Permittivity Behavior Research Articles

Cesium Iron (III) Pyrophosphate Prepared Using a Solid‐State Process: Structure, Mössbauer Spectroscopy, and Relaxation Dynamics

AbstractThis study aims to synthesize the cesium iron (III) pyrophosphate compound CsFeP2O7 using a conventional solid‐state reaction method. The refinement of the X‐ray diffraction pattern indicated that the sample crystallized in a monoclinic structure at room temperature. The morphology and composition of the CsFeP2O7 compound were further analyzed using scanning electron microscopy (SEM) in conjunction with energy‐dispersive X‐ray spectroscopy (EDX). The Mössbauer spectroscopy confirmed the paramagnetic behavior of the CsFeP2O7 phosphate material at room temperature. The FTIR spectrum revealed absorption peaks corresponding to the fundamental modes of P2O74− anion vibrations. The electrical and dielectric properties were characterized using impedance spectroscopy as a function of frequency and temperature. The activation energy for continuous conductivity, (σdc), was found to be 0.13 eV for the temperature range [453–533 K] and 0.44 eV for the temperature range [553–673 K]. The permittivity behavior was analyzed using the Maxwell–Wagner model of interfacial polarization. The contribution of the grains and grain boundaries to the conduction mechanism was confirmed by Nyquist plots, which were fitted with an appropriate equivalent circuit. The imaginary parts of impedance (Z″) and modulus (M″) curves indicate a dielectric relaxation in the sample.

Modified negative permittivity and X-band microwave absorption in polyvinyl Alcohol–MWCNT metacomposites

Metacomposite films with modifiable negative permittivity are promising for wearable cloaking, sensing, electromagnetic interference shielding, and microwave absorption. The purpose of this study is to fabricate metacomposite films composed of polyvinyl alcohol (PVA) and multi-walled carbon nanotubes (MWCNTs) and demonstrate control of permittivity by varying MWCNT concentration. Drude-Lorentz and Drude models show negative permittivity behaviour as the MWCNT content increases. The Drude-Lorentz and Drude models confirm that at 1 wt% MWCNT loading, percolation occurs, leading to increased conductivity and a transition from positive to negative permittivity (−9 at 10 kHz and −200 at 34 kHz). Drude's model predicts negative permittivity across the entire frequency range of PVA with 3 wt% MWCNT. Metacomposite films exhibit electrical percolation, conductivity switching, permittivity shift, and capacitive-to-inductive transitions. These composites also demonstrate excellent X-band microwave absorption properties (up to −50 dB reflection loss) and a shielding efficiency of 22 dB, suggesting an absorption-dominated shielding mechanism.

Tunable negative permittivity behavior and excellent electromagnetic shielding performance of pyrolytic carbon‐glass fiber felt/epoxy resin metacomposites

AbstractEffective and accurate adjustment of negative permittivity behavior is worthy of further investigation. Herein, pyrolytic carbon‐glass fiber felt/epoxy resin (PyC‐GFF/ER) metacomposites with tunable negative permittivity were prepared using an impregnation‐calcination method. The permittivity, electrical conductivity, and electromagnetic shielding performance of the polymer metacomposites were investigated. Due to the inherent three‐dimensional structural network of GFF, the PyC adhering to the surface of glass fiber easily formed a conductive network in the composites. As the PyC content increased in the ER composites, the conductivity mechanism changed from hopping conduction to metal‐like conduction. The ER composites with high PyC contents showed negative permittivity behavior and the epsilon‐near‐zero response owing to the low frequency plasma state of free electrons in the PyC‐conduction network. By controlling the PyC content, the negative permittivity behavior of ER composites could be effectively tuned. With the increase in PyC content, the values of negative permittivity increased, and the epsilon‐near‐zero frequency shifted to a higher frequency. Moreover, the ER composites with high PyC contents showed excellent electromagnetic shielding properties (29.4 dB) at X‐band. This work not only provided a feasible method to realize the tunable negative permittivity of polymer metacomposites, but also promoted its application in the microwave field.Highlights The pyrolytic carbon‐glass fiber felt/epoxy resin composites were fabricated. The negative permittivity was first reported in the PyC‐GFF/ER composites. Tunable negative permittivity could be well explained by Drude model. The polymer composites had excellent electromagnetic shielding property.

