Giant energy density and high efficiency achieved in bismuth ferrite-based film capacitors via domain engineering

Enhanced Energy Storage Properties of Highly Polarized BMT-Based Thin Films through the Multiscale Structure Synergistic Regulation Strategy

For solving the trade-off relationship of the polarization and breakdown electric field, ferroelectric films with high polarization are playing a critical role in energy storage capacitor applications, especially at moderate/low electric fields. In this work, we propose a multiscale structure (including defect, domain, and grain structures) synergetic optimization strategy to optimize the polarization behavior and energy storage performances of BiMg0.5Ti0.5O3 (BMT) ferroelectric films by introducing Sr0.7La0.2TiO3 (SLT) without compromising the breakdown strength. At a moderate electric field of 2917 kV/cm, a high discharge density of 72.2 J/cm3 has been achieved in 0.9BMT-0.1SLT films, together with good frequency, thermal, and cycle stabilities for energy storage. Importantly, the phase difference Δφ is utilized to quantitatively evaluate the polarization switching mobility of the ferroelectric domain/PNRs at an external electric field stimulation. This research demonstrates that a multiscale structure optimization strategy could effectively regulate the energy storage performance, and ecofriendly BMT-based materials are promising candidates for next-generation energy storage capacitors, especially at moderate/low electric fields.

Metadielectrics for high-temperature energy storage capacitors

Dielectric capacitors are highly desired for electronic systems owing to their high-power density and ultrafast charge/discharge capability. However, the current dielectric capacitors suffer severely from the thermal instabilities, with sharp deterioration of energy storage performance at elevated temperatures. Here, guided by phase-field simulations, we conceived and fabricated the self-assembled metadielectric nanostructure with HfO2 as second-phase in BaHf0.17Ti0.83O3 relaxor ferroelectric matrix. The metadielectric structure can not only effectively increase breakdown strength, but also broaden the working temperature to 400 oC due to the enhanced relaxation behavior and substantially reduced conduction loss. The energy storage density of the metadielectric film capacitors can achieve to 85 joules per cubic centimeter with energy efficiency exceeding 81% in the temperature range from 25 °C to 400 °C. This work shows the fabrication of capacitors with potential applications in high-temperature electric power systems and provides a strategy for designing advanced electrostatic capacitors through a metadielectric strategy.

Partitioning polar-slush strategy in relaxors leads to large energy-storage capability

Relaxor ferroelectric (RFE) films are promising energy-storage candidates for miniaturizing high-power electronic systems, which is credited to their high energy density (Ue) and efficiency. However, advancing their Ue beyond 200 joules per cubic centimeter is challenging, limiting their potential for next-generation energy-storage devices. We implemented a partitioning polar-slush strategy in RFEs to push the boundary of Ue. Guided by phase-field simulations, we designed and fabricated high-performance Bi(Mg0.5Ti0.5)O3-SrTiO3-based RFE films with isolated slush-like polar clusters, which were realized through suppression of the nonpolar cubic matrix and introduction of highly insulating networks. The simultaneous enhancement of the reversible polarization and breakdown strength leads to a Ue of 202 joules per cubic centimeter with a high efficiency of ~79%. The proposed strategy provides a design freedom for next-generation high-performance dielectrics.

Polymorphic Heterogeneous Polar Structure Enabled Superior Capacitive Energy Storage in Lead-Free Relaxor Ferroelectrics at Low Electric Field

High-performance energy storage dielectrics capable of low/moderate field operation are vital in advanced electrical and electronic systems. However, in contrast to achievements in enhancing recoverable energy density (Wrec), the active realization of superior Wrec and energy efficiency (η) with giant energy-storage coefficient (Wrec/E) in low/moderate electric field (E) regions is much more challenging for dielectric materials. Herein, lead-free relaxor ferroelectrics are reported with giant Wrec/E designed with polymorphic heterogeneous polar structure. Following the guidance of Landau phenomenological theory and rational composition construction, the conceived (Bi0.5Na0.5)TiO3-based ternary solid solution that delivers giant Wrec/E of ≈0.0168 µC cm-2, high Wrec of ≈4.71 J cm-3 and high η of ≈93% under low E of 280 kV cm-1, accompanied by great stabilities against temperature/frequency/cycling number and excellent charging-discharging properties, which is ahead of most currently reported lead-free energy storage bulk ceramics measured at same E range. Atomistic observations reveal that the correlated coexisting local rhombohedral-tetragonal polar nanoregions embedded in the cubic matrix are constructed, which enables high polarization, minimized hysteresis, and significantly delayed polarization saturation concurrently, endowing giant Wrec/E along with high Wrec and η. These findings advance the superiority and feasibility of polymorphic nanodomains in designing highly efficient capacitors for low/moderate field-region practical applications.

Generative learning facilitated discovery of high-entropy ceramic dielectrics for capacitive energy storage

Dielectric capacitors offer great potential for advanced electronics due to their high power densities, but their energy density still needs to be further improved. High-entropy strategy has emerged as an effective method for improving energy storage performance, however, discovering new high-entropy systems within a high-dimensional composition space is a daunting challenge for traditional trial-and-error experiments. Here, based on phase-field simulations and limited experimental data, we propose a generative learning approach to accelerate the discovery of high-entropy dielectrics in a practically infinite exploration space of over 1011 combinations. By encoding-decoding latent space regularities to facilitate data sampling and forward inference, we employ inverse design to screen out the most promising combinations via a ranking strategy. Through only 5 sets of targeted experiments, we successfully obtain a Bi(Mg0.5Ti0.5)O3-based high-entropy dielectric film with a significantly improved energy density of 156 J cm-3 at an electric field of 5104 kV cm-1, surpassing the pristine film by more than eight-fold. This work introduces an effective and innovative avenue for designing high-entropy dielectrics with drastically reduced experimental cycles, which could be also extended to expedite the design of other multicomponent material systems with desired properties.

Ceramic-Based Dielectric Materials for Energy Storage Capacitor Applications

Materials offering high energy density are currently desired to meet the increasing demand for energy storage applications, such as pulsed power devices, electric vehicles, high-frequency inverters, and so on. Particularly, ceramic-based dielectric materials have received significant attention for energy storage capacitor applications due to their outstanding properties of high power density, fast charge-discharge capabilities, and excellent temperature stability relative to batteries, electrochemical capacitors, and dielectric polymers. In this paper, we present fundamental concepts for energy storage in dielectrics, key parameters, and influence factors to enhance the energy storage performance, and we also summarize the recent progress of dielectrics, such as bulk ceramics (linear dielectrics, ferroelectrics, relaxor ferroelectrics, and anti-ferroelectrics), ceramic films, and multilayer ceramic capacitors. In addition, various strategies, such as chemical modification, grain refinement/microstructure, defect engineering, phase, local structure, domain evolution, layer thickness, stability, and electrical homogeneity, are focused on the structure-property relationship on the multiscale, which has been thoroughly addressed. Moreover, this review addresses the challenges and opportunities for future dielectric materials in energy storage capacitor applications. Overall, this review provides readers with a deeper understanding of the chemical composition, physical properties, and energy storage performance in this field of energy storage ceramic materials.

