Ferroelectricity in polyvinylidene fluoride

Changes induced in the orientation of the axes of crystallites in thin films of polyvinylidene fluoride by the application of 6×107 V/m at 100 °C for 1/2 h have been observed. The changes were observed by measuring the intensity of x rays diffracted from the film as a function of the orientation of the film relative to the diffracting x-ray beam. A simple model calculation shows that the results are consistent with the assumption that the changes are induced by the interaction of the applied electric field with the dipole moments of the polyvinylidene fluoride molecules. The model uses the fact that the orthorhombic symmetry of the unit cell results from a small distortion of a hexagonal primitive lattice, the distortion being a 1% decrease in the separation between molecules in the direction of the dipole moments. This model is consistent with the assumption that polyvinylidene fluoride is ferroelectric.