Microstructure and tunable dielectric properties of Ba_0.6Sr_0.4TiO₃/Y₂O₃ composite ceramics

(100−x) at.% Ba_0.6Sr_0.4TiO₃−x at.% Y₂O₃ (BST/Y₂O₃) composite ceramics were prepared by conventional solid-state reaction methods. Phase constitution, microstructure, and element distribution of the composite ceramics were characterized, and the dielectric properties of BST/Y₂O₃ composite ceramics were measured. The results revealed that some of Y³⁺ were dissolved into the lattice of BST and the rest remained at grain boundaries in oxide form of Y₂O₃. With the increase of the content of Y₂O₃, Curie peak of BST/Y₂O₃ composite ceramics moved to a lower temperature, the dielectric permittivity and dielectric loss of BST/Y₂O₃ composite ceramics decreased significantly, meanwhile, the dielectric tunability still maintains a relatively high value. Furthermore, a multipolarization mechanism model is employed to describe the field dependence of the dielectric permittivity in BST/Y₂O₃ composite, which suggests that the existence of the second phase of Y₂O₃ diminishes the contribution of polar clusters in BST matrix, leading to the decrease of dielectric tunability. P–E loop measurement indicates that the breakdown strength of BST/Y₂O₃ ceramics increases during addition of Y₂O₃ in BST matrix. Therefore, the BST/Y₂O₃ composites with good tunable dielectric properties and enhanced breakdown strength can be exploited for phase shifter and capacitor device applications.