Maxwell-Wagner Polarization Research Articles

A study on the complex dielectric (ε*)/electric-modulus (M*)/impedance (Z*), tangent-loss (tanδ), and ac conductivity (σac) of the Al/(S:DLC)/p-Si/Au (MIS)-type Schottky structures in a wide range of frequency and voltage at room temperature (RT)

In this work, the Al/(S:DLC)/p-Si/Au Schottky structures were fabricated, and the real and imaginary parts of complex-permittivity (ε*), complex electric-modulus (M*), complex-impedance (Z*), loss-tangent (δ), electrical-conductivity (σac), and phase-angle (θ) were investigated in the wide-frequency-range of 2 kHz-2 MHz between −3.0V/4.0V. All these-factors were found to be heavily dependent on frequency and voltage because of the surface states (Nss), Maxwell-Wagner polarization, and interlayer. The voltage-dependent profile of tanδ and M″ exhibits a significant shift in peak location towards forward-bias voltages as frequency increases due to the relaxation process of the Nss and dipole polarization. The ε′ was found to be 571.81 (at 2 kHz) and 59.72 (at 1 MHz). The value of ε′, even at 2 kHz, is about 151.5 times higher than the maximum value of traditional SiO2 (3.8) insulators, and hence, it can be successfully used instead of insulators to store more electric charges or energy.

The Effect of Salt Concentration on Dielectric Permittivity and Interfacial Polarization in Carbonate Rocks with Complex Pore Structure

Summary Broadband dielectric dispersion measurements are attractive options for the assessment of water-filled porosity. Dielectric permittivity is influenced by salinity as well as other rock/fluid properties. However, the effect of salinity on Maxwell-Wagner polarization (i.e., interfacial polarization) and dielectric permittivity in rock samples with complex pore structures requires further investigation. The objectives of this work are (a) to perform frequency-domain dielectric permittivity numerical simulations on 3D pore-scale rock samples at different salt concentration levels, (b) to quantify the effect of salinity on dielectric permittivity and interfacial polarization in the frequency range between 20 MHz and 5 GHz, and (c) to quantify the critical frequency (i.e., the frequency at which the relative permittivity becomes frequency-independent). We first perform pore-scale frequency domain dielectric permittivity simulations in fully water-saturated carbonate samples with complex pore structures to obtain the complex dielectric permittivity in the frequency range of 0.01–5 GHz and at different salinity levels. Next, we numerically create partially water/hydrocarbon-saturated water-wet samples and perform simulations at different salinity and water saturation levels to investigate the combined effect of salinity and water saturation on dielectric permittivity. Finally, we investigate how reliable conventional mixing models, such as the complex refractive index model (CRIM) and Hanai-Bruggeman (HB), are in the assessment of water saturation at different salinity levels. We used 3D pore-scale rock samples with complex pore structures from Austin Chalk, Estaillades Limestone, and Happy Spraberry formations. The increase in salinity from 2 to 50 parts per thousand (PPT) resulted in the relative permittivity to increase by 18% at 20 MHz. Similarly, an increase in salinity from 2 PPT to 50 PPT resulted in electrical conductivity to increase by 15 times at 20 MHz. However, at 5 GHz, the difference between the relative permittivity of the samples at different salinities was negligible. We demonstrated that the critical frequency was above 1 GHz. Thus, if complex dielectric permittivity at 1 GHz is being used, an accurate salinity assumption is required in the interpretation of conventional dielectric mixture models in carbonate formations. Finally, we observed 52% and 42% average relative errors in water saturation quantification when applying CRIM and HB models at all the frequencies of interest, respectively. The results also indicated that conventional models should not be used in the presence of uncertainty in salinity at lower frequencies. The results of this work quantified the frequency at which the water-filled pore volume rather than the Maxwell-Wagner polarization controls the relative permittivity of rock samples saturated with a wide range of brine salinity. Moreover, the results demonstrated that the relative permittivity of the rock samples with complex pore structures may still be significantly affected by the interfacial polarization even at 1 GHz. Moreover, the results suggested that the conventional mixture methods cannot reliably take into account the salt concentration of formation water, and this can lead to significant errors in reserves assessment.

