Showing papers on "Relative permittivity published in 2009"

High energy density nanocomposites based on surface-modified BaTiO(3) and a ferroelectric polymer.

Abstract: The dielectric permittivity and electric breakdown strength of nanocomposites comprising poly(vinylidene fluoride-co-hexafluoro propylene) and phosphonic acid surface-modified BaTiO3 nanoparticles have been investigated as a function of the volume fraction of nanoparticles. The mode of binding of pentafluorobenzylphosphonic acid on the BaTiO3 particles was investigated using infrared and 31P solid-state nuclear magnetic resonance spectroscopy, and the phosphonic acid was found to form well ordered, tightly bound monolayers. The effective permittivity of nanocomposites with low volume fractions (<50%) was in good agreement with standard theoretical models, with a maximum relative permittivity of 35. However, for nanoparticle volume fractions of greater than 50%, the effective permittivity was observed to decrease with increasing nanoparticle volume fraction, and this was correlated with an increase in porosity of the spin-coated nanocomposite films. The dielectric breakdown strength was also found to decre...

Bi2O3–MoO3 Binary System: An Alternative Ultralow Sintering Temperature Microwave Dielectric

Abstract: Preparation, phase composition, microwave dielectric properties, and chemical compatibility with silver and aluminum electrodes were investigated on a series of single-phase compounds in the Bi2O3–MoO3 binary system. All materials have ultralow sintering temperatures <820°C. Eight different xBi2O3–(1−x)MoO3 compounds between 0.2≤x≤0.875 were fabricated and the associated microwave dielectric properties were studied. The β-Bi2Mo2O9 single phase has a positive temperature coefficient of resonant frequency (TCF) about +31 ppm/°C, with a permittivity ɛr=38 and Qf=12 500 GHz at 300 K and at a frequency of 6.3 GHz. The α-Bi2Mo3O12 and γ-Bi2MoO6 compounds both have negative temperature coefficient values of TCF∼−215 and ∼−114 ppm/°C, with permittivities of ɛr=19 and 31, Qf=21 800 and 16 700 GHz at 300 K measured at resonant frequencies of 7.6 and 6.4 GHz, respectively. Through sintering the Bi2O3–2.2MoO3 at 620°C for 2 h, a composite dielectric containing both α and β phase can be obtained with a near-zero temperature coefficient of frequency TCF=−13 ppm/°C and a relative dielectric constant ɛr=35, and a large Qf∼12 000 GHz is also observed. Owing to the frequent difficulty of thermochemical interactions between low sintering temperature materials and the electrode materials during the cofiring, preliminary investigations are made to determine any major interactions with possible candidate electrode metals, Ag and Al. From the above results, the low sintering temperature, good microwave dielectric properties, chemical compatibility with Al metal electrode, nontoxicity and price advantage of the Bi2O3–MoO3 binary system, all indicate the potential for a new material system with ultralow temperature cofiring for multilayer devices application.

Dielectric response of high permittivity polymer ceramic composite with low loss tangent

Abstract: The present communication investigates the dielectric response of the Sr9Ce2Ti12O36 ceramics loaded high density polyethylene and epoxy resin. Sr9Ce2Ti12O36 ceramic filled polyethylene and epoxy composites were prepared using hot blending and mechanical mixing, respectively. 40 vol % ceramic loaded polyethylene has relative permittivity of 12.1 and loss tangent of 0.004 at 8 GHz, whereas the corresponding composite using epoxy as matrix has permittivity and loss tangent of 14.1 and 0.022, respectively. The effective medium theory fits relatively well for the observed permittivity of these composites.

Relaxor ferroelectric-like high effective permittivity in leaky dielectrics/oxide semiconductors induced by electrode effects: A case study of CuO ceramics

Abstract: The electrical behavior of copper oxide (CuO) ceramics sintered at 920 °C has been characterized by a combination of fixed, radio frequency (rf) capacitance measurements, and impedance spectroscopy (IS). Fixed rf capacitance measurements on ceramics with sputtered Au electrodes revealed a temperature- and frequency-dependent high effective permittivity of ∼104 in the temperature range of 150–320 K. The response is similar to that observed for relaxor-ferroelectrics, however, the magnitude of the effect can be suppressed by thermal annealing of the ceramics with Au electrodes in air at 300 °C or by changing the work function of the electrode material by using In–Ga as opposed to Au. IS data analysis revealed the ceramics to be electrically heterogeneous semiconductors with a room temperature dc resistivity <104 Ω cm, consisting of semiconducting grains with relative permittivity, er, <10 and slightly more resistive grain boundaries with “effective” permittivity, eeff, of ∼110. Samples with Au electrodes ex...

