Increase In Dielectric Loss Research Articles

Enhancement of the Optical and Dielectric Properties at Low Frequency of (Sr1-xCax)5Ti4O13, (0 ≤ x ≤ 0.06) Structure Ceramics.

Low loss Ruddlesden-Popper (RP) series, i.e., (Sr1-xCax)5Ti4O13, 0.0 ≤ x ≤ 0.06, has been synthesized by a mixed oxide route. In this work, the substitution of Ca2+ cation in Sr5Ti4O13 sintered ceramics was chosen to enhance the structural, optical, and dielectric properties of the product. It was found that the Ca2+ content has significant effects on enhancing the dielectric properties as compared to Mn and glass additions. It was observed that the relative density, band gap energy, and dielectric loss (tangent loss) increase while relative permittivity decreases along with Ca2+ content. High relative density (96.7%), low porosity, and high band gap energy (2.241 eV) values were obtained in (Sr1-xCax)5Ti4O13, 0.0 ≤ x ≤ 0.06 sintered ceramics. These results will play a key role in the application of dielectric resonators.

Studies on structural and electrical properties of NaI doped PEO/CMC blend solid polymer electrolyte

Solid polymer blend electrolyte (SPE) films of Polyethylene oxide(PEO)/Carboxymethyl cellulose (NaCMC) doped with Sodium iodide (NaI), were prepared by solution cast method and their structural, optical and electrical properties were investigated using X-Ray diffraction, Fourier transform infrared spectroscopy, UV–Vis spectrophotometer and Electrical impedance analyser respectively. X-Ray diffraction spectra indicate that, deformation occurred in the structure of the blend followed by doping with NaI salt. The variation in intensity and shifting of characteristic bands in FTIR spectra provides the evidence for formation of complex due to the interaction occurred in the blend with the dopant. Optical energy band gap decreases in the blend samples upon doping and is confirmed by UV–Vis spectrophotometer analysis. Increase of dielectric constant and loss upon doping, exhibits usual behaviour of the polymer electrolytes. An increase in AC conductivity is observed upon doping and maximum conductivity of 9.41 × 10−3 Scm−1 is obtained for 10/90 sample doped with 0.03% Sodium iodide and DC conductivity for the same sample at room temperature is 1.05 × 10–2 Scm−1. In addition, I-T studies confirm the conductivity exhibited by the sample as due to ions and I-V studies show electrochemical stability in the range of good working potential. From the results obtained, it can be inferred that, the prepared sample can be used as polymer electrolytes in the manufacturing of energy storage devices.

Analysis of Load-Bearing Electrical Properties of Composite Materials Based on Homogenization Theory

In this study, the broadband dielectric spectrum of polyimide composites was examined using the homogenization theory. The findings demonstrate that the addition of boron nitride nanosheets (BNNSs) and silver nanoparticles (AgNPs) causes an increase in conductivity, dielectric constant, and dielectric loss of the composites but does not result in a surge in the three parameters; the results also demonstrate that an increase in temperature causes an increase in dielectric constant and dielectric loss of the composites. In addition, temperature has a bigger impact on the dielectric loss than it does on the dielectric constant. An increase in the amount of polarized charges and a shallower bulk trap depth can result from the addition of nanomaterials, according to research on thermally stimulated current in composite materials. The presence of the interfacial region, which made it simple to cause charge accumulation and simple to form conduction current, is primarily responsible for the significant increase in bulk conductivity of the composites at 50 Hz that occurred with the addition of more nanomaterials. The large rise in bulk conductivity of the composites at 50 Hz that happened with the addition of more nanomaterials is mostly due to the existence of the interfacial region, which made it simple to produce charge buildup and simple to form conduction current. The variation in volume conductivity when the doping ratio is less than 10 vol% is not significant due to AgNPs’ low concentration and ambiguous contribution to the conduction current. As the polarization temperature rises, the amount of polarization charges increases, but it has minimal effect on the bulk trap depth of the composites.

