Macroscopic Electric Field Research Articles

Macroscopic built-in polarization electric field powers high lithium-ion transport for all-solid-state lithium-sulfur batteries

Traditional liquid lithium-sulfur batteries possess the merits of high energy density and low cost, and have a wide application prospect in the field of energy storage; however, the growth of lithium dendrites, the side reaction of the liquid electrolyte, and the harmful “shuttle effect” of lithium polysulfides have hindered their practical application. Herein, a solid-state composite polymeric electrolyte with a macroscopic built-in polarization electric field is designed to improve lithium-ion transport and depress shuttle effect. The introduction of barium titanate as a functional filler effectively reduces the crystallinity of the polymer and promotes the dissociation of the lithium salt. At the same time, the built-in polarization electric field generated by its crystal structure provides a strong driving force for lithium-ion transport, thus accelerating lithium-ion migration. The experimental results show that the built-in electric field can enhance the lithium-ion transport and accelerate redox kinetics. Furthermore, the macroscopic charges can establish strong chemical interactions between polysulfides, which leads to the suppression of the shuttle effect and effectively improves the cycling stability of all-solid-state lithium-sulfur batteries. Benefiting from these properties, Li||Li symmetric batteries exhibit stable cycling for more than 900 h, and all-solid-state lithium-sulfur batteries have a high cycling stability of more than 200 cycles at a rate of 0.1 C. This work provides a simple and effective method for designing high-performance all-solid-state lithium-sulfur batteries.

Supression of shielding effect of large area field emitter cathode in radio frequency gun environment

Abstract Utilisation of large area field emitters (LAFE) cathodes for rf gun injector hold promise for delivering compact, high power and high brightness electron beam for advanced accelerator technologies. LAFEs subjected to DC electric fields posses significant challenges due to the shielding effect which restricts emission from central emitters and decreases the overall current density. Mitigating the shielding effect of LAFE in rf gun environment is essential for meeting the desired beam quality requirement in an accelerator. The current distribution of LAFE under DC conditions depend on its various geometrical parameters such as emitter height, inter-emitter distance, aspect ratio, number of emitters. Additionally, in rf gunsetup, LAFEs are subjected to variable macroscopic electric field at different emitter position which can potentially alter the current distribution compared to DC fields. In this work, we have systematically studied the shielding effect properties of LAFE in rf gun environment under the influence of various LAFE parameters. A semi-analytical approachhas been adopted to estimate the current distribution which combines the analytically calculated field enhancement factor (γ) and numerically calculated applied rf field values. This new methodology was first validated using COMSOL simulation and then employed for field emission performance estimation of a LAFE cathode integrated in a½ cell S-band (2856 MHz) rf gun. The simulation results reveals that under favourable conditions, a Gaussian spatial distribution of beam can be obtained from LAFE thus countering the shielding effect typical in DC fields. By optimizing the LAFE parameters, the desired current and beam distribution pattern can be achieved. This study highlights the adoption of a promising approach for designing LAFE cathodes suitable for rf gun which can lead to advancement of field emission technologies for accelerator-related applications.

Statistical method accounts for microscopic electric field distortions around neurons when simulating activation thresholds.

Notwithstanding advances in computational models of neuromodulation, there are mismatches between simulated and experimental activation thresholds. Transcranial Magnetic Stimulation (TMS) of the primary motor cortex generates motor evoked potentials (MEPs). At the threshold of MEP generation, whole-head models predict macroscopic (at millimeter scale) electric fields (50-70 V/m) which are considerably below conventionally simulated cortical neuron thresholds (200-300 V/m). We hypothesize that this apparent contradiction is in part a consequence of electrical field warping by brain microstructure. Classical neuronal models ignore the physical presence of neighboring neurons and microstructure and assume that the macroscopic field directly acts on the neurons. In previous work, we performed advanced numerical calculations considering realistic microscopic compartments (e.g., cells, blood vessels), resulting in locally inhomogeneous (micrometer scale) electric field and altered neuronal activation thresholds. Here we combine detailed neural threshold simulations under homogeneous field assumptions with microscopic field calculations, leveraging a novel statistical approach. We show that, provided brain-region specific microstructure metrics, a single statistically derived scaling factor between microscopic and macroscopic electric fields can be applied in predicting neuronal thresholds. For the cortical sample considered, the statistical methods match TMS experimental thresholds. Our approach can be broadly applied to neuromodulation models, where fully coupled microstructure scale simulations may not be practical.

