Dielectric Theory Research Articles

A non-classical theory of elastic dielectrics incorporating couple stress and quadrupole effects: part II - variational formulations and applications in plates

A new Mindlin plate model is developed incorporating the couple stress, quadrupole, and curvature-based flexoelectric effects using a non-classical elastic dielectric theory. The general governing equations and complete boundary conditions are derived simultaneously through a variational approach. The new general plate model includes the model for centrosymmetric materials as a special case. As direct applications of the new plate and to illustrate the flexoelectric effect, the static bending and free vibration problems of a simply supported rectangular plate are analytically solved by directly applying the new centrosymmetric model. The numerical results reveal that the flexoelectric effect is present in centrosymmetric materials and is important when the plate thickness is very thin. The dispersion relations for flexure and fundamental shear modes are obtained. We find electrostatic wave also propagates with the flexure or fundamental shear waves by flexoelectric coupling. The present work can be seen as an extension of mechanical analysis of plate structures with couple stress effects and may be useful to the devices design of micro- or nano-sized objects.

Perspective on scalable high-energy-density polymer dielectrics with ultralow loadings of inorganic nanofillers

Polymer composite dielectrics have been actively developed for electrical power and electronic applications. The latest advances in dielectric polymer composites with ultralow (<1 vol. %) filler loadings have overcome many of the significant drawbacks of polymer composites. Such composites now offer opportunities of gleaning insights into the impact of interfaces on dielectric behaviors and developing dielectric mathematical theories and models with the interface contributions. In this Perspective, we review key developments in the dielectric polymer composites with ultralow contents of small-sized fillers. We highlight the filler–polymer interface characterizations and the current understandings of the underlying mechanisms and examine the dielectric models in order to fit the dielectric data over a wide range of filler contents. We also discuss challenges and opportunities for the polymer composites with ultralow filler loadings in the development of scalable high-energy-density dielectrics.

Dielectric Properties of Textile Materials: Analytical Approximations and Experimental Measurements—A Review

Deciphering how the dielectric properties of textile materials are orchestrated by their internal components has far-reaching implications. For the development of textile-based electronics, which have gained ever-increasing attention for their uniquely combined features of electronics and traditional fabrics, both performance and form factor are critically dependent on the dielectric properties. The knowledge of the dielectric properties of textile materials is thus crucial in successful design and operation of textile-based electronics. While the dielectric properties of textile materials could be estimated to some extent from the compositional profiles, recent studies have identified various additional factors that have also substantial influence. From the viewpoint of materials characterization, such dependence of the dielectric properties of textile materials have given rise to a new possibility—information on various internal components could be, upon successful correlation, extracted by measuring the dielectric properties. In view of these considerable implications, this invited review paper summarizes various fundamental theories and principles related to the dielectric properties of textile materials. In order to provide an imperative basis for uncovering various factors that intricately influence the dielectric properties of textile materials, the foundations of the dielectrics and polarization mechanisms are first recapitulated, followed by an overview on the concept of homogenization and the dielectric mixture theory. The principal advantages, challenges and opportunities in the analytical approximations of the dielectric properties of textile materials are then discussed based on the findings from the recent literature, and finally a variety of characterization methods suitable for measuring the dielectric properties of textile materials are described. It is among the objectives of this paper to build a practical signpost for scientists and engineers in this rapidly evolving, cross-disciplinary field.

Authentic Intelligent Machine for Scaling Driven Discovery: A Case for Chiral Quantum Dots.

The scaling laws have long been used as evidence of science where many fundamental physics laws emerge. As emerging nanomaterials, quantum dots are also sensitive to scaling because of their strong size effect. In this work, we developed the chiral dielectric theory based on the exciton absorption mechanism to explain the increment of the dielectric constant from chirality via its dimensionality. To help researchers discover and develop scaling relevant theories, the Authentic Intelligent Machine (AIM) protocol was developed to generate and interpret experimental data in an analytical and scaling-oriented manner. We show how the AIM protocol interprets spectra such as transient absorption data of chiral quantum dots with theories, where discrepancies concerning the dielectric constant were discovered. Examples for applying the AIM protocol on other spectra, such as absorption spectra and photoluminescence spectra, are also given.

A rationale for non-linear responses to strong electric fields in molecular dynamics simulations.

