Voltage-induced infrared absorption from a spin-cast thin film of ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE))

Voltage-induced infrared spectra of annealed spin-cast thin films of ferroelectric poly(vinylidene fluoride-cotrifluoroethylene) (P(VDF-TrFE)) (molar ratio, 3:1) were measured in a stepwise cyclic external electric field. Most of the observed infrared bands originated from the β ferroelectric crystalline phase. The voltage-induced spectral changes were decomposed into zeroth- (original), first-, and second-derivative spectra, and were attributed to the rotational motions of the polymer chains and the vibrational Stark effect. The values of the original spectral absorbance change ratios, ΔA/A, for the 849-cm ^-1 band (CF ₂ symmetric stretching, a ₁ ) and the 884-cm ^-1 band (CH ₂ rocking, b ₂ ) of the film exhibited double minimum and maximum peak hysteresis loops, respectively. The intensity of each band increased or decreased suddenly near a coercive field of ±0.6 MV/cm. These sudden intensity changes were attributed to the rotational inversion of the polymer chains that are associated with ferroelectricity.