Homogeneous/Inhomogeneous-Structured Dielectrics and their Energy-Storage Performances

Metaelectric multiphase transitions in a highly polarizable molecular crystal

Metaelectric transition, i.e. an abrupt increase in polarization with an electric field is just a phase change phenomenon in dielectrics and attracts increasing interest for practical applications such as electrical energy storage and highly deformable transducers. Here we demonstrate that both field-induced metaelectric transitions and temperature-induced phase transitions occur successively on a crystal of highly polarizable bis-(1H-benzimidazol-2-yl)-methane (BI2C) molecules. In each molecule, two switchable polar subunits are covalently linked with each other. By changing the NH hydrogen location, the low- and high-dipole states of each molecule can be interconverted, turning on and off the polarization of hydrogen-bonded molecular ribbons. In the low-temperature phase III, the tetragonal crystal lattice comprises orthogonally crossed arrays of polar ribbons made up of a ladder-like hydrogen-bond network of fully polarized molecules. The single-step metaelectric transition from this phase III corresponds to the forced alignment of antiparallel dipoles typical of antiferroelectrics. By the transition to the intermediate-temperature phase II, the polarity is turned off for half of the ribbons so that the nonpolar and polar ribbons are orthogonal to each other. Considering also the ferroelastic-like crystal twinning, the doubled steps of metaelectric transitions observed in the phase II can be explained by the additional switching at different critical fields, by which the nonpolar ribbons undergo "metadielectric" molecular transformation restoring the strong polarization. This mechanism inevitably brings about exotic phase change phenomena transforming the multi-domain state of a homogeneous phase into an inhomogeneous (phase mixture) state.

Enhanced Energy Storage Performance of Lead-Free Capacitors in an Ultrawide Temperature Range via Engineering Paraferroelectric and Relaxor Ferroelectric Multilayer Films

Industry has been seeking a thin-film capacitor that can work at high temperature in a harsh environment, where cooling systems are not desired. Up to now, the working temperature of the thin-film capacitor is still limited up to 200 °C. Herein, we design a multilayer structure with layers of paraferroelectric (Ba_0.3Sr_0.7TiO₃, BST) and relaxor ferroelectric (0.85BaTiO₃-0.15Bi(Mg_0.5Zr_0.5)O₃, BT-BMZ) to realize optimum properties with a flat platform of dielectric constant and high breakdown strength for excellent energy storage performance at high temperature. Through optimizing the multilayer structure, a highly stable relaxor ferroelectric state is obtained for the BST/BT-BMZ multilayer thin-film capacitor with a total thickness of 230 nm, a period number N = 8, and a layer thickness ratio of BST/BT-BMZ = 3/7. The optimized multilayer film shows significantly improved energy storage density (up to 30.64 J/cm³) and energy storage efficiency (over 70.93%) in an ultrawide temperature range from room temperature to 250 °C. Moreover, the multilayer system also exhibits excellent thermal stability in such an ultrawide temperature range with a change of 5.15 and 12.75% for the recoverable energy density and energy storage efficiency, respectively. Our results demonstrate that the designed thin-film capacitor is promising for the application in a harsh environment and open a way to tailor a thin-film capacitor toward higher working temperature with enhanced energy storage performance.

Interface-Strengthened Polymer Nanocomposites with Reduced Dielectric Relaxation Exhibit High Energy Density at Elevated Temperatures Utilizing a Facile Dual Crosslinked Network

High-temperature ceramic/polymer nanocomposites with large energy density as the reinforcement exhibit great potential for energy storage applications in modern electronic and electrical power systems. Yet, a general drawback is that the increased dielectric constant is usually achieved at the cost of decreased breakdown strength, thus leading to moderate improvement of energy density and even displaying a marked deterioration under high temperatures and high electric fields. Herein, a new strategy is reported to simultaneously improve breakdown strength and discharged energy density by a step-by-step, controllable dual crosslinking process, which constructs a strengthened interface as well as reduces molecular chains relaxation under elevated temperatures. Great breakdown strength and discharged energy density is achieved in the dual crosslinked network BT-BCB@DPAES nanocomposites at elevated temperatures when compared to noninterfacial-strengthened, BT/DPAES composites, i.e., an enhanced breakdown strength and a discharged energy density of 442 MV m^-1 and 3.1 J cm^-3 , increasing by 66% and 162%, and a stable cyclic performance over 10 000 cycles is demonstrated at 150 °C. Moreover, the enhancement through the synergy of two crosslinked networks is rationalized via a comprehensive phase-field model for the composites. This work offers a strategy to enhance the electric storage performances of composites at high temperatures.

Optimizing the Interdomain Spacing in Alicyclic Polythiourea toward High-Energy-Storable Dielectric Material

Organic dielectric materials have been widely developed and investigated for energy storage capacitors. However, challenges remain in terms of the relatively low dielectric constant and energy density. Enhancing the dipolar polarization to increase the dielectric constant is considered to be an effective way to improve the energy density of polymer dielectrics. Herein, enlightened by the chain-packing structure that affects the dipolar relaxation behavior, a simple and low-cost approach is proposed to tailor the interdomain spacing in an alicyclic polythiourea (PTU) by changing quenching temperatures and further facilitate the dipolar polarization. It is found that the large interdomain spacing is beneficial to promote the localized motion of segmental chains in amorphous regions, but at the same time inevitably reduces the dipole density. Therefore, in order to achieve the highest dielectric constant in the PTU, there is an optimal value for the interdomain spacing. It is worth noting that the dielectric constant of PTU increases from 5.7 to 10, and thus the energy density increases by 53% to 16.3 J cm^-3 . It proposes a simple and feasible strategy to further improve the energy density through optimizing the interdomain spacing toward high-energy-storable dielectric material.

