Landau Theory of Phase Transition in Ferroelectric Vinylidene Fluoride/Trifluoroethylene Copolymer Single Crystals: Hysteresis Loop

摘要

Ferroelectric hysteresis loops in vinylidene fluoride/trifluoroethylene, P[VDF/TrFE], copolymer single crystals are discussed on the basis of the Landau-type free energy function with the anisotropy parameter γ_2. It was found that the coercive field strongly depends on the value of γ_2, and decreases as γ_2 = 0 is approached, because the Landau-type free energy function becomes isotropic in the order parameter space. We successfully reproduced the p-E hysteresis loop with a square shape and a small coercive field in P[VDF/TrFE] on the basis of the Landau theory with the anisotropy parameter γ_2.