Structure and functional properties of ferroelectric polymers

Ferroelectric polymers represented by vinylidene fluoride copolymers with trifluoroethylene (VDF/TrFE) have been investigated with special interest on the relationship between their dynamical properties and structures. Copolymers containing 50-80 mol% VDF exhibit fast polarization reversal due to the rotation of chain molecules about their axes. Annealing of an extruded copolymer yields a highly crystalline film consisting of regularly stacked large lamellae. The switching transient of these extruded copolymers is consistent with the switching mechanism that progresses through a nucleation-growth process with a considerable waiting time (time between the generation of a nuclei and the onset of its growth) and an accelerated growth velocity. TrFE-rich copolymers exhibit a two-step switching transient, suggesting that polarization reversal occurs via a nonpolar stare associated with the copolymer's antiferroelectric-like nature. Piezoelectric and pyroelectric properties were examined for their high frequency and short time characteristics. The time evolution of the charge response induced by laser pulse irradiation consists of intrinsic pyroelectricity and the coupling of thermal expansion and piezoelectric resonance. The intrinsic pyroelectric response for well-annealed VDF-rich copolymers is in the sub-nanosecond range, which promises their use as fast thermal sensors. (C) 1997 Elsevier Science B.V.