Anti-Ferroelectric Ceramics for High Energy Density Capacitors

Ultrahigh Energy Storage Density and Efficiency in Orthorhombic PLZST Antiferroelectric Ceramics via Composition Regulation

PbZrO3-based antiferroelectric (AFE) ceramic materials have emerged as potential candidates for the next generation of high-energy multilayer ceramic capacitors (MLCCs) because of their distinctive characteristics of double hysteresis loops. The energy storage efficiency of orthorhombic AFE ceramics with ultrahigh storage density is relatively low, which hinders their practical application. In this study, the low efficiency limit of PLZST-based orthorhombic ceramics was overcome by precisely adjusting the Sn4+ content in the (Pb0.95Ca0.02La0.02)(Zr0.99-xSnxTi0.01)O3 AFE ceramics. On one hand, the addition of Sn4+ disrupts the original long-range dipole and improves the rapid response of polarization reversal under the applied voltage. As a result, the difference in electric hysteresis under an electric field is reduced, leading to a significant improvement in energy storage efficiency. On the other hand, increasing the Sn4+ content suppresses the formation of oxygen vacancies, inhibiting grain growth and strengthening grain bonding. This results in ceramics with a high breakdown field strength. Ultimately, the resulting PLCZST ceramics reveal an expressively improved recoverable energy density of 10.2 J cm-3 together with a high energy efficiency of 91.4% under a high applied electric field of 560 kV cm-1. The present study demonstrates the tunability of performance in orthorhombic PLZST AFE ceramics, thereby introducing a ceramic material with exceptional energy storage capabilities for MLCC applications.

Renewing Halogen Substitution Strategy for the Rational Design of High-Curie Temperature Metal-Free Molecular Antiferroelectrics

Metal-free molecular antiferroelectric (AFE) holds a promise for energy storage on account of its unique physical attributes. However, it is challenging to explore high-curie temperature (Tc) molecular AFEs, due to the lack of design strategies regarding the rise of phase transition energy barriers. By renewing the halogen substitution strategy, we have obtained a series of high-Tc molecular AFEs of the halogen-substituted phenethylammonium bromides (x-PEAB, x=H/F/Cl/Br), resembling the binary stator-rotator system. Strikingly, the p-site halogen substitution of PEA+ cationic rotators raises their phase transition energy barrier and greatly enhances Tc up to ~473 K for Br-PEAB, on par with the record-high Tc values for molecular AFEs. As a typical case, the member 4-fluorophenethylammonium bromide (F-PEAB) shows notable AFE properties, including high Tc (~374 K) and large electric polarization (~3.2 μC/cm2). Further, F-PEAB also exhibits a high energy storage efficiency (η) of 83.6 % even around Tc, catching up with other AFE oxides. This renewing halogen substitution strategy in the molecular AFE system provides an effective way to design high-Tc AFEs for energy storage devices.

High Performance On-Chip Energy Storage Capacitors with Plasma-Enhanced Atomic Layer-Deposited Hf0.5Zr0.5O2/Al-Doped Hf0.25Zr0.75O2 Nanofilms as Dielectrics

Concurrently achieving high energy storage density (ESD) and efficiency has always been a big challenge for electrostatic energy storage capacitors. In this study, we successfully fabricate high-performance energy storage capacitors by using antiferroelectric (AFE) Al-doped Hf_0.25Zr_0.75O₂ (HfZrO:Al) dielectrics together with an ultrathin (1 nm) Hf_0.5Zr_0.5O₂ underlying layer. By optimizing the Al concentration in the AFE layer with the help of accurate controllability of the atomic layer deposition technique, an ultrahigh ESD of 81.4 J cm^-3 and a perfect energy storage efficiency (ESE) of 82.9% are simultaneously achieved for the first time in the case of the Al/(Hf + Zr) ratio of 1/16. Meanwhile, both the ESD and ESE exhibit excellent electric field cycling endurance within 10⁹ cycles under 5~5.5 MV cm^-1, and robust thermal stability up to 200 °C. Thus, the fabricated capacitor is very promising for on-chip energy storage applications due to favorable integratability with the standard complementary metal-oxide-semiconductor (CMOS) process.

