Dielectric energy storage ceramics have gained significant attention in recent years as critical components in solid-state pulsed power systems. Their superior characteristics, including high energy density, rapid charge and discharge capabilities, exceptional fatigue resistance, and excellent high-temperature stability, make them ideal candidates for a wide range of applications, such as modern energy storage and power management systems. These ceramics are particularly effective in highperformance capacitors, which are essential for pulse power applications such as military defense systems, medical devices, and advanced industrial equipment. This paper provides a comprehensive overview about the influence of key technologies, including material component design and macro/micro structural design, on the energy storage performance of various dielectric materials, including linear dielectrics, ferroelectrics, relaxor ferroelectrics, and antiferroelectrics.

One of the fundamental aspects of dielectric energy storage ceramics is the material selection and component design. Linear dielectrics own the large breakdown strength with low dielectric constant and polarization, resulting in the relative low energy storage density. In contrast, ferroelectrics, which exhibit large spontaneous polarization and high dielectric constants, have shown considerable promise in improving energy density and charge/discharge efficiency. Relaxor ferroelectrics, a subclass of ferroelectrics, have demonstrated even greater potential due to their unique ability to maintain high energy storage capabilities across a wide range of temperatures and frequencies. Antiferroelectrics, which exhibit a unique electric polarization reversal under an applied electric field, offer the possibility of achieving even higher energy densities compared to the traditional ferroelectric materials.

In addition to the material composition, the microstructure of dielectric ceramics plays a crucial role in determining their energy storage performance. The optimization of the ceramic's microstructure involves controlling the grain size, porosity, and the distribution of grain boundaries, all of which can significantly influence the dielectric properties. For instance, a fine-grained microstructure can enhance the dielectric breakdown strength, thereby increasing the energy storage capacity. Moreover, tailoring the porosity of the ceramics can improve their mechanical strength and increase the charge/discharge cycling stability, which is essential for long-term use in high-power applications.

Recent advancements in dielectric energy storage ceramic systems have focused on increasing their energy density and improving their efficiency under extreme operating conditions. Research has been directed toward enhancing the dielectric properties of these materials, optimizing their charge/discharge kinetics, and improving their reliability and durability over extended cycles. Studies have also explored the incorporation of dopants, such as rare earth elements or transition metal ions, to further enhance the electrical and thermal stability of these ceramics. Furthermore, the development of new dielectric materials with tailored polarization characteristics, including high-temperature relaxor ferroelectrics and multiferroic ceramics, holds promise for achieving even higher energy densities and broader operational capabilities.

Looking to the future, the development of pulse capacitor energy storage ceramics will be driven by the need for higher performance and greater versatility in energy storage systems. As energy demands continue to rise and the need for rapid energy release becomes more critical in various applications, dielectric energy storage ceramics will play a pivotal role in the design of next-generation capacitors. Future research will likely focus on improving the materials' energy storage efficiency, expanding their application ranges, and reducing manufacturing costs. By further optimizing the microstructure and introducing novel material compositions, it is anticipated that dielectric ceramics will offer enhanced performance for a wide variety of applications, from military and defense systems to renewable energy storage and electric vehicles.

In conclusion, dielectric energy storage ceramics are positioned to remain a cornerstone of solidstate pulsed power systems due to their excellent energy storage performance and adaptability to diverse applications. With ongoing advancements in material design and manufacturing techniques, these ceramics will continue to offer the enhanced energy storage efficiency and expanded capabilities in emerging technologies, driving innovation in high-performance power systems worldwide.

With increasing awareness of environmental protection, the electrical performance and sintering process of lead-free piezoelectric ceramics are continuously optimized to replace lead-based materials. Exploring an appropriate doping strategy is believed to achieve concurrent improvements in lead-free piezoelectric ceramics. In this work, SiC was selected to optimize the phase structure, defect configuration, and morphology of (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (BCTZ) lead-free piezoelectric ceramics. On the one hand, SiC could promote the sintering process and grain growth due to its excellent thermal conductivity, resulting in the compactness and outstanding insulation of the doped ceramics. On the other hand, the incorporation of Si⁴⁺ in the B-site of the ABO₃ lattice not only deforms the crystal structure and enhances the lattice distortion but also reduces the oxygen vacancy concentration and increases the charge carrier activation energy. As a result, excellent comprehensive piezoelectric responses of piezoelectric coefficient (d₃₃) = 638 pC/N, inverse piezoelectric coefficient (d₃₃*) = 1048 pm/V, planar electromechanical coupling coefficient (k_p) = 58.21%, and Curie temperature (T_c) of ~95 °C were achieved with the optimized composition. Our work demonstrated that SiC-doped BCTZ-based ceramics are potential candidates for replacing lead-based piezoceramics.