Many approaches for calculation of the field-dependent electric properties of water solutions rely on the Onsager and Kirkwood theories of polar dielectrics. Such basic theories implicitly consider the electric field intensity to fulfill the so-called 'weak field conditions', i.e. to produce a linear response in the system. In this work we made use of molecular dynamics simulations to investigate possible non-linear effects induced by high intensity electric fields, specifically continuous wave bursts with nanosecond duration, comparing them with the ones predicted by the theory. We found that field intensities above 0.15 V nm-1 produce remarkable nonlinear responses in the whole 100 MHz-100 GHz frequency window considered, with the onset of higher order polarization signals, which are the clear fingerprint of harmonic distorsions. That non-linear response turned out to depend on the considered frequency. We finally show that MD outcomes are consistent with a modelization based on an extended formulation of the Langevin function including a frequency-dependent parameter.

Decomposition analysis on the excitation behaviors of thiazolothiazole (TTz)-based dyes via the time-dependent dielectric density functional theory approach.

Thiazolothiazole (TTz)-based materials have been attracting much attention because of their widespread applications. In this paper, we discuss the excited electronic behaviors of asymmetric TTz dyes in solvents based on the time-dependent dielectric density functional theory method. Based on dipole moment and charge distribution (population) analyses, we discuss large intramolecular electron transfers, which are triggered by photon excitations, toward the acceptor part of dyes. In addition, we explore the contributions of geometrical changes and solvent reorientations (reorganizations) to the solvatofluorochromic phenomena based on a decomposition technique. The decomposition analysis shows that the solvent reorientation effect mainly contributes to changes in the fluorescent spectra in response to solvents.

The Charge Transfer Band as a Key to Study the Site Selection Preference of Eu3+ in Inorganic Crystals.

On account of the strong oxidizing property of the europium(III) ion, its charge transfer band (CTB) can be easily formed in many inorganic compounds. In this work, the Eu3+ ions were singly doped into the K3LuSi2O7 compound with a hexagonal structure, and two kinds of Eu3+-O2- CTBs were detected by monitoring at specific wavelengths. The qualitative analysis of Eu3+ ion site occupation was illuminated by combining Eu3+-O2- CTBs with the corresponding cell volume. Furthermore, the two kinds of Eu3+ sites are eventually assigned to the K(2) and Lu sites, which means that Eu3+ ions selectively occupy the site with a low coordination number, according to the calculated CT energy by the dielectric theory of complex crystals and the magnitude of CT energy in the excitation spectra. Meanwhile, at high temperatures, the CTB does not show the traditional thermal quenching like f-f transitions but demonstrates thermal enhancement; thus, by using this opposite variation in excitation spectra, a noninvasive optical thermometer is presented, and this opposite variation tendency is thought to be the difference of thermal stability of disparate excited energy states. When new luminescent phosphors are designed with interesting spectral properties, this work will give us an alternative approach to determine the site occupation preference of Eu3+, especially when there are more than two different sites in the compound.

On the role of the energy loss function in the image force on a charge moving over supported graphene

We use a dielectric response theory to describe electrodynamic forces on a charged particle moving parallel to a supported two-dimensional layer. Using a Kramers–Kronig relation, we show that the image force on the particle can be expressed in terms of the energy loss function of the target materials. This enables us to analyze the stopping and the image forces on the particle on equal footing in the frequency–momentum domain encompassing all the energy loss channels in the target. Using the example of a graphene layer on a silicon carbide substrate, we show that both the image and stopping forces can be decomposed into contributions coming from two modes arising from hybridization of the sheet plasmon in doped graphene and a transverse optical phonon in the substrate.

Liquid metal elastomer with flytrap-inspired pillar structure for stress sensing

Flexible and soft capacitive stress sensors are widely used in soft robotics, electronic skins, and human-computer interfaces due to their desirable properties of temperature independence, low energy consumption, and good stability. Increasing the dielectric constant of the dielectric layer of capacitive sensors can effectively improve the sensitivity of the sensor. Mixing materials such as carbon nanotubes and ceramics into the elastomer can increase the dielectric constant, but stiffens the resulting composite. Liquid metals (LMs) are inherently soft and can be mixed with elastomers to produce liquid metal elastomers (LMEs). However, the LME slab is hard to compress, which limits the sensitivity of LME-based stress sensors. The inner surfaces of the Venus flytrap are hair-like soft pillar called trigger hairs, which sense the mechanical stimulation, activating the closure of the Venus flytrap. The trigger hair inspires us to mimic the pillar structure, reducing the effective elastic modulus of the LMEs. Here, this work proposes a capacitive stress sensor based on an LME with flytrap-inspired pillar structure. Mixing LM particles into the elastomer increases the dielectric constant without stiffening the elastomer composite. The mechanism of the sensor is demonstrated through dielectric theory, experiments, and finite element modeling. The sensor has high sensitivity (1.061 kPa−1), large capacitance variation (2.73 pF) and high initial capacitance (2.57 pF). Additionally, the sensor can realize real-time monitoring of human movement and measure the wrist pulse, indicating the potential for various applications.