Translational Boundaries as Incipient Ferrielectric Domains in Antiferroelectric PbZrO_{3}

In the archetypal antiferroelectric PbZrO_{3}, antiparallel electric dipoles cancel each other, resulting in zero spontaneous polarization at the macroscopic level. Yet in actual hysteresis loops, the cancellation is rarely perfect and some remnant polarization is often observed, suggesting the metastability of polar phases in this material. In this work, using aberration-corrected scanning transmission electron microscopy methods on a PbZrO_{3} single crystal, we uncover the coexistence of the common antiferroelectric phase and a ferrielectric phase featuring an electric dipole pattern of ↓↑↓. This dipole arrangement, predicted by Aramberri et al. to be the ground state of PbZrO_{3} at 0 K, appears at room temperature in the form of translational boundaries. The dual nature of the ferrielectric phase, both a distinct phase and a translational boundary structure, places important symmetry constraints on its growth. These are overcome by sideways motion of the boundaries, which aggregate to form arbitrarily wide stripe domains of the polar phase embedded within the antiferroelectric matrix.

Ultrahigh Energy Storage in 2D High-κ Perovskites

Dielectric capacitors have greater power densities than batteries, and, unlike batteries, they do not utilize chemical reactions during cycling. Thus, they can become ideal, safe energy storage devices. However, dielectric capacitors yield rather low energy densities compared with other energy storage devices such as batteries and supercapacitors. Here, we present a rational approach for designing ultrahigh energy storage capacitors using two-dimensional (2D) high-κ dielectric perovskites (Ca₂Na_m-3Nb_mO_3m+1; m = 3-6). Individual Ca₂Na_m-3Nb_mO_3m+1 nanosheets exhibit an ultrahigh dielectric strength (638-1195 MV m^-1) even in the monolayer form, which exceeds those of conventional dielectric materials. Multilayer stacked nanosheet capacitors exhibit ultrahigh energy densities (174-272 J cm^-3), high efficiencies (>90%), excellent reliability (>10⁷ cycles), and temperature stability (-50-300 °C); the maximum energy density is much higher than those of conventional dielectric materials and even comparable to those of lithium-ion batteries. Enhancing the energy density may make dielectric capacitors more competitive with batteries.

Dynamic tilting in perovskites

A new computational analysis of tilt behaviour in perovskites is presented. This includes the development of a computational program - PALAMEDES - to extract tilt angles and the tilt phase from molecular dynamics simulations. The results are used to generate simulated selected-area electron and neutron diffraction patterns which are compared with experimental patterns for CaTiO₃. The simulations not only reproduced all symmetrically allowed superlattice reflections associated with tilt but also showed local correlations that give rise to symmetrically forbidden reflections and the kinematic origin of diffuse scattering.

Superhigh energy storage density on-chip capacitors with ferroelectric Hf0.5Zr0.5O2/antiferroelectric Hf0.25Zr0.75O2 bilayer nanofilms fabricated by plasma-enhanced atomic layer deposition

