Evaluation of the dielectric, and piezoelectric properties and optimizing the figure of merit of the 0–3 KNN-0.8ZnO/PVDF-HFP piezoelectric composite by the Taguchi method

Abstract

Piezoelectric ceramic and composite materials are attractive for various applications, but they can be challenging to process. In this research, KNN-0.8ZnO with high density (ρth=95 %), favorable microstructure, and suitable dielectric and piezoelectric properties (K=875, d33=125 pC/N, tanδ=0.01) was first synthesized. Additionally, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) copolymer, known for its advantageous piezoelectric and mechanical properties, was selected as the polymer phase. subsequently, the KNN-0.8ZnO/xPVDF-HFP composite samples with a 0–3 connectivity pattern were made with the cold sintering method. The Taguchi design of experiment (DOE) was employed to determine the optimal condition for maximizing the figure of merit (FOM). Furthermore, an analysis of variance (ANOVA) was carried out to evaluate the significance of individual factors on each measured property. Phase identification was performed using X-ray diffraction (XRD) analysis, while the microstructure was examined using scanning electron microscopy. Among the different composite samples fabricated using the L9 orthogonal array (OA) of the Taguchi method, the KNN-0.8ZnO/20PVDF-HFP composite containing 20 wt% polymer phase, that was cold-sintered under a pressure of 400 MPa at 200 ͦC for 2 h, exhibited the highest FOM value of 1.945Pm2/N. This result aligns with the optimal conditions predeicated by the Taguchi DOE method. The compressive strength of the KNN-0.8ZnO/20PVDF-HFP composite was assessed through a compression test, yielding a value of 207 MPa, while the elastic modulus was approximately 3 GPa. The findings of this study demonstrate that the cold sintering method is an effective approach for producing dense piezoelectric composites with favorable electrical and mechanical properties, along with a high FOM for energy harvesting applications.