Dielectric Polarization Effects Research Articles

Experimental and numerical analysis of dielectric polarization effects in near‐surface earth materials in the 100 Hz–10 MHz frequency range: First interpretation paths

SummaryThe recent developments of electromagnetic induction and electrostatic prospection devices dedicated to critical zone surveys in both rural and urban contexts necessitate improving the interpretation of electrical properties through complementary laboratory studies. In a first interpretation step, the various experimental results obtained in the 100 Hz–10 MHz frequency range can be empirically fitted by a simple six‐term formula. It allows the reproduction of the logarithmic decrease of the real component of the effective relative permittivity and its corresponding imaginary component, the part associated with the direct current conductivity, one Cole–Cole relaxation and the real and imaginary components of the high‐frequency relative permittivity. For elucidating physical phenomena contributing to both the logarithmic decrease and the observed Cole–Cole relaxation, we first consider the Maxwell–Wagner–Sillars polarization. Using the method of moments, we establish that this continuous medium approach can reproduce a large range of relaxation characteristics. At the microscopic scale, the possible role of the rotation of the water molecules bound to solid grains is then investigated. In this case, contrary to the Maxwell–Wagner–Sillars approach, the relaxation parameters do not depend on the external medium properties.

Nano and micro co‐filled aluminum nitride/magnesium dihydrate—Silicone rubber composites for high voltage insulation

AbstractCo‐filled composites of micro magnesium dihydrate (MDH) and hydrophobically treated nano aluminum nitride (nH‐AlN) fillers in high temperature vulcanizing silicone gum are studied for thermal and dielectric characteristics for use as an insulating material in high voltage applications. The study begins with description of the compounding protocol adopted, followed by spectroscopic and optical characterization. Fourier transform infrared spectroscopy (FTIR) and energy dispersive X‐ray spectroscopy (EDX) analysis are used to verify the presence of nH‐AlN and MDH in the composites. Thermal analysis through thermogravimetric analysis revealed a stark enhancement in the onset of polymer degradation temperature, with an improvement of 208 °C achieved at 30 phr by weight loading level of MDH. Volume resistivity of 9.71 E14 Ω‐cm is obtained at 30 phr weight loading of MDH and 5 phr of nH‐AlN. AC, +DC, and −DC dielectric strength improved by 1.09, 2.06, and 1.08 times for co‐filled composites at 30 phr MDH and 5 phr nH‐AlN loading levels over unitary filled composite. Effect of dielectric polarization on dielectric constant and dissipation factor is studied at various frequencies. Limitations while conducting dry arc resistance test at standard voltage of 12.50 kV is discussed, with modification in dry arc resistance test voltage to 16.95 kV. The results are presented and discussed here.

Effects of Gd doping on microwave absorption properties and mechanism for CaMnO3 perovskites

ABO3 type perovskite oxides have been widely studied due to their unique structure and special electromagnetic properties. CaMnO3 is well known for its excellent thermoelectric performance and temperature stability. In this paper, Ca1-xGdxMnO3 (x = 0, 0.1, 0.2, 0.3, 0.4) perovskites were comprehensively studied by first-principles calculations and experimental characterizations on their crystal structure and electromagnetic properties to finally elaborate the microwave absorption mechanism. It is found that Gd doping significantly enhances the dielectric polarization effects, resulting in better electromagnetic wave absorption performance than undoped CaMnO3. Especially for CG2MO perovskite, its reflection loss and bandwidth below −10 dB at 2–18 GHz reaches −31.9 dB and 3.3 GHz approximately, exhibiting excellent microwave absorption property. Moreover, the microwave absorption mechanism of CGMO perovskites involves various modes of conductive loss, resonance loss, multiple reflection and scattering as well as the polarization phenomenon including interfacial polarization, dipole polarization and defect polarization. Among them, polarization effects and conductive loss contributes the most to the microwave absorption performance.

