Low dielectric loss and enhanced tunable properties of Cr-doped barium strontium titanate solid solution

The dielectric response and tunable properties of Cr-doped Ba_0.6Sr_0.4TiO₃ solid solution were investigated. The XRD patterns revealed that all of the doped specimens are cubic perovskite phase, and the SEM micrographs showed that the grain size increases with the increase of Cr content below 0.6 mol%. The dielectric frequency spectra of the doped BST solid solution showed that an additional relaxation of the doped specimens is observed at frequencies above 10 MHz. Both of the tunability and dissipation factor were improved by doping with Cr concentration lower than 1.0 mol% compared with undoped material. The 0.6 mol% Cr-doped specimen reveals a maximum tunability and figure of merit of 23.3% and 518.3, respectively. Extremely low dissipation factor in order of 5 × 10⁻⁴ is found for 0.4–0.6 mol% Cr-doped BST solid solution. The dramatically low dissipation factor of the specimen is explained by the reducing of Cr³⁺ to Cr²⁺ and the acceptor action of Cr³⁺ and Cr²⁺ which neutralized the donor action of oxygen vacancies.