Dielectric Polarization Mechanisms Research Articles

Dielectric properties of diamond/SiC composite fabricated by Si vapor infiltration process

The dielectric properties and polarization mechanism are important for the application of high thermal conductivity electronic packaging materials. In this work, diamond/SiC composites were prepared by the silicon vapor infiltration process, and the effect of diamond content on permittivity of composites was investigated in detail in the range of 100 MHz to 1 GHz, and the mechanism of dielectric polarization was also discussed. The results show that the real part of permittivity of composite is greater than that of either component, due to the presence of interfaces and defects. As the diamond content increases, both the real and imaginary parts of permittivity show a trend of rapid decrease and then slow increase. Particularly, the minimum values of the real and imaginary parts of permittivity of diamond/SiC composite are 27 and 0.3, respectively. In the low frequency stage (<400 MHz), the dielectric loss of the composite is mainly caused by the conductivity loss, while in the high frequency stage (400 MHz∼1 GHz), the polarization loss plays a dominant role. The polarization loss of diamond/SiC composite mainly originates from several Debye relaxation processes, which are the interfacial polarization formed at the diamond/graphite and graphite/SiC interfaces.

Overview of the dielectric permittivity of lunar surface materials and implications for Chang&amp;rsquo;E-5 samplemeasurements

<p indent="0mm">The dielectric permittivity of lunar surface materials determines the penetration depth of electromagnetic waves in the lunar subsurface; hence, it is crucial to the design of scientific payloads such as radars, microwave radiometers, and lunar surface electromagnetic experiments. Additionally, dielectric permittivity is a key parameter in deciphering radar and microwave radiometer observations, which is important to obtain quantitative information regarding the subsurface structure and physical properties of the Moon. Our current knowledge of the dielectric permittivity of lunar surface materials depends mainly on the inversion of microwave remote sensing data and laboratory measurements of the Apollo and Luna samples. In December 2020, China’s Chang’E-5 mission successfully collected <sc>1.731 kg</sc> of lunar samples from the northern Oceanus Procellarum, thus providing new samples for studying the dielectric properties of lunar materials. In this paper, I will first introduce the basic knowledge of dielectric permittivity, including the dielectric polarization mechanism, dielectric permittivity mixing model, and measurement methods. Then, I will summarize the history and present status of the research on the dielectric permittivity of lunar materials and demonstrate the dielectric permittivity of the Moon. Finally, I will present the latest research results of the geological background and regolith properties of the Chang’E-5 landing region and provide some suggestions regarding the laboratory measurements and potential scientific outcome of the Chang’E-5 lunar samples. The summarization of our current knowledge of the dielectric permittivity of lunar regolith in this paper can provide theoretical guidance and engineering support for microwave sensor design, radar data interpretation, sampling site selection, and sample analysis for China’s future lunar exploration missions.

Magnetic field effect on the dielectric behavior in SrRuO3/Ba(Zr0.3Ti0.7)O3/FeMn/ Ba(Zr0.3Ti0.7)O3/n-Si heterostructure

Interfacial structure plays a dominant role in physical properties of the oxides and their film. In this study, SrRuO3/Ba(Zr0.3Ti0.7)O3/FeMn/Ba(Zr0.3Ti0.7)O3/n-Si heterostructure was fabricated by utilizing pulsed laser deposition technique. The X-ray diffraction was utilized to analyze the multilayers’ crystalline. Dielectric properties of the heterostructure were studied under various magnetic fields. Giant magnetocapacitance characteristic was gained from the heterostructure. It is found that the interfacial polarization between barium zirconate titanate film and iron manganese alloy film is responsible for giant magnetocapacitance. A possible dielectric polarization mechanism was investigated. This work can provide guidance for the development of the multi-functional memory device.

