Multifunctional BaTiO3-Based Relaxor Ferroelectrics toward Excellent Energy Storage Performance and Electrostrictive Strain Benefiting from Crossover Region

High performance relaxor ferroelectric textured ceramics for electrocaloric refrigeration

Relaxor ferroelectric ceramics have emerged as promising candidates for electrocaloric cooling systems due to their relatively higher heating and cooling capacities. However, simultaneously achieving high temperature changes (ΔT) and a wide operating temperature range remains a significant challenge, limiting their practical applications. This work proposes a synergistic strategy that involves precise compositional tuning of the BaTiO3-xKNbO3 system to customize the rhombohedral-to-cubic phase boundary around room temperature, coupled with engineering grain orientation of the ceramics. Based on this approach, a maximum ΔT of 3.9 K is achieved in <111>c-texture BaTiO3-KNbO3 ceramics, outperforming most environmentally friendly ceramics. Notably, the ΔT variation remains within ±10% across a temperature range of 30 °C to 80 °C, demonstrating a promising material for the design and application of electrocaloric cooling devices. This work provides new insights for the design of ceramics with optimized electrocaloric properties, offering significant potential for improving the efficiency and functionality of next-generation cooling technologies and devices.

Preparation and Properties of Nb5+-Doped BCZT-Based Ceramic Thick Films by Scraping Process

A bottleneck characterized by high strain and low hysteresis has constantly existed in the design process of piezoelectric actuators. In order to solve the problem that actuator materials cannot simultaneously exhibit large strain and low hysteresis under relatively high electric fields, Nb5+-doped 0.975(Ba0.85Ca0.15)[(Zr0.1Ti0.9)0.999Nb0.001]O3-0.025(Bi0.5Na0.5)ZrO3 (BCZTNb0.001-0.025BiNZ) ceramic thick films were prepared by a film scraping process combined with a solid-state twin crystal method, and the influence of sintering temperature was studied systematically. All BCZTNb0.001-0.025BiNZ ceramic thick films sintered at different sintering temperatures have a pure perovskite structure with multiphase coexistence, dense microstructure and typical dielectric relaxation behavior. The conduction mechanism of all samples at high temperatures is dominated by oxygen vacancies confirmed by linear fitting using the Arrhenius law. As the sintering temperature elevates, the grain size increases, inducing the improvement of dielectric, ferroelectric and field-induced strain performance. The 1325 °C sintered BCZTNb0.001-0.025BiNZ ceramic thick film has the lowest hysteresis (1.34%) and relatively large unipolar strain (0.104%) at 60 kV/cm, showing relatively large strain and nearly zero strain hysteresis compared with most previously reported lead-free piezoelectric ceramics and presenting favorable application prospects in the actuator field.

Near-Zero Energy Consumption Capacitors by Controlling Inhomogeneous Polarization Configuration

Taking into account the need for energy conservation, achieving near-zero energy loss, namely ultrahigh efficiency (η), in energy storage capacitors with large recoverable energy storage density (Wrec) plays an important role in applications, which is one of the major challenges in dielectric energy storage field. Here, guided by phase-field simulation, inhomogeneous polarization configuration with multiple symmetries and polarization magnitudes is controlled through aliovalent strongly polar double ion design to establish a strongly disordered state. A record-high η of ≈97.4% is realized in lead-free relaxors with a large Wrec of ≈8.6 J cm-3, which also give a giant Wrec of ≈11.6 J cm-3 with an ultrahigh η of ≈96.1% through high-energy ball milling, showing a breakthrough progress in ceramic capacitors with a maximum figure of merit of 330. This work demonstrates that controlling inhomogeneous polarization configuration is an effective avenue to develop new high-performance near-zero energy loss energy storage capacitors.

