Preparation, microstructure and microwave dielectric properties of sprayed PFA/barium titanate composite films

Frequency dependence of the dielectric properties of polymer-ferroelectric composites at different bands of microwave frequencies was investigated in this work. Perfluoroalkoxy (PFA)/barium titanate (BaTiO3) nanocomposite films were prepared by spray deposition. The spraying process was scaled up to fabricate large area (max. 160 mm × 160 mm) uniform composite sheets out of which a controlled bonding process was introduced to form composite blocks. The microstructure of the composite films was examined by SEM with a microtome sample preparation method to evaluate the effectiveness of the spraying process at producing uniform particle distributions. The dielectric properties of the composite films with various BaTiO3 loadings were characterised by an Impedance Analyzer at frequencies between 10 Hz and 1 MHz and Vector Network Analyzer at 12–18 GHz respectively. The Lichtenecker mixing rule was incorporated to fit the measured dielectric constant data, which gives estimates of dielectric constant of the BaTiO3 nanometer sized particles to be 895 and 571 at 10 kHz and 15 GHz respectively. In comparison, the composite effective dielectric constant was approximately reduced by 25% at 10 kHz than that at 15 GHz.