Multifrequency Inversion of Complex Electrical Conductivity Measurements for Simultaneous Assessment of Wettability, Porosity, and Water Saturation

Summary Multifrequency complex electric measurements are influenced by the joint effects of mineralogy, spatial distribution of fluids and solids, properties of fluids and minerals, and interfacial polarization mechanisms. The interpretation of multifrequency electrical conductivity and dielectric permittivity dispersion can yield information about the dominant dielectric polarization mechanisms. The dielectric polarization mechanisms detected in sedimentary rocks are linked to grain size, shape, and orientation relative to the externally applied electric field, electrochemical adsorption/desorption complexation reactions, wettability, porosity, and fluid saturations. In this work, we introduce a new workflow for multifrequency interpretation of complex permittivity measurements. The introduced workflow enables simultaneous assessment of dominant wettability, porosity, and hydrocarbon reserves. These properties are estimated by minimizing a cost function using a combination of downhill gradient-descent and an evolutionary algorithm. The cost function quantifies the difference between measured and numerically calculated multifrequency complex dielectric permittivity through a recently introduced rock-physics model. We successfully applied the new interpretation workflow to multifrequency electrical resistivity/permittivity measurements obtained from two water-wet and two hydrocarbon-wet sandstone core samples. Simultaneous estimates of wettability, water saturation, and porosity obtained by applying the new interpretation workflow were in agreement with experimental measurements. Assessment of hydrocarbon reserves, porosity, and dominant wettability solely from the interpretation of multifrequency complex-valued electrical measurements is a unique contribution of the introduced workflow. Additionally, the new workflow honors rock fabric and, thus, it minimizes the necessity of extensive calibration efforts. All the parameters needed as inputs to the new interpretation workflow are associated with physical mechanisms at microscopic- and pore-scale domains or realistic and quantitative pore geometry features of the rock.

Effect of sintering temperature on the structural, morphological, electrical, and magnetic properties of Ni–Cu–Zn and Ni–Cu–Zn–Sc ferrites

Polycrystalline Ni0.3Cu0.2Zn0.5Fe2O4 and Ni0.3Cu0.2Zn0.5Sc0.05Fe1.95O4 compounds have been prepared by standard solid-state reaction technique and sintered at 1000, 1100, 1150, 1200, and 1250 °C for 5 h in air. The effect of sintering temperature on the structural, morphological, magnetic, dielectric, and electrical properties of these spinel ferrites has been studied thoroughly and comparatively. Formation of the single-phase cubic spinel structure of these compositions is confirmed by X-ray diffraction analysis. The lattice constant increases with sintering temperature as well as with 5% scandium (Sc3+) doping in Ni–Cu–Zn ferrite. Surface morphology reveals that the grain size increases with sintering temperature. Among the prepared ferrites, Ni0.3Cu0.2Zn0.5Sc0.05Fe1.95O4 has the maximum density (5.05 × 103 kg/m3) at sintering temperature 1150 °C, which gives the highest value of initial permeability. It is observed that initial permeability varies with sintering temperature, and it gives the maximum value at optimum sintering temperature. It is noted that Curie temperature decreases with 5% Sc3+ ions doping, whereas it slightly increases with increasing sintering temperature for both compositions. Ni0.3Cu0.2Zn0.5Fe2O4 compound shows the highest Curie temperature 418 °C. Dielectric constant, dielectric loss factor and AC electrical conductivity decrease with 5% Sc3+ ions doping in Ni–Cu–Zn ferrite. The initial permeability decreases sharply at Curie temperature, which indicates a high degree of compositional homogeneity. The ‘Hopkinson’ peak is observed just below the Curie temperature in the real part of initial permeability versus temperature graphs. The mechanism of dielectric polarization and electrical conductivity has been explained based on the electron hopping between Fe3+ and Fe2+ ions. The variation trend of complex impedance and AC electrical conductivity reveals the semiconducting behavior of the ferrite samples. Formation of partial semicircles in the Z/-axis indicates that relaxation process is non-Debye type. The investigated ferrites show relatively high initial permeability, low magnetic loss, and low electrical conductivity in a wide frequency range, which make them potential candidate for various practical applications such as small and compact power suppliers for computers, microprocessors, microwave electronic devices, etc.