Tunable negative permittivity behavior in alumina ceramic composites with different carbon fillers

Carbon/ceramic composites with negative permittivity have motivated a considerable concern due to their special properties and various applications. Herein, series of alumina ceramic composites consisting of different carbon fillers were prepared by the hot-pressed sintering, and the carbon fillers included carbon sphere (CS), carbon black (CB), carbon fibre (CF), carbon nanofibre (CNF) and graphene nanosheet (GN). The impact of various carbon fillers on the electrical performance of composites were investigated comparatively. It was found that CF ceramic had hopping conduction, capacitive character and positive permittivity, and micron-sized CFs were embedded in isolation within the ceramic composite. The other ceramics with carbon nanofillers demonstrated metallic-type conductance, inductive character and negative permittivity. The carbon nanofillers evenly dispersed and easily formed carbon network that improve the flow of free electrons in the composites, and the negative permittivity behavior imputed to the low frequency plasmonic state of abundant free electrons in the carbon networks. Furthermore, the magnitude of negative permittivity was in connection with the type of carbon nanofiller. The one- or two-dimensional carbon nanofillers were more easily connected to each other to form a denser carbon network, and thus the CNF and GN ceramics had the larger absolute values of negative permittivity, which was in accord with Drude model.

Hydrogenation Influences the Created Giant Dielectric Behaviors of (Bi+W) Codoped Anatase TiO2

Introductions: TiO2 nanoparticles ceramic (NPs) codoped with Bi and W ions have been synthesized by a hydrothermal technique. A portion of the prepared ceramic was posthydrogenated. Ceramic NPs were characterized by traditional methods. Crystalline structures and optical properties were investigated using X-Ray diffraction (XRD) and diffuse reflection spectroscopy, respectively. Methods: The present work has focused on the creation of a colossal (giant) dielectric permittivity (GP) behavior with the TiO2 host NCs through the Bi/W codoping to construct electronic core/shell structures. In addition, the influence of post-hydrogenation on the created GP was also examined. Results: It was found a high permittivity of 3.69×104 at 1 kHz, which was reduced to 3.29×104 by the hydrogenation of the sample. This is attributed to the densification of the itinerant electrons by the effect of the catalytic power of the doping W5+ ions to dissociate the adsorbed H2. Conclusion: The present values of GP are much higher than the permittivity of the pure TiO2 and the Bi-doped TiO2 ceramic, which was attributed to the construction of core/shell electronics structures. As a result, the doping process has been studied in detail in relation to scientific expectations.

Epsilon‐negative materials with lower percolation threshold derived from segregated structures

AbstractEpsilon‐negative materials (ENM) at radio frequency, usually designed based on percolation theory, recently drew much attention because of their potential applications in capacitors, transistors, and antennas. However, randomly distributed conductive functional materials cannot achieve directional long‐range electron transportation within the material, resulting in decreased utilization efficiency. The morphology design of the substrate material can change the distribution state and electron transfer pathway of conductive fillers. By controlling the size of the polystyrene (PS) and the content of multi‐walled carbon nanotubes (MWCNTs), PS/MWCNTs composites with random structures and segregated structures were designed, both of which exhibited negative permittivity with increasing MWCNTs content. Further investigation revealed that negative permittivity behavior is due to the establishment of the conductive network and the plasma oscillation of free electrons. Moreover, components with segregated structures have lower percolation thresholds, as directional electron transport is achieved and conductive fillers are efficiently utilized. This work provides a new method for guiding the electron transport pathway and effectively changing the distribution state of conductive fillers in ENM.Highlights Negative permittivity is achieved by plasma oscillation at radio frequency. The segregated structure leads to a decrease in the percolation threshold. Epsilon‐negative materials have good prospects in inductive components.

