Dielectric behavior of semiconductors at microwave frequencies

NASA Technical Reports Server (NTRS)

Dahiya, Jai N.

1992-01-01

A cylindrical microwave resonant cavity in TE(011) (Transverse Electric) mode is used to study the dielectric relaxation in germanium and silicon. The samples of these semiconductors are used to perturb the electric field in the cavity, and Slater's perturbation equations are used to calculate the real and imaginary parts of the dielectric constant. The dielectric loss of germanium and silicon is studied at different temperatures, and Debye's equations are used to calculate the relaxation time at these temperatures.

Optical characteristics of Tl0.995Cu0.005InS2 single crystals

NASA Astrophysics Data System (ADS)

El-Nahass, M. M.; Ali, H. A. M.; Abu-Samaha, F. S. H.

2013-04-01

Optical properties of Tl0.995Cu0.005InS2 single crystals were studied using transmittance and reflectance measurements in the spectral wavelength range of 300-2500 nm. The optical constants (n and k) were calculated at room temperature. The analysis of the spectral behavior of the absorption coefficient in the absorption region revealed indirect transition. The refractive index dispersion data were analyzed in terms of the single oscillator model. Dispersion parameters such as the single oscillator energy (Eo), the dispersion energy (Ed), the high frequency dielectric constant (ε∞), the lattice dielectric constant (εL) and the ratio of free charge carrier concentration to the effective mass (N/m*) were estimated. The third order nonlinear susceptibility (χ(3)) was calculated according to the generalized Miller's rule. Also, the real and imaginary parts of the complex dielectric constant were determined.

Quantification of the dielectric constant of single non-spherical nanoparticles from polarization forces: eccentricity effects.

PubMed

Gomila, G; Esteban-Ferrer, D; Fumagalli, L

2013-12-20

We analyze by means of finite-element numerical calculations the polarization force between a sharp conducting tip and a non-spherical uncharged dielectric nanoparticle with the objective of quantifying its dielectric constant from electrostatic force microscopy (EFM) measurements. We show that for an oblate spheroid nanoparticle of given height the strength of the polarization force acting on the tip depends linearly on the eccentricity, e, of the nanoparticle in the small eccentricity and low dielectric constant regimes (1 < e < 2 and 1 < ε(r) < 10), while for higher eccentricities (e > 2) the dependence is sub-linear and finally becomes independent of e for very large eccentricities (e > 30). These results imply that a precise account of the nanoparticle shape is required to quantify EFM data and obtain the dielectric constants of non-spherical dielectric nanoparticles. Experimental results obtained on polystyrene, silicon dioxide and aluminum oxide nanoparticles and on single viruses are used to illustrate the main findings.

Molecular Dynamics Evaluation of Dielectric-Constant Mixing Rules for H2O-CO2 at Geologic Conditions

PubMed Central

Mountain, Raymond D.; Harvey, Allan H.

2015-01-01

Modeling of mineral reaction equilibria and aqueous-phase speciation of C-O-H fluids requires the dielectric constant of the fluid mixture, which is not known from experiment and is typically estimated by some rule for mixing pure-component values. In order to evaluate different proposed mixing rules, we use molecular dynamics simulation to calculate the dielectric constant of a model H2O–CO2 mixture at temperatures of 700 K and 1000 K at pressures up to 3 GPa. We find that theoretically based mixing rules that depend on combining the molar polarizations of the pure fluids systematically overestimate the dielectric constant of the mixture, as would be expected for mixtures of nonpolar and strongly polar components. The commonly used semiempirical mixing rule due to Looyenga works well for this system at the lower pressures studied, but somewhat underestimates the dielectric constant at higher pressures and densities, especially at the water-rich end of the composition range. PMID:26664009

Molecular Dynamics Evaluation of Dielectric-Constant Mixing Rules for H2O-CO2 at Geologic Conditions.

PubMed

Mountain, Raymond D; Harvey, Allan H

2015-10-01

Modeling of mineral reaction equilibria and aqueous-phase speciation of C-O-H fluids requires the dielectric constant of the fluid mixture, which is not known from experiment and is typically estimated by some rule for mixing pure-component values. In order to evaluate different proposed mixing rules, we use molecular dynamics simulation to calculate the dielectric constant of a model H 2 O-CO 2 mixture at temperatures of 700 K and 1000 K at pressures up to 3 GPa. We find that theoretically based mixing rules that depend on combining the molar polarizations of the pure fluids systematically overestimate the dielectric constant of the mixture, as would be expected for mixtures of nonpolar and strongly polar components. The commonly used semiempirical mixing rule due to Looyenga works well for this system at the lower pressures studied, but somewhat underestimates the dielectric constant at higher pressures and densities, especially at the water-rich end of the composition range.

Dielectric properties of soils as a function of moisture content

NASA Technical Reports Server (NTRS)

Cihlar, J.; Ulaby, F. T.

1974-01-01

Soil dielectric constant measurements are reviewed and the dependence of the dielectric constant on various soil parameters is determined. Moisture content is given special attention because of its practical significance in remote sensing and because it represents the single most influential parameter as far as soil dielectric properties are concerned. Relative complex dielectric constant curves are derived as a function of volumetric soil water content at three frequencies (1.3 GHz, 4.0 GHz, and 10.0 GHz) for each of three soil textures (sand, loam, and clay). These curves, presented in both tabular and graphical form, were chosen as representative of the reported experimental data. Calculations based on these curves showed that the power reflection coefficient and emissivity, unlike skin depth, vary only slightly as a function of frequency and soil texture.

Sensitivity of polarization fluctuations to the nature of protein-water interactions: Study of biological water in four different protein-water systems

NASA Astrophysics Data System (ADS)

Ghosh, Rikhia; Banerjee, Saikat; Hazra, Milan; Roy, Susmita; Bagchi, Biman

2014-12-01

Since the time of Kirkwood, observed deviations in magnitude of the dielectric constant of aqueous protein solution from that of neat water (˜80) and slower decay of polarization have been subjects of enormous interest, controversy, and debate. Most of the common proteins have large permanent dipole moments (often more than 100 D) that can influence structure and dynamics of even distant water molecules, thereby affecting collective polarization fluctuation of the solution, which in turn can significantly alter solution's dielectric constant. Therefore, distance dependence of polarization fluctuation can provide important insight into the nature of biological water. We explore these aspects by studying aqueous solutions of four different proteins of different characteristics and varying sizes, chicken villin headpiece subdomain (HP-36), immunoglobulin binding domain protein G (GB1), hen-egg white lysozyme (LYS), and Myoglobin (MYO). We simulate fairly large systems consisting of single protein molecule and 20000-30000 water molecules (varied according to the protein size), providing a concentration in the range of ˜2-3 mM. We find that the calculated dielectric constant of the system shows a noticeable increment in all the cases compared to that of neat water. Total dipole moment auto time correlation function of water ⟨δMW(0)δMW(t)⟩ is found to be sensitive to the nature of the protein. Surprisingly, dipole moment of the protein and total dipole moment of the water molecules are found to be only weakly coupled. Shellwise decomposition of water molecules around protein reveals higher density of first layer compared to the succeeding ones. We also calculate heuristic effective dielectric constant of successive layers and find that the layer adjacent to protein has much lower value (˜50). However, progressive layers exhibit successive increment of dielectric constant, finally reaching a value close to that of bulk 4-5 layers away. We also calculate shellwise orientational correlation function and tetrahedral order parameter to understand the local dynamics and structural re-arrangement of water. Theoretical analysis providing simple method for calculation of shellwise local dielectric constant and implication of these findings are elaborately discussed in the present work.

Dielectric constant of ionic solutions: a field-theory approach.

PubMed

Levy, Amir; Andelman, David; Orland, Henri

2012-06-01

We study the variation of the dielectric response of a dielectric liquid (e.g. water) when a salt is added to the solution. Employing field-theoretical methods, we expand the Gibbs free energy to first order in a loop expansion and calculate self-consistently the dielectric constant. We predict analytically the dielectric decrement which depends on the ionic strength in a complex way. Furthermore, a qualitative description of the hydration shell is found and is characterized by a single length scale. Our prediction fits rather well a large range of concentrations for different salts using only one fit parameter related to the size of ions and dipoles.

Structural, optical and dielectric properties of graphene oxide

NASA Astrophysics Data System (ADS)

Bhargava, Richa; Khan, Shakeel

2018-05-01

The Modified Hummers method has been used to synthesize Graphene oxide nanoparticles. Microstructural analyses were carried out by X-ray diffraction and Fourier transform infrared spectroscopy. Optical properties were studied by UV-visible spectroscopy in the range of 200-700 nm. The energy band gap was calculated with the help of Tauc relation. The frequency dependence of dielectric constant and dielectric loss were studied over a range of the frequency 75Hz to 5MHz at room temperature. The dispersion in dielectric constant can be explained with the help of Maxwell-Wagner model in studied nanoparticles.

Protein dielectric constants determined from NMR chemical shift perturbations.

PubMed

Kukic, Predrag; Farrell, Damien; McIntosh, Lawrence P; García-Moreno E, Bertrand; Jensen, Kristine Steen; Toleikis, Zigmantas; Teilum, Kaare; Nielsen, Jens Erik

2013-11-13

Understanding the connection between protein structure and function requires a quantitative understanding of electrostatic effects. Structure-based electrostatic calculations are essential for this purpose, but their use has been limited by a long-standing discussion on which value to use for the dielectric constants (ε(eff) and ε(p)) required in Coulombic and Poisson-Boltzmann models. The currently used values for ε(eff) and ε(p) are essentially empirical parameters calibrated against thermodynamic properties that are indirect measurements of protein electric fields. We determine optimal values for ε(eff) and ε(p) by measuring protein electric fields in solution using direct detection of NMR chemical shift perturbations (CSPs). We measured CSPs in 14 proteins to get a broad and general characterization of electric fields. Coulomb's law reproduces the measured CSPs optimally with a protein dielectric constant (ε(eff)) from 3 to 13, with an optimal value across all proteins of 6.5. However, when the water-protein interface is treated with finite difference Poisson-Boltzmann calculations, the optimal protein dielectric constant (ε(p)) ranged from 2 to 5 with an optimum of 3. It is striking how similar this value is to the dielectric constant of 2-4 measured for protein powders and how different it is from the ε(p) of 6-20 used in models based on the Poisson-Boltzmann equation when calculating thermodynamic parameters. Because the value of ε(p) = 3 is obtained by analysis of NMR chemical shift perturbations instead of thermodynamic parameters such as pK(a) values, it is likely to describe only the electric field and thus represent a more general, intrinsic, and transferable ε(p) common to most folded proteins.

Ab Initio study on structural, electronic, magnetic and dielectric properties of LSNO within Density Functional Perturbation Theory

NASA Astrophysics Data System (ADS)

Petersen, John; Bechstedt, Friedhelm; Furthmüller, Jürgen; Scolfaro, Luisa

LSNO (La2-xSrxNiO4) is of great interest due to its colossal dielectric constant (CDC) and rich underlying physics. While being an antiferromagnetic insulator, localized holes are present in the form of stripes in the Ni-O planes which are commensurate with the inverse of the Sr concentration. The stripes are a manifestation of charge density waves with period approximately 1/x and spin density waves with period approximately 2/x. Here, the spin ground state is calculated via LSDA + U with the PAW method implemented in VASP. Crystal structure and the effective Hubbard U parameter are optimized before calculating ɛ∞ within the independent particle approximation. ɛ∞ and the full static dielectric constant (including the lattice polarizability) ɛ0 are calculated within Density Functional Perturbation Theory.

Dielectric characterization of hot-mix asphalt at the smart road using GPR

NASA Astrophysics Data System (ADS)

Al-Qadi, Imad L.; Loulizi, A.; Lahouar, S.

2000-04-01

To better interpret collected ground penetrating radar (GPR) data, a project is currently underway at the Virginia Smart Road. Twelve different flexible pavement sections and a continuously reinforced concrete rigid pavement section are incorporated in the road design. Thirty-five copper plates were placed at different layer interfaces throughout the pavement sections. The copper plates serve as a reflecting material and thus allow the determination of layers' dielectric constant over the GPR frequency range. An initial development of a method to calculate the complex dielectric constant of hot-mix asphalt over the frequency range of 750 to 1750 MHz using an air-coupled GPR system is presented. Utilizing GPR data, this method will be used to predict changes of the dielectric properties of the different SuperPaveTM mixes used at the Smart Road over time. The method is based on equating the overall reflection coefficient as obtained from the radar measurements with the calculated reflection coefficient using electromagnetic theory. The measured overall reflection coefficient is obtained by dividing the reflected frequency spectrum over the incident one. The theoretical overall reflection coefficient is obtained using the multiple reflection model. A Gauss-Newton method is then used to solve for the complex dielectric constant.

Hydration effects on the electrostatic potential around tuftsin.

PubMed

Valdeavella, C V; Blatt, H D; Yang, L; Pettitt, B M

1999-08-01

The electrostatic potential and component dielectric constants from molecular dynamics (MD) trajectories of tuftsin, a tetrapeptide with the amino acid sequence Thr-Lys-Pro-Arg in water and in saline solution are presented. The results obtained from the analysis of the MD trajectories for the total electrostatic potential at points on a grid using the Ewald technique are compared with the solution to the Poisson-Boltzmann (PB) equation. The latter was solved using several sets of dielectric constant parameters. The effects of structural averaging on the PB results were also considered. Solute conformational mobility in simulations gives rise to an electrostatic potential map around the solute dominated by the solute monopole (or lowest order multipole). The detailed spatial variation of the electrostatic potential on the molecular surface brought about by the compounded effects of the distribution of water and ions close to the peptide, solvent mobility, and solute conformational mobility are not qualitatively reproducible from a reparametrization of the input solute and solvent dielectric constants to the PB equation for a single structure or for structurally averaged PB calculations. Nevertheless, by fitting the PB to the MD electrostatic potential surfaces with the dielectric constants as fitting parameters, we found that the values that give the best fit are the values calculated from the MD trajectories. Implications of using such field calculations on the design of tuftsin peptide analogues are discussed.

Dielectric constant of atomic fluids with variable polarizability

PubMed Central

Alder, B. J.; Beers, J. C.; Strauss, H. L.; Weis, J. J.

1980-01-01

The Clausius-Mossotti function for the dielectric constant is expanded in terms of single atom and pair polarizabilities, leading to contributions that depend on both the trace and the anisotropy of the pair-polarizability tensor. The short-range contribution of the anisotropic part to the pair polarizabilities has previously been obtained empirically from light scattering experiments, whereas the trace contribution is now empirically determined by comparison to dielectric experiments. For helium, the short-range trace part agrees well with electronic structure calculations, whereas for argon qualitative agreement is achieved. PMID:16592830

Dielectric constant of atomic fluids with variable polarizability.

PubMed

Alder, B J; Beers, J C; Strauss, H L; Weis, J J

1980-06-01

The Clausius-Mossotti function for the dielectric constant is expanded in terms of single atom and pair polarizabilities, leading to contributions that depend on both the trace and the anisotropy of the pair-polarizability tensor. The short-range contribution of the anisotropic part to the pair polarizabilities has previously been obtained empirically from light scattering experiments, whereas the trace contribution is now empirically determined by comparison to dielectric experiments. For helium, the short-range trace part agrees well with electronic structure calculations, whereas for argon qualitative agreement is achieved.

Constraining Bulk Densities of Near-Earth Asteroid Surfaces from Radar Observations Using Laboratory Measurements of Permittivity

NASA Astrophysics Data System (ADS)

Hickson, D. C.; Boivin, A.; Daly, M. G.; Ghent, R. R.; Nolan, M. C.; Tait, K.; Cunje, A.; Tsai, C. A.

2017-12-01

Planetary radar is widely used to survey the Near-Earth Asteroid (NEA) population and can provide insight into target shapes, sizes, and spin states. The dual-polarization reflectivity is sensitive to surface roughness as well as material properties, specifically the real part of the complex permittivity, or dielectric constant. Knowledge of the behavior of the dielectric constant of asteroid regolith analogue material with environmental parameters can be used to inversely solve for such parameters, such as bulk density, from radar observations. In this study laboratory measurements of the complex permittivity of powdered aluminum oxide and dunite samples are performed in a low-pressure environment chamber using a coaxial transmission line from roughly 1 GHz to 8.5 GHz. The bulk densities of the samples are varied across the measurements by incrementally adding silica aerogel, a low-density material with a very low dielectric constant. This allows the alteration of the proportions of void space to solid particle grains to achieve microgravity-relevant porosities without significantly altering the dielectric properties of the powder sample. The data are then modeled using various electromagnetic mixing equations to characterize the change in dielectric constant with increasing volume fractions of void space (decreasing bulk density). Using spectral analogues as constraints on the composition of NEAs allows us to calculate the range in bulk densities in the near surface of NEAs that have been observed by planetary radar. Utilizing existing radar data from Arecibo Observatory we calculate the bulk density in the near-surface on (101955) Bennu, the target of NASA's OSIRIS-Rex mission, to be ρ = 1.27 ± 0.33 g cm-3 based on an average of the likely range in particle density and dielectric constant of the regolith material.

A full set of langatate high-temperature acoustic wave constants: elastic, piezoelectric, dielectric constants up to 900°C.