Macroscopic and microscopic electrical properties of a ferrofluid in a low frequency field

Using the complex dielectric permittivity measurements, in the frequency range 20 Hz – 2 MHz and at temperatures between (25–70)∘C, the polarizability (α), the electric modulus (M) and the electrical conductivity (σ), of a ferrofluid sample, were determined. The results enabled the computation of the thermal activation energy of electrical conduction, the obtained value being approximately equal, at 0.15 eV. By eliminating the losses arising from electrical conduction, we highlighted the existence of a Schwarz type dielectric relaxation, in the sample, at the frequency above 5 kHz. These results allowed, for the first time, the evaluation of the mechanical mobility, u, of the ions on the particle surface, resulting in a value of, u=3.4⋅108 m/sN. Knowledge of macroscopic and microscopic electrical properties is useful in explaining the dielectric polarization mechanisms and relaxation processes of ferrofluids, and also in the use of ferrofluids in technological and biomedical applications.

Influence of rare-earth doping on the structural and dielectric properties of orthoferrite La0.50R0.50FeO3 ceramics synthesized under high pressure

Abstract The effect of co-doping on the structural and dielectric properties of the La0.50R0.50FeO3 orthoferrites for a full number of substitutions (R = Ce–Lu) has been experimentally and theoretically studied using X-ray diffraction, SEM, EDS, and dielectric spectroscopy methods. The La0.50R0.50FeO3 ceramics with R = Nd, Sm, Gd, Dy, and Er, prepared by a solid-state reaction method under cold pressing at high pressure P = 4 GPa, have been taken as a basis. Structural parameters in the La0.50R0.50FeO3 orthoferrites have been obtained using Rietveld refinement of X-ray experimental data with their further approximation by linear dependence. Monotonic change in crystal lattice parameters, orthorhombic distortion degree, global instability index, and Goldschmidt tolerance factor have been observed for all samples doped by different R-cations. With increase in the radius of R-cation, a growth in an average grain size has been detected. The investigation of dielectric properties in a wide frequency range of 10−1–1010 Hz and their theoretical description with determining main mechanisms of dielectric polarization made it possible to establish regularities among a type of doping R-cation, crystal-chemical parameters and dielectric properties. The studied ceramic La0.50R0.50FeO3 samples demonstrate colossal dielectric constant ∼ 104 and relatively small dielectric loss tangent in a low-frequency range. The obtained results can be useful for further application of orthoferrite-based materials as sensor and switching devices.

Synthesis and study of electrical properties of Li2O modified P2O5-ZnO-Na2O glasses

The transparent glasses of composition 40P2O5-20ZnO-(40-x)Na2O-xLi2O have been prepared using conventional melt quenching technique (where 0 ≤ x ≤ 25 Li2O mol. %). The amorphous nature of the prepared glass samples is confirmed by x-ray powder diffraction (XRD). By increasing the Li2O content, the density and oxygen packing density increase while the molar volume decreases which indicates that the structure is more compact. The differential thermal analysis (DTA) studies showes that 15 mol.% Li2O glass sample has the highest thermal stability and the glass transition temperature (Tg) decreases as the content of Li2O increases till 25 mol.% Li2O . The ac and dc electrical conductivities and dielectric constants of the prepared glass samples have been investigated. It is found that the dc conductivity increases with the concentration of Li2O mol.% and the temperature dependence of the dc conductivity at low temperature (303 – 383 K) and at high temperature (403 – 473 K) obey the Arrhenius law. The activation energies ΔEdc1 (at high temperatures) and ΔEdc2 (at low temperatures) were determined. The values of σdc can be obtained also from the impedance study at different temperatures and different concentrations using Cole-Cole plot. To determine the conduction mechanism, the ac conductivity and its frequency exponent (s) have been analyzed by correlated barrier hoping model (CBH). It is found that s has values between 0.89-0.996; consequently. The correlated barrier hopping (CBH) seems to be the most interesting model related to the obtained results. Real and imaginary parts of dielectric constant (e' and e'') have been found to decrease with increasing frequency and temperature and this result would be discussed by means of dielectric polarization mechanism of material. The maximum value of the maximum barrier height Wm obtained from Guitini equation was found to increase with increasing of Li2O mol. %.

