Breakdown Path Research Articles

Ultrahigh Energy Storage in (Ag,Sm)(Nb,Ta)O3 Ceramics with a Stable Antiferroelectric Phase, Low Domain-Switching Barriers, and a High Breakdown Strength.

AgNbO3 (AN) antiferroelectrics (AFEs) are regarded as a promising candidate for high-property dielectric capacitors on account of their high maximum polarization, double polarization-electric field (P-E) loop characteristics, and environmental friendliness. However, high remnant polarization (Pr) and large polarization hysteresis loss from room-temperature ferrielectric behavior of AN and low breakdown strength (Eb) cause small recoverable energy density (Wrec) and efficiency (η). To solve these issues, herein, we have designed Sm3+ and Ta5+ co-doped AgNbO3. The addition of Sm3+ and Ta5+ reduces the tolerance factor, polarizability of B-site cations, and domain-switching barriers, enhancing AFE phase stability and decreasing hysteresis loss. Meanwhile, adding Sm3+ and Ta5+ leads to decreased grain sizes, increased band gap, and reduced leakage current, all contributing to increased Eb. As a benefit from the above synergistic effects, a high Wrec of 7.24 J/cm3, η of 72.55%, power density of 173.73 MW/cm3, and quick discharge rate of 18.4 ns, surpassing those of many lead-free ceramics, are obtained in the (Ag0.91Sm0.03)(Nb0.85Ta0.15)O3 ceramic. Finite element simulations for the breakdown path and transmission electron microscopy measurements of domains verify the rationality of the design strategy.

Impact of freeze–thaw cycling on the stability and turnover of black soil aggregates

During freeze–thaw cycling, aggregates undergo a dynamic change in breakdown–formation (turnover), however, how the turnover occurs between aggregates of various particle sizes is not clear. To clarify the influence of freeze–thaw cycling on the dynamic changes in the particle size of soil aggregates, soil aggregates from the Black Soil Region of Northeast China were selected as the research objects. The study conducted in situ dynamic monitoring experiments, innovatively applying the rare earth oxide (REO) tracer method to natural conditions of freeze–thaw cycles (autumn freeze–thaw period, freezing period, and spring freeze–thaw period), accurately tracking the turnover paths and quantifying the turnover rates between aggregates of various particle sizes. The results revealed that the total value of the formation paths of the 2–5 mm aggregates and 0.25–2 mm aggregates increased during the autumn freeze–thaw period. The number of freeze–thaw cycles and accumulated snowfall were significantly positively correlated with aggregate stability, with an increase in the number of freeze–thaw cycles and accumulated snowfall resulting in an increase in the proportion of aggregates > 0.25 mm, which improved aggregate stability. In addition, the total value of the breakdown path of macro-aggregates increased during the spring freeze–thaw cycling period. Soil moisture was significantly negatively correlated with aggregate stability, with increased soil moisture resulting in a decrease in the percentage of aggregates > 0.25 mm, which resulted in a decrease in aggregate stability. The study can provide a reference understanding for the effects of freeze–thaw cycles on the structure of black soil and provide a theoretical basis for improving the quality of arable land.

Scalable multilayered dielectric polymer film exhibiting significantly improved high-temperature energy density

Dielectric polymers, serving as crucial dielectric media in high-power-density energy storage devices, play a pivotal part in modern industries and electrical systems. However, the rapid degradation of breakdown strength and charge-discharge efficiency in elevated temperature environment imposes formidable limitations on the utilization of polymer dielectric under extreme conditions. Here, a series of polyetherimide/polysulfone alternating multilayer composite films are prepared using a non-equilibrium processing method, which effectively blocks the development of breakdown paths by the interface barriers in the multilayer structure. The deep trap sites within the interface capture the charge carriers excited at high temperatures, thus decreasing conduction loss and enhancing the efficiency and breakdown field strength of the dielectric polymer. Consequently, excellent capacitive performances including a high energy density of 5.4 J cm−3 with an efficiency exceeding 90% at 200 °C and cycle stability up to 106 cycles have been obtained. Furthermore, the multilayer polymer capacitors (MLPC) constructed from composite films also exhibit significant flexibility and thermal stability. This work provides valuable insights for the advancement of high-temperature energy storage polymers with commercial application value.

