Dielectric Breakdown Strength Research Articles

Realizing Outstanding Energy Storage Performance in KBT-Based Lead-Free Ceramics via Suppressing Space Charge Accumulation.

The great potential of K1/2Bi1/2TiO3 (KBT) for dielectric energy storage ceramics is impeded by its low dielectric breakdown strength, thereby limiting its utilization of high polarization. This study develops a novel composition, 0.83KBT-0.095Na1/2Bi1/2ZrO3-0.075 Bi0.85Nd0.15FeO3 (KNBNTF) ceramics, demonstrating outstanding energy storage performance under high electric fields up to 425kVcm-1: a remarkable recoverable energy density of 7.03Jcm-3, and a high efficiency of 86.0%. The analysis reveals that the superior dielectric breakdown resistance arises from effective mitigation of space charge accumulation at the interface, influenced by differential dielectric and conductance behaviors between grains and grain boundaries. Electric impedance spectra confirm the significant suppression of space charge accumulation in KNBNTF, attributable to the co-introduction of Na1/2Bi1/2ZrO3 and Bi0.85Nd0.15FeO3. Phase-field simulations reveal the emergence of a trans-granular breakdown mode in KNBNTF resulting from the mitigated interfacial polarization, impeding breakdown propagation and increasing dielectric breakdown resistance. Furthermore, KNBNTF exhibits a complex local polarization and enhances the relaxor features, facilitating high field-induced polarization and establishing favorable conditions for exceptional energy storage performance. Therefore, the proposed strategy is a promising design pathway for tailoring dielectric ceramics in energy storage applications.

Improved dielectric and breakdown traits of polymer composites filled with KH-550 encapsulated multilayer black phosphorus

Polymer/particles composites are attractive for dielectric energy-storage, but they express difficultly-reconcilable conflict in high dielectric constant and breakdown strength. Here, multilayer black phosphorus (BP) coated by γ-aminopropyl triethoxysilane (KH-550) as filler, and poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) as matrix were used to prepare composite films. KH-550 encapsulation enhances BP/matrix interfacial compatibility. Dielectric constant of polymer/BP@KH-550 composite is ∼207 at 20 Hz when filler load is 10 wt% (dielectric loss ∼0.11), combined with direct-current breakdown strength of ∼288 MV m−1. This work is beneficial to facile preparation of dielectric composites with well-balanced dielectric and breakdown properties for capacitive energy-storage.

Surface functionalization of naturally occurring silicate minerals infused hydrocarbon polymer matrix for ultra‐low dielectric performance at high frequency domain

AbstractThe expanding realm of high‐frequency electronics necessitates materials with exceptional attributes: notably, a low dielectric constant (Dk) to minimize signal propagation delays, high thermal conductivity for effective heat dissipation, higher breakdown strength, and robust mechanical properties to withstand demanding operational environments. While cycloolefin copolymers (COC) excel in electrical insulation, chemical resistance, and mechanical durability, their intrinsic slightly higher dielectric constant compared to other polymers, along with challenges such as poor dispersibility and low compatibility with nanoparticles, hinder their full potential in this domain. Considering these drawbacks, this study fabricated a series of COC/mica composites by integrating natural mica particles into the COC matrix via a CTAB‐assisted surface modification of mica to enhance dispersibility and mitigating particle aggregation through in‐situ mixing and hot‐press methods. The resultant composites demonstrate an outstanding ultra‐low Dk of 1.44, marking a significant decrease of over 36% compared to pristine COC with a Dk of 2.26, along with exceptionally low dielectric loss (δ) of 0.00013 at the frequency of 10 GHz, high dielectric breakdown strength ~49.40 kV/mm and enhanced thermal conductivity up to 0.88 W/(m K) at 40% mica loading. Additionally, the composites heightened mechanical performances like tensile strength 69 MPa at 6.5% elongation at break, impact strength up to ~17.9 kJ × m−2, and exceptional water resistance with absorption below 0.097%. These exceptional ultra‐low dielectric performance with above mentioned properties can meet the stringent requirements of modern high‐frequency electronics packaging for next generation electronics development.Highlights Surface modification by CTAB enhanced homogeneous dispersibility of composites. Achieved ultra‐low dielectric constant and loss compared to pure COC. Thermal conductivity improved significantly with incorporation of mica. Unlocking high‐frequency applications potential with ultralow Dk performance.