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.

The role of PN-like junction effects in energy storage performances for Ag2O nanoparticle dispersed lead-free K0.5Na0.5NbO3-BiMnO3 films

This work designs a PN-like junction structure by introducing Ag₂O nanoparticles into lead-free 0.92K_0.5Na_0.5NbO₃-0.08BiMnO₃ solid solution films to investigate the role of PN-like junction effects in energy storage performances. It is shown that the energy storage performances are obviously improved with the energy density increasing to 65.1 J cm^-3 from 20.1 J cm^-3 and the efficiency to 62.6% from 50.7%. The enhancement is attributed to the formation of the depletion layer with high resistance derived from a PN-like junction structure at the interface between Ag₂O nanoparticles and matrices. The rectification effect of the high resistance region in PN-like junction improves the insulation and breakdown strength, and the internal local field derived from the high resistance region divides the macroscopic domains, which are attributed to the enhancement of energy storage performances. This work provides an alternative strategy to improve the energy storage performances by designing a PN-like junction structure.

Ultrahigh Energy Efficiency and Large Discharge Energy Density in Flexible Dielectric Nanocomposites with Pb0.97La0.02(Zr0.5SnxTi0.5-x)O3 Antiferroelectric Nanofillers

Flexible dielectric capacitors have been widely studied recently on account of their fast charge-discharge speed, high power density, and superior wearable characteristics. Inorganic ferroelectric fillers/polymer matrix composites combining large maximum electric displacement (D_max) of ferroelectric materials with good flexibility and high electric breakdown strength (E_b) of the polymer are regarded as the most promising materials for preparing flexible dielectric capacitors with superior energy storage properties. However, simultaneously achieving large discharge energy density (W_d) and high energy efficiency (η) in these composites remains challenging on account of a large remnant electric displacement (D_r) and low D_max - D_r values of ferroelectric fillers. In contrast, antiferroelectrics (AFEs) exhibit near zero D_r and larger D_max - D_r values and are thus attractive composite fillers to simultaneously achieve large W_d and high η. On the basis of these factors, in this report, we design and prepare Pb_0.97La_0.02(Zr_0.5Sn_xTi_0.5-x)O₃ (PLZST) AFE nanoparticles (NPs)/poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) nanocomposites and investigate the effects of the Sn and AFE NPs contents on the energy storage capacity of the nanocomposites. Through reasonable adjustment of the Sn content and the PLZST AFE fillers content, because of the large D_max - D_r value of 7.75 μC/cm² and small D_r value of 0.26 μC/cm² at the E_b as high as 3162 kV/cm, the Pb_0.97La_0.02(Zr_0.5Sn_0.38Ti_0.12)O₃ AFE NPs/P(VDF-HFP) polymer nanocomposite with 7 wt % fillers exhibits the most superior energy storage properties with an ultrahigh η of 93.4% and a large W_d of 12.5 J/cm³. These values are superior to those of the recently reported dielectric nanocomposites with a single-layer structure containing ferroelectric nanowires, nanofibers, nanobelts, nanotubes, and nanosheets or core-shell structure fillers, which are prepared via a very complicated method. This work not only shows that, in principle, the polarization characteristics of the composites depend mainly on those of the inorganic fillers but also demonstrates a convenient, effective, and scalable way to fabricate dielectric capacitors with superior flexibility and energy storage capacities.

Flexible and printable dielectric polymer composite with tunable permittivity and thermal stability

Lightweight and printable polymer dielectrics are ubiquitous in flexible hybrid electronics, exhibiting high breakdown strength and mechanical reliability. However, their advanced electronic applications are limited due to their relatively low permittivity, compared to their ceramic counterparts. Here, we report flexible all organic percolative nanocomposites that contain in situ grown conductive polymer networks and dielectric polymer matrix, in which their dielectric properties can be designed and guided from the percolation theory. High dielectric constant of all organic percolative nanocomposites is shown over a broad frequency range under intensive bending cycles, while their thermal stability is attributed to thermally conductive 2D montmorillonite nanosheets. The printable polymer composites with high dielectric performance and thermal stability will find broader interest in flexible hybrid electronics and radio frequency devices.

Local Structure Heterogeneity in Sm-Doped AgNbO3 for Improved Energy-Storage Performance

AgNbO₃-based antiferroelectric ceramics have been actively studied for energy-storage applications, where numerous compositional modifications have been implemented to improve their energy-storage performance. In this work, Sm₂O₃-doped AgNbO₃ ceramics were fabricated; the microstructure, dielectric property, and phase transition behavior were investigated. Because of the structure heterogeneity induced by the rare-earth dopant, a diffused antiferroelectric-to-paraelectric phase transition was observed. High-resolution transmission electron microscopy observations confirm the existence of a local pseudo-rhombohedral structure consisting of different lattice orderings, being responsible for the local nanoscale heterogeneity. Of particular significance is the fact that the Sm³⁺ dopant effectively decreases the dielectric loss and increases the critical antiferroelectric-ferroelectric phase transition electric field, leading to a high energy-storage density of 4.5 J/cm³.