Programming Polarity Heterogeneity of Energy Storage Dielectrics by Bidirectional Intelligent Design

Dielectric capacitors, characterized by ultra-high power densities, are considered as fundamental energy storage components in electronic and electrical systems. However, synergistically improving energy densities and efficiencies remains a daunting challenge. Understanding the role of polarity heterogeneity at the nanoscale in determining polarization response is crucial to the domain engineering of high-performance dielectrics. Here, a bidirectional design with phase-field simulation and machine learning is performed to forward reveal the structure-property relationship and reversely optimize polarity heterogeneity to improve energy storage performance. Taking BiFeO3-based dielectrics as typical systems, this work establishes the mapping diagrams of energy density and efficiency dependence on the volume fraction, size and configuration of polar regions. Assisted by CatBoost and Wolf Pack algorithms, this work analyzes the contributions of geometric factors and intrinsic features and find that nanopillar-like polar regions show great potential in achieving both high polarization intensity and fast dipole switching. Finally, a maximal energy density of 188 J cm-3 with efficiency above 95% at 8 MV cm-1 is obtained in BiFeO3-Al2O3 systems. This work provides a general method to study the influence of local polar heterogeneity on polarization behaviors and proposes effective strategies to enhance energy storage performance by tuning polarity heterogeneity.

High energy density in artificial heterostructures through relaxation time modulation

Electrostatic capacitors are foundational components of advanced electronics and high-power electrical systems owing to their ultrafast charging-discharging capability. Ferroelectric materials offer high maximum polarization, but high remnant polarization has hindered their effective deployment in energy storage applications. Previous methodologies have encountered problems because of the deteriorated crystallinity of the ferroelectric materials. We introduce an approach to control the relaxation time using two-dimensional (2D) materials while minimizing energy loss by using 2D/3D/2D heterostructures and preserving the crystallinity of ferroelectric 3D materials. Using this approach, we were able to achieve an energy density of 191.7 joules per cubic centimeter with an efficiency greater than 90%. This precise control over relaxation time holds promise for a wide array of applications and has the potential to accelerate the development of highly efficient energy storage systems.

High Energy Density Achieved in Novel Lead-Free BiFeO3-CaTiO3 Ferroelectric Ceramics for High-Temperature Energy Storage Applications

The development of high-performance electrostatic energy storage dielectrics is essential for various applications such as pulsed-power technologies, electric vehicles (EVs), electronic devices, and the high-temperature aviation sector. However, the usage of lead as a crucial component in conventional high-performance dielectric materials has raised severe environmental concerns. As a result of this, there is an urgent need to explore lead-free alternatives. Ferroelectric ceramics offer high energy density but lack stability at high temperatures. Here we present a lead-free (1 - x)BiFeO3-xCaTiO3 (x = 0.6, 0.7, and 0.8; BFO-CTO) ceramic capacitor with low dielectric loss, high thermal stability, and high energy density up to ∼200 °C. The introduction of CTO (x = 0.7) to the BFO matrix triggers a transition from the normal ferroelectrics to the relaxor ferroelectrics state, resulting in a high recoverable energy density of 1.18 J cm-3 at 190 °C with an ultrafast dielectric relaxation time of 44 μs. These results offer a promising, environmentally friendly, high-capacity ceramic capacitor material for high-frequency and high-temperature applications.

Ultrahigh-Efficiency Superior Energy Storage in Lead-Free Films with a Simple Composition

Dielectric capacitors are highly desired in modern electronic devices and power systems to store and recycle electric energy. However, achieving simultaneous high energy density and efficiency remains a challenge. Here, guided by theoretical and phase-field simulations, we are able to achieve a superior comprehensive property of ultrahigh efficiency of 90-94% and high energy density of 85-90 J cm-3 remarkably in strontium titanate (SrTiO3), a linear dielectric of a simple chemical composition, by manipulating local symmetry breaking through introducing Ti/O defects. Atomic-scale characterizations confirm that these Ti/O defects lead to local symmetry breaking and local lattice strains, thus leading to the formation of the isolated ultrafine polar nanoclusters with varying sizes from 2 to 8 nm. These nanoclusters account for both considerable dielectric polarization and negligible polarization hysteresis. The present study opens a new realm of designing high-performance dielectric capacitors utilizing a large family of readily available linear dielectrics with very simple chemistry.

Multifunctional Flexible Ferroelectric Thin Films with Large Electrocaloric Effect and High Energy Storage Performance

Flexible ferroelectric films with high polarization hold great promise for energy storage and electrocaloric (EC) refrigeration. Herein, we fabricate a lead-free Mn-modified 0.75 Bi(Mg0.5Ti0.5)O3-0.25 BaTiO3 (BMT-BTO) thin film based on a flexible mica substrate. Excellent EC performance with maximum adiabatic temperature change (ΔT ∼23.5 K) and isothermal entropy change (ΔS ∼33.1 J K-1 kg-1) is achieved in the flexible BMT-BTO film, which is attributed to the local structural transition and lattice disorder near 90 °C. Meanwhile, a good energy storage density of ∼70.6 J cm-3 and a quite high efficiency of ∼82% are realized in the same ferroelectric film, accompanied by excellent stability of frequency and electric fatigue (500-10 kHz and 108 cycles). Furthermore, there is no apparent variation in performance under different bending strains. These prominent properties indicate that the multifunctional BMT-BTO ferroelectric film is a promising candidate for applications of flexible energy storage and EC refrigeration.

A Superparaelectric State in Relaxor Ferroelectric (Sr,Bi)TiO3-Bi(Mg,Ti)O3-Modified BaTiO3 Ceramics to Achieve High Energy Storage Performance

Dielectric ceramic capacitors are highly regarded for their rapid charge-discharge, high power density, and cyclability in various advanced applications. However, their relatively low energy storage density has prompted intensive research aiming at developing materials with a higher energy density. To enhance energy storage properties, research has focused on modifying ferroelectric materials to induce relaxor ferroelectricity. The present study aims to induce a superparaelectric (SPE) state in relaxor ferroelectrics near room temperature by altering BaTiO3 ferroelectric ceramics using the (Sr,Bi)TiO3-Bi(Mg0.5Ti0.5)O3 system ((1-x)BT-x(SBT-BMT)). X-ray diffraction and Raman spectroscopy analysis demonstrated a shift in the crystal structure from tetragonal to cubic with an increasing x content. Notably, the compositions (except x = 0.1) satisfied the criteria for the SPE state manifestation near room temperature. The x = 0.2 specimen displayed characteristics at the boundary between the relaxor ferroelectric and SPE phases, while x ≥ 0.3 specimens exhibited increased SPE state fractions. Despite reduced maximum polarization, x ≥ 0.3 specimens showcased impressive energy storage capabilities, attributed to the enhanced SPE state, especially for x = 0.3, with impressive characteristics: a recoverable energy density (Wrec) of ~1.12 J/cm3 and efficiency (η) of ~94% at 170 kV/cm applied field. The good stability after the charge-discharge cycles reinforces the significance of the SPE phase in augmenting energy storage in relaxor ferroelectric materials, suggesting potential applications in high-energy density storage devices.

