Permittivity Behavior Research Articles

Jahn-Teller assisted polaronic electron hopping in LiCuNb3O9

The role of A-sited elements in double perovskite colossal dielectric LiCuNb3O9 has been analyzed by replacing the Cu ions with Li ions. Structural analysis revealed the presence of Jahn-Teller effect because of the Cu ions. Two thermally activated relaxations have been observed: the lower temperature one has been assigned to be a polaronic relaxation following Mott variable-range-hopping mechanism. Impedance analysis and humidity sensitive test proved that the higher temperature one is a Maxwell-Wagner relaxation. Our work highlights that the polaronic hopping is responsible for the colossal dielectric permittivity behavior of LiCuNb3O9.

Application Properties Analysis as a Dielectric Capacitor of End-Of-Life Tire-Reinforced HDPE.

The purpose of the present research is to obtain waste of polymeric composite as an insulator capacitive application. Rubber materials, once they end their useful life, may be difficult to reuse or recycle. At present, research only uses one tire recycling method, which involves grinding and separating steel and fibers from vulcanized rubber, and then using the rubber particles for industrial capacitors. The methodology for this research is to compare the permittivity (ε′ and ε″) between high-density polyethylene (HDPE) and the polymer matrix compound, consisting of an HDPE polymeric matrix blended with end-of-life tire particles (ground tire rubber (GTR)), to analyze the feasibility of using such tires as electrically insulating materials (dielectrics). The incorporation of carbon black in the GTR compounds modifies conductivity; GTRs carry a significant amount of carbon black, and therefore some electrical properties may change significantly compared to highly insulating polymer substrates. The performed experimental study is based on a dynamic electric analysis (DEA) test developed in the frequency range of 10−2 Hz to 3 MHz and at different temperatures (from 35 to 70 °C) of different samples type: HDPE neat and HDPE compounds with 10%, 20% and 40% of GTR loads. A sample’s electrical behavior is checked for its dependence on frequency and temperature, focused on the permittivity property; this is a key property for capacitive insulators and is key for examining the possible applications in this field, for HDPE + GTR blends. Results for the permittivity behavior and the loss factor show different electrical behavior. For a neat HDPE sample, no dependence with frequency nor temperature is shown. However, with the addition of 10%, 20%, and 40% amount of GTR the HDPE compounds show different behaviors: for low frequencies, interfacial polarization relaxation is seen, due to the Maxwell–Wagner–Sillars (MWS) effect, performed in heterogeneous materials. In order to analyze thermal and morphological properties the differential scanning calorimetry (DSC) test and scanning electron microscopy (SEM) have been used. Results obtained show that adding waste tire particles in an HDPE matrix allows HDPE + 40% GTR blends to act as a dielectric in capacitors, increasing the capacitor dielectric efficiency in the low frequencies due to the MWS effect, which increases the dielectric constant.

Nonlinear dielectric properties of random paraelectric-dielectric composites

The challenge of designing new tunable nonlinear dielectric materials with tailored properties has attracted an increasing amount of interest recently. Herein, we study the effective nonlinear dielectric response of a stochastic paraelectric-dielectric composite consisting of equilibrium distributions of circular and partially penetrable disks (or parallel, infinitely long, identical, partially penetrable, circular cylinders) of a dielectric phase randomly dispersed in a continuous matrix of a paraelectric phase. The random microstructures were generated using the Metropolis Monte Carlo algorithm. The evaluation of the effective permittivity and tunability were carried out by employing either a Landau thermodynamic model or its Johnson’s approximation to describe the field-dependent permittivity of the paraelectric phase and solving continuum-electrostatics equations using finite element calculations. We reveal that the percolation threshold in this composite governs the critical behavior of the effective permittivity and tunability. For microstructures below the percolation threshold, our simulations demonstrate a strong nonlinear behaviour of the field-dependent effective permittivity and very high tunability that increases as a function of dielectric phase concentration. Above the percolation threshold, the effective permittivity shows the tendency to linearization and the tunability dramatically drops down. The highly reduced permittivity and extraordinarily high tunability are obtained for the composites with dielectric impenetrable disks at high concentrations, in which the triggering of the percolation transition is avoided. The reported results cast light on distinct nonlinear behaviour of 2D and 3D stochastic composites and can guide the design of novel composites with the controlled morphology and tailored permittivity and tunability.

