New High-Dielectric-Constant Polymer-Ceramic Composites
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EE13.58.1
New High-Dielectric-Constant Polymer-Ceramic Composites Milind Arbatti, Xiaobing Shan, and Z.-Y. Cheng Materials Research and Education Center, Auburn University, Auburn, AL 36849 ABSTRACT A ceramic-powder polymer composite, making use of a newly developed ceramics CaCu3Ti4O12 (CCTO) - that has a giant dielectric constant as the filler, is developed. In this work, poly(vinylidene fluoride - trifluoroethylene) [P(VDF-TrFE)] 55/45 mol% copolymer was used as matrix. It is found that the wettability between the copolymer and CCTO is poor, which makes the solution cast composites have a poor uniformity. The uniformity and thus the dielectric constant of the composites can be significantly improved by using hot-press technology to form “sandwich” structure. It is also found that the thermal annealing process can improve the dielectric constant of the composite. The experimental data show that for the flexible composites the dielectric constant at 1 kHz can reach more than 300 at room temperature and more than 700 at ~70 oC. INTRODUCTION Capacitors are widely used to store energy and/or to perform specific functions. The development of electronic devices and circuit of reduced size led to a need for significantly smaller capacitors having increased performance. The electronic industry requires materials that have high dielectric constants and that are flexible, strong, and easy to process. One of the key issues related to the device specification is the dielectric constant. In general, dielectrics with a high dielectric constant are the key to developing high performance devices and to miniaturizing the devices. Finding single component materials possessing all these properties is difficult. Therefore, a great deal of efforts has gone in to developing polymer-ceramic composites that are flexible and easy to process and are of relative high dielectric constant and high breakdown strength [1-6]. In order to develop composite with high dielectric constant, it is desirable that both ceramic powers and polymer are of high dielectric constant. The ceramics used in composite development are ferroelectrics and relaxor ferroelectrics due to the high dielectric constant. For example, a dielectric constant as high as 20,000 can be obtained in relaxor ferroelectrics [7]. However, the dielectric constant of relaxor ferroelectrics is strongly dependent on the temperature. Due to the low dielectric constant of polymer matrix (usually below 10 at room temperature), the dielectric constant of ceramic-polymer composites is usually smaller than 100. Recently, relaxor ferroelectric phenomena were discovered in some electroactive polymers, such as high-energy-electron irradiated P(VDF-TrFE) and some newly synthesized terpolymers – poly(vinylidene fluoride–trifluoroethylene–chlorofluoroethylene) [P(VDF-TrFE-CFE)] and poly(vinylidene fluoride–trifluoroethylene–chlorotrifluoroethylene) [P(VDF-TrFE-CTFE)] [810]. It is found that the dielectric constant of these polymers can reach more than 50. The ceramic-polymer composites using these
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