Effects of amount of yttria on dielectric breakdown strength of sintered reaction‐bonded silicon nitride

AbstractWe prepared sintered reaction‐bonded silicon nitride (Si3N4) ceramics using various amounts of yttria (Y2O3) and a fixed amount of magnesia as sintering additives and evaluated their effects on the microstructure and dielectric breakdown strength (DBS). The DBS tests were conducted at substrate thicknesses of approximately .3, .2, .1, and .05 mm for each sample. All the prepared samples exhibited a high relative density (> 98%) and were composed of grains of almost identical sizes and shapes. The DBS decreased as the amount of added Y2O3 increased, with the degree of decrease being more pronounced for the thinner substrates. In the case of substrates with the largest Y2O3 amount (5 mol%), the DBS decreased to the level observed for the thinnest substrate of .05 mm. The presence of yttrium ions around the grains increased the electrical conductivity of the glassy phase, resulting in a decreased DBS. Therefore, a smaller amount of Y2O3 led to a higher DBS. The observed decrease in the DBS (.05 mm) was attributed to the connection between the top and bottom surfaces of the substrate through a highly conductive path.

Effects of firings in hydrogen on the insulation performances of a 95 wt% alumina ceramic

To investigate the effects of point defects on the insulation performances of alumina ceramics, we fire a 95 wt% alumina ceramic in wet hydrogen, dry hydrogen, and supplementary air, to change the concentrations of aluminum vacancy (VAl‴) and oxygen vacancy (VO••). The dielectric breakdown strength (DBS) and flashover voltage (FV) are tested, and the point defects are characterized by XPS and optical reflectance. Firing in wet hydrogen decreases the concentration of VO••, improving DBS but deteriorating FV. Nevertheless, firing in dry hydrogen increases the concentration of VAl‴, improving FV but deteriorating DBS. Supplementary firing in air weakens the effects of firing in dry hydrogen on the point defects and insulation performances. The effects of firings on insulation performances are attributed to the concentrations of electrical carriers that are determined by the point defects, and this is confirmed by the results of electrical resistivity.

Electric-Tree Resistant Performance and Thermal Charge-Carrier Dissipation Mechanism of Voltage Stabilizer-Modified EPDM

In order to improve electric-tree resistant performance and dielectric breakdown strength of ethylene-propylene-diene misch-polymere (EPDM) material used for cable accessory reinforce insulation, the two specific aromatic ketone compounds—vinylphenylacetone (VPE) and 4-propylene oxyxy-2-hydroxydibenzenone (AOHBP) are employed as two paradigms of voltage stabilizer for chemical-graft modifications. Electric-tree resistances and insulation performances of modified EPDM materials and their charge trapping mechanism of thermoelectron inhibitions are studied by the accelerated electric-tree aging experiments, alternating current (AC) dielectric breakdown tests, surface potential trap-level analyses and first-principles calculations. Both the two species of voltage stabilizers are effective for promoting electric-tree inception voltage and dielectric breakdown strength, leading to a high extension of electric-tree morphology and smaller dimension of electric-trees growth, in which AOHBP is more significant. The two species of voltage stabilizers have been successfully grafted onto EPDM molecular-chains in thermal-chemistry crosslinking reactions of EPDM, introducing multiple shallow levels of charge traps, which reduces the energy released by trapping charge carriers and thus alleviates electric-tree aging of EPDM. The AOHBP and VPE represent a high electron affinity and a small electronic energy gap, which is competent of assimilating the kinetic energies of hot charge carriers whilst restricting Auger electronic excitation. Especially, the benzene group in voltage stabilizer renders shallow level charge traps with a larger carrier capture cross-section than deep traps and simultaneously possesses the high atomic vibration frequencies similar as electronic-transition energies, which results in effective dissipation on the kinetic energies of hot charge carriers. This mechanism dominates to increase electric-tree resistance and insulation strength of EPDM. The present study proves the important role of voltage stabilizers in improving insulation performance of EPDM material, and reveals the refrigeration mechanism on hot charge carriers for restricting electric-tree growth, which provides a significant strategy of chemical modifications for developing high-insulation cable accessory materials.

