Wagner Effect Research Articles

Investigating the impact of strontium doping on neodymium manganite Nanoperovskites: Analysis of structural, optical, and dielectric properties

Nd1-xSrxMnO3 (x = 0, 0.3, 0.5, 0.7) nanoperovskites were fabricated through combustion process, a low-cost technique in contrast to the vacuum methodologies for growth. The singular phase orthorhombic Pbnm crystallized for x = 0 to 0.5; nevertheless, both orthorhombic and monoclinic phases were discerned at x = 0.7. Employing X-ray photoelectron spectroscopy (XPS) spectra, the surface chemistry has been conducted, encompassing the intricate parameters associated with the oxygen reduction reaction (ORR).The BDS analysis at ambient temperature, encompassing the frequency span from 1 Hz to 1000 KHz, elucidates various facets of dielectric properties. Elevated dielectric constants at the low-frequency spectrum are explained by the Maxwell–Wagner effect. With an escalation in doping concentration, there is a concurrent rise in the dielectric constant. The escalation in AC conductivity within the high-frequency domain conforms to Johnscher's universal power law, whereas the ramifications of electrode polarization are delineated through a log-log representation.

Maxwell–Wagner effect and second harmonic generation in gradient structures

AbstractFor the first time, we have registered, studied, and modeled the Maxwell–Wagner effect in structures with a smooth gradient of charge carriers’ mobility. The Maxwell–Wagner charge, formed after applying a DC voltage to the gradient structure at room temperature, is distributed over the entire region of the gradient. The experiments were performed with slides of a soda‐lime glass subjected to sodium‐to‐potassium ion exchange, where the ions concentration gradient provides gradient of conductivity while dielectric permittivity stays the same. The electric field generated by the Maxwell–Wagner charge is concentrated in potassium‐enriched less conductive regions of the slide and is sufficiently high to induce the second order optical nonlinearity in the initially isotropic glass. The effect causes over 100‐fold increase in a second harmonic signal relative to the signal from the surface of a virgin glass. This phenomenon in graded‐concentration structures is perspective for characterizing interfacial charges, geometry of the gradient regions, and spatial distribution of electrical conductivity in micro‐ and optoelectronic semiconductor structures.

The stability analysis of In–Ga–ZnO thin film transistors with polyimide substrates based on Maxwell–Wagner effect

Flexible organic light-emitting diode display devices fabricated on polyimide (PI) substrates have more obvious residual image problems due to the abnormal threshold-voltage (Vth) shifts of a thin film transistor (TFT). In this paper, the Vth shift of TFT fabricated on a PI substrate was analyzed. We explained the worse bias stability and worse recovery of TFT with a PI substrate compared with TFT with a glass substrate, by an interlayer charging effect (Maxwell–Wagner effect) and a technology computer-aided design (Silvaco). When bias stress was applied for a long time, the interface between the PI substrate and the buffer layer will have a charging effect under the action of an electric field, and the charging charge will react on the channel and hinder the formation of the channel. We found that there are differences in the scale of charge under different voltage stress conditions, and this will result in different Vth shifts of driving TFTs for displays units.

Charges at the heterogeneous interface of dielectrics

The heterogeneous interface of two different dielectrics is commonly observed in diverse electronic devices. Charge emerging will take place at the heterogeneous interface and may greatly influence the device performance. Typically, charge emerging behavior is attributed to the Maxwell–Wagner effect. The emerged charge by the Maxwell–Wagner effect is unipolar. Nevertheless, bipolar phenomena are also frequently observed. This paper reports the change characteristic of accumulated charge between unipolar and bipolar at the heterogeneous interface composed of two different dielectrics. A theoretical analysis is proposed. As an illustration, the laminated membrane is formed by thermally pressing two non-polar polymers, fluorinated ethylene propylene (FEP) and polypropylene (PP). Its interfacial charge nature is studied by means of electret research. It is found that the bipolar charge derives from contact electrification and is determined by the electronegativity of the atoms at two dielectrics’ interface. The unipolar charge originates from the Maxwell–Wagner effect and is determined by the dielectric constant and conductivity of dielectrics. In the absence of external electric field, the charge nature shows bipolar in the form of dipole electric double-layer. In the presence of external electric field, the change of charge nature from bipolarity to unipolarity will occur depending on the electric field and temperature. Its regulation is closely related to the connection mode of external electric field with the heterogeneous interface of dielectrics. When negative electrode is connected with FEP, the charge nature at the interface evolves from bipolarity to positive polarity. When positive electrode is connected with FEP, the charge nature transforms from bipolarity to negative polarity. A critical point exists for a polarizing voltage to induce the change of charge nature.

