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VOLUME 99 | ISSUE 8 | PAGE 511
Optical probe, local fields, and Lorentz factor in ferroelectrics
Abstract
An optical probe is suggested that allows measurements of the local field and Lorentz factor (L) in ferroelectric medium. The copolymer poly (vinyliden fluoride/trifluoroethylene) is mixed with Pd-tetraphenylporphyrin (TPP-Pd) that has a very narrow absorption band. Thus TPP-Pd serves as a molecular optical probe of the local field. During the switching of the electric field lower than the coercive one the factor L of a non-polarized ferroelectric mixture is found to be of about 1/3 that corresponds to the random distribution of molecular dipoles in the ferroelectric. With increasing field the dipole orientation acquires a lower symmetry and L tends to zero as predicted by lattice sum calculations for vinyliden-fluoride. The knowledge of the field dependence of L and the usage of the optical probe makes it possible to measure directly the local and macroscopic fields in the individual elements of various ferroelectric-dielectric heterostructures.