Reduction Of Permittivity Research Articles

Structural elucidation, morphological properties, dielectric properties and their physical interpretation of cerium-substituted cobalt and barium-based M-type hexagonal nano ferrites

This research uses the sol–gel method to look into how adding Co2+ and Ce3+ dopant cations changes the structure, shape, and electrical properties of M-type Ba hexagonal ferrites that have been synthesized. x-ray diffraction (XRD) analysis confirms the successful formation of the targeted hexagonal M-type crystal structure. We observed a reduction in unit cell volume and lattice parameters as the dopant concentration increased, indicating the effective incorporation of dopant ions into the crystal lattice. When the doping process happened, needle-like grain shapes appeared, which could be seen with a field emission scanning electron microscope (FESEM). As the concentration of the dopant increased, the dielectric spectroscopic measurements revealed an increase in the loss tangent (tan δ) from 0.05 to 3.68, and a decrease in the dielectric constant (ε′) from 283 to 3.41. This suggests a reduction in polarization and dielectric permittivity, as well as increased energy dissipation within the material. The electric modulus spectra showed relaxation behaviour that was non-Debye-type, which is another sign that there are complex and multifaceted ways for charges to move. The measurements of relaxation time and AC conductivity showed that the relaxation intervals were not regular and that the conductivity dropped from 2.22*10–4 Ω−1m−1 to 1.4*10–7 Ω−1m−1 as the doping concentration increased. Based on these findings, it seems that the processes of conductivity and dielectric relaxation play a big role in how charges move around in the doped ferrites. We validated complex impedance data obtained through electrochemical impedance spectroscopy (EIS) software against calculated impedance values. The derived grain and grain boundary characteristics also agreed with the observed grain distribution and boundaries from the micrographs, further corroborating the analysis.

Changes over time in ferroelectricity of nanocomposites containing cellulose combined with [NH4][Zn(HCOO)3

ABSTRACT For the first time, a composite based on a ferroelectric metal-organic framework of [NH4][Zn(HCOO)3] combined with nanocellulose at different cellulose concentrations from 0 to 75 wt% was synthesised to investigate the changes over time in phase transition and ferroelectric switching. A comparative study for fresh samples and the samples after 288 h was conducted. Electrophysical parameters were measured in a temperature range of 140 to 245 K under a weak electric field with an amplitude of 2 V.cm−1 at a frequency of 1 kHz. The results indicated that the increase in cellulose content led to increasing the phase transition temperature from 190.1 to 238.5 K. Besides, the coercive field was also found to increase from 3.78 to 14.12 kV.cm−1 along with the reduction of dielectric permittivity and maximum polarisation. After 288 h, this phase transition decreased significantly over time even to 231.6 K in the case of highest cellulose content (75 wt%). Meanwhile, the coercive field was found to decrease from 14.12 to 10.57 kV.cm−1. Remarkable changes were detected for samples with cellulose content of higher 25 wt%. The weaker interaction between ferroelectric part and cellulose over time due to the softness of cellulose was responsible for the obtained phenomena.

Peculiar dielectric properties of (1-x)(K,Na)(Nb,Sb)O3−x(Bi,Na)ZrO3 ceramics

In spite of the significance from both scientific and technological viewpoints, systematical studies on the dielectric spectra of (K,Na)NbO3-based lead-free ceramics particularly in the poled state had been scarcely performed so far. In this study, the compositional series of (1-x)(K0.48Na0.52)(Nb0.96Sb0.04)O3−x(Bi0.50Na0.50)ZrO3 ceramics were chosen representatively to shed more light on the characters of dielectric properties. All the ceramics in the unpoled state show dielectric spectra of large dispersion with the relaxational characteristic frequency higher than the measured upper limit of 60 MHz at room temperature. Additional resonance peaks due to the electromechanical coupling of piezoelectric effect appear and are accompanied by a large step-like reduction of dielectric permittivity ε′ in the dielectric spectra after poling. An abnormal phenomenon that poling induces the increase of low-frequency ε′ occurs in those ceramics with x ≥ 0.04 at room temperature, and is confirmed to associate closely with the orthorhombic-tetragonal and rhombohedral-orthorhombic polymorphic phase transitions. Further study of domain structure indicates that the origin of this abnormal phenomenon should be ascribed to the enhancement of domain-wall mobility because of the large reduction of domain-wall density due to the poling.

