High Value Of Dielectric Constant Research Articles

Effect of Sintering Atmosphere on Microstructure and Dielectric Properties of Sr(Fe0.5Nb0.5)O3 Ceramics

The Sr(Fe0.5Nb0.5)O3 (SFN) dense ceramics were sintered at 1450°C in N2, air and O2 atmosphere for 3 h, respectively. All ceramics sintered at various atmospheres exhibited a single phase with perovskite structure in the space group Pmm(221). The microstructure and dielectric properties of SFN ceramics were related to the sintering atmospheres. The dielectric constant of the sample sintered in N2 atmosphere reached the highest value (about 23,000) at room temperature. With the increasing of the oxygen partial pressure, the dielectric constant decreased significantly. Moreover, the complex plane impedance plots even demonstrated that the samples were electrically heterogeneous and consisted of low resistive grains and high resistive grain boundaries. The giant dielectric phenomenon of SFN ceramics was therefore attributed to the IBLC model. The resistivity of grain boundary increased drastically with increasing the oxygen concentration while the resistivity of grain increased inconspicuously. With XPS analysis, it was illustrated that the oxygen vacancy concentrations of SFN ceramics decreased with increasing oxygen concentration, which indicated that a higher value of dielectric constant of SFN ceramics was obtained at lower oxygen concentration. The results strongly indicated that further improvement of the dielectric characteristics in the present ceramics is expected by optimizing sintering atmospheres.

Synthesis of Graphene-Based Nanocomposite and Investigations of Its Thermal and Electrical Properties

We describe the synthesis of acid functionalized graphene (GE) which is grafted to chitosan (CH) by first reacting the oxidized GE with thionyl chloride to form acyl-chlorinated GE. This product is subsequently dispersed in chitosan and covalently grafted to form GE-chitosan. GE-chitosan is further grafted onto polymetanitroaniline (PMNA) by free radical polymerization conditions to yield GE-CH-PMNA. We have characterized the structure of synthesized GE-CH-PMNA composites by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy, and conductivity measurements. XRD data suggest the strongly crystalline character of the prepared specimen. Our measurement shows that the dielectric constants of these nanocomposites are remarkably enhanced due to interfacial polarization effect. This study demonstrates that functionalized graphene sheets are ideal nanofillers for the development of new polymer composites with high dielectric constant values.

Effect of Post-Annealing on the Microstructure and Microwave Dielectric Properties of Ba(Co0.7Zn0.3)1/3Nb2/3O3 Ceramics

The effects of post-annealing on the crystal structure, microstructure, and microwave dielectric properties for Ba(Co0.7Zn0.3)1/3Nb2/3O3 ceramics were investigated. The as-prepared materials were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The microwave dielectric properties are measured at 6 GHz using a network analyzer. Ba5Nb4O15 and/or Ba8(Co,Zn)1Nb6O24 secondary phases were found on the surface according to sintering conditions due to volatilization of some Zn and Co elements. The experimental results show that the beneficial effect of the annealing steps to improved the microwave dielectric properties. Excellent microwave dielectric properties were achieved for the coarse-grained microstructures by a higher sintering temperature and with a shorter holding time followed by annealing steps at lower temperatures with a longer holding time. This improvement can be attributed to 1:2 cation ordering within the crystal, which is taking place during annealing process. The Ba(Co0.7Zn0.3)1/3Nb2/3O3 ceramic could be used successfully for realization of dielectric microwave resonators, since it has a high quality factor Qf value of 123,700 GHz, a high dielectric constant εr value of 34.5 and a temperature coefficient of the resonant frequency τf of 0 ppm/°C.

