Effect of nano- and micron-sized K0.5Na0.5NbO3 fillers on the dielectric and piezoelectric properties of PVDF composites

Abstract

Polymer nanocrystal composites were fabricated by embedding polyvinylidene fluoride (PVDF) with K 0.5 Na 0.5 NbO 3 (KNN) nanocrystallites of different volume fraction using the hot-pressing technique. For comparison, PVDF-KNN microcrystal composites of the same compositions were also fabricated which facilitated the studies of the crystallite size (wide range) effect on the dielectric and piezoelectric properties. The structural, morphological, dielectric, and piezoelectric properties of these nano and micro crystal composites were investigated. The incorporation of KNN fillers in PVDF at both nanometer and micron scales above 10 vol% resulted in the formation of polar β-form of PVDF. The room temperature dielectric constant as high as 3273 at 100 Hz was obtained for the PVDF comprising 40 vol% KNN nanocrystallites due to dipole-dipole interactions (as the presence of β-PVDF is prominent), whereas it was only 236 for the PVDF containing the same amount (40 vol%) of micron-sized crystallites of KNN at the same frequency. Various theoretical models were employed to predict the dielectric constants of the PVDF-KNN nano and micro crystal composites. The PVDF comprising 70 vol% micron-sized crystallites of KNN exhibited a d 33 value of 35 pC/N, while the nanocrystal composites of PVDF-KNN did not exhibit any piezoelectric response perhaps due to the unrelieved internal stress within each grain, besides the fact that they have less domain walls.

Hybrid lead-free polymer-based nanocomposites with improved piezoelectric response for biomedical energy-harvesting applications: A review

“…The content and orientation of the γ and β phases and the degree of crystallinity are the essential features that determine the piezoelectric performance of polymer NGs based on PVDF and its copolymers [44]. Recently, researchers have attempted to improve the dielectric and piezoelectric characteristics of this polymer without compromising its mechanical strength or flexibility through the incorporation of various nucleating agents (nanofillers) into the polymer matrix [45][46][47]. This approach has emerged as a new paradigm for the development of highenergy-density capacitors.…”

“…KNN is another lead-free piezoelectric filler with a complex orthorhombic structure that exhibits spontaneous polarization along the [110] direction, and has been widely studied due to its favourable electromechanical properties (k p = 0.36, d 33 = 80 pC/N) [46].…”

Influence of Matrix and Surfactant on Piezoelectric and Dielectric Properties of Screen-Printed BaTiO3/PVDF Composites

“… Performing BaTiO 3 particle calcination at high temperature [ 33 ]. Using other matrices (epoxy, PU, PLLA) [ 46 , 47 ] or ceramics (KNN, BZT-BCT) [ 48 , 49 ], and comparing the results. Testing other solvents (DMAc, DMF, etc.…”

K0.5Na0.5NbO3-SrTiO3/PVDF Polymer Composite Film with Low Remnant Polarization and High Discharge Energy Storage Density

“…Although polymer material has good mechanical properties and high breakdown electric field, it has lower dielectric constant. In order to improve the dielectric constant, an effective strategy that combining the polymer with the functional inorganic fillers has been carried out, and the electrical, optical or magnetic performance can be tailored by adjusting the shape and size or modified surface of the filled particles [7,8,9,10]. Recently, the composition of inorganic fillers into polymer matrix has been reported to enhance the energy storage density of polymer composites.…”