Excellent energy storage properties in ZrO2 toughened Ba0.55Sr0.45TiO3-based relaxor ferroelectric ceramics via multi-scale synergic regulation

Lead-free ceramic capacitors offer ultrahigh power density and ultrafast discharging rates, making them critical energy storage components for advanced pulsed power systems. However, the greatest obstacle to broader applications remains the relatively low energy storage density. In this study, a relaxor ferroelectric ceramic based on (0.6-x)Ba0.55Sr0.45TiO3-0.4Bi0.5Na0.5TiO3-xSrZrO3 ((0.6-x)BST-0.4BNT-xSZ) is prepared using the tape casting method, resulting in an excellent energy density (Wrec ≈ 10.0 J cm−3) and high energy storage efficiency (η ≈ 91 %). The solid solution of linear dielectrics SrZrO3 synergistically regulates both relaxor properties and breakdown strength. The variation of relaxor property was explored utilizing New Glass model and the multi-polarization model, with confirmation provided by piezoresponse force microscopy. Furthermore, the breakdown strength could be attributed to improvements in electric insulation and the widening of the bandgap. As SrZrO3 content increases, the in-situ emergence of the second phase ZrO2, accompanied by a martensitic transformation, not only improves the fracture toughness of ceramics but also serves to elongate the breakdown path. Encouragingly, x = 0.20 ceramics also achieve excellent temperature stability (−95–125 ℃), frequency stability (1–1000 Hz), cycling reliability (1–106 cycles), and great charging-discharging properties. This multiscale synergic regulation strategy plays a guiding role in the screening of high-performance energy storage dielectric materials.

Significantly Enhanced Energy Density of Polyvinylidene Fluoride/Polyimide-Based Nanocomposites by Core-Shell BaTiO3@SiO2.

Improving the limited energy storage capacity of dielectric materials has long been an attractive challenge. In this work, a four-phase hybridized nanocomposite was designed. The linear polymer polyimide (PI) was added to the ferroelectric polymer polyvinylidene fluoride (PVDF) and compounded with a nanoceramic BT@SiO2 with a core-shell structure. The results show that PVDF-PI/BT@SiO2 nanocomposites prepared by a straightforward spin-coating method have a significantly increased discharge energy density. The polymer blends obtain a tightly extended conformation in the amorphous region. Also, this provides an excellent matrix environment for the homogeneous dispersion of fillers. The core-shell structure, as a physical barrier, not only hinders the expansion of the breakdown path but also extends multiple polarization surfaces with gradient variations at the microscopic level. Therefore, the synergistic effect generated by polymer blending and core-shell structure effectively enhances the dielectric and stored energy characteristics of nanocomposites. The dielectric constant is stable at 11.39-18.7, and the dielectric loss is always lower than 0.136. The discharge energy density is 2.5 J/cm3, almost 110% higher than that of the BOPP films (about 1.2 J/cm3). These experimental results suggest that the composite system using core-shell structure and polymer blending is a new way to improve the energy density of dielectric materials.

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.

Phase field model for electric-thermal coupled discharge breakdown of polyimide nanocomposites under high frequency electrical stress

In contrast to conventional transformers, power electronic transformers, as an integral component of new energy power system, are often subjected to high-frequency and transient electrical stresses, leading to heightened concerns regarding insulation failures. Meanwhile, the underlying mechanism behind discharge breakdown failure and nanofiller enhancement under high-frequency electrical stress remains unclear. An electric-thermal coupled discharge breakdown phase field model was constructed to study the evolution of the breakdown path in polyimide nanocomposite insulation subjected to high-frequency stress. The investigation focused on analyzing the effect of various factors, including frequency, temperature, and nanofiller shape, on the breakdown path of Polyimide (PI) composites. Additionally, it elucidated the enhancement mechanism of nano-modified composite insulation at the mesoscopic scale. The results indicated that with increasing frequency and temperature, the discharge breakdown path demonstrates accelerated development, accompanied by a gradual dominance of Joule heat energy. This enhancement is attributed to the dispersed electric field distribution and the hindering effect of the nanosheets. The research findings offer a theoretical foundation and methodological framework to inform the optimal design and performance management of new insulating materials utilized in high-frequency power equipment.

Analysis of internal material characteristics of cathode crater of micro-cathodic arc thruster

In this study, the material loss relationship between the electrodes of a micro-cathodic arc thruster was investigated by adjusting the input voltage. The crater morphology of the micro-cathodic arc thruster was observed with a scanning electron microscope. The internal crater material was analyzed with an energy spectrum analyzer. On this basis, the arc path is obtained and the material loss of the structure between the electrodes of the micro-cathodic arc thruster was studied through further numerical simulation. The experimental and simulation results show that with a change in the Power processing unit (PPU) input voltage of the micro-cathodic arc thruster, the material distribution in the cathode crater and the discharge channel between the electrodes changed, affecting the bombardment of ions between the electrodes of the thruster on the insulating structure and conductive coating. In engineering applications, regulation of the arc breakdown path can effectively reduce the total energy of ion bombardment on the wall.

