Ferroelectric Polymers with Chemically Tunable Dielectric Constants
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0949-C04-01
Ferroelectric Polymers with Chemically Tunable Dielectric Constants Yingying Lu1, Jason Claude1, Kun Li1, Qiming Zhang1,2, and Qing Wang1 1 Materials Science and Engineering, The Pennsylvania State University, University Park, PA, 16802 2 Electrical Engineering, The Pennsylvania State University, University Park, PA, 16802 ABSTRACT We present a modular approach toward poly(vinylidene fluoride) based ferroelectric polymers with high dielectric constants and energy densities. This strategy is based on a two-step reaction including the co-polymerization of vinylidene fluoride (VDF) and chlorotrifluoroethylene (CTFE) and a subsequent hydrogenation reaction. Due to the similar reactivity of VDF and CTFE in free radical polymerization and quantitative yield of dechlorination reaction, the chemical compositions of the resulting terpolymers can be precisely controlled, leading to tunable Curie temperatures and dielectric constants. A library of the ferroelectric polymers with dielectric constants varying from 11 to 50 measured at 1 kHz and room temperature has been prepared. The structural characteristics including microstructure, chain conformation, and crystallinity of the polymers have been carefully elucidated as a function of the chemical composition by 1H and 19F NMR, Fourier transform infrared spectroscopy, and wide angle X-ray diffraction. The influence of the polymer compositions on thermal transitions and dielectric constants has also been investigated. INTRODUCTION Compared to the traditional electroactive ceramics, polymeric dielectric materials enjoy inherent advantages such as high mechanical elasticity, high electrical breakdown strength, ease of processing in large areas, and self-healing ability.1 Polymers with high electric energy density are attractive for applications in electrical-energy storage with reduced volume, weight and cost, such as stationary power generation and miniature capacitors for telecommunications, portable electronics and hybrid electric vehicles. High-dielectric-constant polymers also hold a great potential as nonvolatile memory elements and gate dielectrics with low operational voltages in flexible integrated circuits, flat panel devices and sensor arrays.2,3 However, unlike their inorganic counterparts, the dielectric permittivities of most polymers are in a limited region ranging from 2 to 12.1 Ferroelectric poly(vinylidene fluoride) (PVDF) and its copolymers are the most interesting dielectric polymers due to the strong polarization originating from C-F bonds and the spontaneous orientation of dipoles in the crystalline phases.4,5 Since ferroelectric materials typically exhibit dielectric anomaly near the Curie temperature, a phase transition point between ferroelectric (polar) and paraelectric (nonpolar) crystalline domains, many research efforts have been devoted to a general goal of moving the Curie transition close to the application temperatures for a high electric-field response.6-9 The lowest Curie temperature observed is about 70 0C for the P(VDF-TrFE) with 4
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