Effects of Composition on Dielectric Properties of (Ba,Ca)(Zr,Ti)O₃ Ceramics for Energy Storage Capacitors

Ba_1−xCa_xZr_0.2Ti_0.8O₃ (x = 0, 0.05, 0.10) and Ba_0.95Ca_0.05Zr_yTi_1−yO₃ (y = 0.20, 0.25, 0.30) ceramics have been prepared by a citrate method and their structure, energy storage density, ferroelectric phase transition behavior, and dielectric nonlinearity investigated. All specimens showed cubic perovskite structure at room temperature. The energy storage density of the specimens at given electric field of 120 kV/cm was similar at around 0.40 J/cm³. In contrast, the degree of relaxor behavior of the specimens varied with changing A- or B-site composition. Compared with increasing calcium content at A-site, increasing zirconium content at B-site more readily induced pronounced relaxor behavior. The dielectric constant of the specimens under bias electric field dropped to a common level at high field. Fitting the nonlinear dielectric response under bias field using a multipolarization mechanism model resolved the contributions of various polarization mechanisms. It turned out that the extrinsic contribution of polar nanoregions faded out within the low-field range, with intrinsic lattice phonon polarization governing the overall dielectric response at high field. Moreover, characteristic parameters of the polarization mechanisms were determined from the fitting. Based on these fitting results, the differing composition dependence of the energy storage density and relaxor behavior were explained.