Ultrahigh Energy Storage in Tungsten Bronze Dielectric Ceramics Through a Weakly Coupled Relaxor Design

Dielectric energy-storage capacitors, known for their ultrafast discharge time and high-power density, find widespread applications in high-power pulse devices. However, ceramics featuring a tetragonal tungsten bronze structure (TTBs) have received limited attention due to their lower energy-storage capacity compared to perovskite counterparts. Herein, a TTBs relaxor ferroelectric ceramic based on the Gd0.03 Ba0.47 Sr0.485-1.5 x Smx Nb2 O6 composition, exhibiting an ultrahigh recoverable energy density of 9 J cm-3 and an efficiency of 84% under an electric field of 660 kV cm-1 is reported. Notably, the energy storage performance of this ceramic shows remarkable stability against frequency, temperature, and cycling electric field. The introduction of Sm3+ doping is found to create weakly coupled polar nanoregions in the Gd0.03 Ba0.47 Sr0.485 Nb2 O6 ceramic. Structural characterizations reveal that the incommensurability parameter increases with higher Sm3+ content, indicative of a highly disordered A-site structure. Simultaneously, the breakdown strength is also enhanced by raising the conduction activation energy, widening the bandgap, and reducing the electric field-induced strain. This work presents a significant improvement on the energy storage capabilities of TTBs-based capacitors, expanding the material choice for high-power pulse device applications.

Lateral electric field switching in thin ferroelectric nematic liquid crystal cells

This study shows that, in cells with small thicknesses, the permanent polarization in the ferroelectric nematic phase of RM734 is aligned in the direction opposite to the rubbing direction. The electrode configuration induces an in-plane field near one substrate and a normal field near the other substrate. At low voltages, the permanent polarization rotates parallel to the substrate plane when its original orientation is at an angle with the electric field. The rotation occurs over a distance of more than 100 μm, where the applied electric field is very small. At higher voltages, the polarization aligns perpendicularly to the substrates under the influence of the transverse electric field. After removing the voltage, sometimes a slow reorientation of the polarization can be observed, which is ascribed to the slow release of ionic species. The results provide insight into the complex mechanisms that are involved in the switching of ferroelectric nematic liquid crystals.

High Entropy Nonlinear Dielectrics with Superior Thermally Stable Performance

A high configurational entropy, achieved through a proper design of compositions, can minimize the Gibbs free energy and stabilize the quasi-equilibrium phases in a solid-solution form. This leads to the development of high-entropy materials with unique structural characteristics and excellent performance, which otherwise could not be achieved through conventional pathways. This work develops a high-entropy nonlinear dielectric system, based on the expansion of lead magnesium niobate-lead titanate. A dense and uniform distribution of nano-polar regions is observed in the samples owing to the addition of Ba, Hf, and Zr ions, which lead to enhanced performance of nonlinear dielectrics. The fact that no structural phase transformation is detected up to 250 °C, and no noticeable change or a steep drop in structural and electrical characteristics is observed at high temperatures suggests a robust thermal stability of the dielectric systems developed. With these advantages, these materials hold vast potential for applications such as dielectric energy storage, dielectric tunability, and electrocaloric effect. Thus, this work offers a new high-entropy configuration with elemental modulation, with enhanced dielectric material features.

Giant Energy Density via Mechanically Tailored Relaxor Ferroelectric Behavior of PZT Thick Film

Relaxor ferroelectrics (RFEs) are being actively investigated for energy-storage applications due to their large electric-field-induced polarization with slim hysteresis and fast energy charging-discharging capability. Here, a novel nanograin engineering approach based upon high kinetic energy deposition is reported, for mechanically inducing the RFE behavior in a normal ferroelectric Pb(Zr0.52 Ti0.48 )O3 (PZT), which results in simultaneous enhancement in the dielectric breakdown strength (EDBS ) and polarization. Mechanically transformed relaxor thick films with 4 µm thickness exhibit an exceptional EDBS of 540 MV m-1 and reduced hysteresis with large unsaturated polarization (103.6 µC cm-2 ), resulting in a record high energy-storage density of 124.1 J cm-3 and a power density of 64.5 MW cm-3 . This fundamental advancement is correlated with the generalized nanostructure design that comprises nanocrystalline phases embedded within the amorphous matrix. Microstructure-tailored ferroelectric behavior overcomes the limitations imposed by traditional compositional design methods and provides a feasible pathway for realization of high-performance energy-storage materials.

AgNbO3-Based Multilayer Capacitors: Heterovalent-Ion-Substitution Engineering Achieves High Energy Storage Performances

The demand for miniaturization and integration in next-generation advanced high-/pulsed-power devices has resulted in a strong desire for dielectric capacitors with high energy storage capabilities. However, practical applications of dielectric capacitors have been hindered by the challenge of poor energy-storage density (Urec) and efficiency (η) caused by large remanent polarization (Pr) and low breakdown strength (BDS). Herein, we take a method of heterovalent ion substitution engineering in combination with the multilayer capacitor (MLCC) technology and thus achieve a large maximum polarization (Pmax), zero Pr, and high BDS in the AgNbO3 (AN) system simultaneously and obtain excellent Urec and η. The substitution of Sm3+ for Ag+ in SmxAN+Mn MLCCs at x ≥ 0.01 decreases the M1-M2 phase transition temperature, and the antiferroelectric (AFE) M2 phase appears at room temperature, which is beneficial to achieving a low Pr value. Due to the low Pr value and high BDS ∼ 1300 kV·cm-1, an excellent Urec ∼9.8 J·cm-3 and PD,max ∼ 34.8 MW·cm-3 were achieved in SmxAN+Mn MLCCs at x = 0.03. The work suggests a paradigm that can enhance the energy storage capabilities of AFE MLCCs to meet the demanding requirements of advanced energy storage applications.

Broad-high operating temperature range and enhanced energy storage performances in lead-free ferroelectrics

The immense potential of lead-free dielectric capacitors in advanced electronic components and cutting-edge pulsed power systems has driven enormous investigations and evolutions heretofore. One of the significant challenges in lead-free dielectric ceramics for energy-storage applications is to optimize their comprehensive characteristics synergistically. Herein, guided by phase-field simulations along with rational composition-structure design, we conceive and fabricate lead-free Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3-Sr(Sc0.5Nb0.5)O3 ternary solid-solution ceramics to establish an equitable system considering energy-storage performance, working temperature performance, and structural evolution. A giant Wrec of 9.22 J cm-3 and an ultra-high ƞ ~ 96.3% are realized in the BNKT-20SSN ceramic by the adopted repeated rolling processing method. The state-of-the-art temperature (Wrec ≈ 8.46 ± 0.35 J cm-3, ƞ ≈ 96.4 ± 1.4%, 25-160 °C) and frequency stability performances at 500 kV cm-1 are simultaneously achieved. This work demonstrates remarkable advances in the overall energy storage performance of lead-free bulk ceramics and inspires further attempts to achieve high-temperature energy storage properties.

