Dielectric Constant Increases Research Articles

Modulation of dielectric properties of hexagonal/cubic boron nitride composites

In this work, we synthesized mixed-phase hexagonal-boron nitride (h-BN)/cubic-BN (c-BN) composites with varying ratios and investigated their frequency and temperature-dependent dielectric properties. As the ratio of c-BN increased, we observed a corresponding increase in the dielectric constant of the composites. Furthermore, we used spark-plasma sintering (SPS) to treat the mixed-phase composite, which resulted in a phase transformation from mixed phase to pure h-BN phase. Remarkably, the composite exhibited an increase in dielectric constant after the SPS process, which can be attributed to the densification of the composite and the enhancement in grain size. Our approach presents a promising strategy for effectively modulating the dielectric properties of BN, which is crucial for advanced electronics.

Temperature-dependent dielectric response of free standing PVDF-MoS2 nanocomposite films

Poly(vinylidene fluoride) (PVDF) and its copolymers are known for possessing the highest electroactive response including dielectric constant, piezoelectric and ferroelectric effects which has a wide range of applications such as in energy transfer, energy generation and storage, monitoring and control, and include the development of capacitors, sensors, actuators and so on. We report an enhancement in dielectric properties in PVDF generated by the addition of MoS2 nanosheets. The addition of 1 wt% MoS2 nanosheets as a filler in PVDF, stabilize its beta phase over the alpha phase, resulting in a significant increase in dielectric constant (ε’) across a wide range of frequencies (100 Hz to 1 MHz) and temperatures (140 K- 340 K). The high dielectric constant was achieved by the PVDF-MoS2 nanocomposite while maintaining a relatively low tangent loss factor of 0.94. Such properties in soft polymer-based piezoelectric materials were previously challenging and unachievable. The nanocomposite exhibits excellent ferroelectric properties with 11 times enhancement in remnant polarization compared to pristine PVDF in ambient conditions. The stored energy density (Us) is 39.43 mJ/cm3 for the PVDF-MoS2 film. These lead-free and soft polymer-based nanocomposites can bring remarkable advances in various flexible sensors, data storage, and energy harvesting applications.

Structural and dielectric analysis of Cu-doped NiCo2O4 nanoparticles synthesized by green synthesis approach

The synthesis process of nanoparticles profoundly influences the chemical and physical properties of materials. Green synthesis, utilizing plant extracts as precursor materials, presents an environmentally friendly approach for producing metal oxide nanoparticles. In this study, we synthesized copper-doped nickel cobaltite (Ni1-xCuxCo2O4, x = 0.5) nanoparticles via a green synthesis method employing aloe vera leaf extract. Analysis of the XRD pattern revealed the formation of cubic spinel Ni0.5Cu0.5Co2O4 nanoparticles well-crystalline in nature (space group: Fd-3m), free from secondary impurity phases. Crystalline size, determined using Debye Scherrer, modified Scherrer, and Williamson-Hall models, yielded values of ∼ 27 nm, ∼ 35 nm, and ∼ 62 nm, respectively. Dielectric studies conducted at room temperature revealed a frequency-dependent increase in dielectric constant. At lower frequencies, tangent loss (tan δ) showed higher values, which gradually decreased as frequency increased. Additionally, the AC conductivity demonstrated a significant increase with higher external field frequencies.

A comprehensive investigation of Bi2O3 on the physical, structural, optical, and electrical properties of K2O.ZnO.V2O5.B2O3 glasses