Semiconductor split-ring resonators for thermally tunable terahertz metamaterials

Abstract: As the variation of temperature alters the intrinsic carrier density in a semiconductor, numerical simulations indicate that the consequent variation of the relative permittivity in the terahertz regime provides a way to realize thermally tunable split-ring resonators. Electromagnetic metasurfaces and metamaterials that are thermally tunable in the terahertz regime can thus be implemented.

Dielectric properties and electric breakdown strength of a subpercolative composite of carbon black in thermoplastic copolymer

Abstract: We investigate the dielectric properties and electric breakdown strength of subpercolative composites of conductive carbon black particles in a rubber insulating matrix A significant increase in the permittivity in the vicinity of the insulator to conductor transition was observed, with relatively low increases in dielectric loss; however, a rapid decrease in electric breakdown strength was inevitable A steplike feature was ascribed to agglomeration effects The low ultimate values of the electric field strength of such composites appear to prohibit practical use

Dielectric properties and energy storage capability of antiferroelectric Pb0.92La0.08Zr0.95Ti0.05O3 film-on-foil capacitors

Abstract: Antiferroelectric (AFE) Pb0.92La0.08Zr0.95Ti0.05O3 (PLZT) films were grown on nickel foils with lanthanum nickel oxide buffer by chemical solution deposition. We observed field-induced AFE-to-ferroelectric (FE) phase transition. The electric field for the AFE-to-FE phase transition (EAF ≈ 270 kV/cm) and that for the reverse phase transition (EFA ≈ 230 kV/cm) were measured at room temperature on samples with PLZT films of ≈1-µm thickness. Relative permittivity of ≈560 and dielectric loss of 5000 h when the capacitors are operated at room temperature with an applied field of ≈300 kV/cm.

Broad-frequency dielectric behaviors in multiwalled carbon nanotube/rubber nanocomposites

Abstract: Broad-frequency dielectric behaviors of multiwalled carbon nanotubes (MWCNTs) embedded in room temperature vulcanization silicone rubber (RT-SR) matrix were studied by analyzing alternating current (ac) impedance spectra, which would make a remarkable contribution for understanding some fundamental electrical properties in the MWCNT/RT-SR nanocomposites. Equivalent circuits of the MWCNT/RT-SR nanocomposites were built, and the law of polarization and mechanism of electric conductance under the ac field were acquired. Two parallel RC circuits in series are the equivalent circuits of the MWCNT/RT-SR composites. At different frequency ranges, dielectric parameters including conductivity, dielectric permittivity, dielectric loss, impedance phase, and magnitude present different behaviors.

Enhanced dielectric constants and shielding effectiveness of, uniformly dispersed, functionalized carbon nanotube composites

Abstract: It was seen that composites constituted of functionalized single-walled nanotubes (SWNTs) dispersed in a reactive ethylene terpolymer (RET) matrix possess a complex dielectric permittivity an order of magnitude larger than composites composed of pristine SWNTs and two orders of magnitude larger than functionalized multiwalled nanotube-RET composites. We seek to understand such an enhancement, both in terms of uniform nanotube dispersion and through a parallel resistor-capacitor model. We subsequently show that the ac electrical conductivity is a good predictor of the electromagnetic interference shielding effectiveness of nanocomposites.

Comparative investigation of resonance characteristics and electrical size of the double-sided srr, bc-srr and conventional srr type metamaterials for varying substrate parameters

Abstract: This paper introduces a planar µ-negative (MNG) metamaterial structure, called double-sided split ring resonator (DSRR), which combines the features of a conventional SRR and a broadside-coupled SRR (BC-SRR) to obtain much better miniaturization at microwave frequencies for a given physical cell size. In this study, electromagnetic transmission characteristics of DSRR, BC-SRR and conventional SRR are investigated in a comparative manner for varying values of substrate parameters which are thickness, the real part of relative permittivity and dielectric loss tangent. Simulation results have shown that magnetic resonance patterns of all these three structures are affected in a similar way from variations in permittivity and in loss tangent. However, changes in substrate thickness affect their resonance characteristics quite differently: In response to decreasing substrate thickness, resonance frequency of the SRR increases slowly while the bandwidth and the depth of its resonance curve do not change much. For the DSRR and BC- SRR structures, on the other hand, resonance frequency, half power bandwidth and the depth of resonance curve strongly decrease with decreasing substrate thickness. Among these three structures, all having the same unit cell dimensions, the newly suggested DSRR is found to reach the lowest resonance frequency, hence the smallest electrical size, which is a highly desired property not only for more effective medium approximation but also for miniaturization in RF design. The BC-SRR, on the other hand, provides the largest

The permittivity of thermodynamically ideal liquid mixtures and the excess relative permittivity of binary dielectrics.

