cgs esu and several times larger than those of other films. The large piezoelectricity of PVF
2 is due to the large value of
γ31T. It is suggested that the previously reported shear-type piezoelectricity of the natural polymers are caused also by electrostriction and spontaneous polarization.
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