A rational design for reconciling high permittivity and breakdown strength in layered PVDF composites from TaB2@Ta2O5 nanofiller induced Schottky barrier effect

Abstract

A contradiction between high permittivity and breakdown strength has long been problematic for obtaining high energy density in conductor/polymer composites. Recently, a gradient-sandwich strategy has been employed to achieve favorable dielectric and breakdown properties in metallic inorganic nanoparticles filled polymer nanocomposites. However, a desirable high breakdown strength cannot be retained once the filler concentration is further increased. In this work, metallic TaB₂@semiconducting Ta₂O₅ nanoparticles were employed to prepare polyvinylidene fluoride (PVDF) nanocomposites with a gradient-sandwich construction to induce an interface barrier effect for depressing the growth of electric trees. Interface polarization (between Ta₂O₅ and PVDF) and interface barrier (between two adjacent sub-layers) effects contributed to an elevation of the permittivity and breakdown strength, respectively. The novelty lies in utilizing the Schottky barrier effect (between Ta₂O₅ and TaB₂) to simultaneously improve the permittivity and breakdown strength of the composites based on the TaB₂ electron-trap and induced electron–hole dipoles. A combination of triple effects (Schottky barrier, interface barrier and interface polarization effects) resulted in high permittivity and breakdown strength at the same time. Tri-effect cooperation from the core–shell filler, gradient sandwich structure and organic–inorganic blend was helpful to decrease the temperature-dependence of the electrical properties, increase the electric insulation at high applied field and elevate the dielectric tunability. The comprehensive electric performances of two composite systems filled with TaB₂@Ta₂O₅ and TaB₂ were compared. The superiority of the core–shell filler was confirmed. A high breakdown strength of ∼286 MV m⁻¹ and permittivity of ∼126 @ 1 kHz were achieved. This work might open up a door to large-scale preparation of high-performance nanocomposite dielectrics.