Investigation on electromagnetic shielding and mechanical properties of zirconia graded carbon fiber/epoxy nanocomposite

AbstractThe present study is on the fabrication of epoxy nanocomposites for electromagnetic interference (EMI) shielding in the X‐band and Ku‐band frequency range. Single‐layer unidirectional carbon fiber along with nano zirconia is used to achieve the required EMI shielding and mechanical strength. The microstructural study of the fabricated samples has revealed the good lamination of carbon fiber in epoxy matrix and the uniform dispersion nanoparticles provide a reduction of wettability. Dielectric parameter studies indicate an increase in permittivity and dielectric loss with the addition of zirconia nanoparticles. The shielding effectiveness (SE) shows as high as 25 dB when the electric field is parallel with the carbon fiber orientation. The addition of zirconia nanoparticles to the carbon fiber reinforced epoxy composite have enhanced the ability of microwave absorption shielding. Mechanical properties of the epoxy carbon fiber nano zirconia composites show an improvement in storage modules, activation energy, and impact resistance. It is realized that 3 wt% zirconia added epoxy carbon fiber composite shows high shielding effectiveness with good mechanical properties.

Raman spectroscopy, thermal stability and dielectric properties of CdS Quantum dots polyaniline nanocomposites

In this article, we have discussed the Raman spectroscopy, thermal stability and dielectric properties of Polyaniline Cadmium Sulfide Quantum dots (QDs) (PANI-CdS QDs) nanocomposites. We found that nanocomposites of PANI with CdS QDs have greater thermal stability and stability is further increased by incorporating the greater amount of CdS QDs in PANI. Dielectric properties were measured using LCR meter with parallel plate electrodes and results showed that dielectric constant was 10 times increased with increasing content of CdS QDs in PANI and it also increased with increasing temperature but decreases with increasing frequency. Dielectric loss was also measured for the nanocomposites. It has been observed that dielectric constant and dielectric loss decreases as the frequency is increased and they become constant at higher frequencies. Greater percentage of the QDs in PANI results in the increase of Dielectric constant and dielectric loss.

Dielectric polymer composites with ultra-high thermal conductivity and low dielectric loss

Polymer based dielectric materials with simultaneously high thermal conductivity and low dielectric loss are highly desirable in various applications like energy storage, thermal management and electronic packaging. Polymer dielectrics generally benefit from good electrical insulation, high breakdown strength, high toughness and low density but suffer from very low thermal conductivity (0.1–0.5 W m −1 K −1). Herein we propose a new strategy to overcome this compromise; solid-state drawing of ultra-high molecular weight polyethylene (UHMWPE) films doped with a small amount of nanodiamonds (NDs). The resulting orientation of UHMWPE macromolecules and the nanofiller significantly improves the thermal conductivity along the stretching direction, while the dodecane surface functionalization of the NDs endows a robust interface between the matrix and filler, which minimizes the thermal resistance and dielectric loss. Our composites film (2 wt% NDs) shows an ultra-high thermal conductivity of 60 W m −1 K −1 in the drawing direction and very low dielectric loss, both at low and high electric field. More generally, herein we demonstrates that the interfaces introduced by the nanofillers do not necessarily cause an increase in dielectric loss at high electric field and a decrease in thermal conductivity, providing a new direction for the design of novel polymer based dielectric and functional materials.

Multi-stress Cyclic Testing of Roebel Stator Bars for Hydropower

A multi-stress test rig was built to investigate the effect of many start-stops (load cycling) on hydropower generator insulation. To emulate real-life start-stops, stator bars were subjected to accelerated temperature cycling by circulating a 3.5 kA current and then cooling down with fans while high voltage (service voltage) was applied simultaneously to the insulation. A total of 250 load cycles were applied. Partial discharges (PD) were recorded on-line during load cycling, and after every 50 cycles, off-line dielectric loss and PD measurements were conducted. There was an apparent increase in dielectric losses after they had been subjected to a total of 250 load cycles. During load cycling, the PD level generally decreased with temperature, but there was a temporary increase in the PD activity during temperature rise and fall. This trend can be explained by different thermal expansion in copper and insulating material (epoxymica), suggesting that a stator bar that is load-cycled will be exposed to substantially higher PD levels than a stator bar under a uniform load and temperature, leading to further deterioration of the insulation quality.

