Decrease In Dielectric Permittivity Research Articles

Structural, optical and dielectric behavior of PVDF films filled with different concentrations of iodine

Complex formation between polyvinyldene fluoride (PVDF) and different concentrations (≤10 wt%) of iodine were prepared by casting method using dimethyl sulfoxide (DMSO) as a common solvent. Their crystalline structure, optical and dielectric properties were examined. X-ray spectroscopy was adopted for analytical characterization of the films developed for applications. UV–VIS analysis suggests that the addition of iodine leads to formation of charge transfer complex with two different modes. The conductivity and dielectric measurements were carried out on these films as a function of frequency at various temperatures. The addition of iodine significantly improved the ionic conductivity. The conductivity–temperature plots were found to follow an Arrhenius nature. The dielectric behavior was analyzed using dielectric permittivity (ε′), dissipation factor (tan δ) and electric modulus (M′ and M″) of the samples. The decrease in dielectric permittivity was observed with increasing frequency and temperature.

Microwave and infrared dielectric response of tunable Ba 1−xSr xTiO 3 ceramics

The dielectric properties, infrared (IR) dielectric response and Raman spectra of tunable microwave (MW) Ba 1− x Sr x TiO 3 ( x = 0.4, 0.5, 0.6 and 0.7) ceramics were studied systematically as functions of composition and temperature. It was found that, with increasing the content of Sr from 40% to 70%, the permittivity of the Ba 1− x Sr x TiO 3 ceramics decreased from 7200 to 640 while the dielectric tunability decreased from 50.1% to 5.4% measured at 10 kHz. It is particularly interesting that the MW dielectric loss tangent was significantly decreased from 1.5 × 10 −2 to 7.4 × 10 −4. Complex permittivity spectra obtained by fitting the infrared data were also extrapolated to MW frequency and compared with the dielectric data near 1 GHz. For the samples with x = 0.4 and x = 0.5, the dielectric loss measured at ∼1 GHz was much higher than that calculated at 10 GHz, which is presumably due to the Debye-type dielectric relaxation in GHz region. However, the dielectric loss of the samples with x = 0.6 and x = 0.7, extrapolated from IR range, was in agreement with that measured at MW frequency. Low-temperature Raman scattering showed that the band at 760 cm −1 assigned to the Ti−O 3 torsional mode markedly sharpens and shifts upward with increasing content of Sr. This is an indication that the bonding between cations and anions was tightened due to the substitution of Ba with Sr, which explains well the decrease in dielectric permittivity, loss and tunability with increasing concentration of Sr.

Dielectric relaxation study ofN-methyl formamide with glycols using time domain reflectometry technique

The dielectric relaxation study that is static dielectric permittivity (∈0) and relaxation time (τ) of amide of N-methyl formamide (NMF) with increasing volume percent propylene glycol (PLG) and BLG has been carried out at different temperatures. The time domain reflectometry (TDR) technique has been used to measure reflection coefficient in frequency range of 10 MHz to 20 GHz. The dielectric parameters have been obtained by fitting experimental data with the Havriliak–Negami equation. The experimental observation shows that the static dielectric permittivity and relaxation time decreases with increasing temperature. The experimental observation also shows that the static dielectric permittivity decreases and relaxation time increases with increasing percentage volume of Propylene glycol (PLG) and Butylene glycol (BLG) in NMF. The nature of (ϵ0) and (τ) is same for the temperature ranges (20, 30, and 40°C). The thermodynamic parameters enthalpy (ΔH) and entropy (ΔS) of the binary mixture are also reported in this work.

Crater‐associated dark diffuse features on Venus: Properties of surficial deposits and their evolution

In order to assess the nature of crater‐associated radar‐dark diffuse features (DDFs) on Venus and to understand their formation and evolution, we analyzed Magellan radar roughness, emissivity, and reflectivity data in the vicinity of craters accompanied by these features. Following others, we assumed that DDFs are deposits (mantles) of ejected material emplaced during formation of the impact crater. The majority of radar‐dark parabolas (the youngest DDFs) are characterized by a smooth mantle‐atmosphere interface having low root‐mean‐square (rms) slopes on scales of 1–100 m, as derived from Magellan altimeter data. Older DDFs also often have areas with low rms slopes, suggesting that the mantle rms slopes can be preserved for geologically long periods of time. Some parabolas and older DDFs have asymmetric small‐scale (decimeter‐scale) relief that is interpreted to be dunes that formed as a result of eolian processes. This implies that the mantle material is mobile and can saltate under the influence of wind action. On average, aging of these features is accompanied by a decrease of mantle material dielectric permittivity. The most efficient mechanism for parabola degradation seems to be the removal of mantle material from the site of initial deposition by subsequent winds. We found a few examples of features that could be interpreted to be the result of in situ modification of the primary mantle.