Interaction of atmospheric pressure helium plasma jet with tilted dielectric target: split and deviation of ionization waves

Atmospheric pressure plasma jets (APPJs) are commonly used plasma sources in many biomedical applications. Typically, the APPJs are not always perpendicular to the target to be treated. In this paper, the effects of tilted angle (), relative permittivity () of the target, the target potential, the distance () and the discharge parameters on the interaction of a helium APPJ with the target are investigated. Spatio-temporal resolved images show that the ionization wave (IW) split into a surface ionization wave (SIW) and a continued propagate IW when it approaches the target. The split leads to a position deviation of the IW interaction with the target. The measurements show that the split and deviation of IWs are strongly dependent on and . For 9, the split can be only observed with 60°. The deviation gradually decreases as increases from 15° to 90° with 9. With the increase of from 9 to 56, the split and deviation are more pronounced with = 30°. The deviation gradually increases as applied voltage and values increase from 5.5 to 10.0 kV and 19–24 mm, respectively. However, the deviation is independent of the gas flow rate of 400–2000 standard cubic centimeters per minute. The split of IW depends on the combined effect of enhanced electric field due to target polarization and mismatch between the propagation direction of IW and the direction of enhanced electric field caused by variation. An increase in results in a stronger dielectric polarization effect. Changes in cause a misalignment between the propagation direction of IW and the direction of enhanced electric field. Additionally, decreasing shortens the perpendicular distance () between IW and the target surface, further enhancing the electric field in the perpendicular direction. After the split, there is an interaction between the SIW and the IW. The propagation of the SIW is restricted to the local electric field of IW.

Solvent-controlled strategy to perfect microstructure and microwave dissipation ability of pyramid-like carbon embedded with Co3Fe7 and CoFe2O4 nanoparticles

Preparation of microwave absorption materials is one of the most effective way to solve hazards of excessive microwave radiation at current stage. Herein, a series of pyramid-like carbon frameworks embedded with Co3Fe7 and CoFe2O4 phases have been synthesized via a solvent-controlled strategy in solvothermal-annealing process. The solvent ratio of DMF and DW has great impact on the morphology and electromagnetic wave dissipation properties of such composites. The composite can reach the maximal RL of −24.66 dB at 7.68 GHz and the optimal EAB of 6.3 GHz for only 2.62 mm, this realization of wider EAB at thin thickness is due to the synergic effect of dielectric polarization, magnetic resonance, structural damping and so on. Most important of all, the wide range of appropriate impedance matching in as-prepared composite is the first premise. The broad EAB of composite prepared here reveals its prospect for actual application in protection of microwave radiation.

Composition-tailor induced electrocaloric effect near room temperature in (Pb,Ba)HfO3 films

More and more researchers start to pay attention to the electrocaloric temperature change (ΔT) in polar materials, which is caused by an applied electric field. In this paper, Ba-doped PbHfO3 (PBH) films were prepared by sol-gel method. Their components, microstructures, dielectric polarization and electrocaloric effects (ECEs) were investigated. With the addition of Ba2+, PBH films went from antiferroelectric (AFE) to ferroelectric (FE). At the same time, their dielectric peaks shifted toward lower temperature. The maximum ΔT obtained in Pb0.8Ba0.2HfO3 FE film is 41.1 K, which is an order of magnitude larger than PbHfO3 film (ΔT ∼ −4 K at 50 °C) and Pb0.9Ba0.1HfO3 film (ΔT < 4 K at 120 °C). In order to explain this phenomenon, the Landau-Devonshire theory was adopted. Our analysis shows that the rapid variation of energy barrier height near the phase transition temperature is beneficial to obtain large polarization change and high △T, which is needed in solid-state cooling devices.

Dynamic quantification of the overall effect of dielectric polarization

Due to the significance and universality of dielectric polarization, a quantitative assessment of this phenomenon is crucial for the sake of whether to avoid or exploit it. While triboelectrification and electrostatic induction have a direct relationship with dielectric polarization, there has been no prior work on bridging triboelectrification and dielectric polarization. To investigate the dielectric polarization effect, a dielectric-adjustable nanogenerator is built and the interplay of dielectric constant, electrical output, and surface charge is thoroughly investigated. After confirming the occurrence of self-polarization and polarization reversal during device operation, the surface charge accumulation and decay times are studied to understand the impact of dielectric polarization on prolonging the charge decay time and shortening the charge accumulation time, which are responsible for the device electrical output. Consequently, the feasibility of using the dynamic behavior of surface charge to quantify dielectric polarization is systematically studied.

Sea-urchin-like NiCo2S4 modified MXene hybrids with enhanced microwave absorption performance

The development of electromagnetic wave absorbing materials with lightweight and high absorption capacity is an effective way to solve electromagnetic wave pollution. Although the two-dimensional MXene material has become one of the most attractive electromagnetic wave absorbing materials due to its unique structure, the poor impedance matching makes it difficult to obtain both lightweight and efficient absorption capacity. Herein, few-layer MXene sheets and sea-urchin-like NiCo2S4 (NCS) hybrids were successfully synthesized by a simple electrostatic self-assembly method. MXene/NCS hybrids achieve good absorption performances. The maximum absorption bandwidth is 5.6 GHz at a matching thickness of only 1.53 mm with a filling ratio of only 10 wt%. In addition, the excellent microwave absorption performance is attributed to the improved impedance matching of MXene and the synergistic effects of dielectric loss and interfacial polarization. This work provides new ideas for the design and synthesis of materials with lightweight and efficient electromagnetic wave absorption.