Preparation of benzocyclobutene-functionalized organic–inorganic hybrid microspheres and their reduction of permittivity to DVSBCB resin

BCB-functionalized microspheres with narrow particle size distribution are easy to synthesize and have a significant effect on reducing the dielectric constant of BCB resins.

Intriguing dielectric phenomena in (K,Na)1-xLixNbO3 ceramics

The (K,Na)NbO3-based ceramics are a very promising type of lead-free piezoelectric materials. In spite of the scientific and technological importance, systematical investigations on the dielectric spectra had been rarely performed so far. This paper reports our study results obtained in the (K0.50Na0.50)1-xLixNbO3 ceramics with either x = 0.03 or x = 0.065 (denoted as KNLN-030 and KNLN-065 ceramics, respectively) in the unpoled state and the poled state, respectively. Before poling, the KNLN-030 ceramic shows a dielectric spectrum of strong frequency dependence with a broad peak of dielectric loss around 1 MHz, while the KNLN-065 one has a dielectric spectrum of weak frequency dependence below 60 MHz at room temperature. After poling, piezoelectric resonance peaks appear and are accompanied by a large step-like reduction of dielectric permittivity ε′ in the dielectric spectra of both two ceramics. More interestingly, the KNLN-065 ceramic exhibits an abnormal phenomenon that there is a marked increases in low-frequency ε′ upon poling, whereas the KNLN-030 one shows normally a large decrease of low-frequency ε′. Further, the KNLN-065 ceramic displays the larger low-frequency ε′ in the poled state than in the unpoled state over a considerably wide temperature range. By contrast, such abnormal phenomenon is recognized only in a limited region above the orthorhombic-tetragonal phase transition in the KNLN-030 ceramic. The analysis of domain structure suggests that the observed abnormal dielectric phenomenon possibly arises from the enhancement of domain-wall mobility.

Ultra-low-permittivity, high hydrophobic, and excellent thermally stable fluoroelastomer/polyimide composite films employing dielectric reduction

Dielectric materials with low permittivity are urgently needed in the field of microelectronics due to the development of integration and miniaturization of integrated circuits. In this work, a series of all-organic polyimide (PI) films with ultra-low-permittivity and high hydrophobicity were successfully synthesized by introducing a kind of fluoroelastomer (FEM). And the significant permittivity reduction phenomenon was discussed through molecular dynamics simulations and practical tests. It was assumed that the hydrogen bond significantly inhibited the dipolar polarization of the FEM/PI composite system, which played an important role in determining the dielectric properties of FEM/PI composite films. At a low filler content of 7 wt%, FEM/PI composites exhibited the optimum permittivity (ε) of 1.21 at 106 Hz, which was the lowest permittivity of the PI films, while a low water absorption of 0.44 % and high thermal stability with a 10 % decomposition temperature (Td10%) of 548 °C were also observed. This simple and effective strategy of fabricating ultra-low-permittivity PI film is a potential way to realize commercial process.

Circularly polarized tunable graphene-patch over SiO2 substrate for THz applications

In this communication, a graphene-based radiator is designed and analyzed at THz frequency. A tilted dumbbell-shaped aperture is loaded on a graphene patch for creating degenerated orthogonal mode with 90° phase shift, which in turn produces circularly polarized (CP) waves. Graphene patch is placed over SiO2 substrate. Slot loading in graphene patch shifts the frequency band due to a reduction in effective permittivity. Another important feature of the proposed antenna is to provide a tunable feature in the frequency response and axial ratio by changing the chemical potential. The proposed antenna operates from 5.85 to 6.05 THz. 3-dB axial ratio is obtained from 5.85 to 5.95 THz. Good value of gain, as well as left-handed circular polarization characteristics, makes the proposed THz antenna in sensing applications.

Fast Near-Infrared Photodetection Using III-V Colloidal Quantum Dots.

Colloidal quantum dots (CQDs) are promising materials for infrared (IR) light detection due to their tunable bandgap and their solution processing; however, to date, the time response of CQD IR photodiodes is inferior to that provided by Si and InGaAs. It is reasoned that the high permittivity of II-VI CQDs leads to slow charge extraction due to screening and capacitance, whereas III-Vs-if their surface chemistry can be mastered-offer a low permittivity and thus increase potential for high-speed operation. In initial studies, it is found that the covalent character in indium arsenide (InAs) leads to imbalanced charge transport, the result of unpassivated surfaces, and uncontrolled heavy doping. Surface management using amphoteric ligand coordination is reported, and it is found that the approach addresses simultaneously the In and As surface dangling bonds. The new InAs CQD solids combine high mobility (0.04 cm2 V-1 s-1 ) with a 4× reduction in permittivity compared to PbS CQDs. The resulting photodiodes achieve a response time faster than 2ns-the fastest photodiode among previously reported CQD photodiodes-combined with an external quantum efficiency (EQE) of 30% at 940nm.