The multi-component glass system has a composition of 10K2O–10ZnO–55 B2O3–(25–x)V2O5–xBi2O3 (x = 4, 5, 7.5, 9, 10 mol%) are synthesized by the melt-quenching method. Using X-ray diffraction examination, the amorphous phase in the material was confirmed. The physical characteristics of the produced compositions are examined using density (D) and molar volume (Vm). Calculations of physical properties showed that adding Bi2O3 from 4 to 10 mol% increased the glass density from 2.7878 to 3.3617 g cm−3 and decreased the molar volume from 40.4196 to 38.5895 cm3/mol. Studies of glass samples using the FTIR show bands of absorption for oxides in different structural groups. Octahedral [BiO6\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\ ext{BiO}}}_{6}$$\\end{document}], [BO4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\ ext{BO}}}_{4}$$\\end{document}], and tetrahedral [BO3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\ ext{BO}}}_{3}$$\\end{document}] structural units are observed in the present glass matrices. The cutoff wavelength (λC\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\lambda }_{C}$$\\end{document}), and optical band gap energy were determined using UV absorption spectra. The increase in non-bridging oxygens can be linked to the decrease in optical band gap energy (Eopt\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${E}_{opt}$$\\end{document}) (direct and indirect) and the increase in cutoff wavelength with an increase in Bi2O3 content. This is attributed to the existence of bismuth ions and the creation of non-bridging oxygens. Besides that, the values of optical parameters, viz., optical electronegativity, refractive index, and molar refractivity, are calculated. The metallization criterion values are less than 1 and the glass samples exhibit an increased tendency towards metallization. Both the conductivity and the dielectric constant increase with the rise in Bi2O3 content, however, the dielectric loss and the impedance reduce. The behavior and values of conductivity for the studied glasses reveal the semiconducting properties of all glass samples. These results suggest that the produced glass samples may be employed as amorphous semiconductors in electronics and memory switching devices.

Heart rate monitoring system based on piezoelectric poly(vinylidene fluoride-co-trifluoroethylene) composites with barium strontium titanate ceramic particles

A heart rate sensor device has been designed and developed based on a composite material based on poly(vinylidene fluoride – co – trifluoroethylene), P(VDF-TrFE) as polymer matrix and barium strontium titanate (BST) particles as ceramic fillers. The composite films were prepared by solvent casting varying the ceramic particles content between up to 40 wt%, allowing to tailor the dielectric and piezoelectric response. The morphology, polymer phase and thermal properties are independent of the ceramic filler content, whereas the dielectric constant increases significantly with increasing filler content, the largest dielectric constant, ε’ = 38 at 1 kHz, being obtained for the composite with 40 wt% of ceramic particles. Further, the highest piezoelectric response, also dependent on ceramic filler content, is |d33|= 29 pC/N, being obtained for the 10 wt% ceramic particle content film. It is also shown by piezoresponse force microscopy that higher ceramic particles are characterized by more stable ferroelectric domains. The composite has been successfully proved for its potential in heart rate monitoring applications, exhibiting high levels of precision as well as reliability. This work on heart rate sensing presents a material suitable for its incorporation into wearable gadgets, medical devices, and sports equipment, compatible with integration by printing technologies, enabling consumers to access immediate data relevant to their cardiovascular health.

The study of BMN cubic pyrochlores based multi-layer capacitors

The multi-layer ceramic capacitor (MLCC) is prepared with Bi1.5MgNb1.5O7 (BMN) pyrochlores, which has medium dielectric constant, large dielectric tunability, and especially the very small dielectric loss. The multilayer ceramic capacitors with Bi1.5MgNb1.5O7 as the dielectric material are prepared by a tape-casting method. The dielectric constant of the BMN thick film was observed to be superior to that of the bulk material, indicating its potential application in electronic devices. The increase in dielectric constant during the preparation of multilayer ceramic capacitors was explained by investigating the interdiffusion between the ceramic thick films and the electrodes. The BMN thick films and Ag0.7/Pd0.3 electrodes showed a dense microstructure and serial interfaces when sintering at 1050 °C for 1.5 h. The capacitor exhibited good temperature stability with a dielectric constant temperature coefficient of −249.94 ppm/°C, a relative dielectric constant of 216, and a dielectric loss of 0.00036. Provides insights for the development and optimization of high-performance dielectric tunable electronic device.