BEP-Like Correction of Nonequilibrium Thermodynamic Parameters of the Solvent-Assisted Reactions: The DFT and Ab Initio Study of Hydration, Peroxidation, and Enolization of Acetone and 1,1,1-Trifluoroacetone in Aqueous Solutions.

The mechanisms of enolization and reactions of nucleophilic addition to carbonyl compounds were analyzed by density functional theory (DFT) (PBE1PBE) and ab initio (DLPNO-CCSD(T)) level of theory using the interaction of water and hydrogen peroxide with acetone and 1,1,1-trifluoroacetone (TFA) as the reference reactions. The transition states of the studied reactions were localized within the integrated approach that includes both the dielectric continuum theory (polarizable continuum model (PCM)) and the cyclic or two-cluster explicit solvation models. The considered models provide proton transfer in the enolization, hydration, and peroxidation reactions by the Grotthuss mechanism. It is shown that the calculated activation parameters at a sufficiently high level of theory and a sufficiently flexible solvation model can be additionally refined using the Bell-Evans-Polanyi (BEP)-like correction (in a form of the Bell-Evans-Polanyi equation), which is linear scaling of the model potential energy surface according to the equilibrium parameters of the reference reaction (experiment or high-level calculation). Quite good correspondence of the corrected and reference activation parameters and the lower sensitivity of the calculation results to the choice of the solvation model indicate the high reliability of the proposed BEP-like correction technique.

Dielectric Susceptibility of Water in the Interface.

It has long been anticipated that dielectric constants of polar liquids are reduced in the interfacial layer. Recent experiments and computer simulations support these expectations. A strong reduction of the dielectric constant is found in the direction perpendicular to a planar substrate, while the parallel response is bulk-like. This Perspective highlights recent theoretical calculations and simulations with an eye on relating them to properties observable in the laboratory. The average interface dielectric constant computed from simulations connects to thin films experiments, but this cannot be extended to screening of charges. In contrast to dielectric theories where a single dielectric constant gauges both the polarization energy and screening, these two signatures of dielectric polarization diverge on the molecular scale. The reduction of the dielectric constant of water in thin films is currently viewed as a combined effect of geometric confinement imposed by the substrate and the reconstruction of water hydrogen bonds in the surface layer.

Effect of structure and orientation of incident carbon-cluster ions Cn+(n≤4) on secondary-ion emission induced by electronic excitation

We present experimental results that show the secondary-ion yield depends on the structure and orientation of incident cluster ions. A beam of carbon-cluster ions ${{\mathrm{C}}_{n}}^{+}$ ($n\ensuremath{\le}4$) with an energy of 0.9 MeV per atom, which were obtained from a tandem electrostatic accelerator, was incident on a glycine target deposited on a carbon foil. The structure and orientation of the cluster ions after passing through the target were determined by the Coulomb explosion imaging method, and the positive secondary ions were simultaneously measured by time-of-flight mass spectrometry. When looking at the orientation dependence of linear structured ${{\mathrm{C}}_{2}}^{+}, {{\mathrm{C}}_{3}}^{+}$, and ${{\mathrm{C}}_{4}}^{+}$ projectiles, parallel orientations with respect to the beam direction were found to enhance the secondary-ion yield compared with perpendicular orientations. Additionally, comparison of the structure dependence of ${{\mathrm{C}}_{3}}^{+}$ and ${{\mathrm{C}}_{4}}^{+}$ projectiles with linear and ring structures showed that the secondary-ion yield was larger for linear structures. Interestingly, there was a clear correlation between the secondary-ion yield and the deposited energy density in the cluster-ion track. The energy density was calculated with electronic stopping power for incident cluster ions using linear-response dielectric theory and the cross section of the track of the incident cluster considering its geometrical structure and orientation. These results suggest that the deposited energy density in the cluster-ion track is a key parameter in the secondary-ion emission process induced by swift cluster-ion impacts.