Morphology, Acoustic Phonon Confinement, Phonon-induced Strain and Dielectric Permittivity of Nominally Undoped Nano- and Micro-Crystalline Diamond

Physical nature of experimentally detected decrease in dielectric permittivity of nano- and micro-crystalline diamond films and powders observed at the grain size diminishment is discussed within frameworks of several well-known approaches. Most of them presume considerable contribution of sp2-coordinated (graphite-like) fraction to dielectric properties of the granular material, which contradicts with available set of corresponding experimental data. An alternative explanation, based on Pekar model and an assumption on dominant contributions of phonon-induced strain and polarization effects of sp3-coordinated intra-granular carbon atoms is proposed. Obtained simulation results are compared with experimentally measured counterparts.

CaCu 3Ti 4O 12 ceramics from co-precipitation method: Dielectric properties of pellets and thick films

Dielectric properties of CaCu 3Ti 4O 12 (CCTO)-based ceramics and thick films ( e ∼50 μm) 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 ( ɛ r ∼1.4 × 10 5) 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 ( ɛ r ∼5 × 10 4). 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.

Electrical properties and microstructural characteristics of nonstoichiometric CaCu3xTi4O12 ceramics

The influence of copper on the microstructure, electrical properties, resistances of grain and grain boundary of nonstoichiometric CaCu3xTi4O12 ceramics, with x = 0.8, 0.9, 1.0, 1.1 and 1.2) prepared by solid state reaction were investigated. The second phase TiO2 and CaTiO3 are found in copper deficiency samples while CuO appears in the other samples. The grain size changes dramatically with the increase of copper. Frequency dependence dielectric permittivity exhibits that the deficient and excess of copper promote to a decrease of dielectric permittivity. Impedance complex plane shows both copper deficient and copper excess result in the increases of resistances of grain, grain boundary and contact resistance between electrode and ceramics.

Computer study of the absorption of ethane by aqueous ultradispersed medium: IR spectra

Absorption of ethane molecules by water clusters containing 10–20 molecules is studied by the molecular dynamics method. The (H2O)n (I), C2H6(H2O)n (II), and (C2H6)2(H2O)n (III) cluster systems are composed on the basis of specific statistical weights. Spectral characteristics of system and single clusters are determined in the frequency range of 0 ≤ ω ≤ 1000 cm−1. In this frequency range, both real and imaginary parts of dielectric permittivity decrease monotonically after the absorption of C2H6 molecules by an aqueous ultradispersed system. Integral coefficient of IR absorption increases, while average (over frequency) reflection coefficient decreases after the absorption of ethane molecules. The intensity of IR scattering by the systems of clusters containing C2H6 molecules lowers. Maximal values of radiation power for water clusters with various sizes are balanced with the capture of ethane molecules by the clusters, whereas oscillations in the size dependence of the density of electrons that are active with respect to IR radiation decrease.

Oxidation of 2‐Phenylethylamine with N‐Bromosuccinimide in Acid and Alkaline Media: A Kinetic and Mechanistic Study

AbstractA kinetic study of oxidation of 2‐phenylethylamine (PEA), a bioactive compound, with potent oxidant, N‐bromosuccinimide (NBS) has been carried out in HCl and NaOH media at 313 K. The experimental rate laws obtained are: ‐d [NBS] /dt = k[NBS][PEA][H+] in hydrochloric acid medium and ‐d [NBS]/dt = k[NBS][PEA]x[OH−]y in alkaline medium where x and y are less than unity. Accelerating effect of [Cl−], and retardation of the added succinimide on the reaction rate have been observed in acid medium. Variation of ionic strength of the medium shows negligible effect on rate of reaction in both media. Decrease in dielectric permittivity of the medium decreased the rate in both media. The stoichiometry of the reaction was found to be 1:1 in acid medium and 1:2 in the case of alkaline medium. The oxidation products of PEA were identified as the corresponding aldehyde and nitrile in acid and alkaline medium, respectively. The reactions were studied at different temperatures and the activation parameters have been evaluated. The reaction constants involved in the proposed mechanisms were computed. The reaction was found to be faster in alkaline medium in comparison with the acid medium, which is attributed to the involvement of different oxidizing species. The proposed mechanisms and the derived rate laws are consistent with the observed experimental results.

