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

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.