Simulation study on the electric field of HVDC-GIL based on the dynamic conductivity model subjected to different current-carrying capacities

In this paper, we propose a thermal-electric coupling model based on the dynamic conductivity model, which considering the charge-trapping process. The charge accumulation characteristic under different current-carrying capacities was also investigated. The saturation time of average charge density and the average temperature in the space are approximate, which could be concluded that the charge accumulation is accompanied by the establishment of a temperature field. When the current-carrying capacity reaches 3000 A, the maximum surface electric field of the basin insulator will continue to rise 14.2% compared with 1500 A. The charge migration and accumulation near the enclosure results in a greatly distorted electric field near the triple junction of the ground enclosure. This paper could offer theoretical insights from a dielectric charge transport theory and perspective to be helpful for the design of spacer in HVDC-GIL.

Analysis on the effect of polyetherimide on energy distribution of radio frequency heating of viscous sauce

Abstract Radio frequency (RF) sterilization of low-moisture, high-oil, high-protein, and viscous sauces for instant food (LHHVS) demonstrates many advantages, but uneven heating is a main problem that must be addressed. Main factors that affect heating uniformity are generally considered dielectric properties, shape and size of the sample and its position relative to the electrode plate, in addition the structure and voltage of RF electrode. A method based on texture characteristics of the solid–gel–liquid mixing system of LHHVS for adjustment and control of energy distribution in the RF field is proposed in this study to improve the heating uniformity. First, energy conversion principles and control equations of RF heating were analyzed on the basis of dielectric theory. Second, the influence of RF electromagnetic field-medium polyetherimide (PEI) on the RF heating of peanut butter (RHPB) was investigated on the basis of the numerical model of RHPB that was verified through experiments. Finally, the influence mechanism and its regulation and control effect were analyzed and discussed. The following conclusions can be drawn from this study: the increase of electrode gaps exerts minimal effect although it reduces the unevenness of the energy distribution. However, RF heating protocols must use the smallest possible electrode gap to heat agrifoods and increase the heating rate significantly. The energy distribution on the part of the sample close to PEI varies with the change of geometry and size of PEI when its placement is bias or symmetric. The area of energy enhancement continues to expand where the sample is in contact with PEI as PEI gradually increases. The area where the temperature increases under the influence of PEI will expand along the direction of the sample radius when the thickness of PEI remains unchanged and the radius gradually enlarges; otherwise, it will expand along the direction of the sample thickness. The influence of PEI on the energy distribution of RHPB demonstrates local characteristics. PEI significantly influences the energy distribution and heating mode of RHPB, which is easy to adjust and control, but does not reduce the processing speed and does not increases energy consumption. Hence, PEI is an effective means to interfere with energy distribution of RHPB. Uniform energy distribution can be obtained by selecting the appropriate PEI shape and size. Results of this study can help determine the experimental protocol for RHPB with the optimal uniform distribution and promote the fast commercial application of this technology.

On the Capacitance of Piezoelectric Metal–Insulator–Semiconductor Junctions

We study the capacitance of piezoelectric metal–insulator–semiconductor junctions. The linearized macroscopic theories of piezoelectric dielectrics and semiconductors are used. An analytical solution is obtained with an explicit expression for the junction capacitance. The contribution from the semiconductor part is characterized by the Debye length. When the semiconductor part is long compared to the Debye length, the junction capacitance can be written as a serial connection of two capacitors of the insulator and semiconductor parts. Because of piezoelectric coupling, a charge-stress coefficient is introduced to describe the junction behavior completely.

A non-classical theory of elastic dielectrics incorporating couple stress and quadrupole effects: part I – reconsideration of curvature-based flexoelectricity theory

A new non-classical theory of elastic dielectrics is developed using the couple stress and electric field gradient theories that incorporates the couple stress, quadrupole and curvature-based flexoelectric effects. The couple stress theory and an extended Gauss’s law for elastic dielectrics with quadrupole polarization are applied to derive the constitutive relations of this new theory through energy conservation. The governing equations and the complete boundary conditions are simultaneously obtained through a variational formulation based on the Gibbs-type variational principle. The constitutive relations of general anisotropic and isotropic materials with the corresponding independent material constants are also provided, respectively. To illustrate the newly proposed theory and to show the flexoelectric effect in isotropic materials, one pure bending problem of a simply supported beam is analytically solved by directly applying the formulas derived. The analytical results reveal that the flexoelectric effect is present in isotropic materials. In addition, the incorporation of both the couple stress and flexoelectric effects always leads to increased values of the beam bending stiffness.