PubMed

Davulis, Peter M; da Cunha, Mauricio Pereira

2013-04-01

A full set of langatate (LGT) elastic, dielectric, and piezoelectric constants with their respective temperature coefficients up to 900°C is presented, and the relevance of the dielectric and piezoelectric constants and temperature coefficients are discussed with respect to predicted and measured high-temperature SAW propagation properties. The set of constants allows for high-temperature acoustic wave (AW) propagation studies and device design. The dielectric constants and polarization and conductive losses were extracted by impedance spectroscopy of parallel-plate capacitors. The measured dielectric constants at high temperatures were combined with previously measured LGT expansion coefficients and used to determine the elastic and piezoelectric constants using resonant ultrasound spectroscopy (RUS) measurements at temperatures up to 900°C. The extracted LGT piezoelectric constants and temperature coefficients show that e11 and e14 change by up to 62% and 77%, respectively, for the entire 25°C to 900°C range when compared with room-temperature values. The LGT high-temperature constants and temperature coefficients were verified by comparing measured and predicted phase velocities (vp) and temperature coefficients of delay (TCD) of SAW delay lines fabricated along 6 orientations in the LGT plane (90°, 23°, Ψ) up to 900°C. For the 6 tested orientations, the predicted SAW vp agree within 0.2% of the measured vp on average and the calculated TCD is within 9.6 ppm/°C of the measured value on average over the temperature range of 25°C to 900°C. By including the temperature dependence of both dielectric and piezoelectric constants, the average discrepancies between predicted and measured SAW properties were reduced, on average: 77% for vp, 13% for TCD, and 63% for the turn-over temperatures analyzed.

Dynamics of a Liquid Dielectric Attracted by a Cylindrical Capacitor

ERIC Educational Resources Information Center

Nardi, Rafael; Lemos, Nivaldo A.

2007-01-01

The dynamics of a liquid dielectric attracted by a vertical cylindrical capacitor are studied. Contrary to what might be expected from the standard calculation of the force exerted by the capacitor, the motion of the dielectric is different depending on whether the charge or the voltage of the capacitor is held constant. The problem turns out to…

Effect of fiber content on the thermal conductivity and dielectric constant of hair fiber reinforced epoxy composite

NASA Astrophysics Data System (ADS)

Prasad Nanda, Bishnu; Satapathy, Alok

2018-03-01

This paper reports on the dielectric and thermal properties of hair fibers reinforced epoxy composites. Hair is an important part of human body which also offers protection to the human body. It is also viewed as a biological waste which is responsible for creating environmental pollution due to its low decomposition rate. But at the same time it has unique microstructural, mechanical and thermal properties. In the present work, epoxy composites are made by solution casting method with different proportions of short hair fiber (SHF). Effects of fiber content on the thermal conductivity and dielectric constant of epoxy resin are studied. Thermal conductivities of the composites are obtained using a UnithermTM Model 2022 tester. An HIOKI-3532-50 Hi Tester Elsier Analyzer is used for measuring the capacitance of the epoxy-SHF composite, from which dielectric constant (Dk) of the composite are calculated. A reduction in thermal conductivity of the composite is noticed with the increase in wt. % of fiber. The dielectric constant value of the composites also found to be significantly affected by the fiber content.

Dielectric properties of organic solvents from non-polarizable molecular dynamics simulation with electronic continuum model and density functional theory.

PubMed

Lee, Sanghun; Park, Sung Soo

2011-11-03

Dielectric constants of electrolytic organic solvents are calculated employing nonpolarizable Molecular Dynamics simulation with Electronic Continuum (MDEC) model and Density Functional Theory. The molecular polarizabilities are obtained by the B3LYP/6-311++G(d,p) level of theory to estimate high-frequency refractive indices while the densities and dipole moment fluctuations are computed using nonpolarizable MD simulations. The dielectric constants reproduced from these procedures are evaluated to provide a reliable approach for estimating the experimental data. An additional feature, two representative solvents which have similar molecular weights but are different dielectric properties, i.e., ethyl methyl carbonate and propylene carbonate, are compared using MD simulations and the distinctly different dielectric behaviors are observed at short times as well as at long times.

Pressure dependence of the refractive index and dielectric constant in a fluoroperovskite, KMgF3

NASA Astrophysics Data System (ADS)

Uchino, Kenji; Nomura, Shoichiro; Vedam, K.; Newnham, Robert E.; Cross, Leslie E.

1984-06-01

The hydrostatic-pressure dependence of the refractive index and the low-frequency dielectric constant of a perovskite-type single crystal, KMgF3, have been determined at room temperature. The refractive index n for λ=589.3 nm increases monotonously in proportion to pressure p with a slope of ∂n∂p=2.46×10-4kbar-1. On the other hand, the dielectric constant at 10 kHz decreases with increasing pressure, from which the electric-displacement-related electrostrictive coefficient Qh (=Q11+2Q12) is calculated as 0.24 m4 C-2. These data are compared with the ∂n∂p values and the Qh coefficients of various alkali fluorides and perovskite oxides.

Temperature-dependent ac conductivity and dielectric response of vanadium doped CaCu3Ti4O12 ceramic

NASA Astrophysics Data System (ADS)

Sen, A.; Maiti, U. N.; Thapa, R.; Chattopadhyay, K. K.

2011-09-01

Successful incorporation of vanadium dopant within the giant dielectric material CaCu 3Ti 4O12 (CCTO) through a conventional solid-state sintering process is achieved and its influence on the dielectric as well as electrical properties as a function of temperature and frequency is reported here. Proper crystalline phase formation together with dopant induced lattice constant shrinkage was confirmed through X-ray diffraction. The temperature dependence of the dielectric constant at different constant frequencies was investigated. We infer that the correlated barrier hopping (CBH) model is dominant in the conduction mechanism of the ceramic as per the temperature-dependent ac conductivity measurements. The electronic parameters such as density of the states at the Fermi level, N( E f) and hopping distance, R ω of the ceramic were also calculated using this model.

High-throughput screening of inorganic compounds for the discovery of novel dielectric and optical materials

DOE PAGES

Petousis, Ioannis; Mrdjenovich, David; Ballouz, Eric; ...

2017-01-31

Dielectrics are an important class of materials that are ubiquitous in modern electronic applications. Even though their properties are important for the performance of devices, the number of compounds with known dielectric constant is on the order of a few hundred. Here, we use Density Functional Perturbation Theory as a way to screen for the dielectric constant and refractive index of materials in a fast and computationally efficient way. Our results constitute the largest dielectric tensors database to date, containing 1,056 compounds. Details regarding the computational methodology and technical validation are presented along with the format of our publicly availablemore » data. In addition, we integrate our dataset with the Materials Project allowing users easy access to material properties. Finally, we explain how our dataset and calculation methodology can be used in the search for novel dielectric compounds.« less

High-throughput screening of inorganic compounds for the discovery of novel dielectric and optical materials

PubMed Central

Petousis, Ioannis; Mrdjenovich, David; Ballouz, Eric; Liu, Miao; Winston, Donald; Chen, Wei; Graf, Tanja; Schladt, Thomas D.; Persson, Kristin A.; Prinz, Fritz B.

2017-01-01

Dielectrics are an important class of materials that are ubiquitous in modern electronic applications. Even though their properties are important for the performance of devices, the number of compounds with known dielectric constant is on the order of a few hundred. Here, we use Density Functional Perturbation Theory as a way to screen for the dielectric constant and refractive index of materials in a fast and computationally efficient way. Our results constitute the largest dielectric tensors database to date, containing 1,056 compounds. Details regarding the computational methodology and technical validation are presented along with the format of our publicly available data. In addition, we integrate our dataset with the Materials Project allowing users easy access to material properties. Finally, we explain how our dataset and calculation methodology can be used in the search for novel dielectric compounds. PMID:28140408

High-throughput screening of inorganic compounds for the discovery of novel dielectric and optical materials.

PubMed

Petousis, Ioannis; Mrdjenovich, David; Ballouz, Eric; Liu, Miao; Winston, Donald; Chen, Wei; Graf, Tanja; Schladt, Thomas D; Persson, Kristin A; Prinz, Fritz B

2017-01-31

Dielectrics are an important class of materials that are ubiquitous in modern electronic applications. Even though their properties are important for the performance of devices, the number of compounds with known dielectric constant is on the order of a few hundred. Here, we use Density Functional Perturbation Theory as a way to screen for the dielectric constant and refractive index of materials in a fast and computationally efficient way. Our results constitute the largest dielectric tensors database to date, containing 1,056 compounds. Details regarding the computational methodology and technical validation are presented along with the format of our publicly available data. In addition, we integrate our dataset with the Materials Project allowing users easy access to material properties. Finally, we explain how our dataset and calculation methodology can be used in the search for novel dielectric compounds.

Effect of bromine deficiency on the lattice dynamics and dielectric properties of alpha-phase diisopropylammonium bromide molecular crystals

NASA Astrophysics Data System (ADS)

Alsaad, Ahmad; Marin, Chris M.; Alaqtash, Nabil; Chao, Hsien-Wen; Chang, Tsun-Hsu; Cheung, Chin Li; Ahmad, A.; Qattan, I. A.; Sabirianov, Renat F.

2018-02-01

Diisopropylammonium bromide (DIPAB) molecular ferroelectric crystals were synthesized and examined to exhibit a large electric polarization (∼23μC/cm2), a large dielectric constant in the α-phase. Although the PXRD pattern indicates that the α-DIPAB sample has an overall excellent crystallinity, our analysis of its FT-IR and Raman vibrational spectra suggests the presence of disorder in the synthesized crystals as indicated by the presence of broad features in the Raman spectrum. Using vdW+DF2 calculations, we identified the majority of vibrational modes in the experimental spectra and analyzed the ones due to Br-disorder. We found that the bromine (Br) deficiency strongly affects the electric properties of α-DIPAB. Particularly, the experimentally measured dielectric constant of α-DIPAB is large (∼20), whereas the DFT-based calculations of the ideal DIPAB give much smaller values (∼2-3). We find that Br-deficiency is responsible for large dielectric constant of the DIPAB crystal with calculated value of ∼15-20. Furthermore, we showed that the van der Waals forces have a slight effect on the structural parameters, only causing a small shift in the vibrational frequencies. The main vibrational features of the DIPAB crystal in the Raman spectrum were shown to be driven by covalent bonding in the DIPA molecules and hydrogen bonds between the molecules with Br.

Examination of Effective Dielectric Constants Derived from Non-Spherical Melting Hydrometeor

NASA Astrophysics Data System (ADS)

Liao, L.; Meneghini, R.

2009-04-01

The bright band, a layer of enhanced radar echo associated with melting hydrometeors, is often observed in stratiform rain. Understanding the microphysical properties of melting hydrometeors and their scattering and propagation effects is of great importance in accurately estimating parameters of the precipitation from spaceborne radar and radiometers. However, one of the impediments in the study of the radar signature of the melting layer is the determination of effective dielectric constants of melting hydrometeors. Although a number of mixing formulas are available to compute the effective dielectric constants, their results vary to a great extent when water is a component of the mixture, such as in the case of melting snow. It is also physically unclear as to how to select among these various formulas. Furthermore, the question remains as to whether these mixing formulas can be applied to computations of radar polarimetric parameters from non-spherical melting particles. Recently, several approaches using numerical methods have been developed to derive the effective dielectric constants of melting hydrometeors, i.e., mixtures consisting of air, ice and water, based on more realistic melting models of particles, in which the composition of the melting hydrometeor is divided into a number of identical cells. Each of these cells is then assigned in a probabilistic way to be water, ice or air according to the distribution of fractional water contents for a particular particle. While the derived effective dielectric constants have been extensively tested at various wavelengths over a range of particle sizes, these numerical experiments have been restricted to the co-polarized scattering parameters from spherical particles. As polarimetric radar has been increasingly used in the study of microphysical properties of hydrometeors, an extension of the theory to polarimetric variables should provide additional information on melting processes. To account for polarimetric radar measurements from melting hydrometeors, it is necessary to move away from the restriction that the melting particles are spherical. In this study, our primary focus is on the derivation of the effective dielectric constants of non-spherical particles that are mixtures of ice and water. The computational model for the ice-water particle is described by a collection of 128x128x128 cubic cells of identical size. Because of the use of such a high-resolution model, the particles can be described accurately not only with regard to shape but with respect to structure as well. The Cartesian components of the mean internal electric field of particles, which are used to infer the effective dielectric constants, are calculated at each cell by the use of the Conjugate Gradient-Fast Fourier Transform (CG-FFT) numerical method. In this work we first check the validity of derived effective dielectric constant from a non-spherical mixed phase particle by comparing the polarimetric scattering parameters of an ice-water spheroid obtained from the CGFFT to those computed from the T-matrix for a homogeneous particle with the same geometry as that of the mixed phase particle (such as size, shape and orientation) and with an effective dielectric constant derived from the internal field of the mixed-phase particle. The accuracy of the effective dielectric constant can be judged by whether the scattering parameters of interest can accurately reproduce those of the exact solution, i.e., the T-matrix results. The purpose of defining an effective dielectric constant is to reduce the complexity of the scattering calculations in the sense that the effective dielectric constant, once obtained, may be applicable to a range of particle sizes, shapes and orientations. Conversely, if a different effective dielectric constant is needed for each particle size or shape, then its utility would be marginal. Having verified that the effective dielectric constant defined for a particular particle with a fixed shape, size, and orientation is valid, a check is performed to see if this effective dielectric constant can be used to characterize a class of particle types (with arbitrary sizes, shapes and orientations) if the fractional ice-water contents of melting particles remain the same. Among the scattering and polarimatric parameters used for examination of effective dielectric constant in this study, are the radar backscattering, extinction and scattering coefficients, asymmetry factor, differential reflectivity factor (ZDR), phase shift and linear polarization ratio (LDR). The goal is to determine whether the effective dielectric constant approach provides a means to compute accurately the radar polarimetric scattering parameters and radiometer brightness temperature quantities from the melting layer in a relatively simple and efficient way.

Technique for Performing Dielectric Property Measurements at Microwave Frequencies

NASA Technical Reports Server (NTRS)

Barmatz, Martin B.; Jackson, Henry W.

2010-01-01

A paper discusses the need to perform accurate dielectric property measurements on larger sized samples, particularly liquids at microwave frequencies. These types of measurements cannot be obtained using conventional cavity perturbation methods, particularly for liquids or powdered or granulated solids that require a surrounding container. To solve this problem, a model has been developed for the resonant frequency and quality factor of a cylindrical microwave cavity containing concentric cylindrical samples. This model can then be inverted to obtain the real and imaginary dielectric constants of the material of interest. This approach is based on using exact solutions to Maxwell s equations for the resonant properties of a cylindrical microwave cavity and also using the effective electrical conductivity of the cavity walls that is estimated from the measured empty cavity quality factor. This new approach calculates the complex resonant frequency and associated electromagnetic fields for a cylindrical microwave cavity with lossy walls that is loaded with concentric, axially aligned, lossy dielectric cylindrical samples. In this approach, the calculated complex resonant frequency, consisting of real and imaginary parts, is related to the experimentally measured quantities. Because this approach uses Maxwell's equations to determine the perturbed electromagnetic fields in the cavity with the material(s) inserted, one can calculate the expected wall losses using the fields for the loaded cavity rather than just depending on the value of the fields obtained from the empty cavity quality factor. These additional calculations provide a more accurate determination of the complex dielectric constant of the material being studied. The improved approach will be particularly important when working with larger samples or samples with larger dielectric constants that will further perturb the cavity electromagnetic fields. Also, this approach enables the ability to have a larger sample of interest, such as a liquid or powdered or granulated solid, inside a cylindrical container.

Microwave dielectric study of polar liquids at 298 K

NASA Astrophysics Data System (ADS)

Maharolkar, Aruna P.; Murugkar, A.; Khirade, P. W.

2018-05-01

Present paper deals with study of microwave dielectric properties like dielectric constant, viscosity, density and refractive index for the binary mixtures of Dimethylsulphoxide (DMSO) and Methanol over the entire concentration range were measured at 298K. The experimental data further used to determine the excess properties viz. excess static dielectric constant, excess molar volume, excess viscosity& derived properties viz. molar refraction&Bruggman factor. The values of excess properties further fitted with Redlich-Kister (R-K Fit) equation to calculate the binary coefficients and standard deviation. The resulting excess parameters are used to indicate the presence of intermolecular interactions and strength of intermolecular interactions between the molecules in the binary mixtures. Excess parameters indicate structure breaking factor in the mixture predominates in the system.

Ab initio molecular dynamics in a finite homogeneous electric field.

PubMed

Umari, P; Pasquarello, Alfredo

2002-10-07

We treat homogeneous electric fields within density functional calculations with periodic boundary conditions. A nonlocal energy functional depending on the applied field is used within an ab initio molecular dynamics scheme. The reliability of the method is demonstrated in the case of bulk MgO for the Born effective charges, and the high- and low-frequency dielectric constants. We evaluate the static dielectric constant by performing a damped molecular dynamics in an electric field and avoiding the calculation of the dynamical matrix. Application of this method to vitreous silica shows good agreement with experiment and illustrates its potential for systems of large size.

Calculation of the orientational linear and nonlinear correlation factors of polar liquids from the rotational Dean-Kawasaki equation.

PubMed

Déjardin, P M; Cornaton, Y; Ghesquière, P; Caliot, C; Brouzet, R

2018-01-28

A calculation of the Kirkwood and Piekara-Kielich correlation factors of polar liquids is presented using the forced rotational diffusion theory of Cugliandolo et al. [Phys. Rev. E 91, 032139 (2015)]. These correlation factors are obtained as a function of density and temperature. Our results compare reasonably well with the experimental temperature dependence of the linear dielectric constant of some simple polar liquids across a wide temperature range. A comparison of our results for the linear dielectric constant and the Kirkwood correlation factor with relevant numerical simulations of liquid water and methanol is given.