Combined transport and dielectric models and experimental characterization based on impedance spectroscopy for studying the microstructural and transport properties of electro-ceramic perovskites

Collective investigations on the electrical resistivity, complex dielectric permittivity, complex impedance, conductivity, and electric modulus properties of La0.55Ca0.45Mn0.8Nb0.2O3 (LCMNO) are conducted. The impedance spectroscopy (IS) technique is reviewed to examine the electrical and dielectric responses of the material according to the carrier displacement, including core-shell structure, grain boundary effects, dielectric relaxation (local relaxation), and long-range conduction (non-local relaxation). This technique can correlate the electrical and dielectric responses with the ceramics’ microstructural effects (grain boundary and grain (core-shell) zones). For LCMNO, the electrical resistivity study confirms the presence of a metal-semiconductor transition at TM-SC=66 K. It points towards a gradual crossover from the thermally activated Small Polaron Hopping (SPH) to the Variable Range Hopping (VRH) process at low temperatures and for T> TM-SC. The dielectric results confirm the presence of various types of polarization effects. The occurrence of a dipolar reorientation is attributed to long-range electrical conduction. In addition, the accumulation of the activated charge carriers increases the Maxwell-Wagner polarization resulting from an internal barrier layer capacitor (IBLC) microstructure. The electric modulus study confirms the existence of a correlation between the mobile charge carrier’s motions. From the complex impedance, dielectric, and electric modulus, it is possible to label a material’s conductive and dielectric natures (non-Debye-relaxation-type).

Morphology-tailored microwave absorption in MOF-derived Co9S8/Co@N, S dual-doped carbon composites via ligand-exchange induced progressive hollow engineering

Flexible manipulations of morphology and composition have been considered as an art to achieve excellent microwave absorption performance for absorbers derived from metal-organic frameworks (MOFs). In this work, a strategy combining ligand-exchange induced hollow engineering and high-temperature one-step sulfuration has been proposed to fabricate the Co9S8/Co@N, S dual-doped carbon-based absorbers with tailored solid, yolk-shelled and entirely hollow polyhedral morphologies. The progressive hollow engineering not only enables composition control in the sulfuration process, but also endows the proposed absorbers with superior microwave absorption capacity due to the enhanced conductivity loss and Maxwell-Wagner polarization as well as optimized impedance matching. The yolk-shelled Co9S8/Co@N, S dual-doped carbon-based composite achieves a broad effective absorption bandwidth of 5.13 GHz at 1.88 mm with 20 wt% loading and realizes a minimum microwave loss of − 51.78 dB @ 11.63 GHz with 2.37 mm. This work reveals that the joint strategy of ligand-exchange induced hollow engineering and gas-solid reactive thermal process is an effective path to construct high-efficient lightweight multi-interfacial microwave absorbers for addressing the electromagnetic pollutions.

Synthesis and properties of zirconium-cerium composite via solid-state route

This study synthesized CeO2-doped ZrO2 nanoparticles using the solid-state reaction, employing varying quantities of 0.05mol.%, 0.15mol.%, and 0.25mol.% CeO2. The structures of CeO2-doped ZrO2 were investigated through XRD, revealing the presence of monoclinic ZrO2 in all samples, while the average size of the crystallite increased as the concentration of CeO2 doping increased. The optical band gap of CeO2-doped ZrO2 was determined using diffuse reflectance spectra, showing that the band gap decreased with increasing doping concentrations. The investigation focused on characterizing parameters such as dielectric constants, dielectric loss, and AC conductivity, emphasizing their frequency dependence at room temperature (RT). The dielectric constant and dielectric loss of Zr1-x CexO2 exhibited a significant drop as the frequency increased (Maxwell-Wagner polarization). Furthermore, the dielectric constant and dielectric loss factor in the lower frequency band exhibited an increase as the cerium content in ZrO2 increased. The incorporation of cerium significantly impacted the optical and electrical characteristics of composite ceramics consisting of CeO2 and ZrO2.

