Enhanced tunable dielectric properties of Ba_0.6Sr_0.4TiO₃/PVDF composites through dual-gradient structural engineering

Materials with tunable dielectric properties were expected to be applied in electronic devices such as phased array antennas, tunable filters and phase shifters. The dielectric tunability of material greatly depends on the dielectric constant and breakdown strength. Herein, two kinds of Ba_0.6Sr_0.4TiO₃/PVDF (BST/PVDF) composite materials with different dual-gradient structures were designed to obtain the serialized relative permittivity and improved breakdown strength. The numerical simulation based on Yamada theory confirmed that the multilayer dual-gradient structure design was beneficial to improve the dielectric constant, and the enhancement of breakdown strength was further identified by finite element simulation. The optimal composition has a high dielectric tunability of 78.27 % which is 45 % higher than the ungraded composite due to the high permittivity of 33.8 and high breakdown strength of 1900 kV/cm. The dielectric theoretical model of multilayer structure was developed by introducing the effect factor of layer number m into the Yamada model, and the calculated results are consistent with the experimental results especially m= 1.6–1.7. This work provides a new strategy to effectively improve the dielectric tunability of ceramic/polymer composite materials.