Dielectric Properties of P(VDF-TrFE-CTFE) Composites Filled with Surface-Coated TiO2 Nanowires by SnO2 Nanoparticles

Nanocomposites containing inorganic fillers embedded in polymer matrices have exhibited great potential applications in capacitors. Therefore, an effective method to improve the dielectric properties of polymer is to design novel fillers with a special microstructure. In this work, a combination of hydrothermal method and precipitation method was used to synthesize in situ SnO₂ nanoparticles on the surface of one-dimensional TiO₂ nanowires (TiO₂ NWs), and the TiO₂NWs@SnO₂ fillers well-dispersed into the poly (vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) [P(VDF-TrFE-CTFE)] polymer. Hybrid structure TiO₂NWs @SnO₂ introduce extra interfaces, which enhance the interfacial polarization and the dielectric constant. Typically, at 10 vol.% low filling volume fraction, the composite with TiO₂NWs @SnO₂ shows a dielectric constant of 133.4 at 100 Hz, which is almost four times that of polymer. Besides, the TiO₂ NWs prevents the direct contact of SnO₂ with each other in the polymer matrix, so the composites still maintain good insulation performance. All the improved performance indicates these composites can be widely useful in electronic devices.

Dielectric Properties of Graphene/Titania/Polyvinylidene Fluoride (G/TiO2/PVDF) Nanocomposites

Flexible electronics have gained eminent importance in recent years due to their high mechanical strength and resistance to environmental conditions, along with their effective energy storage and energy generating abilities. In this work, graphene/ceramic/polymer based flexible dielectric nanocomposites have been prepared and their dielectric properties were characterized. The composite was formulated by combining graphene with rutile and anatase titania, and polyvinylidene fluoride in different weight ratios to achieve optimized dielectric properties and flexibility. After preparation, composites were characterized for their morphologies, structures, functional groups, thermal stability and dielectric characterizations by using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, thermal gravimetric analysis and impedance spectroscopy. Dielectric results showed that prepared flexible composite exhibited dielectric constant of 70.4 with minor leakage current (tanδ) i.e., 0.39 at 100 Hz. These results were further confirmed by calculating alternating current (AC) conductivity and electric modulus which ensured that prepared material is efficient dielectric material which may be employed in electronic industry for development of next generation flexible energy storage devices.

High energy-storage performance of PLZS antiferroelectric multilayer ceramic capacitors

A design methodology for developing antiferroelectric multilayer ceramic capacitors with high energy-storage performance.

Fabrication of BaTiO3-Loaded Graphene Nanosheets-Based Polyarylene Ether Nitrile Nanocomposites with Enhanced Dielectric and Crystallization Properties

In this paper, barium titanate@zinc phthalocyanine (BT@ZnPc) and graphene oxide (GO) hybrids (BT@ZnPc-GO) connected by calcium ions are prepared by electrostatic adsorption, and then introduced into polyarylene ether nitrile (PEN) to obtain composites with enhanced dielectric and crystallization properties. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) results confirm the successful fabrication of the BT@ZnPc-GO. BT@ZnPc-GO and PEN composites (BT@ZnPc-GO/PENs) are obtained through the solution-casting method. BT@ZnPc-GO demonstrates well compatibility with PEN due to its unique structure and the organic layer of ZnPc at the periphery of BT. On the other hand, BT and GO contribute a high dielectric constant of the composites obtained. In addition, the BT@ZnPc-GO can be used as a nucleating agent to promote the crystallization of the nanocomposites. As a result, The BT@ZnPc-GO/PEN exhibits a dielectric constant of 6.4 at 1 kHz and crystallinity of 21.03% after being isothermally treated at 280 °C for 2 h at the GO content of 0.75 wt %. All these results indicate that the hybrid nanofiller BT@ZnPc-GO can be an effective additive for preparing high-performance PEN-based nanocomposites.

Superior Thermal Stability of High Energy Density and Power Density in Domain-Engineered Bi0.5Na0.5TiO3-NaTaO3 Relaxor Ferroelectrics

Thermal-stable dielectric capacitors with high energy density and power density have attracted increasing attention in recent years. In this work, (1 - x)Bi_0.5Na_0.5TiO₃-xNaTaO₃ [(1 - x)BNT-xNT, x = 0-0.30] lead-free relaxor ferroelectric ceramics are developed for capacitor applications. The x = 0.20 ceramic exhibits superior thermal stability of discharged energy density (W_D) with a variation of less than 10% in an ultrawide temperature range of -50 to 300 °C, showing a significant advantage compared with the previously reported ceramic systems. The W_D reaches 4.21 J/cm³ under 38 kV/mm at room temperature. Besides, a record high of power density (P_D ≈ 89.5 MW/cm³) in BNT-based ceramics is also achieved in x = 0.20 ceramic with an excellent temperature insensitivity within 25-160 °C. The x = 0.20 ceramic is indicated to be an ergodic relaxor ferroelectric with coexisted R3c nanodomains and P4bm polar nanoregions at room temperature, greatly inducing large maximum polarization, maintaining low remnant polarization, and thus achieving high W_D and P_D. Furthermore, the diffuse phase transition from R3c to P4bm phase on heating is considered to be responsible for the superior thermal stability of the high W_D and P_D. These results imply the large potential of the 0.80BNT-0.20NT ceramic in temperature-stable dielectric capacitor applications.