Synergistic effects of constituents in rare earth-based composites: Enhanced structural, electrical and magnetic properties for water splitting applications

Rare earth-based Bi0.85La0.15FeO3 (BLFO) and NdMnO3 (NMO) particles were synthesised using the solid-state route, and their roles affecting structural, electrical, magnetic properties along with hydroelectric application in different concentrations i.e., (1–x)BLFO:xNMO (where x = 0, 0.10, 0.20, 0.30 and 1.0) ceramics composites were investigated. X-ray diffraction analyses confirm the pure-phase formation of BLFO:NMO composites, featuring micrometer-scale crystallite sizes. Fourier transform infrared (FT-IR) spectra of BLFO:NMO composites reveal peak shifts with rising NMO content, indicating composite formation. These composites exhibit robust Maxwell–Wagner polarization and a pronounced composition-dependent behavior. The addition of NMO to BLFO results in a rise in dielectric permittivity at lower frequencies, confirming relaxor behavior and indicating success in achieving the transition temperature. Impedance spectroscopy facilitates a clearer understanding of how charge carriers contribute to these composites and the impact of grain/grain boundaries. The saturation magnetization maximum value (i.e., 0.807 emu/g) was attained in 0.7BLFO-0.3NMO. The coercivity decreases with the addition of NMO in BLFO. The results suggest the composite's enhanced suitability for microelectronics and hydropower cells, showing improved hydroelectric cell performance with increased NMO in BLFO, highlighting a notable ion diffusion mechanism.

Dielectric and electrocaloric properties of BCTZ composite with cobalt zinc ferrite nanoparticles

Dielectric and electrocaloric properties of a multiferroic composite constituted from Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCTZ) and Co0.4Zn0.6Fe2O4 (CZF), chosen for their closely related transition temperatures, are reported. Dielectric characteristics of the composites in the 1 kHz−10 MHz angular frequency range are described by two Cole-Cole relaxation models (domain wall and charge carrier) whereas for frequency <1 kHz, it is explained by Maxwell-Wagner type interfacial polarization using Jonscher power law. The effect of CZF phase on the dipolar mechanisms as a function of CZF mole fraction and the temperature are discussed. The electrocaloric property of the composites is estimated indirectly by Maxwell thermodynamic relation.

Dielectric Properties of Ni-Co Nanoferrites Synthesized using Green Synthesis Process

Aim: A series of nickel doped cobalt (NixCo1-xFe2O4, x=0.0 to 1.0) were successfully synthesized using green synthesized process. Methods: Tensile strain of all positive slope samples observed from the W-H (Williamson Hall) plot. It was discovered that as Ni-substitution increased, the dielectric constant (є’) increased from 148.07 to 243.62. Conversely, when the amount of Ni-substitution increases, the dielectric loss (tan δ from 0.23 to 0.05), imaginary part (є’’ from 98.81 to 17.87), and ac conductivity (σac from 1.62 to 0.15) all decreases at 1MHz frequency. objective: The purpose of current work is to investigate Williamson Hall effect and dielectric properties to find out the effects of nickel doping on the vibrational mode and crystal structure of cobalt ferrite. Results: This demonstrates that when Ni-substitution increases, energy losses at high frequencies decrease. Dielectric constant and ac conductivity, of all samples act in accordance with Koop's theory, the Maxwell-Wagner polarization procedure, and electron hopping Conclusion: This makes them suitable materials for high-frequency applications

Structural, magnetic and dielectric properties of Co0.4Zn0.6-xCrxFe2O4 (x=0, 0.05, 0.10, 0.15, 0.20) nanoferrites

Cobalt zinc chromium ferrites, which have been doped with chromium Co0.4Zn0.6-xCrxFe2O4 (x = 0.05, 0.10, 0.15, 0.20) (CZC) nanoferrites, are employed by the auto-combustion route. The magnetic and dielectric characteristics of Co–Zn nanoferrites were improved by Cr3+. Analysis using XRD, FTIR, and FESEM reveals the cubic spinel phase for CZC nanoferrites. SEM reveals a lot of clustering. The ferrite samples have cluster form with a spherical shape in the range 54.64–73.38 nm, as seen by the FESEM results. TEM studies show agglomeration. The Cr3+ concentration determines the magnetic properties of specimens. Ms declines from 62.38 emu/g to 42.59 emu/g by increasing Cr3+. For all samples, a frequency-dependent evaluation of the dielectric properties, including dielectric constant, dielectric loss, and ac conductivity, is performed. On the basis of Koop's theory, the Maxwell-Wagner polarization procedure, and the movement of electrons, the fluctuation of dielectric features at frequencies between 50 Hz and 108 Hz has been mentioned. The dielectric constant and dielectric loss tangent decreased with increasing frequency. The conduction of ferrite samples is influenced by the grain boundaries. Both recording media and high-frequency devices can benefit from using these nanoferrites.

