Effect of MgO on structure and nonlinear dielectric properties of Ba_(0.6)Sr_(0.4)TiO_3/MgO composite ceramics prepared from superfine powders

摘要

Composite ceramics with a nominal composition of Ba_(0.6)Sr_(0.4)TiO_3 +x wt. percent MgO (x = 0-60) were prepared using superfine Ba_(0.6)Sr_(0.4)TiO_3 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 deg C attained relative densities of around 95 percent. The relatively low sintering temperature of the composites suppressed the diffusion of Mg~(2+) into the lattice of the Ba_(0.6)Sr_(0.4)TiO_3 phase, which consequently led to a small shift of the temperature for dielectric constant maximum (T_m) to -10 deg 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 Ba_(0.6)Sr_(0.4)TiO_3 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 percent at 10 kHz, while maintained a roughly good tunability of 17.3 percent and a high figure of merit of 127 at 10 kHz and 20 kV/cm.