Multilayer BOPET dielectric film with internal double electron barrier for high temperature applications

With the continuous development of modern electronic and power equipment, practical applications in harsher environment call for film capacitors with higher temperature resistance. Here, we designed a multilayer film including two outer layers of biaxially oriented polyethylene terephthalate (BOPET), two inorganic layers of boron nitride nanosheets (BNNSs), and an intermediate epoxy layer. Due to the blocking effect of the BNNSs layer, the propagation of the breakdown path is hindered, which improves the breakdown strength of the film. Meanwhile, the carrier transport in the medium is effectively hindered, reducing the conduction loss of the composite film. As a result, the optimized multilayer composite film had a high discharged energy density of 8.76 J/cm3, maintaining a high charge-discharge efficiency of 95% at 25 °C, while remarkable values of 7.04 J/cm3 and 73% were obtained even at 150 °C, which showed prominent improvements compared with BOPET. Thus, it turns out to be a promising strategy of fabricating high temperature dielectric films.

Sandwich-structured BOPET films with high energy density and low loss for high temperature film capacitors

Film capacitors have widely been used in modern electrical/electronic equipment because of their high insulation property and high-power density. However, the traditional dielectric films suffered a high conduction loss under high temperature and electric field conditions, which leads to the depression of high temperature energy storage properties. Herein, sandwich-structured composite films using biaxially oriented polyethylene terephthalate (BOPET) as the outer layers were prepared to construct the interfacial barrier, which was beneficial for hindering the propagation of breakdown path. In addition, epoxy resin was applied as the adhesive inner layer to bind the outer layers up tightly, while the boron nitride nanosheets (BNNSs) in the inner layer further improved the breakdown strength of the film and inhibited the conduction loss, especially under high temperature and electric field conditions. The composite film with optimized BNNSs content had a high discharged energy density of 9.11 J/cm3 and a ultrahigh charge–discharge efficiency of 95% at 25 °C, while the values were 6.45 J/cm3 and 70% at 150 °C, respectively, of which both were much higher than those of pure BOPET. Thus, the sandwich-structure method points out a promising way of preparing dielectric films with excellent energy storage performances.

Effect of sintering temperature on dielectric and electrical properties of bio-waste derived beta-dicalcium silicate

Beta-dicalcium silicate ceramics were synthesized by mechanochemical-assisted solid-state reaction route using rice husks and chicken eggshells as silica and calcium oxide sources. The ceramics were sintered at 900, 1000, and 1100 °C for 2 h in air. The effect of sintering temperature on these ceramics' morphological, breakdown strength, dielectric, and electrical properties was investigated. It was found that the ceramic sintered at the optimized temperature of 1100 °C formed the pure β-dicalcium silicate (β-Ca2SiO4). Scanning electron micrographs showed that with the increase in sintering temperature, the average grain size and pore size of the sintered ceramics increased while the grain boundary density decreased, which promoted the breakdown path and resulted in a decrease in breakdown strength. The dielectric behavior examined from 25 to 300 °C and in a frequency range of 4–5 MHz found that the dielectric constant and loss tangent decreased with increasing frequency. Nyquist plot of impedance confirmed a non-Debye type relaxation, and grain and grain boundary contributions were revealed from equivalent circuit fitting. Variations of impedance spectroscopy reflect the positive and negative temperature coefficient of resistance behavior for these ceramics. Electric modulus spectra revealed that with the sintering temperature increase, the samples' conductivity activation energies increased from 0.35 to 0.46 eV. All the sintered samples attained low dielectric loss (0.004 < tanδ < 0.1) above 103 Hz, which makes them suitable materials for capacitor application.

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 ≈20ns. 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.

Glass fiber network reinforced polyethylene terephthalate composites for support insulators

Epoxy resin has long been used as an insulating material in high-voltage apparatus, although its poor recyclability greatly limits its future application. Fiber network reinforced polyethylene terephthalate (PET), as a low-cost and recyclable material, has great potential to substitute epoxy resin as a high-voltage insulation material. The enhanced fiber network combined with the PET matrix form a semi-‘steel-reinforced concrete’ structure, and can collaboratively improve the tensile strength by more than 50% and the dielectric strength by 25.4%. Furthermore, the breakdown path as well as the fiber distribution are clearly rebuilt in 3D coordinates based on a 3D x-ray microscope for the first time. Experimental and computational evidence show that the fiber network lengthens the breakdown path and improves the dielectric strength. This work provides new perspectives for subsequent research on the electrical properties of bone-enhanced dielectric polymer composite.