Ferroelectric and Magnetic Properties of SrO-B2O3-SiO2 Glass-Doped BiFeO3 Ceramics

BiFeO3 ceramics doped with varying amounts of SrO-B2O3-SiO2 glass, i.e., xwt% (x = 0, 0.2, 0.4, 0.6, 0.8) have been successfully developed via a solid state reaction route. Phase identification using XRD showed that a relatively pure BiFeO3 phase could be obtained at the reaction temperature of 760° for 2h. The sintering temperature of these glass-doped BiFeO3 ceramics was controlled at about 800°, on the basis of the studies of the optimized bulk density, although the bulk density varied with the different doping levels of SrO-B2O3-SiO2 glass. The dielectric constant and dielectric loss of sintered ceramics are affected by the glass doping level, while the BiFeO3 doped with 0.6% SrO-B2O3-SiO2 glass exhibited a comparatively higher dielectric constant value and minimum dielectric loss. At x = 0.6 and 0.8, the glass-doped BiFeO3 ceramics show saturated hysteresis loops with the respective saturation polarizations of 1.2μC/cm2 and 1.4μC/cm2. Too high a glass doping level in BiFeO3 gave rise to weakened magnetic behavior.

Dielectric Properties of 0–3BCTZO/High Calcium Fly Ash Geopolymer Composites

0–3 Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCTZO)/geopolymer composites were fabricated by normal mixing of geopolymer paste and BCTZO ceramic particles. Four composites were prepared with BCTZO concentrations of 0, 30, 50 and 70% wt. of total solid (BCTZO+FA). Phase and morphology of composite samples were characterized. The effect of addition of BCTZO ceramic particles on the dielectric properties of composite samples was also investigated. The results showed that high dielectric constant values in the order of ∼105 at frequency of 103 Hz for all composites were obtained. This was due to space charge polarization mechanism.

PKa predictions for proteins, RNAs, and DNAs with the Gaussian dielectric function using DelPhi pKa.

We developed a Poisson-Boltzmann based approach to calculate the pKa values of protein ionizable residues (Glu, Asp, His, Lys and Arg), nucleotides of RNA and single stranded DNA. Two novel features were utilized: the dielectric properties of the macromolecules and water phase were modeled via the smooth Gaussian-based dielectric function in DelPhi and the corresponding electrostatic energies were calculated without defining the molecular surface. We tested the algorithm by calculating pKa values for more than 300 residues from 32 proteins from the PPD dataset and achieved an overall RMSD of 0.77. Particularly, the RMSD of 0.55 was achieved for surface residues, while the RMSD of 1.1 for buried residues. The approach was also found capable of capturing the large pKa shifts of various single point mutations in staphylococcal nuclease (SNase) from pKa-cooperative dataset, resulting in an overall RMSD of 1.6 for this set of pKa's. Investigations showed that predictions for most of buried mutant residues of SNase could be improved by using higher dielectric constant values. Furthermore, an option to generate different hydrogen positions also improves pKa predictions for buried carboxyl residues. Finally, the pKa calculations on two RNAs demonstrated the capability of this approach for other types of biomolecules.

Development and characterization of functionalized Al2O3 and TiO2-reinforced polybenzoxazine nanocomposites

In the present work, benzoxazine was synthesized using caprolactam amine and cardanol, and its molecular structure was confirmed with FTIR and NMR spectroscopic techniques. Alumina (Al2O3) and titania (TiO2) were functionalized using 3-aminopropyltrimethoxysilane (APTMS). The nanocomposites were developed by reinforcing with varying weight (1, 3, 5, and 7) percentages of functionalized Al2O3 (F-Al2O3) and functionalized TiO2 (F-TiO2) with benzoxazine. The developed nanocomposites (F-Al2O3/CPBz and F-TiO2/CPBz) were characterized from their thermal, dielectric, and UV shielding studies. Data obtained from thermal studies show that 7 wt% of F-Al2O3-reinforced cardanol-based polybenzoxazine nanocomposite exhibits higher thermal stability than that of 7 wt% F-TiO2-reinforced cardanol-based polybenzoxazine nanocomposite. Dielectric and UV shielding studies show that 7 wt% F-TiO2 nanocomposite show higher value of dielectric constant (10.2) and UV shielding value (93%) than those of neat and other weight percentages of F-Al2O3 and F-TiO2 reinforced composites.