Synthesis and characterization of Li2O modified sodium phosphate glasses

The transparent glasses 55 P2O 5 - (45-x) Na2O - xLi2O where (x=0, 3, 10, 15, 30, 35) were prepared by conventional melt quenching technique. Structural and characterization have been investigated by using X-Ray diffraction (XRD) and the results show that all samples are amorphous structure. The glass transition (Tg) and crystallization temperature (Tc) are evaluated using the differential thermal analyzer (DTA), which indicate that 15 mol% Li2O contained glasses exhibits maximum thermal stability h’ of glass samples. Density, molar volume and oxygen packing density insure that Li2O incorporated in sodium phosphate glass by increasing Li2O content. The ac and dc electrical conductivity and dielectric constants of the prepared glass samples have been investigated. The variation of dc conductivity with the concentration of Li2O mol% passes through a maximum at 15 mol% Li2O. Temperature dependence of the dc conductivity of these glasses is found to obey the Arrhenius law. It reveals that the values of activation energies ΔEdc1 and ΔEdc2 at low and high temperatures lie in the range 0.452-0.93 eV. Also it was found that the values of σdc to be the same as the values obtained from the impedance study. Conductivity mechanism for grain resistance at room temperature was discussed using Cole-Cole plot. To determine the conduction mechanism, the ac conductivity and its frequency exponent have been analyzed by correlated barrier hoping model (CBH). It was found that the exponent (s) has values between 0.62-0.9; consequently the (CBH) seems to be the most interesting model related to the obtained results. The variation of dielectric constants e’ and e’’ with the concentration of Li2O mol% pass through a maximum at 15 mol% Li2O and this result would be discussed by means of dielectric polarization mechanism of material. The maximum value of the maximum barrier height Wm obtained from Guitini equation was found to increase with increasing of Li2O mol%.

Structural, Morphological and Temperature Dependent Dielectric Studies of Sr-Cu Nano Sized Hexa Ferrites

A series of polycrystalline SrCu nano ferrites substituted with Sn-Co having generic formula Sr2Cu2Fe12-X(SnCo)X/2O22 (where x changes from 0 to 2.5 in equal steps of 0.5) have been synthesized by novel microwave assisted sol gel process using urea as fuel. Structural characterization of the prepared compounds have been performed using X-ray powder diffraction pattern, which shows formation of single Y-type hexagonal phase and belonging to space group R3-m(no.166). The lattice parameters, X-ray density (Dx), measured density (Dm), and porosity (P) of samples are calculeted from XRD data. We observed that the lattice parameters “a” and “c” increasewith content of SnCo. The crystallite size is in the range 13- 47nm, shows nanometer size of prepared compounds. The microstructure is studied by transmission electron microscopy (TEM).The ac electrical conductivity (σac) dielectric constant (∊’), and dielectric loss (tan δ) are studied a function of temperature. The plot of conductivity verses 1/T shows semiconducting nature of the compounds. The results of dielectric constant and dielectric loss are explained on the basis of the assumption that the mechanism of dielectric polarization is similar to that of conduction process.

Mechanisms of dielectric polarization in thermotropic liquid-crystalline complexes based on lanthanides

The components of the dielectric constant of a terbium-based liquid-crystalline complex have been measured in the frequency range of 350–5 × 106 Hz. The magnitude and sign of the dielectric anisotropy of the complex have been determined. Dispersion of the dielectric constants in the liquid-crystalline and isotropic phases has been found. The mechanisms responsible for the relaxation phenomena that appear in the studied sample have been determined. The time of dielectric relaxation, the activation energy, and the dipole moment of the complex have been obtained.