Thin and strong Janus separator based on nanocellulose and Ti3C2Tx for dendrite-free aqueous zinc-ion batteries

Glass fiber separators are commonly used for aqueous zinc-ion batteries (AZIBs), whereas easily leading to Zn dendrites and parasitic reactions. Although various strategies have been proposed to address this issue, most of those modified separators still suffer from large thickness and poor mechanical properties. Herein, wheat straw-derived nanocellulose is combined with Ti3C2Tx to form a Janus separator, which is merely 32 μm in thickness and owns remarkable strength and modulus of 215.3 MPa and 8.8 GPa, respectively. In addition, the Ti3C2Tx layer brings about Maxwell–Wagner and low lattice mismatch effects, which can facilitate Zn2+ ion transfer, accelerate desolvation procedure, enhance interfacial charge transport, reduce nucleation overpotential, promote homogeneous and horizontal Zn deposition, and inhibit side reactions. With the use of such Janus separator, the Zn//Zn cell provides a high cumulative plating capacity of 2500 mAh cm−2, and the Cu//Zn cell achieves a large average Coulombic efficiency of 98.95 % over 1000 cycles. Furthermore, the Janus separator renders Zn//MnO2 battery with great rate capability and excellent cycling stability. This work offers new insights into separator modifications for AZIBs towards practical applications.

Electrical properties of tissues from a microscopic model of confined electrolytes

Objective. In the presence of oscillatory electric fields, the motion of electrolyte ions in biological tissues is often limited by the confinement created by cell and organelle walls. This confinement induces the organization of the ions into dynamic double layers. This work determines the contribution of these double layers to the bulk conductivity and permittivity of tissues. Approach. Tissues are modeled as repeated units of electrolyte regions separated by dielectric walls. Within the electrolyte regions, a coarse-grained model is used to describe the associated ionic charge distribution. The model emphasizes the role of the displacement current in addition to the ionic current and enables the evaluation of macroscopic conductivities and permittivities. Main results. We obtain analytical expressions for the bulk conductivity and permittivity as a function of the frequency of the oscillatory electric field. These expressions explicitly include the geometric information of the repeated structure and the contribution of the dynamic double layers. The low-frequency limit of the conductivity expression yields a result predicted by the Debye permittivity form. The model also provides a microscopic interpretation of the Maxwell–Wagner effect. Significance. The results obtained contribute to the interpretation of the macroscopic measurements of electrical properties of tissues in terms of their microscopic structure. The model enables a critical assessment of the justification for the use of macroscopic models to analyze the transmission of electrical signals through tissues.

A review on insects flight aerodynamics, noise sources, and flow control mechanisms

Wildlife always acts as an inspiration source for humans to help them study and mimic flight methods. Insects are one of the most important sources of biological systems’ inspiration to control flow and reduce aerodynamic noise. Insects are classified into different kinds, and most can fly by fluttering their wings. In general, insects’ flight muscles are divided into direct and indirect types that act synchronously and asynchronously with nerve impulses, respectively. These muscles help insects use a mixture of rotating, flapping, and pitching movements to achieve specific wing kinematics. Insects use various mechanisms for generating aerodynamic forces, including the Weis-Fogh or clap and fling mechanism, delayed stall due to unsteady motion (Wagner effect), wing rotation (Kramer effect), wake capture or wing–wake interaction, added mass, and absence of stall. On the other hand, the insect noises are divided into aerodynamic and structural. Insects’ aerodynamic noise is created by fluctuating forces, flow–solid interaction, shed vortex, and turbulence inflow. Meanwhile, insects’ structural noise is made by frictional and tymbal mechanisms. Their flow control methods are classified into two categories: wing shape and sub-structures. Wing shape features such as planform, chord length and location, twist, sweep, wingtip, and aspect ratio influence the flow around the insects. The sub-structures such as leading edge, trailing edge, swallowtail, and surface textures affect the flow too. A thorough understanding of insects’ fly, aerodynamic noise, and their control flow techniques will significantly help engineers to produce competitive products with better aerodynamic performance and aeroacoustic signature.

