Variation Of Dielectric Permittivity Research Articles

Three-State Dielectric Switching within a Narrow Temperature Range in Isopropylammonium Lead Iodide, a One-Dimensional Perovskite with Polar Phase.

The phenomenon of dielectric switching has garnered considerable attention due to its potential applications in electronic and photonic devices. Typically, hybrid organic-inorganic perovskites, HOIPs, exhibit a binary (low-high) dielectric state transition, which, while useful, represents only the tip of the iceberg in terms of functional relevance. One way to boost the versatility of applications is the discovery of materials capable of nonbinary switching schemes, such as three-state dielectric switching. The ideal candidate for that task would exhibit a trio of attributes: two reversible, first-order phase transitions across three distinct crystal phases, minimal thermal hysteresis, and pronounced, step-like variations in dielectric permittivity, with a substantial change in its real part. Here, we demonstrate a one-dimensional lead halide perovskite with the formula (CH3)2C(H)NH3)PbI3, abbreviated as ISOPrPbI3, that fulfills these criteria and demonstrates three-state dielectric switching within a narrow temperature range of ca. 45 K. Studies on ISOPrPbI3 also revealed the polar nature of the low-temperature phase III below 266 K through pyrocurrent experiments, and the noncentrosymmetric character of the intermediate phase II and low-temperature phase III is confirmed via second harmonic generation measurements. Additionally, luminescence studies of ISOPrPbI3 have demonstrated combined broadband and narrow emission properties. The introduction of ISOPrPbI3 as a three-state dielectric switch not only addresses the limitations posed by the wide thermal gap between dielectric states in previous materials but also opens new avenues for the development of nonbinary dielectric switchable materials.

Structural and temperature dependent dielectric behaviour of BxFe(3−x)O4 nanoferrite particles

AbstractThe auto‐combustion technique was employed to synthesize nano particles of BxFe(3−x)O4 (x = 0.0, 0.7, 1.18, 1.36 and 1.54). The resulting structural and dielectric properties of the boron doped Fe3O4 were evaluated. XRD analysis confirmed the presence of a single spinel structure with crystallite dimensions ranging from 21.18 to 26.43 nm and lattice parameters of 8.211 to 8.487 Ǻ. The morphological images revealed homogenous and spherical grain sizes, while EDX confirmed the presence of constituent elements used. The X‐ray density increased whereas the bulk density and the porosity decreased with boron substitution. The study of dielectric properties and AC conductivity (σAC) was demonstrated and the AC conductivity decreased with increasing boron concentration, indicating a hopping mechanism. Moreover, noticeable variations in dielectric loss, AC conductivity, and dielectric permittivity with temperature and frequency were observed. These observations were attributed to the Maxwell–Wagner interfacial polarization and the hopping of charges between Fe3+ and Fe2+ ions.

Defect engineering in rare-earth-doped SrTiO3 ceramics: Route to colossal capacitance material up to X9R capacitor standard

With the advent of the electronic information era, capacitors have become a hot research topic due to their economic and strategic significance. Such microelectronic components play an irreplaceable role in important fields such as scientific research and military industries. Therefore, there is an urgent need to develop dielectric materials capable of withstanding more demanding conditions. In this work, a defect engineering method was incorporating Tm3+ rare earth ions into strontium titanate were proposed, resulting in a colossal dielectric permittivity, low dielectric loss, and excellent frequency and temperature stability. For the sample with x=0.01, the dielectric permittivity exceeds 345,804, the dielectric loss is below 0.011, and the dielectric permittivity variation within the temperature range from −55–200°C is less than 15%, which meets the ELA X9R capacitor standard (X: −55 °C, 9: +200 °C, R: Δεr ≤ ± 15%). The excellent performance is ascribed to the electron pinning defect dipole effect (EPDD) and internal barrier layer capacitor effect (IBLC), which is verified by XPS and impedance spectra. A deeper understanding of these mechanisms could help to reveal the origin of the colossal capacitance and thus contribute to the design of materials with colossal capacitance.

