Electrical and optical dielectric constants of β-phase poly(vinylidene fluoride-trifluoroethylene) ferroelectric films

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 10²-10⁶ Hz 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 (∼877.4 cm⁻¹) comes from the CF₂/CC symmetric stretching. The B₂ mode (∼840.4 cm⁻¹) arises from CH₂ rocking and CF₂ antisymmetric stretching. The results are helpful for the ferroelectric P(VDF-TrFE)-based flexible photoelectronic biomedical sensor.