Characterization and dielectric properties of modified Ba_0.6Sr_0.4TiO₃/poly(vinylidene fluoride) composites with high dielectric tunability

MgO-Al₂O₃-ZnO co-doped Ba_0.6Sr_0.4TiO₃ (BMAZ)/poly(vinylidene fluoride) (PVDF) composites were prepared via the solution casting method. The effects of the volume fraction of BMAZ on microstructure and dielectric properties of BMAZ/PVDF composites were investigated. In addition, logarithmic mixture rule and Yamada mixing laws were used for the theoretical prediction of these properties. The permittivity and loss tangent of the composites increased and decreased from 10 to 34 and 0.07 to 0.02, respectively, with increasing amount (i.e., from 10 vol% to 40 vol%) of BMAZ filler. Moreover, for shape factors of 1.5-3, the permittivity values predicted by using Yamada's model exhibited close correspondence to those determined experimentally. However, the dielectric tunability of the composites improved with increasing amount of BMAZ filler. In fact, a high dielectric constant tunability of 10.9% (under a bias of 1.0 kV/mm) were obtained for the composite with 40 vol% BMAZ; this value was higher than those of some Ba_0.6Sr_0.4TiO₃-based ferroelectric ceramics, which rendered the composite with 40 vol% BMAZ suitable for tunable capacitor and phase shifter applications.