Thanks to their excellent compatibility with the complementary metal-oxide-semiconductor (CMOS) process, antiferroelectric (AFE) HfO₂/ZrO₂-based thin films have emerged as potential candidates for high-performance on-chip energy storage capacitors of miniaturized energy-autonomous systems. However, increasing the energy storage density (ESD) of capacitors has been a great challenge. In this work, we propose the fabrication of ferroelectric (FE) Hf_0.5Zr_0.5O₂/AFE Hf_0.25Zr_0.75O₂ bilayer nanofilms by plasma-enhanced atomic layer deposition for high ESD capacitors with TiN electrodes. The effects of the FE/AFE thickness composition and annealing conditions are investigated, revealing that the Hf_0.5Zr_0.5O₂ (1 nm)/Hf_0.25Zr_0.75O₂ (9 nm) bilayer can generate the optimal ESD after optimized annealing at 450 °C for 30 min. This is mainly ascribed to the factor that the introduction of a 1 nm Hf_0.5Zr_0.5O₂ layer enhances the formation of the tetragonal (T) phase with antiferroelectricity in the AFE Hf_0.25Zr_0.75O₂ layer as well as the breakdown electric field of the bilayer while fixing the FE/AFE bilayer thickness at 10 nm. As a result, a ESD as high as 71.95 J cm^-3 can be obtained together with an energy storage efficiency (ESE) of 57.8%. Meanwhile, with increasing the measurement temperature from 300 and 425 K, the capacitor also demonstrates excellent stabilities of ESD and ESE. In addition, superior electrical cycling endurance is also demonstrated. Further, by integrating the capacitor into deep silicon trenches, a superhigh ESD of 364.1 J cm^-3 is achieved together with an ESE of 56.5%. This work provides an effective way for developing CMOS process-compatible, eco-friendly and superhigh ESD three-dimensional capacitors for on-chip energy storage applications.

Superior Energy-Storage Properties in Bi0.5Na0.5TiO3-Based Lead-Free Ceramics via Simultaneously Manipulating Multiscale Structure and Field-Induced Structure Transition

Pratical applications have put forward great challenges to the comprehensive energy-storage performance of ceramic material. Here, a novel route of simultaneously manipulating multiscale structure and the field-induced structural transformation in (Bi_0.5Na_0.5)TiO₃-based ceramics is proposed to address the above concern. The multiscale structure of 0.88(Bi_0.5Na_0.5)TiO₃-0.12BaTiO₃ solid solutions such as grain and domain size, band gap, and phase structure can be adjusted by adding antiferroelectric NaNbO₃. Simultaneously, a field-induced P4bm relaxor antiferroelectric to P4mm ferroelectric phase transformation can be obtained by constructing a P4mm-P4bm phase boundary, which is expected to require a lower energy barrier compared with the field-induced P4bm relaxor antiferroelectric to R3c ferroelectric transformation in other (Bi_0.5Na_0.5)TiO₃-based ceramics. The optimized field-induced structural transformation behavior and the formation of nanodomains enables a minimized polarization hysteresis but an enhanced maximum polarization. Moreover, the decreased grain size together with increased band gap leads to a significantly improved breakdown strength. Accordingly, a giant energy density W_rec ∼ 8.0 J/cm³, a high efficiency η ∼ 86%, a short discharging time t_0.9 ∼ 41 ns, and a good temperature stability (W_rec = 1.32 ± 0.12 J/cm³, η = 88.5% ± 2.5% @ 25-200 °C) are simultaneously obtained in 0.63(Bi_0.5Na_0.5)TiO₃-0.12BaTiO₃-0.25NaNbO₃ relaxor antiferroelectric ceramics, demonstrating large potentials for the ceramic capacitor applications.

Ferroelectric/paraelectric superlattices for energy storage

The polarization response of antiferroelectrics to electric fields is such that the materials can store large energy densities, which makes them promising candidates for energy storage applications in pulsed-power technologies. However, relatively few materials of this kind are known. Here, we consider ferroelectric/paraelectric superlattices as artificial electrostatically engineered antiferroelectrics. Specifically, using high-throughput second-principles calculations, we engineer PbTiO₃/SrTiO₃ superlattices to optimize their energy storage performance at room temperature (to maximize density and release efficiency) with respect to different design variables (layer thicknesses, epitaxial conditions, and stiffness of the dielectric layer). We obtain results competitive with the state-of-the-art antiferroelectric capacitors and reveal the mechanisms responsible for the optimal properties.

