Structural control of the dielectric, pyroelectric and ferroelectric properties of poly(vinylidene fluoride--trifluoroethylene) thin films

• Published in: Physical chemistry chemical physics : PCCP 2020-01, Vol.22 (4), p.2414-2423
• Main Authors: Ng, C. Y. B, Gan, W. C, Velayutham, T. S, Goh, B. T, Hashim, R
• Format: Article
• Language: English
• Subjects: Annealing; Crystal structure; Crystallinity; Die casting; Dielectric polarization; Dielectric properties; Dielectric relaxation; Dimethyl sulfoxide; Electric fields; Elongated structure; Ferroelectric materials; Ferroelectricity; Fluorides; Hysteresis loops; Lattice vibration; Methyl ethyl ketone; Molecular dynamics; Polarity; Solvents; Thin films; Vinylidene; Vinylidene fluoride
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c9cp01556f

The effects of solvents and temperature on the crystal formation were investigated for vinylidene fluoride/trifluoroethylene copolymer P(VDF-TrFE). Highly crystalline P(VDF-TrFE) thin films were fabricated by spin-casting using various polar solvents such as diethyl carbonate (DEC), methyl ethyl ketone (MEK), N , N -dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). Ferroelectric polarisation reversal of the P(VDF-TrFE) was evidenced by a displacement ( D ) - electric field ( E ) hysteresis loop measurement and supported by the presence of pyroelectric activity. The samples which were annealed above 100 °C gave elongated rod-like crystalline structures and the highest crystallinity, X c of 83% was formed at 120 °C. Consequently, remnant polarisation (85 mC m −2 ) and the pyroelectric coefficient (30 μC m −2 K −1 ) were enhanced. Thus, annealing plays a substantial role in controlling the crystalline structure of P(VDF-TrFE) films regardless of the choice of solvent. Although, the crystalline structure control is almost independent of the solvent's polarity, the choice of solvent is essential in preparing a smoother film surface. Molecular dynamics of P(VDF-TrFE) are discussed from the observation of two dielectric relaxation processes, β and γ related to the segmental micro-Brownian and local modes, respectively. The complete ferroelectric polarization reversal caused a reduction in the dielectric polarization and reduced the lattice spacing of the 110/200 planes. P(VDF-TrFE) is optimized effectively via thermal treatment and its molecular motions after poling are revealed.