Dielectric, electrochemical and magnetic properties of the hydrothermally synthesized double perovskite La2NiMnO6 for energy storage applications

Double perovskite materials are greatly appealing because of their multiferroic properties. Among such materials, double perovskite with rare earth metals are widely studied by researchers. Presently, the double perovskite La2NiMnO6 (LNMO) samples are synthesized using the hydrothermal method by varying the concentration of the solvent (NaOH). The Powder X-ray diffraction analysis confirmed the formation of monoclinic structure with the P21/n space group for prepared LNMO samples. The SEM image of the prepared samples revealed a cube-like structure. The impedance, dielectric, AC conductivity and modulus are studied in a wide frequency range from 100 Hz to 5 MHz to analyse the electrical and microstructure properties of the synthesized LNMO samples. The presence of a non- Debye type of relaxation peak is confirmed by impedance, dielectric and modulus studies. The effect of grains and grain boundaries are analysed by the Nyquist plot and the polarization of the materials are explained by the Maxwell-Wagner interfacial polarization model and Koop's theory. Using a three electrode system, the electrochemical behaviour of prepared LNMO samples are studied in various concentration of electrolyte (KOH) at different scan rates and found to have a pseudocapacitive nature. The highest specific capacitance value for LNMO10 is 44.60 F/g, LNMO20 is 50.14 F/g and LNMO30 is 25.81 F/g at a scan rate of 10 mV/s for 3 M KOH. The room temperature magnetic behaviour of synthesized LNMO samples analysed by Vibrating Sample Magnetometer paves way for magnetic storage applications.

Induced polarization of clay-rich materials — Part 2: The effect of anisotropy

The anisotropy in the complex conductivity of a clay-rock formation is investigated through laboratory and in situ measurements. Laboratory measurements have been conducted on four samples from two cores of the Callovo-Oxfordian Formation from the Paris Basin (France). This clay-rock formation is anisotropic with a well-defined bedding plane. Two of the cylindrical core samples are taken in the transverse direction with respect to the bedding plane, whereas two other core samples are taken in the in-plane direction. The complex conductivity spectra are performed in the frequency range of 20 mHz to 45 kHz and in a broad pore water saturation range from near saturation to a residual saturation of approximately 25%. The complex conductivity spectra are fitted with a double Cole-Cole model, whereas the low-frequency contribution corresponding to the induced polarization effect and the high-frequency contribution is related to the Maxwell-Wagner polarization. The six Cole-Cole parameters are investigated as a function of saturation, and we evaluate their degree of anisotropy versus the effect of saturation. The low-frequency instantaneous conductivity and normalized chargeability indicate a consistent degree of anisotropy with an anisotropy ratio equal to 3.8 ± 0.5 for one core sample and 6.5 ± 0.9 for the second core sample. These values represent a substantial level of anisotropy. The low-frequency Cole-Cole exponent and relaxation time do not indicate substantial amount of anisotropy. The monitoring of the evolution of the weight in the controlled humidity chamber seems to indicate that their relative permeabilities do not indicate a strong anisotropic behavior. Finally, the laboratory data are discussed in the context of field data obtained with an azimuthal array of 12 electrodes.

