Influence of Process Condition on the Dielectric Properties of CCTO-P(VDF-TrFE) 0-3 Composites
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Influence of Process Condition on the Dielectric Properties of CCTO-P(VDF-TrFE) 0-3 Composites Xiaobing Shan, Lin Zhang and Z.-Y. Cheng Materials Research and Education Center Auburn University, Auburn, AL 36849 Abstract A high dielectric constant was observed in 0-3 composites using P(VDF-TrFE) copolymer as matrix and CaCu3TiO4 (CCTO) ceramic powders as fillers with a composition of 50 vol% CCTO. CCTO-P(VDF-TrFE) 0-3 composites with a CCTO content from 0 to 50 vol% were prepared and their dielectric properties, including frequency dependence and temperature dependence of the dielectric constant and loss, were characterized. It was experimentally observed that the hot-press process, inlcuding the configuration and hot-press time, has a strong influence on the dielectric properties of the composites. Additionally, the influence of the CCTO partice size on the dielectric properties of the composites was studied. Introduction Dielectric materials with a high dielectric constant and high dielectric strength (electric breakdown field) are highly desirable for use in miniaturizing electronic circuits and components, as well as the development of capacitors with high energy storage density. From an application point of view, flexible dielectric materials are very desirable for device fabrication and dielectric materials with a low process temperature are needed to integrate electronic components. In general, a high dielectric constant is observed in brittle inorganic materials and high dielectric strength is obtained in flexible polymers. Therefore, flexible ceramic-polymer 0-3 composites are interesting for the development of flexible dielectric materials with a high dielectric constant and strength. This has been a hot topic over last three decades. For the development of ceramic-polymer 0-3 composites with a high dielectric constant, the ceramics used are usually ferroelectric-based materials, such as relaxor ferroelectrics, due to the fact that these materials exhibit a very high dielectric constant [1,2]. Unfortunately, the ferroelectric-based materials exhibit a strong electromechanical effect, which is desirable for electromechanical devices, such as transducers and actuators, but not desirable for dielectric applications, such as capacitors. Additionally, the dielectric constant of the ferroelectric-based materials exhibits a strong dependence on temperature [1]. Regarding the polymers used in the development of composites, a polymer with a high dielectric constant is highly desirable. PVDF-based polymers, which exhibit a dielectric constant of about 10 that is much higher than ~5 obtained in most of the polymers, are widely used [2]. In the last decade, ceramics with giant dielectric constants and weak electromechanical coupling effects have been developed. For example, CaCu3TiO4 (CCTO), which does not have a piezoelectric effect, exhibits a giant dielectric constant, 104 ~ 105 [3-4]. It was also been found that the dielectric constant of the CCTO is almost independent of temperature over a broad temperature range
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