Dependent Permittivity Research Articles

New surface waves in a hyperbolic graded-index crystal

The transverse electric surface waves propagating along the surface of the crystal characterized by a spatial dependence of the dielectric permittivity are theoretically described. A hyperbolic profile of the dielectric permittivity of the crystal is used to obtain an exact analytical solution to the wave equation, which is expressed by Whittaker function. The influence of the parameters of the hyperbolic profile of the dielectric constant on the localization of the electric field near the crystal surface is analyzed. The dependencies of the effective refractive index on the parameters of a hyperbolic profile of the dielectric permittivity are explored. The way to effectively control the localization and intensity of the surface waves by changing the values of the parameters of the hyperbolic profile using the obtained exact solution is found.

3R-CuCrO2 delafosite: crystal growth, crystal structure, dielectric and DC conductivity properties

Single-crystal samples of the 3R-CuCrO2 phase (R3m, a = 2.9613(2) Å, c = 17.098(2) Å) with a delafossite structure were grown by the flux method. Structural parameters were refined by X-ray structural analysis. The elemental composition of the grown crystals was confirmed by Auger electron spectroscopy. A threshold electric field switching effect from a high-resistance to a low-resistance state was discovered. The effect is characterized by a jump in electrical resistance (up to 5 orders of magnitude at E = 4.7 kV/cm, T = 120 K) and S-shaped current–voltage characteristics with a region of negative differential resistance. The temperature dependences of dielectric permittivity and dielectric loss tangent exhibit a Debye-type relaxation process with an activation energy of 0.51(3) eV. The observed features of dc conductivity, current–voltage characteristics, and dielectric properties interpreted on the basis of the existence of charge carriers in a small polaron state and the destruction of this state by the electric field.

Interpretation of dielectric spectroscopy measurements of ferroelectric nematic liquid crystals

The magnitude of the relative permittivity of the ferroelectric nematic phase (NF) has been the subject of lively scientific discussion since the phase was recently discovered. Dielectric spectroscopy measurements (DSMs) give a huge value of relative permittivity, which depends on the cell thickness, but this is argued to result from a misinterpretation of the DSM results. We have conducted DSM using a set of cells differing in thickness of the NF layer, type of electrodes, and presence/absence of nanoscale-thick surface polymer layers. To model the DSM results, cells are presented by an equivalent electric circuit that includes a capacitor due to the NF layer with frequency dependent complex relative permittivity, capacitors due to surface layers, and a resistor describing the limited conductivity of electrodes. DSM results for different cells with the same liquid crystal in the NF phase are semiquantitatively reproduced by the same set of physical parameters if a huge relative permittivity of the NF, which is even orders of magnitude larger than the measured apparent values, is assumed. We show that the capacitance of surface layers should also be considered in cells with no polymer alignment layer on the electrodes. Published by the American Physical Society 2024

Phase transition investigation of ferroelectric and dielectric properties of (NH 2 CH 2 COOH)3 H2SO4 crystal using green function method and two sublattice PLCM model Hamiltonian

The Greens function technique and extended two sublattice pseudospin lattice coupled-mode (PLCM) model Hamiltonian have been applied to study the phase transition mechanism in (NH2CH2COOH)3H2SO4 compound. The two sublattice PLCM model Hamiltonian is modified by considering anharmonic phonon interactions, extra spin-lattice interactions, and an external applied electric field term. By using the double-time thermal-dependent Green function technique, the theoretical equations for the total shift, total width, normal mode frequency, transition temperature, relative permittivity, dielectric tangent loss, acoustic attenuation and spontaneous polarization are derived. By fitting the distinct model parameters in the theoretical equations, we calculated the temperature dependence of normal mode frequency, relative permittivity, tangent loss, acoustic attenuation and spontaneous polarization. The numerically obtained results are hold well and correlated with experimental data.

