Annealing effect on ferroelectric phase transitional behavior of vinylidene fluoride-trifluoroethylene copolymers: An interpretation based on the concept of domain and trans-gauche conformational disorder

The annealing effect on the structure and ferroelectric phase transitional behavior of vinylidene fluoride-trifluoroethylene (VDF-TrFE) copolymer with VDF 73 molar % has been investigated by the thermal analysis, X-ray diffraction and Fourier-transform Raman scattering measurements. Heat treatment of the sample in the temperature region below 125°C increases the transition temperature largely, which correlates intimately with an increment of the domain size along the chain axis and the growth of the all-trans chain stems in a crystallite. When the sample is annealed in the temperature region between the phase transitional point and the melting point, the X-ray coherent domain size decreases and the gauche-type disordered region increases within the domain, resulting in the decrement of the transition temperature.