Analysis of geometrically exact beams with torsion-warping deformation by weak form quadrature elements

Geometrically exact beams with torsion-warping deformation are studied. With three-dimensional finite strains, the Wagner effects as well as initial curvature and twist are taken into account in a weak form quadrature element formulation. The cross-section warping function of arbitrary cross-sections is obtained by a two-dimensional weak form quadrature element analysis, enhancing the overall accuracy of the beam formulation. Typical examples with different cross-sections and loading cases are presented to illustrate the effectiveness and robustness of the formulation.

Generalized line-element formulations for geometrically nonlinear analysis of nonsymmetric tapered steel members with warping and Wagner effects

With advancements in manufacturing technology, steel members can be innovatively fabricated in nonsymmetric section shapes and tapered along the length to bring certain benefits in material utilization and aesthetic appearance. The frame analysis of the steel structures with these members is quite challenging because of lacking the suitable line-element formulations to robustly and efficiently consider tapered section characteristics together with the Warping and Wagner effects resulting from nonsymmetric section shapes. This research proposes generalized line-element formulations for geometrically nonlinear analysis of tapered steel members with nonsymmetric cross-sections, adequately assessing the member buckling behaviors. The element stiffness matrix is derived via the total potential energy, considering the axial and transverse elastic strains, the Warping deformations, and the Wagner effects. Parametric studies have been conducted to generate approximate equations for the geometric parameters of common shapes of nonsymmetric cross-sections, thereby reflecting the variable cross-section properties along the length. Afterwards, the generalized line-element tangent stiffness matrix is obtained, compatible with the existing frame analysis frameworks for easy programming. The element formulation is validated through several examples with the benchmark results generated by shell finite-elements. This work could be helpful for the sustainable development of modern steel structures with efficient material utilization and futuristic geometry.

Co-Rotational Formulations for Geometrically Nonlinear Analysis of Beam-Columns Including Warping and Wagner Effects

The warping effects may predominate in geometrically nonlinear analysis of open cross-section members. The formulation of conventional beam-column elements incorporating the warping effects is cumbersome due to the method considering the inconsistency between the shear center and centroid. To develop a concise warping element formulation, this paper presents a transformation matrix to integrate the inconsistent effects into the element stiffness matrix. The co-rotational (CR) method used to establish the element equilibrium conditions in the geometrically nonlinear analysis is adopted to simplify the element formulation and improve the efficiency of nonlinear analysis. A new beam-column element explicitly considering the warping deformation and the Wagner effects is derived based on the CR method and the Euler–Bernoulli beam theory. A detailed kinematic description is provided for considering large deflections and rigid body motions. Based on the mechanical characteristic, the coordinate and the rigid body motion transformation matrices are given. The secant relationship is developed to evaluate the element internal forces accurately and effectively in each iteration. Several verification examples are provided to validate the proposed method’s reliability and robustness. The verifications demonstrate that the proposed element leads to considerable computational advantages. The results of this paper are useful for future upgrading of frame analysis software with warping degrees-of-freedom (DOFs).