Deposition of ultra-thin coatings by a nature-inspired Spray-on-Screen technology

Nanometre-thick, ultrathin coatings applied over a large area are of paramount importance for various application fields such as biomedicine, space and automotive, organic electronics, memory devices, or energy storage devices. So far wet chemical deposition as a cost-effective, scalable, and versatile method can only be used for thicker deposits. Here the formation of uniform ultra-thin coatings with thicknesses below 15 nm using a nature-inspired, roll-to-roll compatible Spray-on-Screen (SoS) technology is reported. For this, the finite micro-droplet generation of Ultrasonic Spray Coating (USSC) is combined with the coating formation from a screen printing mesh. Hydrophobic micro-threads of the mesh, resembling the micro-hair on the legs of water striders, produce millidroplets from micro droplets, and when applying an external pressure to the mesh, dynamic wetting is enforced. The proposed technology is applicable for a wide variety of substrates and applications. It is shown by theory and experiment that ultra-thin coatings below 5 nm homogeneous over a large area can be deposited without the use of extended ink formulation or high substrate temperatures during or after deposition. This simple yet effective technique enables the deposition of ultra-thin films on any substrates, and is very promising to fabricate the organic, inorganic electronics devices and batteries cost effectively.

Rachith Kumar and coworkers report a bio-inspired coating technique able to deposit uniform films with thicknesses below 15 nm on various substrates. This method will not require the use of extended ink formulation or high substrate temperature as existing techniques do, potentially reducing the fabrication cost of future electronic devices and batteries.

Machine Learning-Enabled Superior Energy Storage in Ferroelectric Films with a Slush-Like Polar State

Heterogeneities in structure and polarization have been employed to enhance the energy storage properties of ferroelectric films. The presence of nonpolar phases, however, weakens the net polarization. Here, we achieve a slush-like polar state with fine domains of different ferroelectric polar phases by narrowing the large combinatorial space of likely candidates using machine learning methods. The formation of the slush-like polar state at the nanoscale in cation-doped BaTiO₃ films is simulated by phase field simulation and confirmed by aberration-corrected scanning transmission electron microscopy. The large polarization and the delayed polarization saturation lead to greatly enhanced energy density of 80 J/cm³ and transfer efficiency of 85% over a wide temperature range. Such a data-driven design recipe for a slush-like polar state is generally applicable to quickly optimize functionalities of ferroelectric materials.

Chemical Design of Pb-Free Relaxors for Giant Capacitive Energy Storage

Dielectric capacitors have captured substantial attention for advanced electrical and electronic systems. Developing dielectrics with high energy density and high storage efficiency is challenging owing to the high compositional diversity and the lack of general guidelines. Herein, we propose a map that captures the structural distortion (δ) and tolerance factor (t) of perovskites to design Pb-free relaxors with extremely high capacitive energy storage. Our map shows how to select ferroelectric with large δ and paraelectric components to form relaxors with a t value close to 1 and thus obtaining eliminated hysteresis and large polarization under a high electric breakdown. Taking the Bi_0.5Na_0.5TiO₃-based solid solution as an example, we demonstrate that composition-driven predominant order-disorder characteristic of local atomic polar displacements endows the relaxor with a slushlike structure and strong local polar fluctuations at several nanoscale. This leads to a giant recoverable energy density of 13.6 J cm^-3, along with an ultrahigh efficiency of 94%, which is far beyond the current performance boundary reported in Pb-free bulk ceramics. Our work provides a solution through rational chemical design for obtaining Pb-free relaxors with outstanding energy-storage properties.

Superior Energy Density Achieved in Unfilled Tungsten Bronze Ferroelectrics via Multiscale Regulation Strategy

The most promising candidates for energy storage capacitor application are relaxor ferroelectrics, among which, the perovskite structure ferroelectric ceramics have witnessed great development progress. However, less attention has been paid on tetragonal tungsten bronze structure (TTBS) ceramics because of their lower breakdown strength and polarization. Herein, a multiscale regulation strategy is proposed to tune the energy storage performances (ESP) of TTBS ceramics from grain, domain, and macroscopic scale. The enhanced relaxor behavior with dynamic polar nanodomains guarantees low remanent polarization, while the refined grains and enlarged bandgap ensure increased breakdown strength. Hence, excellent ESP is realized in unfilled TTBS Sr_0.425 La_0.1 □_0.05 Ba_0.425 Nb_1.4 Ta_0.6 O₆ (SLBNT) ceramics with an ultrahigh recoverable energy density of 5.895 J cm^-3 and a high efficiency of 85.37%. This achievement notably surpasses previous studies in TTBS ceramics and is comparable to that of perovskite components. Meanwhile, the energy density exhibits a wide temperature, frequency, and cycling fatigue stability. In addition, high power density (257.89 MW cm^-3 ), especially the ultrafast discharge time (t_0.9 = 16.4 ns) are achieved. The multiscale regulation strategy unlocks the energy storage potential of TTBS ceramics and thus highlights TTBS ceramics as promising candidates for energy storage, like perovskite structured ceramics.

Tailoring high-energy storage NaNbO3-based materials from antiferroelectric to relaxor states

Reversible field-induced phase transitions define antiferroelectric perovskite oxides and lay the foundation for high-energy storage density materials, required for future green technologies. However, promising new antiferroelectrics are hampered by transition´s irreversibility and low electrical resistivity. Here, we demonstrate an approach to overcome these problems by adjusting the local structure and defect chemistry, delivering NaNbO₃-based antiferroelectrics with well-defined double polarization loops. The attending reversible phase transition and structural changes at different length scales are probed by in situ high-energy X-ray diffraction, total scattering, transmission electron microcopy, and nuclear magnetic resonance spectroscopy. We show that the energy-storage density of the antiferroelectric compositions can be increased by an order of magnitude, while increasing the chemical disorder transforms the material to a relaxor state with a high energy efficiency of 90%. The results provide guidelines for efficient design of (anti-)ferroelectrics and open the way for the development of new material systems for a sustainable future.

Heterovalent-doping-enabled atom-displacement fluctuation leads to ultrahigh energy-storage density in AgNbO3-based multilayer capacitors

Dielectric capacitors with high energy storage performance are highly desired for next-generation advanced high/pulsed power capacitors that demand miniaturization and integration. However, the poor energy-storage density that results from the low breakdown strength, has been the major challenge for practical applications of dielectric capacitors. Herein, we propose a heterovalent-doping-enabled atom-displacement fluctuation strategy for the design of low-atom-displacements regions in the antiferroelectric matrix to achieve the increase in breakdown strength and enhancement of the energy-storage density for AgNbO₃-based multilayer capacitors. An ultrahigh breakdown strength ~1450 kV·cm^-1 is realized in the Sm_0.05Ag_0.85Nb_0.7Ta_0.3O₃ multilayer capacitors, especially with an ultrahigh U_rec ~14 J·cm^-3, excellent η ~ 85% and P_D,max ~ 102.84 MW·cm^-3, manifesting a breakthrough in the comprehensive energy storage performance for lead-free antiferroelectric capacitors. This work offers a good paradigm for improving the energy storage properties of antiferroelectric multilayer capacitors to meet the demanding requirements of advanced energy storage applications.

