Improvement In Permittivity Research Articles

Systematic determination of the optimized Zr content of Ba(ZrxTi1-x)O3 with high dielectric constant at room temperature for high-voltage system application

In this study, by replacing the B-site element in BaTiO3, a ferroelectric material, with an element with a larger ionic radius, a ferroelectric material with high permittivity at room temperature was synthesized. The powders were prepared by solid-state reaction to perform lattice substitution with Zr4+ (0.72 Å), which has a larger ionic radius than Ti4+ (0.605 Å). To perform effective solid-state reaction and better understand the correlation between variables, this study introduced a design of experiment (DOE) based on the orthogonal array (OA) method included in the PIAno software. By substituting 0.222 mol of Zr, which has a large ionic radius, the crystal structure was deformed through an effective diffuse phase transition (DPT), and this resulted in the largest improvement in permittivity at room temperature. In addition, the powder, which underwent solid-state reaction at 1300 °C, formed the densest structure during sintering, which established the conditions for realizing the best dielectric properties. These results can be utilized as a key material for improving the properties of passive devices used in high-voltage industrial systems in societies undergoing the fourth industrial revolution.

In-situ grown a zeolitic imidazolate framework for boosting sensitivity of breathable wearable electronics

Wearable electronics have emerged as versatile platforms for various biomedical applications. However, developing sensors that are both air-permeable and highly sensitive for long-term, subtle physiological signal monitoring remains a challenge. To overcome this, an innovative in-situ growth method was employed to decorate electrospun polyvinylidene fluoride (PVDF) nanofibers with a zeolitic imidazolate framework (known as ZIF-8). This approach has led to a remarkable 300% increase in sensitivity (5.94 kPa−1) compared to sensors prepared using pure PVDF nanofiber (1.42 kPa−1). This in-situ growth method effectively prevented ZIF-8 agglomeration, contributing to the desired improvement in permittivity (∼1.6), unlike blended ZIF-8/PVDF nanofiber. Furthermore, atomic force microscope and simulations were utilized to demonstrated that the nano-scale structures formed by the uniform growth of ZIF-8 significantly contribute to the enhanced sensitivity of the sensor. In addition to satisfactory air-permeability (10 mm/s) and high sensitivity, the as-prepared sensor exhibits excellent flexibility, enabling it to conform to irregular organ surfaces for real-time monitoring of pulse, respiration, and swallowing. This approach holds great promise for the development of highly sensitive and skin-friendly wearable electronics, offering significant benefits for healthcare advancement.

Phase structure and electrical properties of BiFeO3–BaTiO3 ceramics near the morphotropic phase boundary

As a promising lead-free high-temperature piezoelectric material, BiFeO3–BaTiO3 (BF-BT) is still under debate on its crystal structure, especially for the compositions in the morphotropic phase boundary (MPB). Herein, the crystal structure of (1-x)BF-xBT ceramics near the MPB with x = 0.20–0.33 was analyzed by X-ray diffraction and Raman spectroscopy. With the addition of BT, the phase transition from distorted rhombohedral to pseudo-cubic structure was determined by Rietveld refinement. Raman analysis showed the weakening interactions between the A-site cations and BO6 octahedron, as well as the degenerated distortions of BO6 octahedron. Intriguingly, the results of X-ray photoelectron spectroscopy suggested the inhibition of Fe3+ reduction and decrease in oxygen vacancy concentration by the incorporation of BT. In terms of the electrical properties, the significant decline in Curie temperature, improvement in permittivity, and reduction in high-temperature dielectric loss can be observed with the increase of BT content. The increased remnant polarization, enhanced dielectric response and decreased coercive field were helpful for the piezoelectric performance. The maximum room-temperature piezoelectric coefficient of ∼160 pC/N and high-temperature piezoelectric coefficient of ∼324 pC/N were acquired in the x = 0.30 ceramics. This work provides a clear scope for further research on the structural transformation and high-temperature piezoelectric applications of BF-BT system.

