Effect of coupling agents on the dielectric properties of CaCu3Ti4O12/PVDF composites

Phase-pure calcium copper titanate (CaCu3Ti4O12, CCTO) ceramic particles were synthesized via a sol–gel route. The CCTO was treated by bis[3-(triethoxysilyl)propyl]tetrasulfide (Si69) to give CCTO@Si69. The dielectric composites based on CCTO (or CCTO@Si69) and polyvinylidene fluoride (PVDF) were molded with desirable dielectric properties by mechanical mixing process and hot-pressing. The structures of CCTO and CCTO@Si69 were investigated by scanning electron microscopy (SEM) energy spectrum, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. The stretching vibration of SO at 1096 cm−1 in FTIR is an indication that chemical bond was formed between Si69 and CCTO. The influence of Si69 on the preparation and the dielectric properties of CCTO/PVDF dielectric composites were discussed. When the content of Si69 was 0.1 mL (relative to 1 g of CCTO), the dielectric constant (ε) (at a frequency of 1 kHz) of CCTO@Si69/PVDF composites reached the maximum value of 84, this value is 5.25 times that of an equal amount of CCTO of CCTO/PVDF composites (ε ≈ 16). The CCTO/PVDF and CCTO@Si69/PVDF composites had very stable dielectric properties over a wide range of temperatures (20–160 °C). These composites can be applied as high-energy–density capacitors in electronic and electrical engineering fields.