Decrease In Permittivity Research Articles

Ruthenium Nanoparticles Supported on Bentonite: Enhanced Crystallinity, Conductivity, and Dielectric Performance for Advanced Applications

We used the wet impregnation method to synthesize Ru nanoparticles supported on bentonite (Ru/Bento). The X-ray diffraction and Energy-Dispersive (EDX) Spectrometer characterisations of the synthesized structures revealed that the montmorillonite is the predominant phase. The reduced crystallite size and lower diffraction peak intensities for Ru/Bento indicate improvement in crystallinity. EDX confirmed the successful incorporation of Ru, suggesting fewer reactive hydroxyl groups on the bentonite surface. Dielectric studies show a decrease in permittivity with increasing frequency, consistent with the Maxwell-Wagner polarization mechanism. Ru/Bento exhibits higher permittivity at elevated temperatures due to enhanced interfacial polarization, and higher low-frequency dielectric loss attributed to resistive interfacial regions. Electric modulus analysis indicates significant relaxation processes in Ru/Bento at higher temperatures. Conductivity studies demonstrate increased charge carrier mobility with frequency and temperature, following a correlated barrier hopping mechanism, with Ru nanoparticles enhancing conductivity by reducing barrier height. HOMO and LUMO analysis suggest improved conductivity and reactivity for Ru/Bento due to lower energy gaps and chemical hardness. Molecular dynamics calculations confirm the geometric stability of Ru nanoparticles on bentonite, making Ru/Bento bentonite a promising material for high conductivity applications.

Li-ion solvation structure at electrified solid-liquid interface: Understanding solvation structure dynamics and its role in electrochemical energy storage through binary ethylene carbonate and dimethyl carbonate solvent.

Binary solvent electrolytes can provide interpretations for designing advanced electrolytes of next generation batteries. This study investigates the adsorption mechanisms of solvated lithium ions in binary solvents near charged electrodes. Molecular dynamic simulations are performed for lithium hexafluorophosphate (LiPF6) in ethylene carbonate and dimethyl carbonate (EC:DMC) solvent sandwiched between two electrodes. Results show that lithium ions form a tetrahedral solvation structure with two EC and two DMC molecules. The solvated lithium ion shows anti-electrostatic interaction with electrodes. This can be attributed to the electrostatic attraction of the polar end of the DMC molecule, which keeps the cation anchored to the positive electrode. Meanwhile, the solvation structure adopts a fix orientation at the negative electrode, which leads to unchanged electrostatic interaction at high charge density. Finally, EC molecules are swapped by DMC molecules near the negative electrode at high charge density. This leads to a decrease in local relative permittivity and, therefore, a decrease in differential capacitance. The differential capacitance of the positive electrode continuously decreases with increasing charge density. This is caused by the partial anchoring of solvent molecules holding the cations, which cancels the adsorption of anions near the positive electrode. This study provides insights into designing better electrolytes for efficient battery performance.

Evolution of high temperature oxidation properties of SiCf/SiCN composites with BN interphase

In this study, SiC/SiCN composites with BN interphase were prepared using chemical vapor infiltration (CVI) and polymer infiltration and pyrolysis (PIP) methods. The evolution and related mechanisms of mechanical and microwave absorption properties of the composites after oxidation at 800 °C, 1000 °C, 1200 °C, and 1400 °C were investigated. The results showed that with the elevating of oxidation temperature, the flexural strength of SiC/SiCN composites gradually decreased, with a retention rate of 56.7 % after oxidation at 1400 °C. The main reasons for the deterioration of mechanical properties were the changes in the crystal structure of SiC fibers under high-temperature conditions and the formation of brittle SiO2 phases on the surface and interior of the SiCN matrix. With the increase in oxidation temperature, the microwave absorption performance of the composites showed an enhancing trend. The main reasons were that after oxidation treatment, the reduction of free carbon content and the formation of SiO2 film layers from the oxidation of SiC and SiCN led to a decrease in the complex permittivity of the composites, resulting in better impedance matching and dielectric loss capabilities. The contributions of BN interphase to stress dispersion, interface polarization, and oxidation protection significantly enhance the mechanical and electromagnetic absorption properties of the composites. Therefore, SiC/SiCN composites are high-temperature structural microwave absorbing materials with great application prospects.