High thermal conductivity and low dielectric polyimide nanocomposites using diamine-assisted mechanochemical exfoliation boron nitride and in-situ polymerization under pressure

Advanced integrated circuit materials demand polymer composites with exceptional thermal conductivity and low dielectric constant to minimize power consumption and improve signal transmission. However, conventional methods of improving the thermal conductivity of composites by incorporating thermal conductive fillers result in an increase in dielectric constant, producing a huge challenge in simultaneously achieving enhanced thermal conductivity and low dielectric constant. Herein, a brick-and-mortar structure has been successfully constructed through in-situ polymerization of the diamine-assisted mechanochemical exfoliated (DAME) boron nitride (BN) with trifluoromethyl-containing PI and microporous polyhedral oligomeric silsesquioxane (POSS) under pressure. The DAME functionalized BNNS (f-BN) exhibit high aspect ratios, few lattice defects, high yields and excellent dispersion in the POSS/PI matrix. Notably, the obtained 40 wt% f-BN/POSS/PI nanocomposite exhibits a high in-plane thermal conductivity of 17.76 W m−1 K−1 with a 488% enhancement compared to 40 wt% hBN/POSS/PI, and simultaneously maintains low dielectric constant of 2.76 and low dielectric loss of 0.0042 at 1 MHz close to the pure POSS/PI matrix. Density functional theory is utilized to reveal the possible chemical reactions between f-BN and diamine, and the impacts of interfacial functionalization on the thermal conductivity and dielectric properties of nanocomposites are illustrated by molecular dynamics simulations. Furthermore, the DAME method demonstrates good universality among polyimide matrices, and shows excellent practical implementation as a thermal interface material and flexible printed circuit board. This material provides a promising solution for integrated circuits by successfully addressing the challenge of combining low dielectric constant and high thermal conductivity in microelectronic systems.

First-principles study on structural, electronic, and optical properties of mixed alloys of Cs2Ag(SbxBi1−x)Br6 double perovskites for optoelectronic applications

Halide perovskites have attracted promising capabilities of solar cells and light-emitting diode applications due to their high stability and optoelectronics performance. In this work, the effect of chemical substitution on the structural, electronics, and optical properties of mixed alloy Cs2Ag(SbxBi1-x)Br6 perovskites (when x is a mixing ratio varying from 0.0 to 1.0) was explored by using the virtual crystal approximation within the first-principle framework based on DFT-GGA, GGA-TB09, RPA, and BSE. Calculation results reveal that the lattice constant increases linearly as a function of the mixing ratio of a(x) = 11.246–0.0012x Å. These results satisfied the Vegard’s law as well as the reliability of virtual crystal approximation. The band structure calculated with and without the spin–orbit coupling was compared. Band gap of the mixed alloys are lower than that of pure Sb or pure Bi compounds. The band gap increases as a quadratic function of Eg = 2.07 – 0.279x – 0.121x2 eV. The smaller band gap of the mixed alloy results from the energy mismatch between Sb and Bb s and p orbitals. Calculations from DFT-TB09 are in good agreement with experimental results. Blue-shifted absorption spectra to the ultraviolet region were found when the Sb content increased. A linear increase of the static dielectric constant was found when the Sb content increased as a function of εs(x) = 2.849 + 0.266x. BSE@PBEsol calculations are consistent with experimental profiles. Calculation results indicate that the mixed alloy Cs2Ag(SbxBi1-x)Br6 can be tuned regarding its electronic and optical properties.

Using the modified Pitzer model to analyze the solubilities of sodium and potassium halides in aqueous mixtures of amides (Formamide, N-methylformamide and N-Methylacetamide) at T = 298.15 K

In this work the solubilities of the potassium halides (KCl, KBr, and KI) in solvent mixtures water-amide (Formamide, N-Methylformamide, and N-Methylacetamide), were measured at temperature T = 298.15 K. These data along with those previously measured in another work for the corresponding sodium halides (NaF, NaCl, NaBr, and NaI), in the same solvent mixtures and at the same temperature, were correlated using the modified Pitzer model. The calculated solubility data are in good agreement with the experimental data for all systems over a wide range of co-solvent concentration. The solubility of a given potassium (or sodium) halide decreases with the weight percentage of the co-solvent due to the solventing-out effect. For all ternary systems, it was found that by changing the amide in the order (FA, NMF, and NMA), the dielectric constant increases and the density decreases, influencing these properties with a decrease in the solubility of the salt. The maximum crystallization yields were determined for an extractive crystallization process with different amides at T = 298.15 K, which also demonstrated the usefulness of the modified Pitzer model in the simulation of separation processes of inorganic salts.

