Electrically tunable dielectric properties of Ba_(0.6)Sr_(0.4)TiO3-MgO composite ceramics

摘要

40 wt.% Ba_(0.6)Sr_(0.4)TiO3-60 wt.% MgO composite ceramics were prepared from Ba_(0.6)Sr_(0.4)TiO3 powder synthesized by a citrate method and fine MgO powder. The composite ceramics sintered at 1150-1270 °C attained reasonable densification. The structure and dielectric properties of the specimens were investigated. The results showed an important role of sintering temperature in controlling the microstructurc and dielectric properties of the specimens. Sintering at 1250 °C was determined to be preferred in terms of the nonlinear dielectric properties of the specimens under bias electric field. The specimen sintered at 1250 °C attained a dielectric constant (ε_r) of 207 and a dielectric loss (tan8) of 0.11% at 10 kHz together with a tunability of 18.5% and a figure of merit (FOM) of 168 at 10 kHz and 30 kV/cm. It was found that the nonlinear dielectric properties of the specimen measured in continuous cycles of bias electric field sweep were dependent on field history. The phenomenon is qualitatively explained in relation to the polarization reorientation of polar nano-regions (PNRs) in Ba_(0.6)Sr_(0.4)TiO3 phase of the composite specimen.