Geometric and material nonlinear analysis of steel members with nonsymmetric sections

Steel members using nonsymmetric sections are often used for their structural efficiency in contemporary construction. Notwithstanding, the conventional concentrated plasticity (CP) analysis approach is commonly used in material nonlinear analysis and derived for regular hot-rolled steel sections with symmetrical shapes, leading to significant differences when analyzing members with nonsymmetric sections. This research develops the modified tangent modulus (MTM) method, proposed by Ziemian and McGuire in 2002, for the material nonlinear analysis of steel members with nonsymmetric sections, as a straightforward extension of the conventional CP analysis approach. Regarding the geometric nonlinear behaviors, an improved line-element formulation is formulated based on the nonsymmetric section assumption, explicitly modelling the noncoincidence of the shear center and centroid for considering the Wagner effects, which can capture complex buckling behaviors of the members with nonsymmetric sections. As part of the proposed method, a rigorous cross-section analysis method has been developed to generate the yield surfaces of arbitrary steel sections regardless of shapes. Such yield surfaces will be used to evaluate the full-yield condition, and the gradients to the yield surfaces will be calculated and used to control the plastic flow. The development of this methodology is presented in detail, as well as the derivation of the mathematical formulations. Six groups of verification examples are provided to validate the accuracy of the proposed method.

Ti doping and low-temperature sintering of BiFeO3 nanoparticles synthesized by the solvothermal method

In this study, nanoparticles of ferroelectric BiFeO3 (BFO) doped with 0, 5, and 10 mol% Ti were synthesized by an ethanol-based solvothermal method, and their densification behavior was investigated. The nanoparticles were densified via a normal sintering process at a low temperature of about 600 °C, resulting in dense bulk ceramics of undoped and Ti-doped BFO with a relative density of over 90%. The weight loss due to bismuth evaporation during sintering was suppressed below 0.6% because of the low sintering temperature. The crystal structure analysis of the resulting ceramics confirmed the incorporation of Ti ions into the Fe3+ site of BFO. The results of dielectric and X-ray photoelectron spectroscopies showed that Ti doping effectively decreased the concentration of Fe4+ in the ceramics, leading to suppression of the extrinsic dielectric responses due to the Maxwell–Wagner effect and the hopping motion of the localized holes.

Efficient elastic buckling assessment algorithm for steel members with random non-uniform corrosion

This paper developed an efficient algorithm to study the elastic buckling strengths of non-uniformly corroded steel members. The algorithm is derived based on the authors’ previous work on buckling strength assessment for the steel members by further introducing random non-uniform corrosion damage to the cross-section along member. In the algorithm, the random nature of the corrosion is captured by the Monte Carlo simulations. Moreover, the non-symmetric section effects, including the noncoincidence of section shear center and centroid and Wagner effects, caused by the non-uniform corrosion are considered in the algorithm. The proposed algorithm permits more than ten million times of Monte Carlo simulations being completed efficiently, which greatly reduces the computational expense compared with the existing finite element analysis algorithms. The effects of corrosion depth, corrosion ratio, and corrosion location on the flexural buckling (FB), lateral-torsional buckling (LTB), and axial-torsional buckling (ATB) strengths of the steel member are studied. It is found that corrosion has the most adverse effect on ATB than LTB and FB strengths of the member. When the corrosion distributes more compactly through the section, its adverse effect on the buckling strength of the member could be more significant. Even for the same corrosion ratio, corrosion depth, and total corrosion region number, the reduction factor of the buckling strength can be varied by up to more than 20% due to the difference of the corrosion locations. The reduction factor of the FB strength is generally linear against the corrosion depth. While for the LTB and ATB strength, the reduction factors show nonlinear as per the corrosion depth.

Simultaneous Enhancement of Piezoelectricity and Temperature Stability in KNN‐Based Lead‐Free Ceramics Via Layered Distribution of Dopants

AbstractThe past two decades have seen a great enhancement of piezoelectric coefficients (d33) to higher than 570 pC/N in (K, Na)NbO3 (KNN) piezoelectrics, but one notoriously unresolved issue is their severe temperature instability, obstructing them toward practical applications. The present work demonstrates a facile approach to overcome this problem by introducing a layered distribution of key dopants (Li and Sb) in a monolithic ceramic, featuring stepwise varied polymorphic phase transition (PPT) temperatures along the thickness direction. The dopant‐graded ceramic exhibits an outstanding d33 of 508 pC/N and a very large piezoelectric strain (Suni, of 0.18%). More importantly, an excellent temperature stability (d33 variation within 13% over the temperature range of 25–150 °C) is achieved, which is superior to that of most state‐of‐art KNN counterparts. These are attributed to the construction of spatially diffused PPT in combination with enhanced polarization, permittivity, and piezoresponse through interfacial effect, including the Maxwell–Wagner effect and intergranular stress by gradient doping. The results offer an alternative strategy for designing high‐performance piezoelectric materials with desirable temperature reliability.

