Abstract
Influences of process conditions on microstructure and dielectric properties of ceramic-polymer composites are systematically studied using CaCu3Ti4O12 (CCTO) as filler and P(VDF-TrFE) 55/45 mol.% copolymer as the matrix by combining solution-cast and hot-pressing processes. It is found that the dielectric constant of the composites can be significantly enhanced–up to about 10 times – by using proper processing conditions. The dielectric constant of the composites can reach more than 1,000 over a wide temperature range with a low loss (tan δ ~ 10−1). It is concluded that besides the dense structure of composites, the uniform distribution of the CCTO particles in the matrix plays a key role on the dielectric enhancement. Due to the influence of the CCTO on the microstructure of the polymer matrix, the composites exhibit a weaker temperature dependence of the dielectric constant than the polymer matrix. Based on the results, it is also found that the loss of the composites at low temperatures, including room temperature, is determined by the real dielectric relaxation processes including the relaxation process induced by the mixing.
Highlights
The dielectric response of a dielectric polymer filled with conductive particles – conductor-dielectric composite (CDC) – is determined by a percolation phenomenon
In a study of CCTO-PVDF composites using CCTO prepared by a wet chemical process, it was reported that the composites using nano-sized CCTO exhibited a dielectric constant of >106 at 100 Hz at room temperature, but with an extremely high loss[33]
The dielectric properties of CCTO ceramics at room temperature are presented in Fig. 1, where the SEM micrograph of the cross section is shown
Summary
The dielectric response of a dielectric polymer filled with conductive particles – conductor-dielectric composite (CDC) – is determined by a percolation phenomenon. It was reported that CCTO-P(VDF-TrFE) composites with a φ of 50 vol.% at room temperature exhibit a dielectric constant of ~400 at 100 Hz with a dielectric loss of about 0.625. The dielectric constant observed in the CCTO-P(VDF-TrFE) is significantly higher than that observed in other DDCs. Since the report, CCTO-polymer composites become an interesting topic and have been studied by many research groups[26,27,28,29,30,31,32,33,34,35,36,37,38,39,40]. In a study of CCTO-PVDF composites using CCTO prepared by a wet chemical process, it was reported that the composites using nano-sized CCTO exhibited a dielectric constant of >106 at 100 Hz at room temperature, but with an extremely high loss (tan δ ~ 50)[33]. Most reported composites are prepared using a one-step process, such as solution cast, spin-coating, hot mold, etc.[5]
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