Double-Layered metamaterial resonator operating at millimetre wave for detection of dengue virus

In this paper, a metamaterial-based resonator is proposed for the detection of dengue infection. The replaceable top layer can measure the dielectric characteristics of blood samples to detect the dengue virus. The sensor observed a shift in the resonant frequency towards higher frequencies with the reduction in the blood's permittivity. The sensor showed a 0.325 GHz shift in resonance per unit change in the dielectric permittivity. To corroborate the sensor’s practical sensing capability, a sensor prototype was fabricated and validated with alcohol-aqueous solutions. The sensor exhibited shifting of resonance towards lower frequencies with the addition of water contents in methylated alcohol. With the enhanced sensitivity and repeatable measuring capability, the results suggested that this sensor can be applied with real-time applications on the Internet of Medical Things (IoMT) for early remote detection of the dengue outbreak.

Study of effective permittivity and loss reduction of SISL using ring resonator

AbstractA ring resonator used to study the effective permittivity and the loss of substrate integrated suspended line (SISL) is presented in this article. The effective permittivity is obtained by calculating resonant frequency and the relative value of loss is calculated by comparing unloaded quality factor (Q factor). For the four cases of uniform ring resonators, their S‐parameter, effective permittivity, unloaded Q factors are simulated, measured and investigated. The effect caused by the height of air cavity, the material of dielectric substrate, dielectric loss tangent is also investigated. Finally, the calculated results indicate that the effective permittivity of SISL structure at operating frequency is very closed to 1, which manifests that within a certain substrate‐material range the relative permittivity of substrate has little influence on SISL platform that is instructive for SISL circuits design. And the use of metalized via‐hole connection with dielectric removal can reduce the circuit loss dramatically.

Low-Permittivity Copolymerized Polyimides with Fluorene Rigid Conjugated Structure.

As the miniaturization of electronic appliances and microprocessors progresses, low-permittivity interlayer materials are becoming increasingly important for their suppression of electronic crosstalk, signal propagation delay and loss, and so forth. Herein, a kind of copolyimide (CPI) film with a “fluorene” rigid conjugated structure was prepared successfully. By introducing 9,9-Bis(3-fluoro-4-aminophenyl) fluorene as the rigid conjugated structure monomer, a series of CPI films with different molecular weights were fabricated by in situ polymerization, which not only achieved the reduction of permittivity but also maintained excellent thermodynamic stability. Moreover, the hydrophobicity of the CPI film was also improved with the increasing conjugated structure fraction. The lowest permittivity reached 2.53 at 106 Hz, while the thermal decomposition temperature (Td5%) was up to 530 °C, and the tensile strength was ≥ 96 MPa. Thus, the CPI films are potential dielectric materials for microelectronic and insulation applications.

Confined Water's Dielectric Constant Reduction Is Due to the Surrounding Low Dielectric Media and Not to Interfacial Molecular Ordering.

Liquid water confined within nanometer-sized channels exhibits a surprisingly low dielectric constant along the direction orthogonal to the channel walls. This is typically assumed to result from a pronounced heterogeneity across the sample: the dielectric constant would be bulk-like everywhere except at the interface, where it would be dramatically reduced by strong restrictions on interfacial molecules. Here we study the dielectric properties of water confined within graphene slit channels via classical molecular dynamics simulations. We show that the permittivity reduction is not due to any important alignment of interfacial water molecules, but instead to the long-ranged anisotropic dipole correlations combined with an excluded-volume effect of the low-dielectric confining material. The bulk permittivity is gradually recovered only over several nanometers due to the impact of long-range electrostatics, rather than structural features. This has important consequences for the control of, e.g., ion transport and chemical reactivity in nanoscopic channels and droplets.