Mechanistic Investigation of Oxidation of Phenylpropanolamine with N‐Bromobenzenesulfonamide in Alkaline Medium: A Kinetic Approach

The kinetics of oxidation of phenylpropanolamine (PPA) with sodium N‐bromobenzenesulfonamide or bromamine‐B (BAB) has been investigated in alkaline medium at 308 K. The oxidation reaction obeys the rate law, – d[BAB]/dt = k [BAB] [PPA]x [OH‐], where x is less than unity. The variation of ionic strength of the medium, addition of the reduction product, benzenesulfonamide, and chloride ion had no pronounced effect on the reaction rate. Decrease of dielectric permittivity of the medium by increasing the CH3CN content increased the rate. The reaction was studied at different temperatures and the activation parameters have been evaluated from the Arrhenius plot. The stiochiometry of the reaction was found to be 1:1, and the oxidation product of phenylpropanolamine was identified as benzaldehyde and ethylideneamine. The rate decreased in D2O medium and the normal isotope effect k′ (H2O) / k′ (D2O) is 2.18. Proton inventory studies have been made in H2O ‐ D2O mixtures. Formation and decomposition constant of BAB‐PPA complexes in the reaction scheme have been determined. The conjugate acid, C6H5SO2NHBr is assumed to be the reactive species. The proposed mechanism and the derived rate law are consistent with the observed experimental results.

Spin-deposited nanocrystalline lithium ferrite thin films: Fabrication and characterization

Thin films of lithium ferrite (with general composition Li 0.5Fe 2.5O 4) were fabricated at low temperatures (up to 650 °C) by citrate-route using spin-deposition technique. Deposited films consisted of nanometer-sized grains as evidenced by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. XRD patterns for annealed films showed broad peaks exhibiting a spinel phase. Size of nanocrystallites is estimated to be 3–7 nm using Scherrer's equation. Average grain size ∼8.5 nm is observed from TEM images of films annealed at 650 °C. Scanning electron micrographs show the formation of spherical aggregates of around 130 nm in diameter. The AFM analysis clearly evidenced the development of nanograins even at low (∼500 °C) annealing temperatures. Significant decrease in complex dielectric permittivity ( ∈′ − j ∈″) with frequency is observed in the low frequency (100 Hz–1 MHz) as well as in X-band microwave frequency (8–12 GHz) region. ∈′ is found to be in the range of 15.7–33.9 in low frequency region, whereas in X-band microwave frequency region, it is found to lie between 3.9 and 4.9. Similarly, ∈″ is found to be 0.16–5.9 in the low frequency region, and 0.002–0.024 in the X-band microwave frequency region. Room temperature dc resistivity of these films is estimated to lie in the range of 10 6–10 8 Ω cm. These results strongly suggest that citrate-route processed nanocrystalline lithium ferrite thin films are promising candidates for monolithic microwave integrated circuits (MMICs).

Effects of Maxwell‐Wagner polarization on soil complex dielectric permittivity under variable temperature and electrical conductivity

The presence of free charges and numerous discontinuities separating liquid, gas, and solid phases in partially saturated soils give rise to Maxwell‐Wagner polarization that may significantly affect bulk dielectric permittivity measurements. Evidence suggests a complex interplay shaping the response of low‐frequency (<100 MHz) dielectric permittivity to changes in ambient temperature and amount of ionic charges present in a wet soil. Model calculations based on the Maxwell‐Wagner‐Brugermann‐Hanai (MWBH) theory are supported by direct measurements using a network analyzer, showing an increase in soil bulk dielectric permittivity with increasing temperature and with higher bulk electrical conductivity at low frequency range (<100 MHz). Beyond a certain frequency the decrease in permittivity of free water becomes dominant and results in a decrease in soil bulk dielectric permittivity with increasing temperature. The value of this crossover frequency can be predicted as a function of solution electrical conductivity (EC) as confirmed in limited tests. The dielectric permittivity inferred from TDR waveform travel time analysis is not significantly influenced by the low frequency range of the dielectric spectrum. In contrast, dielectric permittivity sensors operating at frequencies lower than 100 MHz are likely to show significant sensitivity to factors affecting the Maxwell‐Wagner effect (temperature and electrical conductivity), hence requiring special care in measurement interpretation.