Enhanced energy storage and temperature-stable dielectric properties in (1-x)[(Na0.4K0.1Bi0.5)0.94Ba0.06TiO3]-xLa0.2Sr0.7TiO3 lead-free relaxor ceramics

With the continuous growth in sustainable and renewable technologies, ceramic capacitors are emerging as a promising energy storage device. Lead-free (1-x)[(Na0.4K0.1Bi0.5)0.94Ba0.06TiO3]-xLa0.2Sr0.7TiO3 (0 ≤ x ≤ 0.40) ceramics were prepared using the solid-state reaction technique for obtaining relaxor characteristics with improved energy storage density, efficiency, and temperature stability of dielectric permittivity. A high recoverable energy density (Wr) ∼ 2.39 J/cm3 with a good efficiency (η) of ∼ 75.21% was obtained for x = 0.30 composition under 220 kV/cm applied field. The specimen x = 0.30 exhibited excellent fatigue resistance during 105 cycles and good temperature stability of energy storage characteristics (Wr > 0.87 J/cm3, η > 74%) in the temperature range of 25–180 °C under 100 kV/cm. In addition, the temperature range in which the dielectric permittivity variation was less than ±15% was very wide (204 °C (63–267 °C) and 275 °C (39–314 °C) for x = 0.30 and 0.20 specimens, respectively). Significant improvements in material performance were attributed to A-site engineering, which resulted in a mixture of P4bm and R3c polar nano regions (PNRs), leading to reduced hysteresis loss and temperature-stable dielectric permittivity. Additionally, the size of PNRs ranged between 3 and 6 nm, with the P4bm phase dominating in the x = 0.30 specimen, leading to a large maximum polarization under an applied electric field. Therefore, (1-x)[(Na0.4K0.1Bi0.5)0.94Ba0.06TiO3]-xLa0.2Sr0.7TiO3 relaxor ceramics are promising for high energy density materials and electronic applications requiring high permittivity stability over a wide temperature range.

Magnetoelectric behaviour of Pb-free Na0.5Bi0.5TiO3-Ni0.5Co0.5Fe2O4 particulate novel ceramic composites

Magnetoelectric (ME) multiferroic composites are more promising candidates for low-power consumption devices, next-generation spintronic devices, and multistate memory devices since they exhibit significantly higher Magnetoelectric interaction over single-phase multiferroics. In this regard magnetic behaviour, dielectric, and magnetoelectric characteristics of a novel Pb-free (1-x) Na0.5Bi0.5TiO3-(x) Ni0.5Co0.5Fe2O4, (x = 0, 0.2, 0.4, 0.6, 0.8 & 1) particulate composites were explored. Solid-state synthesis was adopted to prepare the single-phase Na0.5Bi0.5TiO3 (NBT), Ni0.5Co0.5Fe2O4 (NCFO), and their composites. The presence of rhombohedral NBT and cubic inverse spinel NCFO in the composites were confirmed with X-ray diffraction (XRD) patterns. Microstrain (ε) induced in the prepared samples was estimated by using the Williamson-Hall (W-H) method. The piezoelectric NBT phase shows the tensile strain and the ferromagnetic NCFO shows the comprehensive strain. Among all the composites 0.8NBT-0.2NCFO shows a higher strain value of 0.012%, and the decrement in the strain values was observed upon increases in ferrite concentration. Backscattered scanning electron microscope (BS-SEM) images revealed the existence of highly dense uniformly distributed elements and Energy dispersive spectroscopy (EDS) confirmed the existing elements in the composites. UV–vis absorbance spectra disclosed a rise in energy gap values from 1.14 eV to 3.0 eV with increasing NBT percentage. Variations of dielectric permittivity and dielectric loss with respect to AC frequency were studied at room temperature (RT), and the 0.2NBT-0.8NCFO sample shows a high dielectric permittivity of 8500 at ∼100Hz. M − H (Magnetization-Magnetic field) hysteresis loops demonstrate the pure ferrite phase has a coercive field (Hc) = 578 Oe, remnant magnetization (Mr) = 21.43 emu/g and saturation magnetization (Ms) = 71.29 emu/g. The Ms and Mr values in the composites are enhanced with increasing ferrite percentage. Studies on ME behaviour of (1-x) NBT-(x) NCFO, (x = 0.2,0.4,0.6 & 0.8) show the coupling effect between both the phases at room temperature and the highest coupling coefficient value 3.16mV/Cm. Oe was observed for the 0.8NBT-0.2NCFO further the reasons and mechanisms are discussed.