Excellent stability and low dielectric loss of Ba(Fe0.5Nb0.5)O3 synthesized by a solution precipitation method

A solution precipitation method was applied to prepare Ba(Fe0.5Nb0.5)O3 powders. Nano-size BFN powders with uniform particles size (∼40 nm) were synthesized by solution precipitation method, which is beneficial to calcine at low temperature (1223 K). The sintering sample with dense microstructure and uniform grain size (15 μm) was obtained at 1673 K, which exhibits enhanced dielectric properties. The dielectric loss of BFN ceramic could be significantly reduced by solution precipitation method. The frequency and temperature stability of BFN ceramics could also be improved. The complex impedance spectroscopy analysis results suggested that the obtained Ba(Fe0.5Nb0.5)O3 ceramics, consisting of semiconducting grains and insulating grain boundaries, were electrically heterogeneous. The grain boundary effect was responsible for such a high value of dielectric constant.

Synthesis and Properties of Lead Free Ferroelectric Na<sub>0.5</sub>Bi<sub>0.5</sub>TiO<sub>3</sub> Ceramic at Different Sintering Temperature

Lead Free Ferroelectric Na0.5Bi0.5TiO3 (NBT) Ceramic has been synthesized using sol gel method. The prepared NBT samples have been sintered at different temperatures 850°C, 950°C, 1050°C and 1150°C to achieve best sintering temperature. Structural analyses have been carried out using XRD and FTIR measurements. XRD patterns confirm perovskite structure having rhombohedral symmetry for all samples which is also supported by characteristic absorption band at ~627cm-1 in FTIR spectra. Dielectric properties of NBT samples with frequency and temperature have been studied. NBT sample sintered at 1050°C exhibit comparatively high value of dielectric constant (ε’) and phase transition temperature (Tm). Ferroelectric properties of NBT samples have been studied at room temperature. Comparatively, better ferroelectric properties are observed for NBT sample having remnant polarization (Pr)~ 14.7 μC/cm2and coercive field (Ec)~ 26.8 kV/cm sintered at 1050°C.

Effect of indium substitution on the electrical and magnetic properties of Ni–Zn ferrite

Indium-substituted polycrystalline nickel zinc ferrites of different compositions Ni0.65Zn0.35Fe2−x In x O4 (x = 0.00, 0.04, 0.08, 0.12, 0.16, 0.2) have been prepared by solid-state reaction route. Calcination and sintering of all samples were done in air atmosphere at 950 °C and 1250 °C, respectively, followed by natural cooling to room temperature. Characterization of the basic composition was done by X-ray diffractometry, saturation magnetization and Curie temperature. The effect of incorporation of larger indium ions in place of iron was studied with the help of saturation magnetization, Curie temperature, permeability, magnetic loss factor, DC electrical resistivity and dielectric properties. The highest magnetization and permeability values of the present system under study are 74.1 emu/g and 438 for the basic composition (concentration x = 0). The DC electrical resistivity was found to decrease up to x = 0.3 and increase thereafter. The variation in the electric and magnetic properties of this ferrite system is dominated by the decrease in iron concentration. Characteristic high dielectric constant values were recorded for these bulk ceramic materials.

Influence of substrate and Ca substitution on multiferroic BiMnO3 thin films

BiMnO3 (BMO) and Ca (10 at%) substituted BiMnO3 (BCMO) thin films are grown on n-type Si (100) and Pt/Ti/SiO2/Si (100) substrates by RF magnetron sputtering. The structural, elemental, morphological, magnetic, dielectric and ferroelectric properties of the films are investigated by X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDAX), atomic force microscope (AFM), vibrating sample magnetometer (VSM), dielectric and ferroelectric measurements, respectively. The XRD pattern shows that the films acquire monoclinic structure with C2 space group. The elemental composition and surface roughness of the films are also measured by EDAX and AFM analysis, respectively. The VSM results exhibit that all the films possess room temperature ferromagnetism and the BCMO film deposited on the Si substrate has better magnetic properties (M rem = 1.8 × 10−3 emu cm−3) than the other films. The dielectric measurement also reveals that the BCMO film has the highest value of dielectric constant (497) with less dielectric loss (0.3). Similarly, the ferroelectric measurement implies that all the films possess room temperature ferroelectricity.