Controlling negative permittivity and permeability behavior in LaFeO3 through sintering temperature

In this paper, the resonance behavior of LaFeO3 in the GHz range was investigated. Synthesis of LaFeO3, by solid state reaction between Fe2O3 and La2O3, was confirmed by X-ray diffractometry. LaFeO3 exhibited dielectric resonance and magnetic resonance, which can lead to negative permittivity and negative magnetic permeability. By controlling sample synthesis parameters, specifically sintering temperature, the peak in negative permeability can be tuned between 2.6 and 2.8 GHz, while the peak in negative permittivity can be tuned between 0.8 and 1.2 GHz. This material can be applied to fields such as electromagnetic metamaterials, where it could be used to increase the gain of an antenna, or to control the transmission of microwaves.

Polyvinyl alcohol/carbon fibers composites with tunable negative permittivity behavior

Random composites with negative permittivity behavior have drawn increasing attention due to their great unique properties. However, there is an urgent requirement in modulating negative permittivity for practical applications. In this study, a novel design approach to tunable negative permittivity according to the regulation of insulating component was proposed. Polyvinyl alcohol (PVA) was introduced into the graphitizing carbon fibers (CFs) skeleton by an impregnation process to prepare CFs/PVA composites. When the content of PVA reached 35.4 wt%, the CFs skeleton was thoroughly covered with insulating PVA film. Along with the great change of microstructure, the Drude-like negative permittivity of the resulting composites decreased by several orders of magnitude and showed a low plasma frequency, which was attributed to the dilution of electron density. Further investigation revealed that the negative permittivity was in association with the inductive character, resulting from the conductive closed paths among the CFs/PVA composites. The tunable negative permittivity in CFs/PVA composites has great potential applications in electromagnetic shielding.

Dielectric dispersion of copper/rutile cermets: Dielectric resonance, relaxation, and plasma oscillation

In this work, dielectric behaviors of dielectric resonance, relaxation, and plasma-like negative permittivity are observed in percolative copper/rutile cermets. Transition for permittivity changing from positive to negative is associated with composition and determined by percolation. The resonance and relaxation responses are related to isolated metallic particles or clusters. Negative permittivity is induced by the plasmonic state of electrons within percolating pathways and dielectric loss of epsilon-negative composites is dominated by conduction loss. Besides, the percolative cermets change from electrical capacitive to inductive with the permittivity transition. Epsilon-negative cermets are expected to be used for electromagnetic shielding and coil-less electrical inductors.

Compressible sliver nanowires/polyurethane sponge metacomposites with weakly negative permittivity controlled by elastic deformation

Flexible and compressible metacomposites with negative permittivity have a great value in wearable devices, sensors, electronic skin, etc. To balance the negative permittivity behavior and flexibility, a novel preparation strategy was proposed in this study. The polyurethane sponge (PUS) was impregnated with synthesized sliver nanowires (AgNWs) to achieve flexible AgNWs/PUS composites, and the effect of compressed elastic deformation on negative permittivity was investigated. For the composites with 3.1 wt% AgNWs, when the compressed elastic deformation reached 60%, the permittivity changed from positive to negative values, conforming to Lorentz-like negative permittivity. When the content of AgNWs reached 6.3 wt%, the Drude-like negative permittivity began to appear without the action of an applied load, and the negative permittivity was as small as about − 2, indicating a weakly negative permittivity. Meanwhile, with the increase in deformation, the absolute values of Drude-like negative permittivity increased owing to the improvement of electron density. It manifested that the compressed elastic deformation played an important role in negative permittivity. Further investigation revealed that the inductive character was responsible for the negative permittivity. This paper provides a novel approach to controlling the negative permittivity according to elastic deformation.

Effect of Porosity on Functional Properties of Lead-Free Piezoelectric BaZr0.15Ti0.85O3 Porous Ceramics.

The present paper reports the dependence of dielectric, ferroelectric and piezoelectric properties on the porosity level in BaZr0.15Ti0.85O3 ceramics with porosity from 5% to 21%. Microporosity with 0–3 connectivity has been produced using PMMA microspheres as a sacrificial template. The functional properties (dielectric, ferroelectric and piezoelectric effect) are mostly affected by the “dilution effect”: permittivity decreases by 40% when porosity increases by 21%, and Pmax decreases from 13 to 5 µC/cm2 while the Prem is in the range of (2–8) µC/cm2. However, the reduction of the zero-field permittivity and hysteretic behaviour of ε(E) while the tunability level is still high makes from porous ceramics interesting materials for tunability application.