Superior Energy Storage Capability and Stability in Lead-Free Relaxors for Dielectric Capacitors Utilizing Nanoscale Polarization Heterogeneous Regions

The development of high-performance lead-free dielectric ceramic capacitors is essential in the field of advanced electronics and electrical power systems. A huge challenge, however, is how to simultaneously realize large recoverable energy density (W_rec ), ultrahigh efficiency (η), and satisfactory temperature stability to effectuate next-generation high/pulsed power capacitors applications. Here, a strategy of utilizing nanoscale polarization heterogeneous regions is demonstrated for high-performance dielectric capacitors, showing comprehensive properties of large W_rec (≈6.39 J cm^-3 ) and ultrahigh η (≈94.4%) at 700 kV cm^-1 accompanied by excellent thermal endurance (20-160 °C), frequency stability (5-200 Hz), cycling reliability (1-105 cycles) at 500 kV cm^-1 , and superior charging-discharging performance (discharge rate t_0.9 ≈ 28.4 ns, power density PD ≈161.3 MW cm^-3 ). The observations reveal that constructing the polarization heterogeneous regions in a linear dielectric to form novel relaxor ferroelectrics produces favorable microstructural characters, including extremely small polar nanoregions with high dynamics and multiphase coexistence and stable local structure symmetry, which enables large breakdown strength and ultralow polarization switching hysteresis, hence synergistically contributing to high-efficient capacitive energy storage. This study thus opens up a novel strategy to design lead-free dielectrics with comprehensive high-efficient energy storage performance for advanced pulsed power capacitors applications.

Lead-Free Relaxor Ferroelectric Ceramics with Ultrahigh Energy Storage Densities via Polymorphic Polar Nanoregions Design

One of the long-standing challenges of current lead-free energy storage ceramics for capacitors is how to improve their comprehensive energy storage properties effectively, that is, to achieve a synergistic improvement in the breakdown strength (E_b ) and the difference between maximum polarization (P_max ) and remnant polarization (P_r ), making them comparable to those of lead-based capacitor materials. Here, a polymorphic polar nanoregions (PNRs) structural design by first introducing 0.06 mol BaTiO₃ into Bi_0.5 Na_0.5 TiO₃ is proposed to construct the morphotropic phase boundary with coexisting structures of micrometer-size domains and polymorphic nanodomains, enhance the electric field-induced polarization response (increase P_max ). Then Sr(Al_0.5 Ta_0.5 )O₃ (SAT)-doped 0.94 Bi_0.5 Na_0.5 TiO₃ -0.06BaTiO₃ (BNBT) energy storage ceramics with polymorphic PNRs structures are synthesized following the guidance of phase-field simulation and rational composition design (decrease P_r ). Finally, a large recoverable energy density (W_rec ) of 8.33 J cm^-3 and a high energy efficiency (η) of 90.8% under 555 kV cm^-1 are obtained in the 0.85BNBT-0.15SAT ceramic prepared by repeated rolling process method (enhance E_b ), superior to most practical lead-free competitors increased consideration of the stability of temperature (a variation <±6.2%) and frequency (W_rec > 5.0  cm^-3 , η > 90%) at 400 kV cm^-1 . This strategy provides a new conception for the design of other-based multifunctional energy storage dielectrics.

Achieving Ultrahigh Energy Storage Density of La and Ta Codoped AgNbO3 Ceramics by Optimizing the Field-Induced Phase Transitions

Energy storage capacitors are extensively used in pulsed power devices because of fast charge/discharge rates and high power density. However, the low energy storage density and efficiency of dielectric capacitors limit their further commercialization in modern energy storage applications. Lead-free AgNbO₃-based antiferroelectric (AFE) ceramics are considered to be one of the most promising environmentally friendly materials for dielectric capacitors because of their characteristic double polarization-electric field hysteresis loops with small remanent polarization and large maximum polarization. An enhancement of these characteristics allows achieving a synergistic improvement of both the energy storage density and efficiency of the antiferroelectric materials. This work reports on a feasible codoping strategy enabling the preparation of AgNbO₃-based ceramics with high energy storage performance. An introduction of La³⁺ and Ta⁵⁺ ions into the AgNbO₃ perovskite lattice was found to increase the structural stability of the antiferroelectric phase at the expense of a reduction of local polar regions, resulting in the shifting of the electric field-induced antiferroelectric-ferroelectric phase transition toward higher fields. An ultrahigh recoverable energy storage density of 6.73 J/cm³ and high energy storage efficiency of 74.1% are obtained for the Ag_0.94La_0.02Nb_0.8Ta_0.2O₃ ceramic subjected to a unipolar electric field of 540 kV/cm. These values represent the best energy performance in reported lead-free ceramics so far. Hence, the La³⁺/Ta⁵⁺ codoping has been shown to be a good route to improve the energy storage properties of AgNbO₃ ceramics.

Energy Storage Properties of Sol-Gel-Processed SrTiO3 Films

Dielectric films with a high energy storage density and a large breakdown strength are promising material candidates for pulsed power electrical and electronic applications. Perovskite-type dielectric SrTiO₃ (STO) has demonstrated interesting properties desirable for capacitive energy storage, including a high dielectric constant, a wide bandgap and a size-induced paraelectric-to-ferroelectric transition. To pave a way toward large-scale production, STO film capacitors were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by the sol-gel method in this paper, and their electrical properties including the energy storage performance were studied as a function of the annealing temperature in the postgrowth rapid thermal annealing (RTA) process. The appearance of a ferroelectric phase at a high annealing temperature of 750 °C was revealed by X-ray diffraction and electrical characterizations (ferroelectric P-E loop). However, this high dielectric constant phase came at the cost of a low breakdown strength and a large hysteresis loss, which are not desirable for the energy storage application. On the other hand, when the RTA process was performed at a low temperature of 550 °C, a poorly crystallized perovskite phase together with a substantial amount of impurity phases appeared, resulting in a low breakdown strength as well as a very low dielectric constant. It is revealed that the best energy storage performance, which corresponds to a large breakdown strength and a medium dielectric constant, is achieved in STO films annealed at 650 °C, which showed a large energy density of 55 J/cm³ and an outstanding energy efficiency of 94.7% (@ 6.5 MV/cm). These findings lay out the foundation for processing high-quality STO film capacitors via the manufacturing-friendly sol-gel method.

Phase and Band Structure Engineering via Linear Additive in NBT-ST for Excellent Energy Storage Performance with Superior Thermal Stability

Lead-free relaxor ferroelectric ceramics with ultrahigh energy-storage performance are vital for pulsed power systems. We herein propose a strategy of phase and band structure engineering for high-performance energy storage. To demonstrate the effectiveness of this strategy, (1 - x)(0.75Na_0.5Bi_0.5TiO₃-0.25SrTiO₃)-xCaTi_0.875Nb_0.1O₃ (NBT-ST-xCTN, x = 0.1, 0.2, 0.3, 0.4, and 0.5) samples were designed and fabricated via the solid-state reaction method. The linear dielectric CTN was used as a modulator to tune both phase and band structures of the tested system. Our results show that both rhombohedral phase (R-phase) and tetragonal phase (T-phase) coexist in the samples. The R/T ratio decreases, while the band gap increases with increasing CTN content. The best energy-storage properties with large energy storage density (W_rec = 7.13 J/cm³), a high efficiency (η = 90.3%), and an ultrafast discharge time (25 ns) were achieved in the NBT-ST-0.4CTN sample with R/T = 0.121. Importantly, along with its excellent energy-storage performance, the sample exhibited superior thermal stability with the variations of W_rec ≤ 7% and η ≤ 10% over the wide temperature range of 233-413 K. This work suggests that this engineering of phase and band structures is a promising strategy to achieve superior energy-storage properties in lead-free ceramics.