Nonuniqueness in defining the polarization: Nonlocal surface charges and the electrostatic, energetic, and transport perspectives

Ionic crystals, ranging from dielectrics to solid electrolytes to complex oxides, play a central role in the development of modern technologies for energy storage, sensing, actuation, and other functional applications. Mesoscale descriptions of these crystals are based on the continuum polarization density field to represent the effective physics of charge distribution at the scale of the atomic lattice. However, a long-standing difficulty is that the classical electrostatic definition of the macroscopic polarization — as the dipole or first moment of the charge density in a unit cell — is not unique; rather, it is sensitive to translations of the unit cell in an infinite periodic system. This unphysical non-uniqueness has been shown to arise from starting directly with an infinite system — wherein the boundaries are ill-defined — rather than starting with a finite body and taking appropriate limits. This limit process shows that the electrostatic description requires not only the bulk polarization density, but also the surface charge density, as the effective macroscopic descriptors; that is, a nonlocal effective description. Other approaches to resolve this difficulty include the popular modern theory of polarization that completely sets aside the polarization as a fundamental quantity in favor of the change in polarization from an arbitrary reference value and then relates the change in polarization to the transport of charge (the “transport” definition); or, in the spirit of classical continuum mechanics, to define the polarization as the energy-conjugate to the electric field (the “energetic” definition).This work examines the relation between the classical electrostatic definition of polarization, and the transport and energy-conjugate definitions of polarization. We show the following: (1) The transport of charge does not correspond to the change in polarization in general; instead, one requires additional simplifying assumptions on the electrostatic definition of polarization for these approaches to give rise to the same macroscopic electric fields. Thus, the electrostatic definition encompasses the transport definition as a special case. (2) The energy-conjugate definition has both bulk and surface contributions; while traditional approaches neglect the surface contribution, we find that accounting for the nonlocal surface contributions is essential to be consistent with the classical definition and obtain the correct macroscopic electric fields.

Directing the photogenerated charge flow in a photocathodic metal protection system with single‐domain ferroelectric PbTiO3 nanoplates

AbstractPhotocathodic protection (PCP) is arguably an ideal alternative technology to the conventional electrochemical cathodic protection methods for corrosion mitigation of metallic infrastructure due to its eco‐friendliness and low‐energy‐consumption, but the construction of highly‐efficient PCP systems still remains challenging, caused primarily by the lack of driving force to guide the charge flow through the whole PCP photoanodes. Here, we tackle this key issue by equipping the PCP photoanode with ferroelectric single‐domain PbTiO3 nanoplates, which can form a directional “macroscopic electric field” throughout the entire photoanode controllable by external polarization. The properly poled PCP photoanode allows the photogenerated electrons and holes to migrate in opposite directions, that is, electrons to the protected metal and holes to the photoanode/electrolyte interface, leading to largely suppressed charge annihilation and consequently a considerable boost in the overall solar energy conversion efficiency of the PCP system. The as‐fabricated photoanode can not only supply sufficient photocurrent to 304 stainless steel to initiate cathodic protection, but also shift the metal potential to the corrosion‐free range. Our findings provide a viable design strategy for future high‐performance PCP systems based on ferroelectric nanomaterials with enhanced charge flow manipulation.

Revisiting Dynamic Processes and Relaxation Mechanisms in a Heterocyclic Glass-Former: Direct Observation of a Transient State.