Abstract: The ideal relative permittivity of liquid mixtures is demonstrated to be a volume-fraction-weighted average of the pure-component relative permittivities. This generalised-thermodynamics result is used to define the molar electric dipole, permittivity, dielectric polarization and electric susceptibility of thermodynamically ideal liquid mixtures and the corresponding excess properties. A hyperbolic approach is developed to the analysis of averaging formulae that are frequently used to predict the effective permittivity of composite materials. Some of these formulae are shown to be segments of rectangular hyperbolae with fixed asymptote values, whereas others can be understood in terms of rectangular hyperbolae with composition-dependent asymptote values. Relative permittivities of binary mixtures between tetraglyme and hexane, cyclohexane or benzene covering the complete composition range are reported at various temperatures. These data are used to outline a novel method for analysing the excess relative permittivity of liquid mixtures.

Determination of the nanoscale dielectric constant by means of a double pass method using electrostatic force microscopy

Abstract: We present a method to determine the local dielectric permittivity of thin insulating layers. The measurement is based on the detection of force gradients in electric force microscopy by means of a double pass method. The proposed experimental protocol is simple to implement and does not need any modification of standard commercial devices. Numerical simulations based on the equivalent charge method make it possible to carry out quantification whatever the thickness of film, the radius of the tip, and the tip-sample distance. This method has been validated on a thin SiO2 sample for which the dielectric permittivity at the nanoscale has been characterized in the literature. We also show how we can quantitatively measure the local dielectric permittivity for ultrathin polymer film of poly(vinyl acetate) and polystyrene.

Modified Plane Wave Method Analysis of Dielectric Plasma Photonic Crystal

Abstract: Dispersion characteristics of two types of two-dimension dielectric plasma photonic crystal are studied based on modified plane wave method. Firstly, the eigenvalue equations of TM mode of type-1 and type-2 structures are derived respectively; their dispersion curves are confirmed by the software simulation. Secondly, the influences of normalized plasma frequency, filling factor and relative dielectric constant on photonic band gap, and relative photonic band gap width are analyzed respectively, and some corresponding physical explanations are also given. These results would provide theoretical instructions for designing new photonic crystal devices using plasma- dielectric structure.

Preparation, characterization and properties of Sm2Si2O7 loaded polymer composites for microelectronic applications

Abstract: The dielectric and thermo-mechanical properties of Sm2Si2O7 filled polyethylene and polystyrene composites for microwave packaging applications are reported in this paper. The composites were synthesized by melt mixing and hot pressing methods. The effect of different volume fractions of the ceramic (vf = 0–0.5) on the dielectric properties of the composites was investigated at 1 MHz and at 8 GHz. The dielectric properties (relative permittivity and dielectric loss) were found to increase with the ceramic filler content. It was observed that the addition of 0.5 vf of Sm2Si2O7 filler to polyethylene, increased the relative permittivity and the dielectric loss to 5.3 and 0.009 respectively whereas the corresponding values for the polystyrene–Sm2Si2O7 composite are 4.6 and 0.01 respectively at 8 GHz. The variation of relative permittivity with temperature in the range −25 °C to 60 °C was investigated for both the composites. The relative permittivities obtained experimentally were compared with that of the theoretical predictions and Effective Medium Theory was found to agree well for both the composites. The thermal conductivity, thermal expansion coefficient and Vickers microhardness of the composites were also investigated.

The effect of dispersion on the increased relative permittivity of TiO2/SEBS composites

Abstract: Polymer composites are currently suggested for use as improved dielectric materials in many applications. Here, the effect of particle size and dispersion on the electrical properties of composites of rutile TiO2 and poly(styrene–ethylene–butadiene–styrene) (SEBS) are investigated. Both 15 and 300 nm particles are mixed with SEBS, with amounts of sorbitan monopalmitate surfactant from 0 to 3.3 vol%, and their dielectric and mechanical properties are measured. Composites with the 300 nm TiO2 particles result in increases of 170% in relative permittivity over the pure polymer, far above those predicted by standard theories, such as Bruggeman (140%) and Yamada (114%), and improving dispersion with surfactant has little effect. The composites with 15 nm particles showed surprisingly large relative permittivity increases (350%), but improving the dispersion by the addition of any surfactant causes the relative permittivity to decrease to 240% of the pure polymer value. We suggest that the increase is due to the formation of a highly conductive layer in the polymer around the TiO2 particles.