High Energy Storage Performance and Large Electrocaloric Response in Bi0.5Na0.5TiO3-Ba(Zr0.2Ti0.8)O3 Thin Films

With regard to the global energy crisis and environmental pollution, ferroelectric thin films with unique polarization behavior have garnered considerable attention for energy storage and electrocaloric refrigeration. Herein, a series of (1 - x)Bi_0.5Na_0.5TiO₃-xBa(Zr_0.2Ti_0.8)O₃ (x = 0.3-0.9; (1 - x)BNT-xBZT) films were fabricated on Pt(111)/Ti/SiO₂/Si substrates. Incorporating BZT can tune the polarization behavior and phase transition temperature of BNT. A high recoverable energy density ≈ 82 J cm^-3 and optimized efficiency ≈ 81% were realized for the (1 - x)BNT-xBZT thin film with x = 0.7. The thin film exhibits excellent stability in energy storage performance, a wide working frequency range (0.5-20 kHz), a broad operating temperature window (20-200 °C), and reduplicative switching cycles (10⁷ cycles). In addition, the 0.5BNT-0.5BZT film exhibits a desirable electrocaloric effect with a large adiabatic temperature change (ΔT ≈ -22.9 K) and isothermal entropy change (ΔS ≈ 33.4 J K^-1 kg^-1) near room temperature under a moderate applied electric field of 2319 kV cm^-1. These remarkable performances signify that the (1 - x)BNT-xBZT system is a promising multifunctional electronic material for energy storage and solid-state cooling applications.

Glass-Ceramic Capacitors with Simultaneously High Power and Energy Densities under Practical Charge-Discharge Conditions

Developing dielectric capacitors with both a high power density and a high energy density for application in power electronics has been a long-standing challenge. Glass-ceramics offer the potential of retaining the high relative permittivity of ceramics and at the same time of exhibiting the high dielectric breakdown strength and fast charge/discharge rate of glasses, thus producing concurrently high power and energy densities in a single material. In this work, glass-ceramics are fabricated to achieve simultaneously high power and energy densities, high efficiency, and thermal stability by tuning the glass crystallization process via a suitable nucleating agent and a high oxygen partial pressure. Under the same practical charge-discharge test conditions, the as-prepared glass-ceramics combine the high energy density of ceramics and ultrafast discharge rate of glasses, producing the highest power density among glass- and ceramic-based dielectric materials. This work demonstrates the significant potential of achieving both high power and energy densities in glass-ceramics by optimizing the glass crystallization process.

Interlayer Coupling Enhanced Energy Storage Performance in a Flexible BMT-BTO/BMT Multilayer Ferroelectric Film Capacitor

Flexible ferroelectric capacitors with high energy density and storage efficiency are highly desirable in the next generation of flexible electronic devices. To develop high-performance ferroelectric capacitors, a conventional approach is chemical modification. Here, a novel approach of interlayer coupling is proposed to achieve high energy storage performance in BiMg_0.5Ti_0.5O₃-BaTiO₃/BiMg_0.5Ti_0.5O₃ (BMT-BTO/BMT)_N multilayer ferroelectric films fabricated on flexible mica substrates via a sol-gel coating method. The interlayer electrostatic coupling between the ferroelectric BMT and relaxor ferroelectric BMT-BTO layers leads to small remnant polarization and large breakdown field strength, resulting in an outstanding energy storage density of ∼106.8 J cm^-3 and a good efficiency of ∼75.6% in the multilayer thin films. Further, the energy storage performance remains stable in a wide range of temperatures (25-200 °C) and frequencies (500 Hz to 10 kHz) after 10⁸ electrical loading cycles. The energy storage performance also has no obvious deterioration when the multilayer film experiences 10⁴ mechanical bending cycles with a bending radius of 4 mm. The approach proposed in the present work should be generally implementable in other multilayer flexible ferroelectric capacitors and offers a novel avenue to enhance energy storage performance by tuning the interlayer coupling.

Achieving Ultrahigh Energy-Storage Density with Excellent Thermal Stability in Sr0.7Bi0.2TiO3-Based Relaxors via Polarization Behavior Modulation

Dielectric capacitors possessing the inherent superiorities of high power density and ultrafast charge-discharge speed make their utilization in energy-storage devices extremely propitious, although the relatively low recoverable energy-storage density (W_rec) may impede their applications. In this work, unlike the mainstream approach of destroying long-range ferroelectric/antiferroelectric order and inducing relaxor properties to achieve a high W_rec value, we have selected end members with a high polarization gene to promote the polarization behavior of the typical relaxor Sr_0.7Bi_0.2TiO₃. Therefore, an ultrahigh W_rec ∼ 8 J/cm³ and a superior efficiency (η) ∼ 91% are accomplished in the 0.98[0.56(Sr_0.7Bi_0.2)TiO₃-0.44(Bi_0.5Na_0.5)TiO₃]-0.02 Bi(Mg_0.5Ti_0.5)O₃ sample. The achieved W_rec value is record high in Sr_0.7Bi_0.2TiO₃-based systems as far as we know. The polarization-enhancement behavior can be explained by the phase field simulation results, phase content variance in X-ray diffraction Rietveld refinement, hardening trend in Raman spectroscopy, domain morphology, and local symmetry in transmission electron microscope analysis. Meanwhile, the ceramic possesses excellent thermal stability (ΔW_rec < 12.7% and Δη < 10.4%, -50-200 °C), frequency (ΔW_rec < 2.69% and Δη < 2.06%, 0.5-500 Hz), and fatigue-resistant stability (ΔW_rec < 0.08% and Δη < 0.2%, up to 1 × 10⁵ cycles). Accordingly, this work proposes a design idea to tailor the polarization behavior and energy-storage properties of typical relaxors.

Microstructural Origin of the High-Energy Storage Performance in Epitaxial Lead-Free Ba(Zr0.2Ti0.8)O3 Thick Films

In our previous work, epitaxial Ba(Zr_0.2Ti_0.8)O₃ thick films (~1-2 μm) showed an excellent energy storage performance with a large recyclable energy density (~58 J/cc) and a high energy efficiency (~92%), which was attributed to a nanoscale entangled heterophase polydomain structure. Here, we propose a detailed analysis of the structure-property relationship in these film materials, using an annealing process to illustrate the effect of nanodomain entanglement on the energy storage performance. It is revealed that an annealing-induced stress relaxation led to the segregation of the nanodomains (via detailed XRD analyses), and a degraded energy storage performance (via polarization-electric field analysis). These results confirm that a nanophase entanglement is an origin of the high-energy storage performance in the Ba(Zr_0.2Ti_0.8)O₃ thick films.