Large-scale preparation of Co nanoparticles as an additive in carbon fiber for microwave absorption enhancement in C band

Recent studies have found that the core–shell structured metal nanoparticles and porous carbon nanofibers (PCNF) are combined into a microwave absorbing material through electrospinning, which exhibits excellent microwave absorption performance. In this study, the core–shell structure Co nanoparticles prepared by the self-developed HEIBE process (production rate of > 50 g/h) were combined with porous carbon fibers, and their absorbing properties were greatly improved. The morphology of Co/PCNF demonstrated that CoNPs are randomly dispersed in the porous carbon nanofibers and carbon nanofiber form complex conductive network which enhances the dielectric loss of the materials. Meanwhile, the Co/PCNF has a low graphitization and shows a significant improvement in permittivity due to the combination of CoNPs and high conductivity of carbon material. The maximum reflection loss (RL) of Co/PCNF reaches − 63.69 dB at 5.28 GHz with a thickness of 5.21 mm and the absorption bandwidth (RL ≤ − 10.0 dB) is 12.92 GHz. In terms of 5.60 mm and 6.61 mm absorber, there are two absorption peaks of − 47.64 dB and − 48.30 dB appear around 12.50 GHz and 14.10 GHz, respectively. The results presented in this paper may pave a way for promising applications of lightweight and high-efficiency microwave absorbing materials (MAMs).

Structural, elastic, optical and dielectric properties of Li0.5Fe2.5 O4 nanopowders with different particle sizes

LiFe5O8 (Li0.5Fe2.5O4) nanopowders were synthesized by the sol-gel auto-combustion method and were annealed at different temperatures of 500, 600, 700, and 1100 °C. The spinel phase formation of these samples has been confirmed by X-ray powder diffraction (XRD) technique and Fourier transform infrared (FTIR) spectroscopy. XRD analysis revealed order to disorder phase transition of Li0.5Fe2.5O4 during the annealing temperature. This structural transition was also confirmed by differential scanning calorimetry (DSC). The scanning electronic microscopy images reveal that nanoparticles size increases from 9 nm to 500 nm with increasing annealing temperature. The influence of particle size on elastic parameters has been investigated by FTIR spectroscopy. The band gap energy estimated by UV–vis spectroscopy of LiFe5O8 nanoparticles decreased from 1.41 to 1.27 eV when the annealing temperature increases. Furthermore, impedance spectroscopy measurements have been carried out over large frequency and temperature ranges. The conductivity spectrum indicates that the tested specimens are defective. It also shows that the conductivity runs to frequency according to Jonscher’s law. Static conductivity responds to temperature in conformity with a small polaron hopping model whereas dispersive one evaluates according to correlated hopping model. The conductivity gets mixed (electronic and ionic) only when samples were annealed at 700 °C and 1100 °C. According to the Nyquist diagram, each sample is capacitive and resistive. Increasing annealing temperature led to major improvements in permittivity, and a giant low-frequency dielectric constant was observed in the sample annealed at 1100 °C. The total loss (ɛ″) is governed by the conduction mechanism and described by Giuntini's theory. The improved electrical, optical, and elastic properties indicates the potential application LiFe5O8 nanoparticles in future multifunctional devices (microelectro-mechanical systems (MEMS), optoelectronic and photovoltaic, photocatalytic activity under visible light, bolometer, low temperature co-fired ceramics (LTCC) and gas sensor applications.).

Dielectric and electro-optic studies of a ferroelectric liquid crystal dispersed with different sizes of silica nanoparticles

ABSTRACT The impact of the size of silica nanoparticles (SNPs) on the properties of ferroelectric liquid crystals (KCFLC 10R) has been investigated by electro-optical and dielectric techniques. We have found that the doping of silica nanoparticles in the host ferroelectric liquid crystal strongly affects the various properties of doped systems. Doping of silica nanoparticles shows a small decrease in spontaneous polarisation and faster switching time. An improvement in permittivity and conductivity with the temperature at a constant frequency was also noticed after dispersion. This dependence is stronger for large size particles (40 nm) and weaker for small size particles (~12 nm). The Goldstone mode (GM) shifts towards the higher relaxation frequency. These results would be useful to manufacture better optical and electronic devices for display, switching and beam steering applications.

Influences of dielectric and conductive fillers on dielectric and mechanical properties of solid silicone rubber composites