First-Principles Study of n*AlN/n*ScN Superlattices with High Dielectric Capacity for Energy Storage

As a paradigm of exploiting electronic-structure engineering on semiconductor superlattices to develop advanced dielectric film materials with high electrical energy storage, the n*AlN/n*ScN superlattices are systematically investigated by first-principles calculations of structural stability, band structure and dielectric polarizability. Electrical energy storage density is evaluated by dielectric permittivity under a high electric field approaching the uppermost critical value determined by a superlattice band gap, which hinges on the constituent layer thickness and crystallographic orientation of superlattices. It is demonstrated that the constituent layer thickness as indicated by larger n and superlattice orientations as in (111) crystallographic plane can be effectively exploited to modify dielectric permittivity and band gap, respectively, and thus promote energy density of electric capacitors. Simultaneously increasing the thicknesses of individual constituent layers maintains adequate band gaps while slightly reducing dielectric polarizability from electronic localization of valence band-edge in ScN constituent layers. The AlN/ScN superlattices oriented in the wurtzite (111) plane acquire higher dielectric energy density due to the significant improvement in electronic band gaps. The present study renders a framework for modifying the band gap and dielectric properties to acquire high energy storage in semiconductor superlattices.

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.

Anomalous structural behavior and antiferroelectricity in BiGdO3: detailed temperature and high-pressure study

A comprehensive temperature and high-pressure investigation on BiGdO₃is carried out by means of dielectric constant, piezoelectric current, polarization-electric field loop, Raman scattering and x-ray diffraction measurements. Temperature dependent dielectric constant and dielectric loss show two anomalies at about 290 K (T_r) and 720 K (T_C). The latter anomaly is most likely due to antiferroelectric to paraelectric transition as hinted by piezoelectric current and polarization-electric field loop measurements at room temperature, while the former anomaly suggests reorientation of polarization. A small deviation from linear behaviour of both the Raman modes due to structural modification in the vicinity ofT_C; and sharp decrease in integrated intensities of these two modes aboveT_Cprovide further proof for the above antiferroelectric to paraelectric transition. Cubic to monoclinic structural transition is observed at about 10 GPa in high-pressure x-ray diffraction studies accompanied by anisotropic lattice parameter changes and large unit cell volume collapse during the transition. This structural transition is corroborated by anomalous softening and large increase in full width half maximum of M₂(640 cm^-1) Raman mode above 10 GPa. We speculate that enhancement of large structural distortion and large reduction inc/aratio above 10 GPa might be associated with antiferroelectric to ferroelectric transition in the system.

Enhancement of Energy-Storage Density in PZT/PZO-Based Multilayer Ferroelectric Thin Films

PbZr_0.35Ti_0.65O₃ (PZT), PbZrO₃ (PZO), and PZT/PZO ferroelectric/antiferroelectric multilayer films were prepared on a Pt/Ti/SiO₂/Si substrate using the sol–gel method. Microstructures and physical properties such as the polarization behaviors, leakage current, dielectric features, and energy-storage characteristics of the three films were systematically explored. All electric field-dependent phase transitions, from sharp to diffused, can be tuned by layer structure, indicated by the polarization, shift current, and dielectric properties. The leakage current behaviors suggested that the layer structure could modulate the current mechanism, including space-charge-limited bulk conduction for single layer films and Schottky emission for multilayer thin films. The electric breakdown strength of a PZT/PZO multilayer structure can be further enhanced to 1760 kV/cm, which is higher than PZT (1162 kV/cm) and PZO (1373 kV/cm) films. A recoverable energy-storage density of 21.1 J/cm³ was received in PZT/PZO multilayers due to its high electric breakdown strength. Our results demonstrate that a multilayer structure is an effective method for enhancing energy-storage capacitors.