High-entropy enhanced capacitive energy storage

Electrostatic dielectric capacitors are essential components in advanced electronic and electrical power systems due to their ultrafast charging/discharging speed and high power density. A major challenge, however, is how to improve their energy densities to effectuate the next-generation applications that demand miniaturization and integration. Here, we report a high-entropy stabilized Bi₂Ti₂O₇-based dielectric film that exhibits an energy density as high as 182 J cm^-3 with an efficiency of 78% at an electric field of 6.35 MV cm^-1. Our results reveal that regulating the atomic configurational entropy introduces favourable and stable microstructural features, including lattice distorted nano-crystalline grains and a disordered amorphous-like phase, which enhances the breakdown strength and reduces the polarization switching hysteresis, thus synergistically contributing to the energy storage performance. This high-entropy approach is expected to be widely applicable for the development of high-performance dielectrics.

Thin-Film Ferroelectrics

Over the last 30 years, the study of ferroelectric oxides has been revolutionized by the implementation of epitaxial-thin-film-based studies, which have driven many advances in the understanding of ferroelectric physics and the realization of novel polar structures and functionalities. New questions have motivated the development of advanced synthesis, characterization, and simulations of epitaxial thin films and, in turn, have provided new insights and applications across the micro-, meso-, and macroscopic length scales. This review traces the evolution of ferroelectric thin-film research through the early days developing understanding of the roles of size and strain on ferroelectrics to the present day, where such understanding is used to create complex hierarchical domain structures, novel polar topologies, and controlled chemical and defect profiles. The extension of epitaxial techniques, coupled with advances in high-throughput simulations, now stands to accelerate the discovery and study of new ferroelectric materials. Coming hand-in-hand with these new materials is new understanding and control of ferroelectric functionalities. Today, researchers are actively working to apply these lessons in a number of applications, including novel memory and logic architectures, as well as a host of energy conversion devices.

Vacancy-Induced Temperature-Dependent Thermal and Magnetic Properties of Holmium-Substituted Bismuth Ferrite Nanoparticle Compacts

Multiferroics have gained widespread acceptance for room-temperature applications such as in spintronics, ferroelectric random access memory, and transistors because of their intrinsic magnetic and ferroelectric coupling. However, a comprehensive study, establishing a correlation between the magnetic and thermal transport properties of multiferroics, is still missing from the literature. To fill the void, this work reports the temperature-dependent thermal and magnetic properties of holmium-substituted bismuth ferrite (BiFeO₃) and their dependencies on oxygen vacancies and structural modifications. Two distinct magnetic transitions on temperature-dependent magnetic and heat capacity responses are identified. Experimental analysis suggests that the excess of oxygen vacancies shifts the magnetic transition temperature by ∼64 K. The holmium substitution-induced structural modification increases BiFeO₃ heat capacity by 30% up to the antiferromagnetic phase transition temperature. Furthermore, an unsaturated heat capacity even at temperatures as high as 850 K is observed and is ascribed to anharmonicity and partial densification of the nanoparticles used during heat capacity measurements. The room-temperature thermal conductivity of BiFeO₃ is ∼0.33 ± 0.11 W m^-1 K^-1 and remains unchanged at high temperatures due to defect scattering from porosities.

Domain Engineering in Bulk Ferroelectric Ceramics via Mesoscopic Chemical Inhomogeneity

Domain engineering in ferroelectrics endows flexibility for different functional applications. Whereas the domain engineering strategy for single crystals and thin films is diverse, there is only a limited number of strategies for bulk ceramics. Here, a domain engineering strategy for achieving a compact domain architecture with increased domain-wall density in (K,Na)NbO3 (KNN)-based ferroelectric ceramics via mesoscopic chemical inhomogeneity (MCI) is developed. The MCI-induced interfaces can effectively hinder domain continuity and modify the domain configuration. Besides, the MCI effect also results in diffused phase transitions, which is beneficial for achieving enhanced thermal stability. Modulation of chemical inhomogeneity demonstrates great potential for engineering desirable domain configuration and properties in ferroelectric ceramics. Additionally, the MCI can be easily controlled by regulating the processing condition during solid-state synthesis, which is advantageous to industrial production.

Outstanding Ferroelectricity in Sol-Gel-Derived Polycrystalline BiFeO3 Films within a Wide Thickness Range

As a promising lead-free ferroelectric, BiFeO₃ has a very large intrinsic polarization of ∼100 μC/cm², enabling its great potential in electronic applications especially in a film format. In this sense, reliable ferroelectric properties are desired; however, pure-phase BiFeO₃ films are notorious for their large leakage current, especially of those processed by using the sol-gel method─a facile and industrially scalable method for film preparation. In this study, a protection layer, which can be easily integrated in the sol-gel process, is used to ensure the acquirement of remnant polarization of ∼65 μC/cm² in ∼200 nm BiFeO₃ thin films, whereas O₂ annealing can enhance that to ∼120 μC/cm² in ∼400-700 nm films. Reliable ferroelectricity of BiFeO₃ films on Si wafers within a wide thickness range was thus achieved. The obtained ferroelectricity is among the best-achieved properties to date of BiFeO₃ films for both thin and intermediate thicknesses, including both chemically and physically derived. These results are helpful to advance potential use of sol-gel-processed BiFeO₃ films in electromechanical devices with different desired thicknesses.

Nanocrystalline Engineering Induced High Energy Storage Performances of Fatigue-Free Ba2Bi3.9Pr0.1Ti5O18 Ferroelectric Thin Films

Electrostatic capacitors, though presenting faster rate capability and higher power density, are hindered in applications because of their low energy density. Accordingly, many efforts in electrostatic capacitors, for electronics and electrical power systems, have mainly concentrated on the development of dielectric materials with high-energy density (U_d) and charge-discharge efficiency (η) as well as good stability performances of thermal and fatigue endurance. Herein, we demonstrate that an excellent U_d (∼90 J/cm³) and high η (∼84.2%), as well as outstanding fatigue cycles (1 × 10⁸ st), frequency stability (20-2000 Hz), and a wide temperature range (RT ∼ 160 °C), can be attained in Ba₂Bi_3.9Pr_0.1Ti₅O₁₈ (BBPT) ferroelectric thin films via nanocrystalline engineering. It is revealed that nanocrystalline engineering of the BBPT ferroelectric thin films could be controlled via the heat-treatment temperature, which could effectively regulate the breakdown strength and polarization. The enhanced breakdown strength and polarization of the nanocrystalline engineering is further verified through the theoretical phase-field simulations along with experimental results. These results indicate that this is a feasible and scalable route to develop dielectric thin film materials with a high energy storage capability.

