Significantly Enhanced Energy Storage Performance of Lead-Free BiFeO3-Based Ceramics via Synergic Optimization Strategy

High-Entropy Strategy for Improved Mechanical and Energy Storage Properties in BaTiO3-BiFeO3-Based Ceramics

Dielectric capacitors are employed extensively due to their exceptional performance, including a rapid charge-discharge speed and superior power density. However, their practical implementation is hindered by constraints in energy-storage density (ESD), efficiency (ESE), and thermal stability. To achieve domain engineering and improved relaxor behavior in 0.67BiFeO3-0.33BaTiO3-based Pb-free ceramics, the concerns have been addressed here by employing a synergistic high-entropy strategy involving the design of the composition of Sr(Mg1/6Zn1/6Ta1/3Nb1/3)O3 with B-site multielement coexistence and high configuration entropy. Remarkably, in (0.67-x)BiFeO3-0.33BaTiO3-xSr(Mg1/6Zn1/6Ta1/3Nb1/3)O3 ceramics with x = 0.08, a good ESE (η) of 75% and a recoverable ESD (Wrec) of 2.4 J/cm3 at 190 kV/cm were attained together with an ultrahigh hardness of ∼7.2 GPa. The high-entropy strategy, which is tailored by an increase in configuration entropy, can be attributed to the superior mechanical and ES properties. It also explains the enhanced random field and relaxation behavior, the structural coexistence of ferroelectric rhombohedral (R3c) and nonpolar pseudocubic (Pm-3m) symmetries, the decreased domain size, and evenly distributed polar nanoregions (PNRs). Moreover, improved thermal stability and outstanding frequency stability are also obtained. By boosting the configuration entropy, BiFeO3-BaTiO3 materials dramatically improved their complete energy storage performance. This suggests that designing high-performance dielectrics with high entropy can be a convenient yet effective technique, leading to the development of advanced capacitors.

Tailoring Phase Fraction Induced Saturation Polarization Delay for High-Performance BaTiO3-Based Relaxed Ferroelectric Capacitors

Electrostatic capacitors based on dielectric materials are essential for enabling technological advances, including miniaturization and integration of electronic devices. However, maintaining a high polarization and breakdown field strength simultaneously in electrostatic capacitors remains a major challenge for industrial applications. Herein, a universal approach to delaying saturation polarization in BaTiO3-based ceramic is reported via tailoring phase fraction to improve capacitive performance. The ceramic of 0.85(0.7BaTiO3-0.3Bi0.5Na0.5TiO3)-0.15Bi0.5Li0.5(Ti0.75Ta0.2)O3 delivers an ultrahigh recoverable energy density (Wrec) of 7.16 J cm-3 along with an efficiency (η) of approximately 90% at a breakdown electric field of 700 kV cm-1, outperforming the current BaTiO3-based ceramics and other lead-free ceramics. Meanwhile, the Wrec and η exhibit wide frequency, temperature, and cycling fatigue stability. Additionally, both an extremely fast discharge time of 115 ns and a large power density of 106.16 MW cm-3 are concurrently attained. This work offers a promising pathway for delaying saturation polarization design in order to create scalable high-energy-density ceramics capacitors and highlight the research prospects of pulse power applications.

Outstanding Energy Storage Performance of NBT-Based Ceramics under Moderate Electric Field Achieved via Antiferroelectric Engineering

Ultrahigh energy-storage performance of dielectric ceramic capacitors is generally achieved under high electric fields (HEFs). However, the HEFs strongly limit the miniaturization, integration, and lifetime of the dielectric energy-storage capacitors. Thus, it is necessary to develop new energy-storage materials with excellent energy-storage densities under moderate electric fields (MEFs). Herein, the antiferroelectric material Ag0.9Ca0.05NbO3 (ACN) was used to modify the relaxor ferroelectric material 0.6Na0.5Bi0.5TiO3-0.4Sr0.7Bi0.2TiO3 (NBT-SBT). The introduction of ACN results in high polarization strength, regulated composition of rhombohedral (R3c) and tetragonal (P4bm), nanodomains, and refined grain size. An outstanding recoverable energy density (Wrec = 4.6 J/cm3) and high efficiency (η = 82%) were realized under an MEF of 260 kV/cm in 4 mol % ACN-modified NBT-SBT ceramic. The first-principles calculation reveals that the interaction between Bi and O is the intrinsic mechanism of the increased polarization. A new parameter ΔP/Eb was proposed to be used as the figure of merit to measure the energy-storage performance under MEFs (∼200-300 kV/cm). This work paves a new way to explore energy-storage materials with excellent-performance MEFs.

Improved Electric Breakdown Strength and Energy Storage Performances in La(Mg2/3Nb1/3)O3 and MnO2-Modified BiFeO3-SrTiO3 Ceramics

Dielectric capacitors have become an important component in current pulsed power devices and thus have attracted great research interest in recent years. Among all kinds of dielectric materials, the bismuth ferrite (BiFeO₃)-based ceramic capacitors show possible applications in dielectric energy storage because of their large polarization. However, the relatively high conductivity badly limits the improvement of electric breakdown strength, thus leading to low energy density. Herein, the perovskite end-member La(Mg_2/3Nb_1/3)O₃ and sintering aid MnO₂ were simultaneously introduced into BiFeO₃-SrTiO₃ solid solutions to improve the relaxation features and electric breakdown strength. Accordingly, a high recoverable energy density of 6.3 J/cm³ and an acceptable efficiency of 74.3% were realized under 450 kV/cm. In addition, the good frequency/thermal stability and superior charge-discharge performances were also realized. This work provides feasible approaches to modify the capacitive energy storage of BiFeO₃-based relaxor ferroelectric ceramics.