Nature of Overcharging and Charge Inversion in Electrical Double Layers.

Understanding overcharging and charge inversion is one of the long-standing challenges in soft matter and biophysics. To study these phenomena, we employ the modified Gaussian renormalized fluctuation theory, which allows for the self-consistent accounting of spatially varying ionic strength as well as the spatial variations in dielectric permittivity and excluded volume effects. The underlying dependence of overcharging on the electrostatic coupling is elucidated by varying the surface charge, counterion valency, and dielectric contrast. Consistent with simulations, three characteristic regimes corresponding to weak, moderate, and strong coupling are identified. Important features like the inversion of zeta potential, crowding, and ionic layering at the surface are successfully captured. For weak coupling, there is no overcharging. In the moderate coupling regime, overcharging increases with the surface charge. Finally, in the strong coupling regime, ionic crowding and saturation in overcharging are observed. Our theory predicts a nonmonotonic dependence of charge inversion on multivalent salt concentration as well as the addition of monovalent salt, in quantitative agreement with experiments.

Ultrahigh thermal stability of dielectric permittivity in 0.6Bi(Mg1/2Ti1/2)O3–0.4Ba0.8Ca0.2(Ti0.875Nb0.125)O3

0.6Bi(Mg1/2Ti1/2)O3–0.4Ba0.8Ca0.2(Nb0.125Ti0.875)O3 ceramics with a pseudo-cubic structure and re-entrant dipole glass behavior have been investigated via x-ray diffraction and dielectric permittivity–temperature spectra. It shows excellent dielectric–temperature stability with small variations of dielectric permittivity (±5%, 420–802 K) and dielectric loss tangent (tanδ < 2.5%, 441–647 K) in a wide temperature range. Three dielectric anomalies are observed from 290 to 1050 K. The low-temperature, weakly coupled re-entrant relaxor behavior was described using the Vogel–Fulcher law and the new glass model. The mid- and high-temperature dielectric anomalies are characterized by isothermal impedance and electrical modulus. The activation energy of both dielectric relaxation and conductivity follows the Arrhenius law in the temperature ranges of 633–753 and 833–973 K, respectively. The ultrahigh thermal stability of dielectric permittivity is attributed to the weak coupling of polar clusters, the formation of diffuse phase transition, and the local phase transition of calcium-containing perovskite. The results provide new insights into the defects behavior and the modification way of re-entrant relaxor behavior.

Synthesis, crystal structure, thermal, spectroscopic and dielectric properties of partial substituted hybrid compound: (C6H5NH3)2[Cd1.44Zn0.06Cl5

A novel partial substituted (C6H5NH3)2[Cd1.44Zn0.06Cl5] organic–inorganic hybrid compound was grown by slow evaporation method at room temperature and characterized by Infra-red spectroscopy and Raman scattering, single crystal X-ray diffraction (SC-XRD), room temperature RT-XRPD and variable temperature (VT-XRPD) X-ray powder temperature, thermal properties (TGA and DSC) and dielectric permittivity. SC-XRD illustrates that the studied material belongs to the centrosymmetric orthorhombic space group Pcab with the following cell parameters: a = 7.4013(16)Å, b = 19.290(4)Å, c = 24.402(5)Å, Z = 8. The atomic arrangement of the crystal structure is described as inorganic infinite layers between wich organic cations are intercalated. Its structure provided a new interesting example of infinite two-dimensional inorganic layers built up [Cd/Zn1.5Cl5]n-2n octahedral following the c→ crystallography direction. The crystal packing is governed by non-covalent interactions such as hydrogen bonds and Columbic interactions (cations-anions), forming a three dimensional supramolecular network. The intermolecular interactions were studied by Hirshfeld surface analysis and 2D fingerprint plots. RT-XRPD proves that the crystalline material is pure. Differential scanning calorimetry (DSC) analysis reveals that the studied material undergoes one phase transition of order–disorder type around 59 °C. VT-XRPD and dielectric measurements were performed in the aim to confirm and to discuss the mechanism of phase transition.