Drug-amino acid interaction: Molecular dynamics in aqueous medium using time domain reflectometry

Present work reports dielectric response of the non-steroidal anti-inflammatory drug (NSAID) aceclofenac in aqueous valine solutions at various concentrations and temperatures (278.15 K–298.15 K) in the frequency range of 0.01 GHz to 30 GHz using Time-domain reflectometry (TDR) technique. The frequency dependent complex dielectric permittivity has been analyzed by Harviliak-Negami equation. Debye model is used for the description of complex dielectric permittivity spectra ε*(ν). The structural and dynamical properties of water has been investigated at different concentrations of valine and aceclofenac using dielectric as well as thermodynamic parameters that includes static dielectric constant (ε0), relaxation time (τ0), Kirkwood correlation factor (g), free energy of activation (ΔF), entropy of activation (ΔS), and enthalpy of activation (ΔH). Towards the measured low temperature and high concentrations of Valine and Aceclofenac (ACF), static dielectric constant (ε0) was found to be increasing. This could be due to increased effective dipole-dipole parallel alignment and can be confirmed by the increasing values of correlation factor (g > 1). The dipole-dipole interaction between Drug-Amino acid resulted in increased dielectric relaxation time (τ0) of system due to increased steric hindrance for the rotation of dipoles. The free energy of activation was found to be in the range of 2.22 and 2.58 Kcal mol-1. The entropy is more negative at high concentration suggesting more ordered structure. The slope of log (Tτ0) vs. 1000/T gives the value of enthalpy (ΔH).

New Piezoceramic SrBi2Nb2-2xWxSnxO9: Crystal Structure, Microstructure and Dielectric Properties.

By using the method of high-temperature solid-phase reaction, the new piezoceramic SrBi2Nb2-2xWxSnxO9 was obtained, where partial substitution of niobium (Nb) atoms with Sn4+ and W6+ atoms in the compound SrBi2Nb2O9 occurred in the octahedra of the perovskite layer (B-position). X-ray diffraction investigations showed that these compounds are single-phase SrBi2Nb2-2xWxSnxO9 (x = 0.1, 0.2) and two-phase SrBi2Nb2-2xWxSnxO9 (x = 0.3, 0.4), but all of them had the structure of Aurivillius-Smolensky phases (ASPs) with close parameters of orthorhombic unit cells. It corresponded to the space group A21am. The temperature dependences of the relative permittivity ε/ε0 and the tangent of the dielectric loss angle tan d were defined at various frequencies. It was found that doping SrBi2Nb2-2xWxSnxO9 (x = 0.1) improved the electrophysical properties of the compound: losses decreased, and the relative permittivity increased. This result was obtained for the first time. Moreover, a new result was obtained that indicated an improvement in the electrophysical properties of SrBi2Nb2O9 using the chemical element Sn (tin). This refutes the previously existing opinion about the impossibility to use Sn as a doping element.

Finding the best frequency dependent performance of 3d transition metals (Co, Ni, and Mn) substituted nano magnetite for miniaturizing device applications

Ferrite samples with enhanced magneto-dielectric properties are more essential in electromagnetic applications. Therefore, a parent composition of Fe3O4 has been modified by substituting 3d transition metal elements (Co, Ni, Mn) at a single Fe atom using the co-precipitation synthesis method. The structural properties of the synthesized Fe3O4, NiFe2O4, CoFe2O4, and MnFe2O4 samples have been evaluated from the X-ray diffraction patterns. The surface morphology and microstructures of the studied samples were studied by field emission scanning electron microscopy and the average grain size of all the studied samples varied from 60.11 to 106.03 nm. The magneto-dielectric properties were analyzed by frequency dependent permeability (μ) and permittivity (ε) measurements for the range of 100 Hz to 100 MHz. The conduction process for the synthesized ferrites has been noticed from the ac conductivity (σac). The localized relaxation mechanism for the studied ferrites has been observed from the variation of imaginary portion of the electric modulus (M") and the impedance (Z"). Moreover, the mismatch (Z/ηο) between the impedance of the antenna substrates (Z) made of the studied samples and air (ηο) has been evaluated from the permeability and permittivity. Finally, NiFe2O4 has been derived as a suitable ferrite for miniaturizing devices over a frequency range of 10 kHz-6.5 MHz.