CaCu3Ti4O12 ceramics from co-precipitation method: Dielectric properties of pellets and thick films

Abstract: Dielectric properties of CaCu3Ti4O12 (CCTO)-based ceramics and thick films (e ∼50m) prepared from powders synthesized by a soft chemistry method (co-precipitation) are presented and discussed. The characteristics of pellets and thick films are compared. The pellets exhibit high values of the dielectric permittivity (er ∼1.4×105) and relatively small dielectric losses (tan δ ∼0.16) at 1 kHz and room temperature. These properties are independent of the nature of the metallization of the electrodes. In addition, the dielectric permittivity decreases when the diameter of the electrodes of the pellets increases, while the losses remain constant. This result, which is strongly related to the nature of the dielectric material in between the electrodes, constitutes a strong indication that the high dielectric permittivity values observed in this material are not related to an interfacial (electrode material) related mechanism but is an internal barrier layer capacitor (IBLC) type. Very high values of the dielectric permittivity of CCTO thick films are measured (er ∼5×104). The differences in dielectric permittivity between thick films and dense pellets may be attributed to the difference in grain size due to different CuO contents, and to the different reactivity of the materials.

Microwave Dielectric Properties and Low-Temperature Sintering of Cerium Oxide for LTCC Applications

Abstract: The effect of glass additives on the microstructure, densification, and microwave dielectric properties of cerium oxide for low-temperature co-fired applications was investigated. Different weight percentages of quenched glass such as B2O3, B2O3–SiO2, Al2O3–SiO2, ZnO–B2O3, BaO–B2O3–SiO2, MgO–B2O3–SiO2, PbO–B2O3–SiO2, ZnO–B2O3–SiO2, 2MgO–Al2O3–5SiO2, LiO–B2O3–SiO2, Bi2O3–ZnO–B2O3–SiO2, and LiO–MgO–ZnO–B2O3–SiO2 were added to CeO2 powder. The crystal structure of the ceramic–glass composites was studied by X-ray diffraction, microstructure by scanning electron microscopy, and phase composition using the energy-dispersive X-ray analysis technique. The microwave dielectric properties such as relative permittivity (ɛr), quality factor (Quxf), and coefficient of temperature variation of resonant frequency (τf) of the ceramics have been measured in the frequency range 4–6 GHz. Addition of B2O3 and Bi2O3–ZnO–B2O3–SiO2 lowered the sintering temperature of ceria to about 900°C. The 20 wt% B2O3 and 10 wt% Bi2O3–ZnO–B2O3–SiO2-added CeO2 and sintered at 900° and 950°C showed: Quxf=24 200 and 12 000 GHz, ɛr= 13.2 and 22.4, and τf=−46 and –57.2 ppm/°C, respectively.

Microstructure, electrical properties of CeO2-doped (K0.5Na0.5)NbO3 lead-free piezoelectric ceramics

Abstract: CeO2-doped K0.5Na0.5NbO3 lead-free piezoelectric ceramics have been fabricated by a conventional ceramic fabrication technique. The ceramics retain the orthorhombic perovskite structure at low doping levels (<1 mol.%). Our results also demonstrate that the Ce-doping can suppress the grain growth, promote the densification, decrease the ferroelectric–paraelectric phase transition temperature (TC), and improve the dielectric and piezoelectric properties. For the ceramic doped with 0.75 mol.% CeO2, the dielectric and piezoelectric properties become optimum: piezoelectric coefficient d33 = 130 pC/N, planar electromechanical coupling coefficient kp = 0.38, relative permittivity er = 820, and loss tangent tanδ = 3%.

Giant magnetodielectric effect and magnetic field tunable dielectric resonance in spinel MnZn ferrite

Abstract: The sensitive response of the dielectric permittivity under the application of magnetic fields in Mn0.60Zn0.40Fe2.12O4+δ polycrystalline ferrite is presented. A magnetic field of 3.5 kOe induced a giant magnetodielectric {MD=[e′(H)−e′(0)]/e′(0)} response, of 1800% at f=7 MHz, at room temperature. The ferrite exhibits a large magnetic field-induced frequency response of 180 Hz/Oe. We suggest that this effect arises primarily from a spin-dependent space charge polarization mechanism in response to the application of dc magnetic fields.