Energy Storage Ceramics: A Bibliometric Review of Literature

Energy storage ceramics is among the most discussed topics in the field of energy research. A bibliometric analysis was carried out to evaluate energy storage ceramic publications between 2000 and 2020, based on the Web of Science (WOS) databases. This paper presents a detailed overview of energy storage ceramics research from aspects of document types, paper citations, h-indices, publish time, publications, institutions, countries/regions, research areas, highly cited papers, and keywords. A total of 3177 publications were identified after retrieval in WOS. The results show that China takes the leading position in this research field, followed by the USA and India. Xi An Jiao Tong Univ has the most publications, with the highest h-index. J.W. Zhai is the most productive author in energy storage ceramics research. Ceramics International, Journal of Materials Science-Materials in Electronics, and the Journal of Alloys and Compounds are the most productive journals in this field, and materials science—multidisciplinary is the most frequently used subject category. Keywords, highly cited papers, and the analysis of popular papers indicate that, in recent years, lead-free ceramics are prevalent, and researchers focus on fields such as the microstructure, thin films, and phase transition of ceramics.

Recent Advances in the Synthesis of Polymer-Grafted Low-K and High-K Nanoparticles for Dielectric and Electronic Applications

The synthesis of polymer-grafted nanoparticles (PGNPs) or hairy nanoparticles (HNPs) by tethering of polymer chains to the surface of nanoparticles is an important technique to obtain nanostructured hybrid materials that have been widely used in the formulation of advanced polymer nanocomposites. Ceramic-based polymer nanocomposites integrate key attributes of polymer and ceramic nanomaterial to improve the dielectric properties such as breakdown strength, energy density and dielectric loss. This review describes the "grafting from" and "grafting to" approaches commonly adopted to graft polymer chains on NPs pertaining to nano-dielectrics. The article also covers various surface initiated controlled radical polymerization techniques, along with templated approaches for grafting of polymer chains onto SiO2, TiO2, BaTiO3, and Al2O3 nanomaterials. As a look towards applications, an outlook on high-performance polymer nanocomposite capacitors for the design of high energy density pulsed power thin-film capacitors is also presented.

Excellent Reliability and High-Speed Antiferroelectric HfZrO2 Tunnel Junction by a High-Pressure Annealing Process and Built-In Bias Engineering

Hafnia-based ferroelectric tunnel junctions (FTJs) have great potential for use in logic in nonvolatile memory because of their complementary metal-oxide-semiconductor process compatibility, low power consumption, high scalability, and nondestructive readout. However, typically, ferroelectrics have a depolarization field, resulting in poor endurance owing to the early dielectric breakdown. Herein, an outstandingly reliable and high-speed antiferroelectric HfZrO tunnel junction (AFTJ) is probed to understand whether it is a promising candidate for next-generation nonvolatile memory applications. High-reliability AFTJ can be explained by less charge injection due to the low depolarized field. The formation of two stable nonvolatile states, even with antiferroelectric materials, is possible if asymmetric work function electrodes and fixed oxide charges are employed, generating a built-in bias and shifting the polarization-voltage curve. In addition, via high-pressure annealing, a critical voltage that determines the transition from the t-phase to the o-phase is effectively reduced (22%). The AFTJ shows a higher endurance property (>10⁹ cycles) and faster switching speed (<30 ns) than FTJ. Hence, it is proposed that with the help of internal bias modulation and high-pressure annealing, AFTJs can be employed in next-generation memory devices.

Re-evaluation of the Energy Density Properties of VDF Ferroelectric Thin-Film Capacitors

Large dielectric constants and small remanent polarization of the relaxor-ferroelectric (RFE) polymers are favored for energy-harvesting applications. Here, the energy harvesting of RFE thin films of vinylidene fluoride (VDF)-based terpolymers were re-evaluated. VDF-based terpolymers with trifluoroethylene (TrFE) and chlorofluoroethylene (CFE), CFE terpolymer, and those with TrFE and chlorotrifluoroethylene were used. Thermally annealed CFE terpolymer exhibited an energy density of 8.3 J cm^-3 and an energy efficiency of 82% at a field of 280 MV m^-1. The high-energy efficiency was related to the narrow bipolar hysteresis of displacement (D)-electric field (E) of the CFE terpolymer film. This narrow D-E hysteresis was a sum of the unipolar hysteresis directed toward the positive electric field region and that toward the negative electric field region, which suggested antiferroelectric-like behavior.