First-principles investigation of band offsets and dielectric properties of Silicon-Silicon Nitride interfaces

NASA Astrophysics Data System (ADS)

Pham, Tuan Anh; Li, Tianshu; Gygi, Francois; Galli, Giulia

2011-03-01

Silicon Nitride (Si3N4) is a possible candidate material to replace or be alloyed with SiO2 to form high-K dielectric films on Si substrates, so as to help prevent leakage currents in modern CMOS transistors. Building on our previous work on dielectric properties of crystalline and amorphous Si3N4 slabs, we present an analysis of the band offsets and dielectric properties of crystalline-Si/amorphous Si3N4 interfaces based on first principles calculations. We discuss shortcomings of the conventional bulk-plus line up approach in band offset calculations for systems with an amorphous component, and we present the results of band offsets obtained from calculations of local density of states. Finally, we describe the role of bonding configurations in determining band edges and dielectric constants at the interface. We acknowledge financial support from Intel Corporation.

Modification of the erythrocyte membrane dielectric constant by alcohols.

PubMed

Orme, F W; Moronne, M M; Macey, R I

1988-08-01

Aliphatic alcohols are found to stimulate the transmembrane fluxes of a hydrophobic cation (tetraphenylarsonium, TPA) and anion (AN-12) 5-20 times in red blood cells. The results are analyzed using the Born-Parsegian equation (Parsegian, A., 1969, Nature (London) 221:844-846), together with the Clausius-Mossotti equation to calculate membrane dielectric energy barriers. Using established literature values of membrane thickness, native membrane dielectric constant, TPA ionic radius, and alcohol properties (partition coefficient, molar volume, dielectric constant), the TPA permeability data is predicted remarkably well by theory. If the radius of AN-12 is taken as 1.9 A, its permeability in the presence of butanol is also described by our analysis. Further, the theory quantitatively accounts for the data of Gutknecht and Tosteson (Gutknecht, J., Tosteson, D.C., 1970, J. Gen. Physiol. 55:359-374) covering alcohol-induced conductivity changes of 3 orders of magnitude in artificial bilayers. Other explanations including perturbations of membrane fluidity, surface charge, membrane thickness, and dipole potential are discussed. However, the large magnitude of the stimulation, the more pronounced effect on smaller ions, and the acceleration of both anions and cations suggest membrane dielectric constant change as the primary basis of alcohol effects.

Free-Space Time-Domain Method for Measuring Thin Film Dielectric Properties

DOEpatents

Li, Ming; Zhang, Xi-Cheng; Cho, Gyu Cheon

2000-05-02

A non-contact method for determining the index of refraction or dielectric constant of a thin film on a substrate at a desired frequency in the GHz to THz range having a corresponding wavelength larger than the thickness of the thin film (which may be only a few microns). The method comprises impinging the desired-frequency beam in free space upon the thin film on the substrate and measuring the measured phase change and the measured field reflectance from the reflected beam for a plurality of incident angles over a range of angles that includes the Brewster's angle for the thin film. The index of refraction for the thin film is determined by applying Fresnel equations to iteratively calculate a calculated phase change and a calculated field reflectance at each of the plurality of incident angles, and selecting the index of refraction that provides the best mathematical curve fit with both the dataset of measured phase changes and the dataset of measured field reflectances for each incident angle. The dielectric constant for the thin film can be calculated as the index of refraction squared.

Theory of space-charge polarization for determining ionic constants of electrolytic solutions

NASA Astrophysics Data System (ADS)

Sawada, Atsushi

2007-06-01

A theoretical expression of the complex dielectric constant attributed to space-charge polarization has been derived under an electric field calculated using Poisson's equation considering the effects of bound charges on ions. The frequency dependence of the complex dielectric constant of chlorobenzene solutions doped with tetrabutylammonium tetraphenylborate (TBATPB) has been analyzed using the theoretical expression, and the impact of the bound charges on the complex dielectric constant has been clarified quantitatively in comparison with a theory that does not consider the effect of the bound charges. The Stokes radius of TBA +(=TPB-) determined by the present theory shows a good agreement with that determined by conductometry in the past; hence, the present theory should be applicable to the direct determination of the mobility of ion species in an electrolytic solution without the need to measure ionic limiting equivalent conductance and transport number.

Theoretical and Numerical Approaches for Determining the Reflection and Transmission Coefficients of OPEFB-PCL Composites at X-Band Frequencies

PubMed Central

Ahmad, Ahmad F.; Abbas, Zulkifly; Obaiys, Suzan J.; Ibrahim, Norazowa; Hashim, Mansor; Khaleel, Haider

2015-01-01

Bio-composites of oil palm empty fruit bunch (OPEFB) fibres and polycaprolactones (PCL) with a thickness of 1 mm were prepared and characterized. The composites produced from these materials are low in density, inexpensive, environmentally friendly, and possess good dielectric characteristics. The magnitudes of the reflection and transmission coefficients of OPEFB fibre-reinforced PCL composites with different percentages of filler were measured using a rectangular waveguide in conjunction with a microwave vector network analyzer (VNA) in the X-band frequency range. In contrast to the effective medium theory, which states that polymer-based composites with a high dielectric constant can be obtained by doping a filler with a high dielectric constant into a host material with a low dielectric constant, this paper demonstrates that the use of a low filler percentage (12.2%OPEFB) and a high matrix percentage (87.8%PCL) provides excellent results for the dielectric constant and loss factor, whereas 63.8% filler material with 36.2% host material results in lower values for both the dielectric constant and loss factor. The open-ended probe technique (OEC), connected with the Agilent vector network analyzer (VNA), is used to determine the dielectric properties of the materials under investigation. The comparative approach indicates that the mean relative error of FEM is smaller than that of NRW in terms of the corresponding S21 magnitude. The present calculation of the matrix/filler percentages endorses the exact amounts of substrate utilized in various physics applications. PMID:26474301

Atomistic and Ab Initio Calculations or Ternary II-IV-V2 Semiconductors

DTIC Science & Technology

1999-12-07

consisting of two- and three-body terms is developed reproducing crystal lattice constants, elastic and dielectric constants very well. The calculated...the lattice . This difference may well be due to defect-induced lattice distortion which plays a key role in stabilizing the hole states in the... lattice . 15. SUBJECT TERMS Chalcopyrites, Defects, Atomistic and AB Initio Calculations 16. SECURITY CLASSIFICATION OF: a. REPORT u b. ABSTRACT U

Electrostatic contribution to the binding stability of protein-protein complexes.

PubMed

Dong, Feng; Zhou, Huan-Xiang

2006-10-01

To investigate roles of electrostatic interactions in protein binding stability, electrostatic calculations were carried out on a set of 64 mutations over six protein-protein complexes. These mutations alter polar interactions across the interface and were selected for putative dominance of electrostatic contributions to the binding stability. Three protocols of implementing the Poisson-Boltzmann model were tested. In vdW4 the dielectric boundary between the protein low dielectric and the solvent high dielectric is defined as the protein van der Waals surface and the protein dielectric constant is set to 4. In SE4 and SE20, the dielectric boundary is defined as the surface of the protein interior inaccessible to a 1.4-A solvent probe, and the protein dielectric constant is set to 4 and 20, respectively. In line with earlier studies on the barnase-barstar complex, the vdW4 results on the large set of mutations showed the closest agreement with experimental data. The agreement between vdW4 and experiment supports the contention of dominant electrostatic contributions for the mutations, but their differences also suggest van der Waals and hydrophobic contributions. The results presented here will serve as a guide for future refinement in electrostatic calculation and inclusion of nonelectrostatic effects. Proteins 2006. (c) 2006 Wiley-Liss, Inc.

Rationally designed polyimides for high-energy density capacitor applications.

PubMed

Ma, Rui; Baldwin, Aaron F; Wang, Chenchen; Offenbach, Ido; Cakmak, Mukerrem; Ramprasad, Rampi; Sotzing, Gregory A

2014-07-09

Development of new dielectric materials is of great importance for a wide range of applications for modern electronics and electrical power systems. The state-of-the-art polymer dielectric is a biaxially oriented polypropylene (BOPP) film having a maximal energy density of 5 J/cm(3) and a high breakdown field of 700 MV/m, but with a limited dielectric constant (∼2.2) and a reduced breakdown strength above 85 °C. Great effort has been put into exploring other materials to fulfill the demand of continuous miniaturization and improved functionality. In this work, a series of polyimides were investigated as potential polymer materials for this application. Polyimide with high dielectric constants of up to 7.8 that exhibits low dissipation factors (<1%) and high energy density around 15 J/cm(3), which is 3 times that of BOPP, was prepared. Our syntheses were guided by high-throughput density functional theory calculations for rational design in terms of a high dielectric constant and band gap. Correlations of experimental and theoretical results through judicious variations of polyimide structures allowed for a clear demonstration of the relationship between chemical functionalities and dielectric properties.

SHALLOW ELECTRON TRAPS IN SINGLE CRYSTALS OF RUTILE STUDIED BY X-RAY IRRADIATION USING LOW FREQUENCY DIELECTRIC MEASUREMENTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Srivastava, K.G.

1962-04-01

Defect structure in single crystals of rutile was studied by dielectric measurements at 2 cps and above, before and after irradiation with hard x rays. The results were analyzed by a Cole-Cole plot, which is a circle with its cenier shifted away from the dielectric constant axis. X irradiation shifts the center of the Cole-Cole plot toward the dielectric constant axis, indicating a decrease in distribution of relaxation times by evacuation of electrons from their shallow traps, which after release produce interfacial polarization. An attempt was also made to calculate the a-c behavior from d-c data, but the errors atmore » frequencies of measurement were toe high, thus defying comparison with experimental data. (auth)« less

Investigation on the growth of CaCu 3Ti 4O 12 thin film and the origins of its dielectric relaxations

NASA Astrophysics Data System (ADS)

Yuan, Wen-Xiang; Hark, S. K.; Xu, H. Y.; Mei, W. N.

2012-01-01

Using the radio frequency magnetron sputtering, CaCu 3Ti 4O 12 (CCTO) thin films were deposited on platinized silicon substrates. The influence of annealing temperature on structures and morphologies of the thin films was investigated. The high annealing temperature increased the crystallinity of the films. Temperature dependence of the dielectric constant revealed an amazing different characteristic of the dielectric relaxation at ˜10 MHz, whose characteristic frequency abnormally increased with the decrease of the measuring temperature unlike the relaxations due to extrinsic origins. Meanwhile, the dielectric constant at high frequencies was close to the value derived from the first principle calculation. All these gave the evidences to ascribe this relaxation to the intrinsic mechanism.

Theoretical Study of the Transverse Dielectric Constant of Superlattices and Their Alloys. Ph.D Thesis

NASA Technical Reports Server (NTRS)

Kahen, K. B.

1986-01-01

The optical properties of III to V binary and ternary compounds and GaAs-Al(x)Ga(1-x)As superlattices are determined by calculating the real and imaginary parts of the transverse dielectric constant. Emphasis is given to determining the influence of different material and superlattice parameters on the values of the index of refraction and absorption coefficient. In order to calculate the optical properties of a material, it is necessary to compute its electronic band structure. This was accomplished by introducing a partition band structure approach based on a combination of the vector k x vector p and nonlocal pseudopotential techniques. The advantages of this approach are that it is accurate, computationally fast, analytical, and flexible. These last two properties enable incorporation of additional effects into the model, such as disorder scattering, which occurs for alloy materials and excitons. Furthermore, the model is easily extended to more complex structures, for example multiple quantum wells and superlattices. The results for the transverse dielectric constant and absorption coefficient of bulk III to V compounds compare well with other one-electron band structure models and the calculations show that for small frequencies, the index of refraction is determined mainly by the contibution of the outer regions of the Brillouin zone.

Dielectric and conformational studies of hydrogen bonded 2-ethoxyethanol and ethyl methyl ketone system

NASA Astrophysics Data System (ADS)

Pattebahadur, Kanchan. L.; Deshmukh, S. D.; Mohod, A. G.; Undre, P. B.; Patil, S. S.; Khirade, P. W.

2018-05-01

The Dielectric constant, density and refractive index of binary mixture of 2-ethoxy ethanol (2-EE) with ethyl methyl ketone (EMK) including those of the pure liquids were measured for 11 concentrations at 25°C temperature. The experimental data is used to calculate the Excess molar volume, Excess dielectric constant, Kirkwood correlation factor and Bruggemann factor. The excess parameters results were fitted to the Redlich-Kister type polynomial equation to derive its fitting coefficient. The Kirkwood correlation factor of the mixture has been discussed to yield information about solute solvent interaction. The Bruggeman plot shows a deviation from linearity. The FT-IR spectra of pure and their binary mixtures are also studied.

Anisotropic dielectric properties of two-dimensional matrix in pseudo-spin ferroelectric system

NASA Astrophysics Data System (ADS)

Kim, Se-Hun

2016-10-01

The anisotropic dielectric properties of a two-dimensional (2D) ferroelectric system were studied using the statistical calculation of the pseudo-spin Ising Hamiltonian model. It is necessary to delay the time for measurements of the observable and the independence of the new spin configuration under Monte Carlo sampling, in which the thermal equilibrium state depends on the temperature and size of the system. The autocorrelation time constants of the normalized relaxation function were determined by taking temperature and 2D lattice size into account. We discuss the dielectric constants of a two-dimensional ferroelectric system by using the Metropolis method in view of the Slater-Takagi defect energies.

Nonempirical range-separated hybrid functionals for solids and molecules

DOE PAGES

Skone, Jonathan H.; Govoni, Marco; Galli, Giulia

2016-06-03

Dielectric-dependent hybrid (DDH) functionals were recently shown to yield accurate energy gaps and dielectric constants for a wide variety of solids, at a computational cost considerably less than that of GW calculations. The fraction of exact exchange included in the definition of DDH functionals depends (self-consistently) on the dielectric constant of the material. Here we introduce a range-separated (RS) version of DDH functionals where short and long-range components are matched using system dependent, non-empirical parameters. We show that RS DDHs yield accurate electronic properties of inorganic and organic solids, including energy gaps and absolute ionization potentials. Moreover, we show thatmore » these functionals may be generalized to finite systems.« less

Anomalous response of supported few-layer hexagonal boron nitride to DC electric fields: a confined water effect?

NASA Astrophysics Data System (ADS)

Oliveira, Camilla; Matos, Matheus; Mazzoni, Mário; Chacham, Hélio; Neves, Bernardo

2013-03-01

Hexagonal boron nitride (h-BN) is a two-dimensional compound from III-V family, with the atoms of boron and nitrogen arranged in a honeycomb lattice, similar to graphene. Unlike graphene though, h-BN is an insulator material, with a gap larger than 5 eV. Here, we use Electric Force Microscopy (EFM) to study the electrical response of mono and few-layers of h-BN to an electric field applied by the EFM tip. Our results show an anomalous behavior in the dielectric response for h-BN for different bias orientation: for a positive bias applied to the tip, h-BN layers respond with a larger dielectric constant than the dielectric constant of the silicon dioxide substrate; while for a negative bias, the h-BN dielectric constant is smaller than the dielectric constant of the substrate. Based on first-principles calculations, we showed that this anomalous response may be interpreted as a macroscopic consequence of confinement of a thin water layer between h-BN and substrate. These results were confirmed by sample annealing and also also by a comparative analysis with h-BN on a non-polar substrate. All the authors acknowledge financial support from CNPq, Fapemig, Rede Nacional de Pesquisa em Nanotubos de Carbono and INCT-Nano-Carbono.

Influence of Al3+ substitution on the electrical resistivity and dielectric behavior of Ni0.25Cu0.20Zn0.55AlxFe2-xO4 ferrites synthesized by solid state reaction technique

NASA Astrophysics Data System (ADS)

Rahman, K. R.; Chowdhury, F.-U.-Z.; Khan, M. N. I.

2017-12-01

In this paper, the effect of Al3+ substitution on the electrical and dielectric properties of Ni0.25Cu0.20Zn0.55AlxFe2-xO4 ferrites with x = 0.0, 0.05. 0.10, 0.15 and 0.20, synthesized by solid state reaction has been reported. Using two probe method, the DC resistivity has been investigated in the temperature range from 30 °C to 300 °C. Activation energy was calculated from the Arrhenius plot. The electrical conduction is explained on the basis of the hopping mechanism. The frequency dependent dielectric properties of these spinel ferrites have been studied at room temperature by measuring AC resistivity, conductivity (σac), dielectric constant and dielectric loss tangent (tan δ) in the frequency range between 1 kHz and 120 MHz. The study of dielectric properties showed that the dielectric constant and dielectric loss increased with increasing non-magnetic Al ions. The dependence of dielectric constant with frequency has been explained by Maxwell-Wagner interfacial polarization. Cole-Cole plots show semicircular arc(s) for the samples, and equivalent RC circuits have been proposed to clarify the phenomena involved therein. The analysis of complex impedance spectroscopy has been used to distinguish between the grain and grain boundary contribution to the total resistance.

