Ceramics fillers enhancing effects on the dielectric properties of poly(vinylidene fluoride) matrix composites prepared by the torque rheometer method

The dielectric properties of ceramic-polymer composites were investigated using different lead-free ferroelectrics, 0.50[Ba(Zr0.2Ti0.8)O3]–0.50(Ba0.7Ca0.3)TiO3 (BZT-BCT) and 0.96(K0.48Na0.52)(Nb0.95Sb0.05)O3–0.04Bi0.5(Na0.82K0.18)0.5ZrO3 (KNNS-BNKZ), as fillers to fabricate composites using poly(vinylidene fluoride) (PVDF) as the matrix. The composites were prepared at x  = 35, 45, 50, and 65 wt% according to the formulas x(BZT-BCT)–(1-x)PVDF and xKNNS-BNKZ–(1-x)PVDF by applying melt mixing using a torque rheometer and a hot-pressing process. The distribution of the ceramic filler in the PVDF matrix was examined using a scanning electron microscope and X-ray diffraction analysis. Dielectric, ferroelectric, and piezoelectric analyses were also carried out, the results of which are discussed herein. The dielectric constant and dielectric loss were determined for the pure components and for composites with different ceramic contents within the frequency range of 100 Hz–1 MHz. An increase in the BZT-BCT or KNNS-BNKZ amount resulted in an increase in the dielectric constant of the composites, and at RT and a 1 kHz frequency for x  = 65 wt%, both composites showed the highest dielectric constant (e′) of ~48. The piezoelectric coefficient d33 reached peaks of 10 pC/N (BZT-BCT/PVDF) and 5 pC/N (KNNS-BNKZ/PVDF) measured 24 h after poling at 100 Hz.