Microstructure and dielectric property relationships in spherical inclusion ferroelectric composite ceramics

Dense Ba0.4Sr0.6TiO3-Mg2TiO4 composite ceramics with different grain sizes were prepared by three different sintering methods: spark plasma sintering, two-step sintering, and conventional sintering, respectively. The dielectric response, tunability, and loss properties of composite ceramics as a function of volume fraction of Mg2TiO4 were systematically investigated. The results showed that the dielectric constant and tunability are strongly dependent on the concentration of Mg2TiO4, grain sizes, and composite modes. In particular, near the percolation threshold for Mg2TiO4 volume fraction (∼60 vol. %), a remarkable variation of the tunability was observed. Nevertheless, the dielectric loss exhibited a relatively weak dependence on inclusion concentrations. The results are also in agreement with the theoretical predictions of the modified effective medium approximation approaches in the spherical inclusion model of composites.