Large energy storage density performance of epitaxial BCT/BZT heterostructures via interface engineering

We grew lead-free BaZr_0.2Ti_0.8O₃ (BZT)/Ba_0.7Ca_0.3TiO₃ (BCT) epitaxial heterostructures and studied their structural, dielectric, ferroelectric and energy density characteristics. The BZT/BCT epitaxial heterostructures were grown on SrRuO₃ (SRO) buffered SrTiO₃ (STO) single crystal substrate by optimized pulsed laser deposition (PLD) technique. These high-quality nanostructures exhibit high dielectric permittivity (∼1300), slim electric field-dependent polarization (P-E) curve with high saturation polarization (∼100 µC/cm²) and low remnant polarization (∼20 µC/cm²) through interface engineering to develop new lead-free ferroelectric system for energy storage devices. We observe an ultrahigh discharge and charge energy densities of 42.10 and 97.13 J/cm³, respectively, with high efficiency, which might be highly promising for both high power and energy storage electrical devices.

Accelerated Search for BaTiO3-Based Ceramics with Large Energy Storage at Low Fields Using Machine Learning and Experimental Design

The problem that is considered is that of maximizing the energy storage density of Pb-free BaTiO3-based dielectrics at low electric fields. It is demonstrated that how varying the size of the combinatorial search space influences the efficiency of material discovery by comparing the performance of two machine learning based approaches where different levels of physical insights are involved. It is started with physics intuition to provide guiding principles to find better performers lying in the crossover region in the composition-temperature phase diagram between the ferroelectric phase and relaxor ferroelectric phase. Such an approach is limiting for multidopant solid solutions and motivates the use of two data-driven machine learning and design strategies with a feedback loop to experiments. Strategy I considers learning and property prediction on all the compounds, and strategy II learns to preselect compounds in the crossover region on which prediction is carried out. By performing only two active learning loops via strategy II, the compound (Ba0.86Ca0.14)(Ti0.79Zr0.11Hf0.10)O3 is synthesized with the largest energy storage density ≈73 mJ cm-3 at a field of 20 kV cm-1, and an insight into the relative performance of the strategies using varying levels of knowledge is provided.

Ultrahigh β-phase content poly(vinylidene fluoride) with relaxor-like ferroelectricity for high energy density capacitors

Poly(vinylidene fluoride)-based dielectric materials are prospective candidates for high power density electric storage applications because of their ferroelectric nature, high dielectric breakdown strength and superior processability. However, obtaining a polar phase with relaxor-like behavior in poly(vinylidene fluoride), as required for high energy storage density, is a major challenge. To date, this has been achieved using complex and expensive synthesis of copolymers and terpolymers or via irradiation with high-energy electron-beam or γ-ray radiations. Herein, a facile process of pressing-and-folding is proposed to produce β-poly(vinylidene fluoride) (β-phase content: ~98%) with relaxor-like behavior observed in poly(vinylidene fluoride) with high molecular weight > 534 kg mol⁻¹, without the need of any hazardous gases, solvents, electrical or chemical treatments. An ultra-high energy density (35 J cm⁻³) with a high efficiency (74%) is achieved in a pressed-and-folded poly(vinylidene fluoride) (670-700 kg mol⁻¹), which is higher than that of other reported polymer-based dielectric capacitors to the best of our knowledge.

Dielectric materials are candidates for electric high power density energy storage applications, but fabrication is challenging. Here the authors report a pressing-and-folding processing of a dielectric with relaxor-like behavior, leading to high energy density in a polymer-based dielectric capacitor.

Perovskite Sr1-x(Na0.5Bi0.5)xTi0.99Mn0.01O3 Thin Films with Defect Dipoles for High Energy-Storage and Electrocaloric Performance

Dielectric capacitors have received more and more attention because of fast charge/discharge capability. However, the energy-storage performance still cannot meet the demand. In this work, lead-free perovskite Sr_1-x(Na_0.5Bi_0.5)_xTi_0.99Mn_0.01O₃ (x = 0, 0.005, 0.01, and 0.02) thin films prepared by the sol-gel method were carefully studied. Defect dipoles and local lattice distortion were created by doping Mn at the B-site, enabling ferroelectric polarization behavior. To further enhance polarization, co-substitution at the A-site was adopted. Na⁺ and Bi³⁺ can make up Na⁺-Bi³⁺ ion pairs. Meanwhile, off-center Na_Sr⁺ and Bi_Sr³⁺ ions with a small radius can lead to the distortion of the octahedral [TiO₆] in the lattice to induce local polarization regions. Under the combined action of A-site and B-site doping, polarization and breakdown strength were greatly improved. Finally, a high energy density (53 J cm^-3) and good thermal stability were achieved. Furthermore, the negative electrocaloric effect was also achieved. The adiabatic temperature change is about -8.5 at 300 K. This work demonstrates that the Sr_0.99(Na_0.5Bi_0.5)_0.01(Ti_0.99Mn_0.01)O₃ thin film with excellent energy-storage performance and the negative electrocaloric effect is a promising multifunctional material.

