Dielectric properties of BSTO/MgO ceramic composites

Ba_0.55Sr_0.45TiO₃/MgO ceramic composites with 50wt% MgO content were studied in terms of the phase distribution, microstructure and electric properties, prepared by traditional ceramic process-solid phase synthesis. The results show that a small amount of Mg²⁺ ions have entered BSTO lattices to substitute for Ti⁴⁺ and behave as electron acceptors, contributing to the decrease of the dielectric loss. Ba_0.55 Sr_0.45TiO₃/MgO composites in the paraelectric state at room temperature still have a high tunability because of a field-induced hardening of the soft phonon and the presence of micro- or nano-polar phases in the paraelectric phase. For Ba_0.55Sr_0.45TiO₃/MgO ceramic composites, the microwave loss at 2.5 GHz is 7.1 × 10⁻³ and the value of tunability is 13.8% with the external DC field 4 kV ⋅ mm⁻¹. It can basically meet the requirements of phase shifters working at microwave frequencies. The phase shift of 122^∘ was obtained at 9.2 GHz using the designed phase shifter with the bias voltage 2 kV ⋅ mm⁻¹.