Growth and characterization of diammonium copper disulphate hexahydrate single crystal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siva Sankari, R.; Perumal, Rajesh Narayana, E-mail: r.shankarisai@gmail.com

2014-03-01

Graphical abstract: Diammonium copper disulphate hexahydrate (DACS) is one of the most promising inorganic dielectric crystals with exceptional mechanical properties. Good quality crystals of DACS were grown by using solution method in a period of 30 days. The grown crystals were subjected to single crystal X-ray diffraction analysis in order to establish their crystalline nature. Thermo gravimetric, differential thermal analysis, FTIR, and UV–vis–NIR analysis were performed for the crystal. Several solid state physical parameters have been determined for the grown crystals. The dielectric constant and the dielectric loss and AC conductivity of the grown crystal were studied as a functionmore » of frequency and temperature has been calculated and plotted. - Highlights: • Diammonium copper disulphate is grown for the first time and CCDC number obtained. • Thermal analysis is done to see the stability range of the crystals. • Band gap and UV cut off wavelength of the crystal are determined to be 2.4 eV and 472.86 nm, respectively. • Dielectric constant, dielectric loss and AC conductivity are plotted as a function of applied field. - Abstract: Diammonium copper disulphate hexahydrate is one of the most promising inorganic crystals with exceptional dielectric properties. A good quality crystal was harvested in a 30-day period using solution growth method. The grown crystal was subjected to various characterization techniques like single crystal X-ray diffraction analysis, thermo gravimetric, differential thermal analysis, FTIR, and UV–vis–NIR analysis. Unit cell dimensions of the grown crystal have been identified from XRD studies. Functional groups of the title compounds have been identified from FTIR studies. Thermal stability of the samples was checked by TG/DTA studies. Band gap of the crystal was calculated. The dielectric constant and dielectric loss were studied as a function of frequency of the applied field. AC conductivity was plotted as a function of temperature.« less

Electronic and optical properties of RESn{sub 3} (RE=Pr & Nd) intermetallics: A first principles study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pagare, G., E-mail: gita-pagare@yahoo.co.in; Abraham, Jisha A.; Department of Physics, National Defence Academy, Pune-411023

2015-06-24

A theoretical study of structural, electronic and optical properties of RESn{sub 3} (RE = Pr & Nd) intermetallics have been investigated systematically using first principles density functional theory. The calculations are carried out within the PBE-GGA and LSDA for the exchange correlation potential. The ground state properties such as lattice parameter (a{sub 0}), bulk modulus (B) and its pressure derivative (B′) are calculated and the calculated lattice parameters show well agreement with the experimental results. We first time predict elastic constants for these compounds. From energy dispersion curves, it is found that these compounds are metallic in nature. The linearmore » optical response of these compounds are also studied and the higher value of static dielectric constant shows the possibility to use them as good dielectric materials.« less

Optical properties of Sulfur doped InP single crystals

NASA Astrophysics Data System (ADS)

El-Nahass, M. M.; Youssef, S. B.; Ali, H. A. M.

2014-05-01

Optical properties of InP:S single crystals were investigated using spectrophotometric measurements in the spectral range of 200-2500 nm. The absorption coefficient and refractive index were calculated. It was found that InP:S crystals exhibit allowed and forbidden direct transitions with energy gaps of 1.578 and 1.528 eV, respectively. Analysis of the refractive index in the normal dispersion region was discussed in terms of the single oscillator model. Some optical dispersion parameters namely: the dispersion energy (Ed), single oscillator energy (Eo), high frequency dielectric constant (ɛ∞), and lattice dielectric constant (ɛL) were determined. The volume and the surface energy loss functions (VELF & SELF) were estimated. Also, the real and imaginary parts of the complex conductivity were calculated.

Hydration and dielectrical properties of aqueous pyrrolidinium trifluoroacetate solutions

NASA Astrophysics Data System (ADS)

Lyashchenko, A. K.; Balakaeva, I. V.; Simonova, Yu. A.; Timofeeva, L. M.

2017-10-01

Results from microwave measurements of the dielectrical properties of aqueous pyrrolidinium trifluoroacetate solutions at maximum water dispersion frequencies (13-25 GHz) and temperatures of 288, 298, and 308 K are given. The static dielectrical constants, times, and activation parameters of the dielectrical relaxation of solutions are calculated. The enthalpy and time of dielectrical relaxation activation are increased by deceleration of the motion of water molecules in the hydrate shells of ions. The changes in dielectrical parameters are in this case minimal in a series of aqueous solutions of diallylammonium salts with cations of different structures and degrees of substitution. It is shown that pyrrolidinium ions are characterized by weak hydrophobic hydration.

Concentration dependence of molal conductivity and dielectric constant of 1-alcohol electrolytes using the compensated arrhenius formalism.

PubMed

Fleshman, Allison M; Petrowsky, Matt; Frech, Roger

2013-05-02

The molal conductivity of liquid electrolytes with low static dielectric constants (ε(s) < 10) decreases to a minimum at low concentrations (region I) and increases to a maximum at higher concentrations (region II) when plotted against the square root of the concentration. This behavior is investigated by applying the compensated Arrhenius formalism (CAF) to the molal conductivity, Λ, of a family of 1-alcohol electrolytes over a broad concentration range. A scaling procedure is applied that results in an energy of activation (E(a)) and an exponential prefactor (Λ0) that are both concentration dependent. It is shown that the increasing molal conductivity in region II results from the combined effect of (1) a decrease in the energy of activation calculated from the CAF, and (2) an inherent concentration dependence in the exponential prefactor that is partly due to the dielectric constant.

Static dielectric constant of water within a bilayer using recent water models: a molecular dynamics study

NASA Astrophysics Data System (ADS)

Meneses-Juárez, Efrain; Rivas-Silva, Juan Francisco; González-Melchor, Minerva

2018-05-01

The water confined within a surfactant bilayer is studied using different water models via molecular dynamics simulations. We considered four representative rigid models of water: the SPC/E and the TIP4P/2005, which are commonly used in numerical calculations and the more recent TIP4Q and SPC/ε models, developed to reproduce the dielectric behaviour of pure water. The static dielectric constant of the confined water was analyzed as a function of the temperature for the four models. In all cases it decreases as the temperature increases. Additionally, the static dielectric constant of the bilayer-water system was estimated through its expression in terms of the fluctuations in the total dipole moment, usually applied for isotropic systems. The estimated dielectric was compared with the available experimental data. We found that the TIP4Q and the SPC/ε produce closer values to the experimental data than the other models, particularly at room temperature. It was found that the probability of finding the sodium ion close to the head of the surfactant decreases as the temperature increases, thus the head of the surfactant is more exposed to the interaction with water when the temperature is higher.

Dielectric and physiochemical study of binary mixture of nitrobenzene with toluene

NASA Astrophysics Data System (ADS)

Mohod, Ajay G.; Deshmukh, S. D.; Pattebahadur, K. L.; Undre, P. B.; Patil, S. S.; Khirade, P. W.

2018-05-01

This paper presents the study of binary mixture of Nitrobenzene (NB) with Toluene (TOL) for eleven different concentrations at room temperature. The determined Dielectric Constant (ɛ0) Density (ρ) and Refractive index (nD) values of binary mixture are used to calculate the excess properties i.e. Excess Dielectric Constant (ɛ0E), Excess Molar Volume (VmE), Excess Refractive Index (nDE) and Excess Molar Refraction (RmE) of mixture over the entire composition range and fitted to the Redlich-Kister equation. The Kirkwood Correlation Factor (geff) and other parameters were used to discuss the information about the orientation of dipoles and the solute-solvent interaction of binary mixture at molecular level over the entire range of concentration.

The effect of concentration- and temperature-dependent dielectric constant on the activity coefficient of NaCl electrolyte solutions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Valiskó, Mónika; Boda, Dezső, E-mail: boda@almos.vein.hu

2014-06-21

Our implicit-solvent model for the estimation of the excess chemical potential (or, equivalently, the activity coefficient) of electrolytes is based on using a dielectric constant that depends on the thermodynamic state, namely, the temperature and concentration of the electrolyte, ε(c, T). As a consequence, the excess chemical potential is split into two terms corresponding to ion-ion (II) and ion-water (IW) interactions. The II term is obtained from computer simulation using the Primitive Model of electrolytes, while the IW term is estimated from the Born treatment. In our previous work [J. Vincze, M. Valiskó, and D. Boda, “The nonmonotonic concentration dependencemore » of the mean activity coefficient of electrolytes is a result of a balance between solvation and ion-ion correlations,” J. Chem. Phys. 133, 154507 (2010)], we showed that the nonmonotonic concentration dependence of the activity coefficient can be reproduced qualitatively with this II+IW model without using any adjustable parameter. The Pauling radii were used in the calculation of the II term, while experimental solvation free energies were used in the calculation of the IW term. In this work, we analyze the effect of the parameters (dielectric constant, ionic radii, solvation free energy) on the concentration and temperature dependence of the mean activity coefficient of NaCl. We conclude that the II+IW model can explain the experimental behavior using a concentration-dependent dielectric constant and that we do not need the artificial concept of “solvated ionic radius” assumed by earlier studies.« less

Two-electron bond-orbital model, 1

NASA Technical Reports Server (NTRS)

Huang, C.; Moriarty, J. A.; Sher, A.; Breckenridge, R. A.

1975-01-01

Harrison's one-electron bond-orbital model of tetrahedrally coordinated solids was generalized to a two-electron model, using an extension of the method of Falicov and Harris for treating the hydrogen molecule. The six eigenvalues and eigenstates of the two-electron anion-cation Hamiltonian entering this theory can be found exactly general. The two-electron formalism is shown to provide a useful basis for calculating both non-magnetic and magnetic properties of semiconductors in perturbation theory. As an example of the former, expressions for the electric susceptibility and the dielectric constant were calculated. As an example of the latter, new expressions for the nuclear exchanges and pseudo-dipolar coefficients were calculated. A simple theoretical relationship between the dielectric constant and the exchange coefficient was also found in the limit of no correlation. These expressions were quantitatively evaluated in the limit of no correlation for twenty semiconductors.

Structural, magnetic and spectral properties of Gd and Dy co-doped dielectrically modified Co-Ni (Ni0.4Co0.6Fe2O4) ferrites

NASA Astrophysics Data System (ADS)

Ditta, Allah; Khan, Muhammad Azhar; Junaid, Muhammad; Khalil, R. M. Arif; Warsi, Muhammad Farooq

2017-02-01

Gadolinium (Gd) and Dysprosium (Dy) co-doped Ni-Co (Ni0.4Co0.6Fe2O4) ferrites were prepared by micro-emulsion route. X-ray diffraction (XRD) analysis indicated the development of cubic spinel structure. The lattice parameter and X-ray density were found to increase from 8.24 to 8.31 Å and 5.57 to 5.91 (gm/cm3) respectively as the Gd-Dy contents increased in nickel-cobalt ferrites. The crystallite size calculated from the Scherrer's formula exhibited the formation of nanocrystalline ferrites (13-26 nm). Two foremost absorption bands observed in FTIR spectra within 400 cm-1 (υ2) to 600 cm-1 (υ1) which correspond to stretching vibrations of tetrahedral and octahedral complexes respectively. The dielectric constant (ε) and dielectric loss (tanδ) were decreased by the optimization of frequency and abrupt decrease in the low frequency region and higher values in the high frequency region were observed. The dielectric dispersion was due to rapid decrease of dielectric constant in the low frequency region. This variation of dielectric dispersion was explicated in the light of space charge polarization model of Maxwell-Wagner. The dielectric loss occurs in these ferrites due to electron hopping and defects in the dipoles. The electron hopping was possible at low frequency range but at higher frequency the dielectric loss was decreased with the decrease of electron hopping. Magnetic properties were observed by measuring M-H loops. Due to low dielectric loss and dielectric constant these materials were appropriate in the fabrication of switching and memory storage devices.

Dielectric Response and Born Dynamic Charge of BN Nanotubes from Ab Initio Finite Electric Field Calculations

NASA Astrophysics Data System (ADS)

Guo, Guang-Yu; Ishibashi, Shoji; Tamura, Tomoyuki; Terakura, Kiyoyuki

2007-03-01

Since the discovery of carbon nanotubes (CNTs) in 1991 by Iijima, carbon and other nanotubes have attracted considerable interest worldwide because of their unusual properties and also great potentials for technological applications. Though CNTs continue to attract great interest, other nanotubes such as BN nanotubes (BN-NTs) may offer different opportunities that CNTs cannot provide. In this contribution, we present the results of our recent systematic ab initio calculations of the static dielectric constant, electric polarizability, Born dynamical charge, electrostriction coefficient and piezoelectric constant of BN-NTs using the latest crystalline finite electric field theory [1]. [1] I. Souza, J. Iniguez, and D. Vanderbilt, Phys. Rev. Lett. 89, 117602 (2002); P. Umari and A. Pasquarello, Phys. Rev. Lett. 89, 157602 (2002).

Determination of dispersive optical constants of nanocrystalline CdSe (nc-CdSe) thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Kriti; Al-Kabbi, Alaa S.; Saini, G.S.S.

2012-06-15

Highlights: ► nc-CdSe thin films are prepared by thermal vacuum evaporation technique. ► TEM analysis shows NCs are spherical in shape. ► XRD reveals the hexagonal (wurtzite) crystal structure of nc-CdSe thin films. ► The direct optical bandgap of nc-CdSe is 2.25 eV in contrast to bulk (1.7 eV). ► Dispersion of refractive index is discussed in terms of Wemple–DiDomenico single oscillator model. -- Abstract: The nanocrystalline thin films of CdSe are prepared by thermal evaporation technique at room temperature. These thin films are characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-raymore » diffraction (XRD) and photoluminescence spectroscopy (PL). The transmission spectra are recorded in the transmission range 400–3300 nm for nc-CdSe thin films. Transmittance measurements are used to calculate the refractive index (n) and absorption coefficient (α) using Swanepoel's method. The optical band gap (E{sub g}{sup opt}) has been determined from the absorption coefficient values using Tauc's procedure. The optical constants such as extinction coefficient (k), real (ε{sub 1}) and imaginary (ε{sub 2}) dielectric constants, dielectric loss (tan δ), optical conductivity (σ{sub opt}), Urbach energy (E{sub u}) and steepness parameter (σ) are also calculated for nc-CdSe thin films. The normal dispersion of refractive index is described using Wemple–DiDomenico single-oscillator model. Refractive index dispersion is further analysed to calculate lattice dielectric constant (ε{sub L}).« less

Dielectric studies on PEG-LTMS based polymer composites

NASA Astrophysics Data System (ADS)

Patil, Ravikumar V.; Praveen, D.; Damle, R.

2018-02-01

PEG LTMS based polymer composites were prepared and studied for dielectric constant variation with frequency and temperature as a potential candidate with better dielectric properties. Solution cast technique is used for the preparation of polymer composite with five different compositions. Samples show variation in dielectric constant with frequency and temperature. Dielectric constant is large at low frequencies and higher temperatures. Samples with larger space charges have shown larger dielectric constant. The highest dielectric constant observed was about 29244 for PEG25LTMS sample at 100Hz and 312 K.

Slots in dielectric image line as mode launchers and circuit elements

NASA Astrophysics Data System (ADS)

Solbach, K.

1981-01-01

A planar resonator model is used to investigate slots in the ground plane of dielectric image lines. An equivalent circuit representation of the slot discontinuity is obtained, and the launching efficiency of the slot as a mode launcher is analyzed. Slots are also shown to be useful in the realization of dielectric image line array antennas. It is found that the slot discontinuity can be shown as a T-junction of the dielectric image line and a metal waveguide. The launching efficiency is found to increase with the dielectric constant of the dielectric image line, exhibiting a maximum value for guides whose height is slightly less than half a wavelength in the dielectric medium. The measured launching efficiencies of low permittivity dielectric image lines are found to be in good agreement with calculated values

Multilayer thin films with compositional PbZr0.52Ti0.48O3/Bi1.5Zn1.0Nb1.5O7 layers for tunable applications

PubMed Central

Yu, Shihui; Li, Lingxia; Zhang, Weifeng; Sun, Zheng; Dong, Helei

2015-01-01

The dielectric properties and tunability of multilayer thin films with compositional PbZr0.52Ti0.48O3/Bi1.5Zn1.0Nb1.5O7 (PZT/BZN) layers (PPBLs) fabricated by pulsed laser deposition on Pt/TiO2/SiO2/Si substrate have been investigated. Dielectric measurements indicate that the PZT/BZN bilayer thin films exhibit medium dielectric constant of about 490, low loss tangent of 0.017, and superior tunable dielectric properties (tunability = 49.7% at 500 kV/cm) at a PZT/BZN thickness ratio of 3, while the largest figure of merit is obtained as 51.8. The thickness effect is discussed with a series connection model of bilayer capacitors, and the calculated dielectric constant and loss tangent are obtained. Furthermore, five kinds of thin–film samples comprising single bilayers, two, three, four and five PPBLs were also elaborated with the final same thickness. The four PPBLs show the largest dielectric constant of ~538 and tunability of 53.3% at a maximum applied bias field of 500 kV/cm and the lowest loss tangent of ~0.015, while the largest figure of merit is 65.6. The results indicate that four PPBLs are excellent candidates for applications of tunable devices. PMID:25960043

Dielectric and structural properties of aqueous nonpolar solute mixtures.