Dielectric property and electrical conductivity of ZnS_PVK nanocomposites

The Zinc Sulphide (ZnS)/poly (N-vinylcarbazole) (PVK) nanocomposites thin films for various ZnS concentrations were synthesized by chemical casting method. The thin films are characterized by X-ray diffraction (XRD), which shows the crystalline structure of ZnS in a polymer matrix. The Atomic Force Microscope (AFM), Scanning Electron microscope (SEM) and XRD patterns show an increase in particle size and decrease in roughness with an increase of the ZnS concentration in PVK. The electrical properties of the nano-composites such as conductivity, dielectric constant, and dielectric loss have been investigated. The dielectric constant decreases whereas dielectric loss and conductivity increase as a function of ZnS.

Colossal dielectric behavior of (Nb, Ga) co-doped TiO2 single crystal

(Nb0.5Ga0.5)xTi1−xO2 (x = 0.05%,0.2%,0.5%,1%,5%) single crystals were prepared by Verneuil method. Even if the doping amount is 0.05%, the dielectric permittivity (ε′) is obviously higher than that of pure rutile TiO2 (260), reaching more than 104. As the doping amount x increase, the ε′ increases, and reaches the maximum value when x = 5%, but the dielectric loss increases correspondingly. The best dielectric performance (ε′=1.0 ×105, tanδ=0.034 under 1 kHz) is obtained when the doping amount is 0.5%. Even at 106 Hz, the dielectric loss is only 0.019, much lower than the reported ceramic samples. This may be due to the fact crystalline materials can effectively reduce defects such as grain boundary, second phase, porosity and segregation. The dielectric spectra, impedance analysis, XPS and DC bias results show that the colossal permittivity (CP) properties could be attributed to EPDD polarization. With the increase of doping concentration (>1%), the hopping polarization occurs, resulting in a slight increase in dielectric loss. These results indicate that TiO2 crystal materials with lower dielectric loss are good candidates for dielectric materials. Taking TiO2 crystal as the research object, we can have a clearer understanding of the origin of TiO2 dielectric properties and the influence of doping ion content, which is of great significance to the development of TiO2-based dielectric materials.

Core@double-shell structured fillers for increasing dielectric constant and suppressing dielectric loss of PVDF-based composite films

High dielectric constant polymer dielectrics have attracted a great deal of attention in flexible electronics. However, it appears to be a paradox for polymer dielectrics that the enhancement of their dielectric constant often comes along with the increase of dielectric loss. Hence, we reported core@double shell structured filler/poly(vinylidene fluoride) (PVDF) composites to overcome this paradox. The hybrid filler with BaTiO3 (BT) as the core, conductive carbon as the inner shell, and insulating polydopamine (PDA) as the outer shell was synthesized. As a result, the BT@C@PDA/PVDF composites at the filler content of 11 vol% exhibit an outstanding dielectric performance with a dielectric constant of 45 and a dielectric loss of 0.053 at 103 Hz. This phenomenon can be attributed to the increased interfacial polarization induced by the inner carbon shell and the conductive paths blockade caused by the outside PDA shell inside the BT@C@PDA/PVDF composites. This work reveals that rational design of core@double shell structured hybrid fillers maybe a promising way to optimize the overall dielectric performance of the PVDF-based composites.