Plasma propagation in single-particle packed dielectric barrier discharges: joint effects of particle shape and discharge gap

In this work, a single Al2O3 particle packed dielectric barrier discharge (DBD) reactor with adjustable discharge gap is built, and the influences of the particle shape (ball and column) and the residual gap between the top electrode and particle on the electrical and optical characteristics of plasma are studied. Our research confirms that streamer discharge and surface discharge are the two main discharge patterns in the single-particle packed DBD reactor. The strong electric field distortion at the top of the ball or column caused by the dielectric polarization effect is an important reason for the formation of streamer discharge. The length of streamer discharge is proportional to the size of the residual gap, but the number of discharge times of a single voltage cycle shows an opposite trend. Compared to the column, a smooth spherical surface is more conducive to the formation of large and uniform surface discharges. The surface discharge area and the discharge intensity reach a maximum when the gap is equal to the diameter of the ball. All in all, the results of this study will provide important theoretical support for the establishment of the synergistic characteristics of discharge and catalysis in plasma catalysis.

Hemoglobin glycation increases the electric charges on red blood cells: Effects of dielectric polarization

It is generally accepted that the glycated hemoglobin (HbA1c) is an efficient marker of glucose accumulating during certain period in order to efficiently detect diabetes disorder. We have, experimentally, estimated the HbA1c level using broadband dielectric spectroscopy (BBDS) on human, normal and diabetic, blood samples (NGBSs). This technique has achieved a better understanding to the glycation processes on both the academic and the medical applications as well, e.g., we draw the attention to search for new way of diabetes treatment by eliminating the extra electric charges created due to glycation processes. The dielectric properties of NGBSs are studied using BBDS, systematically studying the dependence of BBDS on glycation growth rate GG. We have covered a frequency range from 101 Hz to 3.2 × 107 Hz. Strong Debye-relaxation (beta-relaxation) arising from RBCs forced-oscillations in that frequency range has been clearly detected. In addition, we present a theoretical model to explain the experimental results. So, we have got some theoretical relations (supported by experimental data) describing the growth rate of HbA1c as function of time: The ac-electrical conductivity and dielectric constant as function of frequency for different HbA1c concentrations during 140 days. The experimental data confirm an increase of electric charges on RBCs with glycation. The broad frequency range presents valuable new information on the dynamic processes in NGBSs; and it opens a possible way for new technique to treat glycted blood by eliminating the extra charges accumulated on the RBC due to glycation, that would eliminate the glycation at all.

Impact of copper oxide on the structural, optical, and dielectric properties of sodium borophosphate glass

Sodium borophosphate glasses containing copper oxide (CuO) have produced by melt annealing technique. Phosphate units are presented in Q2, whereas the borate groups are presented as trigonal and tetraborate units. The addition of CuO in the network former modifies the characteristic mid region of infrared bands or peaks. The base glass sample has a density of 2.57 g/cm3 raising to 2.71 g/cm3 after doping with 0.1 CuO. The absorption edges of such glass shifted towards lower photon energy due to the formation of non-bridging oxygens (NBOs). With the increase in the copper content from 0 to 0.1 mole fraction, the optical transition values decreased from 3.682 to 1.672 eV. The real and imaginary part of dielectric constants decreased as the applied frequency increase due to the dipolar, interfacial, and dielectric polarization effects. The relaxation process has observed at high frequency and 0.1 CuO sample correlated to the formation of NBOs.

Dielectric polarization effect and transient relaxation in FAPbBr3 films before and after PMMA passivation.