PubMed

Shvab, I; Sadus, Richard J

2012-09-28

The dielectric properties and molecular structure of water mixtures with different nonpolar solutes (methane and noble gases) are studied using molecular dynamics. The water-water, water-solute, and solute-solute interactions are calculated using the combination of a polarizable potential [J. Li, Z. Zhou, and R. J. Sadus, J. Chem. Phys. 127, 154509 (2007)] for water plus the Lennard-Jones potential. The effect of solute size and concentration on the solubility of the system, hydrogen bonding, dielectric constant, and dipole moment are investigated over a temperature range of 278-750 K and solute percentage mole fractions up to 30%. Solute particles affect the structure of water, resulting in the compression of oxygen-oxygen and oxygen-hydrogen radial distribution functions. The influence of the solute extends both to relatively low concentrations and high temperatures. The coordination numbers of aqueous solutions of the nonpolar solutes appear to be proportional to the size of the solute particles. Our study shows the destructive influence of the nonpolar solute on both the tetrahedral water structure and hydrogen bond formation at solute concentrations greater than 30%. The presence of nonpolar particles typically decreases both the dielectric constant and dipole moment. The decrease of dielectric constant and water dipole moment is directly proportional to the solute concentration and temperature.

Effective transport properties of composites of spheres

NASA Astrophysics Data System (ADS)

Felderhof, B. U.

1994-06-01

The effective linear transport properties of composites of spheres may be studied by the methods of statistical physics. The analysis leads to an exact cluster expansion. The resulting expression for the transport coefficients may be evaluated approximately as the sum of a mean field contribution and correction terms, given by cluster integrals over two-sphere and three-sphere correlation functions. Calculations of this nature have been performed for the effective dielectric constant, as well as the effective elastic constants of composites of spheres. Accurate numerical data for the effective properties may be obtained by computer simulation. An efficient formulation uses multiple expansion in Cartesian coordinates and periodic boundary conditions. Extensive numerical results have been obtained for the effective dielectric constant of a suspension of randomly distributed spheres.

Dipolar correlations and the dielectric permittivity of water.

PubMed

Sharma, Manu; Resta, Raffaele; Car, Roberto

2007-06-15

The static dielectric properties of liquid and solid water are investigated within linear response theory in the context of ab initio molecular dynamics. Using maximally localized Wannier functions to treat the macroscopic polarization we formulate a first-principles, parameter-free, generalization of Kirkwood's phenomenological theory. Our calculated static permittivity is in good agreement with experiment. Two effects of the hydrogen bonds, i.e., a significant increase of the average local moment and a local alignment of the molecular dipoles, contribute in almost equal measure to the unusually large dielectric constant of water.

Plasmon mediated inverse Faraday effect in a graphene-dielectric-metal structure.

PubMed

Bychkov, Igor V; Kuzmin, Dmitry A; Tolkachev, Valentine A; Plaksin, Pavel S; Shavrov, Vladimir G

2018-01-01

This Letter shows the features of inverse Faraday effect (IFE) in a graphene-dielectric-metal (GDM) structure. The constants of propagation and attenuation of the surface plasmon-polariton modes are calculated. The effective magnetic field induced by surface plasmon modes in the dielectric due to the IFE is estimated to reach above 1 tesla. The possibility to control the distribution of the magnetic field by chemical potential of graphene is shown. The concept of strain-driven control of the IFE in the structure has been proposed and investigated.

The Casimir effect

NASA Astrophysics Data System (ADS)

Lang, Andrew Stuart

1998-12-01

This thesis contains several quantum field theoretic calculations using both the massless scalar field and the electromagnetic field. The main result being the calculation of the expectation of the energy density in the vacuum region for the geometry in which half of space is filled by a non- dispersive dielectric of constant susceptibility and the other half of space is vacuum. As we approach the surface of the dielectric the expectation of the energy density is found to diverge. In the final Chapter of this dissertation we prove that, under physically reasonable conditions, the quantum field theory representations for certain current models of dispersive dielectrics remain the same as that for the free electromagnetic field in vacuum. This is good news for the theories discussed.

FIBER AND INTEGRATED OPTICS. OPTOELECTRONICS: Method for calculation of the parameters of guided waves in anisotropic dielectric waveguides

NASA Astrophysics Data System (ADS)

Goncharenko, I. A.

1989-07-01

The method of shift formulas is applied to anisotropic dielectric waveguides capable of conserving a given state of polarization of the transmitted signal. Equations are derived for calculation of the propagation constants and of the dispersion of the fundamental modes in waveguides with an anisotropic permittivity and a noncircular shape of the transverse cross section. Distributions of electric and magnetic fields of these modes are obtained in a transverse cross section of the waveguide. It is shown that under the influence of the anisotropy of the dielectric an energy spot describing the distribution of the mode field becomes of an ellipse with its axes oriented along the coordinates coinciding with the principal axes of the permittivity tensor.

Synthesis and dielectric properties of zinc oxide nanoparticles using a biotemplate

DOE Office of Scientific and Technical Information (OSTI.GOV)

P, Sharmila P, E-mail: sharmilavishram@gmail.com; Tharayil, Nisha J., E-mail: nishajohntharayil@gmail.com

Zinc Oxide nanoparticles are synthesized using DNA as capping agent. Zinc oxide nanoparticles are synthesized using DNA as a capping agent. Structural and morphological characterizations are done using SEM, FTIR and XRD. The particle size and lattice parameters are calculated from the diffraction data. The optical properties are studied using UV-Vis absorption spectroscopy and bandgap variation with temperature is determined. The dielectric property of nanoparticles is studied by varying temperature and frequency. The dielectric constant and dispersion parameters are found out. Method of Cole-Cole analysis is used to study the high temperature dispersion of relaxation time. The variation of bothmore » AC and DC conductivity are studied and activation energy calculated.« less

Improved Dielectric Films For Capacitors

NASA Technical Reports Server (NTRS)

Yen, Shiao-Ping S.; Lewis, Carol R.; Cygan, Peter J.; Jow, T. Richard

1994-01-01

Dielectric films made from blends of some commercially available high-dielectric-constant cyanoresins with each other and with cellulose triacetate (CTA) have both high dielectric constants and high breakdown strengths. Dielectric constants as high as 16.2. Films used to produce high-energy-density capacitors.

Microwave measurement and modeling of the dielectric properties of vegetation

NASA Astrophysics Data System (ADS)

Shrestha, Bijay Lal

Some of the important applications of microwaves in the industrial, scientific and medical sectors include processing and treatment of various materials, and determining their physical properties. The dielectric properties of the materials of interest are paramount irrespective of the applications, hence, a wide range of materials covering food products, building materials, ores and fuels, and biological materials have been investigated for their dielectric properties. However, very few studies have been conducted towards the measurement of dielectric properties of green vegetations, including commercially important plant crops such as alfalfa. Because of its high nutritional value, there is a huge demand for this plant and its processed products in national and international markets, and an investigation into the possibility of applying microwaves to improve both the net yield and quality of the crop can be beneficial. Therefore, a dielectric measurement system based upon the probe reflection technique has been set up to measure dielectric properties of green plants over a frequency range from 300 MHz to 18 GHz, moisture contents from 12%, wet basis to 79%, wet basis, and temperatures from -15°C to 30°C. Dielectric properties of chopped alfalfa were measured with this system over frequency range of 300 MHz to 18 GHz, moisture content from 11.5%, wet basis, to 73%, wet basis, and density over the range from 139 kg m-3 to 716 kg m-3 at 23°C. The system accuracy was found to be +/-6% and +/-10% in measuring the dielectric constant and loss factor respectively. Empirical, semi empirical and theoretical models that require only moisture content and operating frequency were determined to represent the dielectric properties of both leaves and stems of alfalfa at 22°C. The empirical models fitted the measured dielectric data extremely well. The root mean square error (RMSE) and the coefficient of determination (r2) for dielectric constant and loss factor of leaves were 0.89 and 0.99, and 0.52 and 0.99 respectively. The RMSE and r2 values for dielectric constant and loss factor of stems were 0.89 and 0.99, and 0.77 and 0.99 respectively. Among semi empirical or theoretical models, Power law model showed better performance (RMSE = 1.78, r2 = 0.96) in modeling dielectric constant of leaves, and Debye-ColeCole model was more appropriate (RMSE = 1.23, r2 = 0.95) for the loss factor. For stems, the Debye-ColeCole models (developed on an assumption that they do not shrink as they dry) were found to be the best models to calculate the dielectric constant with RMSE 0.53 and r2 = 0.99, and dielectric loss factor with RMSE = 065 and r2 = 0.95. (Abstract shortened by UMI.)

Morphology, Structural and Dielectric Properties of Vacuum Evaporated V2O5 Thin Films

NASA Astrophysics Data System (ADS)

Sengodan, R.; Shekar, B. Chandar; Sathish, S.

Vanadium pentoxide (V2O5) thin films were deposited on well cleaned glass substrate using evaporation technique under the pressure of 10-5 Torr. The thickness of the films was measured by the multiple beam interferometry technique and cross checked by using capacitance method. Metal-Insulator-Metal (MIM) structure was fabricated by using suitable masks to study dielectric properties. The dielectric properties were studied by employing LCR meter in the frequency range 12 Hz to 100 kHz for various temperatures. The temperature co- efficient of permittivity (TCP), temperature co-efficient of capacitance (TCC) and dielectric constant (ɛ) were calculated. The activation energy was calculated and found to be very low. The activation energy was found to be increasing with increase in frequency. The obtained low value of activation energy suggested that the hopping conduction may be due to electrons rather than ions.

Material Science Smart Coatings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rubinstein, A. I.; Sabirianov, R. F.; Namavar, Fereydoon

2014-07-01

The contribution of electrostatic interactions to the free energy of binding between model protein and a ceramic implant surface in the aqueous solvent, considered in the framework of the nonlocal electrostatic model, is calculated as a function of the implant low-frequency dielectric constant. We show that the existence of a dynamically ordered (low-dielectric) interfacial solvent layer at the protein-solvent and ceramic-solvent interface markedly increases charging energy of the protein and ceramic implant, and consequently makes the electrostatic contribution to the protein-ceramic binding energy more favorable (attractive). Our analysis shows that the corresponding electrostatic energy between protein and oxide ceramics dependsmore » nonmonotonically on the dielectric constant of ceramic, ε C. Obtained results indicate that protein can attract electrostatically to the surface if ceramic material has a moderate ε C below or about 35 (in particularly ZrO 2 or Ta 2O 5). This is in contrast to classical (local) consideration of the solvent, which demonstrates an unfavorable electrostatic interaction of protein with typical metal oxide ceramic materials (ε C>10). Thus, a solid implant coated by combining oxide ceramic with a reduced dielectric constant can be beneficial to strengthen the electrostatic binding of the protein-implant complex.« less

Bimodal dielectric relaxation of electrolyte solutions in weakly polar solvents.

PubMed

Yamaguchi, Tsuyoshi; Koda, Shinobu

2014-12-28

The dielectric relaxation spectra of dilute electrolyte solutions in solvents of small dielectric constants are investigated both theoretically and experimentally. The theoretical calculation in our previous work [T. Yamaguchi, T. Matsuoka, and S. Koda, J. Chem. Phys. 135, 164511 (2011)] is reanalyzed, and it is shown that the dielectric relaxation spectra are composed of three components, namely, the relaxation of ionic atmosphere, the reorientational relaxation of ion pairs, and the collision between ions. The relaxation frequency of the slowest one increases with increasing the concentration, and the slower two relaxations, those of ionic atmosphere and ion pairs, merge into one at the concentration where the Debye length is comparable to the size of ions. Experimentally, the dielectric relaxation spectra of some electrolytes in two solvents, tetrahydrofuran and tetraglyme, are determined at frequencies from 300 kHz to 200 MHz, and the presence of the slower two relaxations was confirmed. The concentration dependence of the relaxation frequency is also in harmony with the theoretical calculation. The relationship between the dielectric relaxation spectra and the concentration dependence of the ionic conductivity is discussed.

Bimodal dielectric relaxation of electrolyte solutions in weakly polar solvents

NASA Astrophysics Data System (ADS)

Yamaguchi, Tsuyoshi; Koda, Shinobu

2014-12-01

The dielectric relaxation spectra of dilute electrolyte solutions in solvents of small dielectric constants are investigated both theoretically and experimentally. The theoretical calculation in our previous work [T. Yamaguchi, T. Matsuoka, and S. Koda, J. Chem. Phys. 135, 164511 (2011)] is reanalyzed, and it is shown that the dielectric relaxation spectra are composed of three components, namely, the relaxation of ionic atmosphere, the reorientational relaxation of ion pairs, and the collision between ions. The relaxation frequency of the slowest one increases with increasing the concentration, and the slower two relaxations, those of ionic atmosphere and ion pairs, merge into one at the concentration where the Debye length is comparable to the size of ions. Experimentally, the dielectric relaxation spectra of some electrolytes in two solvents, tetrahydrofuran and tetraglyme, are determined at frequencies from 300 kHz to 200 MHz, and the presence of the slower two relaxations was confirmed. The concentration dependence of the relaxation frequency is also in harmony with the theoretical calculation. The relationship between the dielectric relaxation spectra and the concentration dependence of the ionic conductivity is discussed.

Determination of the reduced matrix of the piezoelectric, dielectric, and elastic material constants for a piezoelectric material with C∞ symmetry.

PubMed

Sherrit, Stewart; Masys, Tony J; Wiederick, Harvey D; Mukherjee, Binu K

2011-09-01

We present a procedure for determining the reduced piezoelectric, dielectric, and elastic coefficients for a C(∞) material, including losses, from a single disk sample. Measurements have been made on a Navy III lead zirconate titanate (PZT) ceramic sample and the reduced matrix of coefficients for this material is presented. In addition, we present the transform equations, in reduced matrix form, to other consistent material constant sets. We discuss the propagation of errors in going from one material data set to another and look at the limitations inherent in direct calculations of other useful coefficients from the data.

Processing of Al2O3/SrTiO3/PDMS Composites With Low Dielectric Loss

NASA Astrophysics Data System (ADS)

Yao, J. L.; Guo, M. J.; Qi, Y. B.; Zhu, H. X.; Yi, R. Y.; Gao, L.

2018-05-01

Polydimethylsiloxane (PDMS) is widely used in the electrical and electronic industries due to its excellent electrical insulation and biocompatible characteristics. However, the dielectric constant of pure PDMS is very low which restricts its applications. Herein, we report a series of PDMS/Al2O3/strontium titanate (ST) composites with high dielectric constant and low loss prepared by a simple experimental method. The composites exhibit high dielectric constant (relative dielectric constant is 4) after the composites are coated with insulated Al2O3 particles, and the dielectric constant gets further improved for composites with ST particles (dielectric constant reaches 15.5); a lower dielectric loss (tanδ= 0.05) is also found at the same time which makes co-filler composites suitable for electrical insulation products, and makes the experimental method more interesting in modern teaching.

Optical constants, dispersion energy parameters and dielectric properties of ultra-smooth nanocrystalline BiVO4 thin films prepared by rf-magnetron sputtering

NASA Astrophysics Data System (ADS)

Sarkar, S.; Das, N. S.; Chattopadhyay, K. K.

2014-07-01

BiVO4 thin films have been prepared through radio frequency (rf) magnetron sputtering of a pre-fabricated BiVO4 target on ITO coated glass (ITO-glass) substrate and bare glass substrates. BiVO4 target material was prepared through solid-state reaction method by heating Bi2O3 and V2O5 mixture at 800 °C for 8 h. The films were characterized by X-ray diffraction, UV-Vis spectroscopy, LCR meter, field emission scanning electron microscopy, transmission electron microscopy and atomic force microscopy. BiVO4 thin films deposited on the ITO-glass substrate are much smoother compared to the thin films prepared on bare glass substrate. The rms surface roughness calculated from the AFM images comes out to be 0.74 nm and 4.2 nm for the films deposited on the ITO-glass substrate and bare glass substrate for the deposition time 150 min respectively. Optical constants and energy dispersion parameters of these extra-smooth BiVO4 thin films have been investigated in detail. Dielectric properties of the BiVO4 thin films on ITO-glass substrate were also investigated. The frequency dependence of dielectric constant of the BiVO4 thin films has been measured in the frequency range from 20 Hz to 2 MHz. It was found that the dielectric constant increased from 145 to 343 at 20 Hz as the film thickness increased from 90 nm to 145 nm (deposition time increased from 60 min to 150 min). It shows higher dielectric constant compared to the literature value of BiVO4.

Numerical study of the electronic structure, elastic and optical properties of defect quaternary semiconductor CuGaSnSe4

NASA Astrophysics Data System (ADS)

Shen, Kesheng; Lu, Hai; Zhang, Xianzhou; Jiao, Zhaoyong

2018-06-01

The electronic structure, elastic and optical properties of the defect quaternary semiconductor CuGaSnSe4 in I 4 bar structure are systematically investigated using first-principles calculations. We summarize and discuss some of the studies on CuGaSnSe4 in partially ordered chalcopyrite structure and find that there are three atomic arrangements so far, but it is still uncertain which is the most stable. Through detailed simulation and comparison with the corresponding literature, we get three models and predict that M1 model should be the most stable. The band structure and optical properties of compound CuGaSnSe4, including dielectric constant, refractive index and absorption spectrum, are drawn for a more intuitive understanding. The elastic constants are also calculated, which not only prove that CuGaSnSe4 in I 4 bar structure is stable naturally but also help solve the problem of no data to accurately predict axial thermal expansion coefficients. The calculated values of the zero frequency dielectric constant and refractive index are comparable to those of the corresponding chalcopyrite structure but slightly larger.