Excellent Energy-Storage Properties Achieved in BaTiO3-Based Lead-Free Relaxor Ferroelectric Ceramics via Domain Engineering on the Nanoscale

Barium titanate-based energy-storage dielectric ceramics have attracted great attention due to their environmental friendliness and outstanding ferroelectric properties. Here, we demonstrate that a recoverable energy density of 2.51 J cm^-3 and a giant energy efficiency of 86.89% can be simultaneously achieved in 0.92BaTiO₃-0.08K_0.73Bi_0.09NbO₃ ceramics. In addition, excellent thermal stability (25-100 °C) and superior frequency stability (1-100 Hz) have been obtained under 180 kV cm^-1. The first-order reversal curve method and transmission electron microscopy measurement show that the introduction of K_0.73Bi_0.09NbO₃ makes ferroelectric domains to transform into highly dynamic polar nanoregions (PNRs), leading to the concurrently enhanced energy-storage properties by the transition from ferroelectric to relaxor ferroelectric (RFE). Furthermore, it is confirmed by piezoresponse force microscopy that the appearance of PNRs breaks the long-range order to some extent and reduces the stability of the microstructure, which explains the excellent energy-storage performance of RFE ceramics. Therefore, this work has promoted the practical application ability of BaTiO₃-based energy-storage dielectric ceramics.

Mutual Insight on Ferroelectrics and Hybrid Halide Perovskites: A Platform for Future Multifunctional Energy Conversion

An insight into the analogies, state-of-the-art technologies, concepts, and prospects under the umbrella of perovskite materials (both inorganic-organic hybrid halide perovskites and ferroelectric perovskites) for future multifunctional energy conversion and storage devices is provided. Often, these are considered entirely different branches of research; however, considering them simultaneously and holistically can provide several new opportunities. Recent advancements have highlighted the potential of hybrid perovskites for high-efficiency solar cells. The intrinsic polar properties of these materials, including the potential for ferroelectricity, provide additional possibilities for simultaneously exploiting several energy conversion mechanisms such as the piezoelectric, pyroelectric, and thermoelectric effect and electrical energy storage. The presence of these phenomena can support the performance of perovskite solar cells. The energy conversion using these effects (piezo-, pyro-, and thermoelectric effect) can also be enhanced by a change in the light intensity. Thus, there lies a range of possibilities for tuning the structural, electronic, optical, and magnetic properties of perovskites to simultaneously harvest energy using more than one mechanism to realize an improved efficiency. This requires a basic understanding of concepts, mechanisms, corresponding material properties, and the underlying physics involved with these effects.

Enhanced Dielectric Performance of P(VDF-HFP) Composites with Satellite-Core-Structured Fe2O3@BaTiO3 Nanofillers

Polymer dielectric materials are extensively used in electronic devices. To enhance the dielectric constant, ceramic fillers with high dielectric constant have been widely introduced into polymer matrices. However, to obtain high permittivity, a large added amount (>50 vol%) is usually needed. With the aim of improving dielectric properties with low filler content, satellite–core-structured Fe₂O₃@BaTiO₃ (Fe₂O₃@BT) nanoparticles were fabricated as fillers for a poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) matrix. The interfacial polarization effect is increased by Fe₂O₃ nanoparticles, and thus, composite permittivity is enhanced. Besides, the satellite–core structure prevents Fe₂O₃ particles from directly contacting each other, so that the dielectric loss remains relatively low. Typically, with 20 vol% Fe₂O₃@BT nanoparticle fillers, the permittivity of the composite is 31.7 (1 kHz), nearly 1.8 and 3.0 times that of 20 vol% BT composites and pure polymers, respectively. Nanocomposites also achieve high breakdown strength (>150 KV/mm) and low loss tangent (~0.05). Moreover, the composites exhibited excellent flexibility and maintained good dielectric properties after bending. These results demonstrate that composite films possess broad application prospects in flexible electronics.

Interface design for high energy density polymer nanocomposites

This review provides a detailed overview on the latest developments in the design and control of the interface in polymer based composite dielectrics for energy storage applications. The methods employed for interface design in composite systems are described for a variety of filler types and morphologies, along with novel approaches employed to build hierarchical interfaces for multi-scale control of properties. Efforts to achieve a close control of interfacial properties and geometry are then described, which includes the creation of either flexible or rigid polymer interfaces, the use of liquid crystals and developing ceramic and carbon-based interfaces with tailored electrical properties. The impact of the variety of interface structures on composite polarization and energy storage capability are described, along with an overview of existing models to understand the polarization mechanisms and quantitatively assess the potential benefits of different structures for energy storage. The applications and properties of such interface-controlled materials are then explored, along with an overview of existing challenges and practical limitations. Finally, a summary and future perspectives are provided to highlight future directions of research in this growing and important area.

Tailoring frequency-insensitive large field-induced strain and energy storage properties in (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3-modified (Bi0.5Na0.5)TiO3 lead-free ceramics

Lead-free (Bi_0.5Na_0.5)TiO₃-based relaxor ferroelectrics are attracting growing research interest due to their very large field-induced strain response and excellent energy storage performance. While extensive explorations have been made of these performances separately, being able to optimize both field-induced strain and energy storage performance of polycrystalline materials together, and hence achieve a synergistic result, would also be highly desirable for their practical applications. Herein, lead-free relaxor-ferroelectric (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃-modified (Bi_0.5Na_0.5)TiO₃ (BNT-BCZT) ceramics were designed and demonstrated to be feasible candidates for both actuator and pulsed power capacitors. Optimal field-induced strain performances were realized in 0.92BNT-0.08BCZT ceramics with not only a high strain of 0.46% but also an impressive frequency stability (0.5 Hz-100 Hz), superior to those of other reported BNT-based materials under a similar frequency range. Moreover, the 0.5BNT-0.5BCZT compositions in the complete ER region delivered a relatively high W_rec of 0.95 J cm^-3 and η of 69%, while still remaining insensitive to changes in temperature, frequency, and cycle number. More importantly, a short discharge time (of ∼0.41 μs) was also measured for this composition. Introducing BCZT into the composition was found to promote a non-ergodic-to-ergodic relaxor (NR-ER) phase transition and the formation of dynamic polar nanoregions (PNRs), generating the high strain responses and superior energy storage performances of the given compositions. These features may offer a new strategy to simultaneously tailor lead-free relaxor ferroelectrics toward high field-induced strain and superior energy storage performance for ceramics actuators and capacitor applications.