Influence of Cr-ion substitution on the magnetization and dielectric properties of the frustrated Ca3CoMnO6 compound

The Cr-doped Ca3CoMn1-xCrxO6 (x=0, 0.05, 0.1, 0.15) polycrystalline samples were prepared using a modified sol-gel method. The structural, magnetic and dielectric properties were systemically investigated. With increasing Cr3+-doping level, the partial Co2+ ions change to Co3+, leading to a decreased lattice volume. Correspondingly, the length of the short-range magnetic correlation is inhibited and a faster dynamic behavior in time dependent magnetization is found. At the benefit of the magnetic structural changes with the introduction of Cr3+ ions, the relaxor degree of the ferroelectric transition that induced by the exchange striction becomes lower, while the activation energy of the frozen polar-nanoregions increases. The replacement of Mn4+ by Cr3+ also leads to a reduced intra-chain antiferromagnetic coupling and the emergence of Co3+-Co3+ ferromagnetic interaction. As consequence, the Curie-Weiss temperature (θ) increases monotonously. The variation in dielectric permittivity with magnetic field confirms the existence of large magnetodielectric coupling in the Ca3CoMn1-xCrxO6 (0 ​≤ ​x ​≤ ​0.15) samples. Especially for the x ​= ​0.15 sample, the permittivity changes by about 7% under the magnetic field of H=4 ​T.

Coupling Dielectric Functionality with Magnetic Properties in Coordination Metal Complexes.

Significant research has been conducted on molecular ferroelectric materials, including pure organic and inorganic compounds; however, studies on ferroelectric materials based on coordination metal complexes are scarce. Ferroelectric materials based on coordination metal complexes have tunable structures and designs, with coexistence or synergy between the ferroelectric behavior and magnetic properties. Compared to inorganic compounds, few coordination metal complexes exhibit coupling between the magnetic and dielectric properties. Coordination metal complexes with strong coupling between the magnetic and dielectric properties exhibit dielectric permittivity variations under external magnetic fields. Therefore, they have attracted substantial interest for their potential use in magnetoelectric devices. In this review, we discuss recent advances in coordination metal complexes, that exhibit coupled magnetic functionalities and ferroelectricity or dielectric properties, including single-molecule magnets, electron delocalization systems, and external stimuli responsive compounds.

Microwave Cavity Sensor for Measurements of Air Humidity under Reduced Pressure.

A high-sensitivity sensor for measuring moisture content in the air or air humidity under low pressure was designed on the basis of a half-wave coaxial microwave cavity. The method of measuring small variations in the signal phase at a cavity excitation frequency of 1.63 GHz was applied to detect low densities of water vapor. It allows the detection of variations in dielectric air permittivity in the seventh decimal place. A prototype of the sensor was tested in a vacuum chamber. It was calibrated by comparing the test results with the readings of a commercial pressure gauge and using the independent method of measuring the moisture content in rarefied air on the basis of the absorption of millimeter waves in the local line of water vapor at 183 GHz. The developed sensor can be used in laboratory experiments and full-scale geophysical research in the atmosphere onboard various aircrafts.

Исследование зависимости диэлектрической проницаемости дражируемой массы от размеров драже

The pellet size can be determined without stopping the shell build-up by the dielectric permittivity of the pellet mass. To confi rm this hypothesis, mathematical expressions describing the relationships between the amount of materials of the pellet shell, pelleted objects and air have been compiled and analysed. During theoretical study of the shell build-up, assumptions were made on simultaneous increase in diameter of the pellet objects and on spherical shape of the formed pellets. The authors made calculations using the example of fl at electrodes with the pellet mass placed between them. The pellet mass is treated as a material substance that fi lls the space between the electrodes and has a variable dielectric permittivity. It was found that increasing the pellet size leads to a decrease in the dielectric permittivity of the pelleted object structure. The dielectric permittivity of the medium is proved to be a function of the object diameter that depends on the number of objects between the plates. The identifi ed relationship was used to obtain information about the shell build-up in a continuous mode. Under production conditions, the dielectric permittivity of the pellet mass may be measured by the value of alternating electric current fl owing through the medium under analysis.