Technology and Dielectric Properties of BLT4 Ceramics Modified with Special Glass

Lead-boron special glass was doped into Ba0.996La0.004Ti0.999O3 (BLT4) ceramics in order to control the sintering process and grain growth, consequently obtaining materials with a well-developed microstructure. Changes in the microstructure resulted in a significant decrease in electrical permittivity along with a substantial increase in its frequency dispersion. Glass-doped ceramics, similar to pure BLT4, are characterized by a first-order phase transition from the ferroelectric phase to the paraelectric phase. The temperature of this transition shifts slightly towards higher values with the increase in glass dopant concentration.

Electromagnetic properties of coal using microstrip and an algorithm based on the Nicolson-Ross-Weir method

The work implements an experimental methodology to find the dielectric parameters: electrical permittivity, effective permittivity, magnetic permeability, conductivity, absorption coefficient, impedance, and loss tangent of bituminous coal from the municipality of Morcá and Tópaga belonging to the Sogamoso-Jericó sub-basin of the Guaduas formation, one of the most important coal reserves in Colombia. The methodology, known for its efficiency, includes constructing a microstrip-type circuit, measuring scattering parameters or S-parameters at frequencies between 300 kHz and 1 GHz with a vector network analyzer, and extracting electromagnetic properties using the Nicolson-Ross-Weir algorithm. The implemented algorithm allowed us to see the behavior of the coal in a fraction of the ultra-high frequency band and to find quickly and easily the approximate values of the parameters as a function of frequency, which are very important for investigations in mathematical modeling and computational electromagnetics. The results show that the real and imaginary components of the relative dielectric permittivity decrease with increasing frequency, and the absorption coefficient and the loss tangent of the coal increase as a function of frequency, indicating that the coal behaves as a dissipative dielectric.

Influence of the presence of ions on the dielectric properties of reverse micelle systems

AOT/isooctane/water reverse micelle solution was doped with ionic salts solutions: sodium chloride, potassium chloride, tetramethylammonium chloride, tetramethylammonium bromide, sodium butyrate and sodium benzoate. Each system was investigated for the influence of ionic additives on dielectric properties: electric permittivity, conductivity and nonlinear dielectric effect (NDE). Studies showed that addition of salts noticeably changes the dielectric parameters. Based on the salts used in this research, the most common effect is a decrease of electric permittivity, conductivity and NDE effect. However, addition of some ions can lead to their increase, which was proved in the case of sodium benzoate. The registered changes were explained based on the percolation effect and changes in rigidity of the micellar surfactant shell due to the incorporation of the dissolved ions into the micellar structure.

Phase Transformations Driving Biaxial Stress Reduction During Wake‐Up of Ferroelectric Hafnium Zirconium Oxide Thin Films

AbstractBiaxial stress is identified to play an important role in the polar orthorhombic phase stability in hafnium oxide‐based ferroelectric thin films. However, the stress state during various stages of wake‐up has not yet been quantified. In this work, the stress evolution with field cycling in hafnium zirconium oxide capacitors is evaluated. The remanent polarization of a 20 nm thick hafnium zirconium oxide thin film increases from 9.80 to 15.0 µC cm−2 following 106 field cycles. This increase in remanent polarization is accompanied by a decrease in relative permittivity that indicates that a phase transformation has occurred. The presence of a phase transformation is supported by nano‐Fourier transform infrared spectroscopy measurements and scanning transmission electron microscopy that show an increase in ferroelectric phase content following wake‐up. The stress of individual devices field cycled between pristine and 106 cycles is quantified using the sin2(ψ) technique, and the biaxial stress is observed to decrease from 4.3 ± 0.2 to 3.2 ± 0.3 GPa. The decrease in stress is attributed, in part, to a phase transformation from the antipolar Pbca phase to the ferroelectric Pca21 phase. This work provides new insight into the mechanisms controlling and/or accompanying polarization wake‐up in hafnium oxide‐based ferroelectrics.

