Dielectric response of MgO-added Ba0.6Sr0.4TiO3 ceramics under bias electric field: Examination of contributing mechanisms

The structure and dielectric properties of (1−x)wt% Ba0.6Sr0.4TiO3-xwt% MgO (x=0.5–60) ceramics were studied. The specimens with x≤1 had a single-phase perovskite structure and those with higher MgO contents presented a biphasic structure comprising Ba0.6Sr0.4TiO3 and MgO phases. The temperature dependence of the dielectric properties showed a frequency-dispersion behavior. The dielectric constants of the ceramics under bias electric field displayed an obvious deviation from the behavior as predicted by the phenomenological Johnson model. These dielectric phenomena were explained in relation to Mg2+ doping and polar nano-regions (PNRs) in Ba0.6Sr0.4TiO3 phase. Fitting the dielectric constants to a multipolarization mechanism model resolved intrinsic and extrinsic contributions to the dielectric non-linearity of the ceramics. Characteristic parameters of the contributions were determined from the fitting. Increasing MgO content led to a monotonous enhancement of the anharmonic coefficient (α). The polarization of PNRs tended to decrease with the increase of MgO content while the size of PNRs was insensitive to MgO content.