Ferroelectric switching characteristics in a copolymer of vinylidene fluoride and trifluorethylene

Abstract

Ferroelectric switching characteristics have been measured in the 65/35-mol % copolymer of vinylidene fluoride and trifluoroethylene by applying a step-function high electric field up to 100 MV/m at temperatures between −80 and 90 °C. The amount of reversed polarization is 160 mC/m2 being independent of applied field and temperature. The switching time τs follows an exponential law with an activation field ranging from 0.8 to 1.8 GV/m. Extrapolation to the infinite field yields a switching time of ∼1 nsec. Observed switching transients were fitted by a function, 1−exp[−(t/τs)n]. It is found that the value of the exponent n becomes as large as 5, reflecting an extremely high rate of polarization change with time t. Such a large exponent leads to a switching model which assumes random nucleation of reversed chain molecules and their subsequent two-dimensional growth with accelerated velocity.