Time-Domain Free-Field Measurements of the Relative Permittivity of Building Materials

Abstract: Time-domain free-field measurements comprised the dielectric properties of several common building materials using dual-ridged guide antennas and 1 mtimes1 m samples placed on an optical table covered with an absorber. The samples are polycarbonate, gypsum, plywood, a brick wall, and a concrete wall. Time gating and deconvolution are used to isolate a sample's front and back surfaces to obtain the measured reflection coefficients (RCs) and transmission coefficients. Theoretical reflection and transmission equations were generated from a plane-wave model. Relative permittivity is obtained by varying the parameters in the Kirkwood-Fuoss equation until a best fit between the theoretical and measured reflection and transmission coefficients is obtained.

A comparative approach to predicting effective dielectric, piezoelectric and elastic properties of PZT/PVDF composites

Abstract: The present study addresses the problem of quantitative prediction of effective relative permittivity, dielectric loss factor, piezoelectric charge coefficient, and Young's modulus of PZT/PVDF diphasic ceramic–polymer composite as a function of volume fraction of PZT in the different compositions. Theoretical results for effective relative permittivity derived from several dielectric mixture equations like those of Knott, Rother–Lichtenecker, Bruggeman, Maxwell–Wagner–Webmann–Skipetrov or Dias–Dasgupta, Furukawa, Lewin, Wiener, Jayasundere–Smith, Modified Cule–Torquato, Taylor, Poon–Shin and Rao et al. were fitted to the experimental data taken from previous works of Yamada et al. Similarly, the results for effective piezoelectric coefficient and Young's modulus, derived from different appropriate equations were fitted to the corresponding experimental data taken from the literature. The study revealed that only a few equations like modified Rother–Lichtenecker equation, Dias–Dasgupta equation and Rao equation for dielectric and piezoelectric properties while the four new equations developed in the present study of elastic property (Young's modulus) well fitted the corresponding experimental results. Further, the acceptable data put to various regression analyses showed that in most of the cases the third order polynomial regression analysis provided more acceptable fits.

Quantitative assessment of dielectric parameters for membrane lipid bi-layers from RF permittivity measurements.

Abstract: In this article, we propose and validate theoretical and experimental methods to quantitatively assess the Debye dielectric model of membrane lipid bi-layers. This consists of two steps: permittivity measurements of biological solutions (liposomes), and estimation of the model parameters by inverse application of the Effective Medium Theory. The measurements are conducted in the frequency domain between 100 MHz and 2 GHz using a modified coaxial connector, at the temperatures of 27 and 30 °C. Estimations have been performed using a three-layered model based on the Maxwell–Wagner formulation. Debye parameters (mean value ± standard error) found from fitting experimental data are: es = 11.69 ± 0.09, e∞ = 4.00 ± 0.07, frelax = 179.85 ± 6.20 MHz and es = (1.1 ± 0.1) × 10−7 S/m. This model can be used in microdosimetric studies aiming to precisely determine the E-field distribution in a biological target down to the single cell level. In this context the use of an accurate membrane dielectric model, valid through a wide frequency range, is particularly appropriate. Bioelectromagnetics 30:286–298, 2009. © 2009 Wiley-Liss, Inc.

Wide range dielectric spectroscopy on perovskite dielectrics

Abstract: Wide band dielectric spectra from the kilohertz to terahertz range were discussed for SrTiO3 (ST) and BaTiO3-based ceramics. The dielectric permittivity of BaTiO3 (BT) is determined by the ionic polarization of the Slater mode as well as the dipole polarization of domain-wall vibrations in micro-sized domains. (Bax,Sr1 − x)TiO3 (BST) shows relatively high dielectric permittivity with a low dielectric loss up to GHz region, while Ba(ZrxTi1 − x)O3 (BZT) shows a high permittivity with dielectric relaxation at MHz range. The dielectric dispersion in the BZT was due to the dipole fluctuation in polar nano-regions (PNR) in relaxors. The change of dielectric spectrum from BT to BZT was interpreted by the change from normal ferroelectrics to relaxors via ferroelectrics with diffuse phase transition (DPT-ferro.). Wide band dielectric spectra were also measured for BT ceramics with different grain and domain sizes to elucidate the size effect observed in BT ceramics. The low-frequency permittivity increased with decreasing grain size when the grain size was above 1 μm. It was found that the dipole polarization due to the domain-wall motion was enhanced with increasing domain density. We demonstrated wide band dielectric spectroscopy is a powerful tool to investigate the polarization mechanism of dielectric and ferroelectric materials.