Despite decades of studies, a clear understanding of near-Tg phenomena remains challenging for glass-forming systems. This review delves into the intricate molecular dynamics of the small, heterocyclic thioether, 6-methyl-2,3-dihydro-1,4-benzodithiine (MeBzS2), with a particular focus on its near-Tg cold crystallization and relaxation mechanisms. Investigating isothermal crystallization kinetics at various temperatures reveals a significant interplay between its molecular dynamics and recrystallization from a supercooled liquid. We also identify two independent interconversion paths between energetically privileged conformers, characterized by strained transition states. We demonstrate that these spatial transformations induce substantial alterations in the dipole moment orientation and magnitude. Our investigation also extends to the complex salt PdCl2(MeBzS2), where we observe the transient conformers directly, revealing a direct relationship between their abundance and the local or macroscopic electric field. The initially energetically privileged isomers in an undisturbed system become less favored in the presence of an external electric field or ions, resulting even in an unexpected inversion of states. Consequently, we confirm the intramolecular character of secondary relaxation in MeBzS2 and its mechanism related to conformational changes within the heterocyclic ring. The research is based on the combination of broadband dielectric spectroscopy, X-ray diffraction, and quantum density functional theory calculations.

Electron-field instability: Excitation of electron plasma waves by an electric field

Electric fields are commonplace in plasmas and affect transport by driving currents and, in some cases, instabilities. The necessary condition for instability in collisionless plasmas is commonly understood to be described by the Penrose criterion, which quantifies a sufficient relative drift between different populations of particles that must be present for wave amplification via inverse Landau damping. For example, electric fields generate drifts between electrons and ions that can excite the ion-acoustic instability. Here, we use particle-in-cell simulations and linear stability analysis to show that the electric field can drive a fundamentally different type of kinetic instability, named the electron-field instability. This instability excites electron plasma waves with wavelengths ≳30λDe, has a growth rate that is proportional to the electric field strength, and does not require a relative drift between electrons and ions. The Penrose criterion does not apply when accounting for the electric field. The large value of the observed frequency, near the electron plasma frequency, further distinguishes it from the standard ion-acoustic instability, which oscillates near the ion plasma frequency. The ubiquity of macroscopic electric fields in quasineutral plasmas suggests that this instability is possible in a host of systems, including low-temperature and space plasmas. In fact, damping from neutral collisions in such systems is often not enough to completely damp the instability, adding to the robustness of the instability across plasma conditions.

Stark polarization spectroscopy of neon spectral lines for estimating cathode sheath parameters in Grimm-type glow discharge sources

We present the results of the optical emission spectroscopy (OES) study of the Ne I 503.775 nm and Ne I 508.038 nm atomic spectral lines observed in two DC glow discharge sources (GDS), standard Grimm analytical source and the modified plane cathode Grimm design. The standard Grimm GDS enables OES recording end-on only, i.e. when the radiation is collected from the entire discharge, in the direction perpendicular to the cathode surface. Our modification of Grimm GDS, on the other hand, allows for spectra recording of the complex line shapes from two optical directions, both end-on and side-on, the latter collecting radiation from a narrow slice of the discharge parallel to the cathode surface. Side-on observations enable spatially resolved Stark polarization spectroscopy at different positions along the whole cathode sheath (CS) region of the discharge. This allows the study of the Stark shifts of differently polarized (σ, π, or unpolarized) line components' dependence on the macroscopic CS electric field strength. Stark components of neon lines, encountered in side-on observations in the CS, are preserved in the end-on recordings as characteristic features – wavy wings with intensity maxima corresponding to the distinctly resolved Stark components in the CS. Following OES measurements in a broad range of discharge conditions (pressure, voltage, current), we report on a sustained correlation between the value of the maximum electric field strength Emax in the CS and the end-on recorded wing feature shifts Δλe. This correlation can be extrapolated to estimate the cathode sheath parameters Emax and the CS thickness dc in the standard Grimm-type GDS, with end-on optical access available only.

