Currently, the development of dielectric ceramic capacitors is restricted by the contradiction between high efficiency and high recoverable density. Therefore, a novel strategy was designed to achieve a superior balance between them. Firstly, introducing Sr_0.85La_0.1TiO₃ can enhance the content of the weak polar phase (P4bm) to become the main component, which can optimize the relaxor behaviour and improve efficiency. Then, the electric breakdown strength was effectively enhanced by grain refinement and viscous polymer processing. Finally, a high recoverable energy density of ~5.3 J/cm³ and an excellent efficiency of ~92.2% were attained in 0.9Bi_0.5Na_0.5TiO₃-0.1Na_0.8Sr_0.1NbO₃ ceramic with the addition of 0.35Sr_0.85La_0.1TiO₃ after viscous polymer processing. The piezoelectric force microscope had been applied to prove the high activity of the polar nanoregions and finite element analysis was adopted to explain the reasons for the enhancing electric breakdown strength. In addition, this ceramic exhibits good temperature and frequency stability, and a fast discharging rate of 0.11 μs, making it a potential candidate for the actual application.

In the last few decades, dielectric capacitors have gotten a lot of attention because they can store more power and charge and discharge very quickly. But it has a low energy-storage density (W_rec), efficiency (η), and temperature stability. By adding Pb(Mg_1/3Nb_2/3)O₃ (PMN) and (Bi_0·1Sr_0.85)TiO₃ (BST) to a nonstoichiometric (Bi_0·51Na_0.5)TiO₃ (BNT) matrix, the goal is to change the phase transition properties and make the material more relaxor ferroelectric (RFE) by lowering the remnant polarization P_r and keeping the maximum polarization P_max. A viscous polymer process (VPP) is used to improve the electric breakdown strength, which is also a key part of being able to store energy. By working together, ceramics with the formula 0.79[0.85BNT-0.15PMN]-0.21BST (BP-0.21BST) are made. The phase structure has been changed from a rhombohedral phase to a rhombohedral-tetragonal coexisted phase. This is beneficial for RFE properties and gives a W_rec of 6.45 J/cm³ and a η of 90% at 400 kV/cm. Also, the energy-storage property is very temperature stable between 30 and 150 ℃. These results show that process optimization and composition design can be used to improve the energy storage properties, and that the dielectric ceramic materials made can be used in high-powder pulse dielectric capacitors.

Large electrostrains with high temperature stability and low hysteresis are essential for applications in high-precision actuator devices. However, achieving simultaneously all three of the aforementioned features in ferroelectric ceramics remains a considerable challenge. In this work, we firstly report a high unipolar electrostrain (0.12% at 60 kV/cm) in (1–x)NaNbO₃-x[(Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃] (NN-xBCZT) ferroelectric polycrystalline ceramics with excellent thermal stability (variation less than 10% in the temperature range of 30–160 ℃) and ultra-low hysteresis (< 6%). Secondly, the high-field electrostrain response is dominated by the intrinsic electrostrictive effect, which may account for more than 80% of the electrostrain. Furthermore, due to the thermal stability of the polarization in the pure tetragonal phase, the large electrostrain demonstrates extraordinarily high stability from room temperature to 140 ℃. Finally, in-situ piezoelectric force microscopy reveals ultra-highly stable domain structures, which also guarantee the thermal stability of the electrostrain in (NN-xBCZT ferroelectrics ceramics. This study not only clarifies the origin of thermally stable electrostrain in NN-xBCZT ferroelectric perovskite in terms of electrostrictive effect, but also provides ideas for developing applicable ferroelectric ceramic materials used in actuator devices with excellent thermal stability.

Lead-free (Bi_0.5Na_0.5)TiO₃ (BNT)-based relaxor ferroelectric (RFE) ceramics have attracted a lot of attention due to their high power density and rapid charge-discharge capabilities, as well as their potential application in pulse power capacitors. However, because of the desire for smaller electronic devices, their energy storage performance (ESP) should be enhanced even further. We describe a defect engineering strategy for enhancing the antiferroelectric-like RFE feature of BNT-based ceramics by unequal substitution of rare-earth La³⁺ in this paper. The ESP of La³⁺-doped samples is raised by 25% with the same synthetic procedure and thickness, due to an increase in the critical electric field (E-field) and saturated E-field during polarization response, which is induced by a modification in the energy barrier between the lattice torsion. More impressively, an ultrahigh recoverable energy storage density W_rec of 8.58 J/cm³ and a high energy storage efficiency η of 94.5% are simultaneously attained in 3 at.% La³⁺-substituted 0.6(Bi_0.5Na_0.4K_0.1)LaTiO₃-0.4[2/3SrTiO₃-1/3Bi(Mg_2/3Ni_1/3)O₃] RFE ceramics with good temperature stability (W_rec = 4.6 ± 0.2 J/cm³ and higher η of ≥90% from 30 ℃ to 120 ℃), frequency stability, and fatigue resistance. The significant increase in ESP achieved through defect engineering not only proves the effectiveness of our strategy, but also presents a novel dielectric material with potential applications in pulse power capacitors.

Owing to the complex composition architecture of these solid solutions, some fundamental issues of the classical (1−x)Bi_1/2Na_1/2TiO-xBi_1/2K_1/2TiO₃ (BNT-xBKT) binary system, such as details of phase evolution and optimal Na/K ratio associated with the highest strain responses, remain unresolved. In this work, we systematically investigated the phase evolution of the BNT-xBKT binary solid solution with x ranging from 0.12 to 0.24 using not only routine X-ray diffraction and weak-signal dielectric characterization, but also temperature-dependent polarization versus electric field (P-E) and current versus electric field (I-E) curves. Our results indicate an optimal Na/K ratio of 81/19 based on high-field polarization and electrostrain characterizations. As the temperature increased above 100 °C, the x = 0.19 composition produces ultrahigh electrostrains (> 0.5%) with high thermal stability. The ultrahigh and stable electrostrains were primarily due to the combined effect of electric-field-induced relaxor-to-ferroelectric phase transition and ferroelectric-to-relaxor diffuse phase transition during heating. More specifically, we revealed the relationship between phase evolution and electrostrain responses based on the characteristic temperatures determined by both weak-field dielectric and high-field ferroelectric/electromechanical property characterizations. This work not only clarifies the phase evolution in BNT-xBKT binary solid solution, but also paves the way for future strain enhancement through doping strategies.

The luminescence modulation behaviour under the in-situ electric field of rare-earth doped KSr₂Nb₅O₁₅ ceramics opened a new door for the development of dielectric materials. Where the understanding the effect of rare-earth doping on the electric properties of host, especially at the similar doping concentration with luminescence researches (low concentrations) is very important for the exploration of mechanism of electric-luminescent coupling effect. In this work, Nd³⁺-doped KSr₂Nb₅O₁₅ (KSN-xNd) ceramics were synthesized, and the electric properties were investigated systematically. Our results suggest that the Nd³⁺ doping slightly increased the phase transition temperatures and improved the piezoelectric response of KSr₂Nb₅O₁₅. Most importantly, a bidirectional dielectric tunability is revealed in KSr₂Nb₅O₁₅. The dielectric permittivity can be adjusted by the DC electric bias, with tunability ranging from −12.3% to 21.9%. The related mechanism and relationship between the bidirectional dielectric tunability and ferroelectricity are revealed by temperature-dependent dielectric and ferroelectric characterization. The researches of electric properties and bidirectional dielectric tunability of KSN-based ceramics paved the way to further exploration of electric-luminescent coupling mechanism.