47 CFR 73.184 - Groundwave field strength graphs.

Code of Federal Regulations, 2011 CFR

2011-10-01

... a dielectric constant of the ground (referred to air as unity) equal to 15 for land and 80 for sea..., Washington, DC 20554, (202) 632-7000. (c) Provided the value of the dielectric constant is near 15, the... dielectric constant, the following procedure may be used to determine the dielectric constant of the ground...

Application of the compensated Arrhenius formalism to explain the dielectric constant dependence of rates for Menschutkin reactions.

PubMed

Petrowsky, Matt; Glatzhofer, Daniel T; Frech, Roger

2013-11-21

The dependence of the reaction rate on solvent dielectric constant is examined for the reaction of trihexylamine with 1-bromohexane in a series of 2-ketones over the temperature range 25-80 °C. The rate constant data are analyzed using the compensated Arrhenius formalism (CAF), where the rate constant assumes an Arrhenius-like equation that also contains a dielectric constant dependence in the exponential prefactor. The CAF activation energies are substantially higher than those obtained using the simple Arrhenius equation. A master curve of the data is observed by plotting the prefactors against the solvent dielectric constant. The master curve shows that the reaction rate has a weak dependence on dielectric constant for values approximately less than 10 and increases more rapidly for dielectric constant values greater than 10.

Strip dielectric wave guide antenna-for the measurement of dielectric constant of low-loss materials

NASA Astrophysics Data System (ADS)

Rastogi, Alok Kumar; Tiwari, A. K.; Shrivastava, R. P.

1993-07-01

The value of dielectric constant are the most important parameters in material science technology. In micro-wave and millimeter wave circuits using dielectric materials the values of this parameters should be known accurately. It is observed that the number of methods are reported in litrature, however these methods impose difficulties in experimentation and are not very accurate. In this paper a novel approach to the measurement of the dielectric constant of low loss materials at micro-wave and millimeter wave frequencies has been discussed. In this method by using antenna theory, a metallic strip dielectric guide is taken in to constideration and band reject phenomenon of dielectric antenna is used. Frequency response of an antenna in band reject mode is a function of the dimensional parameters, such as the metallic strip period, the profile of the metallic strip and the dielectric constant of the material used. Hence if one measure the frequency responce of the antenna in band reject mode, the dielectric constant of the material is determined provided all other parameters are known. This method gives a direct measure of dielectric constant and is quite accurate as computer techniques are used for evaluating the dielectric constant. This method verified experimentally also.

Dielectric constant and low-frequency infrared spectra for liquid water and ice Ih within the E3B model.

PubMed

Shi, L; Ni, Y; Drews, S E P; Skinner, J L

2014-08-28

Two intrinsic difficulties in modeling condensed-phase water with conventional rigid non-polarizable water models are: reproducing the static dielectric constants for liquid water and ice Ih, and generating the peak at about 200 cm(-1) in the low-frequency infrared spectrum for liquid water. The primary physical reason for these failures is believed to be the missing polarization effect in these models, and consequently various sophisticated polarizable water models have been developed. However, in this work we pursue a different strategy and propose a simple empirical scheme to include the polarization effect only on the dipole surface (without modifying a model's intermolecular interaction potential). We implement this strategy for our explicit three-body (E3B) model. Our calculated static dielectric constants and low-frequency infrared spectra are in good agreement with experiment for both liquid water and ice Ih over wide temperature ranges, albeit with one fitting parameter for each phase. The success of our modeling also suggests that thermal fluctuations about local minima and the energy differences between different proton-disordered configurations play minor roles in the static dielectric constant of ice Ih. Our analysis shows that the polarization effect is important in resolving the two difficulties mentioned above and sheds some light on the origin of several features in the low-frequency infrared spectra for liquid water and ice Ih.

Tunable surface plasmon devices

DOEpatents

Shaner, Eric A [Rio Rancho, NM; Wasserman, Daniel [Lowell, MA

2011-08-30

A tunable extraordinary optical transmission (EOT) device wherein the tunability derives from controlled variation of the dielectric constant of a semiconducting material (semiconductor) in evanescent-field contact with a metallic array of sub-wavelength apertures. The surface plasmon resonance wavelength can be changed by changing the dielectric constant of the dielectric material. In embodiments of this invention, the dielectric material is a semiconducting material. The dielectric constant of the semiconducting material in the metal/semiconductor interfacial region is controllably adjusted by adjusting one or more of the semiconductor plasma frequency, the concentration and effective mass of free carriers, and the background high-frequency dielectric constant in the interfacial region. Thermal heating and/or voltage-gated carrier-concentration changes may be used to variably adjust the value of the semiconductor dielectric constant.

Crystal growth, structure analysis and characterisation of 2 - (1, 3 - dioxoisoindolin - 2 - yl) acetic acid single crystal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sankari, R. Siva, E-mail: sivasankari.sh@act.edu.in; Perumal, Rajesh Narayana

2014-04-24

Single crystal of dielectric material 2 - (1, 3 - dioxoisoindolin - 2 - yl) acetic acid has been grown by slow evaporation solution growth method. The grown crystal was harvested in 25 days. The crystal structure was analyzed by Single crystal X - ray diffraction. UV-vis-NIR analysis was performed to examine the optical property of the grown crystal. The thermal property of the grown crystal was studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The dielectric measurements were carried out and the dielectric constant was calculated and plotted at all frequencies.

Dielectric relaxation of ethylene carbonate and propylene carbonate from molecular dynamics simulations

DOE PAGES

Chaudhari, Mangesh I.; You, Xinli; Pratt, Lawrence R.; ...

2015-11-24

Ethylene carbonate (EC) and propylene carbonate (PC) are widely used solvents in lithium (Li)-ion batteries and supercapacitors. Ion dissolution and diffusion in those media are correlated with solvent dielectric responses. Here, we use all-atom molecular dynamics simulations of the pure solvents to calculate dielectric constants and relaxation times, and molecular mobilities. The computed results are compared with limited available experiments to assist more exhaustive studies of these important characteristics. As a result, the observed agreement is encouraging and provides guidance for further validation of force-field simulation models for EC and PC solvents.

A polymer dataset for accelerated property prediction and design.

PubMed

Huan, Tran Doan; Mannodi-Kanakkithodi, Arun; Kim, Chiho; Sharma, Vinit; Pilania, Ghanshyam; Ramprasad, Rampi

2016-03-01

Emerging computation- and data-driven approaches are particularly useful for rationally designing materials with targeted properties. Generally, these approaches rely on identifying structure-property relationships by learning from a dataset of sufficiently large number of relevant materials. The learned information can then be used to predict the properties of materials not already in the dataset, thus accelerating the materials design. Herein, we develop a dataset of 1,073 polymers and related materials and make it available at http://khazana.uconn.edu/. This dataset is uniformly prepared using first-principles calculations with structures obtained either from other sources or by using structure search methods. Because the immediate target of this work is to assist the design of high dielectric constant polymers, it is initially designed to include the optimized structures, atomization energies, band gaps, and dielectric constants. It will be progressively expanded by accumulating new materials and including additional properties calculated for the optimized structures provided.

Interaction of slow highly charged ions with a metal surface covered with a thin dielectric film. The role of the neutralization energy in the nanostructures formation

NASA Astrophysics Data System (ADS)

Majkić, M. D.; Nedeljković, N. N.; Dojčilović, R. J.

2017-09-01

We consider the slow highly charged ions impinging upon a metal surface covered with a thin dielectric film, and formation of the surface nanostructures (craters) from the standpoint of the required energy. For the moderate ionic velocities, the size of the surface features depends on the deposited kinetic energy of the projectile and the ionic neutralization energy. The neutralization energy is calculated by employing the recently developed quasi-resonant two-state vector model for the intermediate Rydberg state population and the micro-staircase model for the cascade neutralization. The electron interactions with the ionic core, polarized dielectric and charge induced on the metal surface are modelled by the appropriate asymptotic expressions and the method for calculation of the effective ionic charges in the dielectric is proposed. The results are presented for the interaction of \\text{X}{{\\text{e}}Z+} ions (velocity v=0.25 a.u.; 25) with the metal surface (Co) covered with a thin dielectric film, for model values of dielectric constant inside the interaction region. In the absence of dielectric film, the neutralization energy is lower than the potential (ionization) energy due to the incomplete neutralization. The presence of dielectric film additionally decreases the neutralization energy. We calculate the projectile neutralization energy in the perturbed dielectric (perturbation is caused by the ionic motion and the surface structure formation). We correlate the neutralization energy added to the deposited kinetic energy with the experimentally obtained energy necessary for the formation of the nano-crater of a given depth.

Effects of interlayer screening and temperature on dielectric functions of graphene by first-principles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, J. Y.; Liu, L. H., E-mail: lhliu@hit.edu.cn; Department of Physics, Harbin Institute of Technology, Harbin 150001

2016-07-21

The dielectric functions of few-layer graphene and the related temperature dependence are investigated from the atomic scale using first-principles calculations. Compared with ellipsometry experiments in the spectral range of 190–2500 nm, the normalized optical constants of mono-layer graphene demonstrate good agreement and further validate first-principles calculations. To interpret dielectric function of mono-layer graphene, the electronic band structure and density of states are analyzed. By comparing dielectric functions of mono-, bi-, and tri-layer graphene, it shows that interlayer screening strengthens intraband transition and greatly enhances the absorption peak located around 1 eV. The strengthened optical absorption is intrinsically caused by the increasing electronmore » states near the Fermi level. To investigate temperature effect, the first-principles calculations and lattice dynamics are combined. The lattice vibration enhances parallel optical absorption peak around 1 eV and induces redshift. Moreover, it is observed that the van der Waals force plays a key role in keeping the interlayer distance stable during dynamics simulations.« less

Investigation of Fumed Silica/Aqueous NaCl Superdielectric Material.

PubMed

Jenkins, Natalie; Petty, Clayton; Phillips, Jonathan

2016-02-20

A constant current charge/discharge protocol which showed fumed silica filled to the point of incipient wetness with aqueous NaCl solution to have dielectric constants >10⁸ over the full range of dielectric thicknesses of 0.38-3.9 mm and discharge times of 0.25->100 s was studied, making this material another example of a superdielectric. The dielectric constant was impacted by both frequency and thickness. For time to discharge greater than 10 s the dielectric constant for all thicknesses needed to be fairly constant, always >10⁸, although trending higher with increasing thickness. At shorter discharge times the dielectric constant consistently decreased, with decreasing time to discharge. Hence, it is reasonable to suggest that for time to discharge >10 s the dielectric constant at all thicknesses will be greater than 10⁸. This in turn implies an energy density for a 5 micron thick dielectric layer in the order of 350 J/cm³ for discharge times greater than 10 s.

Investigation of Fumed Silica/Aqueous NaCl Superdielectric Material

PubMed Central

Jenkins, Natalie; Petty, Clayton; Phillips, Jonathan

2016-01-01

A constant current charge/discharge protocol which showed fumed silica filled to the point of incipient wetness with aqueous NaCl solution to have dielectric constants >108 over the full range of dielectric thicknesses of 0.38–3.9 mm and discharge times of 0.25–>100 s was studied, making this material another example of a superdielectric. The dielectric constant was impacted by both frequency and thickness. For time to discharge greater than 10 s the dielectric constant for all thicknesses needed to be fairly constant, always >109, although trending higher with increasing thickness. At shorter discharge times the dielectric constant consistently decreased, with decreasing time to discharge. Hence, it is reasonable to suggest that for time to discharge >10 s the dielectric constant at all thicknesses will be greater than 109. This in turn implies an energy density for a 5 micron thick dielectric layer in the order of 350 J/cm3 for discharge times greater than 10 s. PMID:28787918

Improving the treatment of coarse-grain electrostatics: CVCEL.

PubMed

Ceres, N; Lavery, R

2015-12-28

We propose an analytic approach for calculating the electrostatic energy of proteins or protein complexes in aqueous solution. This method, termed CVCEL (Circular Variance Continuum ELectrostatics), is fitted to Poisson calculations and is able to reproduce the corresponding energies for different choices of solute dielectric constant. CVCEL thus treats both solute charge interactions and charge self-energies, and it can also deal with salt solutions. Electrostatic damping notably depends on the degree of solvent exposure of the charges, quantified here in terms of circular variance, a measure that reflects the vectorial distribution of the neighbors around a given center. CVCEL energies can be calculated rapidly and have simple analytical derivatives. This approach avoids the need for calculating effective atomic volumes or Born radii. After describing how the method was developed, we present test results for coarse-grain proteins of different shapes and sizes, using different internal dielectric constants and different salt concentrations and also compare the results with those from simple distance-dependent models. We also show that the CVCEL approach can be used successfully to calculate the changes in electrostatic energy associated with changes in protein conformation or with protein-protein binding.

Influence of Zn doping on structural, optical and dielectric properties of LaFeO3

NASA Astrophysics Data System (ADS)

Manzoor, Samiya; Husain, Shahid

2018-05-01

The effect of Zn doping on structural, optical and dielectric properties of nano-crystalline LaFe1‑xZnxO3 (0.0 ≤ x ≤ 0.3) samples have been investigated. These samples are synthesized using conventional solid state reaction route. X-ray diffraction patterns with Rietveld analysis confirm the single phase nature of samples. Further, the sample formation has been confirmed by FTIR spectroscopy. All the samples are formed in orthorhombic crystal symmetry with Pbnm space group. The average crystallite sizes, calculated from the Scherer’s formula, lie in the range below 50 nm. Rietveld refinement technique is used to determine lattice parameters, bond lengths and unit cell volume. Williamson-Hall analysis has been performed to calculate the crystallite size and lattice strain. Crystallite sizes are found to be of nanometer range while the strain is of the order of 10‑3. Zn doping leads to the expansion of volume due to the tensile strain. Optical bandgap has been determined from Kubelka-Munk function using Tauc’s relation. Zinc doping in LaFeO3 leads to decrease in optical bandgap. Dielectric constant as a function of frequency is measured in the frequency range of 75 kHz–5 MHz. The dielectric behavior has been investigated by analyzing ‘universal dielectric response’ (UDR) model. The dielectric constant (ε‧) shows colossal value with Zn doping in the whole frequency range. However, the imaginary part (ε″) shows relaxational behavior which may be attributed to the strong correlation that exists between conduction mechanism and dielectric behavior in ferrites. Cole-Cole analysis has been done that confirms the dielectric material does not follow the ideal Debye theory but shows distribution of relaxation times. The a.c conductivity increases with frequency and with Zn doping due to the increased polaron hopping.

The electrical characteristics of the dielectric barrier discharges

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yehia, Ashraf, E-mail: yehia30161@yahoo.com; Department of Physics, Faculty of Science, Assiut University, Assiut 71516

2016-06-15

The electrical characteristics of the dielectric barrier discharges have been studied in this paper under different operating conditions. The dielectric barrier discharges were formed inside two reactors composed of electrodes in the shape of two parallel plates. The dielectric layers inside these reactors were pasted on the surface of one electrode only in the first reactor and on the surfaces of the two electrodes in the second reactor. The reactor under study has been fed by atmospheric air that flowed inside it with a constant rate at the normal temperature and pressure, in parallel with applying a sinusoidal ac voltagemore » between the electrodes of the reactor. The amount of the electric charge that flows from the reactors to the external circuit has been studied experimentally versus the ac peak voltage applied to them. An analytical model has been obtained for calculating the electrical characteristics of the dielectric barrier discharges that were formed inside the reactors during a complete cycle of the ac voltage. The results that were calculated by using this model have agreed well with the experimental results under the different operating conditions.« less

Dielectric Performance of a High Purity HTCC Alumina at High Temperatures - a Comparison Study with Other Polycrystalline Alumina

NASA Technical Reports Server (NTRS)

Chen, Liangyu

2014-01-01

A very high purity (99.99+%) high temperature co-fired ceramic (HTCC) alumina has recently become commercially available. The raw material of this HTCC alumina is very different from conventional HTCC alumina, and more importantly there is no glass additive in this alumina material for co-firing processing. Previously, selected HTCC and LTCC (low temperature co-fired ceramic) alumina materials were evaluated at high temperatures as dielectric and compared to a regularly sintered 96% polycrystalline alumina (96% Al2O3), where 96% alumina was used as the benchmark. A prototype packaging system based on regular 96% alumina with Au thickfilm metallization successfully facilitated long term testing of high temperature silicon carbide (SiC) electronic devices for over 10,000 hours at 500 C. In order to evaluate this new high purity HTCC alumina for possible high temperature packaging applications, the dielectric properties of this HTCC alumina substrate were measured and compared with those of 96% alumina and a previously tested LTCC alumina from room temperature to 550 C at frequencies of 120 Hz, 1 KHz, 10 KHz, 100 KHz, and 1 MHz. A parallel-plate capacitive device with dielectric of the HTCC alumina and precious metal electrodes were used for measurements of the dielectric constant and dielectric loss of the co-fired alumina material in the temperature and frequency ranges. The capacitance and AC parallel conductance of the capacitive device were directly measured by an AC impedance meter, and the dielectric constant and parallel AC conductivity of the dielectric were calculated from the capacitance and conductance measurement results. The temperature and frequency dependent dielectric constant, AC conductivity, and dissipation factor of the HTCC alumina substrate are presented and compared to those of 96% alumina and a selected LTCC alumina. Other technical advantages of this new co-fired material for possible high packaging applications are also discussed.

Role of dielectric constant in electrohydrodynamics of conducting fluids

NASA Technical Reports Server (NTRS)

Rhodes, Percy H.; Snyder, Robert S.; Roberts, Glyn O.