Efficient algorithm for elastic buckling of corroded I-section steel members with Monte Carlo simulation

Monte Carlo simulation has been widely used to deal with random problems. Corrosion of steel structures is of high random nature. Current studies on the behavior of steel structures considering corrosion effect are usually executed by using the commercial finite element analysis software, which costs huge computational time to ensure sufficient Monte Carlo simulation. In this paper, an efficient algorithm to deal with the buckling behavior of corroded I-section steel member is proposed. The computational time required is significantly reduced. The objective of this paper is focused on the elastic buckling behavior of the member. The nonlinearity in practical buckling design is not considered. The random nature of corrosion is captured by using the Monte Carlo simulation. The warping and Wagner effects due to corrosion are also considered in the algorithm. Three buckling types are studied, namely, flexural buckling, lateral–torsional buckling and axial–torsional buckling. The accuracy of the algorithm is validated against both the experiment and the finite element analysis. Parametric studies are conducted to investigate the effects of the corrosion ratio and corrosion depth on the elastic buckling behavior of the member. It is found that corrosion reduces the axial–torsional​ buckling of the member with the greatest extent. The flexural elastic buckling load is mainly affected by the section area loss ratio. The reduction factor of the flexural buckling is linear against the area loss ratio. With the aid of the proposed algorithm, the deterioration of the elastic buckling load and moment of a steel member with respect to corrosion time is quantified.

Enhanced microwave absorption property of ferroferric Oxide: The role of magnetoelectric resonance

• Direct fluorination was applied to decorate Fe 3 O 4 . • Core–shell fluorinated Fe 3 O 4 was fabricated by controlling the fluorination conditions. • The microwave absorption property of Fe 3 O 4 was enhanced after fluorination. • Electromagnetic wave dissipation model of magnetoelectric resonance was proposed. • The in-depth mechanism of magnetoelectric resonance was elucidated. The modification of ferrites can effectively improve their microwave absorption (MA) properties. However, attempts to improve their high-frequency performance were still limited and considerably cumbersome for practical application. Herein, we present a facile method that effectively improves the MA behavior of Fe 3 O 4 through direct fluorination using F 2 /N 2 gas. Specifically, we fabricated core–shell structured fluorinated Fe 3 O 4 (F-Fe 3 O 4 ) with a fluorine-doped shell and an unmodified Fe 3 O 4 core by carefully controlling the F 2 concentration and fluorination temperature. We found a unique ‘magnetoelectric collaborative resonance’ (MDR) effect in F-Fe 3 O 4 , manifested by the co-occurrence of double dielectric and magnetic resonance peaks at 14.8 and 16.6 GHz. Band gap measurements and molecular simulations results indicated that the smaller energy gap derived from fluorine doping facilitates both electron hopping between the mixed-valence Fe 2+ /Fe 3+ states and electron accumulation at the core–shell interface, which induce simultaneous magnetic exchange interactions and the Maxwell–Wagner effect (interface polarization). As a result, the incident electromagnetic wave can be dissipated via magnetic exchange resonance coupled with dielectric resonance, thereby improving the MA properties at the same frequency of MDR. Compared with those of pristine Fe 3 O 4 , the minimum reflection loss of F-Fe 3 O 4 was four times higher, reaching −64.9 dB, and the effective absorption bandwidth was 5.03 GHz, which is almost 1.6 times higher. We believe this facile and effective modification method and the unique loss mechanism of MDR will advance the structural design of high-performance MA materials.