Application of Johnson's approximation in finite element modeling for electric field‐dependent materials

AbstractJohnson's approximation is implemented in a finite element code to simulate the electric field dependence of a core–shell microstructure material. We show how the microstructure, based here on a 50:50 volume fraction, influences the measured effective permittivity as a function of applied voltage. Using a Johnson's parameter of β = 1.0 × 1010 Vm5/C3, verified from commercial BaTiO3‐based multilayer ceramic capacitors (MLCC), we show how the microstructure and the difference in core and shell conductivities alter the local fields generated and how this influences the voltage dependence of the effective permittivity. Systems that comprise a conductive core‐like material surrounded by a resistive shell experience little or modest voltage dependence due to the shell material providing shielding to large electric fields within the cores. Conversely, if the core material is more resistive than the shell material, substantial voltage dependence occurs with simulations showing over a 50% decrease in the effective permittivity. These simulations give improved understanding of voltage dependence and provide a method to help guide the design of future materials for MLCCs with improved performance.

Enhancement of microwave absorption performance of cobalt ferrite by adding MXene (Ti3C2Tx) nanosheets

In this work, CoFe2O4 powders were combined with various amounts of MXene (Ti3C2Tx) through the solution combustion method for microwave absorption applications. Despite the absence of MXene reflections in X-ray diffraction patterns, the MXene sheets were observed in electron microscopy images. The CoFe2O4 nanoparticles were uniformly dispersed on the MXene nanosheets. The specific surface area increased from 57 to 83 m2 g−1 by adding 20 wt% MXene. The saturation magnetization and coercivity decreased from 44 to 35 emu g−1 and from 834 to 775 Oe, respectively. By adding the MXene, the minimum reflection loss and effective absorption bandwidth increased up to −38 dB and 5.6 GHz at a matching thickness of 1.8 mm, respectively, which was attributed to the enhancement of impedance matching by the decrease of permittivity.

Effect of oxygen defects on ferroelectric oxides: Correlation between linear and nonlinear dielectric responses

Oxygen defects are introduced into PbZr0.5Ti0.5O3 films and their impact on ferroelectric behavior, linear dielectric response (LDR), and nonlinear dielectric response (NDR) is studied. Apart from a notable decrease in both polarization and LDR permittivity, the frequency spectra of LDR exhibit a distinctive loss peak. The peak position varies with temperature and oxygen defect concentration. NDR parameters, including the Rayleigh coefficient (α1), the slope (α2) correlating the imaginary part of permittivity with the ac electric field, and the slope (k) between the real and the imaginary parts of permittivity, demonstrate diverse behaviors in response to temperature and oxygen defect concentration. The similarity in the frequency spectra of tanδ and 1/k reveals the correlation between LDR and NDR induced by the presence of oxygen defects. These observations are attributed to the behavior of the single and composite defects associated with oxygen vacancies.

Role of mixed oxidant and controlled oxygen partial pressure heat treatment to regulate the dielectric properties and resistivity of SrTiO3-based CP ceramics