Design, Synthesis and Characterization of a Novel Antiferroelectric Solid Solution (1-x)PbHfO3-xBiAlO3

Antiferroelectric (AFE) materials are potentially useful for energy storage applications. Lead hafnate (PbHfO3) is one of the prototypical AFE materials. However, its critical field (Ecr) inducing the AFE to ferroelectric phase transition is close to the dielectric breakdown strength. To reduce Ecr, we prepare solid solutions (1-x)PbHfO3–xBiAlO3 (x = 0.00-0.04) via solid state synthesis. The crystal structures, dielectric behaviour, ferroelectric properties, and energy storage properties are investigated. A temperature-composition phase diagram is established. At room temperature, the crystal symmetry of all compositions is orthorhombic with the Pbam space group. Upon heating, the transition to the AFE orthorhombic Imma phase is observed at the temperature TC1, which slightly decreases with increasing x, followed by the transition to the cubic phase at the temperature TC2, which does not depend on x. Distinct dielectric anomalies are observed at TC1 and TC2. It is found that BiAlO3 substitution reduces Ecr and the polarization–electric field relations display characteristic double hysteresis loops. For x = 0.04, at a comparatively small applied field of 130 kV/cm, the obtained values of recoverable energy density (Wrec) and efficiency are 0.24 J/cm3 and 84 %, respectively. At 190 °C, Wrec = 0.75 J/cm3 and a very high efficiency of 92 % are obtained at the field of 50 kV/cm. Thus, the prepared material can potentially be used in high-temperature pulsed power capacitors for energy storage applications within the temperature range from room temperature up to 190 °C.

Machine learning assisted prediction of the phonon cutoff frequency of ABO3 perovskite materials

One of the phonon properties, the phonon cutoff frequency, pertains to the vibration frequency of the strongest bond in a material, and it has a direct impact on the dielectric breakdown strength. In this study, the accurate prediction of the phonon cutoff frequency was achieved using the Light Gradient Boosting Machine (LightGBM) methodology, utilizing only 15 features related to the structural and elemental information of materials. The performance of the LightGBM model yielded R2 of 0.973, RMSE of 2.214, and MAE of 1.289, surpassing other models by a significant margin. Feature analysis revealed a close correlation between the phonon cutoff frequency and the minimum of atomic number among the elements in the composition through SHapley Additive exPlanations (SHAP). Notably, this research successfully predicted the phonon cutoff frequency of ABO3 perovskite materials accurately for bypassing the time-consuming first principles calculations and reveals the correlation between the phonon cutoff frequency and the physical and chemical information of the materials simultaneous.

Dielectric elastomers with large actuation strain and high output force

AbstractDielectric elastomer actuator (DEA) is considered as an ideal artificial muscle with soft and light in nature, widespread application in soft robotics and sensors. Dielectric elastomer (DE), the core component of DEA, with high output force and large actuation strain under relatively low driving electric field is critical for high‐performance DEA. However, the widely used VHB series (3M) DE suffered from very large pre‐strain and high driving voltage to get their high actuation performance, limiting their scope of application. In this work, the DEs with good mechanical and dielectric properties were prepared via UV curing method consisting of acrylic acid (AA) with strong polar groups as functional monomer, n‐butyl acrylate (BA) as soft monomer and urethane acrylate as cross‐linker (c‐p(BA‐AA)). The c‐p(BA‐AA) DE films obtained the simultaneous increasing of dielectric constant and breakdown strength with the increasing content of AA, which guaranteed the good actuation performance. The c‐p(BA‐AA) film exhibited excellent actuating performance (44.11% actuation strain at 45 kV/mm) without pre‐strain. Besides, a simple linear actuator based on the c‐p(BA‐AA) film could easily output weight that is tens of times of its own active weight (654.1 mN/g at 30 kV/mm).

