Piezoelectric and Dielectric Properties of (0.970(0.95(K0.485Na0.515) NbO3-0.05LiSbO3)-0.015CuO-0.015Al2O3)/PVDF Composites at Different Immersing Conditions

Abstract

(KNNLS-CA)/PVDF composites were fabricated by a hot-pressing process using 0.970(0.95(K0.485Na0.515) NbO3-0.05LiSbO3)-0.015CuO-0.015Al2O3 (KNNLS-CA) ceramic powder and polyvinylidene fluoride (PVDF). The crystalline structures, morphology, densities, conductivity, dielectric and piezoelectric properties of (KNNLS-CA)/PVDF 0–3 composites were investigated. It is found that the phase structure is perovskite with orthorhombic symmetry for KNNLS-CA ceramic. When the ceramic content is 60 wt.%, the lattice strain reaches the maximum value. In addition, the ceramic particles can increase the relative fraction of the β-phase and restrain α-phase in PVDF matrix. By immersing the samples under different conditions (de-ionized water and NaOH/KOH solutions), it is found that K+ ions are easier to form electrolytes and enhance the dielectric properties. Water solution can delay the neutralization between alkali metal ions especially Na+ ions and space charges, and improve the piezoelectric properties. In this study, a dielectric constant as ultrahigh as 185723 is obtained at 0.2 M KOH (aq) (100 Hz), which is about 928 times higher than that of the untreated composites. The dielectric properties are well explained in terms of an interfacial percolation model. The piezoelectric coefficient as high as 75 pC/N is obtained at 0.05 M NaOH (aq) and increases more than 97% of that of untreated samples. All samples have good piezoelectric stability.