Effect of MgO on structure and nonlinear dielectric properties of Ba0.6Sr0.4TiO3/MgO composite ceramics prepared from superfine powders

Composite ceramics with a nominal composition of Ba0.6Sr0.4TiO3 + x wt.% MgO (x = 0–60) were prepared using superfine Ba0.6Sr0.4TiO3 powder derived from a citrate method and superfine MgO powder. The sinterability, structure and nonlinear dielectric properties of the specimens were investigated. Adopting the superfine powders was found to be effective in promoting the sinterability of the composites. The specimens sintered at 1230 °C attained relative densities of around 95%. The relatively low sintering temperature of the composites suppressed the diffusion of Mg2+ into the lattice of the Ba0.6Sr0.4TiO3 phase, which consequently led to a small shift of the temperature for dielectric constant maximum (Tm) to −10 °C. The variation of the nonlinear dielectric properties with MgO content was qualitatively interpreted in terms of doping and mixing effects caused by the MgO addition together with connectivity between the Ba0.6Sr0.4TiO3 grains in the composites. At room temperature, the specimen with x = 60 showed a reduced dielectric constant of 420 and a low dielectric loss of 0.14% at 10 kHz, while maintained a roughly good tunability of 17.3% and a high figure of merit of 127 at 10 kHz and 20 kV/cm.