Tunable negative permittivity of Bi2O3–SiO2/MWCNT glass-nanocomposites at radio frequency region

In this work, the negative dielectric constant in the frequency range 1 MHz to 3 GHz and the temperature range 140 K to 300 K are studied. The dielectric parameters (e′, e″, tanδ), conductivity ( $${\sigma }_{\text{ac}}$$ ), reactance (Z′, Z″), and magnetization (Ms) with respect to the multiwall carbon nanotube (MWCNT) loading are discussed in detail. A percolation phenomenon in ac conductivity ( $${\sigma }_{\text{ac}}$$ ) is noticed when the MWCNT content increased from 5 to 10 wt%. The perceived ac conductivity spectra of various trends of present BS/MWCNT glass-nanocomposites are explained by Jonscher’s power law or Drude model. The negative permittivity is observed with the formation of the 3D conductive network, and negative value and frequency range of the real part of permittivity (e′) are precisely adjusted by varying concentration of MWCNT. The resonance frequency-dependent negative permittivity behaviour in the BS/MWCNT glass-nanocomposite with low content MWCNT can be explained by Lorentz model, and the plasma-like negative permittivity behaviour was explained by Drude model. This work offers a favourable outcome to tunable negative dielectric behaviour and high dielectric constant materials.

Origin of ultrahigh thermal stability on dielectric permittivity and dipole glass-like behavior of 0.4Ba0.8Ca0.2TiO3-0.6Bi(Mg0.5Ti0.5)O3 based ceramics

The 0.4Ba0.8Ca0.2TiO3-0.6Bi(Mg0.5Ti0.5)O3 (BCT-BMT) and 5 mol% Si doped 0.4Ba0.8Ca0.2TiO3-0.6Bi(Mg0.5Ti0.5)O3 (BCST-BMT) ceramics with a pseudo-cubic crystal structure were prepared. Both as-prepared and O2 annealing ceramics (BCT-BMT-O2 and BCST-BMT-O2) exhibit a typical re-entrant dipole-glass-like relaxor behavior and excellent thermal stability of dielectric permittivity above Tm. A statistical model was employed to describe the temperature dependence of dielectric permittivity, which reveals the origin of the special dielectric properties. The large dielectric permittivity is attributed to the weakly interacting polar nanoregions (PNRs) associated with complex ionic substitution of both the A-site and B-site. The ultrahigh thermal stability is related to the thermal distribution of active dipoles. The Si doped BCT-BMT ceramic shows that the capacitance variation are lower than ± 5 % (1209 ± 60) in a wide temperature range from 437 K to 796 K with a low dielectric loss (tanδ < 0.025) from 443 K to 714 K, indicating a promising material for use in high-temperature capacitors.

Impedance spectroscopy and conduction mechanism of ferroelectric rich [formula omitted] magnetoelectric composite

In the present work, structural and dielectric properties of 0.7PbZr0.52Ti0.48O3−0.3CoFe2O4 composite prepared by a mixed oxides route were explored. X-ray diffraction analyses confirmed the formation of distinct CoFe2O4 and PbZr0.52Ti0.48O3 phases in the prepared composite. Temperature dependent dielectric permittivity behavior displayed three distinct peaks: a frequency independent peak at high temperature (T = 663K) is identified as structural phase transition of PbZr0.52Ti0.48O3 and two thermally activated frequency dependent peaks which showed a Debye- and relaxor-like behaviors at low and intermediate temperatures, respectively. The mechanism for these relaxations is elucidated on the basis of conduction associated with the single- and doubly-ionized oxygen vacancies. Impedance spectroscopy analysis was used to estimate the activation energy (Ea) of constituent phases and we found that Pb(Zr0.52Ti0.48)O3 phase has a dominant role (i.e., EPZT>ECFO) in describing the relaxation/conduction mechanism of prepared composite. Moreover, the values of Ea calculated from the dielectric, impedance and conductivity data were found to be comparable which clearly indicate that the relaxation and conduction processes in the prepared composite are related to same origin.