The Effect of Electric Fields on the Structure of Water/Acetonitrile Mixtures

We study the effect of macroscopic electric fields on the structure of water/acetonitrile mixtures at high acetonitrile content by molecular dynamics simulations. We find that the linear response regime extends up to roughly 0.1 V nm−1 in these mixtures, then nonlinear behavior sets in. The most pronounced nonlinear effect of an electric field is a change of relative orientations of neighboring acetonitrile molecules, from predominantly antiparallel to predominantly parallel. Nevertheless, the hydrogen bond network topology remains remarkably stable and conserves its overall properties in the whole range of considered applied fields up to 0.5 V nm−1, which is far beyond the dielectric breakdown limit of pure water. Additionally, we report on a comparison of simulation results at zero field with experimental results and available ab-initio data using four different recently proposed acetonitrile force fields, where we find that the force field by Kowsari and Tohidifar [J. Comput. Chemistry 39, 1843, 2018] performs best. Furthermore, we demonstrate that analyzing the hydrogen bond network can be a useful tool in investigating the formation and structure of water nanodomains and their confinement by an acetonitrile matrix in water/acetonitrile mixtures.

Microscopic derivation of Ginzburg–Landau theory and the BCS critical temperature shift in general external fields

We consider the Bardeen–Cooper–Schrieffer (BCS) free energy functional with weak and macroscopic external electric and magnetic fields and derive the Ginzburg–Landau functional. We also provide an asymptotic formula for the BCS critical temperature as a function of the external fields. This extends our previous results in Deuchert et al. (Microscopic derivation of Ginzburg-Landau theory and the BCS critical temperature shift in a weak homogeneous magnetic field, PMP 4(1), 1–89 (2023)) for the constant magnetic field to general magnetic fields with a nonzero magnetic flux through the unit cell.

Possible Locking Shock Time in 2–48 Hours

An hourly scale precursor of inland earthquakes (EQs) is revealed in this paper. Several EQ cases in China have been reported. As indicated by a table listing 23 inland EQs and their shock time, epicenter location, magnitude, near-epicenter weather conditions, precursor start time and precursor duration, when the weather conditions are fair near the epicenter, an anomalously negative atmospheric electrostatic signal is readily observable approximately 2–48 h before the EQ occurs. Moreover, a successful single-station alarm for nearby moderate-magnitude EQs is demonstrated, and a possible mechanism for the precursor signal is proposed. The change in the electrostatic field during an EQ process is explained as the release of radioactive gases from the subsurface into the atmosphere via large (regional-scale) preexisting microfractures in the rock at the source depth. These gases considerably ionize the atmosphere, and the separated positive and negative ions establish a special macroscopic electric field. The final critical stage of 2–48 h before an EQ may indicate a stable tectonic process.

A separator modified by barium titanate with macroscopic polarization electric field for high-performance lithium-sulfur batteries.

The detrimental "shuttling effect" of lithium polysulfides and the sluggish kinetics of the sulfur redox reaction in lithium-sulfur batteries (LSBs) impede the practical application. Considering the high polar chemistry facilitates the anchoring of polysulfides, ferroelectric materials have gradually been employed as functionalized separators to suppress the "shuttling effect". Herein, a functional separator coated with BaTiO3 with a macroscopic polarization electric field (poled-BaTiO3) is designed for retarding the problematic shuttle effect and accelerating redox kinetics. Theoretical calculations and experiments revealed that resultant positive charged alignments on the poled-BaTiO3 coating can chemically immobilize polysulfides, effectively improving the cyclic stability of LSBs. Moreover, the simultaneous reinforcement of the built-in electric field in the poled-BaTiO3 coating can also improve Li-ion transportation for accelerating redox kinetics. Benefiting from these attributes, the as-developed LSB attains an initial discharge capacity of 1042.6 mA h g-1 and high cyclic stability of over 400 cycles at 1 C rate. The corresponding LSB pouch cell was also assembled to validate the concept. This work is anticipated to provide new insight into the development of high-performing LSBs through engineering ferroelectric-enhanced coatings.