Potentially Ferroelectric {CuIIL2}n Based Two-Dimensional Framework Exhibiting High Polarization and Guest-Assisted Dielectric Anomaly

Ferroelectrics in metal–organic materials have attracted recent interest owing to their synthetic simplicity and tunable nature. Utilizing isomeric dipodal phosphoramide ligands, L1 [PhPO(NH4Py)2] and L2 [PhPO(NH2Py)2], two new CuIIL2 derivatives, 1 ({[CuL12(H2O)2]·(NO3)2·(H2O)1.5·(CH3OH)}∞) and 2 ([CuL22]·(NO3)2), were synthesized. Compound 1 crystallizes in a noncentrosymmetric polar space group Cc as a two-dimensional framework, and 2 is a centrosymmetric complex. Electrical hysteresis (P–E loop) measurements on 1 at room temperature gave the remnant (Pr) and saturation (Ps) polarization values of 27.96 and 21.79 μC·cm–2, respectively, which are the highest among all of the known metal–organic ferroelectric materials. Also, the Pr value obtained for 1 is comparable to that of barium titanate and higher than most of the organic, polymeric, and inorganic ferroelectric materials. The permittivity measurements on 1 and 2 result in high dielectric constant values of 186.3 and 53.24, respectively, at 1 Hz fr...

High performance sol–gel spin-coated titanium dioxide dielectric based MOS structures

High-κ TiO2 thin films have been fabricated using cost effective sol–gel and spin-coating technique on p-Si (100) wafer. Plasma activation process was used for better adhesion between TiO2 films and Si. The influence of annealing temperature on the structure-electrical properties of titania films were investigated in detail. Both XRD and Raman studies indicate that the anatase phase crystallizes at 400°C, retaining its structural integrity up to 1000°C. The thickness of the deposited films did not vary significantly with the annealing temperature, although the refractive index and the RMS roughness enhanced considerably, accompanied by a decrease in porosity. For electrical measurements, the films were integrated in metal-oxide-semiconductor (MOS) structure. The electrical measurements evoke a temperature dependent dielectric constant with low leakage current density. The Capacitance–voltage (C–V) characteristics of the films annealed at 400°C exhibited a high value of dielectric constant (~34). Further, frequency dependent C–V measurements showed a huge dispersion in accumulation capacitance due to the presence of TiO2/Si interface states and dielectric polarization, was found to follow power law dependence on frequency (with exponent ‘s’=0.85). A low leakage current density of 3.6×10−7A/cm2 at 1V was observed for the films annealed at 600°C. The results of structure-electrical properties suggest that the deposition of titania by wet chemical method is more attractive and cost-effective for production of high-κ materials compared to other advanced deposition techniques such as sputtering, MBE, MOCVD and ALD. The results also suggest that the high value of dielectric constant ‘κ‘ obtained at low processing temperature expands its scope as a potential dielectric layer in MOS device technology.

Enhanced dielectric properties of polyamide 11/multi‐walled carbon nanotubes composites

ABSTRACTComposites with multi‐walled carbon nanotubes (MWNTs) involved in polyamide 11 (PA11) were prepared via a conventional melt blending method. The structure, morphology, crystallization behavior, electrical, and dielectric properties of composites were investigated. The results demonstrated that the dispersed uniformly MWNTs favored the formation of α crystal of PA11 when the composites were quenched from melt. The dielectric constant of composites was dependent on the electric field frequency and MWNTs content, and the highest value of dielectric constant was as high as 350 for the composite with 1.21 vol % MWNTs at 103 Hz, accompanied by a low dielectric loss. The enhanced dielectric properties could be interpreted by the formation of abundant nanocapacitors within the composites and the interfacial polarization effect resulting from accumulation of charge carriers at the internal interfaces between MWNTs and PA11. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42642.

