Ultrahigh Energy Storage Density and High Efficiency in Lead-Free (Bi0.9Na0.1)(Fe0.8Ti0.2)O3-Modified NaNbO3 Ceramics via Stabilizing the Antiferroelectric Phase and Enhancing Relaxor Behavior

Translational Antiphase Boundaries in NaNbO3 Antiferroelectrics

Planar defects are known to be of importance in affecting the functional properties of materials. Translational antiphase boundaries (APBs) in particular have attracted considerable attention in perovskite oxides, but little is known in lead-free antiferroelectric oxides that are promising candidates for energy storage applications. Here, we present a study of translational APBs in prototypical antiferroelectric NaNbO3 using aberration-corrected (scanning) transmission electron microscopy (TEM) techniques at different length scales. The translational APBs in NaNbO3 are characterized by a 2-fold-modulated structure, which is antipolar in nature and exhibits a high density, different from the polar nature and lower density in PbZrO3. The high stability of translational APBs against external electric fields and elevated temperatures was revealed using ex situ and in situ TEM experiments and is expected to be associated with their antipolar nature. Density functional theory calculations demonstrate that translational APBs possess only slightly higher free energy than the antiferroelectric and ferroelectric phase energies with differences of 29 and 33 meV/f.u., respectively, justifying their coexistence down to the nanoscale at room temperature. These results provide a detailed atomistic elucidation of translational APBs in NaNbO3 with antipolar character and stability against external stimuli, establishing the basis of defect engineering of antiferroelectrics for energy storage devices.

Giant Energy Storage Density with Antiferroelectric-Like Properties in BNT-Based Ceramics via Phase Structure Engineering

Driven by the information industry, advanced electronic devices require dielectric materials which combine both excellent energy storage properties and high temperature stability. These requirements hold the most promise for ceramic capacitors. Among these, the modulated Bi0.5 Na0.5 TiO3 (BNT)-based ceramics can demonstrate favorable energy storage properties with antiferroelectric-like properties, simultaneously, attaching superior temperature stability resulted from the high Curie temperature. Inspired by the above properties, a strategy is proposed to modulate antiferroelectric-like properties via introducing Ca0.7 La0.2 TiO3 (CLT) into Bi0.395 Na0.325 Sr0.245 TiO3 (BNST) ((1-x)BNST-xCLT, x = 0.10, 0.15, 0.20, 0.25). Combining both orthorhombic phase and defect dipole designs successfully achieve antiferroelectric-like properties in BNST-CLT ceramics. The results illustrate that 0.8BNST-0.2CLT presents superior recoverable energy storage density ≈8.3 J cm-3 with the ideal η ≈ 80% at 660 kV cm-1 . Structural characterizations demonstrate that there is the intermediate modulated phase with the coexistence of the antiferroelectric and ferroelectric phases. In addition, in situ temperature measurements prove that BNST-CLT ceramics exhibit favorable temperature stability over a wide temperature range. The present work illustrates that BNT-based ceramics with antiferroelectric-like properties can effectively enhance the energy storage performance, which provides novel perspectives for the subsequent development of advanced pulsed capacitors.

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.

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

Owing to the merits of giant power density and ultrafast charge-discharge time, dielectric capacitors including ceramics and films have inspired increasing interest lately. Nevertheless, the energy storage density of dielectric ceramics should be further optimized to cater to the boosting demand for the compact and portable electronic devices. Herein, an ultrahigh recoverable energy storage density W_rec of 13.44 J/cm³ and a high efficiency η of 90.14% are simultaneously realized in BiFeO₃-BaTiO₃-NaTaO₃ relaxor ferroelectric ceramics with high polarization P_max, reduced remanent polarization P_r, and optimized electric breakdown strength E_b. High P_max originates from the genes of BiFeO₃-based ceramics, and reduced P_r is induced by enhanced relaxor behavior. Particularly, a large E_b is achieved by the synergic contributions from complicated internal and external factors, such as decreased grain size and improved resistivity and electrical homogeneity. Furthermore, the ceramics also exhibit satisfactory frequency, cycling and thermal reliability, and decent charge-discharge property. This work not only indicates that the BiFeO₃-based relaxor ferroelectric materials are promising choices for the next-generation electrostatic capacitors but also paves a potential approach to exploit novel high-performance dielectric ceramics.