Kapok-derived carbon/fly ash ceramic metacomposites with tunable negative permittivity behavior

In this paper, kapok-derived carbon/fly ash (KDC/FA) ceramic metacomposites were fabricated by vacuum hot-press sintering with FA and kapok fiber as raw materials, and their conductivity, dielectric properties, and impedance response were researched. The composition and microstructure of the metacomposites had a significantly impact on the electrical characteristics. With the increase of KDC content, a 3D conductive network was formed inside the composite, accompanied by a shift in the conductive mechanism. The tunable plasma-type negative permittivity behavior was observed. The absolute value of negative permittivity and the plasma oscillation frequency became larger as the KDC contents increased, which were consistent with the analytical results of the Drude model. This study designed and prepared a new environmental metacomposite with adjustable negative permittivity using biomass materials (kapok fibers) and solid waste (FA), which had a great significance for development of metamaterials in the future.

Negative permittivity and permeability behaviour of SrFe12O19/rGO metacomposite for microwave absorption in 2–18 GHz range

Double-negative performance has played a significant role in electronic applications owing to its both permeability and permittivity negative values. Microwave absorption material has a substantial role in electromagnetic shielding, radar absorption, stealth applications, etc. Herein, a novel double-negative metacomposite, SrFe12O19/rGO, was designed by a simple one-pot hydrothermal method, and the microwave absorption properties of the material were studied in the microwave region from 2 to 18 GHz using VNA analysis. The structural and morphological studies were analysed using XRD, FT-IR, and SEM instrumentation techniques and the magnetic property of the material was studied using VSM analysis. Both studies confirmed the hard magnetic nature of the material. The particle sizes of SrFe12O19 and SrFe12O19/rGO measured from XRD are 55.60 nm and 41.55 nm, respectively. Hexagonal plate-like morphology were observed from FESEM images. The coercivity of SrFe12O19/rGO increased, and the magnetocrystalline anisotropy was changed due to the decrease in particle size. The magnetic saturation value decreases due to the presence of non-magnetic rGO. The resultant SrFe12O19/rGO metacomposite shows negative permittivity and permeability values. The minimum reflection loss values observed for pure and rGO-decorated strontium ferrites are −28.49 dB at 7.76 GHz and −23.78 at 11.04 GHz, respectively. In addition to experimental results, simulation studies were also performed to study the reflection loss with matching thickness using a quarter wavelength mechanism. The results show that this composite can be employed as a left-handed metamaterial that finds applications in absorption, antennas, sensors, wireless power transfer systems, etc. The left-handed metamaterial can shift the frequency region from a lower to a higher frequency region. The rGO decorated metacomposite is a promising material for microwave absorption at higher frequency regions.

Evidence for Vogel Fulcher behavior of the 50K-relaxation in (Tm+Ta) co-doped TiO2 ceramics

There is still no consensus about the relaxation behavior of the so-called 50[Formula: see text]K-relaxation in acceptor and donor co-doped TiO2 system. Herein, the relaxation behavior of the 50[Formula: see text]K-relaxation was investigated in (Tm[Formula: see text][Formula: see text][Formula: see text]Ta) co-doped rutile TiO2 ceramics. Dielectric properties of the sample were studied in the temperature range of 2–300[Formula: see text]K under 100 frequencies in the range of 102–106[Formula: see text]Hz. The sample shows a pronounced 50[Formula: see text]K-relaxation. Various relaxation behaviors of Arrhenius, Mott’s variable range hopping, and Vogel Fulcher laws were tried to describe the relaxation. The result indisputably evidences that the 50[Formula: see text]K-relaxation follows the Vogel Fulcher law. This work provides a heuristic hint to understand the fundamental physics underlying the colossal permittivity behavior in the acceptor and donor co-doped TiO2 ceramics system.

Modulating microwave attributes of Ba1−xSrxTiO3 nanoparticles: Insights into strontium concentration, structural intricacies and electromagnetic dynamics