Structural properties, dielectric relaxation, and impedance spectroscopy of NASICON type Na3+xZr2−xPrxSi2PO12${\rm Na}_{3+x} {\rm Zr}_{2-x} {\rm Pr}_{x} {\rm Si}_2 {\rm PO}_{12}$ ceramics

AbstractWe investigate the dielectric and impedance spectroscopic investigation of Pr‐doped NASICON type () samples as a function of temperature and frequency. The Rietveld refinement of X‐ray diffraction patterns confirms the monoclinic phase having C2/c space groups for all the samples. The scanning electron microscopy shows the granular‐like structure and energy dispersive X‐ray analysis confirms the desired compositions. The temperature (90–400 K) and frequency (20 Hz–2 MHz) dependence of electric permittivity are explained using Maxwell–Wagner–Sillars (MWS) polarization and space charge polarization mechanisms. The dielectric relaxation shows nearly equal activation energy for all the samples with a non‐Debye type of relaxation in the measured temperature range. The complex impedance analysis shows the presence of broad grain and grain boundary relaxation peaks. The stretched exponent analysis of electric modulus using the Kohlrausch–Williams–Watts (KWW) function further confirms the non‐Debye type of relaxation. Moreover, scaling analysis of the electric modulus shows a similar type of relaxation for all the samples. The ac conductivity data are fitted using modified power law, where the temperature dependence of exponent () confirms the correlated barrier hopping (CBH) type conduction for all the samples. Our results indicate that the Pr‐doped NASICON samples are potential candidates for charge storage devices due to their large electric permittivity.

Relaxor-like behavior of the dielectric response of dense ferroelectric composites

We study experimentally and theoretically the influence of size effects and structural factors on the dielectric and ferroelectric properties of the dense ferroelectric composites. The composites have the form of the tape-casted films with 28 vol% of nanosized or submicron BaTiO3 particles dispersed in the polyvinyl butyral. We measured and analyzed the temperature dependences of the capacitance and dielectric losses in the temperature range (−200 – +200)oC and frequency range (102–105) Hz. The nonmonotonic temperature dependences of dielectric permittivity of the studied composite films have a wide plateau-like maxima located between 80oС and 160oС, in contrast to the relatively sharp maximum near the Curie temperature (∼124oC) observed in the fine-grained and coarse-grained ceramics, sintered from the same nanosized or submicron BaTiO3 particles at 1250oC. The shift of the dielectric permittivity and losses maxima (in more than 40oC) and their strong frequency dispersion do not agree with the behavior expected for the systems with a weak interaction between ferroelectric particles and a polymeric matrix. In contrast, we reveal the relaxor-like behavior of the composite dielectric response. To explain the observed results, we propose the analytical model, which considers the strong dipole-dipole cross-interaction of the BaTiO3 particles in the dense nanocomposite. The analytical model is corroborated by the structural studies of the BaTiO3 nanosized and submicron particles by X-ray phase analysis and static 137Ba NMR spectra, as well as by the finite element modelling of the composite polar properties, which confirms the strong cross-interactions between the dipole moments of single-domain nanoparticles and/or between the domain walls of different submicron polydomain particles.The obtained results may be useful for development of cheap and flexible lead-free dense ferroelectric nanocomposites with relaxor-like behavior of the dielectric response, which are promising for non-volatile memory and energy-saving elements, modulators, electrical converters and piezoresistive elements.

Assessment of thermochromic phantoms for characterizing microwave ablation devices.