Cerium-modified Bi2FeMoO6: Microstructure, dielectric and optical properties

This paper presents an extensive investigation into the synthesis and characterization of Bi2FeMo1-xCexO6 (x = 0.0, 0.06, and 0.1) double perovskite type ceramic materials, fabricated using a high-temperature solid-state reaction method. The article delves into various aspects of these materials, including their structural, microstructural, dielectric, and optical properties. Structurally, the materials exhibit a rhombohedral crystal structure, having average crystallite sizes of 49.5 nm, 21.8 nm, and 26.4 nm for the respective compositions. Scanning electron microscopy reveals a uniform distribution of cylindrical and fractured spherical-shaped grains, complemented by well-defined grain boundaries. Energy dispersive X-ray spectroscopy analysis and elemental color mapping provide concrete evidence regarding the presence of key elements, such as Bi, Fe, Mo, Ce, and O, affirming the formation of highly dense and pure samples. Dielectric properties are comprehensively characterized across a wide temperature range of 25 °C to 500 °C and frequency range of 1 kHz to 1 MHz, highlighting the occurrence of the Maxwell-Wagner polarization effect at lower frequencies. The impedance study underscores the pivotal role of both grains and grain boundaries in determining the conductivity mechanism, with the x = 0.1 composition exhibiting superior semiconducting characteristics. Further examination of the modulus study and AC conductivity supports this finding. Additionally, the calculation of thermal activation energy suggests that the x = 0.1 composition boasts a more favorable thermally activated relaxation mechanism, rendering it a promising candidate for various device applications. Finally, an assessment of the UV–visible spectra reveals that the x = 0.1 composition possesses an ideal bandgap energy range, making it particularly suited for advanced optoelectronic devices.

Lead-free complex double perovskite SrLiFeWO6: Structural, microstructure, electrical and optical study

In this work, synthesis (solid-state reaction) and characterizations (structural, microstructure, dielectric, conductivity, Raman & UV–vis) of a newly prepared lead-free complex perovskite SrLiFeWO6 are reported. Preliminary X-ray diffraction (XRD) analysis suggests a tetragonal phase. The scanning electron microscope (SEM) micrograph and energy dispersive x-ray analysis (EDX) spectrum show the well-grown grains and sample purity. The study of Raman active lines determines the vibrational modes of the constituent molecules in the reported compound. Dispersed dielectric plots were explained by the Maxwell-Wagner polarization effect. The modulus study reveals the presence of a non-Debye type of relaxation. Jonscher's Power Law is fitted in ac conductivity data which follows a correlated barrier hopping mechanism. The direct bandgap energy of the studied sample is found to be 1.68 eV, which may be a good range for photovoltaic applications. For NTC thermistor applications, the analyzed thermistor constant and sensitivity factor are found to be within the permissible range. The idea of ferroelectric nature is opened up by the study of polarization versus electric field. The examination of current density versus electric field reveals that the sample has an ohmic character in the low region and a space charge-limited conduction (SCLC) mechanism in the higher field region.

Structure and Relaxor Behavior of (0.5 − x)BiFeO3-0.5PbFe0.5Nb0.5O3-xPbTiO3 Ternary Ceramics

Ceramics of the quasi-binary concentration section (0.1 ≤ x ≤ 0.2, Δx = 0.025) of the ternary solid solution system (0.5 − x)BiFeO3-0.5PbFe0.5Nb0.5O3-xPbTiO3 were prepared by the conventional solid-phase reaction method. An X-ray study at different temperatures revealed that (0.5 − x)BF-0.5PFN-xPT ceramics have a cluster morphology. Clusters have different modulation, crystal lattice symmetry, and chemical composition. The presence of a cluster structure in a solid solution with heterovalent substitution, consisting of regions rich in Ti+4, Nb+5, or Fe3+, has led to the appearance of Maxwell–Wagner polarization in the studied ceramics. The study of the dielectric characteristics revealed the relaxor-like behavior of the studied ceramics. The grain morphology, dielectric, pyroelectric, and piezoelectric properties of the selected solid solutions were investigated. The highest piezoelectric coefficient, d33 = 280 pC/N, was obtained in the 0.3BiFeO3-0.5PbFe0.5Nb0.5O3-0.2PbTiO3 ceramics. Study of the dielectric characteristics of all samples revealed relaxor ferroelectric behavior and a region of diffuse phase transition from the paraelectric to ferroelectric phase in the temperature range of 140–170 °C.

Effect of manganese doping on structural, optical, morphological, and dielectric properties of Ba(Ti1-xMnx)O3 lead-free ceramics for energy storage in supercapacitors.