Antiferroelectric Bent-Core Liquid Crystal for Possible High-Power Capacitors and Electrocaloric Devices

We present small-angle X-ray scattering, polarized optical microscopy and electric current measurements of a sulfur-containing bent-core liquid crystal material for characterization of the layer and director structures, thermally and electrically driven transitions between antiferroelectric and ferroelectric structures and switching properties. It was found that the material has polarization-modulated homochiral synclinic ferroelectric (SmCsPFmod), homochiral anticlinic antiferroelectric (SmCaPA) and racemic synclininc antiferroelectric (SmCsPA) structures that can be reversibly switched between each other either thermally and/or electrically. High switching polarization combined with softness of the liquid crystalline structure makes this compound a good candidate for applications in high-power capacitors and electrocaloric devices.

Realizing Stable Relaxor Antiferroelectric and Superior Energy Storage Properties in (Na1-x/2Lax/2)(Nb1-xTix)O3 Lead-Free Ceramics through A/B-Site Complex Substitution

The development of environmentally friendly energy storage dielectrics with high energy storage density has attracted increasing attention in power electronics. The combination of antiferroelectric ceramics with relaxor characteristics proves to be an efficient way to greatly improve energy storage properties. In this work, a novel (Na_1-x/2La_x/2)(Nb_1-xTi_x)O₃ lead-free bulk ceramic exhibits excellent energy storage properties of a giant recoverable energy storage density W_rec ≈ 6.5 J/cm³, a relatively high efficiency η ≈ 66%, and an ultrafast discharge speed t_0.9 ≈ 50 ns at x = 0.18, showing outstanding potential for pulsed power capacitors. The Rietveld structural refinement and Raman spectra suggest a relaxor antiferroelectric orthorhombic R phase at room temperature as x > 0.16. Obviously enhanced breakdown strength can be ascribed to ultrafine grains of ∼0.21 μm and largely improved resistivity after BaCu(B₂O₅) doping. The detailed analysis of high-resolution transmission electron microscopy and in situ field Raman spectra clearly discloses the existence and rapid response feature of antipolar nanoregions and the resulting high driving field (∼30 kV/mm) for the antiferroelectric-to-ferroelectric phase transition, laying a solid foundation for the achievement of desirable energy storage characteristics. These results would provide a reliable strategy and a good understanding for designing new energy storage capacitor dielectrics.

Achieving Remarkable Amplification of Energy-Storage Density in Two-Step Sintered NaNbO3-SrTiO3 Antiferroelectric Capacitors through Dual Adjustment of Local Heterogeneity and Grain Scale

Antiferroelectric (AFE) materials exhibit outstanding advantages against linear or ferroelectric (FE) dielectrics in high-performance energy-storage capacitors. However, their energy-storage performances are usually restricted by both extremely large hysteresis and insufficiently high driving field of the AFE-FE phase transition, which has been a longstanding issue to be overcome in the community. In this work, we report a two-step sintered 0.83NaNbO₃-0.17SrTiO₃ (NN-ST) lead-free relaxor AFE R-phase ceramic with high relative density of ≥95% and large spans of average grain sizes from 1.2 to 8.2 μm, strikingly achieving a giant amplification of recoverable energy-storage density (W_rec) by 176%. Analyses of permittivity-temperature curves, Raman spectrum and microstructure demonstrate that remarkably enhanced W_rec values should be ascribed to the dual adjustment of local heterogeneity (nanoscale) and grain scale (microscale), resulting in the enhanced threshold field strength for dielectric breakdown and the increased critical electric fields for the AFE-FE phase transition. A high W_rec ≈ 1.60 J/cm³, a fast discharging rate t_0.9 ≈ 520 ns, large current density ∼788 A/cm², and large power density ∼55 MW/cm³ are achieved at room temperature in the NN-ST ceramic sample with an average grain size of ∼1.2 μm. These results suggest that the multiscale structure regulation should be an efficient way for achieving enhanced energy-storage properties in NN-ST relaxor AFE ceramics through a two-step sintering technique.

