Depolarization field effect on the ferroelectric behavior of polymers

<jats:title>Abstract</jats:title><jats:p>The effect of the depolarization field in crystallites on the ferroelectric behavior of polymers is discussed on the assumption that the crystallite is a prolate ellipsoid with its major axis directed along the electric field. The theory relates the polarization <jats:styled-content><jats:italic>P</jats:italic></jats:styled-content> and the electric field <jats:styled-content><jats:italic>E</jats:italic></jats:styled-content> in the crystallite to the overall values <jats:italic>P</jats:italic> and <jats:italic>E</jats:italic> for the polymer. The determination of the <jats:styled-content><jats:italic>P</jats:italic></jats:styled-content>‐<jats:styled-content><jats:italic>E</jats:italic></jats:styled-content> hysteresis of a crystallite from the <jats:italic>P</jats:italic>‐<jats:italic>E</jats:italic> hysteresis is given with examples for poly(vinylidene fluoride) (PVDF) and vinylidene fluoride (VDF)–trifluoroethylene (TrFE) copolymer. The ratio <jats:italic>R</jats:italic> = <jats:italic>J</jats:italic>/(<jats:italic>P</jats:italic><jats:sub><jats:italic>s</jats:italic></jats:sub> − <jats:italic>P</jats:italic>), with <jats:italic>J</jats:italic> the switching current density and <jats:italic>P</jats:italic><jats:sub><jats:italic>s</jats:italic></jats:sub> the saturation polarization of polymer, is proved to be free from the depolarization field effect and the plot of log<jats:italic>R</jats:italic> against logarithmic time is shown to have merit for characterization of switching behavior. Examples of the curves are given for PVDF and VDF‐TrFE copolymers. The temporal change of local electric field in the unreversed domains in the crystallite in the course of polarization reversal is predicted by the theory and this change is proved to be a significant mechanism of switching acceleration.</jats:p>