ДЖОНШЕРОВСКИЙ УНИВЕРСАЛЬНЫЙ ДИНАМИЧЕСКИЙ ОТКЛИК В ТОНКИХ ПЛЕНКАХ ПОЛИДИФЕНИЛЕНФТАЛИДА

It is known that the supramolecular structure of organic materials can have a significant effect on the conductivity of polymer films in both constant and alternating fields. In particular, the presence of associative supramolecular formations can lead to a significant increase in the local dielectric constant. At the same time, the presence of different types of supramolecular ordering can lead to the predominance of certain charge transfer mechanisms in polymer films, and, consequently, to the presence of a dependence of conductivity on the electric field strength. The degree of molecular ordering, both on the surface and in the bulk of a polymer film, can also have a significant effect on polarization. In this regard, studying the influence of the supramolecular structure on the conductivity of polymer films in an alternating electric field is an urgent task.Previously, using various methods, it was established that the supramolecular structure of films with a thickness of more than 300 nm is determined mainly by supramolecular formations of an associative structure. The structure of films with a thickness of 100 to 300 nm is determined by the mixed structure of globular and associative formations. The structure of films less than 100 nm thick is determined by supramolecular formations of a globular. It was also established by the method of thermally stimulated depolarization that three regions are observed on the dependence of the activation energy of capture centers on the thickness of the polymer film, corre- sponding to different supramolecular organizations.In this work, the dependence of the conductivity of poly (diphenylene phthalide) films in an alternating electric field in the low-frequency range from 0.1 to 106 Hz on the supramolecular structure of polymer films was studied. It was found that the type of dependence of the conductivity of polymer films on the frequency of an alternating field depends on the thickness and supramolecular structure of the polymer films, as well as the electric field strength. The applicability of the Jonsher’s model, which describes the conductivity of amorphous materials in an alternating electric field, for thin polymer films is discussed. A correlation between the power-law dependence index and the supramolecular structure of the polymer film and the influence of dipole polarization and injection of charge carriers into the bulk of the polymer film on the conductivity of the polymer film have been revealed.

Energy-storage performance of NaNbO3-based ceramic capacitor derived from a high DOP glass network structure

0.75(0.4Na2O-0.1K2O-0.5Nb2O5)-0.25(0.87SiO2-0.13BaO) glass-ceramics were prepared by a traditional melting method to optimize the crystallization kinetics. We obtained a glass network with high degree of polymerization (DOP) by crystallization at different temperatures and achieved a high energy storage density. The increase of crystallization temperature has promoted the precipitation of ferroelectric phases Na0.9K0.1NbO3 and NaNbO3 with high dielectric constant (1200–2000), promoted the increases of grain size from 0.76 μm to 1.33 μm, and reduced the gap width from 3.71eV to 3.22eV. When the crystallization temperature increased to 1000°C–1100 °C, Ba2NaNb5O15 with low dielectric constant (∼460) increases, grain boundaries appear, and dielectric constant and BDS decrease. Among all the samples, the sample crystallized at 900 °C showed homogeneous and dense microstructure (grain size∼0.91 μm). The experimental data confirmed that the glass sample crystallized at 900 °C achieves low dielectric loss (<0.005) and high dielectric constant (∼122). The glass sample crystallized at 900 °C sample had a maximum energy storage density of 3.65 J/cm3, a power density of about 54 MW/cm3 and a super-fast discharge speed of 38 ns at 660 kV/cm.

