The ever-growing global energy demand has driven a surge of research interest in the field of energy harvesting and conversion. Among them, high-power force-electric energy conversion devices based on charge storage via the polarization effect of ferroelectric (FE) materials have attracted tremendous interest for specialized applications, owing to their superiorities of long shelf life, ultrafast response, and high current/voltage output. Nevertheless, the prevailing bottleneck hindering the development and practical deployment of such energy storage systems lies in the low remanent polarization (P_r) and insufficient thermal stability of most state-of-the-art lead-free ferroelectric materials. In this work, a synergistic optimization strategy of composition-driven structural distortions and defect-induced pinning effects via silver niobate (AN) and MnCO₃ doping is applied to bismuth sodium titanate (BNT)-based ferroelectric ceramics. The optimized 0.98Bi_0.5Na_0.5TiO₃-0.02AgNbO₃-0.20 wt.% MnCO₃ lead-free ferroelectric ceramics exhibit a significantly enhanced P_r and thermal stability, achieving an ultrahigh P_r of 52.21 μC/cm² and excellent stability up to 160 °C. The practical benefits of this synergistic strategy are exhibited in force-electric energy conversion application. The multilayer ceramic capacitors (MLCCs-BNT) release a record-breaking peak pulse current of 90 A via pressure-induced phase transition from ferroelectric R3c phase to nonpolar Pnma phase. The proposed strategy provides a highly feasible approach for enhancing the ferroelectricity and thermal stability of lead-free ferroelectric materials, thereby establishing a solid material foundation for the high-power force-electric energy conversion application.

Bi_0.5Na_0.5TiO₃ (BNT) has received much attention because of its excellent dielectric properties for pulsed power systems. Most of the work has focused on inducing the relaxation behavior of BNT-based materials by doping with multiple elements, but the preparation method is complicated because a high maximum polarization (P_max) is sacrificed, which affects the energy storage properties. In this work, we induced antiferroelectric-like relaxor behavior by replacing Bi³⁺ with the single rare-earth ion Pr³⁺ to obtain highly active polar nanoregions (PNRs) that increase the energy storage efficiency (ƞ). In addition, the 6s² lone pair of electrons of Pr³⁺ can produce large ionic displacements similar to those of Bi³⁺. This could maintain the contribution of the A-site polarization to possess large P_max. Moreover, the high energy gap (E_g) and reliability increase the breakdown electric field (E_b). Consequently, the ultrahigh recoverable energy storage density (W_rec) of 11.01 J/cm³ at 552 kV/cm and η of 86.7% are achieved with (Bi_0.5−xPr_xNa_0.5)TiO₃ component (BPNT-18), which is superior to many other multielement components. It also has fast charging and discharging speeds (t_0.9 ≈ 37 ns) and high power densities (P_D ≈ 312 MW/cm³). This research proposes a simple and effective approach in which a single element is used to obtain excellent energy storage performance in lead-free dielectric ceramics.

Multilayer ceramic capacitors (MLCCs) play a crucial role in pulsed power applications because of their rapid charge/discharge capabilities. However, the combination of high energy density and high efficiency is the main challenge in practical applications. This study presents barium titanate-based (BaTiO₃-) lead-free relaxor ferroelectric (RFE) MLCCs formulated with 0.84BaTiO₃–0.16Bi(Mg_0.2Ni_0.2Zn_0.2Zr_0.2Nb_0.2)O₃ (0.84BT–0.16BMNZZN) and platinum inner electrodes via a tape-casting method. The introduction of the high-entropy component BMNZZN effectively enhances the relaxation behavior and local nanodomains while promoting grain refinement, resulting in a comprehensive improvement in insulation performance and energy storage performance. As a result, MLCCs exhibit excellent recoverable energy density (W_rec = 15.7 J∙cm⁻³) and ultrahigh efficiency (η) of 96.4% (@1614 kV∙cm⁻¹), simultaneously showing good temperature stability over a range of −120‒100 °C (W_rec ≈ 8.9 J∙cm⁻³ with a variation of less than ±4.85%, @1078 kV∙cm⁻¹) and excellent fatigue resistance (W_rec ≈ 9.2 J∙cm⁻³ with a variation of less than ±0.82% over 10⁷ cycles, and η greater than 95%, @1078 kV∙cm⁻¹). These findings indicate that BT–BMNZZN RFE MLCCs offer a viable solution for high-power energy storage capacitors.