Photodielectricity and magnetic field modified photodielectric property of BiAlO3/La0.67Sr0.33MnO3 heterostructure

The investigation on photoferroelectrics regained attention these years as their potential in various applications. In this work, BiAlO 3 /La 0.67 Sr 0.33 MnO 3 (BAO/LSMO) heterostructure was deposited on SrTiO 3 (STO) substrate with pulse laser deposition method. An abnormal region around 240 K on temperature dependent permittivity is ascribed to phase transition of BAO/LSMO heterostructure. Significant reduction (maximum variation of −32.6%) in dielectric permittivity upon ultraviolet light illumination (intensity of about 0.5 W/cm 2 ) can be attributed to redistribution of built-in electric field in BAO/LSMO interface. The positive magnetodielectricity (maximum variation of 17.2%) stems from negative magnetic resistance and magnetostriction of LSMO. Furthermore, magnetic field significantly modified photodielectricity, exhibiting multifield coupling effect on the BAO/LSMO heterostructure, revealing its potential use for advanced magneto-optoelectronic devices. • BAO/LSMO (ferroelectric/ferromagnetic) heterostructure was deposited on STO substrate with pulse laser deposition method. • Photodielectric property as well as magnetodielectricity of BAO/LSMO heterostructure were detected. • Magnetic field modified photodielectricity were conducted on the heterostructure to achieve multifield regulation.

Simultaneous enhancement of tunability and reduction of permittivity in P(VDF-TrFE)-MgO ferroelectric-dielectric composite films

Ferroelectric-dielectric composite has the potential to combine low dielectric constant of the dielectrics with the high tunability of ferroelectrics. However, one significant drawback of the composites is that the decreased dielectric constant is at the expense of tunability. Here, we eliminate the doping effect through organic-inorganic compositing and redistribute electric field to let the tunability increases while dielectric constant decreases. Poly(vinylidene fluoride-trifluoroethylene) copolymers based ferroelectric-dielectric composite films were prepared through spinning-coating method and the effect of MgO content on the dielectric tunable properties was studied. With increasing MgO content up to 30 wt%, the tunability of composite films increased while the dielectric constant decreased. The tunability of P(VDF-TrFE)-MgO composite films with 30 wt% MgO at 10 kHz under 32.5 kV/mm can reach to 25.6%, 1.22 times that of pure P(VDF-TrFE) (20.9%). This research paves a new pathway to increase the tunability and decrease the dielectric constant of ferroelectric materials simultaneously.

Wet chemical porosification with phosphate buffer solutions for permittivity reduction of LTCC substrates

The wireless high-frequency technology requires a robust, cost-effective, and highly integrated substrate technology offering the capability for areas of tailored permittivity. The wet-chemical porosification of low temperature co-fired ceramics (LTCC) substrates offers such an approach by locally embedding air. Porosification of LTCC in both extremely acidic and alkaline media has been investigated in previous works. However, for improving the available knowledge on the porosification of LTCC with H3PO4 as a standard and a widely used etching solution, the impact of solution concentration was systematically investigated and a substantial improvement in the etching performance was achieved. Moreover, in the present study, for the first time, the intermediate pH values, and the impact of pH as a key parameter on the etching process have been investigated. For this purpose, the applicability of phosphate buffer solution (PBS) as a prospective novel etchant mixture for the porosification of a commercially available LTCC tape (Ceramtape GC) was explored. Valuable information about surface morphology, crystalline composition, and the pore structure of the etched LTCCs was gathered employing scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, and mercury porosimetry measurements. Based on these findings, the performance of PBS-based etchant systems towards the generation of porous LTCCs combining high depths of porosification with acceptable surface characteristics for subsequent metallization is demonstrated. Based on the obtained results, by application of a 0.2 mol L−1 solution of PBS, the effective relative permittivity of test samples with a thickness of approximately 600 µm and a porosification depth of 186 µm from each side, could be reduced up to 10% of its initial “as fired” value. Also, based on the measurement results and by measuring the depth of porosification, the permittivity of the etched layer was estimated to show a reduction of up to 22% compared to the initial “as fired” value.

Universal Reduction in Dielectric Response of Confined Fluids.