Glass fiber strengthened BNNS/ST/polyolefin composites with high dielectric constant and high thermal conductivity

The present research presents an examination of the consequential effects brought about by the introduction of short-cut E-glass fibers (GF) on the properties of high-dielectric constant, high-thermal conductivity microwave composite systems (xGF/(8-x)BNNS/78 wt%ST/polyolefin, x = 0-8 wt%, BNNS: hexagonal boron nitride nanosheets). The GF is modified using KH550, with the success of the surface modification definitively confirmed by X-ray Photoelectron Spectroscopy (XPS) and Fourier Transform infrared spectroscopy (FTIR). All components are found to exhibit consistently ultra-high and stable dielectric constants within the 8–12 GHz frequency range (Dk = 17.7–18.08). Based on thermogravimetry analysis (TGA) and dynamic mechanical analysis (DMA) results, the incorporation of modified GF improve the thermal stability of the composite materials, enhancing thermal decomposition temperature, residual carbon content and glass transition temperature. Furthermore, replacing BNNS with GF significantly amplifies the mechanical properties of the composite substrate. This substitution leads to a notable reduction in the coefficient of thermal expansion (CTE) in all directions while simultaneously increasing the bending and tensile strength. At the same time, the composites can maintain reasonably high thermal conductivity values. Overall, with a GF concentration of 4 wt%, the composite showcases an appreciable increase in dielectric constants (17.81), a high thermal conductivity (1.3 W/m·K) and enhances mechanical properties (cross-plane CTE: 15.44 μm/(m·°C), in-plane CTE: 26.06 μm/(m·°C), bending strength: 65.6 MPa, tensile strength: 17.42 MPa). Considering its superior performance metrics, the composite can be identified as an optimal choice for microwave composite dielectric substrate material.

Temperature Dependent Dielectric Properties Using Reflectrometric Technique of (Drumstick) Moringa oleifera Lam.

Abstract: The use of dielectric properties of agricultural products for sensing moisture in seeds and their powder form and their applications in microwave dielectric heating are discussed briefly. Values of dielectric properties of products in powder form are presented in tables and graphically to show the dependence of these properties on frequency, moisture content, and temperrature. Use of dielectric properties of Moringa oleifera Lam. For moisture measurement has been most prominent agricultural applications for such data. The results show that, there was a systematic increase in dielectric constant (ε') and loss factor (ε") with increasing values of relative packing fraction (δr) and decrease in dielectric constant and loss factor with increasing temperature. The moisture percentage measured by Thermo -gravimetric method. Experimental results of different relative packing fractions were further used to obtain transformation to 100% solid bulk using correlation equations of Landau-Lifshitz- Looyenga and Bottcher. The result shows that, there is a fair agreement between experimental values and theoretical values of different dielectric parameters.

Enhanced optical, dielectric, and non-Ohmic properties in Ta-doped Bi2/3Cu3Ti4O12 ceramics

In this paper, Ta-doped Bi2/3Cu3Ti4O12 (BCTO) ceramics are prepared by solid-state method. Phase structure, microstructure, optical, dielectric, and non-Ohmic properties of all samples are systematically investigated. Cu/Ta-rich phases at grain boundaries (GB) together with defects affect the microstructure, causing grain size and compactness to increase first and then decrease. Moreover, Ta doping increases the optical band gap of BCTO from 4.03 to 4.25 eV as well as the GB activation energy and GB barrier. An increase in dielectric constant (Ɛr), nonlinear coefficient (α) and breakdown field (Eb), and a decrease in the dielectric loss (tanδ) are observed in Ta-doped BCTO ceramics. The improvement in dielectric and non-Ohmic properties can be attributed to the internal barrier layer caused by GB Schottky barrier structure. In particular, Bi2/3Cu3Ti3.95Ta0.05O12 ceramic exhibits the high Ɛr of ∼45997 and the low tanδ of ∼0.035 at 10 kHz along with α of ∼5.62, and Eb of ∼3.45 kV/cm. The temperature-independent (-110-210 °C) dielectric response confirms that temperature stability of specimens increases with doping. These results suggest that improved optical, dielectric, and non-Ohmic properties in Bi2/3Cu3Ti4O12 can be achieved simultaneously via defect engineering.

