A statistical theory of ferroelectric phase transition of vinylidene fluoride and trifluoroethylene copolymers

Abstract

Abstract A theory of phase transition in polymer ferroelectrics is developed on the basis of statistical mechanics. In the present models a crystal consists of linear dipole chains composed of the trans and gauche bondings in two ways; the first being free for the g + g − bonding (Model I) and the second being forbidden for it (Model II). By introducing two order parameters, polarization and gauche content, into a dipolar chain crystal, both models show that the ferroelectric phase transition changes from the second order to the first order, depending on the relative value of the energy difference between the trans and gauche bondings. The theory also provides semi-quantative descriptions of thermal hysteresis and the compositional dependence of Curie temperature in vinylidene fluoride and trifluoroethylene copolymers.