Thermochromic gel phantoms provide a controlled medium for visual assessment of thermal ablation device performance. However, there are limited studies reporting on the comparative assessment of ablation profiles assessed in thermochromic gel phantoms against those in ex vivo tissue. The objective of this study was to compare microwave ablation zones in a thermochromic tissue mimicking gel phantom and ex vivo bovine liver, and to report on measurements of the temperature dependent dielectric and thermal properties of the phantom. Thermochromic polyacrylamide phantoms were fabricated following a previously reported protocol. Phantom samples were heated to temperatures in the range of 20 - 90 °C in a temperature-controlled water bath, and colorimetric analysis of images of the phantom taken after heating were used to develop a calibration between color changes and temperature to which the phantom was heated. Using a custom, 2.45 GHz water-cooled microwave ablation antenna, ablations were performed in fresh ex vivo liver and phantoms using 65 W applied for 5 min or 10 min ( n = 3 samples in each medium for each power/time combination). Broadband (500 MHz - 6 GHz) temperature-dependent dielectric and thermal properties of the phantom were measured over the temperature range 22 - 100 °C. Colorimetric analysis showed that the sharp change in gel phantom color commences at a temperature of 57 °C. Short and long axes of the ablation zone in the phantom (as assessed by the 57 °C isotherm) for 65 W, 5 min ablations were aligned with extents of the ablation zone observed in ex vivo bovine liver. However, for the 65 W, 10 min setting, ablations in the phantom were on average 23.7% smaller in short axis and 7.4 % smaller in long axis than those observed in ex vivo liver. Measurements of the temperature dependent relative permittivity, thermal conductivity, and volumetric heat capacity of the phantom largely followed similar trends to published values for ex vivo liver tissue. Thermochromic tissue mimicking phantoms provide a controlled, and reproducible medium for comparative assessment of microwave ablation devices and energy delivery settings, though ablation zone size and shapes may not accurately represent ablation sizes and shapes observed in ex vivo liver tissue under similar conditions.

Investigation of the temperature dependence of the dielectric relaxation of chlorobenzene, bromobenzene and iodobenzene

This paper deals with the investigation results of temperature dependence of complex permittivity’sε∗ = έ − iε˝ of chloro, bromo and iodo- benzene at wavelength 11,50 cm and 12,80 cm within the temperature range 20 ÷ -80˚. It is established that dielectric properties of given liquids are characteristic of one relaxation time. The dielectric spectra were studied taking into account other frequencies given in the literature. In all investigated liquids, a jump appears in the real and imaginary parts of the complex permittivity at the point of the phase transition. The temperature dependence of the dielectric relaxation time of molecules in the liquid state has been determined. It was found that with an increase in the amount of the halogen substituent, an increase in the relaxation time occurs. Macroscopic and molecular relaxation times were calculated from the experimental values. The thermodynamic quantities characterizing the process of dielectric relaxation are calculated. The activation enthalpy of dielectric relaxation processes is compared. The studies were carried out using the dielectric spectroscopy method. This method allows a more detailed study of the dielectric properties of the objects of study due to the large equilibrium (“static”) dielectric constant of the object. It has been determined that the height of the potential barrier separating the two equilibrium positions of a polar molecule is greatest in the state of a pure polar liquid and decreases with dilution in a non-polar solvent.

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.

Density dependence for the dielectric permittivity of simple gases and liquids

The present work is devoted to the analysis of polarization effects in atomic systems of the argon type. Special attention is given to the manifestation of the polarizabilities of two particles in the density dependence of the dielectric permittivity of a system and its effective molecular polarizability. It is shown that the effective polarizability of a molecule in the liquid state of a system is mainly caused by deviation of the molecular distribution in the first coordination layer from the spherical one. Due to this, the atomic polarizability inherent to rarefied gas increases practically twice near the triple point. The interconnection between the atomic polarizability and the proper volume of an atom is discussed in detail. It is established that the optimal size of an atom follows from the kinematic shear viscosity measurements.