Enhancement of dielectric properties of acrylic resin elastomer‐based composites with SiO2 loaded carbon nanotubes

AbstractThe inherent balance between dielectric constant and loss restricts the actual usage of dielectric elastomer actuators with high actuation strains, proposing a method that can break this trade‐off has been an urgent query. In this work, silica‐loaded carbon nanotubes (called SiO2@CNT) were prepared as dopants for acrylic resin elastomers (abbreviated as ARE) using the sol–gel method, and the obtained SiO2@CNT/ARE composites reached a dielectric constant of 282.5 at 100 Hz at a filler content of 3.22 vol%, which is 86 times higher than that of the pure ARE, whereas the dielectric loss remains at 0.17. The equilibrium between dielectric constant and loss is broken mainly based on the loading of SiO2 which inhibits the formation of carbon nanotube conductive network and concurrently reinforces the compatibility of the filler with ARE. Such a design offers a generalizable strategy for the subsequent preparation of polymer‐based composite films with excellent dielectric properties.Highlights Preparation of fillers with excellent dispersibility in the organic phase. The ARE‐based composites exhibit excellent dielectric properties at 100 Hz. The mechanism of increase in dielectric constant is explained using two models.

Micro-discharge in tortuous pores： “splitting-quenching” of primary ionization wave and the role of pre-ionization

Abstract Porous discharge has been widely studied recent years, however the discharge development inside the pores with complicated structure was little involved. In this paper, the discharge developments in vertical and tortuous pore are studied using a 2D fluid model established by COMSOL Multiphysics. The discharge develops symmetrically and bilaterally in vertical pore, and along the higher potential sidewall in tortuous pore, respectively. For tortuous pore, there are two pre-ionization process with negative and positive polarity successively, the latter one splits off from the former one and is in the form of multiple ionizing heads propagating simultaneously in string. The negative one can induce the primary discharge to deflect at the channel elbow joint in a “splitting-quenching” way or directly deflect it by bridging with it. For the postive one, the multiple ionizing heads can distort the electric field and short cut the potential and thus accelerate the primary discharge. Furthermore, the discharge can be enhanced deep inside the tortuous pore by the large number of seed electrons provided by pre-ionization. The influence of the dielectric constant is also studied, with the dielectric constant increases, the discharge can maintain bilateral morphology in tortuous pores for a deeper development distance.

Exploration of structural and dielectric properties of orthorhombic Ta2O5 nanoplatelets towards the potential optoelectronic devices

The dielectric characteristics of tantalum pentoxide (Ta2O5) nanostructures, synthesized by hydrothermal process, have been investigated in the temperature range of 80 K to 400 K and frequency range of 20 Hz to 2 MHz. X-ray diffraction (XRD) confirms the formation of highly crystalline and orthorhombic phase of the nanostructures sintered at 950 ºC. The electron microscope images reveal that the synthesized nanostructures change their morphology to nanoplatelets upon increasing the sintering temperature. Further, UV–visible absorbance, FTIR and Raman spectra of the synthesized nanostructures were obtained to investigate their optical properties. The experimentally obtained dielectric results indicate that both the dielectric constant (ε) and dielectric loss (D) values increase with increasing operating temperature. Also, the dielectric constant increases to 20 while the dielectric loss decreases to <0.025 at room temperature on increasing the sintering temperature. At 300 K and 1 kHz, the value of ε becomes almost twice that of as-synthesized nanostructures i.e. from 10 to 20 on increasing the sintering temperature to 950 ºC. The enhancement in dielectric constant can be justified by the thermally activated orientational and interfacial polarization associated with the increase in the grain size of the Ta2O5 nanoplatelets at higher sintering temperatures. Furthermore, the frequency dependence of ε indicates the high effect of the distribution of relaxation time in the Ta2O5 nanoplatelets at lower frequencies. Overall, this study provides a better understanding of the structural and dielectric behaviour of Ta2O5 nanostructures in correlation with varying sintering temperature. The results suggest that the orthorhombic Ta2O5 nanoplatelets have potential applications as alternative dielectric materials in various electronic and optoelectronic devices.

The Effect of Water Content on Engine Oil Monitoring Based on Physical and Chemical Indicators.