The effect of nanographite addition on the physical properties of poly(vinylidene fluoride)/hydroxypropyl cellulose blend

In this study, polymeric films of poly(vinylidene fluoride) (PVDF)/hydroxypropyl cellulose (HPC) blend filled with various graphite-nanoparticles (GNP) contents were prepared via solvent-mixing technique. The compatibility between PVDF and HPC polymers was studied. The variations in structure, dielectric and thermal properties were investigated over the frequency range (20 Hz–3 MHz) and temperature range (20–110 °C). The X-ray diffraction and differential scanning calorimetry results reveal that the crystallinity of PVDF was affected by the presence of HPC and GNP. The dielectric results reveal that the great enhancement of dielectric constant ( $$\upvarepsilon^{{\prime }}$$ ) and ac conductivity (σac) were observed. The dielectric properties were explained in terms of the dielectric polarization mechanism. Both HPC and GNP additions enhance the $$\upvarepsilon^{{\prime }}$$ of PVDF due to the formation of β-phase polymorph and the interface effect between the GNP and blend matrix. The improvement of the thermal stability was observed due to the regular arrangement of the side chains. The easy processing, high dielectric constant, low tangent loss and high thermal stability of the composites make the composites attractive for practical applications in embedded capacitors.

Effects of Bi2O3 on FMR linewidth and microwave dielectric properties of LiZnMn ferrite

Effects of Bi2O3 on ferromagnetic resonance (FMR) linewidth and microwave dielectric properties for LiZnMn ferrite prepared by a conventional ceramic method were investigated. The FMR linewidth had been separated to anisotropy and porosity line broadening contributions by an approximate calculation based on spin-wave approach. The results manifest that, Bi2O3 content significantly affects FMR linewidth via promoting grain growth and densification. With Bi2O3 concentration increasing, anisotropy contribution is changeless with a constant about 80Oe. The variation of the porosity line broadening contribution, however, is unanimous with the FMR linewidth. Meanwhile, the mechanism of dielectric polarization and dielectric loss of the samples were discussed. When the amount of Bi2O3 is 1.00wt%, the sample shows low FMR linewidth (ΔH, 133Oe) and low dielectric loss tangent (tan δε, 5×10−4) at 9.2GHz, high saturation magnetization (Ms, 415kA/m), and high squareness ratio (Br/Bs, 0.87).

Dispersion Spectra of Permeability and Permittivity for LiZnMn Ferrite Doped With ${\hbox {Bi}}_{2}{\hbox {O}}_{3}$

The effects of Bi2O3 on dispersion spectra of permeability and permittivity for LiZnMn ferrite prepared by a conventional ceramic method were investigated. Optimum content of Bi2O3 can obviously affect the permeability and permittivity of LiZnMn ferrite via promoting grain growth and densification. The permeability spectra of LiZnMn ferrite were resolved into two contribution components, domain wall movement and spin rotation magnetization. The fitting results manifest that, with Bi2O3 concentration increasing, the major contribution to dynamic magnetization changes from spin rotation magnetization mechanism to domain wall movement, and the domain wall spectra change from resonance-type to relaxation-type, but the spin rotation spectra behave in the opposite way. Meanwhile, the mechanism of dielectric polarization and dielectric loss of the samples were discussed.

Assembled Fe3O4 nanoparticles on graphene for enhanced electromagnetic wave losses

We present an one-step procedure for the synthesis of hybrid Fe3O4 nanoparticles/graphene composite with self-assemble superlattices of Fe3O4 nanoparticles. We find that the Fe3O4/graphene nanocomposite exhibits both enhanced dielectric losses and magnetic losses at 2–18 GHz, resulting from the interfacial polarizations between the Fe3O4 nanoparticles and the graphene, as well as the coupling between the neighbouring Fe3O4 nanoparticles. Theoretical simulations uncover the origins of the electromagnetic losses of hybrid Fe3O4/graphene nanocomposite and provide additional insight into the microscopic dielectric polarization mechanism.