Chemical Framework to Design Linear-like Relaxors toward Capacitive Energy Storage

ABO3-type perovskite relaxor ferroelectrics (RFEs) have emerged as the preferred option for dielectric capacitive energy storage. However, the compositional design of RFEs with high energy density and efficiency poses significant challenges owing to the vast compositional space and the absence of general rules. Here, we present an atomic-level chemical framework that captures inherent characteristics in terms of radius and ferroelectric activity of ions. By categorizing A/B-site ions as host framework, rattling, ferroelectrically active, and blocking ions and assembling these four types of ions with specific criteria, linear-like relaxors with weak locally correlated and highly extendable unit-cell polarization vectors can be constructed. As example, we demonstrate two new compositions of Bi0.5K0.5TiO3-based and BaTiO3-based relaxors, showing extremely high recoverable energy densities of 17.3 and 12.1 J cm-3, respectively, both with a high efficiency of about 90%. Further, the role of different types of ions in forming heterogeneous polar structures is identified through element-specific local structure analysis using neutron total scattering combined with reverse Monte Carlo modeling. Our work not only opens up new avenues toward rational compositional design of high energy storage performance lead-free RFEs but also sheds light on atomic-level manipulation of functional properties in compositionally complex ferroelectrics.

Excellent Energy-Storage Performance in Lead-Free Capacitors with Highly Dynamic Polarization Heterogeneous Nanoregions

Lead-free dielectric ceramics with excellent energy-storage performance are crucial to the development of the next-generation advanced pulse power capacitors. However, low energy-storage density limits the evolution of capacitors toward lightweight, miniaturization, and integration. Here, an effective strategy of constructing highly dynamic polarization heterogeneous nanoregions is proposed in lead-free relaxors to realize an ultrahigh energy-storage density of ≈8.0 J cm-3 , making almost ten times the growth of energy-storage density compared with pure Bi0.5 Na0.5 TiO3 ceramic, accompanied by a higher energy efficiency of ≈80% as well as an ultrafast discharge rate of ≈20 ns. Ultrasmall polarization heterogeneous nanoregions with different orientations and ultrahigh flexibility, and significantly decreased grain size to submicron lead to reduced heat loss, improved breakdown electric field and polarization, enhanced relaxation, and delayed polarization saturation behaviors, contributing to the remarkable energy-storage performance. Moreover, the breakdown path distribution or electrical tree evolution behaviors are systematically studied to reveal the origin of ultrahigh breakdown electric field through phase field simulations. This work demonstrates that constructing highly dynamic polarization heterogeneous nanoregions is a powerful approach to develop new lead-free dielectric materials with high energy-storage performance.

Improved Energy Storage Density and Efficiency of Nd and Mn Co-Doped Ba0.7Sr0.3TiO3 Ceramic Capacitors Via Defect Dipole Engineering

In this paper, we investigate the structural, microstructural, dielectric, and energy storage properties of Nd and Mn co-doped Ba0.7Sr0.3TiO3 [(Ba0.7Sr0.3)1-xNdxTi1-yMnyO3 (BSNTM) ceramics (x = 0, 0.005, and y = 0, 0.0025, 0.005, and 0.01)] via a defect dipole engineering method. The complex defect dipoles (MnTi"-VO∙∙)∙ and (MnTi"-VO∙∙) between acceptor ions and oxygen vacancies capture electrons, enhancing the breakdown electric field and energy storage performances. XRD, Raman, spectroscopy, XPS, and microscopic investigations of BSNTM ceramics revealed the formation of a tetragonal phase, oxygen vacancies, and a reduction in grain size with Mn dopant. The BSNTM ceramics with x = 0.005 and y = 0 exhibit a relative dielectric constant of 2058 and a loss tangent of 0.026 at 1 kHz. These values gradually decreased to 1876 and 0.019 for x = 0.005 and y = 0.01 due to the Mn2+ ions at the Ti4+- site, which facilitates the formation of oxygen vacancies, and prevents a decrease in Ti4+. In addition, the defect dipoles act as a driving force for depolarization to tailor the domain formation energy and domain wall energy, which provides a high difference between the maximum polarization of Pmax and remnant polarization of Pr (ΔP = 10.39 µC/cm2). Moreover, the complex defect dipoles with optimum oxygen vacancies in BSNTM ceramics can provide not only a high ΔP but also reduce grain size, which together improve the breakdown strength from 60.4 to 110.6 kV/cm, giving rise to a high energy storage density of 0.41 J/cm3 and high efficiency of 84.6% for x = 0.005 and y = 0.01. These findings demonstrate that defect dipole engineering is an effective method to enhance the energy storage performance of dielectrics for capacitor applications.