Nonstoichiometric charge defect induced relaxor antiferroelectric ordering in La modified Bi0.5 (Na0.80K0.20)0.5TiO3 relaxor ferroelectric

The effect of A-site nonstoichiometric in La³⁺ modified Bi_0.5(Na_0.80K_0.20)_0.5TiO₃/BNKT solid solution on crystal structure and electrical properties have been investigated. Evolution of crystal structure from rhombohedral (R3c) to tetragonal (P4bm) symmetry with reduction of the lattice distortion has been observed. The Raman spectra analysis is well supported to the crystal structure study from the XRD patterns analysis. The presence of charge defects due to non-stoichiometric composition and the reduction of oxygen vacancies have been confirmed by the x-ray photoelectron spectra (XPS) of the respective elements. The FESEM (field emission scanning electron microscopy) micrographs clearly show the reduction of grain size with the incorporation of La³⁺ in A-site of BNKT. The multiple dielectric anomalies near depolarization temperature (T _d) and temperature at maximum dielectric value (T _m) in the temperature dependent dielectric curves ascribe the diffuse phase transition with relaxor ferroelectric nature. The dielectric anomalies at T _d and T _m become more pronounce with the increase in addition of La³⁺ into BNKT lattice. The presence of charge defects with A-sites complexity leads to interrupt the long range polar ferroelectric domains and, forms the polar nanoregions (PNRs). The competition between ferroelectric R3c symmetry and non-polar P4bm symmetry with the addition of La³⁺ into the BNKT lattice induces an intermediate modulated phase, which exhibits the antiferroelectric in nature having pinched ferroelectric hysteresis loop.

Giant Negative Electrocaloric Effect in Anti-Ferroelectric (Pb0.97La0.02)(Zr0.95Ti0.05)O3 Ceramics

A giant electrocaloric effect is reported in (Pb_0.97La_0.02)(Zr_0.95Ti_0.05)O₃ anti-ferroelectric ceramics. These samples were fabricated by a solid-state mixed oxide technique. Dielectric analyses were employed to investigate the anti-ferroelectric (AFE) and ferroelectric (FE) phase transitions of the sample. During the heating process, the phase transition from the orthorhombic anti-ferroelectric phase (AFE_O) to the tetragonal anti-ferroelectric phase (AFE_T) occurs at 155 °C, and the phase transition from AFE_T to PE occurs at 225 °C. Using the Maxwell relationship, the entropy change ΔS and adiabatic temperature change ΔT were obtained at different electric fields ranging from 40 to 65 kV/cm. The maximum adiabatic temperature change (ΔT _max = -7.47 K) was obtained at 50 kV/cm, which was attributed to the field-induced phase transformation between the anti-ferroelectric and ferroelectric phases. These results showed that PLZT2/95/5 ceramics possess a large negative electrocaloric effect value, which could be applied in achieving cooling power as refrigerants.

Achieving ultrahigh energy storage density and energy efficiency simultaneously in sodium niobate-based lead-free dielectric capacitors via microstructure modulation

Recently, dielectric capacitors have drawn much attention from researchers and engineers due to their ultrahigh power density, ultrafast charge–discharge rate, and good temperature and fatigue stability.