Relative Dielectric Permittivity Variations during Compaction as a Mean of Compaction Quality Control: Case Study on Laterite Samples from Senegal

This study explores an alternative to the classical use of direct methods, as water content and dry density measurements, for compaction quality control. For this purpose, the dielectric properties of lateritic materials are determined by radar method and are compared with the permittivity determined from the Topp formula and from the CRIM model. This approach allowed to establish a relationship between the geotechnical properties determined during compaction such as dry density, water content or porosity with dielectric permittivity. The obtained results made it possible to determine an optimum dielectric permittivity corresponding to the optimum dry density and the optimum water content that could be used for non-destructive in situ compaction testing. Such an approach should improve the implementation and effectiveness of in situ compaction quality control of geotechnical infrastructures.

Dielectric, optical and absorption studies of f-MWCNTs dispersed nematic liquid crystal

Dielectric, conductivity, birefringence and UV-Vis spectral studies for functionalized multiwalled carbon nanotubes (f-MWCNTs) dispersed 4-methoxybenzylidene-4’-butylaniline (MBBA) liquid crystalline sample have been carried out. The variation of dielectric permittivity, relaxation loss factor and conductivity as a function of frequency for f-MWCNTs dispersed MBBA and pure MBBA sample has been reported. Relative permittivity value increases with the doping of MWCNT due to the π-π* interactions between host and dispersed molecules and local anchoring fields developed along the nematic director that collectively amplify the orientational order. The conductivity of the dispersed sample increased as f-MWCNTs concentration in pure MBBA sample increases. In the tan delta analysis, a variation in relaxation frequencies was observed for dispersed sample due to enhanced dielectric anisotropy. UV-Vis absorbance analysis reveals that after doping MWCNTs into pure NLC, the absorbance has increased. The birefringence was determined for both pure and dispersed systems, and an increase in its value for both dispersed systems has been reported.

Detection of hydrocarbon spills by means of a coaxial impedance dielectric sensor

Leakages from storage tanks or pipes frequently produce pollution of soils and groundwater reservoirs by hydrocarbons. Common practices for monitoring and characterising site contamination involve soil drilling, sampling and chemical analysis, complemented with geophysical surveys. This study evaluates the presence of paraffin oil inside soil pores by means of dielectric permittivity measurements, using a coaxial impedance device in laboratory-scale models. The real dielectric permittivity of unsaturated sand is measured before, during and after a contamination process. Monitoring small variations in real dielectric permittivity allows detection of the partial replacement of air (κ′ = 1) by paraffin oil (κ′ ≈ 2) in soil pores. These variations in soil dielectric properties enable pollution levels to be assessed, knowing in advance the κ′ of the soil at the initial stage and measuring the influence of oil and water content on κ′. The technique proposed can also be used for monitoring the lateral extension of a contaminant plume and can be successfully applied at the laboratory scale for oil leakage detection by periodically monitoring changes in the soil dielectric permittivity.

Experimental Study on the Variation of Soil Dielectric Permittivity under the Influence of Soil Compaction and Water Content

The dielectric permittivity of common soils is mainly controlled by water content and porosity, while the latter is closely related to the characteristics of compaction. By studying the changes in dielectric permittivity of soil samples with different soil water content and compaction levels, the influence of the controlling factors on the relationship model between soil water content and dielectric permittivity can be evaluated. In this paper, network analyzer was used to measure the dielectric permittivity of 7 groups of soil samples with gravimetric water content ranging from 8.09% to 14.52% and dry density ranging from 1.61 g/cm3 to 1.96 g/cm3. The results show that the dielectric permittivity increases with the increase of water content and dry density, and the effect of water content on permittivity is more significant for soils with higher dry density. Furthermore, when the water content is less than or equal to the optimal water content, Topp formula and the complex refractive index model (CRIM) can better predict the soil dry density. When the water content approaches the saturated state of soil, there is a deviation between the predicted value and the actual value. At last, the modified Topp formula and the complex refractive index model (CRIM) can accurately predict soil compactness. This provides an important basis for rapid detection of water content and compactness of highway subgrade soil by ground penetrating radar.

Effect of Dielectric Saturation on Ion Activity Coefficients in Ion Exchange Membranes.