Sr0.99La0.01TiO3 (SLT10) colossal permittivity (CP) ceramic materials were synthesized using solid phase method and secondary heat treated using mixed oxidant 35%Bi2O3–10%Al2O3–20%MgO–25%CuO–10%SiO2 oxidant. The heat treatment atmospheres were chosen as O2, air, and Ar to correspond to different oxygen partial pressures. The dielectric properties of the Sr0.99La0.01TiO3-Percolated (SLT10-P) ceramics were investigated, and the contribution of the oxidant to the resistivity enhancement was verified by complex impedance spectroscopy and DC resistivity tests. Excellent dielectric properties were obtained for SLT10-P Air ceramic sample (16543 for dielectric permittivity and 0.016 for loss tangent), and the resistivity was increased from 2.13 × 108 Ω cm (SLT10) to 1.23 × 1011 Ω cm (SLT10-P Air). The resistance degradation mechanism of SLT10-P ceramics and oxygen vacancy migration in the process of resistance degradation were studied by using resistance monitoring device and thermally stimulated depolarization currents (TSDC) test. The introduction of oxidant optimizes the temperature stability and resistivity of SLT10 ceramics, but it will lead to the decrease of dielectric permittivity. The atmosphere of heat treatment changed the concentration of oxygen vacancy in ceramics. When SLT10-P O2 was treated in O2 atmosphere, the concentration of oxygen vacancy in ceramics decreased, which led to the decrease of dielectric permittivity and the increase of grain boundary resistance. For SLT10-P Ar ceramic, more oxygen vacancies and free electrons are induced by low oxygen partial pressure heat treatment, which enhances the dipole effect of electron pinning defects and leads to colossal dielectric permittivity, but high concentration of oxygen vacancies will affect the resistance decline. In SLT10-P Air ceramic, the coexistence of colossal permittivity and low loss tangent and high resistance is realized.

Electrical properties evaluation of corn oil biodiesel mixed with lubricant as a potential source of energy

The main aim of this study is to assess the electrical characteristics pertaining to a biodiesel derived from corn oil and lubricant. The first step in the synthesis of biodiesel from corn oil involves the transesterification process. Subsequently, the biodiesel is combined with a base lubricant (20W-40T) in varying proportions, spanning from 5% to 40% of the overall volume. The measurement and analysis of biodiesel blends necessitate consideration of crucial electrical parameters, including breakdown voltage, resistivity, permittivity and electrical conductivity. The decrease in breakdown voltage, permittivity, and electrical conductivity that ensues from an increase in diameter may be attributed to the corresponding increase in diameter. Nevertheless, a positive association exists between the greater quantity of base lubricant and an elevation in resistivity. Despite the positive correlation between resistivity and diameter, this phenomenon persists. The potential cause for the enhancement of the electrical properties might be attributed to the dispersion of the fundamental lubricant.

Temperature-Dependent Ferroelectric Properties and Aging Behavior of Freeze-Cast Bismuth Ferrite-Barium Titanate Ceramics.

Lead-free BiFeO3-BaTiO3 (BF-BT) piezoceramics have sparked considerable interest in recent years due to their high piezoelectric performance and high Curie temperature. In this paper, we show how the addition of highly aligned porosity (between 40 and 60 vol %) improves the piezoelectric performance, sensing, and energy harvesting figures of merit in freeze-cast 0.70BiFeO3-0.30BaTiO3 piezoceramics compared to conventionally processed, nominally dense samples of the same composition. The dense and porous BF-BT ceramics had similar longitudinal piezoelectric coefficients (d33) immediately after poling, yet the dense samples were observed to age faster than those of porous ceramics. After 24 h, for example, the porous samples had significantly higher d33 values ranging from 112 to 124 pC/N, compared to 85 pC/N for the dense samples. Porous samples exhibited 3 and 5 times higher longitudinal piezoelectric voltage coefficient g33 and energy harvesting figure of merit d33g33 than dense samples due to the unexpected increase in d33 and decrease in relative permittivity with porosity. Spontaneous polarization (Ps) and remnant polarization (Pr) decrease as the porosity content increased from 37 to 59 vol %, as expected due to the lower volume of active material; however, normalized polarization values with respect to porosity level showed a slight increase in the porous materials relative to the dense BF-BT. Furthermore, the porous ceramics showed improved temperature-dependent strain-field response compared to the dense. As a result, these porous materials show excellent potential for use in high temperature sensing and harvesting applications.

Influences of divalent ion substitution on the magnetic and dielectric properties of W-type barium ferrite

Abstract Saturation magnetization, magneto-crystalline anisotropy field and dielectric properties are closely related to microwave devices applied at different frequencies. For regulating the magnetic and dielectric properties of W-type barium ferrites, single-phase BaMe 2Fe16O27 (Me = Fe, Mn, Zn, Ni, Co) with different Me ions were synthesized by the high-temperature solid-state method. The saturation magnetization (M s) range from 47.77 emu/g to 95.34 emu/g and the magnetic anisotropy field (H a) range from 10700.60 Oe to 13739.57 Oe, depending on the type of cation substitution in the hexagonal lattice. The dielectric permittivity and dielectric loss decrease with increasing frequency of the AC electric field in the low-frequency region, while they almost remain constant in the high-frequency region. The characteristics of easy regulation and preparation make it a potential candidate for use in microwave device applications.