Multilayer Lead-Free Ceramic Capacitors with Ultrahigh Energy Density and Efficiency

The utilization of antiferroelectric (AFE) materials is thought to be an effective approach to enhance the energy density of dielectric capacitors. However, the high energy dissipation and inferior reliability that are associated with the antiferroelectric-ferroelectric phase transition are the main issues that restrict the applications of antiferroelectric ceramics. Here, simultaneously achieving high energy density and efficiency in a dielectric ceramic is proposed by combining antiferroelectric and relaxor features. Based on this concept, a lead-free dielectric (Na_0.5 Bi_0.5 )TiO₃ -x(Sr_0.7 Bi_0.2 )TiO₃ (NBT-xSBT) system is investigated and the corresponding multilayer ceramic capacitors (MLCCs) are fabricated. A record-high energy density of 9.5 J cm^-3 , together with a high energy efficiency of 92%, is achieved in NBT-0.45SBT multilayer ceramic capacitors, which consist of ten dielectric layers with the single-layer thickness of 20 µm and the internal electrode area of 6.25 mm² . Furthermore, the newly developed capacitor exhibits a wide temperature usage range of -60 to 120 °C, with an energy-density variation of less than 10%, and satisfactory cycling reliability, with degradation of less than 8% over 10⁶ cycles. These characteristics demonstrate that the NBT-0.45SBT multilayer ceramic is a promising candidate for high-power energy storage applications.

Boosting the Recoverable Energy Density of Lead-Free Ferroelectric Ceramic Thick Films through Artificially Induced Quasi-Relaxor Behavior

Dielectric ceramic film capacitors, which store energy in the form of electric polarization, are promising for miniature pulsed power electronic device applications. For a superior energy storage performance of the capacitors, large recoverable energy density, along with high efficiency, high power density, fast charge/discharge rate, and good thermal/fatigue stability, is desired. Herein, we present highly dense lead-free 0.942[Na_0.535K_0.480NbO₃]-0.058LiNbO₃ (KNNLN) ferroelectric ceramic thick films (∼5 μm) demonstrating remarkable energy storage performance. The nanocrystalline KNNLN thick film fabricated by aerosol deposition (AD) process and annealed at 600 °C displayed a quasi-relaxor ferroelectric behavior, which is in contrast to the typical ferroelectric nature of the KNNLN ceramic in its bulk form. The AD film exhibited a large recoverable energy density of 23.4 J/cm³, with an efficiency of over 70% under the electric field of 1400 kV/cm. Besides, an ultrahigh power density of 38.8 MW/cm³ together with a fast discharge speed of 0.45 μs, good fatigue endurance (up to 10⁶ cycles), and thermal stability in a wide temperature range of 20-160 °C was also observed. Using the AD process, we could make a highly dense microstructure of the film containing nano-sized grains, which gave rise to the quasi-relaxor ferroelectric characteristics and the remarkable energy storage properties.

High Energy Storage Density and Impedance Response of PLZT2/95/5 Antiferroelectric Ceramics

(Pb_0.97La_0.02)(Zr_0.95Ti_0.05)O₃ (PLZT2/95/5) ceramics were successfully prepared via a solid-state reaction route. The dielectric properties were investigated in the temperature region of 26–650 °C. The dielectric diffuse anomaly in the dielectric relaxation was found in the high temperature region of 600–650 °C with increasing the measuring frequency, which was related to the dynamic thermal process of ionized oxygen vacancies generated in the high temperature. Two phase transition points were detected during heating, which were found to coexist from 150 to 200 °C. Electric field induced ferroelectric to antiferroelectric phase transition behavior of the (Pb_0.97La_0.02)(Zr_0.95Ti_0.05)O₃ ceramics was investigated in this work with an emphasis on energy storage properties. A recoverable energy-storage density of 0.83 J/cm³ and efficiency of 70% was obtained in (Pb_0.97La_0.02)(Zr_0.95Ti_0.05)O₃ ceramics at 55 kV/cm. Based on these results, (Pb_0.97La_0.02)(Zr_0.95Ti_0.05)O₃ ceramics with a large recoverable energy-storage density could be a potential candidate for the applications in high energy-storage density ceramic capacitors.

Antiferroelectric to relaxor ferroelectric phase transition in PbO modified (Pb0.97La0.02)(Zr0.95Ti0.05)O3 ceramics with a large energy-density for dielectric energy storage

The recoverable energy density and energy efficiency of the high energy density electrification PLZT2/95/5 ceramic capacitors as a function of the temperature and electric field.