DC field dependence of the dielectric characteristics of doped Ba0.65Sr0.35TiO3 with various grain sizes in the paraelectric state

Different grain sizes of ferroelectric Ba0.65Sr0.35TiO3 doped with 1.0mol% MgO and 0.05mol% MnO2 were prepared to investigate the DC field dependence of dielectric characteristics. A transition broadening is observed as grain size decreases. The broadening is attributed to the variance of lattice distortion in the materials. As the grain size increases, both the maximum dielectric constant k(max) at T-c and the dielectric tunability (percentage change of dielectric constant under a DC field) increase. A phenomenological equation can be fit to the DC field dependence of the dielectric constant. The phenomenological coefficient obtained is strongly dependent on the grain size and the temperature. Above the phase transition; a ''behavior-transformation'' temperature T-b is observed. At temperatures below T-b, the dielectric loss factor that is dominated by intrinsic loss is reduced when the DC field is applied. While at temperatures above T-b; the loss factor is dominated by the conduction loss and is raised by the DC field.