Synergy of a Stabilized Antiferroelectric Phase and Domain Engineering Boosting the Energy Storage Performance of NaNbO3-Based Relaxor Antiferroelectric Ceramics

Relaxor antiferroelectric (AFE) ceramic capacitors have drawn growing attention in future advanced pulsed power devices for their superior energy storage performance. However, state of the art dielectric materials are restricted by desirable comprehensive energy-storage features, which have become a longstanding hurdle for actual capacitor applications. Here, we report that a large energy density W_rec of 5.52 J/cm³, high efficiency η of 83.3% at 560 kV/cm, high power density P_D of 114.8 MW/cm³, ultrafast discharge rate t_0.9 of 45 ns, and remarkable stability against temperature (30-140 °C)/frequency (5-200 Hz)/cycles (1-10⁵) are simultaneously achieved in 0.7 NaNbO₃-0.3 CaTiO₃ relaxor AFE ceramics via the synergy of stabilized AFE R phase and domain engineering in combination with breakdown strength enhancement. The structural origin for these achievements is disclosed by probing the in situ microstructure evolution by means of the first-order reversal curve method, piezoelectric force microscopy, and Raman spectroscopy. The highly dynamic polar nanoregions and stabilized AFE R phase synergistically generate a linear-like and highly stable polarization field response over a wide temperature and field scope with concurrently improved energy density and efficiency. This work offers a new solution for designing high-performance next-generation pulsed power capacitors.

Phase-Field Simulations of Tunable Polar Topologies in Lead-Free Ferroelectric/Paraelectric Multilayers with Ultrahigh Energy-Storage Performance

Dielectric capacitors are emerging energy-storage components that require both high energy-storage density and high efficiency. The conventional approach to energy-storage enhancement is polar nanodomain engineering via chemical modification. Here, a new approach of domain engineering is proposed by exploiting the tunable polar topologies that have been observed recently in ferroelectric/paraelectric multilayer films. Using phase-field simulations, it is demonstrated that vortex, spiral, and in-plane polar structures can be stabilized in BiFeO₃ /SrTiO₃ (BFO/STO) multilayers by tailoring the strain state and layer thickness. Various switching dynamics are realized in these polar topologies, resulting in relaxor-ferroelectric-, antiferroelectric-, and paraelectric-like polarization behaviors, respectively. Ultrahigh energy-storage densities above 170 J cm^-3 and efficiencies above 95% are achievable in STO/BFO/STO trilayers. This strategy should be generally implementable in other multilayer dielectrics and offers a new avenue to enhancing energy storage by tuning the polar topology and thus the polarization characteristics.

Ferroelectric Polymer Nanofibers Reminiscent of Morphotropic Phase Boundary Behavior for Improved Piezoelectric Energy Harvesting

Ferroelectric and piezoelectric polymers have attracted great attention from many research and engineering fields due to its mechanical robustness and flexibility as well as cost-effectiveness and easy processibility. Nevertheless, the electrical performance of piezoelectric polymers is very hard to reach that of piezoelectric ceramics basically and physically, even in the case of the representative ferroelectric polymer, poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)). Very recently, the concept for the morphotropic phase boundary (MPB), which has been exclusive in the field of high-performance piezoelectric ceramics, has been surprisingly confirmed in P(VDF-TrFE) piezoelectric copolymers by the groups. This study demonstrates the exceptional behaviors reminiscent of MPB and relaxor ferroelectrics in the feature of widely utilized electrospun P(VDF-TrFE) nanofibers. Consequently, an energy harvesting device that exceeds the performance limitation of the existing P(VDF-TrFE) materials is developed. Even the unpoled MPB-based P(VDF-TrFE) nanofibers show higher output than the electrically poled normal P(VDF-TrFE) nanofibers. This study is the first step toward the manufacture of a new generation of piezoelectric polymers with practical applications.

Ultrahigh Energy Storage Performance of Flexible BMT-Based Thin Film Capacitors

Ferroelectric thin film capacitors have attracted increasing attention because of their high energy storage density and fast charge-discharge speed, but less attention has been paid to the realization of flexible capacitors for wearable electronics and power systems. In this work, flexible xMn-BiMg_0.5 Ti_0.7 O₃ (xMn-BMT_0.7 ) thin film capacitors with ultrahigh energy storage density and good stability are deposited on mica substrate. The introduction of excess TiO₂ with an amorphous structure contributes to the forming of the polar nano regions, resulting in the reduced ferroelectric hysteresis. In order to further improve the energy storage performance, Mn doping increases the polarization by regulating chemical pressure in the lattices and inhibits the valence change of Ti⁴⁺ . Especially in the 1.5% Mn-BMT_0.7 film capacitor, an ultrahigh energy storage density of 124 J cm^-3 and an outstanding efficiency of 77% are obtained, which is one of the best energy storage performances recorded for ferroelectric capacitors. In addition, the flexible ferroelectric film capacitor also exhibits good thermal stability (25-200 °C), high frequency reliability (500 Hz-10 kHz), excellent electrical (10⁸ cycles), and mechanical (10⁴ cycles) fatigue properties. This work is expected to pave the way for the application of BMT-based thin film capacitors in flexible energy storage systems.

Structural Phase Transition and In-Situ Energy Storage Pathway in Nonpolar Materials: A Review

Benefitting from exceptional energy storage performance, dielectric-based capacitors are playing increasingly important roles in advanced electronics and high-power electrical systems. Nevertheless, a series of unresolved structural puzzles represent obstacles to further improving the energy storage performance. Compared with ferroelectrics and linear dielectrics, antiferroelectric materials have unique advantages in unlocking these puzzles due to the inherent coupling of structural transitions with the energy storage process. In this review, we summarize the most recent studies about in-situ structural phase transitions in PbZrO₃-based and NaNbO₃-based systems. In the context of the ultrahigh energy storage density of SrTiO₃-based capacitors, we highlight the necessity of extending the concept of antiferroelectric-to-ferroelectric (AFE-to-FE) transition to broader antiferrodistortive-to-ferrodistortive (AFD-to-FD) transition for materials that are simultaneously ferroelastic. Combining discussion of the factors driving ferroelectricity, electric-field-driven metal-to-insulator transition in a (La_1−xSr_x)MnO₃ electrode is emphasized to determine the role of ionic migration in improving the storage performance. We believe that this review, aiming at depicting a clearer structure–property relationship, will be of benefit for researchers who wish to carry out cutting-edge structure and energy storage exploration.

Recent Advances in Multilayer-Structure Dielectrics for Energy Storage Application

An electrostatic capacitor has been widely used in many fields (such as high pulsed power technology, new energy vehicles, etc.) due to its ultrahigh discharge power density. Remarkable progress has been made over the past 10 years by doping ferroelectric ceramics into polymers because the dielectric constant is positively correlated with the energy storage density. However, this method often leads to an increase in dielectric loss and a decrease in energy storage efficiency. Therefore, the way of using a multilayer structure to improve the energy storage density of the dielectric has attracted the attention of researchers. Although research on energy storage properties using multilayer dielectric is just beginning, it shows the excellent effect and huge potential. In this review, the main physical mechanisms of polarization, breakdown and energy storage in multilayer structure dielectric are introduced, the theoretical simulation and experimental results are systematically summarized, and the preparation methods and design ideas of multilayer structure dielectrics are mainly described. This article covers not only an overview of the state-of-the-art advances of multilayer structure energy storage dielectric but also the prospects that may open another window to tune the electrical performance of the electrostatic capacitor via designing a multilayer structure.