Zirconate-based dielectric ceramics are potential materials for base metal electrode multilayer ceramic capacitors (BME-MLCCs) due to their exceptional chemical and thermal stability, as well as excellent dielectric properties. In this work, (Sr_0.7Ca_0.3)_1.02(Zr_0.95−xTi_0.05Mn_x)O_3+δ (SCZTM, 0 ≤ x ≤ 0.05) ceramics with two coexisting phases were prepared using a solid-state reaction method in a reducing atmosphere. This study investigates the impact of Mn doping on sintering temperature, microstructure, and electrical properties of SCZTM ceramics. Mn doping can reduce the sintering temperature from 1450 to 1300 °C. The impact of Mn doping on the structure and phonon vibration is minimal, resulting in a negligible effect on the intrinsic loss. The valence states of Mn ions and defects were characterized by X-ray photoelectron spectroscopy (XPS) and thermally stimulated depolarization current (TSDC) analysis. The results demonstrate the significant role of Mn doping in nonintrinsic loss. Due to the decrease in the concentration of oxygen vacancies ( ${\mathrm{V}}_{\mathrm{O}}^{\cdot \cdot }$), SCZTM (x = 0.01) ceramics exhibit attractive properties: resistivity (ρ) = 8.93×10¹⁴ Ω·cm, dielectric constant (ε_r) = 36.16, dielectric loss (tanδ) = 2.43×10^–4, temperature dependence of dielectric constant (τ_ε) = 15.44 ppm/°C (@−55–200 °C, 1 MHz), Q×f = 30,257 GHz (@6.12 GHz), and temperature coefficient of resonant frequency (τ_f) = –9.9 ppm/°C. SCZTM (x = 0.01) ceramic powders were used to successfully fabricate Ni-based multilayer ceramic capacitors (MLCCs) with a high insulation resistance of IR ≥ 39.6 TΩ, an ultralow dielectric loss of tanδ = 0.2×10^–4, and a wide operating temperature range (temperature coefficient of capacitance (T_cc) = 10.88 ppm/°C, @−55–200 °C, 1 MHz). SCZTM ceramics exhibit properties that make them suitable for use as BME-MLCC materials with potential market applications.

AgNbO₃ (AN) and modified AgNbO₃ have been extensively investigated as promising lead-free antiferroelectric (AFE) energy storage materials. Previous studies have focused mainly on the use of an ion dopant at the A/B site to obtain a stabilized AFE phase; however, simultaneous improvements in the recoverable energy storage density (W_rec) and efficiency (η) are still difficult to realize. Herein, we innovatively constructed a AgNbO₃–NaNbO₃–(Sr_0.7Bi_0.2)TiO₃ (AN–NN–SBT) ternary solid solution to achieve a relaxor AFE in AgNbO₃-based materials. The coexistence of antiferroelectric (M₃) and paraelectric (O) phases in 0.8(0.7AgNbO₃–0.3NaNbO₃)–0.2(Sr_0.7Bi_0.2)TiO₃ confirms the successful realization of a relaxor AFE, attributed to multiple ion occupation at the A/B sites. Consequently, a high W_rec of 7.53 J·cm⁻³ and η of 74.0% are acquired, together with superior stability against various temperatures, frequencies, and cycling numbers. Furthermore, a high power density (298.7 MW·cm⁻³) and fast discharge speed (41.4 ns) are also demonstrated for the AgNbO₃-based relaxor AFE. This work presents a promising energy storage AgNbO₃-based ternary solid solution and proposes a novel strategy for AgNbO₃-based energy storage via the design of relaxor AFE materials.

The lead-free 0.96NaNbO₃-0.04CaSnO₃ ceramics with rare-earth dopants (La, Sm and Lu) (NCLn100x) were prepared and characterized. It is found that a certain amount of La substitution stabilizes the antiferroelectric (AFE) phase but alleviates the lattice distortion in the fresh samples. Re-entrant-like characteristics are observed in the temperature – dielectric constant curves with the room temperature P phase gradually replaced by a possible R phase. Relaxor-like hysteresis loops with suppressed hysteresis loss and remanent polarization were obtained at high La content, achieving a relatively high W_re of 2.1 J/cm³ at a low electric field (250 kV/cm). The relaxation behaviors of the ferroelectric (FE) domain measured by piezoresponse force microscopy suggest an even long characteristic relaxation time of field-induced FE phase, which is different from the situations of other AFE perovskites. Via an explanatory defected diatomic chain model, we propose that a much larger mass of substitutive ion than the origin one helps to induce low-frequency localized mode, which is believed to be in favor of the formation of polar nano-regions and hence strengthens the dynamic stability of FE phase during electric field loading. Our research provides a further understanding of the tuning strategy for enhancing the antiferroelectricity of the NaNbO₃-based system.