Dynamic Simulation of Electron Emission Characteristics Based on Different Numerical Models of a Nanoscale Micro-Protrusion

It is well known that electron emission is one of the key factors to cause electrical breakdown in vacuum gaps. In previous studies, it tended to use simplified numerical models with uniform electric field on emission region to investigate the electron emission characteristics at the cathode micro-protrusion and the influence of the materials of the micro-protrusions. The objective of this article is to introduce an improved numerical model of a nanoscale micro-protrusion with nonuniform electrical field on the emission region, which could be used for micro-protrusions with various irregular geometries. The improved numerical model is used in this article to study the dynamic characteristics of the electron emission of Cu and Cr micro-protrusions under different macroscopic electric fields. First, the electric field distribution is obtained by solving Laplace equation based on finite difference method (FDM). Then, the emission current and Nottingham effect are obtained by calculating the general thermal-field (GTF) equations based on the electric field distribution. Finally, the dynamic characteristics of the electron emission current and temperature distribution are iteratively calculated considering the Joule heating and Nottingham effect. The calculation results of the improved numerical model are compared with those of the previous simplified numerical model. The results show that for Cu and Cr micro-protrusions, the Joule heating, and Nottingham effect would play different roles in the emission process. In general, it is more likely for the Cr micro-protrusions to evaporate than the Cu micro-protrusions. The results of this article may provide some useful information to further understand the vacuum breakdown initiated by electron emission.

Maximizing the electromomentum coupling in piezoelectric laminates

Asymmetric piezoelectric composites exhibit coupling between their macroscopic linear momentum and electric field, a coupling that does not appear at the microscopic scale. This electromomentum coupling constitutes an additional knob to tailor the dynamic response of the medium, analogously to the Willis coupling in elastic composites. Here, we employ topology- and free material optimization approaches to maximize the electromomentum coupling of periodic piezoelectric laminates in the low frequency, long-wavelength limit. We find that the coupling can be enhanced by orders of magnitude, depending on the degrees of freedom in the optimization process. The optimal compositions that we find provide guidelines for the design of metamaterials with maximum electromomentum coupling, paving the way for their integration in wave control applications.

Low-macroscopic field emission structure: Using the shape of the conductor to identify a local difference in electric potential

The emission of electrons from an insulating crystal deposited on a conductor occurs at a macroscopic electric field of a few volts per micrometer, 3 orders of magnitude below the field emission from a clean metal. This is due to the local field enhancement induced by the presence of the insulating crystal. The emission profiles depend on the shape of the conductive substrate; analyzing these profiles enables the local difference in electric potential and the opening angle to be traced. Given the thickness of the crystal, the local difference in potential indicates the local field enhancement of a few volts per nanometer applied to the conductor.

Bright sources under the projection microscope: using an insulating crystal on a conductor as electron source

The development of bright sources is allowing technological breakthroughs, especially in the field of microscopy. This requires a very advanced control and understanding of the emission mechanisms. For bright electron sources, a projection microscope with a field emission tip provides an interference image that corresponds to a holographic recording. Image reconstruction can be performed digitally to form a “real” image of the object. However, interference images can only be obtained with a bright source that is small: often, an ultra-thin tip of tungsten whose radius of curvature is of the order of 10nm. The contrast and ultimate resolution of this image-projecting microscope depend only on the size of the apparent source. Thus, a projection microscope can be used to characterize source brightness: for example, analyzing the interference contrast enables the size of the source to be estimated. Ultra-thin W tips are not the only way to obtain bright sources: field emission can also be achieved by applying voltages leading to a weak macroscopic electric field (< 1V∕μm) to insulating micron crystals deposited on conductors with a large radius of curvature (> 10 μm). Moreover, analyzing the holograms reveals the source size, and the brightness of these new emitters equals that of traditional field emission sources.