Fabrication of graphite-graphene-ionic liquid modified carbon nanotubes filled natural rubber thin films for microwave and energy storage applications

Exploiting polymer nanocomposites as dielectric and heat storage devices is an important approach to develop high performance materials. Graphite (GT), thermally reduced graphene oxide (TRG), and hybrid consisting of TRG and ionic liquid (1-Ethyl-2, 3-dimethylimidazolium bis (trifluoromethylsulfonyl) imide) modified carbon nanotubes (IMCNT) were added to natural rubber and membranes were fabricated via melt mixing method. The amount of the GT, TRG, TRG+IMCNT used in this work was in the range of 0.5 to 5 wt%. Mechanical properties of NR nanocomposites revealed that the hybrid (TRG+IMCNT) (5 wt%) system showed high tensile strength, high modulus and low elongation at break as compared to neat NR, NR reinforced with GT (5 wt%) and NR reinforced with TRG (5 wt%) systems owing to the synergistic hybrid effect caused by the network formation of the hybrid fillers inside NR matrix. Dielectric properties of the prepared membranes were studied at 2.5, 10 and 20 GHz in the microwave frequency region using a Split Post Dielectric Resonator (SPDR) based technique. The incorporation of micro and nanofillers in the natural rubber (NR) matrix results in consistent improvement in dielectric constant and lower loss tangent values. In certain cases the samples containing 5 wt% of filler exhibited high loss or conducting behaviour at higher frequencies (10 and 20 GHz). Different techniques had to be employed for measuring the dielectric constant and loss tangent of the prepared membranes where they showed a high loss or conducting behaviour. Moreover, thermal history like glass transition temperature and the change in heat capacity were estimated using Differential Scanning Calorimetry (DSC). In addition, the dispersion of micro and nanofillers inside the NR was estimated using X-ray followed by Transmission Electron Microscopy for the morphology architecture of nanofillers. The morphology of the prepared membranes was correlated with the mechanical, dielectric and thermal properties. The hybrid system (TRG+IMCNT) exhibited high dielectric constant (5.6) and low heat capacity value (0.32 J/g/°C) as compared to GT and TRG systems.

Synthesis and characterization of nanocomposite of polythiophene with Na2[Fe(CN)3(OH)(NO)C6H12N4] H2O: a potent material for EMI shielding applications

Nanocomposite of polythiophene (PTh) with the photoadduct of sodium pentacyanonitrosylferrate(II) dihydrate and hexamine is synthesized by In-situ polymerization technique. Photoadduct was obtained by photoirradiation followed by substitution with hexamine ligand using Osram UV–visible photo lamp which was proved by Elemental analysis, UV–Vis, and FTIR. From elemental analysis, the empirical formula assigned to the synthesized photoadduct was found to be Na2[Fe(CN)3(OH)(NO)C6H12N4] H2O. Synthesized photoadduct was then milled in high energy ball mill to reduce it to nano size, which was confirmed from XRD and TEM. SEM analysis revealed distinct morphological features of photoadduct, PTh and nanocomposite. XRD showed orthorhombic structure of photoadduct which was retained in nanocomposite. Grain size (D) and strain (e) has been evaluated by fitting different models which were nearly well correlated. TEM measurement clearly showed the polymer coating of photoadduct particles which explained the size increase from photoadduct to nanocomposite. TG revealed higher thermal stability of nanocomposite as compared to pure PTh. DSC exhibits increase in the glass transition temperature of nanocomposite which indicated its rigid nature. A cyclic nanoindentation load-depth curve is used to assess mechanical properties. Dielectric measurement shows high value of dielectric constant (e′) and ac-conductivity (σac = 1010 S/m) which can make it useful for EMI shielding applications.