Dynamic evolution of terahertz permittivity of lignite during oxidation: Microstructural insights

Terahertz technology holds promise for monitoring coal fires and assessing associated risks, relying on the dielectric response of coal during the oxidation process. Besides, unraveling the response mechanism is crucial for enhancing the application's reliability. In light of these, this study focused on investigating the terahertz complex permittivity of lignite with different oxidation temperatures through microstructure analysis. Results indicated that oxidation temperature dependencies in the real and imaginary parts of lignite's permittivity, exhibiting a pattern of initial decrease followed by an increase. The decrease in permittivity during the dehydration and weight loss stage is primarily attributed to moisture content. In the oxygen absorption and weight gain stage, pore development and scattering effects contribute to the continuous decrease in real permittivity and rise in imaginary permittivity. During the oxidative decomposition stage, the hydroxyl group initiates an increased real permittivity. Upon reaching the combustion temperature, there is a sudden surge in permittivity, driven by the dominance of minerals in coal dielectric properties. The conclusions offer theoretical support for terahertz technology in monitoring coal fires, which can contribute to the sustainable development of the coal industry, mineral processing, and safety production.

Reliable ferroelectricity down to cryogenic temperature in wake-up free Hf0.5Zr0.5O2 thin films by thermal atomic layer deposition

The performance and reliability of ferroelectric thin films at temperatures around a few Kelvin are critical for their application in cryo-electronics. In this work, TiN/Hf0.5Zr0.5O2/TiN capacitors that are free from the wake-up effect are investigated systematically from room temperature (300 K) to cryogenic temperature (30 K). We observe a consistent decrease in permittivity (ε r) and a progressive increase in coercive electric field (E c) as temperatures decrease. Our investigation reveals exceptional stability in the double remnant polarization (2P r) of our ferroelectric thin films across a wide temperature range. Specifically, at 30 K, a 2P r of 36 µC/cm2 under an applied electric field of 3.0 MV/cm is achieved. Moreover, we observed a reduced fatigue effect at 30 K in comparison to 300 K. The stable ferroelectric properties and endurance characteristics demonstrate the feasibility of utilizing HfO2 based ferroelectric thin films for cryo-electronics applications.

Structural, dielectric, and antimicrobial evaluation of PMMA/CeO2 for optoelectronic devices

In the current report, we have successfully synthesized nanocomposites of PMMA incorporating different doping of CeO2 through a chemical approach. XRD results reflects decent matching for CeO2 nanoparticles with 29 nm crystallite size. FTIR spectroscopy demonstrates the characteristic functional groups validating the successful formation of the composite. The optical study of PMMA and the nanocomposites has proven that the optical properties such as band gap, refractive index, optical permittivity, and loss tangent factor are affected by adding CeO2 to the PMMA matrix.The peak residing around 420 nm by UV measurements is allocated to occurring electrons photoexcitation from the valence to conduction band inherent in CeO2. The dielectric measurements were achieved using broadband dielectric spectroscopy upon a wide span of frequencies (10–1–107 Hz) and within temperatures from − 10 to 80 °C with a step of 10 °C. The permittivity decreases by adding CeO2 and the dielectric parameters are thermally enhanced, however, the temperature influence is based on CeO2 content, the higher the CeO2 amount, the higher the influence of temperature. The results of the nanocomposites revealed antibacterial activity counter to gram-positive bacteria strain (S. aureus, and B. subtilis), and gram-negative bacteria (E. coli, and K. pneumoniae), yeast (C. albicans, as well as fungi (A. niger). Inherently, the change in CeO2 concentration from 0.01 to 0.1 wt% delivers maximum influence against gram-negative bacteria. These PMMA CeO2-doped composites are beneficial for optoelectronic areas and devices.

