Dielectric ceramic capacitors are widely used in the field of high energy pulse because of their high power density, ultra-fast charge-discharge speed and good stability. However, compared with other capacitors, the low recoverable energy storage density (W_rec) affects its development in the field of energy storage. The typical ferroelectric BaTiO₃ (BT) with good dielectric and insulation properties is restricted in the development of energy storage field due to the low breakdown strength and large residual polarization. It is indicated that the combination of multi-component solid solution and ion doping induces the polar nanoregions (PNRs) and the transformation of BaTiO₃ ceramics from ferroelectrics to relaxation ferroelectrics due to the reduction of P_r and the improvement of energy storage performance. In addition, obtaining simutanously the high W_rec and energy storage efficiency (η) is a challenge. In this paper, (1-x){0.88(Ba_0.6Ca_0.4)TiO₃-0.12Bi[Zn_2/3(Nb_0.85Ta_0.15)_1/3]O₃}-xCeO₂ (abbreviated as BCT-BZNT-xCe, x = 0, 0.010, 0.015, 0.020, 0.025) ceramics were prepared by a conventional solid-state reaction method. The structure and energy storage properties of the ceramics with differet Ce⁺⁴ doping contents were investigated.

High purity BaCO₃, CaCO₃, TiO₂, Bi₂O₃, ZnO, Nb₂O₅, Ta₂O₅ and CeO₂ were used as raw materials. The raw materials were weighted and mixed according to stoichometric ratio. The mixed raw materials were firstly ground in a ball mill, and then dried and calcined in air at 900 ℃ for 4 h. Afterwards, the calcined powder was further ground, dried and pressed into discs with 10 mm in diameter. The discs were sintered at 1 200 ℃ for 2 h to obtain the ceramic samples. The ceramic samples were thinned and polished to 0.05 mm, and sputtered with Au electrodes for the energy storage properties.

The phase structure of the samples was analyzed by a model SmartLab X-ray diffractometer (XRD, Rigaku Co., Japan) in the range of 20°-80°. The Raman spectra of the samples were analyzed by a model Renishaw inVia Laser Confocal Raman Microspectroscopy (Renishaw Co., UK). The microstructure and elemental analysis (EDS) were determined by a model Merlin Compact Field Emission Scanning Electron Microscope (FE-SEM, Zeiss Co., Germany). The dielectric properties were analyzed by a model HCT1821 High-Low Temperature Dielectric Testing System (Tongguo Technology Co., China). The unipolar P-E curves were measured by a model TF2000 ferroelectric tester (aixACCT Co., Germany) to investigate the ferroelectric performance. The pulsed performance of the samples was examined by a model CFD-003 plus high-voltage charge-discharge measuring instrument (Tongguo Technology Co., China).

All the samples are a multiphase structure with a tetragonal phase BaTiO₃ (BT) as a main phase and an orthorhombic phase CaTiO₃ (CT) as a second phase. The excessive Ce⁴⁺ causes the appearance of the diffraction peak at 28.5° of 2θwhen x=0.025. Also, the diffraction peaks move to a low angle from the magnified (200). The minimum average grain size (AGS) of both coarse and fine grains is obtained when x=0.02. The BCT-BZNT-0.02Ce ceramic obtains a high breakdown strength. The EDS analysis indicates that the coarse grains contain more Ba, while the fine grains contain more Ca.

The dielectric permittivity of samples decreases with increasing the frequency. A large valence difference betweent the A-site and B-site ions induces PNRs, having a typical relaxation behavior. Besides, the diffuseness parameter (γ) as x=0.02 is the maximum value (i.e., 1.917), which is similar to that of the ideal relaxation ferroelectric. The unipolar P-E curves of all the samples are slender and exhibit good relaxation characteristics. The breakdown strength and maximum polarization strength (P_max) increase with the increase of Ce content, and reach the maximum values as x=0.02. A high W_rec of 5.49 J/cm³ and a high η of 89.4% are obtained at 600 kV/cm in BCT-BZNT-0.02Ce ceramic, which is attributed to the increasse of breakdown strength and P_max. Moreover, the superior charge-discharge performance is obtained in BCT-BZNT-0.02Ce ceramic. The ultra-high current density (i.e., C_D=1 757.07 A/cm²) and power density (i.e., P_D=237.20 MW/cm³) are obtained at 270 kV/cm. Besides, a discharge energy density (W_D) of 1.55 J/cm³ and an ultra-fast charge-discharge speed (t_0.9) of 23.8 ns are obtained simultaneously. The W_D is smaller than the W_rec due to the unremarkable contribution of domain wall motion at higher frequencies from the perspective of dynamics. The BCT-BZNT-0.02Ce ceramic with ultra-high W_rec (5.49 J/cm³), η (89.4%), C_D (1 757.07 A/cm²), P_D (237.20 MW/cm³) and ultra-fast t_0.9 (23.8 ns) can be used in pulsed capacitors.

The grains size of BCT-BZNT-xCe ceramics was refined via the introduction of rare-earth element Ce. The γ of the BCT-BZNT-xCe ceramics was improved, and the BCT-BZNT-0.02Ce ceramic showed a typical relaxation ferroelectric performance (i.e., γ =1.917). The superior energy storage performance (i.e., W_rec=5.49 J/cm³, η=89.4%) of BCT-BZNT-0.02Ce ceramic was achieved at 600 kV/cm at room temperature due to the breakdown strength and P_max. Also, the BCT-BZNT-0.02Ce ceramic exhibited a superior charge-discharge performance (i.e., C_D=1 757.07 A/cm², P_D=237.20 MW/cm³, and t_0.9=23.8 ns). The BCT-BZNT-0.02Ce ceramic with the superior comprehensive properties could have a great application prospect in pulsed capacitors.