Dielectric elastomers are materials being used for electromechanical transduction applications. Their electromechanical response depends on permittivity, Young’s modulus and electric breakdown strength. A factor that limits its application is high operating voltages that can be reduced through improvement in permittivity. One of the methods is by incorporating high permittivity fillers into polymer matrix to obtain dielectric–dielectric composites (DDC).These composites show high permittivity at the cost of reduced flexibility. An alternative solution is development of composites by incorporating organic or inorganic conductive fillers into polymer matrix. These composites show high permittivity with high dielectric loss and low breakdown strength. To overcome both the above limitations both dielectric and conductive fillers are incorporated into dielectric polymer matrix to obtain conductor–dielectric composites (CDC). In this study, high temperature vulcanized solid silicone rubber as matrix has been used to prepare DDC composites with barium titanate (BT) filler and CDC composites with both BT as dielectric and ketjenblack as conductive fillers, using Taguchi design of experiments. The effect of factors such as amount of fillers and curing agent, mixing time in roll mill and curing temperature on the dielectric and mechanical properties are reported. Lichtenecker model predicts the permittivity of the DDC composite more accurately. For the CDC composites permittivity increased by 390%, effective resistivity decreased by 80%, Young’s modulus increased by 368% and Shore A hardness increased by 90% as compared to those of reference matrix. Important interaction effects are observed among both the fillers that are uniformly dispersed without any aggregation.

A Liquid-Metal-Elastomer Nanocomposite for Stretchable Dielectric Materials.

Stretchable high-dielectric-constant materials are crucial for electronic applications in emerging domains such as wearable computing and soft robotics. While previous efforts have shown promising materials architectures in the form of dielectric nano-/microinclusions embedded in stretchable matrices, the limited mechanical compliance of these materials significantly limits their practical application as soft energy-harvesting/storage transducers and actuators. Here, a class of liquid metal (LM)-elastomer nanocomposites is presented with elastic and dielectric properties that make them uniquely suited for applications in soft-matter engineering. In particular, the role of droplet size is examined and it is found that embedding an elastomer with a polydisperse distribution of nanoscale LM inclusions can enhance its electrical permittivity without significantly degrading its elastic compliance, stretchability, or dielectric breakdown strength. In contrast, elastomers embedded with microscale droplets exhibit similar improvements in permittivity but a dramatic reduction in breakdown strength. The unique enabling properties and practicality of LM-elastomer nanocomposites for use in soft machines and electronics is demonstrated through enhancements in performance of a dielectric elastomer actuator and energy-harvesting transducer.

Facile preparation and enhanced dielectric performance of rod-like TiO2/P(VDF-TrFE-CFE) composites

In this study, rod-like TiO2 filler was synthesized one-step hydrothermal method and was incorporated into P(VDF-TrFE-CFE) polymer matrix to obtain composites with high dielectric constant. It is found that the morphology and content of TiO2 fillers play a vital role in tailoring the performance of the as-fabricated composites. The rod-like TiO2 assembled by numerous nanoparticles maintained its primary shape and homogenously distributed in the matrix, thus achieved sophisticated interface and strong interfacial adhesion with P(VDF-TrFE-CFE) polymer, which together contributed to a dramatic improvement in permittivity of composites. Typically, the dielectric constant of composite with 10 vol% rod-like TiO2 reaches 160 at 100 Hz, in contrast to 102.5 for the composite with 10 vol% commercial TiO2 and 47 for pristine P(VDF-TrFE-CFE). This study provides a solution for obtaining high-k dielectric composites with low dielectric loss, which is highly desired for advanced electronic devices.

Study of Cu2O particle morphology on microwave field enhancement

The dielectric enhancement and modulation of a cuprous oxide (Cu2O) microwave-active catalyst material is investigated from an experimental and computational point of view. Experimental synthesis of two particle morphologies that included a cube and spike were carried out using an EDTA hydrothermal synthesis method. The permittivity for the spiked particles at low volume fraction in a paraffin composite exhibited a 20% increase when compared to the cube-shaped particles at the same volume fraction. Using a finite difference time domain (FDTD) simulation, the improvement in permittivity was attributed to the enhanced electric field near the tip of the spike particles and the neighboring interaction at higher volume fractions. The increased electric field at the tips of the particles induces a change in polarizability (dipole density) within the matrix material, which increases the effective dielectric properties of the composite. Furthermore, it was determined that an electrically conductive particle within a high permittivity matrix material is advantageous for generating high localized electric fields that can be utilized for microwave-assisted catalytic reactions.

