40 wt.% Ba0.6Sr0.4TiO3-60 wt.% MgO composite ceramics were prepared from Ba0.6Sr0.4TiO3 powder synthesized by a citrate method and fine MgO powder. The composite ceramics sintered at 1150-1270 oC 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 microstructure and dielectric properties of the specimens. Sintering at 1250 oC was determined to be preferred in terms of the nonlinear dielectric properties of the specimens under bias electric field. The specimen sintered at 1250 oC attained a dielectric constant (εr) of 207 and a dielectric loss (tanδ) 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 Ba0.6Sr0.4TiO3 phase of the composite specimen.

Keywords: Ba0.6Sr0.4TiO3-MgO, Composite ceramics, Nonlinear dielectric properties, Microstructure.