In organic-inorganic hybrid ionic lead halide perovskites with a naturally arranged layered structure, the dielectric polarization effect caused by the dielectric mismatch between the organic and inorganic layers takes effect in their optical responses. But this effect has received little attention. Here we used infrared transient spectroscopy to study FAPbBr3 perovskite polycrystalline films before and after PMMA film passivation and found that there is a dielectric polarization effect at the interface between the organic cation layer and the inorganic lattice layer inside the perovskite lattice, and also at the interface between the PMMA film and perovskite film. Due to the dielectric polarization effect and the spatial confinement of the surface electronic (or polaron) state, the luminescence intensity of the passivated perovskite film is significantly enhanced, and the exciton lifetime is greatly increased. Dielectric polarization enhances their efficient transient absorption (TA) and leads to the intramolecular vibration frequency red-shifts, which exhibited the combined relaxation kinetics of the large polaron with dielectric polarization in the perovskite film. Dielectric polarization between the internal lattice and the nanocrystal surface of the perovskite film shows different relaxation processes. The polarization-dependent TA spectrum reveals that the dielectric polarization field causes light-induced anisotropy by changing the chemical bond configurations. These direct TA experimental observations help us to understand the influence of the dielectric polarization effect on the electronic state in various organic-inorganic nanocomposite perovskites.

LO-Phonons and dielectric polarization effects on the electronic properties of doped GaN/InN spherical core/shell quantum dots in a nonparabolic band model

The electron energy spectrum of a core/shell spherical quantum dot made of zincblende GaN/InN compounds is investigated taking into account the presence of an off-center donor atom and the influence of band nonparabolicity. The interaction of both the charge carrier and the Coulombic core with longitudinal optical phonons is included through Fro hlich and Aldrich-Bajaj theories, respectively. The ground state energy is determined by solving the resulting conduction band effective mass equation via the variational Ritz principle. A detailed analysis of the features of electron and hole spectra as functions of the core and shell sizes is presented, highlighting the possibility of transitioning between type-I and type-II structures. A detailed discussion about the effects of conduction band nonparabolicity, dielectric mismatch and electron-phonon interaction onto the impurity binding energy is provided. It was found that, in general, nonparabolicity of the conduction band leads to larger impurity binding energy, and that LO-phonon and dielectric mismatch effects tend to reduce the value of the latter quantity.

Dielectric Polarization and Electrorheological Response of Poly(ethylaniline)-Coated Reduced Graphene Oxide Nanoflakes with Different Reduction Degrees.

We prepared poly(ethylaniline)-coated graphene oxide nanoflakes and then treated them with different concentrations of hydrazine solution to form dielectric composite nanoflakes having different reduction degrees of reduced graphene oxide core and insulating polyethylaniline shell (PEANI/rGO). The morphology of PEANI/rGO was observed by scanning electron microscopy, while the chemical structure was confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectrometer. The influence of reduction degrees on the conductivity, dielectric polarization and electrorheological effect of PEANI/rGO in suspensions was investigated by dielectric spectroscopy and rheological test under electric fields. It shows that the PEANI/rGO has two interfacial polarization processes respectively due to rGO core and PEANI shell. As the number of hydrazine increases, the conductivity and polarization rate of rGO core increase. As a result, the difference between the polarization rate of rGO core and that of the PEANI shell gradually becomes large. This increased difference does not significantly decrease the yield stress but causes the flow instability of PEANI/GO suspensions under the simultaneous action of electric and shear fields.

Hyaluronic acid — gelatin hydrogels as bioelectrets: Charge transport and dielectric polarization effects

In this work, we study the role of water molecules on the polarization processes activated on hyaluronic acid (HA), and gelatin (Gel) hydrogels at rather low hydration levels, by employing mainly broadband dielectric spectroscopy (BDS) and thermally stimulated depolarization currents (TSDC) technique. Our results suggest that the polarization capability of the hydrogels depends strongly on the water fraction, already at temperatures as low as −90 °C, and that charge (protons) long-range mobility is inevitably related with polarization processes in the biomaterials. The polarizabilty enhances strongly at temperatures above the onset temperature for structural rearrangements and conformational fluctuations in the hydrogels. At temperatures below this critical temperature, the polarizability is related to water secondary relaxation process (ν-process) and to polarization process within ice-like structures of hydration water. These findings imply that polarization effects in biomaterials are strongly affected by contributions due to hydration water (even for traces of water).

Influences of dispersion, dielectric constant and polarization on the double-parameter asymmetric Gaussian potential quantum dot qubit

Selecting the double-parameter asymmetric Gaussian (AG) potential to describe the confinement effects of electrons in quantum dot (QD), the effect of dielectric constant, dispersion and polarization on the properties of the QD qubit is studied by LLP–Pekar transformation variation method. By discussing the oscillation period of the qubit with the AG potential, the mechanism of influence of the material parameters such as the dielectric constant ratio and the electron–phonon coupling (EPC) constant on qubit survival time and information storage is clarified. Based on the Fermi gold rule and the even-order approximation, the qubit decoherence with AG potential is studied. It is revealed that increasing the dielectric constant ratio, the dispersion or the EPC constant of materials is all ways to solve the qubit decoherence due to spontaneous emission of phonons. The theoretical basis for phase rotation control of qubit spheres is given by improving dispersion coefficient or dielectric constant ratio of materials.