Enhanced Energy Storage Performance and Efficiency in Bi0.5(Na0.8K0.2)0.5TiO3-Bi0.2Sr0.7TiO3 Relaxor Ferroelectric Ceramics via Domain Engineering

Dielectric materials are highly desired for pulsed power capacitors due to their ultra-fast charge-discharge rate and excellent fatigue behavior. Nevertheless, the low energy storage density caused by the low breakdown strength has been the main challenge for practical applications. Herein, we report the electric energy storage properties of (1 - x) Bi_0.5(Na_0.8K_0.2)_0.5TiO₃-xBi_0.2Sr_0.7TiO₃ (BNKT-BST; x = 0.15-0.50) relaxor ferroelectric ceramics that are enhanced via a domain engineering method. A rhombohedral-tetragonal phase, the formation of highly dynamic PNRs, and a dense microstructure are confirmed from XRD, Raman vibrational spectra, and microscopic investigations. The relative dielectric permittivity (2664 at 1 kHz) and loss factor (0.058) were gradually improved with BST (x = 0.45). The incorporation of BST into BNKT can disturb the long-range ferroelectric order, lowering the dielectric maximum temperature T_m and inducing the formation of highly dynamic polar nano-regions. In addition, the T_m shifts toward a high temperature with frequency and a diffuse phase transition, indicating relaxor ferroelectric characteristics of BNKT-BST ceramics, which is confirmed by the modified Curie-Weiss law. The rhombohedral-tetragonal phase, fine grain size, and lowered T_m with relaxor properties synergistically contribute to a high P_max and low P_r, improving the breakdown strength with BST and resulting in a high recoverable energy density W_rec of 0.81 J/cm³ and a high energy efficiency η of 86.95% at 90 kV/cm for x = 0.45.

Superior Capacitive Energy-Storage Performance in Pb-Free Relaxors with a Simple Chemical Composition

Chemical design of lead-free relaxors with simultaneously high energy density (W_rec) and high efficiency (η) for capacitive energy-storage has been a big challenge for advanced electronic systems. The current situation indicates that realizing such superior energy-storage properties requires highly complex chemical components. Herein, we demonstrate that, via local structure design, an ultrahigh W_rec of 10.1 J/cm³, concurrent with a high η of 90%, as well as excellent thermal and frequency stabilities can be achieved in a relaxor with a very simple chemical composition. By introducing 6s² lone pair stereochemical active Bi into the classical BaTiO₃ ferroelectric to generate a mismatch between A- and B-site polar displacements, a relaxor state with strong local polar fluctuations can be formed. Through advanced atomic-resolution displacement mapping and 3D reconstructing the nanoscale structure from neutron/X-ray total scattering, it is revealed that the localized Bi enhances the polar length largely at several perovskite unit cells and disrupts the long-range coherent Ti polar displacements, resulting in a slush-like structure with extremely small size polar clusters and strong local polar fluctuations. This favorable relaxor state exhibits substantially enhanced polarization, and minimized hysteresis at a high breakdown strength. This work offers a feasible avenue to chemically design new relaxors with a simple composition for high-performance capacitive energy-storage.