Enhanced microwave electromagnetic properties of core/shell/shell-structured Ni/SiO2/polyaniline hexagonal nanoflake composites with preferred magnetization and polarization orientations

Core/shell/shell-structured Ni/SiO2/polyaniline hexagonal nanoflakes possessing in-plane [111] easy magnetization (M) and out-of-plane interfacial polarization (P) are synthesized by a three-step liquid chemical method, and their physicochemical properties and growth mechanism are investigated. Three characteristic types of paraffin-bonded ring-shaped nanoflake composites having random (R), vertical–horizontal (V–H), and horizontal–vertical (H–V) orientations of the orthogonal M and P to their two major surfaces are prepared by randomly, vertically, and horizontally aligning the nanoflakes in the paraffin matrix under a magnetic alignment and thermal curing process. The composites are evaluated experimentally and theoretically in the L–Ku (1–18 GHz) bands of microwaves in order to investigate the orientation effect of the orthogonal M and P on their microwave electromagnetic properties. The in-plane M in the H–V-oriented composite and the out-of-plane P in the V–H-oriented composite, which are parallel to the effective magnetic and electric field vectors of incident microwaves, result in a significant enhancement in permeability with multiple magnetic natural resonances and an obvious improvement in permittivity in comparison with other composites, respectively. The observations agree with the theoretical predictions based on the Landau–Lifshitz–Gilbert equation and Bruggeman's effective medium theory for permeability and the Debye's polarization theory for permittivity. As a result, the H–V-oriented composite achieves the best microwave electromagnetic impedance matching and absorption with a broad absorbing bandwidth of 4 GHz, a wide thickness range of 7–10 mm, and a minimal reflection loss of −41.5 dB in the Ku (12–18 GHz) band.

Electrical and mechanical behavior of PMN-PT/CNT based polymer composite film for energy harvesting

Abstract The pyrochlore-free 30-PMN-PT/CNT/PVDF based piezoelectric flexible composite film has been synthesized for potential application in piezoelectric energy harvesting. Electrical characterization reveals that the maximum output voltage and current generated by the 30 vol.% PMN-PT/CNT/PVDF composite is ∼4 V and 30 nA respectively, comparable with the available literature. Further, impedance analysis has revealed a significant improvement in permittivity at low frequency and high temperature with a minimal dielectric loss. AC conductivity behavior fits well with Johnscher’s universal power law that predicts the motion of the charge carriers is translational with sudden hopping. The Nyquist plots indicate the contributions of both grain and grain boundaries at lower temperature (25–100 °C) and additional electrode effect of higher temperature (100–150 °C) on the capacitive and resistive properties of the composite. Mechanical characterization of the composite shows an increase in Young’s modulus of 705 MPa compared to 597 MPa in pure PVDF.

Grain size effects on the dielectric properties of CaCu3Ti4O12 ceramics for supercapacitor applications

CaCu3Ti4O12 ceramic specimens for supercapacitor applications were prepared by the conventional mixed oxide method. The specimens were prepared under different sintering conditions at 1125°C. The SEM results indicated that the mean grain size of CaCu3Ti4O12 increased with increasing sintering time (30min–12h). Using SEM analysis, it was observed that at a sintering time of 2h, CaCu3Ti4O12 ceramic specimens had large-sized grains and the agglomerated parts consisted of small-sized grains and grain boundaries. The X-ray diffraction patterns showed single-phase ceramics with a cubic structure. Increasing sintering times led to substantial improvements in permittivity. The different spectra of frequency dependent impedance spectroscopy for large grains and small grains were compared and analyzed using Cole–Cole plots. AC conductivity as a function of the as a function of sintering times of CaCu3Ti4O12 ceramics was investigated.

Effect of holding time on the dielectric properties and non-ohmic behavior of CaCu3Ti4O12 capacitor-varistors

Giant dielectric ceramics CaCu3Ti4O12 (CCTO) with non-ohmic electrical properties were prepared by a sol–gel processing method. Crystal structure and microstructure of the ceramics have been characterized using X-ray diffraction and Scanning electron microscopy. The effects of sintering duration and cooling rate on electrical properties of the ceramics were investigated by measuring the properties of permittivity, I–V and grain-boundary barriers. Prolonging holding time led to substantial improvement in permittivity, furthermore, the quenched sample showed larger dielectric permittivity than the furnace-cooling one. The non-ohmic behavior relating current density (J) to the applied electric field (E) at different temperatures was characterized. A low-voltage and giant dielectric permittivity CCTO varistor with breakdown voltages in the range of Eb = 0.2–3 kV cm−1, nonlinearity coefficient α = 2–6 and dielectric permittivity e = 4,000–30,000 was obtained. A linear relationship between ln(J) and E1/2 indicated that a Schottky barrier should exist at the grain boundary.

