Microstructure and dielectric properties of highly tunable Ba0.6Sr0.4TiO3/MgO/Al2O3/ZnO composite

The effect of co-doping ZnO, Al2O3 and MgO on the microstructures and dielectric properties of Ba0.6Sr0.4TiO3 ceramics prepared by the mixed-oxide route at 1400 °C was investigated. And a comparison criterion for the BST-based tunable ceramics was proposed. The results show that a cubic perovskite phase Ba0.6Sr0.4TiO3 and a face-centered-cubic spinel phase Mg(Zn)Al2O4 were observed in BST/MgO/Al2O3/ZnO (BMAZ) composite ceramics. When Zn2+ content exceeds solid solubility limit in the BST, excess ZnO will react with Al2O3 to produce ZnAl2O4 phase. With the increase of ZnO, the paraelectric–ferroelectric phase transition points of BMAZ ceramics shift to the lower temperatures, and the maximum of dielectric constant increased first and then decreased. A higher tunability which amounts to 27.4% under 1.0 kV/mm biasing was obtained for BMAZ ceramics doped with 1.0 wt% ZnO.

► ZnO doping mechanism in the Ba0.6Sr0.4TiO3 lattice is discussed by calculating tolerance factor. When Zn2+ content exceeds solid solubility limit, more ZnO will react with Al2O3 to produce ZnAl2O4 phase.
► A comparison criterion for the BST-based tunable ceramics is proposed. We define T0 as the tunability under unit applied electric bias to compare the tunability of various BST-based ferroelectric materials.
► A higher tunability which amounts to 27.4% under 1.0 kV/mm biasing is obtained for BMAZ ceramics doped with 1.0 wt% ZnO.