Dielectric Properties of Pb(Fe0.5Nb0.5)O3 (PFN) Material Synthesized by B-site Precursor Method

Abstract: B-site precursor method was employed for the synthesis of Pb(Fe0.5Nb0.5)O3 (PFN) Ceramic material. Formation of Perovskite was confirmed by XRD. Study of electrical and dielectric properties were carried out. The increase in dielectric loss and decrease in ac resistivity was observed at higher temperature. Keywords: Perovskite, XRD, B-site precursor, AC conductivity, Dielectric constant.

Structural, Morphological, Optical and Electrical Characterization of Gahnite Ferroan Nano Composite Derived from Fly Ash Silica and ZnO Mixture.

The synthesis of a high value-added product, gahnite ferroan nano composite, from a mixture of fly ash silica and ZnO is a low-cost and non-expensive technique. The XRD pattern clearly reveals the synthesized product from fly ash after leaching is a product of high-purity gahnite ferroan composite. The grains are mostly cubical in shape. The optical band gap of powdered gahnite ferroan nano composite is 3.37 eV, which acts as a UV protector. However, the bulk sample shows that the 500 to 700 nm wavelength of visible light is absorbed, and UV light is allowed to pass through. So, the bulk sample acts as a band pass filter of UV light which can be used in many optical applications for conducting UV-irradiation activity. Dielectric permittivity and dielectric loss increase with a rise in temperature. The increase in the ac conductivity at higher temperatures denotes the negative temperature coefficient resistance (NTCR) behavior of the material.

Varying electrical and dielectric properties of Ni:SnO2 films by MWCNTs and GNPs coating

In this research, pure SnO2 and Ni-doped SnO2 (Ni:SnO2) nanocomposite films were produced by chemical bath deposition method and the latter were coated with multi-walled carbon nanotubes (Ni:SnO2/MWCNTs) or graphene nanoplatelets (Ni:SnO2/GNPs) by spin coating. All samples have tetragonal rutile SnO2 structure with the presence of carbon (002) peak in MWCNTs- or GNPs-coated films. Crystallite size of SnO2 films decreased remarkably with Ni doping followed by a slight decrease with MWCNTs coating and slight increase with GNPs coating. Scanning electron microscope images manifested a dispersed agglomerative nature of SnO2 nanoparticles which reduced especially with MWCNTs coating due to the porous surface provided by carbon nanotubes. From the photoluminescence measurements, oxygen defects-related peaks were spotted in the SnO2-based structures with different luminescence intensities. The most significant decrease in resistance was observed with the addition of GNPs into Ni-doped SnO2 nanocomposites compared to the other produced films mainly due to the synergetic effect that promotes excellent charge transfer between surfaces of Ni:SnO2 and graphene nanosheet. The huge increase in conductivity of GNPs-coated films led to a huge increase in dielectric losses and this followed by a drop down of dielectric constant of the GNPs-coated films.

Microwave absorption in epoxy composites filled with MoS2 and carbon nanotubes

In this study, the microwave absorbing properties of epoxy composites filled with micro-sized MoS2 and carbon nanotubes (CNT)/MoS2 were investigated in the frequency range of 1–67 GHz. Sample characterization was performed using electron microscopy and Raman spectroscopy methods. Direct current (DC) conductivity, complex permittivity, and shielding properties of composite materials with 50 wt. % of MoS2 and 1.5–2 wt. %CNT/50 wt.%MoS2 were measured. The permittivity of 50 wt. % MoS2/epoxy composite was found to be equal to 7.3, decreasing monotonically down to 4.5 at 67 GHz, while the imaginary part is equal to 1 and does not change. The addition of 2 wt. % of CNTs increases the real part of permittivity εr′ up to 30 at 1 GHz (13 at 67 GHz) and also leads to a large increase of the imaginary part of permittivity, with the most pronounced relaxation peak εr′′=10 at 10 GHz. Such an increase of dielectric loss correlates with the increase of DC conductivity up to 3.2 × 10−5 S/m as compared to the two-phase composite 50 wt. %MoS2/epoxy (σdc = 1.7 × 10−9 S/m). It was shown that 50 wt. %MoS2/epoxy composite exhibited an effective microwave absorption bandwidth of 9.9 GHz at the sample thickness of 2.0 mm with reflection loss minimum of -20.0 dB at 51.5 GHz. 2 wt. %CNT/50 wt. %MoS2/epoxy composite with a thickness of 0.9 mm showed a reflection loss minimum of −38 dB at 20.2 GHz with the absorption bandwidth of 3.68 GHz. The influence of sample thickness on position, width, and depth of EMR absorption maximums for the composites filled with MoS2 and mixed filler CNT/MoS2 was also determined.