Biomimetic piezoelectric nanocomposite membranes synergistically enhance osteogenesis of deproteinized bovine bone grafts

Purpose: The combination of a bone graft with a barrier membrane is the classic method for guided bone regeneration (GBR) treatment. However, the insufficient osteoinductivity of currently-available barrier membranes and the consequent limited bone regeneration often inhibit the efficacy of bone repair. In this study, we utilized the piezoelectric properties of biomaterials to enhance the osteoinductivity of barrier membranes. Methods: A flexible nanocomposite membrane mimicking the piezoelectric properties of natural bone was utilized as the barrier membrane. Its therapeutic efficacy in repairing critical-sized rabbit mandible defects in combination with xenogenic grafts of deproteinized bovine bone (DBB) was explored. The nanocomposite membranes were fabricated with a homogeneous distribution of piezoelectric BaTiO₃ nanoparticles (BTO NPs) embedded within a poly(vinylidene fluoridetrifluoroethylene) (P(VDF-TrFE)) matrix. Results: The piezoelectric coefficient of the polarized nanocomposite membranes was close to that of human bone. The piezoelectric coefficient of the polarized nanocomposite membranes was highly stable, with more than 90% of the original piezoelectric coefficient (d₃₃) remaining up to 28 days after immersion in culture medium. Compared with commercially-available polytetrafluoroethylene (PTFE) membranes, the polarized BTO/P(VDF-TrFE) nanocomposite membranes exhibited higher osteoinductivity (assessed by immunofluorescence staining for runt-related transcription factor 2 (RUNX-2) expression) and induced significantly earlier neovascularization and complete mature bone-structure formation within the rabbit mandible critical-sized defects after implantation with DBB Bio-Oss® granules. Conclusion: Our findings thus demonstrated that the piezoelectric BTO/P(VDF-TrFE) nanocomposite membranes might be suitable for enhancing the clinical efficacy of GBR.

Significantly Enhanced Energy Density by Tailoring the Interface in Hierarchically Structured TiO2-BaTiO3-TiO2 Nanofillers in PVDF-Based Thin-Film Polymer Nanocomposites

Dielectric polymer nanocomposites with a high breakdown field and high dielectric constant have drawn significant attention in modern electrical and electronic industries due to their potential applications in dielectric and energy storage systems. The interfaces of the nanomaterials play a significant role in improving the dielectric performance of polymer nanocomposites. In this work, polydopamine (dopa)-functionalized TiO₂-BaTiO₃-TiO₂ (TiO₂-BT-TiO₂@dopa) core@double-shell nanoparticles have been developed as novel nanofillers for high-energy-density capacitor applications. The hierarchically designed nanofillers help in tailoring the interfaces surrounding the polymer matrix as well as act as individual capacitors in which the core and outer TiO₂ shell function as a capacitor plate because of their high electrical conductivity while the middle BT layer functions as a dielectric medium due to high dielectric constant. Detailed electrical characterizations have revealed that TiO₂-BT-TiO₂@dopa/poly(vinylidene fluoride) (PVDF) possesses a higher relative dielectric permittivity (ε_r), breakdown strength ( E_b), and energy density as compared to those of PVDF, TiO₂/PVDF, TiO₂@dopa/PVDF, and TiO₂-BT@dopa/PVDF polymer nanocomposites. The ε_r and energy density of TiO₂-BT-TiO₂@dopa/PVDF were 12.6 at 1 kHz and 4.4 J cm^-3 at 3128 kV cm^-1, respectively, which were comparatively much higher than those of commercially available biaxially oriented polypropylene having ε_r of 2.2 and the energy density of 1.2 J cm^-3 at a much higher electric field of 6400 kV cm^-1. It is expected that these results will further open new avenues for the design of novel architecture for high-performance polymer nanocomposite-based capacitors having core@multishell nanofillers with tailored interfaces.

Perovskite ferroelectric tuned by thermal strain

Modern environmental and sustainability issues as well as the growing demand for applications in the life sciences and medicine put special requirements to the chemical composition of many functional materials. To achieve desired performance within these requirements, innovative approaches are needed. In this work, we experimentally demonstrate that thermal strain can effectively tune the crystal structure and versatile properties of relatively thick films of environmentally friendly, biocompatible, and low-cost perovskite ferroelectric barium titanate. The strain arises during post-deposition cooling due to a mismatch between the thermal expansion coefficients of the films and the substrate materials. The strain-induced in-plane polarization enables excellent performance of bottom-to-top barium titanate capacitors akin to that of exemplary lead-containing relaxor ferroelectrics. Our work shows that controlling thermal strain can help tailor response functions in a straightforward manner.