High dielectric breakdown strength of antipolar CaTiGeO5 ceramics sintered at optimized temperature

Titanite CaTiSiO5 (CTS) is considered to be a promising dielectric material for preparing high-voltage multilayer ceramic capacitors because it exhibits a positive bias dependence of the dielectric permittivity due to its antipolar crystal structure. In this study, we investigated the dielectric response and breakdown strength of CaTiGeO5 (CTG), a structural analog of CTS, inspired by its higher low-field dielectric permittivity. Particular attention was paid to the sintering temperature to reveal the effect of the microstructure and loss of volatile Ge on the electrical properties of CTG. Dense CTG ceramics with relative densities above 97 % and grain sizes between 1.3 and 3.4 μm were obtained through a conventional solid-state reaction route at sintering temperatures between 1150 and 1250 °C. A secondary phase of CaTiO3 was formed in the ceramics sintered at 1200 and 1250 °C due to Ge loss, but this phase was easily removed by surface polishing alone. The sintering temperature largely affected the dielectric breakdown strength through microstructural development, resulting in the highest breakdown strength of 1190 kV cm−1 for a sample sintered at 1200 °C, while it did not change the low-field dielectric properties of the samples. Furthermore, the sample retained high breakdown strength of >900 kV cm−1 at elevated temperatures up to 150 °C and exhibited a nonlinear polarization response, resulting in the positive electric field dependence of the dielectric permittivity.

Comments on the dielectric spectroscopy results on a new series of fluorinated hydrogen-bonded liquid crystals

Recently, a work entitled “Synthesis, thermal, dielectric and electro-optic properties of new series of fluorinated hydrogen-bonded liquid crystals” is published by M. Derbali et al., in J Mol Liq, 367 (2022) 120510. Authors reported SmA and SmC mesophases in the synthesised liquid crystalline materials. However, dielectric data reported here are erroneous when tested even from some fundamental aspects. Inadvertent omissions by the authors in presenting and explaining the dielectric results in terms of frequency dependent permittivity and loss are discussed here so that appropriate precautions may be taken by the readers to avoid such fundamental gross mistakes. Some problems related to other studies are also discussed in brief.

Ferroelectric and antiferroelectric chiral multilactate liquid crystalline materials with negative dielectric anisotropy

In this work, the mesomorphic, electro-optic and dielectric properties have been discussed in the light of molecular structure-property correlations of two chiral multilactate liquid crystalline materials possessing the orthogonal paraelectric Smectic A* phase, tilted ferroelectric Smectic C* phase and the tilted antiferroelectric Smectic CA* phase, over a substantially broad temperature range. Interestingly, a reasonably rare re-entrant Smectic C* phase (SmCre*) has also been identified in one of the investigated materials. These materials differ in their linkage groups (keto or ether) and an additional chiral unit in the terminal chain. The phase transition temperatures and transition enthalpies were determined from Polarizing Optical Microscopy and Differential Scanning Calorimetry (DSC) measurements. The compounds exhibit negative dielectric anisotropy (Δε) throughout the mesomorphic range (maximum −18 and −4 in SmA* for both the compounds) and moderately high values of spontaneous polarization (∼153 nC/cm2 in SmCre* phase). The temperature dependence of the response time (τ), bulk viscosity (η) and the activation energies (Ea) throughout the mesomorphic phase have been determined from the spontaneous polarization measurements. To emphasize the structure-property correlations in more detail, dielectric spectroscopy measurement has also been performed to measure the dielectric strength, dielectric loss, frequency dependent permittivities, relaxation time and relaxation frequencies. The clear evidence of the relatively rare SmCre* phase has also been confirmed from the temperature and frequency dependence of the dielectric permittivity. These results shed important light on the emergence of these materials as a smart alternative for their application in multicomponent mixtures targeted for advanced electro-optic and photonic devices.