Engine oil oxidation is one of the major reasons for oil aging which can result in variations in the physical and chemical properties of oil. Organic acids generated by oil oxidation can react with water to form inorganic acids and acidic substances (including organic and inorganic acids) that corrode engine parts, resulting in the generation of rust or damage to engine parts. This is one of the important reasons why oil should be regularly changed. One of the most commonly applied methods for judging the aging degree of engine oil is monitoring its acid number (AN). However, generally, the effect of oil water content on acid value measurement is not considered. When oils are used in engines, they are often contaminated by water due to condensation, which accelerates engine oil aging. Therefore, it is crucial to explore the water content effect on AN in the process of engine oil aging. In this research, a water content sensor was applied to characterize moisture content in oxidized oil samples. The sensor could also obtain oil sample electrical conductivity which corresponded to its dielectric constant. Using a mid-infrared spectrometer to measure oil sample AN at this point to obtain the variation in AN with oxidation time, oil sample AN was connected in series with the water content, dielectric constant and electrical conductivity. These parameters were monitored through sensors, and the effect of water content on AN was studied. Experimental results revealed that with the increase in oxidation time, the water content, electrical conductivity, dielectric constant increase and AN of oil were increased. At the same time, since the temperature had a greater effect on electrical conductivity, the application of an air-conditioned constant-temperature environment removed the effect of temperature change on electrical conductivity.

Influence of Congored on the Optical, Dielectric and Thermal Behavior of Polymethyl Methacrylate and Polyvinyl Chloride

Polymethyl methacrylate (PMMA)/Congo Red (CR) and polyvinyl chloride (PVC)/CR composite films were prepared on optical glass by the drop method for optical measurements and also prepared as tablets under pressure for dielectrical measurements. The optical transmission spectra measurements for PMMA and PVC film doped with CR showed a highly absorption in the ultraviolet-visible (UV-Vis) optical range (at 353 nm and 518 nm) and considerably blocking in broad visible range (190 nm–640 nm). PMMA/CR and PVC/CR composite films containing congo red at a concentration of 1 wt% showed maximum absorption bands at 290 nm and 416 nm, but their transmittance percentages were reasonably reduced compared to those of pure PMMA and PVC. Both of composites indicated high transmittances between 640 nm and 800 nm. The optical constants of the PMMA/CR and PVC/CR composite films such as optical band energy gaps (Eg) estimated using Tauc’s model, refractive index and reflectance (%) were calculated. UV–Vis, Fourier transform infrared spectroscopy (FTIR) and Thermogravimetry Analysis (TGA) measurements were used to confirm the breakdown of the -N = N- azo group bonds attached to the aromatic ring as a result of thermal decomposition of CR at 500 °C, and it was suggested that N2 gas was eliminated from the CR above 360 °C. The dielectric plots showed that the dielectric constant increased when the CR is doped up to 70 wt% in the polymer matrices. A further increase in the doping concentration of CR resulted in an increase of the dielectric constant. The dielectric constant decreased with an increase in the frequency for all of the samples. The ac (alternating current) conductivity values of PMMA and PVC showed an increase with increasing CR dopant in the polymer composites, while the ac conductivity values were found to be values between those of the pure polymers and CR.

Effects of rare-earth Pr3+-Dy3+ doping on structural, magnetic, optical and dielectric properties of Zn2Y hexaferrite

This study was conducted to investigate the properties of Pr3+-Dy3+ doped Zn2Y-type hexaferrite for potential technological applications. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and field-emission scanning electron microscopy (FESEM) were used to analyze structural properties. The crystallite size in the synthesized samples varies between 57.54 and 68.57 nm. The vibrational bands at 400 and 600 cm−1, common to all hexaferrites, were confirmed through FTIR. The FESEM analysis reveals an agglomeration of magnetic grains and a decrease in the average grain size from 1.24 to 1.06 μm. The M-H loops show that, with x values of 0.0, 0.1, and 0.2, the saturation magnetization is determined to be 34.76, 34.23, and 32.52 emu/g, respectively. The corresponding coercivity values are 21.24, 30.39, and 33.99 Oe. UV–visible spectroscopy using Tauc theory reveals an increase in the optical band gap from 2.32 to 2.50 eV, indicating a tunable energy band structure by incorporating Pr3+-Dy3+ ions. The dielectric constant increases, whereas AC conductivity decreases with increased Pr3+-Dy3+ concentration. The obtained results suggest the potential suitability of these materials for various technological applications.