A sol-gel strategy for constructing a hydroxyapatite nanowire/aramid nanofiber electric insulating composite with excellent flame retardancy and mechanical property

With the increasing demand for high power and miniaturization of modern large-scale electrical equipment, preparing high-performance electrical insulation materials with high thermal stability and excellent mechanical properties has become an urgent problem. In this study, hydroxyapatite (HAP) nanowires and aramid nanofibers (ANF) multifunctional composites were prepared by sol-gel-membrane strategy. Aramid fibers containing an amide structure and HAP can form an ordered hydrogen bonding network and exhibit strong hydrogen bonding. The prepared HAP/ANF nanocomposite films with nanowire/nanofiber network skeleton and laminate structure have good tensile strength (69.6 MPa), dielectric breakdown strength (65.7 kV mm−1), and processing properties. Particularly emphasized is that the multifunctional HAP/ANF nanocomposite films are fireproof and high-temperature resistant, and the interfacial hydrogen-bonding enhancement between HAP nanowires and aramid fibers facilitates the construction of multifunctional insulating materials.

Enhancing energy storage performance of polyethylene via passivation with oxygen atoms through C–H vacancy carbonylation

Low energy density of polymer film capacitors is regarded as one of the most serious drawbacks facing growing demands for equipment integration and miniaturization. Herein, ultraviolet light and ozone (UVO) surface modification is utilized to simultaneously improve dielectric constant and breakdown strength of polyethylene (PE) films. As a result, after 3 min of UVO treatment, an enhanced recoverable energy density of 4.79 J/cm3 with a charge-discharge efficiency of >95% is obtained under 650 MV/m at room temperature (RT). Significantly, stable energy storage performance under 200 MV/m is maintained throughout a broad temperature range from −90 °C to 90 °C and during 20,000 cycles of charge-discharge procedures. According to first-principles calculations and thermally stimulated depolarization current measurements, formation of carbonyl groups (C=O) after UVO treatment could effectively passivate initial deep-level defect states caused by H vacancies, which explains the improvement in capacitive energy storage. Moreover, the metalized UVO-modified PE exhibits valuable breakdown self-clearing ability, and the self-cleared specimen maintains stable energy storage performance over 20,000 cycles at 200 MV/m and RT. This work offers an effective and user-friendly method for enhancing comprehensive dielectric characteristics of PE-based materials and potential for applications in modern power systems and electronic devices.

Engineering Phase Separation in Niobate Glass through Ab Initio Molecular Dynamics for Enhanced Energy Storage Performance and Unprecedented Thermal Stability in Niobate-Based Glass Ceramics.

