The excellent tunable performance of BaSn_xTi_1−xO₃ ceramics at low electric field

BaSn_xTi_1−xO₃ ceramics with excellent tunable properties are prepared via solid-state reaction method. The content of Sn⁴⁺ has an important influence on the micromorphology, dielectric and tunable performance. It is shown that the Sn⁴⁺ has a negative effect on the grain growth, leading to the gradual decrease of grain size as x increases. Meanwhile, when the B-site is partially occupied by Sn⁴⁺, it is effortless to form polar nano-regions (PNRs) due to the weaker orbital hybridization between Sn⁴⁺ and O²⁻ atoms. Influenced by the PNRs, the diffusion phase transition (DPT) behavior at the low- and high-temperature region are distinctly discrepant. The DPT behavior of high-temperature region is stronger than that of low-temperature region. Owing to the influence of grain size and formed PNRs, BaSn_0.12Ti_0.88O₃ and BaSn_0.15Ti_0.85O₃ ceramics possess the large dielectric constant at room temperature. However, the high loss tangent results in the small figure of merit though possessing higher tunability (> 75%) at an electric field of ~ 8 kV/cm. When Sn⁴⁺ content is 0.18, an ultralow tan δ (< 0.01%) with a moderate tunability (~ 46%) is obtained at ~ 8 kV/cm, resulting in the ultrahigh FOM value of ~ 5790. The ultrahigh FOM at low electric field makes it more attractive to be used in microwave tunable devices.