High energy-storage density of lead-free (Sr1-1.5xBix)Ti0.99Mn0.01O3 thin films induced by Bi3+-VSr dipolar defects

Capacitors with high energy storage density, low cost, ultrafast charge-discharge capability, and environmental friendliness are in high demand for application in new energy vehicles, modern electrical systems, and high-energy laser weapons. Here, lead-free (Sr1-1.5xBix)Ti0.99Mn0.01O3 (x = 0.01, 0.05, 0.1) thin films grown on Pt/Ti/SiO2/Si substrates were obtained by a sol-gel method. All the thin films have a relatively high dielectric breakdown strength (BDS) due to the added 1% Mn and pinched polarization hysteresis loops can be observed in 5 and 10 mol% Bi-doped SrTiO3 thin films. The ferroelectric behaviors of the Bi-doped SrTiO3 thin films come from the rotation of the TiO6-octahedra induced by the formation of Bi3+-VSr dipolar defects. With the increase of doping concentration, the Pmax-Pr values of the Bi-doped SrTiO3 thin films increased dramatically and can reach 34.3 μC cm-2 upon doping with 10 mol% Bi. A high recoverable energy-storage density of 24.4 J cm-3 with excellent temperature stability was obtained for the 10 mol% Bi-doped ST thin film, which shows that the (Sr0.85Bi0.1)Ti0.99Mn0.01O3 thin film is a promising candidate for high-power energy storage applications. This finding demonstrates an improved energy density of SrTiO3-based thin film systems and a reasonable explanation for the source of the ferroelectricity based on first-principles calculations is given.

Phase-field modeling of the coupled domain structure and dielectric breakdown evolution in a ferroelectric single crystal

The coupled evolution of domain structure and dielectric breakdown is simulated via a phase-field model.

Competing Polar and Antipolar Structures in the Ruddlesden-Popper Layered Perovskite Li2SrNb2O7

Over the past few years, several studies have reported the existence of polar phases in n = 2 Ruddlesden-Popper layer perovskites by trilinear coupling of oxygen octahedral rotations (OOR) and polar distortions, a phenomenon termed as hybrid improper ferroelectricity. This phenomenon has opened an avenue to expand the available compositions of ferroelectric and piezoelectric layered oxides. In this study, we report a new polar n = 2 Ruddlesden-Popper layered niobate, Li2SrNb2O7, which undergoes a structural transformation to an antipolar phase when cooled to 90 K. This structural transition results from a change in the phase of rotation of the octahedral layers within the perovskite slabs across the interlayers. First-principles calculations predicted that the antipolar Pnam phase would compete with the polar A 2 1 a m phase and that both would be energetically lower than the previously assigned centrosymmetric Amam phase. This phase transition was experimentally observed by a combination of synchrotron X-ray diffraction, powder neutron diffraction, and electrical and nonlinear optical characterization techniques. The competition between symmetry breaking to yield polar layer perovskites and hybrid improper antiferroelectrics provides new insight into the rational design of antiferroelectric materials that can have applications as electrostatic capacitors for energy storage.

Optimizing sandwich-structured composites based on the structure of the filler and the polymer matrix: toward high energy storage properties

Polymer-based energy storage materials have been widely applied in the energy storage industry, such as in the hybrid electric vehicle and power-conditioning equipment, due to their moderate energy density and ultrafast charging/discharging speed. Accordingly, the improvement of the energy storage density of polymer matrix composites has become the focus of current research. In this study, different fillers (e.g., 0.5Ba(Zr_0.2Ti_0.8)O₃–0.5(Ba_0.7Ca_0.3)TiO₃ nanofibers (BCZT NFs), BCZT + Ag NFs and BCZT + Ag@Al₂O₃ NFs) were synthesized via electrospinning and were added to the poly(vinylidene fluoride) (PVDF) matrix as a middle layer in sandwich-structure composites. The PVDF polymer-containing PMMA was prepared as the outer layer in the sandwich structure composites. These sandwich-structured composites have low loss, low current density, better breakdown strength and higher efficiency. In particular, 40% PMMA/PVDF/3 vol% BCZT + Ag@Al₂O₃/PVDF/40% PMMA/PVDF composites have an energy density of 7.23 J cm⁻³ and efficiency above 75.8% at 370 kV mm⁻¹. This article could open up a convenient and effective means for the practical application of power-pulsed capacitors by tuning the filler nanostructure and polymer nanocomposites.

Inorganic composite fillers and sandwich-structured composite films have been designed for further increasing the energy storage density.

Analogous Anti-Ferroelectricity in Y₂O₃-Coated (Pb0.92Sr0.05La0.02)(Zr0.7Sn0.25Ti0.05)O₃ Ceramics and Their Energy-Storage Performance

Antiferroelectric analogous (Pb_0.92Sr_0.05La_0.02)(Zr_0.7Sn_0.25Ti_0.05)O₃ (PSLZSnT) ceramics were prepared by the solid-state sintering method by introducing a Y₂O₃-coating via the self-combustion method. The synthesized Y₂O₃-doped PSLZSnT ceramics present pseudo-cubic structure and rather uniform microstructural morphology accompanied by relatively small grain size. Excellent energy-storage performance is obtained in the Y₂O₃-doped PSLZSnT ceramics, in which the value of the energy-storage density presents a linearly increasing trend within the electric field measurement range. Such excellent performance is considered as relating to the rather pure perovskite structure, high relative density accompanied by relatively small grain size, and the antiferroelectric-like polarization-electric field behavior.