A supercapacitor (SC) is considered to be one of the best energy storage devices due to its high-power density, long lifespan, fast charge storage capability, and eco-friendliness. Ceramics with low-cost, nontoxic, high efficiency, and stability are the suitable and promising materials for performed supercapacitors at room temperature. As proposal, we synthesized by sol-gel method the ceramics Ba(Ti1-xMnx)O3 (where x = 0, 1, 2, or 3%) to study the effect a low rate of manganese doping on their morphological, structural, dielectric, and optical properties. The microstructure of the sintered ceramics was examined using scanning electron microscope (SEM), and the results reveal that the average grain size (AGS) of the ceramics (0.663-1.018μm) increases with increasing Mn doping content. The optical behavior was studied by UV-visible spectroscopy, and the results indicate that Mn doping reduces the band gap (Eg) from 3.27 to 2.79eV thus, the possibility of using these materials in photocatalyze applications. The dielectric properties of all studied samples were investigated at the temperature range 30-400°C and frequency range 103-106Hz. Significant modification in dielectric permittivity and an appreciable decrease in dielectric losses were observed when adding Mn2+ ions to BaTiO3 ceramics. Variations in dielectric properties and AC conductivity, as a function of frequency, reveal a relaxation mechanism related to the Maxwell-Wagner interfacial polarization. The obtained results suggest the use of prepared ceramics in capacitor and actuator applications at room temperature (RT).

Exploring the coupling effect of ferromagnetic, Co0.8Zn0.2Fe2O4 with the ferroelectric, Ba0.5La0.5TiO3 at different concentrations in composite multiferroics

The solid-state reaction method is followed to fabricate multiferroic particulate composites, (1-x) Ba0.5La0.5TiO3 + (x) Co0.8Zn0.2Fe2O4 (x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0). X-ray diffraction patterns reflect the coexistence of the constituent phases in the composites after 4 h of sintering at 1200 °C. Cubic structures of both ferroelectric and ferrite phases confirmed from Rietveld refinement are distinctively dominant. The Fourier Transform Infrared (FTIR) spectrum confirms the characteristic vibration bonds of Co-ferrite, Zn-ferrite, and Ti-O. A slight variation of lattice parameters is observed with the increasing ferrite concentration. Bulk density reveals the inverse behavior of theoretical density. The obtained average grain size varies from 1.308 µm to 3.046 µm. All the composites have good ferromagnetic properties confirmed by hysteresis loops. The coercive field at x = 0.5 is 297.98 Oe, dramatically higher than other concentrations. The real part of permeability (μi′) gradually increases with increasing ferrite content as per the sum rule of the mixture. To investigate the electric properties of the samples, the dielectric constant (ε′) and loss tangent (tanδ) are measured in the frequency range of 100 Hz to 100 MHz. The dielectric constant (ε′) decreases at first and after x = 0.3, it begins to increase with further addition of the ferrite phase. The maximum dielectric constant (ε′) is 1092.08 at x = 0.9. The dielectric constant (ε′) and loss tangent (tanδ) display Maxwell-Wagner interfacial polarization and reduce from low to high frequency. All of the samples appear to be highly resistive indicating the reduction of leakage current. The dielectric constant (ε′) and resistivity show the opposite trend. P-E hysteresis loops indicate para-electric to ferroelectric transition.

Fluorinated Interface Engineering toward Controllable Zinc Deposition and Rapid Cation Migration of Aqueous Zn-Ion Batteries.

Metallic zinc (Zn) is a highly promising anode material for aqueous energy storage systems due to its low redox potential, high theoretical capacity, and low cost. However, rampant dendrites/by-products and torpid Zn2+ transfer kinetics at electrode/electrolyte interface severely threaten the cycling stability, which deteriorate the electrochemical performance of Zn-ion batteries. Herein, an interfacial engineering strategy to construct alkaline earth fluoride modified metal Zn electrodes with long lifespan and high capacity retention is reported. The compact fluoride layer is revealed to guide uniform Zn stripping/plating and accelerate the transfer/diffusion of Zn2+ via Maxwell-Wagner polarization. A series of in situ and ex situ spectroscopic studies verified that the fluoride layer can guide uniform Zn stripping/plating. Electrochemical kinetics analyses reveal that positive effect on the removal of Zn2+ solvation sheath provided by fluoride layer. Meanwhile, this fluoride coating layer can act as a barrier between the Zn electrode and electrolyte, providing a high electrode overpotential toward hydrogen evolution reaction to hold back H2 evolution. Consequently, the fluoride-modified Zn anode exhibited a capacity retention of 88.2% after 4000 cycles under10 A g-1 . This work opens up a new path to interface engineering for propelling the exploration of advanced rechargeable aqueous Zn-ion batteries.