Charge Imbalance Tolerance of 4H-SiC Superjunction Devices Featuring Breakdown Path Variation

In this letter, the impact of charge imbalance on silicon carbide (SiC) superjunction (SJ) device is studied thoroughly. The breakdown path variation under different degrees of charge imbalance is revealed for the first time by joint analysis of the SiC anisotropy of impact ionization and the charge-imbalanced SJ two-dimensional electric field distribution. Primarily due to this anisotropy, it is a significant finding that the breakdown voltage could be even higher than the balance case when either P or N pillar is slightly under-doped. Furthermore, an SJ design methodology is proposed based on figure-of-merit (FOM) sensitivity and process tolerance, which guides how to better design low-sensitivity SJ devices within a certain range of charge imbalance degree. It is indicated that the wide pillar is suggested for large process tolerance and the under-doped case is less sensitive to charge imbalance than the over-doped case. In brief, the aforementioned revelation can gain new physics-level insights into various charge-imbalanced SJ cases and the methodology can achieve not only the high FOM based on practical process capability but also the required process tolerance based on target performance.

Multilayer nanocomposite films with enhanced piezoelectric properties doping PZT nanofibers

Flexible electronics components, including wearable sensors, miniature energy supply devices, and energy harvesting systems based on polymer piezoelectric materials, have garnered extensive attention. This study focuses on the preparation of PZT nanofibers (PZT NFs) via electrospinning and their modification with polydopamine, the fabrication of PVDF/PZT NFs nanocomposite films through casting, and the production of tri-layer nanocomposite films using hot pressing. The alignment of the PZT NFs perpendicular to the electric field direction enhances the breakdown strength (Eb) and facilitates the polarization of the nanocomposite films. At the interlayer interfaces within the tri-layer structure, electron traps extend the breakdown path, attenuating charge concentration and mitigating the electric field concentration effect. Consequently, the tri-layer films exhibit excellent electrical properties. Notably, the P4P tri-layer nanocomposite films have a high Eb of 290.47 kV/mm and a piezoelectric coefficient of -24 pC/N. This paper presents a promising strategy for enhancing the piezoelectric properties of polymer piezoelectric materials applied in sensors and energy harvesting systems.

Evolution Characteristics of DC Breakdown for Biaxially Oriented Polypropylene Films

Biaxially oriented polypropylene (BOPP) films are the preferred storage dielectric for dry-type film capacitors due to excellent dielectric properties. However, the evolution characteristics of DC Breakdown of BOPP film in air remain unclear. This study focuses on the influence of curvature, contact area and material of electrode on the DC breakdown in BOPP films. The on-line/off-line measurements of surface potential and characterizations of trap distribution are achieved. And the simulations of surface charge, electric field and energy injection are accomplished. The breakdown path and degradation traces in BOPP films are also analyzed. The experimental results show that the effective insulation distance is the key to determine the actual performance of the film, affected by the trap distribution and density. This paper has a reference for the optimization of insulation structure for dry-type film capacitors in the field of high-voltage direct current (HVDC).

Ultrahigh Energy Storage Capacitors Based on Freestanding Single‐Crystalline Antiferroelectric Membrane/PVDF Composites

AbstractInorganic/organic dielectric composites are very attractive for high energy density electrostatic capacitors. Usually, linear dielectric and ferroelectric materials are chosen as inorganic fillers to improve energy storage performance. Antiferroelectric (AFE) materials, especially single‐crystalline AFE oxides, have relatively high efficiency and higher density than linear dielectrics or ferroelectrics. However, adding single‐crystalline AFE oxides into polymers to construct composite with improved energy storage performance remains elusive. In this study, high‐quality freestanding single‐crystalline PbZrO3 membranes are obtained by a water‐soluble sacrificial layer method. They exhibit classic AFE behavior and then 2D–2D type PbZrO3/PVDF composites with the different film thicknesses of PbZrO3 (0.1‐0.4 µm) is constructed. Their dielectric properties and polarization response improve significantly as compared to pure PVDF and are optimized in the PbZrO3(0.3 µm)/PVDF composite. Consequently, a record‐high energy density of 43.3 J cm−3 is achieved at a large breakdown strength of 750 MV m−1. Phase‐field simulation indicates that inserting PbZrO3 membranes effectively reduces the breakdown path. Single‐crystalline AFE oxide membranes will be useful fillers for composite‐based high‐power capacitors.