Electronic and optical properties of plutonium metal and oxides from Reflection Electron Energy Loss Spectroscopy

Reflection Electron Energy Loss Spectra (REELS) have been acquired on plutonium δ-Pu-Ga alloys, α-Pu2O3 and PuO2. The position of the peaks attributable to the Pu 6p excitation can be used as ‘fingerprint’ for these species. X-ray Photoelectron Spectroscopy has been used to aid interpretation of the REELS spectra. The band gap of PuO2 was determined from the onset of the energy loss in the REELS spectrum. The REELS data have been evaluated within the dielectric response theory by means of the QUEELS-∊(k, w)-REELS software [Surf. Interface Anal. 36, (2004) 824]. The Energy Loss Function, dielectric function, refractive index and extinction coefficient for these materials have been determined in the ultraviolet and extreme ultraviolet range and are compared to previously reported results. Crown copyright (C) 2021 Published by Elsevier B. V. All rights reserved.

تعیین خواص دیالکتریک و نوری چارچوب زئولیتی ZIF-8 به وسیله طیف سنجی افت انرژی الکترون بازتابی (REELS)

Specific properties such as pore tunability, structural variety as well as chemical, mechanical, and thermal stability, make zeolitic imidazolate frameworks (ZIFs) suitable and of high importance for practical applications. Optical and chemical sensors and supercapacitors are among these applications which necessitate the detailed study of optical and dielectric properties of ZIFs. Therefore, ZIF-8 as a zinc-based mesoporous material was studied by reflection electron energy loss spectroscopy (REELS) applying the Yubero-Tougaard algorithm which is based on dielectric response theory. The band gap energy (Eg) of ZIF-8 was determined to be 4.2 eV using an extrapolation procedure applied to an experimental REELS spectrum. Its bulk and surface energy loss functions were also determined. Inelastic mean free path (IMFP) values of electrons of different energies transported in ZIF-8 were determined and their large differences with values calculated from the Tanuma-Powell-Penn (TPP) formula were discussed. In addition, the obtained ELF was used to apply the Kramers-Kronig transformation to obtain the real part (e1) and imaginary part (e2) of the dielectric function (e), refractive index (n), extinction coefficient (k), reflection coefficient (R) and absorption coefficient (µ) of ZIF-8 as important optical properties of this widely applicable material.

Physical properties and basic theory of dielectric

At the beginning of human understanding and application of electricity, dielectric materials have been in the world. At that time, however, the dielectric was used only as an insulating material to separate the current. Until the 1930s, the main object of research was insulating materials, mainly focusing on the dielectric constant, loss, conductance and breakdown of insulating materials. After the 1930s, with the emergence and development of new technology, dielectric has been far from being only used as insulation materials to the application, especially the appearance of polar dielectric and widely used, making people’s understanding of dielectric and its category and the past is very different. The research capacity has gradually evolved from the four main parameters of insulators to the study of the internal polarization process. This article from the dielectric polarization, dielectric loss, dielectric conductance and breakdown, dielectric thermal side note relaxation theory and its application of four chapters of the system to learn related content. The properties of dielectric are analyzed from the microscopic point of view, and the related theoretical hypotheses are established to reveal the corresponding macroscopic phenomena. The polarization, loss, conductance and breakdown properties of dielectric are analyzed. The dielectric constant ε, loss Angle tangent tanδ, conductivity γ and breakdown field intensity E are used to describe the properties of dielectric quantitatively.

Exciton radiative lifetime in a monoatomic carbon chain

Linear carbon-based materials such as polyyne and cumulene oligomers provide a versatile platform for nano-physics and engineering. Direct gap quasi-1D polyyne structures are promising for the observation of strong and unusual excitonic effects arising due to the two-dimensional quantum confinement. Recently, we reported on the observation of sharp exciton peaks in low temperature photoluminescence spectra of polyyne chains (Kutrovskaya S et al 2020 Nano Lett. 20 6502–9). Here, we analyze the time-resolved optical response of this system. We extend the non-local dielectric response theory to predict the exciton radiative lifetime dependence on the band-gap value and on the length of the chain. A good agreement between the experiment and the theory is achieved.