Engineering defect concentrations of multiwalled carbon nanotubes by microwave irradiation for tunable electromagnetic absorption properties

Incorporating the dielectric polarization effect induced by atomic-scale structural defects is an effective strategy to improve the electromagnetic absorption performances of materials. Herein, the defect concentration of multiwalled carbon nanotubes (MWCNTs) could be tuned by irradiation time under the 2.45 GHz microwave, depending on the localized “heat” effect. The defect density of the mostly optimized MWCNTs treated by irradiation for 4 min reached a maximum, presenting the defect distance (LD) of 10.83 nm and the concentration (nD) of 2.76×1011 cm−2, achieving the maximum effective absorption bandwidth of 5 GHz, which is higher than original-carbon nanotubes (CNTs) (3.9 GHz). Different from the previous integration of CNTs and heterogeneous magnetic metals, the present work demonstrates a simple microwave irradiation approach for tailoring the electromagnetic absorption properties of MWCNTs by engineering the defect concentration, and this could be extended to variable carbon-related materials and diverse applications.

Electrocaloric effect and dielectric properties in ferroelectric ceramics based on solid solution of barium-calcium titanate

Barium titanate based ceramics is the most common class of lead-free ceramics due to its high values of dielectric constant, polarization, piezo- and electrocaloric effects. In this paper dielectric properties and electrocaloric effect in ceramics based on solid solution of barium-calcium titanate had been studied. It was shown, that increasing of calcium titanate in solid solution leads to increasing of dielectric constant and electrocaloric effect, simultaneouslyit leads to decreasing of leakage currents. While increasing fraction of calcium titanate from 0% to 10%, dielectric constant at frequency of 1 kHz rises from 10500 to 13600, maximum adiabatic electrocaloric response at ΔE = 1.3 V/μm rises from 0.5 K to 0.7 K.

Space charge property at the interface in low-density polyethylene/MgO three-layered nanocomposites

The MgO/low-density polyethylene nanocomposite film and the sandwich-structure LDPE/MgO-LDPE/LDPE nanocomposite film were prepared by melt blending and hot pressing. Based on the Maxwell–Wagner effect, a theoretical model of the three-layer dielectric interface polarization was set up, and the charge density of the three layers of dielectric interface polarization is obtained. Then pulsed electro-acoustic (PEA) is used to study the charge distribution characteristics of the three-layer structure while the breakdown strength of the three-layer structure is tested. The formation and transmission mechanism of the interface charge is systematically analyzed through the above two methods. The results show that the formation of space charge at the interface of sandwich-structure film is likely to be the result of the interaction between the three-layer dielectric polarization effect and the capture charge mechanism at the interface. Compared with the single-layer composite film, the sandwich-structure nanocomposite film has higher breakdown strength, the reason may be that the charge is trapped by the charge trapping mechanism at the interface during the movement of the opposite electrode to form an interfacial space charge, and as the charge accumulates continuously to form a barrier at the interface, the barrier can effectively inhibit the formation of the conductive channel, and the material is improved. The breakdown field is strong.

Boosting the Efficient Energy Output of Electret Nanogenerators by Suppressing Air Breakdown under Ambient Conditions.

By virtue of simple fabrication, low cost, and high conversion efficiency, nanogenerators play a key role in promoting the development of self-powered systems and large-scale mechanical energy harvesting. Efforts have been ongoing for improving the output power of nanogenerators by maximizing their surface charge density via surface modification or structure optimization. Nevertheless, because of inevitable air breakdown during the operation process, enhancing charge density is not retainable, which is the most crucial limitation for the output performance of nanogenerators. Here, a suppressing breakdown strategy is developed to remarkably enhance the output charge density of the nanogenerator by embedding a dielectric film (polyvinylidene fluoride) with high permittivity into air gaps. Because of the air breakdown suppression and strongly field-induced dielectric polarization effect, the output charge density of ∼470 μC m-2 is obtained at ambient condition, which is ∼4 times larger than the value of the conventional nanogenerator with air breakdown. In addition, the effects of different dielectric materials and their different thicknesses are also studied for enhancing the output charge density of the nanogenerator. These results provide a guide to design the state-of-the-art nanogenerator for efficient mechanical energy harvesting.