In this pioneering investigation, we meticulously synthesized Ba1−xSrxTiO3 nanoparticles, with Sr concentrations varying between 0.0 and 0.4 at intervals of 0.1, via a refined chemical approach. The crux of our study lies in establishing the intricate correlations between the chemical constitution (primarily Sr concentration), salient structural attributes (encompassing lattice and microstructural parameters), electrical dynamics and consequential microwave characteristics. X-ray diffraction (XRD) analyses reinforced the unity between the average ionic radii of the Ba/Sr ions and the lattice constants. Scanning electron spectroscopy (SEM) furnished insights into the microstructural intricacies, while the nominal chemical composition was ascertained via energy-dispersive X-ray (EDX) spectroscopy. A deep dive into the electrical realm revealed the temperature and field-dependent behaviors of permittivity, tangent losses and polarization. The electromagnetic traits of Ba1−xSrxTiO3 (where 0.0 < x < 0.4) were meticulously delineated by analyzing the experimentally determined S-parameters across a frequency spectrum of 6 to 18 GHz. Our findings elucidate that the predominant losses of electromagnetic wave energy are attributable to aggregated electrical losses, predominantly steered by polarization processes. Our findings demonstrate a significant attenuation in the reflected wave energy, with values spanning from − 14.3 to − 17.1 dB, highlighting the potential of these nanoparticles for cutting-edge applications in electromagnetic interference mitigation.

Non-drude-like behavior of the photoinduced dielectric permittivity of GaAs and Si in the gigahertz range frequencies

A non-drude-like behavior of the real part of the photoinduced permittivity ReåP of GaAs and Si samples in the gigahertz range was detected by direct resonator measurements under conditions of fiber-optic irradiation at a wavelength of ë = 0.97 microns with power changes P in the range of 0÷1 W. It is shown that, in accordance with the hypothesis of the exciton mechanism of the photoinduced microwave dielectric permittivity, ReåP increases with increasing P (approaching saturation above P = 200 mW) instead of decreasing within the framework of free charge carriers by Drude. The generality of the behavior of the real parts of the photoinduced permittivity observed in semiconductors of different types (straight-band GaAs and non-straight-band Si) in different electrodynamic systems (waveguides, resonators, metastructures) testifying to the universality of the exciton mechanism is demonstrated. Optically controlled metastructures in the GHz band containing resonant electrically conductive elements loaded with GaAs and Si samples are proposed for the first time: a metastructure based on linear dipoles and a half-wave electric dipole based on a multi-pass spiral. Gigahertz responses of metastructures and the transformation of responses associated with changes in the dielectric permittivity of Si and GaAs during photoexcitation were measured for the first time. Based on the hypothesis put forward about the effect of excitons on photoexcitation, the observed saturation effect of gigahertz photoinduced permittivity is discussed.

Thermally activated processes: the underlying mechanism of activated state formation.

In the present manuscript, we highlight the contradictions in the thermally activated processes theory which treats a system's activated state as a state of the phonon subsystem. We offer an alternative model, in which the activated state is treated as an electron subsystem state. The mechanism of the activated state formation is as follows: thermal fluctuations excite electrons of some particles within the activation zone. This excitation is then shared with other particles in the ground state. This creates a locally-equilibrium activated state. We estimate the lifetime of such a state and derive expressions for the activation energy and entropy, necessary to calculate the number of excited particles in the activation zone and the energy of the particle's excitation. We validate the model experimentally, by examining the behavior of nanocrystals of undecylenic acid in pores of silica gels using dielectric spectroscopy and the analysis of the complex dielectric permittivity behavior at different temperatures and with different frequencies of the external field. The estimated number of excited particles in the activation zone of the nanocrystals and the particle excitation energy for the dielectric relaxation process observed in undecylenic acid confirm that the results of the experiment align well with the proposed model.

Establishing the correlation of negative permittivity and AC conductivity of La2−xSrxNiO4 (x = 0, 0.1, 0.3, 1.0) for microwave shielding applications

In Sr-doped La2NiO4, we observed plasma-like negative permittivity behavior along with enhanced shielding effectiveness. The primary shielding mechanism was reflection, attributed to intense impedance mismatching.

Extremely low-frequency plasmonic state achieved in AC-ZnO polymer composite for tuned negative permittivity applications

Flexible composites with negative permittivity behaviour have generated a lot of attention due to their potential applications in the electromagnetic field and novel capacitance. This work aimed to design and explore surface microstructure-induced negative permittivity flexible composites for their metamaterial properties. The composites were synthesized using poly (methyl methacrylate) or PMMA, activated carbon (AC), and zinc oxide (ZnO) through an in-situ polymerization process. The composite was designed to acquire negative permittivity in the extremely low-frequency regime by increasing the AC and ZnO filling content. The microstructure formation, real permittivity, and ac conductivity of the composites were investigated, and it was observed that the negative permittivity and its magnitude could be controlled by changing the amount of the filler, AC_ ZnO. Flexible composites with suitable permittivity values for ELF applications can create heavy industrial demand.

