High-frequency dielectric properties of BSTO ceramic prepared with hydrothermal synthesized SrTiO3 and BaTiO3 powders

BSTO dielectric ceramic was prepared from SrTiO₃ and BaTiO₃ powders synthesized by hydrothermal method, as well as from Ba_0.6Sr_0.4TiO₃ powder synthesized by conventional solid-state reaction. The former can be sintered at a relatively low temperature of 1120 °C. Characterization by SEM showed that the grain shapes of both ceramics are cubical, though the grain size of the former is much smaller. Dielectric constants measured at 20 °C were shown to vary with frequency in the range from 1 kHz to 2 MHz and dc bias field, and further that the dielectric loss of the former to be less than 2 × 10⁻³ in the frequency range of 20 kHz to 1 MHz, much smaller than that of the latter sample. For the former, temperature dependence of dielectric constant is much flatter and there exists an extended phase transition diffusion covering a wide temperature range of Curie temperature T_c. The smaller grain size of the former depresses the dc bias electrical field dependence of dielectric constant. The tunability is 7% under a bias field of 0.6 kV/mm dc.