Finite-size correction for slab supercell calculations of materials with spontaneous polarization

The repeated slab approach has become a de facto standard to accurately describe surface properties of materials by density functional theory calculations with periodic boundary conditions. For materials exhibiting spontaneous polarization, we show that the conventional scheme of passivation with pseudo hydrogen is unable to realize a charge-neutral surface. The presence of a net surface charge induces via Gauss’s law a macroscopic electric field through the slab and results in poor size convergence with respect to the thickness of the slab. We propose a modified passivation method that accounts for the effect of spontaneous polarization, describes the correct bulk limits and boosts convergence with respect to slab thickness. The robustness, reliability, and superior convergence of energetics and electronic structure achieved by the proposed method are demonstrated using the example of polar ZnO surfaces.

Polymer electrets and their applications

AbstractPolymer electrets have revealed great potential application in electromechanical devices because of the low weight, large quasi‐piezoelectric sensitivity, and excellent flexibility. For an electret, a permanent and macroscopic electric field exists on the surface, principally led by a macroscopic electrostatic charge on the surface or a net orientation of polar groups inside the object. Here, progress in the development of polymer electrets is reviewed. After a brief retrospect of the research courses and those typical polymer electrets that are classified into fluorine polymer and nonfluorine polymer, we present a survey on the charging methods, including corona, soft X‐ray, contact, thermal and monoenergetic particle beams. The latest representative applications (i.e., power harvesting, sensors, field effect transistors, and biomedicine) based on polymer electrets are also summarized. Finally, we complete this review with a discussion on perspectives and challenges in this field.

Particle‐in‐cell simulation for breakdown phenomena in vacuum

AbstractThe initiating process of vacuum breakdown is still unknown despite the efforts of many researchers in the long history of vacuum insulation. This paper reports the results of Particle‐In‐Cell Monte Carlo Collision simulation of the electrons, positive ions, and neutrals in the vicinity of an emitter on the cathode. The radius of the emitter re, the temperature of the emitter T, product of macroscopic electric field and electric field enhancement factor β ⋅Emac, and the electric field enhancement factor β itself are used as the parameters. In some combinations of the parameter values, the distort of electric field and the increase in current are observed as the result of the following positive feedback: field emission, positive ion generation, electric field enhancement by approach of positive ions, and increase in field emission electrons. All parameters affect whether the current increase or not. The radius of the emitter re is a key parameter that determines the occurrence of the current increase. This is because the density of the neutrals in the region where ionization occurs becomes larger with re. Necessary conditions to occur the current increase are the field emission current in the order of 0.1 μA or more and the line integral neutral density along z‐direction at the center of the emitter in the order of 1017/m2 or more.

Boosting charge spatial separation efficiency for catalytic H2 bubble evolution under macroscopic spontaneous polarization electric field

Serious recombination of photo-irradiated electrons ( e − ) and holes ( h + ) over photocatalysts restricts solar energy conversion, and directional transfer of e − / h + to reduction/oxidation locations respectively and simultaneously, is enormously difficult under the shackle of Coulomb field. Herein, internal spontaneous polarization electric field (ISPEF) has been constructed by coordination between 4 d 10 orbit of Cd 2+ and sp 2 -hybridized N to induce a non-overlapping state of two opposite charge centers in g -C 3 N 4 , which could thus boost charge spatial division and migration. The significantly improved efficiency for H 2 evolution, accompanying by consecutive emission of visual H 2 bubbles was realized. Photo-irradiated charge spatial separation and photocatalytic mechanism within ISPEF of CdC 3 N 4 was firstly confirmed by theory prediction and Hall effect characterization. The study strategy supplies a novel perspective to design polarized semiconductor materials for significantly effective solar energy transformation, which will bring about another research highlights for constructing efficiently advanced semiconductor materials. • Internal spontaneous polarization electric field (ISPEF) was constructed in g -C 3 N 4 . • Strong ISPEF boosts charge spatial separation and directional transfer effectively. • g -C 3 N 4 was polarized by coupling Cd 2+ 4 d 10 orbit with its sp 2 -hybridized N. • Visual H 2 bubbles were released over photocatalysts within ISPEF. • Theoretical calculation and Hall effect test were adopted to confirm ISPEF action.