The unsteady aerodynamics of insect wings with rotational stroke accelerations, a systematic numerical study

To generate aerodynamic forces required for flight, two-winged insects (Diptera) move their wings back and forth at high wing-beat frequencies. This results in exceptionally high wing-stroke accelerations, and consequently relatively high acceleration-dependent fluid forces. Quasi-steady fluid force models have reasonable success in relating the generated aerodynamic forces to the instantaneous wing motion kinematics. However, existing approaches model the stroke-rate and stroke-acceleration effects independently from each other, which might be too simplified for capturing the complex unsteady aerodynamics of accelerating wings. Here, we use computational-fluid-dynamics simulations to systematically explore how aerodynamic forces and flow dynamics depend on wing-stroke rate, wing-stroke acceleration and wing-planform geometry. Based on this, we developed and calibrated a novel unsteady aerodynamic force model for insect wings with stroke accelerations. This includes improved versions of the translational-force model and the added-mass force model, and we identify a third novel component generated by the interaction of the two. This term reflects the delay in bound-circulation build-up as the wing accelerates. The physical interpretation of this effect is analogous to the Wagner effect experienced by a wing starting from rest. Here, we show that this effect can be modelled in the context of flapping wings as a stroke-acceleration-dependent correction on the translational-force model. Our revised added-mass model includes a viscous force component, which is relatively small but not negligible. We subsequently applied our new model to realistic wing-beat kinematics of hovering Dipteran insects, in a quasi-steady approach. This revealed that stroke-acceleration-related aerodynamic forces contribute substantially to lift and drag production, particularly for high-frequency flapping mosquito wings.

Exploration of alternating current conduction mechanism and dielectric relaxation with Maxwell–Wagner effect in NiO–CdO–Gd2O3 nanocomposites

Exploration of alternating current conduction mechanism and dielectric relaxation with Maxwell–Wagner effect in NiO–CdO–Gd2O3 nanocomposites

Effects of crystallization kinetics on the dielectric and electrical properties of BiFeO3films

BiFeO3 thin films were prepared using the chemical solution route on Pt/TiO2/SiO2/Si(100) substrates under different crystallization kinetics. The crystallization kinetic effects on the dielectric and electrical properties have been investigated. These properties included dielectric permittivity, electric modulus, electrical conductivity measurements as a function of the temperature (300–525 K) and frequency (102–106 Hz), and leakage current measurements electric field range ± 30 kV/cm at room temperature. The differences observed in conductivity and current density of the BiFeO3 films were discussed in terms of possible defects induced by the crystallization kinetic. An anomalous relaxor-like dielectric behavior characterized by a broad maximum in the real dielectric permittivity as a function of temperature and the low-frequency dielectric dispersion has been observed. The nonexpected peaks in the real permittivity were accompanied by increasing at least four orders in the conductivity’s magnitude at high temperatures. The origin of the relaxor-like dielectric anomalies is discussed, suggesting that the dielectric permittivity peaks are artifacts due to carrier migration correlated to the onset of the Maxwell–Wagner effect.

A direct proof for Maxwell–Wagner effect of heterogeneous interface

In this paper, the Maxwell–Wagner effect and the charge characteristics of the heterogeneous interface at the action of higher electric field and elevated temperature are investigated by means of electret technology. A composite membrane with a double-layer structure of a polypropylene (PP) film and a fluorinated ethylene propylene copolymer (FEP) film was made. After being polarized under electric field and elevated temperature, the component PP and FEP films of the composite membranes were separated. The charge density of the PP and FEP films was measured to analyze the characteristics of interfacial charge in the composite membrane. Experimental results directly prove that the charge characteristics at the interface of the composite membranes are consistent with the result calculated by the Maxwell–Wagner effect. The polarity of the interfacial charge can be switched by changing the polarity of the polarizing voltage. The characteristics of the accumulated interfacial charge are strongly dependent on the conductivity, which is affected by the temperature and the polarizing electric field. A new phenomenon, that is, the measured charge density is much higher than that calculated by the Maxwell–Wagner effect, is found. The reason is ascribed to the electret effect from the FEP and PP films. This research provides a new insight into the charge characteristics at the heterogeneous interface.