Influence of Fabrication Parameters on the Phase Formation and Dielectric Properties of CaCu3Ti4O12 Ceramics

The giant dielectric permittivity materials CaCu3Ti4O12 (CCTO) were synthesized by conventional solid-state reaction techniques. X-ray diffraction and Raman scattering for the powder indicate that the powder calcined at 950 °C for 12 h has been completely transformed into the purer CCTO phase. Furthermore, the morphology and size of the grains of the ceramics sintered at 1090 °C in the dwell time range from 0 to 26 h were observed by scanning electron microscopy (SEM). Dielectric properties of the polycrystalline CCTO ceramics were characterized in a broad frequency range (100 Hz–1 MHz) and at a temperature ranged from 300 to 500 K. The longer sintering time may lead to more defect structures and the enhanced conductivity, also leads to substantial improvements in permittivity. Grain size and density differences were not large enough to account for the enhancement in dielectric permittivity. Based on the observations, it is believed that the primary factor affecting dielectric behavior is the development of internal defects. The CCTO ceramics sintered at 1090 °C for 15 h exhibit lower dielectric loss (∼0.05) near room temperature, and the dielectric relaxation behavior above 1 kHz was observed to follow the Arrhenius law. The activation energy (Ea) of 0.65 eV indicates that the doubly ionized oxygen vacancies in the grain boundaries are responsible for the dielectric relaxation of the CCTO ceramics.

Erratum to: Electromagnetic interference shielding effects of polyaniline-coated multi-wall carbon nanotubes/maghemite nanocomposites

Highly conductive nanocomposites were prepared by in situ polymerization of polyaniline (PANi) and multi-walled carbon nanotubes (MWCNTs) as electromagnetic interference shielding materials. γ-Fe2O3 nanoparticles were also incorporated in the nanocomposites to improve the ferromagnetic properties. SEM and TEM images showed the uniformly coated PANi on the surface of MWCNTs and γ-Fe2O3. XRD peaks also confirmed the presence of MWCNT and γ-Fe2O3 in the nanocomposites. The nanocomposites showed significant improvement in permittivity, permeability, and electromagnetic interference shielding efficiency due to the conductive effect of MWCNTs and the magnetic effect of γ-Fe2O3. The electromagnetic interference shielding efficiency of nanocomposites increased up to 34.1 dB due to the synergetic effect of reflection and absorption of electromagnetic interference by MWCNTs and γ-Fe2O3 additives.

Dielectric properties of nanosized ZnFe2O4

In this paper we present the results concerning the dielectric properties of the nanosized ZnFe2O4. Dielectric permittivity, the loss factor, as well as the conductivity, were measured in the temperature range 300-630 K and at 1 Hz, 10 Hz, 100 Hz, 1 kHz and 10 kHz frequencies. Significant improvements in permittivity, loss factor and ionic conductivity comparing to bulk samples have been observed.

Effect of Y doping and composition-dependent elastic strain on the electrical properties of (Ba,Sr)TiO3 thin films deposited at 520 °C

We demonstrate that large and simultaneous improvements in permittivity, tunability, and leakage current density of (Ba,Sr)TiO3 (BST)-based thin-film capacitors can be achieved by yttrium doping. We have found that, for a low deposition temperature (520 °C) sputtering process, Y-doped BST capacitors exhibit tenfold lower leakage current density (<10−9A∕cm2 at 100KV∕cm) and 70% higher permittivity than nominally undoped BST-based capacitors. Furthermore, this work suggests an intriguing correlation between dopant concentration-dependent elastic strain in the films and their enhanced dielectric properties.

The effect of processing on the giant dielectric properties of CaCu 3Ti 4O 12

The effect of processing on the dielectric properties of CaCu 3Ti 4O 12 (CCTO) was researched. CaCu 3Ti 4O 12 was prepared using conventional ceramic solid state reaction processing techniques. Powders mixed via mortar and pestle yielded CCTO with a room temperature permittivity of 11,700 and a loss of 0.047, which is similar to reported values in the literature. However, attrition-milled powders led to CCTO with permittivities close to 100,000 which are in the same range reported for single crystal CCTO. Increasing sintering temperature in the range from 990 to 1050 °C led to an increase in both the dielectric constant (714 to 82,450) and loss (0.014 to 0.98). Increasing sintering times also led to substantial improvements in permittivity. Grain size and density differences were not large enough to account for the enhancement in dielectric constant. The colossal effective dielectric constant of close to one million at room temperature was measured after annealing in flowing argon at 1000 °C. Based on the observations, it is believed that the primary factor affecting dielectric behavior is the development of internal defects. It appeared that higher defect concentration within the ‘core’ of a grain results in higher conductivity of the core and therefore, higher effective dielectric constant but also higher loss. The correlation between grain size and dielectric constant was also observed.