The delay of phase transition to the polar phase in relaxors: influence of ultraviolet illumination

The time dependence behavior of the dielectric permittivity of lead lanthanum zirconate titanate transparent ceramic sample from the moment of the field application at certain temperatures after the zero-field cooled regime is compared to that exhibited by a single-crystal lead magnoniobate. The delay time of the phase transition from the glasslike to the field-induced ferroelectric state was determined from the sharp change in the dielectric permittivity in a lead magnoniobate single crystal. The same transition in lead lanthanum zirconate titanate has more smooth behavior. In the case of ultraviolet illumination, the delay becomes a few times shorter for both cases.

Optical Absorption of a Composite Based on Bilayer Metal–Dielectric Spherical Nanoparticles

Optical properties of core–shell (metal) nanoparticles and composites based on them were investigated in the classical approximation. Frequency dependences of the real and imaginary parts of the dielectric permittivity of bilayer particles and absorption coefficients of composites based on them were calculated. Small-scale oscillations of the real and imaginary parts of the dielectric permittivity and absorption coefficient were found in the low-frequency spectral region. The behavior of the dielectric permittivity of bilayer nanoparticles was analyzed for the limiting cases of thin and thick shells. The influence of the effective mean free pathlength of electrons on the optical characteristics of the bilayer nanoparticles was considered. Two maxima of the composite absorption coefficient were demonstrated to be due to hybridization of polar modes.

Colossal permittivity in (Li + Nb) co-doped Fe2O3 ceramics

(Li + Nb) co-doped (Li + Nb)xFe2-xO3 (with x = 0.0005, 0.005, 0.05, and 0.1) ceramics were prepared by sol-gel method. Their structural, dielectric, humidity, and magnetic properties were investigated. Colossal permittivity (~104) was approached or achieved in all doped samples even with a very small doping level of x = 0.0005. The colossal permittivity behavior is composed of two dielectric relaxations with the low-temperature one being a polaron relaxation due to electrons hopping between Fe3+ and Fe4+ ions and the high-temperature one being a Maxwell-Wagner relaxation caused by humidity-sensing properties.

Tunable radio-frequency negative permittivity of Carbon/CaCu3Ti4O12 metacomposites

Abstract In this paper, metacomposites of carbon nanotubes/CaCu3Ti4O12 (CNTs/CCTO), carbon blacks/CaCu3Ti4O12 (CBs/CCTO), and CNTs-CBs/CCTO were fabricated by low-temperature sintering process. The CNTs-CBs building blocks were fabricated by one-step electrostatic self-assembly method. In carbon/CCTO metacomposites, magnitude of negative permittivity ranged from 103 to 100 while its band-width ranged from 300 MHz to 1 GHz. An electrical percolation phenomenon was verified in ac conductivity spectra, suggesting the transition of conductive mechanism. Negative permittivity was ascribed to low-frequency plasma oscillation in carbon networks, corresponding to inductive character. The pendulum-like simple harmonic motion (SHM) model was applied to clarify the negative permittivity behavior. Accumulating of carbon clusters or networks in composites resulted in colossal dielectric loss (10−1

Permittivity experimental determination as a frequency function

Objective: To determine the behavior of dielectric permittivity of class II ceramic capacitor in function of frequency up to 10MHz.&#x0D; Context: in telecommunications and high frequency circuits is necessary to take into account the diminishing of permittivity on dielectrics of ceramic capacitors with the frequency growth, two quantitative methods are proposed to determine this behavior.&#x0D; Method: First, the impedance meter bridge FLUKE PM5306 was used in the frequency range from 10^2 Hz to 10^5 Hz; and second, a novel low-cost electronic circuit for the frequency range between 10^4 Hz to 10^7.&#x0D; Results: The results from the circuit were validated using the impedance meter bridge RLC FLUKE PM 6306. The measure of the complex capacitance from three capacitors and their loss tangent were obtained.&#x0D; Conclusions: The capacitance decreasing with the increment of the frequency was observed in the impedance meter bridge and the implemented circuit, finding a convergence between both methods in the common frequency region.

Tailorable negative permittivity in Fe/BaTiO3 meta-composites

Meta-composites with negative permittivity are promising candidates for future electronics such as microwave absorbers, novel capacitors, etc. In this work, we proposed to develop the Fe/BaTiO3 meta-composites with tuneable negative permittivity. Fe content influenced the conductivity of composites and even led to the change of the conductive mechanism. The tuneable permittivity behavior was achieved by controlling the Fe fraction, and the plasma oscillation theory was employed to explain the negative permittivity behavior. Meanwhile, a frequency-switched negative permittivity was observed in this composite, which could be used to extend applications of meta-composites.