Dielectric properties of polyacrylate thick films used in sensors and actuators

Dielectric polymers are emerging electro-active materials used in high performanceapplications such as micropumps, robots and artificial muscles. The development of suchapplications requires the use of models taking into account the electrical parameters of thematerial. However, there is still some controversy over the dielectric constant ofthe most widely used dielectric polymer (VHB 4910, 3M, USA). In this paper,we present an exhaustive study relating to changes in the dielectric constantof VHB 4910 over wide frequency and temperature ranges. We found that thepermittivity was a function of: frequency, temperature, the nature of the electrodesand the pre-stress applied to material. Mechanisms of dielectric polarization (β-relaxation) explain the behaviour in temperature and frequency of this parameter. The useof silver grease-compliant electrodes induces an increase in the dielectric constant whichmoves to a value of 5.4 (against 4.7 with gold electrodes). A pre-strain applied to thematerial shows a reduction up to 15% in the value of the dielectric constant. Short-rangedipolar relaxation, local mechanical constraints in the material and a possiblecrystallization of material induced by the stretching are suggested to explain thesebehaviours. Analytic equations of the dielectric constant according to the temperature andpre-strain are then proposed and used to validate the behaviour of these materials foractuator and scavenger devices.

Frequency dispersion of the dielectric characteristics in polymer films based on the [NiSalen] complex

The results of the measurements of the dielectric properties exhibited by metal-containing polymer structures based on Ni(II) complexes in the frequency range f = 102–105 Hz are reported. It is established that, in the range of acoustic frequencies, the permittivity e decreases with increasing frequency, whereas the dielectric loss tangent tan δ increases. At frequencies f > 104 Hz, the dependence tan δ(f) is characterized by a relaxation maximum. The possible mechanisms of dielectric polarization and charge transfer in an alternating-current electric field are considered.

Dielectric charging in radio frequency microelectromechanical system capacitive switches: A study of material properties and device performance

The paper analyze the direct relation between the dielectric polarization mechanisms and the radio frequency microelectromechanical system capacitive switches performance. The dielectric polarization mechanisms are investigated in metal-insulator-metal capacitors with the aid of the thermally stimulated depolarization current method. The performance of microelectromechanical system is studied through the temperature dependence of the bias for the minimum capacitance. The simultaneous assessment allows the discrimination of dipolar and space charge polarization that allows the prediction of the shift of capacitance minimum with temperature.

Dielectric behavior of electroactive fluorinate-based terpolymers

The dielectric and ferroelectric properties of the poly(vinylidene fluoride–trifluoroethylene–chlorotrifluoroethylene) terpolymers are studied in the temperature range 160–380 K. More attention was given to the dielectric loss in the dielectric spectra and the following results were obtained: (1) there are two dielectric polarization mechanisms, modes A and B, contributing to the majority of the dielectric permittivity; (2) by using the Cole–Cole plot method, precise relaxation rates of mode B can be obtained, which follow the Vogel–Fulcher relation with reasonable parameters, TVF=∼160±2 K, UVF=∼0.16±0.01 eV, ν0=1×1012 Hz. The temperature where mode A occurs does not shift with the variation of frequency and a well-developed hysteresis loop is observed, indicating the existence of a normal “paraelectric–ferroelectric” transition in the terpolymer.

Dielectric dispersion of Y-type hexaferrites at low frequencies

A series of polycrystalline Y-type hexaferrites with composition Ba 2Ni 2− x Zn x Fe 12O 22 (where 0.0⩽ x⩽2.0) were prepared by the standard ceramic method to study the effect of the frequency, temperature and composition on their AC electrical conductivity σ′ AC, and dielectric properties. It was found that, the AC conductivity shows dispersion at high frequencies. This dispersion was attributed to the interfacial polarization arising from the inhomogeneous structure of the material. At low frequencies the dielectric constant, ε′, is abnormally high and decreases rapidly with increasing frequency. Dielectric relaxation peaks were observed on the tan δ( F) curves. The results of the dielectric constant and dielectric loss were explained on the basis of the assumption that the mechanism of dielectric polarization is similar to that of the conduction process.