1992-01-01

Electrohydrodynamic (EHD) flows are driven by the interaction of an electric field with variations in electric conductivity or dielectric constant. In reported EHD experiments on the deformation of drops of immiscible dielectric fluids, the role of conductivity has tended to overshadow the role of dielectric constant. Often, large conductivity contrasts were convenient because the conductivities of the dielectric fluid were relatively uncertain. As a result, the observed effects were always qualitatively the same as if there had been no contrast in dielectric constant. Our early experiments studying the EHC deformations of cylindrical streams readily showed the conductivity effect but the dielectric constant effect was not discernible. We have modified our flow chamber and improved our method of observation and can now see an unequivocal dielectric constant effect which is in agreement with the prior theory. In this paper we first give a brief description of the physics of charge buildup at the interface of an immersed spherical drop or flowing cylindrical sample stream and then show how these charge distributions lead to interface distortions and accompanying viscous flows which constitute EHD. We next review theory and experiment describing the deformation of spherical drops. We show that in the reported drop deformation experiments, the contrast in dielectric constant was never sufficient to reverse the deformation due to the conductivity contrast. We review our work describing the deformation of a cylindrical stream of one fluid flowing in a parallel flow of another, and we compare the deformation equations with those for spherical drops. Finally, we show a definite experimental dielectric constant effect for cylindrical stream of aqueous polystyrene latex suspension. The dielectric constant varies with the frequency of the imposed electric field, and the associated EHD flow change is very apparent.

A Numerical Simulation of Scattering from One-Dimensional Inhomogeneous Dielectric Random Surfaces

NASA Technical Reports Server (NTRS)

Sarabandi, Kamal; Oh, Yisok; Ulaby, Fawwaz T.

1996-01-01

In this paper, an efficient numerical solution for the scattering problem of inhomogeneous dielectric rough surfaces is presented. The inhomogeneous dielectric random surface represents a bare soil surface and is considered to be comprised of a large number of randomly positioned dielectric humps of different sizes, shapes, and dielectric constants above an impedance surface. Clods with nonuniform moisture content and rocks are modeled by inhomogeneous dielectric humps and the underlying smooth wet soil surface is modeled by an impedance surface. In this technique, an efficient numerical solution for the constituent dielectric humps over an impedance surface is obtained using Green's function derived by the exact image theory in conjunction with the method of moments. The scattered field from a sample of the rough surface is obtained by summing the scattered fields from all the individual humps of the surface coherently ignoring the effect of multiple scattering between the humps. The statistical behavior of the scattering coefficient sigma(sup 0) is obtained from the calculation of scattered fields of many different realizations of the surface. Numerical results are presented for several different roughnesses and dielectric constants of the random surfaces. The numerical technique is verified by comparing the numerical solution with the solution based on the small perturbation method and the physical optics model for homogeneous rough surfaces. This technique can be used to study the behavior of scattering coefficient and phase difference statistics of rough soil surfaces for which no analytical solution exists.

Capacitive Cells for Dielectric Constant Measurement

ERIC Educational Resources Information Center

Aguilar, Horacio Munguía; Maldonado, Rigoberto Franco

2015-01-01

A simple capacitive cell for dielectric constant measurement in liquids is presented. As an illustrative application, the cell is used for measuring the degradation of overheated edible oil through the evaluation of their dielectric constant.

Dielectric function of a model insulator

NASA Astrophysics Data System (ADS)

Rezvani, G. A.; Friauf, Robert J.

1993-04-01

We have calculated a dielectric response function ɛ(q,ω) using the random-phase approximation for a model insulator originally proposed by Fry [Phys. Rev. 179, 892 (1969)]. We treat narrow and wide band-gap insulators for the purpose of using results in the simulation of secondary-electron emission from insulators. Therefore, it is important to take into account the contribution of the first and second conduction bands. For the real part of the dielectric function we perform a numerical principal value integration over the first and second Brillouin zone. For the imaginary part we perform a numerical integration involving the δ function that results from the conservation of energy. In order to check the validity of our numerical integration methods we perform a Kramers-Kronig transform of the real part and compare it with the directly calculated imaginary part and vice versa. We discuss fitting the model to the static dielectric constant and the f-sum rule. Then we display the wave number and frequency dependence for solid argon, KCl, and model Si.

Effects of dielectric inhomogeneity on electrostatic twist rigidity of a helical biomolecule in Debye-Hückel regime

NASA Astrophysics Data System (ADS)

Rezaie-Dereshgi, Amir; Mohammad-Rafiee, Farshid

2018-04-01

The electrostatic interactions play a crucial role in biological systems. Here we consider an impermeable dielectric molecule in the solvent with a different dielectric constant. The electrostatic free energy in the problem is studied in the Debye-Hückel regime using the analytical Green function that is calculated in the paper. Using this electrostatic free energy, we study the electrostatic contribution to the twist rigidity of a double stranded helical molecule such as a DNA and an actin filament. The dependence of the electrostatic twist rigidity of the molecule to the dielectric inhomogeneity, structural parameters, and the salt concentration is studied. It is shown that, depending on the parameters, the electrostatic twist rigidity could be positive or negative.

Strain-induced phase variation and dielectric constant enhancement of epitaxial Gd{sub 2}O{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shekhter, P., E-mail: Pini@tx.technion.ac.il; Amouyal, Y.; Eizenberg, M.

2016-07-07

One of the approaches for realizing advanced high k insulators for metal oxide semiconductor field effect transistors based devices is the use of rare earth oxides. When these oxides are deposited as epitaxial thin films, they demonstrate dielectric properties that differ greatly from those that are known for bulk oxides. Using structural and spectroscopic techniques, as well as first-principles calculations, Gd{sub 2}O{sub 3} films deposited on Si (111) and Ge (111) were characterized. It was seen that the same 4 nm thick film, grown simultaneously on Ge and Si, presents an unstrained lattice on Ge while showing a metastable phase onmore » Si. This change from the cubic lattice to the distorted metastable phase is characterized by an increase in the dielectric constant of more than 30% and a change in band gap. The case in study shows that extreme structural changes can occur in ultra-thin epitaxial rare earth oxide films and modify their dielectric properties when the underlying substrate is altered.« less

Achieving polydimethylsiloxane/carbon nanotube (PDMS/CNT) composites with extremely low dielectric loss and adjustable dielectric constant by sandwich structure

NASA Astrophysics Data System (ADS)

Fan, Benhui; Liu, Yu; He, Delong; Bai, Jinbo

2018-01-01

Sandwich-structured composites of polydimethylsiloxane/carbon nanotube (PDMS/CNT) bulk between two neat PDMS thin films with different thicknesses are prepared by the spin-coating method. Taking advantage of CNT's percolation behavior, the composite keeps relatively high dielectric constant (ɛ' = 40) at a low frequency (at 100 Hz). Meanwhile, due to the existence of PDMS isolated out-layers which limits the conductivity of the composite, the composite maintains an extremely low dielectric loss (tan δ = 0.01) (at 100 Hz). Moreover, the same matrix of the out-layer and bulk can achieve excellent interfacial adhesion, and the thickness of the coating layer can be controlled by a multi-cycle way. Then, based on the experimental results, the calculation combining the percolation theory and core-shell model is used to analyze the thickness effect of the coating layer on ɛ'. The obtained relationship between the ɛ' of the composite and the thickness of the coating layer can help to optimize the sandwich structure in order to obtain the adjustable ɛ' and the extremely low tan δ.

Negative Dielectric Constant Material Based on Ion Conducting Materials

NASA Technical Reports Server (NTRS)

Gordon, Keith L. (Inventor); Kang, Jin Ho (Inventor); Park, Cheol (Inventor); Lillehei, Peter T. (Inventor); Harrison, Joycelyn S. (Inventor)

2017-01-01

Metamaterials or artificial negative index materials (NIMs) have generated great attention due to their unique and exotic electromagnetic properties. One exemplary negative dielectric constant material, which is an essential key for creating the NIMs, was developed by doping ions into a polymer, a protonated poly (benzimidazole) (PBI). The doped PBI showed a negative dielectric constant at megahertz (MHz) frequencies due to its reduced plasma frequency and an induction effect. The magnitude of the negative dielectric constant and the resonance frequency were tunable by doping concentration. The highly doped PBI showed larger absolute magnitude of negative dielectric constant at just above its resonance frequency than the less doped PBI.

Negative Dielectric Constant Material Based on Ion Conducting Materials

NASA Technical Reports Server (NTRS)

Gordon, Keith L. (Inventor); Kang, Jin Ho (Inventor); Harrison, Joycelyn S. (Inventor); Park, Cheol (Inventor); Lillehei, Peter T. (Inventor)

2014-01-01

Metamaterials or artificial negative index materials (NIMs) have generated great attention due to their unique and exotic electromagnetic properties. One exemplary negative dielectric constant material, which is an essential key for creating the NIMs, was developed by doping ions into a polymer, a protonated poly(benzimidazole) (PBI). The doped PBI showed a negative dielectric constant at megahertz (MHz) frequencies due to its reduced plasma frequency and an induction effect. The magnitude of the negative dielectric constant and the resonance frequency were tunable by doping concentration. The highly doped PBI showed larger absolute magnitude of negative dielectric constant at just above its resonance frequency than the less doped PBI.

Dielectric constant and low-frequency infrared spectra for liquid water and ice Ih within the E3B model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shi, L.; Ni, Y.; Drews, S. E. P.

2014-08-28

Two intrinsic difficulties in modeling condensed-phase water with conventional rigid non-polarizable water models are: reproducing the static dielectric constants for liquid water and ice Ih, and generating the peak at about 200 cm{sup −1} in the low-frequency infrared spectrum for liquid water. The primary physical reason for these failures is believed to be the missing polarization effect in these models, and consequently various sophisticated polarizable water models have been developed. However, in this work we pursue a different strategy and propose a simple empirical scheme to include the polarization effect only on the dipole surface (without modifying a model's intermolecularmore » interaction potential). We implement this strategy for our explicit three-body (E3B) model. Our calculated static dielectric constants and low-frequency infrared spectra are in good agreement with experiment for both liquid water and ice Ih over wide temperature ranges, albeit with one fitting parameter for each phase. The success of our modeling also suggests that thermal fluctuations about local minima and the energy differences between different proton-disordered configurations play minor roles in the static dielectric constant of ice Ih. Our analysis shows that the polarization effect is important in resolving the two difficulties mentioned above and sheds some light on the origin of several features in the low-frequency infrared spectra for liquid water and ice Ih.« less

Assessing the performance of self-consistent hybrid functional for band gap calculation in oxide semiconductors

NASA Astrophysics Data System (ADS)

He, Jiangang; Franchini, Cesare

2017-11-01

In this paper we assess the predictive power of the self-consistent hybrid functional scPBE0 in calculating the band gap of oxide semiconductors. The computational procedure is based on the self-consistent evaluation of the mixing parameter α by means of an iterative calculation of the static dielectric constant using the perturbation expansion after discretization method and making use of the relation \

Piezo-optic tensor of crystals from quantum-mechanical calculations.

PubMed

Erba, A; Ruggiero, M T; Korter, T M; Dovesi, R

2015-10-14

An automated computational strategy is devised for the ab initio determination of the full fourth-rank piezo-optic tensor of crystals belonging to any space group of symmetry. Elastic stiffness and compliance constants are obtained as numerical first derivatives of analytical energy gradients with respect to the strain and photo-elastic constants as numerical derivatives of analytical dielectric tensor components, which are in turn computed through a Coupled-Perturbed-Hartree-Fock/Kohn-Sham approach, with respect to the strain. Both point and translation symmetries are exploited at all steps of the calculation, within the framework of periodic boundary conditions. The scheme is applied to the determination of the full set of ten symmetry-independent piezo-optic constants of calcium tungstate CaWO4, which have recently been experimentally reconstructed. Present calculations unambiguously determine the absolute sign (positive) of the π61 constant, confirm the reliability of 6 out of 10 experimentally determined constants and provide new, more accurate values for the remaining 4 constants.

Piezo-optic tensor of crystals from quantum-mechanical calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erba, A., E-mail: alessandro.erba@unito.it; Dovesi, R.; Ruggiero, M. T.

2015-10-14

An automated computational strategy is devised for the ab initio determination of the full fourth-rank piezo-optic tensor of crystals belonging to any space group of symmetry. Elastic stiffness and compliance constants are obtained as numerical first derivatives of analytical energy gradients with respect to the strain and photo-elastic constants as numerical derivatives of analytical dielectric tensor components, which are in turn computed through a Coupled-Perturbed-Hartree-Fock/Kohn-Sham approach, with respect to the strain. Both point and translation symmetries are exploited at all steps of the calculation, within the framework of periodic boundary conditions. The scheme is applied to the determination of themore » full set of ten symmetry-independent piezo-optic constants of calcium tungstate CaWO{sub 4}, which have recently been experimentally reconstructed. Present calculations unambiguously determine the absolute sign (positive) of the π{sub 61} constant, confirm the reliability of 6 out of 10 experimentally determined constants and provide new, more accurate values for the remaining 4 constants.« less

Dielectric and transport properties of CaTiO3

NASA Astrophysics Data System (ADS)

Bhadala, Falguni; Suthar, Lokesh; Roy, M.; Jha, Vikash Kumar

2018-05-01

The ceramic sample of CaTiO3 (CTO) has been prepared by standard high temperature solid state reaction method using high purity oxides. The formation of the compound as well as structural analysis has been carried out by X-ray diffraction method. The dielectric constant and dielectric loss as a function of frequency (20kHz-10MHz) and temperature (RT-490K) have been measured. The dc conductivity has been measured and activation energy was calculated using the Arrhenius relation. The Enthalpy change (ΔH), Specific heat and Weight-loss of the compound have been measured using DTA/TGA techniques. The results are discussed in detail.

Alternative Dielectric Films for rf MEMS Capacitive Switches Deposited using Atomic Layer Deposited Al2O3/ZnO Alloys

DTIC Science & Technology

2006-07-02

A s c c s r t h s l © K 1 b c A a e t s C t o 0 d Sensors and Actuators A 135 (2007) 262–272 Alternative dielectric films for rf MEMS capacitive...Zn concentrations in the alloy films , which was lower than expected. Atomic force microscopy images evealed an average surface roughness of 0.27 nm...that was independent of deposition temperature and film composition. The dielectric constants of he Al2O3/ZnO ALD alloys films were calculated to be

Numerical study of the defect adamantine compound CuGaGeSe4

NASA Astrophysics Data System (ADS)

Shen, Kesheng; Zhang, Xianzhou; Lu, Hai; Jiao, Zhaoyong

2018-06-01

The electronic structure, elastic and optical properties of the defect adamantine compound CuGaGeSe4 in ? structure are systematically investigated using first-principles calculations. Through detailed calculation and comparison, we obtain three independent atomic arrangements and predict the most stable atomic arrangement according to the lattice constants and enthalpy formation energies. The elastic constants are calculated, which can be used to predict the axial thermal expansion coefficients accurately. The optical properties of compound CuGaGeSe4, including the dielectric function, refractive index and absorption spectrum, are depicted for a more intuitive understanding. Our calculated zero-frequency limits ɛ1(0) and n(0) are very close to the other theoretical values, which proves that our calculations are reliable.

Exploratory studies of new avenues to achieve high electromechanical response and high dielectric constant in polymeric materials

NASA Astrophysics Data System (ADS)

Huang, Cheng

High performance soft electronic materials are key elements in advanced electronic devices for broad range applications including capacitors, actuators, artificial muscles and organs, smart materials and structures, microelectromechanical (MEMS) and microfluidic devices, acoustic devices and sensors. This thesis exploits new approaches to improve the electromechanical response and dielectric response of these materials. By making use of novel material phenomena such as large anisotropy in dipolar response in liquid crystals (LCs) and all-organic composites in which high dielectric constant organic solids and conductive polymers are either physically blended into or chemically grafted to a polymer matrix, we demonstrate that high dielectric constant and high electromechanical conversion efficiency comparable to that in ceramic materials can be achieved. Nano-composite approach can also be utilized to improve the performance of the electronic electroactive polymers (EAPs) and composites, for example, exchange coupling between the fillers and matrix with very large dielectric contrast can lead to significantly enhance the dielectric response as well as electromechanical response when the heterogeneity size of the composite is comparable to the exchange length. In addition to the dielectric composites, in which high dielectric constant fillers raise the dielectric constant of composites, conductive percolation can also lead to high dielectric constant in polymeric materials. An all-polymer percolative composite is introduced which exhibits very high dielectric constant (>7,000). The flexible all-polymer composites with a high dielectric constant make it possible to induce a high electromechanical response under a much reduced electric field in the field effect electroactive polymer (EAP) actuators (a strain of 2.65% with an elastic energy density of 0.18 J/cm3 can be achieved under a field of 16 V/mum). Agglomeration of the particles can also be effectively prevented by in situ preparation. High dielectric constant copper phthalocyanine oligomer and conductive polyaniline oligomer were successfully bonded to polyurethane backbone to form fully functionalized nano-phase polymers. Improvement of dispersibility of oligomers in polymer matrix makes the system self-organize the nanocomposites possessing oligomer nanophase (below 30nm) within the fully functionalized polymers. The resulting nanophase polymers significantly enhance the interface effect, which through the exchange coupling raises the dielectric response markedly above that expected from simple mixing rules for dielectric composites. Consequently, these nano-phase polymers offer a high dielectric constant (a dielectric constant near 1,000 at 20 Hz), improve the breakdown field and mechanical properties, and exhibit high electromechanical response. A longitudinal strain of more than -14% can be induced under a much reduced field, 23 V/mum, with an elastic energy density of higher than 1 J/cm3. The elastic modulus is as high as 100MPa, and a transverse strain is 7% under the same field. (Abstract shortened by UMI.)