The advancement of lead-free glass ceramics (GCs) possessing appropriate energy storage characteristics is crucial for the renewable energy and electronics industry. In this study, we synthesized lead-free GCs predominantly composed of the tungsten bronze phase, Ba3.3Nb10O28.3. Ab initio molecular dynamics initially reveal nonuniform distribution within the Ba/Nb-O regions in niobite glassy melts, offering valuable insights for the subsequent crystallization process. The proposal of a B-site engineering strategy is suggested, which entails the concurrent reduction of grain size and augmentation of the band gap in tungsten bronze GCs doped with Ta. This approach results in a substantial enhancement of the dielectric breakdown strength (BDS). Phase-field simulations have indicated that the refinement of grain sizes plays a pivotal role in augmenting the local electric field distribution and breakdown path, thereby contributing to the enhancement of BDS. As a consequence of these modifications, a notably high recoverable energy density (Wrec) of 5.23 J/cm3 can be achieved, accompanied by an ultrahigh efficiency (η) of 94%, and superior thermal stability in energy storage. These outcomes are particularly evident in the case of 2 mol % Ta2O5-doped P2O5-K2O-BaO-Bi2O3-TeO2-Nb2O5 (PKBBTN-T) GCs, where the Wrec and η can be determined to be 2.87 ± 3% J/cm3 and 95.46 ± 4%, respectively, over a temperature range spanning from 20 to 150 °C. Additionally, this specimen exhibits an exceptionally high discharge energy density (Wdis) of 4.01 J/cm3. This comprehensive investigation, comprising experimental and theoretical analyses, establishes an effective pathway and paradigm for the development of dielectric materials with ultrahigh energy storage properties.

Enhanced dielectric reliability in the X9R‐type Bi1/2Na1/2TiO3‐CaZrO3 relaxor ferroelectric ceramics

AbstractHigh‐performance dielectric ceramic capacitors for automotive applications require high operation temperature, thermal stability, and reliability for dielectric ceramics. A broad composition search has been carried out to replace the existing BaTiO3‐based dielectrics having limited upper operating temperature due to the relatively low Curie temperature at around 120°C. However, most of the developed compositions are too complicated and compositionally sensitive, making them difficult to commercialize. This study introduces a dielectrically reliable ceramic system based on Bi1/2Na1/2TiO3 (BNT) with a wide operation temperature range simply by adding paraelectric CaZrO3 (CZ). At 15 mol% addition of CZ to BNT, the permittivity variation within ±15% from −55 to 280°C was achieved, which surpasses the EIA‐X9R standard. Moreover, the dielectric reliability was shown with low dielectric loss (tanδ < 0.02) for the aforementioned temperature range and remarkable dielectric breakdown strength (∼260 kV/cm) at room temperature. Along with the proposal of a promising high‐performance dielectric material, structural analysis and dielectric behavior investigation as a function of CZ contents were presented.

Achieving improved dielectric energy storage properties and temperature stability in 0.91Na0.5Bi0.5TiO3-0.09K0.7La0.1NbO3 based ferroelectric ceramics by composition design and processing optimization

In this study, a ternary solid solution was designed by incorporating varying concentrations of the B-site composite perovskite Ba(Mg1/3Ta2/3)O3 (BMT) into 0.91Na0.5Bi0.5TiO3-0.09K0.7La0.1NbO3 (NBT-KLN-based) ferroelectric ceramics to optimize their energy storage performance. The introduction of BMT disrupted the long-range ordered state of the A/B site in the original perovskite structure, resulting in increased structural disorder and enhanced relaxor characteristics. The viscous polymer processing (VPP) method was employed to attain a significantly denser structure. The 0.10BMT-vpp ceramic has ultimately achieved optimal energy storage performance, along with exceptional temperature and frequency stability. It boasts a high dielectric breakdown strength (BDS) of 440 kV/cm, an ultra-high effective energy storage density (Wrec) of 6.7 J/cm3, and an energy storage efficiency (η) of 82%. Moreover, the 0.10BMT-vpp ceramic exhibits robust pulse performance, characterized by an ultra-fast discharge time (t0.9) of only 77 ns. Furthermore, within the temperature range of −66 °C–354 °C, the temperature coefficient of capacitance (TCC) of the 0.25BMT ceramics undergoes a variation of no more than ±15%, in compliance with X9R specifications (−55 °C–200 °C). The introduction of BMT endows NBT-KLN-based ceramics with remarkable temperature stability and comprehensive energy storage performance, making it a ceramic material with practical potential for industrial applications.