Sodium potassium niob ate-based piezoelectric ceramics have attracted much attention due to their excellent electrical properties, which has been considered to be one of the most promising lead-free piezoelectric ceramics to replace lead-based ceramics. In this work, the influence of doping Bi_0.44Fe_0.06Ag_0.03Na_0.47ZrO₃ on the crystal structure, micro structure and electrical properties of K_0.48Na_0.52Nb_0.96Sb_0.04O₃ lead-free piezoelectric ceramics were investigated systematically. All the compositions exhibit a pure perovskite structure with rhombohedral and tetragonal coexistence. The grain size of ceramics first increases and then decreases with the increase of Bi_0.44Fe_0.06Ag_0.03Na_0.47ZrO₃. Finally, the optimal electrical performances of d₃₃ = 322pC/N, k_p = 41.34%, ε_r = 2441, tanδ = 0.036, d₃₃^* = 400pm/V, and P_r = 15.94μC/cm² were obtained by optimizing the crystal and microstructure.

The rapidly advancing energy storage performance of dielectric ceramics capacitors have garnered significant interest for applications in fast charge/discharge and high-power electronic techniques. Simultaneously improving the recoverable energy storage density W_rec and efficiency η becomes more prominent at the present time for their practical applications. Herein, a high-entropy concept is implemented on the (K_0·5Na_0.5)NbO₃ (KNN)-based ferroelectric ceramics to design the high-performance dielectric capacitors. First, the strong lattice distortion can absorb some electric energy during the electrical loading process and result in the delayed polarization saturation. Additionally, the large composition fluctuations induce the weak correlation between polar nanoregions and enhance the η. Finally, the high-entropy design and viscous polymer processing method reduce the grain size and improve the E_b. In consequence, excellent W_rec of 11.14 J/cm³ with high η of 87.1% are achieved under an electric field of 750 kV/cm in the high-entropy component. These results demonstrate that the high-entropy concept is a potential avenue to design the KNN-based high-performance dielectric energy storage capacitors.

Piezoelectric energy harvesters (PEHs) have attracted significant attention with the ability of converting mechanical energy into electrical energy and power the self-powered microelectronic components. Generally, material's superior energy harvesting performance is closely related to its high transduction coefficient (d₃₃×g₃₃), which is dependent on higher piezoelectric coefficient d₃₃ and lower dielectric constant ε_r of materials. However, the high d₃₃ and low ε_r are difficult to be simultaneously achieved in piezoelectric ceramics. Herein, lead zirconate titanate (PZT) based piezoelectric composites with vertically aligned microchannel structure are constructed by phase-inversion method. The polyvinylidene fluoride (PVDF) and carbon nanotubes (CNTs) are mixed as fillers to fabricate PZT/PVDF&CNTs composites. The unique structure and uniformly distributed CNTs network enhance the polarization and thus improve the d₃₃. The PVDF filler effectively reduce the ε_r. As a consequence, the excellent piezoelectric coefficient (d₃₃ = 595 pC/N) and relatively low dielectric constant (ε_r = 1,603) were obtained in PZT/PVDF&CNTs composites, which generated an ultra-high d₃₃×g₃₃ of 24,942 × 10⁻¹⁵ m²/N. Therefore, the PZT/PVDF&CNTs piezoelectric composites achieve excellent energy harvesting performance (output voltage: 66 V, short current: 39.22 μA, and power density: 1.25 μW/mm²). Our strategy effectively boosts the performance of piezoelectric-polymer composites, which has certain guiding significance for design of energy harvesters.

Multilayer ceramic actuator (MLCA) has been widely employed in actuators due to the large cumulative displacement under the low driving voltage. In this work, the MLCA devices consisting of a lead-free MnCO₃- and CuO-doped 0.96(K_0.48Na_0.52)(Nb_0.96Ta_0.04)O₃–0.04CaZrO₃ piezoelectric ceramics and a base nickel (Ni) metal inner electrode were well co-fired by the two-step sintering process in a reducing atmosphere. The ceramic layer/electrode interface is well-integrated and clearly continuous without distinct interdiffusion and chemical reaction, which is beneficial to the electrical reliability of the MLCA. As a result, the MLCA laminated with nine active ceramic layers obtains an ultrahigh piezoelectric coefficient d₃₃ of 3157 pC/N, about 9 times than bulk ceramics. The 0.5 mm-thick MLCA composed of a series of ~50 μm-thick ceramic layers and ~3 μm-thick Ni electrodes reaches a high 1.8 μm displacement under the low applied voltage of 200 V (the same displacement requires a voltage as high as 3700 V for ~1 mm-thick bulk ceramics). The excellent electrical performance and low-cost base electrode reveal that the (K,Na)NbO₃ (KNN)-based MLCAs are promising lead-free candidate for actuator application.

