Effect of ferroelectric material activity on dielectric properties of ferroelectric–dielectric composite ceramics

Ba0.6Sr0.4TiO3 ceramic doped with MgO was prepared by a conventional solid state reaction method. The effects of Ba0.6Sr0.4TiO3 pre-sintering at different temperatures on the phase composition, microstructure and microwave dielectric properties of composite ceramics were studied. The effect of different pre-sintering temperatures on composite ceramics is mainly reflected in different ion diffusion degree. The results show that the different pre-sintered ceramics have two crystal phases of perovskite structure Ba0.6Sr0.4TiO3 and cubic phase MgO. As the pre-sintering temperature increases, the dielectric permittivity of the composite ceramic decreases, and the grain size decreases obviously. When the pre-sintering temperature rises above 1200 °C, the Curie peak of composite ceramic was strongly suppressed and broadened. The tunability at room temperature increases with the increase of the pre-sintering temperature of Ba0.6Sr0.4TiO3, which is due to the lower ion diffusion weakens Tc movement to low temperature. In addition, the loss tangent of the samples at room temperature was kept at a low level. When the pre-sintering temperature of Ba0.6Sr0.4TiO3 is 1250 °C, the tunability is up to 29% (at 30 kV/cm), and the best Q value 132 (at 1.37 GHz) was generated which is the most obvious improvement in dielectric properties compared to other pre-sintering temperature. This indicates that with the decrease of ion diffusivity, the properties of the ferroelectric-dielectric composite ceramics were significantly improved.