New transparent PVA‐InTiO hybrid thin films: influence of InTiO on the structure, morphology, optical, and dielectric properties

New hybrid Poly (vinyl) alcohol (PVA)‐InTiO transparent thin film was prepared by dip‐coating method. Characteristic of MO vibrations (InO and TiO) were confirmed from Fourier transform infrared spectroscopy. The X‐ray diffraction patterns revealed that the mixed phases of rutile TiO2 and cubic In2O3 were present in the hybrid film. Scanning electron microscopy images showed spherical shape mixed In2O3 and TiO2 nano particles embedded in the polymer matrix. The presence of elements such as In, Ti, and O are confirmed from energy dispersive X‐ray spectroscopy. High transmittance (80%) and wide band gap energy (4.1 to 3.75 eV) values were observed from optical study. High dielectric constant (18 to 23) and low dielectric loss values were obtained from dielectric study. The observed amorphous nature, enhanced optical, and dielectric properties indicated that the hybrid thin film could be used as high‐к layer in transparent thin film transistor and in opto‐electronic device applications in near future. Copyright © 2015 John Wiley & Sons, Ltd.

Dielectric and I-V Characteristic of Lead Titanate Thin Films Prepared on ITO Glass Substrate

Performance of lead titanate, (PbTiO3) thin films have been successfully investigated on microstructural properties, I-V characteristic, dielectric properties, and ferroelectric properties. PbTiO3offers variety of application as transducer, ferroelectric random access memory, transistor, high performance capacitor, sensor, and many more due to its ferroelectric behavior. Preparation of the films are often discussed in order to improve the structural properties, like existence of grain boundaries, particle uniformity, presents of microcrack films, porosities, and many more. Yet, researchers still prepare PbTiO3thin films at high crystallization temperature, certainly above than 600 ̊C to obtain single crystal perovskite structure that would be the reason to gain high spontaneous polarization behavior. Although this will results to high dielectric constant value, the chances that leads to high leakage current is a major failure in device performance. Thus, preparation the thin films at low annealing temperature quite an essential study which is more preferable deposited on low-cost soda lime glass. The study focuses on low annealing temperature of PbTiO3thin films through sol-gel spin coating method and undergo for dielectric and I-V measurements.

Dielectric and ferroelectric properties of BST ceramics obtained by a hydrothermally assisted complex polymerization method

Ba0.8Sr0.2TiO3 (BST) powder, obtained by a hydrothermal treatment of precursor solution previously prepared by a complex polymerization method (HT-CPM), was uniaxially pressed and sintered at 1280°C for 1–32h. The sintering effect on structural parameters, phase composition, dielectric and ferroelectric properties was investigated. Rietveld refinement analysis of BST ceramics showed that predominant phase was tetragonal BST with monoclinic Ba6Ti17O40 (B6T17) as a secondary phase. Phase contents determined by Rietveld refinement match well with the results of energy dispersive X-ray analysis. Dielectric and ferroelectric properties of BST ceramics have been correlated with density of sintered compacts, phase composition, structural parameters and microstructure. The sample sintered for 16h showed the highest density (93% ρt), as well as the highest value of dielectric constant (~2300) and remanent polarization – Pr (2μC/cm2) among investigated samples.

Dielectric studies of composite paper reinforced with polypyrrole coated pulp fibers from wasted egg holders

ABSTRACTDevelopment of thin, flexible, light‐weight, renewable, low‐cost, and environmentally friendly electrode materials are highly feasible in era of modern disposable electronic technology. This article presents the synthesis and dielectric studies of polypyrrole (PPy) coated pulp fibers, directly collected from wasted egg holder's tray. PPy coated pulp fibers converted into compact sheet for the development of potential renewable and low‐cost electrode materials. The morphology, chemical structure, and thermal stability of naked and PPy coated pulp fibril sheets were investigated by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA), respectively. PPy coated pulp fibers revealed better thermal stability and compactness of sheet morphology. Impedance measurements showed a high value of dielectric constant of 1.15 × 106 at 0.5 Hz and conductivity of 7.45 × 10−4 S/cm at room temperature for PPy coated pulp fibril sheet. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42422.