Local Diverse Polarization Optimized Comprehensive Energy-Storage Performance in Lead-Free Superparaelectrics

Lead-free dielectric ceramics with ultrahigh energy-storage performance are the core components used in next-generation advanced pulse power capacitors. However, the low energy storage density largely hinders their development towards miniaturization, lightweight, and integration. Here, an effective strategy of constructing local diverse polarization is designed in superparaelectrics to realize an ultrahigh energy storage density of ≈10.59 J cm^-3 as well as a large efficiency of ≈87.6%. The excellent comprehensive energy-storage performance is mainly attributed to the design of ultrasmall polar nanoregions with local diverse polarization configuration, confirmed by scanning transmission electron microscopy, leading to the reduced heat loss, substantially enhanced polarization, and breakdown electric field compared to ceramics with single polarization configuration. Benefiting from these features, outstanding temperature/frequency/cycling stability and superior charge/discharge performance (power density ≈187.5 MW cm^-3 , discharge energy density ≈3.52 J cm^-3 , discharge rate ≈77 ns) are also achieved. This work demonstrates that local diverse polarization is a super strategy to design new dielectric materials with high energy-storage performance.

Adjusting the Energy-Storage Characteristics of 0.95NaNbO3-0.05Bi(Mg0.5Sn0.5)O3 Ceramics by Doping Linear Perovskite Materials

Passive electronic components are an indispensable part of integrated circuits, which are key to the miniaturization and integration of electronic components. As an important branch of passive devices, the relatively low energy-storage capacity of ceramic capacitors limits their miniaturization. To solve this problem, this study adopts the strategy of doping linear materials, specifically CT, into 0.95NaNbO₃-0.05Bi(Mg_0.5Sn_0.5)O₃ (0.95NN-0.05BMS) ceramics to increase the disorder of the system through the nonequivalent substitution of A and B sites to achieve the sintering temperature and the residual polarization. Meanwhile, the breakdown electric field strength (E_b) is improved by adjusting the activation energy of the material and the relative density of the sample. Thus, an ultrahigh W_rec of 6.35 J/cm³ and a η of 80% are obtained at an E_b of 646 kV/cm. Additionally, through the analysis of the dielectric temperature spectrum, it is found that the 0.88(0.95NN-0.05BMS)-0.12CT sample can satisfy the technical standards of general ceramic Z5U and patch ceramic X6R. The performance of the ceramics also remains stable within a temperature range of 20-200 °C, a frequency range of 1-100 Hz, and 10⁴ cycles. The charge and discharge tests of the ceramics show that the t_0.9 of the sample floats between 1.02 and 1.04 μs, which illustrates its potential application in the field of pulsed power components.

High-Energy Storage Properties over a Broad Temperature Range in La-Modified BNT-Based Lead-Free Ceramics

The development of high-performance energy storage materials is decisive for meeting the miniaturization and integration requirements in advanced pulse power capacitors. In this study, we designed high-performance [(Bi_0.5Na_0.5)_0.94Ba_0.06]_(1-1.5x)La_xTiO₃ (BNT-BT-xLa) lead-free energy storage ceramics based on their phase diagram. A strategy combining phase adjustment and domain control via doping was proposed to enhance the energy storage performance. The obtained results showed that La³⁺ ions doped into BNT-BT improved the crystal structure symmetry and induced a strong dielectric relaxation behavior, which destroyed the long-term ferroelectric order and effectively promoted the formation of polar nanoregions. At x = 0.12, a high recoverable energy density (W_rec) of ∼5.93 J/cm³ and a relatively large energy storage efficiency (η) of 77.6% were obtained under a high breakdown electric field of 440 kV/cm. By using a two-step sintering approach for the microstructural optimization, the energy storage performance was further improved, yielding much higher W_rec (6.69 J/cm³) and η (87.0%). Additionally, both conventionally sintered and two-step-sintered samples showed excellent frequency stability (0.5-500 Hz), thermal endurance (25-180 °C), and fatigue resistance (10⁵ cycles). Regarding the pulse charge-discharge performance, the samples exhibited ultrashort discharge time (t_0.9 ∼ 89 ns for the conventionally sintered sample and ∼75 ns for the two-step-sintered sample) under an electric field of 240 kV/cm. Furthermore, the breakdown process of the material was simulated based on the finite element analysis, and it was shown that high breakdown strength of the material could be ascribed to fine grains, which significantly hindered the crack propagation during the application of the electric field. These results show that the presented materials have great potential as high-energy storage capacitors.