Intrinsic and extrinsic contributions to energy storage performance in potassium sodium niobate–based ceramics

AbstractBoth the intrinsic and extrinsic contributions to the high energy storage properties of (K0.5Na0.5)NbO3 were investigated herein by employing Bi(Mg2/3Ta1/3)O3 as a second component to synthesize novel environment‐friendly energy storage ceramics. The role of the second component was confirmed to reduce the intrinsic activation of electrons, which effectively improves the band gap values and reduces the probability of intrinsic breakdown. Phase field simulation was employed to confirm that the smaller grain size of the modified ceramic microstructure enhances the extrinsic breakdown and dielectric breakdown strength. Moreover, ab initio molecular dynamics were used to investigate the critical role of the Mg ions in lowering the initial polarization and forming nanodomains, representing the intrinsic contribution to decreasing the initial polarization. An intrinsic structure with moderate polarization rapidly increases the polarization of ceramics under external electric fields, facilitating high energy storage density. The prepared ceramics achieve a recoverable energy density (Wrec) of 3.86 J/cm3 and energy efficiency (η) of 81.2% at 385 kV/cm.

Highly Thermally Conductive Aramid Nanofiber Composite Films with Synchronous Visible/Infrared Camouflages and Information Encryption

AbstractThe development of highly thermally conductive composites that combine visible light/infrared camouflage and information encryption has been endowed with great significance in facilitating the application of 5G communication technology in military fields. This work uses aramid nanofibers (ANF) as the matrix, hetero‐structured silver nanowires@boron nitride nanosheets (AgNWs@BNNS) prepared by in situ growth as fillers, which are combined to fabricate sandwich structured thermally conductive and electrically insulating (BNNS/ANF)‐(AgNWs@BNNS)‐(BNNS/ANF) (denoted as BAB) composite films by “filtration self‐assembly, air spraying, and hot‐pressing” method. When the mass ratio of AgNWs@BNNS to BNNS is 1 : 1 and the total mass fraction is 50 wt %, BAB composite film has the maximum in‐plane thermal conductivity coefficient (λ∥ of 10.36 W/(m ⋅ K)), excellent electrical insulation (breakdown strength and volume resistivity of 41.5 kV/mm and 1.21×1015 Ω ⋅ cm, respectively) and mechanical properties (tensile strength of 170.9 MPa). 50 wt % BAB composite film could efficiently reduce the equilibrium temperature of the central processing unit (CPU) working at full power, resulting in 7.0 °C lower than that of the CPU solely integrated with ANF directly. In addition, BAB composite film boasts adaptive visible light/infrared dual camouflage properties on cement roads and jungle environments, as well as the function of fast encryption of QR code information within 24 seconds.

Highly Thermally Conductive Aramid Nanofiber Composite Films with Synchronous Visible/Infrared Camouflages and Information Encryption.

The development of highly thermally conductive composites that combine visible light/infrared camouflage and information encryption has been endowed with great significance in facilitating the application of 5G communication technology in military fields. This work uses aramid nanofibers (ANF) as the matrix, hetero-structured silver nanowires@boron nitride nanosheets (AgNWs@BNNS) prepared by in situ growth as fillers, which are combined to fabricate sandwich structured thermally conductive and electrically insulating (BNNS/ANF)-(AgNWs@BNNS)-(BNNS/ANF) (denoted as BAB) composite films by "filtration self-assembly, air spraying, and hot-pressing" method. When the mass ratio of AgNWs@BNNS to BNNS is 1 : 1 and the total mass fraction is 50 wt %, BAB composite film has the maximum in-plane thermal conductivity coefficient (λ∥ of 10.36 W/(m ⋅ K)), excellent electrical insulation (breakdown strength and volume resistivity of 41.5 kV/mm and 1.21×1015 Ω ⋅ cm, respectively) and mechanical properties (tensile strength of 170.9 MPa). 50 wt % BAB composite film could efficiently reduce the equilibrium temperature of the central processing unit (CPU) working at full power, resulting in 7.0 °C lower than that of the CPU solely integrated with ANF directly. In addition, BAB composite film boasts adaptive visible light/infrared dual camouflage properties on cement roads and jungle environments, as well as the function of fast encryption of QR code information within 24 seconds.