Two-Dimensional Metal-Organic Framework Incorporated Highly Polar PVDF for Dielectric Energy Storage and Mechanical Energy Harvesting.

Here, we introduce a 2D metal-organic framework (MOF) into the poly(vinylidene fluoride) (PVDF) matrix, which has been comparatively less explored in this field. Highly 2D Ni-MOF has been synthesized in this regard via hydrothermal route and has been incorporated into PVDF matrix via solvent casting technique with ultralow filler (0.5 wt%) loading. The polar phase percentage of 0.5 wt% Ni-MOF loaded PVDF film (NPVDF) has been found to be increased to ~85% from a value of ~55% for neat PVDF. The ultralow filler loading has inhibited the easy breakdown path along with increased dielectric permittivity and hence has enhanced the energy storage performance. On the other hand, significantly enriched polarity and Young's Modulus has helped in improving its mechanical energy harvesting performance, thereby enhancing the human motion interactive sensing activities. The piezoelectric and piezo-tribo hybrid devices made up of NPVDF film have shown improved output power density of ~3.26 and 31 μW/cm2 compared to those of the piezoelectric and piezo-tribo hybrid devices comprising of neat PVDF (output power density ~0.6 and 17 μW/cm2, respectively). The developed composite can thus be considered an excellent candidate for multifunctional applications.

Molecular Bridges Link Monolayers of Hexagonal Boron Nitride during Dielectric Breakdown

We use conduction atomic force microscopy (CAFM) to examine the soft breakdown of monocrystalline hexagonal boron nitride (h-BN) and relate the observations to the defect generation and dielectric degradation in the h-BN by charge transport simulations and density functional theory (DFT) calculations. A modified CAFM approach is adopted, whereby 500 × 500 nm2 to 3 × 3 μm2 sized metal/h-BN/metal capacitors are fabricated on 7 to 19 nm-thick h-BN crystal flakes and the CAFM tip is placed on top of the capacitor as an electrical probe. Current–voltage (I-V) sweeps and time-dependent dielectric breakdown measurements indicate that defects are generated gradually over time, leading to a progressive increase in current prior to dielectric breakdown. Typical leakage currents are around 0.3 A/cm2 at a 10 MV/cm applied field. DFT calculations indicate that many types of defects could be generated and contribute to the leakage current. However, three defects created from adjacent boron and nitrogen monovacancies exhibit the lowest formation energy. These three defects form molecular bridges between two adjacent h-BN layers, which in turn “electrically shorts” the two layers at the defect location. Electrical shorting between layers is manifested in charge transport simulations, which show that the I-V data can only be correctly modeled by incorporating a decrease in effective electrical thickness of the h-BN as well as the usual increase in trap density, which, alone, cannot explain the experimental data. An alternative breakdown mechanism, namely, the physical removal of h-BN layers under soft breakdown, appears unlikely given the h-BN is mechanically confined by the electrodes and no change in AFM topography is observed after breakdown. High-resolution transmission electron microscope micrographs of the breakdown location show a highly localized (<1 nm) breakdown path extending between the two electrodes, with the h-BN layers fractured and disrupted, but not removed.

Prediction of the breakdown voltage and breakdown area of gas switches based on ionization integral

Gas spark switches have a simple structure and high current capacity and are widely used in the field of pulsed power. The breakdown path of gas switches affects their jitter and lifetime. Particle simulations are used to analyze the breakdown path, which requires a large amount of computation resources. In this paper, in order to calculate the ionization integral value of electrode gaps, a simulation-based method using a simplified model is studied. The integration of the ionization coefficient along the E-field curves is calculated for the electrode gap and is used to determine if breakdown occurs for a given curve. The breakdown region of two-electrode self-breakdown switches is estimated using the distribution of breakdown curves, and the trigger voltage of a three-electrode gas-trigger switch is estimated by analyzing the curves. By applying the ionization integral value to different paths to reach the streamer formation condition as the breakdown criterion, the operating voltage and erosion region of the electrodes are estimated. The numerical results for an environmental pressure of 0.2 MPa are in good agreement with the experimental results from a triggering experiment that uses a three-electrode gas-triggered switch. This ionization integral model can be used to predict the breakdown voltage and breakdown region of gas switches, which is conducive to improving the performance of gas switches.