Preparation and wave attenuation properties of GR/Fe93.5Si3.5Gd3 composite powders

In this paper, different graphene (GR)/Fe93.5Si3.5Gd3 composite powders were prepared via high-energy ball milling. Through the analysis of the structural morphology and electromagnetic parameters of the composite powder, the effects of ball milling time and graphene on the wave absorption properties of the composite powder were investigated. It is shown that in the ball-milled composite powder, graphene is compounded with the alloy powder in an amorphous state, and the particle size of the composite powder decreases with the increase of ball milling time. Moreover, the addition of graphene and the introduction of high-energy ball milling did improve the electromagnetic parameters of the composite powder. With other conditions guaranteed to be the same, the real part of dielectric constant of the composite powder rises by up to 472.94% and the real part of permeability increases by up to 23.80%. The optimized change of electromagnetic parameters increases the conduction loss of the composite powder, together with the combined effect of spatial polarization and orientation polarization, it increases the dielectric loss of the composite powder. The magnetic loss of the composite powder is also greatly improved by the change of the main mode of magnetic loss to natural resonance. The increase in dielectric loss and magnetic loss has greatly improved the electromagnetic wave absorption performance of the composite powder. Among them, at 0.3 ∼ 8.5 GHz, the electromagnetic loss of 1.0 wt% GR/Fe93.5Si3.5Gd3 ball milled for 24 h reaches 1.20 ∼ 11.78. With other conditions being the same, it is respectively 718.06% and 708.22% higher than the composite powder without graphene and the composite powder with the shortest ball milling time, showing excellent microwave attenuating performance.

Electrical conduction of PMMA/PLA doped lithium bis(oxalato) borate based hybrid gel polymer electrolyte

The present work highlights the investigation of electrical conduction properties of gel polymer electrolyte (GPE) based poly(methyl) methacrylate (PMMA) and poly(lactic) acid (PLA) blend doped with various compositions of lithium bis(oxalato) borate. The impedance analysis revealed the GPE systems exhibit maximum ionic conductivity of 1.37 × 10−3 S cm−1 for sample PLi20. The electrical properties based on the dielectric permittivity of entire samples decreased with increasing frequency and followed the trend of ionic conductivity. Further analysis was carried out to determine the dielectric response at different temperatures, focusing on the most conducting sample (PLi20). Both dielectric constant and loss increase with the increasing temperature, which suggested that total polarization has occurred. In conclusion, the samples with 20 wt% composition of LiBOB exhibit the highest conducting properties which significantly provides good electrical performance for the application in energy storage devices.

Influence of imidazole derivatives on the dielectric and energy storage performance of epoxy

