High Dielectric Constant 0-3 Ceramic-Polymer Composites

Abstract

0-3 ceramic-polymer composites using both nano-size and micro-size CaCu3Ti4O12 ceramic particles were studied. The micro-size ceramic particles were prepared from the CaCu3Ti4O12 pellets by milling. The CaCu3Ti4O12 ceramics were prepared using conventional solid-state reaction under different conditions, such as molding pressure, milling media and time, and calcination temperature and time. Based on the analysis of the dielectric spectrum, it was found that the dielectric responses of CaCu3Ti4O12 ceramics are determined by three different processes. The effect of thickness of the ceramics on the dielectric properties was observed and studied. Although the dielectric response at low frequency increases with decreasing thickness, the dielectric behavior for the high frequency relaxation process is weakly dependent on thickness. 0-3 composites with different concentrations (0-50 vo% CaCu3Ti4O12 ceramics) were prepared using solution casting. However, a clear polymer-rich layer was found in as-cast film due to the poor wettability between ceramic and polymer matrix. The HP was used to modify the morphology of the composites. Different configurations were studied for the HP process. Composites with a dielectric constant of 510 at 1 kHz were obtained in 50vol% CaCu3Ti4O12 composite with CC HP at room temperature. It was found that the relaxation time of the major relaxation process obtained in the composite changes with processing condition, such as annealing, HP and concentration. It indicates that the interfacial layers between ceramic particles and polymer matrix play an important role on the dielectric response of the composite. As for the HP samples, it was interestingly observed that as HP time changes, there is a critical HP time at which the composite exhibits a much higher dielectric constant. Based on the dielectric spectrum of the composites at different temperatures, it was concluded that the loss of the composites at low frequency is controlled by a relaxation process. For the CaCu3Ti4O12/P(VDF-TrFE) composite, the dielectric response is strongly dependent on temperature due to the fact that the dielectric constant of P(VDF-TrFE) is strongly dependent of temperature. However, as for the CaCu3Ti4O12/P(VDF-CTFE) composites, the dielectric constant of the composite is almost independent of temperature and the composite has a small loss. For example, composites with a dielectric constant of 151 and loss of 0.14 at 1 kHz were obtained at room temperature. A clear difference between nano-size and micro-size CaCu3Ti4O12 composite was observed. Moreover, It was also found that the difference of dielectric constant between nano-size and micro-size particles in P(VDF-CTFE) copolymer is much smaller than that in P(VDF-TrFE) copolymer.