Achieving a Record-High Capacitive Energy Density on Si with Columnar Nanograined Ferroelectric Films

High energy density dielectric film capacitors are desirable in modern electronic devices. Their miniaturization and integration into Si-based microsystems create opportunities for in-circuit energy supply, buffering, and conditioning. Here, we present a CMOS (complementary metal oxide semiconductor)-compatible route for the fabrication of BaTiO₃ film capacitors on Si with a record-high recoverable energy density and good efficiency (∼242 J/cm³ and ∼76% at 8.75 MV/cm). These BaTiO₃ films were sputter-deposited at 350 °C and consisted of slightly compressed superfine columnar nanograins with a (001) texture. Such a nanostructure was endowed with a high breakdown strength, a reduced remnant polarization, and an enhanced maximum polarization, which are accountable for their excellent energy storage performance. Moreover, these BaTiO₃ film capacitors displayed a high electrical fatigue resistance, a wide range of operating temperatures, and an excellent frequency stability. With an engineered nanostructure, the prototype perovskite of BaTiO₃ has shown great promise for capacitive energy storage applications.

Domain Engineered Lead-Free Ceramics with Large Energy Storage Density and Ultra-High Efficiency under Low Electric Fields

Dielectric energy storage materials are becoming increasingly popular due to their potential superiority, for example, excellent pulse performance as well as good fatigue resistance. Although numerous studies have focused on lead-free dielectric materials which possess outstanding energy storage characteristics, the results are still not satisfying in terms of achieving both large discharging energy density (W_d) and high discharging efficiency (η) under low electric fields, which is crucial to be conducted in miniatured electronic components. Here, we adopt the strategy of domain engineering to develop sodium bismuth titanate (Bi_0.5Na_0.5TiO₃)-based ceramics employed in the low-field situation. Remarkably, a large W_d of 2.86 J/cm³ and an ultrahigh η of 90.3% are concurrently obtained in 0.94(Bi_0.5Na_0.5)_0.65(Ba_0.3Sr_0.7)_0.35TiO₃-0.06 Bi(Zn_2/3Nb_1/3)O₃ system when the electric field is as low as 180 kV/cm. Additionally, the ceramic shows brilliant thermal endurance (20-160 °C) and frequency stability (0.1-100 Hz) with high W_d (>1.48 J/cm³) together with an ultra-high η (>90%). What's more, the ceramic displays a fast charge-discharge time (t_0.9 = 109.2 ns). The piezoresponse force microscopy (PFM) results reveal that the introduced Bi(Zn_2/3Nb_1/3)O₃ disrupts the microdomains of (Bi_0.5Na_0.5)_0.65(Ba_0.3Sr_0.7)_0.35TiO₃ ceramics and promotes the formation of nanodomains, leading to enhanced energy storage properties. The current work may arouse interest in developing low-field high-performing dielectric capacitors for energy storage application.

Strategies to Improve the Energy Storage Properties of Perovskite Lead-Free Relaxor Ferroelectrics: A Review

Electrical energy storage systems (EESSs) with high energy density and power density are essential for the effective miniaturization of future electronic devices. Among different EESSs available in the market, dielectric capacitors relying on swift electronic and ionic polarization-based mechanisms to store and deliver energy already demonstrate high power densities. However, different intrinsic and extrinsic contributions to energy dissipations prevent ceramic-based dielectric capacitors from reaching high recoverable energy density levels. Interestingly, relaxor ferroelectric-based dielectric capacitors, because of their low remnant polarization, show relatively high energy density and thus display great potential for applications requiring high energy density properties. In this study, some of the main strategies to improve the energy density properties of perovskite lead-free relaxor systems are reviewed, including (i) chemical modification at different crystallographic sites, (ii) chemical additives that do not target lattice sites, and (iii) novel processing approaches dedicated to bulk ceramics, thick and thin films, respectively. Recent advancements are summarized concerning the search for relaxor materials with superior energy density properties and the appropriate choice of both composition and processing routes to match various applications' needs. Finally, future trends in computationally-aided materials design are presented.