Imidazoles are widely used as curing agents and accelerators for fabricating crosslinked epoxy materials applied in electrical and electronic fields. However, the intrinsic chemical structure of imidazole derivatives would greatly influence the polymerisation process, and further change the electrical properties, which was not emphasised. To achieve an in-depth understanding, commonly used imidazole only containing pyridine-type nitrogen and imidazole with both pyridine and pyrrole-type nitrogen were selected in this study. Electrical properties including dielectric properties, volume resistivity, breakdown strength, and especially energy storage performances were systematically investigated. We figured out that higher breakdown strength, glass transition temperature, and lower dielectric loss can be achieved with imidazole containing pyrrole-type nitrogen. Structure-induced curing mechanism diversity and the generated differences in polymer network were highlighted. With the capability to incorporate into the polymer network, the dielectric constant/loss of epoxy cured by imidazole containing pyrrole-type nitrogen is less sensitive with variation in concentration and a high breakdown strength of 577.9 MV/m was achieved. On the contrary, conspicuous decrease in the breakdown strength and increase in dielectric loss of the epoxy cured by imidazole only containing pyridine-type nitrogen were observed, especially at high concentration. Moreover, we also found that the epoxy can be fabricated into films with an attractive energy storage density/efficiency of 1.1 J/cm3/97%@200 MV/m, which is twice of the commercial dielectric polypropylene film under the same electric field.

Swift Heavy ion irradiation effects on dielectric constant and dielectric loss in poly (ether ether ketone) (PEEK)

The dielectric constant (ε') and dielectric loss (ε״) of pristine and C5+ (70 MeV) ion irradiated samples of the PEEK have been investigated with the variation of temperature at different frequencies (100 Hz, 1 kHz, 10 kHz and 100 kHz). The maxima are obtained around 170 oC in dielectric constant (ε') vs. temperature (T) curve. This relaxation is linked with the movement of ketone (>C=0) dipoles linked to the main chain. The irradiation of polymers increases the orientational polarization due to increase in number of dipoles with fluence. The increase in dielectric constant (ε') and dielectric loss (ε'') is attributed to chain scissioning at higher fluence which results in an increase of free radicals and unsaturations. Copyright © 2018 VBRI Press.

에폭시/실리카 콤포지트의 수분 흡수 및 건조에 따른 전기적 유전특성에 관한 연구

Epoxy-based microcomposites are currently used in a variety of high-voltage-based heavy electric machines (CT/PT, mold transformers, distribution insulators, etc.). Samples were prepared with three types of micro-silica-filled composites (W12est_65wt%, M10_65wt%) and epoxy prototype samples based on epoxy resin. The moisture absorption and drying properties of the three samples were evaluated. The moisture absorption process was performed until the moisture absorption of the sample was saturated in distilled water at 95°C, and the drying process was performed in a drying oven at 105°C until the moisture was saturated without any change. In the evaluation, the relationship between water absorption (M) and dielectric properties was evaluated under the conditions of steady state, moisture absorption and dry conditions. And dielectric characteristics (dielectric constant, dielectric loss and electrical conductivity) were evaluated according to the frequency change at room temperature as an evaluation environment. A large amount of water absorption resulted in a large increase in dielectric constant, dielectric loss, and electrical conductivity. In addition, it was found that the dielectric properties were restored because the dry state was based on the physical bonding with the absorbed water.

Recent Advances in Multilayer-Structure Dielectrics for Energy Storage Application.

An electrostatic capacitor has been widely used in many fields (such as high pulsed power technology, new energy vehicles, etc.) due to its ultrahigh discharge power density. Remarkable progress has been made over the past 10 years by doping ferroelectric ceramics into polymers because the dielectric constant is positively correlated with the energy storage density. However, this method often leads to an increase in dielectric loss and a decrease in energy storage efficiency. Therefore, the way of using a multilayer structure to improve the energy storage density of the dielectric has attracted the attention of researchers. Although research on energy storage properties using multilayer dielectric is just beginning, it shows the excellent effect and huge potential. In this review, the main physical mechanisms of polarization, breakdown and energy storage in multilayer structure dielectric are introduced, the theoretical simulation and experimental results are systematically summarized, and the preparation methods and design ideas of multilayer structure dielectrics are mainly described. This article covers not only an overview of the state‐of‐the‐art advances of multilayer structure energy storage dielectric but also the prospects that may open another window to tune the electrical performance of the electrostatic capacitor via designing a multilayer structure.