Piezoelectric energy harvesters (PEHs) fabricated using piezoceramics could convert directly the mechanical vibration energy in the environment into electrical energy. The high piezoelectric charge coefficient (d₃₃) and large piezoelectric voltage coefficient (g₃₃) are key factors for the high-performance PEHs. However, high d₃₃ and large g₃₃ are difficult to simultaneously achieve with respect to $g_{33}=d_{33}/({\epsilon }_0{\epsilon }_{\text{r}})$ and $d_{33}=2Q{\epsilon }_0{\epsilon }_{\text{r}}{P}_{\text{r}}$. Herein, the energy harvesting performance is optimized by tailoring the CaZrO₃ content in (0.964-x)(K_0.52Na_0.48)(Nb_0.96Sb_0.04)O₃ -0.036(Bi_0.5Na_0.5)ZrO₃-xCaZrO₃ ceramics. First, the doping CaZrO₃ could enhance the dielectric relaxation due to the compositional fluctuation and structural disordering, and thus reduce the domain size to ~30 nm for x = 0.006 sample. The nanodomains switch easily to external electric field, resulting in large polarization. Second, the rhombohedral-orthorhombic-tetragonal phases coexist in x = 0.006 sample, which reduces the polarization anisotropy and thus improves the piezoelectric properties. The multiphase coexistence structures and miniaturized domains contribute to the excellent piezoelectric properties of d₃₃ (354 pC/N). Furthermore, the dielectric relative permittivity (ε_r) reduces monotonously as the CaZrO₃ content increases due to the relatively low ion polarizability of Ca²⁺ and Zr⁴⁺. As a result, the optimized energy conversion coefficient (d₃₃ × g₃₃, 5508 × 10^-15 m²/N) is achieved for x = 0.006 sample. Most importantly, the assembled PEH with the optimal specimen shows the excellent output power (~48 μW) and lights up 45 red commercial light-emitting diodes (LEDs). This work demonstrates that tailoring ferroelectric/relaxor behavior in (K,Na)NbO₃-based piezoelectric ceramics could effectively enhance the electrical output of PEHs.

The ceramics of 0.96K_0.48Na_0.52Nb_(1–x)Ta_xO₃ 0.04BaZrO₃ 0.3%MnCO₃ were prepared via solid-state reaction and subsequent sintering in air and reducing atmospheres. The effects of Ta doping and sintering atmosphere on the microstructure and piezoelectric properties of ceramics were investigated. The results demonstrate that all the ceramics sintered in different atmospheres exhibit a pure perovskite structure. The phase structure of KNN-based ceramics is the coexistence of rhombohedral and orthorhombic phases. Also, the generation of oxygen vacancies is suppressed as Ta doping content is increased. When x = 0.1, the ceramics sintered in a reducing atmosphere exhibit the optimum electrical properties (i.e., d₃₃=172 pC/N, d₃₃^* =294 pm/V, k_p=24.9, ε₃₃^T=820, and tanδ=0.021), which are superior to the counterparts sintered in air atmosphere (i.e., d₃₃=142 pC/N, d₃₃^*=220 pm/V, k_p=21.1,ε₃₃^T=593, and tanδ=0.022). It is indicated that sintering in a reducing atmosphere can suppress the grain growth, thus facilitating the densification of ceramics and improving the piezoelectric properties.

The intrinsic conduction mechanism and optimal sintering atmosphere of (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (BCZT) ceramics were regulated by Mn-doping element in this work. By Hall and impedance analysis, the undoped BCZT ceramics exhibit a typical n-type conduction mechanism, and the electron concentration decreases with the increasing oxygen partial pressure. Therefore, the undoped ceramics exhibit best electrical properties (piezoelectrical constant d₃₃ = 585 pC·N^-1, electro-mechanical coupling factor k_p = 56%) in O₂. A handful of Mn-doping element would transfer the conduction mechanism from n-type into p-type. And the hole concentration reduces with the decreasing oxygen partial pressure for Mn-doped BCZT ceramics. Therefore, the Mn-doped ceramics sintered in N₂ have the highest insulation resistance and best piezoelectric properties (d₃₃ = 505 pC·N^-1, k_p = 50%). The experimental results demonstrate that the Mn-doping element can effectively adjust the intrinsic conduction mechanism and then predict the optimal atmosphere.

The thermal stability and fatigue resistance of piezoelectric ceramics are of great importance for industrialized application. In this study, the electrical properties of (0.99-x)(K_0.48Na_0.52)(Nb_0.975Sb_0.025)O₃- 0.01CaZrO₃-x(Bi_0.5Na_0.5)HfO₃ ceramics are investigated. When x = 0.03, the ceramics exhibit the optimal electrical properties at room temperature and high Curie temperature (T_C = 253 ℃). In addition, the ceramic has outstanding thermal stability (d₃^*₃ ≈ 301 pm/V at 160 ℃) and fatigue resistance (variation of P_r and d₃^*₃ ~10% after 10⁴ electrical cycles). Subsequently, the defect configuration and crystal structure of the ceramics are studied by X-ray diffraction, temperature- dielectric property curves and impedance analysis. On one hand, the doping (Bi_0.5Na_0.5)HfO₃ makes the dielectric constant peaks flatten. On the other hand, the defect concentration and migration are obviously depressed in the doped ceramics. Both of them can enhance the piezoelectrical properties and improve the temperature and cycling reliabilities. The present study reveals that the good piezoelectric properties can be obtained in 0.96(K_0.48Na_0.52)(Nb_0.975Sb_0.025)O₃-0.01CaZrO₃-0.03(Bi_0.5Na_0.5) HfO₃ ceramics.