Ultra Wide Range Dielectric Spectroscopy of Strontium Titanate-Strontium Zirconate Solid Solution

The dielectric properties vary significantly with the B-site cations in ABO3 perovskite-type oxides. In this study, we tried to understand the difference in the dielectric properties between SrTiO3 (STO, εr=290, Qf=3000 GHz) and SrZrO3 (SZO, εr=30, Qf=13700 GHz) by measuring the dielectric spectroscopy of their solid solutions in a wide frequency range. The dielectric permittivity and the loss tangent (tan δ) of SrZrxTi1-xO3 (STZ, 0.0≦x≦1.0) ceramics were evaluated up to a GHz region using the planer electrode method and ring resonator method. The four-parameter-semi-quantum (FPSQ) model was employed to analyze the Infrared-reflectivity (IR-reflectivity) data of the STZ ceramics. Both dielectric properties up to the GHz region and IR reflectivity in the THz region were incorporated in the analysis to accurately determine the optical phonon parameters. Ultra wide band dielectric spectra of the SZT ceramics and the STO single crystal were presented. The ionic polarization dominantly determined the dielectric permittivity of the SZT ceramics and the STO single crystal. High permittivity of STO was due to the Slater mode. The decrease of dielectric permittivity and the Q-factor (=1/tan δ) with an increasing Zr content (x) in STZ ceramics was attributed to the depression of the Slater mode. The effect of the optical phonon parameters on the permittivity and tan δ in the microwave region was simulated to generalize the results obtained for the STZ ceramics.

Dielectric spectroscopy studies on (PVP + PVA) polyblend film

The thermal behavior of (PVP + PVA) polyblend film have been examined using differential scanning calorimetry and scanning electron microscopy. Capacitance and loss tangent values of polyvinyl pyrrolidone (PVP) + polyvinyl alcohol (PVA) polyblend film were measured in the frequency range 1–100 kHz and temperature range 298–423 K. Dielectric permittivity of real part ( ε′) was obtained from capacitance data and dielectric permittivity of imaginary part ( ε″) was obtained from real part of dielectric permittivity and loss tangent values. The decrease in dielectric permittivity was observed with increasing frequency and also observed increase in dielectric permittivity with increasing temperature. The complex dielectric constant ( ε*) has been described by the electric modulus M* = (1/ ε*) = M′ + iM″. The data of M* has been analysed by the stretched exponential decay of the electric field, Φ( t) = exp−( t/ τ 0) β .

Polymer nanocomposite dielectrics - the role of the interface

The incorporation of silica nanoparticles into polyethylene increased the breakdown strength and voltage endurance significantly compared to the incorporation of micron scale fillers. In addition, dielectric spectroscopy showed a decrease in dielectric permittivity for the nanocomposite over the base polymer, and changes in the space charge distribution and dynamics have been documented. The most significant difference between micron scale and nanoscale fillers is the tremendous increase in interfacial area in nanocomposites. Because the interfacial region (interaction zone) is likely to be pivotal in controlling properties, the bonding between the silica and polyethylene was characterized using Fourier transformed infrared (FTTR) spectroscopy, electron paramagnetic resonance (EPR), and x-ray photoelectron spectroscopy (XPS). The picture which is emerging suggests that the enhanced interfacial zone, in addition to particle-polymer bonding, plays a very important role in determining the dielectric behavior of nanocomposites.

Microwave dielectric properties degradation of ceramic-polymer composites by electron irradiation

Composite materials with permittivities of the order of 10 and dielectric losses less than 0.001 are being developed as high-frequency substrates for telecommunication applications. Composites fabricated with a zirconium tin titanate ceramic filler dispersed inside of a thermoset epoxy-based polymer matrix have been studied at 12 GHz as a function of temperature (from 100 K to 473 K) and during electron irradiation on a 2-MeV Van der Graaff electron accelerator up to a total dose of 40 MGy. The results show a dielectric loss increase and permittivity decrease with increasing temperature, and a radiation induced dielectric degradation due to polymer structural changes.