Investigation of Structural and Electrical Properties of Al2O3/Al Composites Prepared by Aerosol Co-Deposition

As the microelectronic industry develops, components that can perform several different tasks receive increasingly more attention, resulting in multifunctional materials being highly sought after. Al2O3 is widely present in electronic applications as a protective coating or as an electrical and thermal insulator due to its mechanical and thermal stabilities and chemical inertness. Al2O3 is also an important dielectric material, with high resistivity and stable permittivity over a wide range of temperatures and electric fields, but its modest permittivity necessitates large effective areas or extremely thin layers when a large capacitance is desired. Composites consisting of discrete conducting phases within an insulating matrix can produce large capacitance via Maxwell–Wagner polarization. In this work, Al2O3/Al composite thick films with different volume ratios of Al were prepared using the aerosol deposition method. A relative dielectric permittivity (εr′) of 800 at 1 MHz was achieved at 27 vol% of Al, a sixty-sevenfold enhancement compared to Al2O3. On the other hand, dielectric losses, tan(δ), at 1 MHz increased from 0.01 for Al2O3 up to 0.58 for the composite with 27 vol% of Al. A finite-element model of the composites was implemented, supporting the nonlinear electrical behavior of the composites as function of vol% of Al. Our results show novel possibilities for the applications of Al2O3-based materials in the microelectronic industry, especially for temperature-sensitive applications, for which the integration strengths of aerosol deposition are valuable.

Numerical characterization of transient electrohydrodynamic deformation and coalescence of single-core double emulsion droplets by AC field dielectrophoresis

Considering its good biocompatibility, the water-in-oil-in-water type compound double emulsion (DE) droplet serves as an ideal microreaction vessel upon their on-demand electro-coalescence. By coupling phase field description to fluid dielectrophoresis, transient numerical simulation is conducted to characterize the dynamic feature of surface charge wave and electric stress induced at various phase interfaces of single-core DE drops subjected to external AC electric fields. A novel prolate/prolate electro-deformation mode is discovered by numerical analysis for A/B/A type two-phase droplet when both the conductivity and permittivity of oil shell are much smaller than that of water phase. Based upon this, AC electrostatic attraction between two opposing single-core DE droplets is then investigated in a broad parametric space. Collision of two adjacent oil shells is always followed by the dielectrophoretic integration of corresponding water cores wrapped within them, leading to three different possible modes of inter-droplet electro-coalescence under distinct core/shell radius ratio. Our numerical analysis herein unveils for the first time the hitherto unknown spatial-temporal electrohydrodynamic behavior of single-core DE droplets driven by Maxwell-Wagner structural polarization, during their deformation and coalescence as a consequence of an active interplay among those induced droplet dipoles.

Study of CoCe0.05Fe1.95O4-polypyrrole composite for efficient electromagnetic interference shielding

The synthesis of nanocomposites with magnetic and microwave absorbing properties was achieved via sol-gel process merge with the self-combustion methodology. The X-ray diffraction results showed that nanocomposites consisted of a single spinel phase and no impurities were detected. The hysteresis loop showed the nanocomposites' ferromagnetic character. Measurements of saturation magnetization, alternating current susceptibility, cation distribution, and Curie temperature were taken to evaluate the magnetic properties. The permittivity (ε′, ε″) varied as a function of frequency in accordance with Maxwell-Wagner type interfacial polarization. The actual and fictitious components of microwave permeability showed a maximum at lower frequencies and decreased as frequency increased. Due to its superparamagnetic behavior, the composite has potential applications in shielding technologies.