Effects of Thickness on Ferroelectricity in Vinylidene Fluoride and Trifluoroethylene Copolymers

Abstract

The effects of thickness on ferroelectricity in vinylidene fluoride and trifluoroethylene copolymers have been investigated mainly through switching measurements. Switching phenomena as a result of ultimately 180° rotations of individual chain molecules around their axes were observed in the copolymer films with thicknesses in the range of 0.03-1 µ m. With decreasing film thickness, the switching times increase, the switching curve becomes broad and the permittivity at the Curie point decreases. However, the amount of reversed polarization is nearly independent of film thickness. These results are generally reproducible if we assume a surface layer with thickness less than 0.01 µ m, low permittivity, and absence of ferroelectric switching even in the presence of an applied electric field.