Temperature dependence of negative permittivity behavior in graphene/alumina ceramic metacomposites

Herein, graphene/alumina (GR/Al2O3) ceramic metacomposites with negative permittivity were prepared by hot press sintering to investigate the inherent connection between negative permittivity and external temperature. An electrical percolation phenomenon was observed in the composites with the increasing GR content. The permittivity changed from positive to negative, which was motivated from the formation of continuous three-dimensional GR networks in the composites. The negative permittivity was attributable to low-frequency plasma state of the freed electrons in the GR networks. In addition, the negative permittivity behavior was temperature-dependent in the composites with high GR contents. The higher external temperatures led to the larger absolute values of negative permittivity, and yet the negative permittivity varied very little by applying various temperature, compared to changing the additive amount of GR. As the external temperature elevated, the variation amplitude of negative permittivity enlarged in the composites with higher GR contents.

Understanding the negative permittivity behavior of polyvinyl alcohol based metamaterials under radio frequency

Functional metamaterials that exhibit negative dielectric permittivity through percolative network formation have attracted immense attention due to their significant potential for a wide range of applications in electronic devices. Negative permittivity has taken off as a research topic recent years in percolative composites. The polymer nanocomposites (PVA/H-Pa-G) were prepared using the α-Fe2O3 modified GNP and HCl doped polyaniline (Pani) based nanofillers (H-Pa-G). The as prepared samples were characterized in order to analyze their dielectric response for understanding the negative permittivity behavior. Below the percolation threshold for the polymer nanocomposite with 0.10%, 0.25% H-Pa-G nanofiller weight fraction, an increase in σac conductivity is observed with increase in frequency. The dielectric study confirmed the negative permittivity behavior for the polymer nanocomposite (0.50%, 1.00% and 2.00%) above the percolation threshold. This can be mainly attributed to the presence of the conductive network of H-Pa-G nanofiller in the PVA matrix. On the contrary, the positive permittivity is due to the insulative nature of PVA matrix. The empirical data of real permittivity was fitted using the Drude model that corresponded well with the experimental data with the fp = 1.31 GHz which is further certified by the equivalent circuit model fitting. This proposed work strongly suggest the implication of the as prepared polymer nanocomposite for the negative permittivity materials based applications.

Structural, optical, dielectric, and ferroelectric properties in [formula omitted] ceramics prepared by a solvothermal reflux approach

Chromium (Cr3+) doped BaTi1−xCrxO3 (x = 0.0, 0.03, 0.06, and 0.09) ceramics were prepared by the solvothermal reflux approach. X-ray diffraction analysis confirmed the development of tetragonal structures with P4mm symmetry in the prepared samples. The SEM analysis showed that Cr3+ doping resulted in a microstructure that was dense, uniform, and had smaller grains. Surface chemical information and oxidation states were studied using X-ray photoelectron spectroscopy. The diffuse reflectance spectrum confirmed the effect of Cr3+ content on the direct optical bandgap of BaTi1−xCrxO3 samples which shifts from 3.21 eV to 2.73 eV with increasing Cr3+ content. Dielectric permittivity was found to increase in the low-frequency region with increasing Cr3+ doping content up to x = 0.06, while it decreased in the high-frequency region compared to an undoped sample. The observed behavior of permittivity might be explained in terms of the formation of oxygen vacancy defects and their effects on the polarization dynamics of the material. Moreover, the addition of Cr3+ doping had a strong effect on the ferroelectric characteristics, as seen by the formation of a pinched hysteresis loop, resulting in the improvement of energy storage properties. Based on the obtained results, the sample with x = 0.06 exhibited an enhancement of about 3.3 times in energy discharge density and 26 % in storage efficiency compared to the undoped sample. This might be due to a large difference between the values of maximum and remnant polarizations, reduced tangent loss, and a smaller grain size, which makes this material attractive for use in energy storage devices.