Effect of Mg doping on the structural and dielectric properties of strontium titanate ceramics

The influence of Mg incorporation into A- and B-sites of the perovskite lattice of SrTiO3 ceramics on the structural, microstructural and low-frequency dielectric properties is studied in this work. Compounds in the systems Sr1-xMgxTiO3 and SrTi1-yMgyO3-δ were synthesised by a conventional solid-state method. The solid solubility of Mg is restricted to x<1% for A-site occupancy (Sr1-xMgxTiO3) and to y<15% for B-site occupancy (SrTi1-yMgyO3-δ). The lattice parameter is found to increase with Mg content for the SrTi1-yMgyO3-δ system, while it is almost invariant in the Sr1-xMgxTiO3 one. The dependence on the lattice-site occupancy is also verified for the grain growth of ceramics. For SrTi1-yMgyO3-δ the average grain size markedly decreases with increasing Mg content. For Sr1-xMgxTiO3 the inverse dependence is observed. Contrary to expectations, Mg does not induce ferroelectricity or relaxor-like behaviour in strontium titanate, located in either A- or B-sites of the SrTiO3 lattice. Moreover, fitting the dielectric behaviour to Barrett’s law demonstrates that B-site doping drives the system away from the ferroelectric instability. In Mg-doped strontium titanate ceramics the dielectric permittivity and dielectric losses decrease. The results are discussed based on the correlation between cation-site occupancy, charge and chemical stoichiometry in both systems.

Impedance spectroscopic and dielectric analysis of PMMA-CO-P4VPNO polymer films

Capacitance and dissipation factor values of polymethyl methacrylate-co-poly 4vinyl pyridine N-oxide (PMMA-CO-P4VPNO) were measured in the frequency range 0.01–100 kHz and temperature range 300–410 K. Dielectric permittivity ε′ was obtained by capacitance data. The decrease in dielectric permittivity was observed with increasing frequency as well as temperature. The loss peak was observed in the dielectric loss spectra and was identified as the β-relaxation. Real part of impedance ( Z′) and imaginary part of impedance ( Zʺ) were evaluated from the dielectric data. Frequency dependent conductivity ( σ ac) was obtained from complex impedance plots (Cole–Cole plots). Activation energy value obtained from the conductivity data was found to be comparable with activation energy values obtained for other polymers.

Effect of DC bias field on the complex materials coefficients of piezoelectric resonators

Abstract In many practical applications, piezoelectric devices are driven under strong electric field or under DC bias field. To evaluate the performance of the piezoelectric devices under these strong field conditions, the materials constants measured under weak field are usually not applicable. In this paper, we report our measurement results on the effect of DC bias field on the complex piezoelectric, dielectric and elastic coefficients of piezoelectric lead zirconate titanate ceramic resonator. A thin plate soft PZT resonator (transverse mode) is used in this study. A recently developed accurate method is used to directly characterize the complex materials coefficients, in which for a thin plate PZT resonator with length extensional vibration mode, normalized electric admittance, Y (=Y/ω) instead of admittance Y spectrum is used to determine the materials coefficients under various DC bias fields applied along the polarization direction. It has been found that with DC bias field increasing, elastic compliance, piezoelectric coefficient and dielectric permittivity decrease with approximately linear relationships. Second-order electromechanical coefficients can be estimated through the measurement of materials coefficients under DC bias conditions. Based on the observation of frequency increasing with DC bias field, it is suggested that the DC bias field can be used for frequency tuning or frequency–temperature compensation.

Ferroelectric and dielectric properties of sol–gel derived Ba xSr 1− xTiO 3 thin films

Ferroelectric thin films of Ba 0.7Sr 0.3TiO 3, Ba 0.8Sr 0.2TiO 3, Ba 0.9Sr 0.1TiO 3 and BaTiO 3 were fabricated by a modified sol–gel technique on Pt/Ti/SiO 2/Si substrates. All the compositions crystallized in perovskite structure and consist of well-defined grains. As the value of x increases grain size of the Ba x Sr 1− x TiO 3 thin films increases while the dielectric permittivity decreases. Ba 0.7Sr 0.3TiO 3 composition possesses the highest dielectric permittivity of 748 (at 100 kHz). Hysteresis loops measured at room temperature for all compositions showed that BaTiO 3 has the largest remnant polarization of 4.8 μC/cm 2. The dielectric and ferroelectric properties of the sol–gel derived Ba x Sr 1− x TiO 3 thin films are strongly dependent on the Sr content and the grain size.