Modeling the Effect of Material Viscoelasticity on the Dielectric Permittivity of Deformed Elastomers.

Elastomers, as a typical category of soft dielectrics, have shown great potential for developing stretchable electronics and soft transducers. However, the performance of dielectric elastomers (DEs) is susceptible to the dielectric permittivity of the material, whether as insulators or actuators. On the other hand, experiments suggest that the material viscoelasticity significantly influences the dielectric permittivity of DEs. Based on the theory of finite-deformation viscoelasticity, this work adopts the Brillouin function to develop a modeling framework to examine the effect of material viscoelasticity on the dielectric permittivity for the first time. A comparison of the data fitting results between the models with and without consideration of the material viscoelasticity is presented. Simulation results also reveal that the viscous network of the elastomer exerts a mitigation effect on the decrease in the dielectric permittivity when the material is deformed. Furthermore, it is found that the loading rate is a key parameter that strongly affects the dielectric permittivity, mainly through the inelastic deformation.

The Impact of Concentration and Electric-Field Dependent Susceptibilities on Electrolyte Models

Electrolytes have a significant role in a range of scientific and technological fields such as fundamental electrochemistry, biochemical systems, semiconductors, and industrial devices. A widely used mathematical framework for describing electrolytes is based on Poisson-Nernst-Planck-type equations and their successors[1], but the Poisson equation assumes a constant dielectric susceptibility. However, recent research has developed a thermodynamically consistent model for the dielectric susceptibility that accounts for its dependence on both concentration and electric field [5,6]. This allows for the inclusion of the dependency of the susceptibility on salt concentration in liquid electrolytes, referred to as dielectric decrement[2,3,4], as well as the decline in susceptibility for large electric fields[8], known as dielectric saturation.The research findings highlight the importance of considering the variable dielectric susceptibility in electrolyte models, particularly in relation to the decrease in dielectric permittivity in front of a charged electrode surface[7]. The study demonstrates the impact of the concentration and electric-field-dependent susceptibility on the overall equation system for electrochemical double layers. By providing insights into the theoretical aspects of the approach, the researchers aim to contribute to the development of more accurate and comprehensive models of electrolytes that consider the complex interplay of various factors.

Unveiling the potential of Dy+3 substituted Ni-Zn ferrites: A study of physical, magnetic, dielectric, and microwave properties

Utilizing microwave ferrites as primary materials holds great potential for high-frequency and high-power devices, opening up exciting possibilities for their application in such systems (circulators, phase shifters). The physical, magnetic, dielectric, and microwave properties of Ni0.5‒xDyxZn0.5Fe2O4; x = 0, 0.02, 0.04, 0.06, 0.08 (DNZF) are thoroughly investigated in the present study. XRD analysis confirms the presence of a distinct cubic spinel structure without additional phases. Dy substitution influences lattice constant and crystallite size, showing a clear correlation. Raman spectroscopy reveals a decline in peak intensity and a shift towards lower wavenumbers, indicating changes in cationic distribution upon Dy substitution. Surface morphology analysis shows an increase in average particle size as Dy substitution inhibits grain growth. XPS analysis indicates partial reduction, transforming Fe³⁺ into Fe²⁺. Saturation magnetization initially increases with Dy concentration, reaching a peak value of 69 emu/g at x = 0.02, and then decreases due to the effect of Dy's atomic size on magnetic moments. Real permittivity (ε') and loss tangent (tan δ) initially increase, reaching maximum values at x = 0.02, but decrease with higher Dy concentrations (x>0.04). The Nyquist plot analysis reveals that grain boundary resistance contributes significantly to the overall resistance. Permeability and permittivity analysis in the frequency range of 12.4 - 18 GHz (Ku band) demonstrates that both real and imaginary components of permittivity decrease with Dy substitution. These findings suggest promising prospects for the utilization of Dy-doped Ni-Zn ferrites in high-frequency devices like circulators and phase shifters, indicating their suitability for such applications.