DC bias electric field and stress dependence of piezoelectric parameters in lead zirconate titanate ceramics – Phenomenological approach

The piezoelectric material behavior, including loss mechanism, under external DC electric field and stress biases have been extensively studied in lead zirconate titanate ceramics. However, in order to achieve a better understanding of these effects, development of a comprehensive model is required. The purpose of this paper is to develop a phenomenological model to explain the nonlinear nature of piezoelectric parameters under DC bias electric field and stress. Therefore, the Landau-Devonshire energy function considering external biases was developed and accordingly the material properties were derived, based on first order approximation. In order to explain the compliance and piezoelectric constants change higher order elastic and electrostrictive terms were introduced into the Gibb's free energy function.Accordingly, thermodynamic theory parameters, including higher order parameters, of a soft PZT were measured and characterized based on inverse permittivity behavior near Curie temperature. Finally, the phenomenological model predictions of material property changes under DC bias electric field and compressive stress were compared with experimental data reported by our group. The proposed model succeeded to explain the material properties change under external biases. Furthermore, the effect of DC electric field and compressive stress on loss parameters were explained based on domain wall motion.

A tri-band left-handed meta-atom enabled designed with high effective medium ratio for microwave based applications

This paper represents a tri-band left-handed meta-atom with high effective medium ratio, which is applicable for tri-band microwave based communication applications. The proposed meta-atom consists of modified complementary split ring resonator (CSRR) with two pi shaped metal strip loaded in the inner side. It shows the behavior of negative permeability and permittivity at 2.85 GHz, 4.83 GHz, 8.39 GHz, and 11.42 GHz resonance frequencies and extracted the double negative (DNG) metamaterial properties. The designed meta-atom dimension is 0.076λ×0.076λ at lower resonance frequency. To develop and analyze the offered meta-atom, the electromagnetic (EM) simulator CST Microwave Studio and MATLAB software were used. The equivalent circuit with RLC components of the proposed metamaterial unit cell is also investigated through ADS simulator and comparing S parameter (transmission coefficients) results with CST results. Analysis and comparison have been carried out with different configurations, such as various design structures, distinct substrate, changing the gap of the splits, and various array measures. All the array configurations proved that the frequency of operation is in the S-, C-, and X-bands. The designed meta-atom has double negative regions of 2.89–2.96 GHz, 4.84–4.99 GHz, 8.42–8.49 GHz, and 11.43–12.32 GHz, with the regions of effective negative refractive index 2.85–3.09 GHz, 4.83–5.36 GHz, 8.40–8.57 GHz, and 11.40–12.55 GHz, respectively. The effective medium ratio is 13.16; this implies that the proposed miniaturized meta-atom design is efficient and compact. The scattering parameter dimension of the meta-atom promising for the microwave based applications at S-, C-, and X-bands.

Polyethylene Composites with Segregated Carbon Nanotubes Network: Low Frequency Plasmons and High Electromagnetic Interference Shielding Efficiency.

Polyethylene (PE) based composites with segregated carbon nanotubes (CNTs) network was successfully prepared by hot compressing of a mechanical mixture of PE and CNT powders. Through comparison with a composite comprising randomly distributed carbon nanotubes of the same concentration, we prove that namely the segregated CNT network is responsible for the excellent electrical properties, i.e., 10−1 S/m at 0.5–1% and 10 S/m at 6–12% of CNT. The investigation of the complex impedance in the frequency range 1 kHz–2 MHz shows that the sign of real part of the dielectric permittivity changes from positive to negative in electrically percolated composites indicating metal-like behavior of CNT segregated network. The obtained negative permittivity and AC conductivity behavior versus frequency for high CNT content (3–12%) are described by the Drude model. At the same time, in contrast to reflective metals, high electromagnetic shielding efficiency of fabricated PE composites in the frequency range 40–60 GHz, i.e., close to 100% at 1 mm thick sample, was due to absorption coursed by multiple reflection on every PE-CNT segregated network interface followed by electromagnetic radiation absorbed in each isolated PE granule surrounded by conductive CNT shells.