MnO2 doping enhances energy storage performances in lead-free BiFeO3-based ceramics

BiFeO3-based ferroelectric ceramics as promising candidates for energy storage devices have attracted a great deal of interest owing to the large ferroelectric polarization and high Curie temperature. However, the Bi volatilization induced oxygen vacancy and Fe2+/Fe3+ ionic hopping limit its energy storage performances (ESP). A charge compensated method by introducing multivalent oxide is proposed to inhibit the oxygen vacancy and Fe2+/Fe3+ ionic hopping, aiming to improve dielectric breakdown strength (BDS), polarization saturation and ESP. Here, we prepared a series of MnO2-modified Bi0.83Sm0.17Fe0.95Sc0.05O3-0.85BaTiO3-0.15Bi(Mg0.5Zr0.5)O3 [BSFS-BT-BMZ-x wt%MnO2] ceramics by traditional solid state sintering. It revealed that a large reversible energy storage density (Wrec) of ∼ 4.1 J/cm3 and a great efficiency (η) of ∼ 88% can be achieved at x = 2.1 ceramics. The improved ESP could be attributed mainly to the effective inhibition of Fe2+ by multi-fold valence states of Mn ions accompanying with the decreasing of oxygen vacancy and Fe3+/Fe2+ ionic hopping, leading to the refinement of grain size, and the enhancement of BDS and ferroelectric polarization. Moreover, the optimized ceramics exhibit the good frequency/thermal stability, excellent fatigue resistance and high powder density. These results demonstrate that a charge compensated method pays a route of improving ESP for dielectric ceramic capacitors.

Effects of the amount of magnesia on mechanical, thermal, and electrical properties of silicon nitride ceramics

Silicon nitride (Si3N4) ceramics were prepared using various amounts of magnesia (MgO) and a fixed amount of yttria as sintering additives, and their effects on the microstructures and four essential properties were evaluated: bending strength, fracture toughness, thermal conductivity, and dielectric breakdown strength (DBS). The microstructure varied with the MgO content; a smaller amount promoted grain growth, while an excess amount formed pores. The properties varied along with these structural changes. It was revealed that the four properties coexist at a high level in the range of 4–7 mol% of MgO. In addition, the large amount of MgO enhanced the electric conductivity of grain boundary and decreased the DBS. It is speculated that tips of multigrain junctions composed of a sufficiently large amount of glass modifier might work as the severe defects for the dielectric breakdown.

Optimizing energy storage under low electric field in A-site dysprosium modified BiFeO3-BaTiO3 ceramics

Electric recoverable energy density and dielectric breakdown strength are crucial factors in the high power-density capacitors. This study highlights the A-site dysprosium (Dy) substituted perovskite 0.5(Bi1−xDyx)FeO3-0.5BaTiO3 relaxor ferroelectric ceramics (x = 0–0.30) in O2-atmosphere sintering. An overall pseudo-cubic structure with a major cubic Pm-3m symmetry was observed in all compositions accompanied by multiple lattice symmetries. Anti-polar orthorhombic Pbam space group and non-polar orthorhombic Pnma symmetry gradually increase while ferroelectric tetragonal P4mm symmetry decreases as Dy content approaches x = 0.3. Recoverable energy densities (Wrec) of 4.8 J/cm3 and 3.6 J/cm3, storing efficiencies (η) of 68% and 75%, and recoverable energy storage intensities (ρ) of ∼3.2×10−2 J/kV·cm2 and ∼2.1×10−2 J/kV·cm2 were attained at x = 0 and 0.10 at electric fields of 150 and 175 kV/cm, respectively. The breakdown strength is improved from 150 to 200 kV/cm as x increases from 0.0 to 0.30. This study suggests that grain boundaries and local nanoclusters may act as barriers to inhibit charge transport and consequently increase the breakdown strength.