Ferroelectric–Dielectric Composites Model of Ba0.5Sr0.5TiO3/Mg2AO4(A = Ti, Si) for Tunable Application

The correspondence between the theoretical model and the experimental results of the dielectric response in two-phase composites of Ba0.5Sr0.5TiO3 and Mg2AO4 (A = Ti, Si)was studied. The Ba0.5Sr0.5TiO3 (BST50)/Mg2AO4 composites in 2-2 model structure consisting of BST50 layers and Mg2AO4 layers were fabricated by tape casting and multilayer technique. The 3-0 model of the two-phase composites is fabricated by conventional ball mill mixing and solid-state reaction process. The ceramics samples with dense structure were obtained because the coefficient of thermal expansion (CTE) of Mg2SiO4 (12.84 ppm/°C) and Mg2TiO4 (12.11 ppm/°C) ceramic specimens are close to the pure BST50(13.15 ppm/°C) ceramic. The microstructure, dielectric, and tunable properties of 2-2 and 3-0 model composites were investigated. The experimental results agree well with the theoretical prediction in 2-2 model. An important feature of 2-2 model composites is that the DC field is efficiently applied to the high-permittivity ferroelectric phase. With the increase in Mg2AO4 volume fraction q, the tunability of the composite remains almost unchanged whereas the permittivity greatly reduced in the 2-2-//model. These results show that the 2-2-//model sample is good candidates for the tunable devices.