Microstructure and dielectric properties of Ba_0.6Sr _0.4TiO₃ ceramics Co-doped Al₂O₃-MgO

The Ba_0.6Sr_0.4TiO3 (BSTO) ceramics were prepared by a traditional electrical ceramic method. Effects of co-doping low dielectric constant oxides Al₂O₃ and MgO on microstructure and dielectric properties of Ba_0.6Sr_0.4TiO₃ ceramics were investigated. The results show that BSTO/MgO/Al₂O ₃ (BMA) ceramics can be sintered at 1300°C. The main crystal phases are cubic perovskite structure Ba_0.6Sr_0.4TiO ₃ and face-centered-cubic spinel structure MgAl₂O ₄. Al³⁺ is easier to enter Ba_0.6Sr _0.4TiO₃ lattice in the replacement of Ti⁴⁺ than Mg²⁺. When Al₂O₃ content exceeds 20wt%, Al₂O₃ would react with BaAl₂O₄ to generate a new phase of BaAl₁₂O₁₉. Proper amount of Al₂O₃-MgO can reduce the dielectric constant of BSTO ceramics and result in the higher tunability. There is obvious frequency dispersion characteristic in BMA ceramics and the curie temperature of ceramics decreases with the increase of Al₂O₃. The BMA ceramics with 20 wt% Al₂O₃ exhibit good dielectric properties, with ε_r of 1314, tanδ of 0.003 at 10 kHz, and the dielectric constant tunability of 35.2% under a dc electric field of 1.0 kV/mm, which are useful for potential tunable device applications.