Polymeric ion exchange membranes are used in water purification processes to separate ions from water. The distribution and transport of ionic species through these membranes depend on a variety of factors, including membrane charge density, morphology, chemical structure, and the specific ionic species present in the fluid. The electrical potential distribution between membranes and solutions is typically described using models based on Donnan theory. An extension of the original theory is proposed to account for the nonideal behavior of ions both in the fluid and in the membrane as well to provide a more robust description of interactions of solutes with fixed charge groups on the polymer backbone. In this study, the variation in dielectric permittivity in the membrane medium with electric field strength is taken into account in a model based on Gouy–Chapman double-layer theory to provide a more accurate description of ion activity coefficients in an ion exchange membrane. A semianalytical model is presented that accounts for the variation in dielectric permittivity of water in a charged polymer membrane. A comparison of this model with Manning’s counterion condensation model clearly demonstrates that by incorporating changes in water dielectric permittivity with electric field strength, much better agreement with experiments can be obtained over a range of salt concentrations for different ions.

Single-slice microwave imaging of breast cancer by reverse time migration.

Microwave imaging of breast cancer is considered and a new microwave imaging prototype including the imaging algorithm, the antenna array, and the measurement configuration is presented. The prototype aims to project the geometrical features of the anomalies inside the breast to a single-slice image at the coronal plane depending on the complex dielectric permittivity variation among the tissues to aid the diagnosis. The imaging prototype uses a solid cylindrical dielectric platform, where a total of 24 optimized Vivaldi antennas are embedded inside to form a uniform circular antenna array. The center of the platform is carved to create a hollow part for placement of the breast and the multistatic, microwave scattering parameters are collected with the antenna array around the hollow center. The dielectric platform further enhances the microwave impedance matching against the breast fat tissue and preserves the vertical polarization during the measurements. In the imaging phase, a computationally efficient inverse electromagnetic scattering method-reverse time migration (RTM)-is considered and adapted in terms of scattering parameters to comply with the actualmeasurements. The prototype system is experimentally tested against tissue-mimicking breast phantoms with realistic dielectric permittivity profiles. The reconstructed single-slice images accurately determined the locations and the geometrical extents of the tumor phantoms. These experiments not only verified the microwave imaging prototype but also provided the first experimental results of the imagingalgorithm. The presented prototype system implementing the RTM method is capable of reconstructing single-slice, nonanatomical images, where the hotspots correspond to the geometrical projections of the anomalies inside the breast.

On the Maxwell-wave equation coupling problem and its explicit finite-element solution

It is well known that in the case of constant dielectric permittivity and magnetic permeability, the electric field solving the Maxwell’s equations is also a solution to the wave equation. The converse is also true under certain conditions. Here we study an intermediate situation in which the magnetic permeability is constant and a region with variable dielectric permittivity is surrounded by a region with a constant one, in which the unknown field satisfies the wave equation. In this case, such a field will be the solution of Maxwell’s equation in the whole domain, as long as proper conditions are prescribed on its boundary. We show that an explicit finite-element scheme can be used to solve the resulting Maxwell-wave equation coupling problem in an inexpensive and reliable way. Optimal convergence in natural norms under reasonable assumptions holds for such a scheme, which is certified by numerical exemplification.

ITO film stack engineering for low-loss silicon optical modulators

The Indium Tin Oxide (ITO) platform is one of the promising solutions for state-of-the-art integrated optical modulators towards low-loss silicon photonics applications. One of the key challenges on this way is to optimize ITO-based thin films stacks for electro-optic modulators with both high extinction ratio and low insertion loss. In this paper we demonstrate the e-beam evaporation technology of 20 nm-thick ITO films with low extinction coefficient of 0.14 (Nc = 3.7·1020 cm−3) at 1550 nm wavelength and wide range of carrier concentrations (from 1 to 10 × 1020 cm−3). We investigate ITO films with amorphous, heterogeneously crystalline, homogeneously crystalline with hidden coarse grains and pronounced coarsely crystalline structure to achieve the desired optical and electrical parameters. Here we report the mechanism of oxygen migration in ITO film crystallization based on observed morphological features under low-energy growth conditions. Finally, we experimentally compare the current–voltage and optical characteristics of three electro-optic active elements based on ITO film stacks and reach strong ITO dielectric permittivity variation induced by charge accumulation/depletion (Δn = 0.199, Δk = 0.240 at λ = 1550 nm under ± 16 V). Our simulations and experimental results demonstrate the unique potential to create integrated GHz-range electro-optical modulators with sub-dB losses.