Interface Modulation of Core-Shell Structured BaTiO₃@polyaniline for Novel Dielectric Materials from Its Nanocomposite with Polyarylene Ether Nitrile

The core-shell structured polyaniline-functionalized-BaTiO₃ (BT@PANI) nanoparticles with controllable shell layer thicknesses are developed via in-situ aniline polymerization technology and characterized in detail. The results prove that the PANI shell layer with the adjustable and controllable thicknesses of 3⁻10 nm are completely stabilized on the surface of the BaTiO₃ core. In addition, the BT@PANI nanoparticles are regarded as the hybrid nanofillers to prepare PEN/BT@PANI nanocomposite films with a PEN matrix. The research results indicate that the surface functionalized nanoparticles facilitate the compatibility and dispersibility of them in the PEN matrix, which improves the properties of the PEN/BT@PANI nanocomposites. Specifically, the PEN/BT@PANI nanocomposites exhibit thermal stability, excellent permittivity-frequency, and dielectric properties-temperature stability. Most importantly, the energy density of nanocomposites is maintained at over 70% at 180 °C compared with that at 25 °C. All these results reveal that a new way to prepare the high-performance PEN-based nanocomposites is established to fabricate an energy storage component in a high temperature environment.

Annealing and Stretching Induced High Energy Storage Properties in All-Organic Composite Dielectric Films

High discharged energy density and charge⁻discharge efficiency, in combination with high electric breakdown strength, maximum electric displacement and low residual displacement, are very difficult to simultaneously achieve in single-component polymer dielectrics. Plenty of researches have reported polymer based composite dielectrics filled with inorganic fillers, through complex surface modification of inorganic fillers to improve interface compatibility. In this work, a novel strategy of introducing environmentally-friendly biological polyester into fluoropolymer matrix has been presented to prepare all-organic polymer composites with desirable high energy storage properties by solution cast process (followed by annealing or stretching post-treatment), in order to simplify the preparation steps and lower the cost. Fluoropolymer with substantial ferroelectric domains (contributing to high dielectric response) as matrix and poly (3-hydroxybutyrate-co-3-hydroxyvalerate) with excellent linear polarization property (resulting in high breakdown strength) as filler were employed. By high-temperature annealing, the size of ferroelectric domains could be improved and interfacial air defects could be removed, leading to elevated high energy storage density and efficiency in composite. By mono-directional stretching, the ferroelectric domains and polyester could be regularly oriented along stretching direction, resulting in desired high energy storage performances as well. Besides, linear dielectric components could contribute to high efficiency from their strong rigidity restrain effect on ferroelectric component. This work might open up the way for a facile fabrication of promising all-organic composite dielectric films with high energy storage properties.

Intrinsic Tuning of Poly(styrene-butadiene-styrene)-Based Self-Healing Dielectric Elastomer Actuators with Enhanced Electromechanical Properties

The electromechanical properties of a thermoplastic styrene-butadiene-styrene (SBS) dielectric elastomer was intrinsically tuned by chemical grafting with polar organic groups. Methyl thioglycolate (MG) reacted with the butadiene block via a one-step thiol-ene "click" reaction under UV at 25 °C. The MG grafting ratio reached 98.5 mol % (with respect to the butadiene alkenes present) within 20 min and increased the relative permittivity to 11.4 at 10³ Hz, with a low tan δ. The actuation strain of the MG-grafted SBS dielectric elastomer actuator was 10 times larger than the SBS-based actuator, and the actuation force was 4 times greater than SBS. The MG-grafted SBS demonstrated an ability to achieve both mechanical and electrical self-healing. The electrical breakdown strength recovered to 15% of its original value, and the strength and elongation at break recovered by 25 and 21%, respectively, after 3 days. The self-healing behavior was explained by the introduction of polar MG groups that reduce viscous loss and strain relaxation. The weak CH/π bonds through the partially charged (δ+) groups adjacent to the ester of MG and the δ- center of styrene enable polymer chains to reunite and recover properties. Intrinsic tuning can therefore enhance the electromechanical properties of dielectric elastomers and provides new actuator materials with self-healing mechanical and dielectric properties.

Achieving Ultrahigh Breakdown Strength and Energy Storage Performance through Periodic Interface Modification in SrTiO3 Thin Film

A periodic layer structure consisting of sol-gel-derived SrTiO₃ and anodized Al₂O₃ has been designed and fabricated by interface engineering. Utilizing the anodized Al₂O₃ to be the blocking layer, not only the local high electric field around the hole and crack defects could be significantly reduced but also, and equally important, the blocking layer undertaking higher electric field could effectively decrease the breakdown probability of a SrTiO₃ layer based on the finite element analysis. As the sample has been modified, the barrier height of the charge carrier was increased through fitting the conductance activation energy ( H_c). In addition, the space charge-limited conductance mechanism was almost eliminated according to the fitted results in the ln E-ln J diagram, indicating that most of the charge carrier released from traps were blocked or isolated by the Al₂O₃ layer. As a result of the periodic interface modification, the leakage current was decreased 2 orders of magnitude and the breakdown strength was enhanced from 144.13 to 754.23 MV m^-1. More importantly, the ultimate energy density is up to 39.49 J cm^-3, which is 1505% greater than the sample without interface modification.