Crystal structure and dielectric properties of Ln2Ti2SiO9 (Ln = Pr and Nd)

Low loss and high dielectric constant materials are essentially desired for wide varieties of applications in electronics and communication technology. Herein the structure and dielectric properties of two titanosilicates, Ln2Ti2SiO9, for Ln = Pr3+ and Nd3+ are reported. Both materials are isostructural and have layered structure with layers of [LnTi2SiO9]3- and Ln3+ ions. Electrical properties of both have been analyzed by using the temperature and frequency dependent permittivity, loss, conductivity and modulus data. At room temperature, appreciable relative permittivity (35 for Nd2Ti2SiO9 and 22 for Pr2Ti2SiO9 over the frequency range of 100 Hz to 5 MHz) and low dielectric loss (like 0.007–0.03 at 100 Hz and 10−4-10−3 at 1 MHz). Analysis of dc-conductivity data of both compounds indicate that the conduction in both materials is due to the correlated barrier hopping (CBH) of polarons. The relaxation peak of modulus spectra indicates more non-Debye like relaxation in Pr2Ti2SiO9 than that in Nd2Ti2SiO9, and that is possibly due to increased correlation in the dynamics of hopping polarons in Pr2Ti2SiO9.

Surface plasmon induced quantum interference at meta-material interface

In this work we investigate quantum interference in a four-level atom coupled to a negative index meta-material (NIMM) anisotropic plasmonic environment that supports both TE and TM polarized surface plasmons (SP). The analysis confirms the creation of the anisotropic environment and two dipoles can interfere with each other even if they are orthogonal by sharing such SP modes. The NIMM/plasmonic environment provides more options to control SP interaction with emitters and their spontaneous emission decays and spectrum. The spectrum depends critically on structure parameters, mode frequency, frequency dependent electric permittivity and magnetic permeability, and the location of the atom etc. We observe orders of magnitudes enhancement in the plasmonic-modified decays and spectrum compared to free space case.

Dielectric Properties and Magnetoelectric Effect of Bi7Fe3Ti3O21 Ceramic Material Doped with Gadolinium Ions

Pure Bi7Fe3Ti3O21 ceramic material and gadolinium ion (Gd3+)-doped ones were prepared by solid-state reaction method using simple oxides. The findings of the XRD measurements confirmed the initial author’s assumption that the dopant ions substituted in perovskite blocks influenced the dimensions of the unit cell parameters. All obtained materials are single-phase and show an orthorhombic structure with the Fm2m space group. Microstructure studies show that the admixture gadolinium doping changes the microstructure of the base material, changing grain shapes from plate-like to rounded. The temperature dependences of the electric permittivity have shown the existence of a maximum, the temperature location of which depends on both the frequency and the concentration of Gd3+ ions. The highest values of electric permittivity were characteristic of the material with an admixture of Gd3+ ions in the amount of x = 0.6 (f = 1 kHz), and the lowest values were for material with x = 0.2 (f = 1 kHz). Studies of the magnetoelectric effect have shown that the strongest coupling between magnetic and electrical properties was demonstrated by a material doped with Gd3+ ions in the amount of x = 0.2, for which the magnetoelectric coupling coefficient is equal to α = 12.58·10−9 s/m.

Antiferroelectricity of titanite-type oxide SrTiGeO5 and its potential for power electronics applications

Antiferroelectric materials have recently received renewed attention due to the increased demand for energy-storage ceramics and power electronics applications. This study demonstrates antiferroelectricity in a titanite-type oxide, SrTiGeO5, through direct observation of a double D-E hysteresis loop by polarization measurements. Temperature dependence of dielectric permittivity shows a cusp around 550 K, indicating a relatively high antiferroelectric phase transition temperature for SrTiGeO5. It is suggested that an electric-field-induced rise of permittivity in SrTiGeO5 has the potential for application in protective circuits of power electronics devices. The present study paves the way for the development of innovative antiferroelectric applications.