Effect of CaCu3Ti4O12 powders prepared by the different synthetic methods on dielectric properties of CaCu3Ti4O12/polyvinylidene fluoride composites

CaCu3Ti4O12 (CCTO) particles were prepared separately by the sol-gel method (sg) and solid-state method (ss). CCTO-sg particles were more uniform, narrower distribution size and smaller (effective diameter of 290 nm) than that of CCTO-ss particles with the value of 480 nm for CCTO-ss particles. The CCTO-sg particles exhibited a small particle size and in turn improved chemical activity and lower crystallization temperature, which give rise to the enhanced dielectric properties. CCTO-sg and CCTO-ss filled polyvinylidene fluoride (CCTO/PVDF) were molded by solution mixing process and hot-pressing. The enhanced dielectric constant, good frequency and temperature stability of CCTO/PVDF composites were significant with increasing the volume fraction of CCTO particles. Compared to two kinds of composites, the CCTO-sg/PVDF composites exhibited better dielectric properties than CCTO-ss/PVDF composites. The dielectric constant of 50 vol% CCTO-sg/PVDF composites reached the maximum value of 62.3, which was 8 times and 2 times larger than that of pure PVDF and 50 vol% CCTO-ss/PVDF composites, respectively. The temperature coefficient (C-T-C-25 degrees C/C-25 degrees C x 100%) of CCTO-sg/PVDF composites was -3 to 10 % from -10 to 150 degrees C at 10 kHz, which was lower than that of CCTO-ss/PVDF composites. Meanwhile, the dielectric constant of CCTO/PVDF obtained by Maxwell-Garnett model and Yamada model were in close agreement with the experimental data, respectively.