Ceramic dielectric capacitors have a broad scope of application in pulsed power supply devices. Relaxor behavior has manifested decent energy storage capabilities in dielectric materials due to its fast polarization response. In addition, an ultrahigh energy storage density can also be achieved in NaNbO₃ (NN)-based ceramics by combining antiferroelectric and relaxor characteristics. Most of the existing reports about lead-free dielectric ceramics, nevertheless, still lack the relevant research about domain evolution and relaxor behavior. Therefore, a novel lead-free solid solution, (1−x)NaNbO₃–xBi(Zn_0.5Sn_0.5)O₃ (abbreviated as xBZS, x = 0.05, 0.10, 0.15, and 0.20) was designed to analyze the domain evolution and relaxor behavior. Domain evolutions in xBZS ceramics confirmed the contribution of the relaxor behavior to their decent energy storage characteristics caused by the fast polarization rotation according to the low energy barrier of polar nanoregions (PNRs). Consequently, a high energy storage density of 3.14 J/cm³ and energy efficiency of 83.30% are simultaneously available with 0.10BZS ceramics, together with stable energy storage properties over a large temperature range (20–100 ℃) and a wide frequency range (1–200 Hz). Additionally, for practical applications, the 0.10BZS ceramics display a high discharge energy storage density (W_dis ≈ 1.05 J/cm³), fast discharge rate (t_0.9 ≈ 60.60 ns), and high hardness (H ≈ 5.49 GPa). This study offers significant insights on the mechanisms of high performance lead-free ceramic energy storage materials.

Lead-free ceramic capacitors have the application prospect in the dielectric pulse power system due to the advantages of large dielectric constant, lower dielectric loss and good temperature stability. Nevertheless, most reported dielectric ceramics have limitation of realizing large energy storage density (W_rec) and high energy storage efficiency (η) simultaneously due to the low breakdown electric field (E_b), low maximum polarization and large remanent polarization (P_r). These issues above can be settled by raising the bulk resistivity of dielectric ceramics and optimizing domain structure. Therefore, we designed a new system by doping (Bi_0.5Na_0.5)_0.7Sr_0.3TiO₃ into 0.9NaNbO₃-0.1Bi(Ni_0.5Zr_0.5)O₃ ceramics, which simultaneously obtained a higher bulk resistivity by decreasing the grain size and achieved a smaller P_r by optimizing domain structure, thus the better E_b of 530 kV/cm and W_rec of 6.43 J/cm³ were achieved, η was improved from 34% to 82%. Besides, the 0.4BNST ceramics show excellent temperature, frequency and fatigue stability under the conditions of 20–180 ℃, 1–100 Hz and 10⁴ cycles, respectively. Meanwhile, superior power density (P_D = 107 MW/cm³), large current density (C_D = 1070 A/cm²) and discharge speed (1.025 μs) were achieved in 0.4BNST ceramic. Finally, the charge-discharge performance displayed good temperature stability in the temperature range of 30 ℃–180 ℃. The above results indicated that the ceramics have potential practical value in the field of energy storage capacitor.

(Ba_1-xBi_0.67xNa_0.33x)(Ti_1-xBi_0.33xSn_0.67x)O₃ (abbreviated as BBNTBS, 0.02 ≤ x ≤ 0.12) ceramics were fabricated via a traditional solid state reaction method. The phase transition of BBNTBS from tetragonal to pseudo cubic is demonstrated by XRD and Raman spectra. The BBNTBS (x = 0.1) ceramics have decent properties with a high ε_r (~2250), small Δε/ε_25°C values of ±15% over a wide temperature range from -58 to 171 ℃, and low tanδ ≤ 0.02 from 10 to 200 ℃. The basic mechanisms of conduction and relaxation processes in the high temperature region were thermal activation, and oxygen vacancies might be the ionic charge transport carriers. Meanwhile, BBNTBS (x = 0.1) exhibited decent energy storage density (J_d = 0.58 J/cm³) and excellent thermal stability (the variation of J_d is less than 3% in the temperature range of 25-120 ℃), which could be a potential candidate for high energy density capacitors.