Effect of sintering conditions on colossal dielectric properties of (Tb1/2Nb1/2)0.01Ti0.99O2 ceramics

In this study, we investigated various sintering temperatures (1200 °C−1450 °C) and durations (2–6 h) conditions for preparing (Tb1/2Nb1/2)0.01Ti0.99O2 (TNTO) ceramics. By employing high sintering temperatures (≥1350 °C) and extended sintering durations (≥4 h), we successfully achieved ultra–high dielectric permittivity values (ε′ ∼ 2.2 − 4.1 × 104) and remarkably low loss tangent values (∼0.025−0.079). Remarkably, the temperature coefficient of the TNTO ceramic, sintered at 1350 °C, exhibited exceptional stability, maintaining a value of approximately 15% even at 200 °C. Additionally, we examined the phase structure and microstructure of the TNTO ceramics to gain insights into their colossal permittivity (CP) behavior. The analysis revealed the presence of rutile TiO2 and TbNbTiO6 phases, and the ceramics exhibited a high–density microstructure under high–temperature sintering conditions. The impedance spectroscopy analysis revealed that the primary contributor to the observed CP behavior was the interfacial polarization mechanism. The observed increase in the ε′ value, correlated with the enlargement of the average grain size, can be attributed to the effect of the internal barrier layer capacitor. However, when the sintering time ≥4 h, the grain size did not significantly affect the ε′ value, possibly due to reaching the maximum capacity of electron production for the interfacial polarization process (i.e., the maximum intensity of polarizability). This study provides valuable insights into optimizing the sintering conditions for TNTO ceramics and related compounds, laying the groundwork for the development of a new CP oxide suitable for practical applications.

Highly tunable negative permittivity of carbon nanofiber/alumina metacomposites at different external temperatures

Effective and precise modulation of negative permittivity behavior still deserved further research. Herewith, alumina (Al2O3) metacomposites with various carbon nanofiber (CNF) contents were fabricated using hot-press sintering, and the effects of CNF content and external temperature on the electrical properties of metacomposites were investigated. As the CNF content increased, a three-dimensional interconnected CNF network was formed in the composites, resulting in the conversion of the impedance characteristic and the conductivity mechanism. The composites with CNF content of 2 wt% exhibited negative permittivity behavior, owing to the low-frequency plasma state of free electrons in the CNF conducting networks, which could be well simulated by the Drude model. Excellent electromagnetic shielding performance was observed in the composites with high CNF contents at Ku band, and shielding effectiveness reached more than 30 dB with a reflection-dominated mechanism. Furthermore, the temperature-dependences of the electrical properties of the composites were explored. Both the negative permittivity and conductivity of the composites increased with external temperature rising, which were mainly attributed to the changes in free electron concentration and mobility. It was worth noting that the values of negative permittivity varied very little, which provided an effective method for precise regulation of negative permittivity. This work not only enriched the adjustment method of negative permittivity but also helped to expand the application field of metacomposites.

High temperature study of dielectric and electrical conduction behaviour of La2NiO4

Materials showing negative permittivity have attracted considerable attention from researchers on account of their notable applications in electronic and electromagnetic devices. Discovering materials exhibiting negative permittivity is a challenging task. Very few single-phase oxides have been reported as negative permittivity materials. In this work, we have attempted to investigate the dielectric properties of La2NiO4 to explore the possibility of negative permittivity. To achieve the goal, powder, and ceramic of La2NiO4 have been synthesized by the conventional solid-state reaction method. Rietveld refinement of the X-ray diffraction data studies has confirmed the tetragonal structure and space group I4/mmm. The Dielectric properties and AC conductivity have been studied in the frequency range of 20 Hz–2 MHz and over a wide temperature range (30 °C–600 °C). The permittivity of La2NiO4 is found to be negative at all the measured frequencies and temperatures. The Drude model fitted the experimental data very well, suggesting that negative permittivity behavior can be assigned to the plasma oscillation of conducting electrons. The trend of AC conductivity with frequency is similar to the skin effect observed in metals. The variation of DC conductivity with temperature indicated small polaron hopping conduction mechanism. Analysis of reactance (Z′′) suggested inductive electrical character in the tested frequency and temperature range. Room temperature negative permittivity behavior of La2NiO4 makes it a potential candidate for practical electronic and electromagnetic devices that work in the Radio-frequency range. Furthermore, this work will add a new member to the family of Perovskite oxides showing tunable negative permittivity.