Antiferroelectric (AFE) materials are promising for the applications in advanced high-power electric and electronic devices. Among them, AgNbO₃ (AN)-based ceramics have gained considerable attention due to their excellent energy storage performance. Herein, multiscale synergistic modulation is proposed to improve the energy storage performance of AN-based materials, whereby the multilayer structure is employed to improve the breakdown strength (E_b), and Sm/Ta doping is utilized to enhance the AFE stability. As a result, ultrahigh recoverable energy storage density (W_rec) up to 15.0 J·cm⁻³ and energy efficiency of 82.8% are obtained at 1500 kV·cm⁻¹ in Sm/Ta co-doped AN multilayer ceramic capacitor (MLCC), which are superior to those of the state-of-the-art AN-based ceramic capacitor. Moreover, the discharge energy density (W_d) in direct-current charge–discharge performance reaches 9.1 J·cm⁻³, which is superior to that of the reported lead-free energy storage systems. The synergistic design of composition and multilayer structure provides an applicable method to optimize the energy storage performance in all dielectric energy storage systems.

Lead-free antiferroelectric ceramics with high energy storage performance show great potential in pulsed power capacitors. However, poor breakdown strength and antiferroelectric stability are the two main drawbacks that limit the energy storage performance of antiferroelectric ceramics. Herein, high-quality (Ag_1-xNa_x)(Nb_1-xTa_x)O₃ ceramics were prepared by the tape casting process. The breakdown strength was greatly improved as a result of the high density and fine grains, while the antiferroelectric stability was enhanced owning to the M₂ phase. Benefiting from the synergistic improvement in breakdown strength and antiferroelectric stability, (Ag_0.80Na_0.20)(Nb_0.80Ta_0.20)O₃ ceramic reveals a benign energy storage performance of W_rec = 5.8 J/cm³ and η = 61.7% with good temperature stability, frequency stability and cycling reliability. It is also found that the high applied electric field can promote the M₂-M₃ phase transition, which may provide ideas to improve the thermal stability of the energy storage performance in AgNbO₃-based ceramics.

AgNbO₃ is an antiferroelectric (AFE) material with double hysteresis loop. Both the antiferroelectricity and ferroelectricity can be enhanced by doping. Herein, the ferroelectricity of AgNbO₃ ceramics was enhanced via K-doping and the phase diagram of the (Ag_1-xK_x)NbO₃ ceramics was upgraded. In details, (Ag_1-xK_x)NbO₃ ceramics are ferrielectric (FIE) M₁ phase as x = 5.00–5.50 mol% and ferroelectric (FE) O phase as x = 5.75–6.00 mol% before poling, and FE O phase as x = 5.00–6.00 mol% after poling at room temperature. With increasing temperature, (Ag_1-xK_x)NbO₃ ceramics show the phase evolutions from FIE M₁, AFE M₂ to paraelectric (PE) T phase at x = 5.00–5.50 mol% and from FE O, FE T to PE T phase at x = 5.75–6.00 mol% before poling, and from FE O, FE T to PE T phase at x = 5.00–6.00 mol% after poling. High d₃₃ values of 180 pC/N and 285 pC/N are obtained at the FE O-FE T and FE T-PE T phase boundaries. This work sheds light on a novel and promising lead-free piezoelectric system.

NaNbO₃-based ceramics usually show ferroelectric-like P-E loops at room temperature due to the irreversible transformation of the antiferroelectric orthorhombic phase to ferroelectric orthorhombic phase, which is not conducive to energy storage applications. Our previous work found that incorporating CaHfO₃ into NaNbO₃ can stabilize its antiferroelectric phase by reducing the tolerance factor (t), as indicated by the appearance of characteristic double P-E loops. Furthermore, a small amount of MnO₂ addition effectively regulate the phase structure and tolerance factor of 0.94NaNbO₃-0.06CaHfO₃ (0.94NN-0.06CH), which can further improve the stability of antiferroelectricity. The XRD and XPS results reveal that the Mn ions preferentially replace A-sites and then B-sites as increasing MnO₂. The antiferroelectric orthorhombic phase first increases and then decreases, while the t shows the reversed trend, thus an enhanced antiferroelectricity and the energy storage density W_rec of 1.69 J/cm³ at 240 kV/cm are obtained for 0.94NN-0.06CH-0.5%MnO₂(in mass fraction). With the increase of Mn content to 1.0 % from 0.5 %, the efficiency increases to 81 % from 45 %, although the energy storage density decreases to 1.31 J/cm³ due to both increased tolerance factor and non-polar phase.