Preparation And Dielectric Properties Of CaCu_3Ti₄O₁₂/Polytetrafluoroethylene Composites

With the rapid development of electric industry, traditional dielectric materials,such as ceramic and polymer, with poor properties cannot satisfy the needs of modem technology. Ceramic/polymer composites, in which particles with high dielectric permittivity are used as filler and polymer is used as matrix, combine the merits of ceramic and polymer. Such kind of materials with high dielectric permittivity and excellent mechanical properties is an important way to address the problem mentioned above.In this study, we investigated polymer-based composites by embedding calcium copper titanate(CaCu3Ti4O12; CCTO) fillers into polytetrafluoroethylene(PTFE) matrix with different volume fraction. The emulsion polymerization method was employed and CCTO fillers were functionalized by titanate coupling agent NDZ-201. The structure, morphology and dielectric properties of the composites were characterized using X-ray diffraction(XRD), scanning electron microscope(SEM), thermal analysis(TG-DSC) and impedance analyzer. The dielectric permittivity of composites increase with increase of CCTO volume fraction, which is the result of intrinsic characteristics of CCTO and interfacial polarization. As interfacial polarization decreases with the increase of frequency, composite with the same filler concentration showed higher dielectric permittivity at low frequency than that at microwave frequency. The dielectric permittivity of 50 vol% CCTO/PTFE composite was 33.64 at 100 Hz and dielectric loss was less than 0.12. Several theoretical models were implemented to compare the theoretical calculations with the experimental results. The effective medium theory and modified Lichtenecker equation were found to fit the best.In order to investigate the influence of particle size on the dielectric properties of composite, we synthesized submicron CCTO particles by oxalate co-precipitation process. Composites with submicron fillers and micro-submicron cofillers were prepared and compared. The results showed that the density of cofilled composite was improved because the finer particles could fill interstitial site of coarser particles, leading to more excellent dielectric properties than that of single-size filled composite at the same concentration. The dielectric permittivity of 30 vol% cofilled composite was 25.62 and dielectric loss was 0.12 at 100 Hz.