Electrical and optical dielectric constants of [formula omitted]-phase poly(vinylidene fluoride-trifluoroethylene) ferroelectric films

Abstract

The β-phase poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE), 70/30] copolymer ferroelectric films were fabricated by a sol–gel method. The electrical dielectric permittivity in the frequency range of 102-106Hz was derived from capacitance and dielectric loss of the P(VDF-TrFE)-based capacitor. It was found that the real dielectric permittivity decreases with the frequency due to the relaxation arising from interfacial polarization. Furthermore, optical constants have been extracted by fitting ultraviolet-infrared ellipsometric spectra with a three-layered structure (air/film/Si) and dielectric models. In the transparent region, the refractive index value is about 1.42. In addition, some main first-order infrared-active modes (3A1 and 3B2) and the corresponding structure vibrations are explained. Particularly, the A1 mode (∼877.4cm−1) comes from the CF2/CC symmetric stretching. The B2 mode (∼840.4cm−1) arises from CH2 rocking and CF2 antisymmetric stretching. The results are helpful for the ferroelectric P(VDF-TrFE)-based flexible photoelectronic biomedical sensor.