Dielectric permittivity is central to many biological and physiochemical systems, as it affects the long-range electrostatic interactions. Similar to many fluid properties, confinement greatly alters the dielectric response of polar liquids. Many studies have focused on the reduction of the dielectric response of water under confinement. Here, using molecular dynamics simulations, statistical-mechanical theories, and multiscale methods, we study the out-of-plane (z-axis) dielectric response of protic and aprotic fluids confined inside slit-like graphene channels. We show that the reduction in perpendicular permittivity is universal for all the fluids and exhibits a Langevin-like behavior as a function of channel width. We show that this reduction is due to the favorable in-plane (x-y plane) dipole-dipole electrostatic interactions of the interfacial fluid layer. Furthermore, we observe an anomalously low dielectric response under an extreme confinement.

Enhanced high permittivity BaTiO3–polymer nanocomposites from the cold sintering process

The dielectric property relations of a series of BaTiO3–polymer composites with a uniquely high-volume fraction of ceramic [(1 − x)BaTiO3–x polytetrafluoroethylene (PTFE), with volume fractions x = 0.025, 0.05, 0.1, and 0.2] are studied. Such high-volume fraction of the BaTiO3 phase is achieved by using the cold sintering process, as it enables a single-step densification of oxides at an extremely low temperature; typically, the volume fractions from other processing methods are limited to ceramic filler volume fractions of ∼0.6. Microstructural and resistivity analyses suggest that the optimal range of the polymer content to effectively enhance the functions is x = 0.05, as higher volume fractions of the polymer hinder the densification of the ceramic. The composite exhibits improved properties such as lower loss tangent, higher resistivity, and high permittivity that vary systematically with x following an empirical mixing law. Here, we consider the composite mixing law trends and the changes to properties, which indicate that size effects are also being induced in the dielectric response, including shift of Tc, broadening of transition, and reduction of permittivity with respect to volume fraction of the PTFE. Our findings provide a new and simple strategy for the fabrication of ceramic–polymer composites with extremely high relative permittivities and resistivities, and these observations all point to a route that can allow us to engineer new types of advanced dielectric materials.

Origin of the abnormal reduction of the dielectric response for ReCOB crystals and its mechanism: theoretical and experimental exploration

The significant influence of ionic displacement polarization on distinct reduction in dielectric permittivity for LaCOB has been confirmed.

Improvement of Dielectric Breakdown Performance by Surface Modification in Polyethylene/TiO2 Nanocomposites.

Dielectric breakdown is a significant property for the insulation system in high voltage power equipment. This paper is dedicated to the improvement of dielectric breakdown by surface-functionalized nanoparticles in low-density polyethylene (LDPE). Prior to the preparation of LDPE/TiO2 nanocomposites, the nanoparticles were surface modified by the silane coupling followed by the chemical reaction process. Results of Fourier transform infrared spectroscopy (FTIR) indicated that some polar groups and chemical bonding were introduced on the surface of TiO2 nanoparticles. A reduction of dielectric permittivity was observed at low nanoparticle loading (<2 wt%) samples, which responded to the restriction of the molecular chain in the interface region. High nanoparticle loadings (2 wt%, 5 wt%, 10 wt%) introduced an obvious relaxation polarization. The trap parameters detected by the thermally stimulated current (TSC) method indicated that the deep traps were introduced by small amounts of nanoparticles (≤2 wt%), while more shallow traps occurred in high loading (5 wt%, 10 wt%) samples. Meanwhile, the increase of breakdown strength at low loading samples were closely related to the deep traps, which was ascribed to the interface region by surface chemical modification.

Modified energy harvesting figures of merit for stress- and strain-driven piezoelectric systems

Piezoelectrics are an important class of materials for mechanical energy harvesting technologies. In this paper we evaluate the piezoelectric harvesting process and define the key material properties that should be considered for effective material design and selection. Porous piezoceramics have been shown previously to display improved harvesting properties compared to their dense counterparts due to the reduction in permittivity associated with the introduction of porosity. We further this concept by considering the effect of the increased mechanical compliance of porous piezoceramics on the energy conversion efficiency and output electrical power. Finite element modelling is used to investigate the effect of porosity on relevant energy harvesting figures of merit. The increase in compliance due to porosity is shown to increase both the amount of mechanical energy transmitted into the system under stress-driven conditions, and the stress-driven figure of merit, FoM33X, despite a reduction in the electromechanical coupling coefficient. We show the importance of understanding whether a piezoelectric energy harvester is stress- or strain-driven, and demonstrate how porosity can be used to tailor the electrical and mechanical properties of piezoceramic harvesters. Finally, we derive two new figures of merit based on the consideration of each stage in the piezoelectric harvesting process and whether the system is stress- (FijX), or strain-driven (Fijx).