Microstructures and dielectric tunable properties of Ba0.5Sr0.5TiO3–MgO–Mg3B2O6 composite ceramics

Ba0.5Sr0.5TiO3–MgO–Mg3B2O6 composite ceramics were fabricated by a solid state reaction method and their dielectric tunable characteristics were investigated. The addition of MgO–Mg3B2O6 into Ba0.5Sr0.5TiO3 forms ferroelectric (Ba0.5Sr0.5TiO3)–dielectric (MgO–Mg3B2O6) composites. Increasing MgO content causes a decrease of Curie temperature TC and an increase of dielectric constant peak εmax. With the increase of the MgO content and the decrease of Mg3B2O6, the dielectric constant of composite ceramics increases slightly; meanwhile, the loss tangent decreases and the tunability increases. When MgO content exceeds 10 wt%, the electric field dependence of the dielectric constant of composite ceramics is well described by an additional “extrinsic” contribution due to the polar clusters, instead of Johnson׳s approximation. The dielectric constant and Qf0 values of composite ceramics at microwave frequency tend to increase with the increase of MgO content. The improved tunability and Qf0 values are beneficial for tunable microwave applications.