Analytical Sciences

Voltage-induced Infrared Absorption from a Spin-cast Thin Film of Ferroelectric Poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE))

Kenji TAKASHIMA and Yukio FURUKAWA

Department of Chemistry and Biochemistry, Graduate School of Advanced Science and Engineering, Waseda University, Shinjuku, Tokyo 169-8555, Japan

Voltage-induced infrared spectra of annealed spin-cast thin films of ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (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 (CF₂ symmetric stretching, a₁) and the 884-cm⁻¹ band (CH₂ rocking, b₂) 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.

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