Microstructures and dielectric tunable properties of Ba0.5Sr0.5TiO3–Li2MgTiO4 and Ba0.5Sr0.5TiO3–Li2Mg3TiO6 composite ceramics

(1−x)Ba0.5Sr0.5TiO3–xLi2MgTiO4 and (1−x)Ba0.5Sr0.5TiO3–xLi2Mg3TiO6 composite ceramics were prepared via the conventional solid-state reaction method. Microstructures and dielectric tunable properties of Ba0.5Sr0.5TiO3–Li2MgTiO4 and Ba0.5Sr0.5TiO3–Li2Mg3TiO6 composite ceramics were investigated. In this composite system, the cubic perovskite BST phase can coexist well with the rock-salt Li2MgTiO4 phase and Li2Mg3TiO6 phase. Only at 1300 °C sintering temperature, due to the decomposition of Li2MgTiO4, a trace of Mg2TiO4 impurity is produced when dielectric content is higher than 55wt% in Ba0.5Sr0.5TiO3–Li2MgTiO4 composite ceramics. At the test frequency of 10 kHz, with the increase of Li2MgTiO4 content from 10wt% to 60wt%, the dielectric constant of Ba0.5Sr0.5TiO3–Li2MgTiO4 composite ceramics sintered at 1300 °C decreases from 962 to 90, the dielectric loss remains below 0.009, and the tunability under an electric field strength of 3 kV/mm gradually decreases from 12.1 to 4.2%. With the gradual increase of Li2Mg3TiO6 content from 10 wt% to 60 wt%, the dielectric constant of Ba0.5Sr0.5TiO3–Li2Mg3TiO6 composite ceramics sintered at 1280 °C decreases from 1042 to 79, the dielectric loss remains below 0.003, and the tunability at 3 kV/mm decreases from 17.2 to 4.9%.