Investigations on structural, optical, electrical, mechanical and third-order nonlinear behaviour of 3-aminopyridinium 2,4-dinitrophenolate single crystal

NASA Astrophysics Data System (ADS)

Mohanbabu, B.; Bharathikannan, R.; Siva, G.

2017-10-01

The single crystals of 3-aminopyridinium 2,4-dinitrophenolate (APDP) have been synthesized and grown by slow evaporation technique at room temperature. The crystal system was identified and lattice dimensions were measured from the single-crystal X-ray diffraction (SXRD) analysis. UV-visible absorption and transmittance spectra have been recorded in the region between 250 and 1100 nm. The different vibrational modes of the molecule were studied by Fourier transform infrared (FTIR) spectroscopic analysis. The decreasing tendency of dielectric constant with increasing frequency was analysed in dielectric study. The polarizability value calculated using Penn analysis well agrees with the value calculated using Clausius-Mossotti equation. The photoconductivity and photoluminescence behaviour were also studied on grown APDP crystal. The mechanical strength of the crystal has been studied using a Vickers' microhardness test. The stiffness constant and yield strength of the crystal were also calculated from the microhardness test. The third-order nonlinear optical parameters such as refractive index, absorption coefficient and third-order susceptibility were estimated by Z-scan studies.

Dielectric studies on struvite urinary crystals, a gateway to the new treatment modality for urolithiasis

NASA Astrophysics Data System (ADS)

Rajan, Reshma; Raj, N. Arunai Nambi; Madeswaran, S.; Babu, D. Rajan

2015-09-01

Struvite or magnesium ammonium phosphate hexahydrate (MAPH) are biological crystals, found in the kidney, which are formed due to the infection caused by urea splitting bacteria in the urinary tract. The struvite crystals observe different morphologies and were developed using single diffusion gel growth technique. The crystalline nature and its composition were studied from different characterization techniques like X-ray Diffraction (XRD) and FTIR. The dielectric behavior of the developed crystal was studied by varying temperature and at different frequencies. The parameters like dielectric constant, dielectric loss, ac conductivity, ac resistivity, impedance and admittance of the struvite crystals were calculated. The studies proved that the dielectric loss or dissipation heat is high in lower frequencies at normal body temperature, which develops a plasma state in the stones and in turn leads to the disintegration of urinary stones. The dielectric nature of the stones leads to the dielectric therapy, which will be a gateway for future treatment modality for urolithiasis.

The electrical and dielectric properties of the Au/Ti/HfO2/n-GaAs structures

NASA Astrophysics Data System (ADS)

Karabulut, Abdulkerim; Türüt, Abdulmecit; Karataş, Şükrü

2018-04-01

In this work, temperature dependent electrical and dielectric properties of the Au/Ti/HfO2/n-GaAs structures were investigated using capacitance-voltage (C-V) and conductance-voltage (G-V) measurements in the temperature range of 60-320 K by steps of 20 K at 1 MHz. The dielectric constant (ε‧), dielectric loss (ε″), dielectric loss tangent (tanδ) and ac electrical conductivities (σac) have been calculated as a function of temperature. These values of the ε‧, ε″, tanδ and σac have been found to be 2.272, 5.981, 2.631 and 3.32 × 10-6 (Ω-1cm-1) at 80 K, respectively, 1.779, 2.315, 1.301 and 1.28 × 10-6 (Ω-1cm-1), respectively at 320 K. These decrease of the dielectric parameters (ε‧, ε″, tanδ and σac) have been observed at high temperatures. The experimental results show that electrical and dielectric properties are strongly temperature and bias voltage dependent.

Application of dielectric constant measurement in microwave sludge disintegration and wastewater purification processes.

PubMed

Kovács, Petra Veszelovszki; Lemmer, Balázs; Keszthelyi-Szabó, Gábor; Hodúr, Cecilia; Beszédes, Sándor

2018-05-01

It has been numerously verified that microwave radiation could be advantageous as a pre-treatment for enhanced disintegration of sludge. Very few data related to the dielectric parameters of wastewater of different origins are available; therefore, the objective of our work was to measure the dielectric constant of municipal and meat industrial wastewater during a continuous flow operating microwave process. Determination of the dielectric constant and its change during wastewater and sludge processing make it possible to decide on the applicability of dielectric measurements for detecting the organic matter removal efficiency of wastewater purification process or disintegration degree of sludge. With the measurement of dielectric constant as a function of temperature, total solids (TS) content and microwave specific process parameters regression models were developed. Our results verified that in the case of municipal wastewater sludge, the TS content has a significant effect on the dielectric constant and disintegration degree (DD), as does the temperature. The dielectric constant has a decreasing tendency with increasing temperature for wastewater sludge of low TS content, but an adverse effect was found for samples with high TS and organic matter contents. DD of meat processing wastewater sludge was influenced significantly by the volumetric flow rate and power level, as process parameters of continuously flow microwave pre-treatments. It can be concluded that the disintegration process of food industry sludge can be detected by dielectric constant measurements. From technical purposes the applicability of dielectric measurements was tested in the purification process of municipal wastewater, as well. Determination of dielectric behaviour was a sensitive method to detect the purification degree of municipal wastewater.

Predictions for Proteins, RNAs and DNAs with the Gaussian Dielectric Function Using DelPhiPKa

PubMed Central

Wang, Lin; Li, Lin; Alexov, Emil

2015-01-01

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. PMID:26408449

Improving Dielectric Properties of PVDF Composites by Employing Surface Modified Strong Polarized BaTiO₃ Particles Derived by Molten Salt Method.

PubMed

Fu, Jing; Hou, Yudong; Zheng, Mupeng; Wei, Qiaoyi; Zhu, Mankang; Yan, Hui

2015-11-11

BaTiO3/polyvinylidene fluoride (BT/PVDF) is the extensive reported composite material for application in modern electric devices. However, there still exists some obstacles prohibiting the further improvement of dielectric performance, such as poor interfacial compatibility and low dielectric constant. Therefore, in depth study of the size dependent polarization and surface modification of BT particle is of technological importance in developing high performance BT/PVDF composites. Here, a facile molten-salt synthetic method has been applied to prepare different grain sized BT particles through tailoring the calcination temperature. The size dependent spontaneous polarizationof BT particle was thoroughly investigated by theoretical calculation based on powder X-ray diffraction Rietveld refinement data. The results revealed that 600 nm sized BT particles possess the strong polarization, ascribing to the ferroelectric size effect. Furthermore, the surface of optimal BT particles has been modified by water-soluble polyvinylprrolidone (PVP) agent, and the coated particles exhibited fine core-shell structure and homogeneous dispersion in the PVDF matrix. The dielectric constant of the resulted composites increased significantly, especially, the prepared composite with 40 vol % BT loading exhibited the largest dielectric constant (65, 25 °C, 1 kHz) compared with the literature values of BT/PVDF at the same concentration of filler. Moreover, the energy storage density of the composites with tailored structure was largely enhanced at the low electric field, showing promising application as dielectric material in energy storage device. Our work suggested that introduction of strong polarized ferroelectric particles with optimal size and construction of core-shell structured coated fillers by PVP in the PVDF matrix are efficacious in improving dielectric performance of composites. The demonstrated approach can also be applied to the design and preparation of other polymers-based nanocomposites filled with ferroelectric particles to achieve desirable dielectric properties.

Analysis of structural and optical properties of annealed fullerene thin films

NASA Astrophysics Data System (ADS)

El-Nahass, M. M.; Ali, H. A. M.; Gadallah, A.-S.; Atta Khedr, M.; Afify, H. A.

2015-08-01

Fullerene thin films were thermally deposited onto different substrates. The films annealed at 523 K for 10 h. X-ray diffraction technique was used to examine the structure of the films. The morphology of films was examined by field emission scanning electron microscopy. Fourier transform infrared spectra were recorded in wavenumber range 400-2000 cm-1. The optical characteristics were analyzed using UV- Vis-NIR spectrophotometric measurements in the spectral range 200-2500 nm. The refractive index and extinction coefficient were determined. Some dispersion parameters were calculated such as single oscillator energy, dispersion energy, dielectric constant at high frequency and lattice dielectric constant. As well as, the nonlinear optical susceptibility χ(3) and nonlinear refractive index n2 were determined.

Resonant tunneling of surface plasmon polariton in the plasmonic nano-cavity.

PubMed

Park, Junghyun; Kim, Hwi; Lee, Il-Min; Kim, Seyoon; Jung, Jaehoon; Lee, Byoungho

2008-10-13

We investigate the reflection and transmission characteristics of the low-dielectric constant cut off barrier in the metal-insulator-metal (MIM) waveguide and propose a novel plasmonic nano-cavity made of two cut off barriers and the waveguide between them. It is shown that the anti-symmetric mode in the MIM waveguide with the core of the low dielectric constant below the specific value cannot be supported and this region can be regarded as a cut off barrier with high stability. The phase shift due to the reflection at the finite-length cut off barrier is calculated and the design scheme of the cavity length for the resonant tunneling is presented. The transmission spectra through the proposed nano-cavity are also discussed.

Effect of heat treatment on morphological, structural and optical properties of CoMTPP thin films

NASA Astrophysics Data System (ADS)

El-Nahass, M. M.; Ammar, A. H.; Farag, A. A. M.; Atta, A. A.; El-Zaidia, E. F. M.

2011-03-01

The morphologies and crystal structures of 5,10,15,20-tetrakis(4-methoxyphenyl)-21 H,23 H-porphine cobalt(II), CoMTPP, thin films were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Optical constants namely the refractive index, n, and the absorption index, k, of CoMTPP were estimated by using spectrophotometric measurements of transmittance and reflectance in the spectral range from 200 to 2500 nm. The dispersion of the refractive index in terms of the single oscillator in the transparent region is discussed. The single oscillator energy ( E0), the dispersion energy ( E d), the high frequency dielectric constant ( ɛ∞) and the lattice dielectric constant ( ɛ L) were calculated. The analysis of the spectral behavior of the absorption coefficient in the intrinsic absorption region reveals two indirect allowed transitions for as-deposited and annealed films.

Identification of elastic, dielectric, and piezoelectric constants in piezoceramic disks.

PubMed

Perez, Nicolas; Andrade, Marco A B; Buiochi, Flavio; Adamowski, Julio C

2010-12-01

Three-dimensional modeling of piezoelectric devices requires a precise knowledge of piezoelectric material parameters. The commonly used piezoelectric materials belong to the 6mm symmetry class, which have ten independent constants. In this work, a methodology to obtain precise material constants over a wide frequency band through finite element analysis of a piezoceramic disk is presented. Given an experimental electrical impedance curve and a first estimate for the piezoelectric material properties, the objective is to find the material properties that minimize the difference between the electrical impedance calculated by the finite element method and that obtained experimentally by an electrical impedance analyzer. The methodology consists of four basic steps: experimental measurement, identification of vibration modes and their sensitivity to material constants, a preliminary identification algorithm, and final refinement of the material constants using an optimization algorithm. The application of the methodology is exemplified using a hard lead zirconate titanate piezoceramic. The same methodology is applied to a soft piezoceramic. The errors in the identification of each parameter are statistically estimated in both cases, and are less than 0.6% for elastic constants, and less than 6.3% for dielectric and piezoelectric constants.

Fundamental Insight on Developing Low Dielectric Constant Polyimides

NASA Technical Reports Server (NTRS)

Simpson, J. O.; SaintClair, A. K.

1997-01-01

Thermally stable, durable, insulative polyimides are in great demand for the fabrication of microelectronic devices. In this investigation dielectric and optical properties have been studied for several series of aromatic polyimides. The effect of polarizability, fluorine content, and free volume on dielectric constant was examined. In general, minimizing polarizability, maximizing free volume and fluorination all lowered dielectric constants in the polyimides studied.

Organic solar cells based on high dielectric constant materials: An approach to increase efficiency

NASA Astrophysics Data System (ADS)

Hamam, Khalil Jumah Tawfiq

The efficiency of organic solar cells still lags behind inorganic solar cells due to their low dielectric constant which results in a weakly screened columbic attraction between the photogenerated electron-hole system, therefore the probability of charge separating is low. Having an organic material with a high dielectric constant could be the solution to get separated charges or at least weakly bounded electron-hole pairs. Therefore, high dielectric constant materials have been investigated and studied by measuring modified metal-phthalocyanine (MePc) and polyaniline in pellets and thin films. The dielectric constant was investigated as a function of temperature and frequency in the range of 20Hz to1MHz. For MePc we found that the high dielectric constant was an extrinsic property due to water absorption and the formation of hydronuim ion allowed by the ionization of the functional groups such as sulphonated and carboxylic groups. The dielectric constant was high at low frequencies and decreasing as the frequency increase. Investigated materials were applied in fabricated bilayer heterojunction organic solar cells. The application of these materials in an organic solar cells show a significant stability under room conditions rather than improvement in their efficiency.

Molecular interactions in ethyl acetate-chlorobenzene binary solution: Dielectric, spectroscopic studies and quantum chemical calculations.

PubMed

Karthick, N K; Kumbharkhane, A C; Joshi, Y S; Mahendraprabu, A; Shanmugam, R; Elangovan, A; Arivazhagan, G

2017-05-05

Dielectric studies using Time Domain Reflectometry method has been carried out on the binary solution of Ethyl acetate (EA) with Chlorobenzene (CBZ) over the entire composition range. Spectroscopic (FTIR and 13 C NMR) signatures of neat EA, CBZ and their equimolar binary solution have also been recorded. The results of the spectroscopic studies favour the presence of (CBZ) CH⋯OC (EA), (EA) methylene CH⋯π electrons (CBZ) and (EA) methyl CH⋯Cl (CBZ) contacts which have been validated using quantum chemical calculations. Dimerization of CBZ has been identified. Presence of β-clusters has been identified in all the solutions. Although EA and CBZ molecules have nearly equal molar volumes, CBZ molecules experience larger hindrance for the rotation than EA molecules. Very small excess dielectric constant (ε E ) values may be correlated with weak heteromolecular forces and/or closed heteromolecular association. Copyright © 2017 Elsevier B.V. All rights reserved.

Molecular interactions in ethyl acetate-chlorobenzene binary solution: Dielectric, spectroscopic studies and quantum chemical calculations

NASA Astrophysics Data System (ADS)

Karthick, N. K.; Kumbharkhane, A. C.; Joshi, Y. S.; Mahendraprabu, A.; Shanmugam, R.; Elangovan, A.; Arivazhagan, G.

2017-05-01

Dielectric studies using Time Domain Reflectometry method has been carried out on the binary solution of Ethyl acetate (EA) with Chlorobenzene (CBZ) over the entire composition range. Spectroscopic (FTIR and 13C NMR) signatures of neat EA, CBZ and their equimolar binary solution have also been recorded. The results of the spectroscopic studies favour the presence of (CBZ) Csbnd H ⋯ Odbnd C (EA), (EA) methylene Csbnd H ⋯ π electrons (CBZ) and (EA) methyl Csbnd H ⋯ Cl (CBZ) contacts which have been validated using quantum chemical calculations. Dimerization of CBZ has been identified. Presence of β-clusters has been identified in all the solutions. Although EA and CBZ molecules have nearly equal molar volumes, CBZ molecules experience larger hindrance for the rotation than EA molecules. Very small excess dielectric constant (εE) values may be correlated with weak heteromolecular forces and/or closed heteromolecular association.

Mars - VLA observations of the northern hemisphere and the north polar region at wavelengths of 2 and 6 cm

NASA Technical Reports Server (NTRS)

Rudy, Donald J.; Muhleman, Duane O.; Berge, Glenn L.; Jakosky, Bruce M.; Christensen, Philip R.

1987-01-01

Calculations based on 2- and 6-cm observations of Mars with the A configuration of the VLA have yielded a whole-disk effective dielectric constant of 2.34 + or - 0.05, implying a subsurface density of 1.24 + or - 0.11 g/cu cm at 2 cm, as well as 1.45 + or - 0.10 g/cu cm effective density and 2.70 + or - 0.10 dielectric constant at 6 cm. These parameters have also been estimated as a function of latitude over the 15 deg S - 60 deg N range; subsurface radio absorption length was estimated to be about 15 wavelengths at most of these latitudes. Most of the subsurface density calculations yielded results in the 1-2-g/cu cm range, implying that the subsurface is not very different from the surface observed by Viking and Mariner spacecraft; the decrease in correlation with depth is in keeping with slow variation of the subsurface in the near-subsurface region.

A polymer dataset for accelerated property prediction and design

DOE PAGES

Huan, Tran Doan; Mannodi-Kanakkithodi, Arun; Kim, Chiho; ...

2016-03-01

Emerging computation- and data-driven approaches are particularly useful for rationally designing materials with targeted properties. Generally, these approaches rely on identifying structure-property relationships by learning from a dataset of sufficiently large number of relevant materials. The learned information can then be used to predict the properties of materials not already in the dataset, thus accelerating the materials design. Herein, we develop a dataset of 1,073 polymers and related materials and make it available at http://khazana.uconn.edu/. This dataset is uniformly prepared using first-principles calculations with structures obtained either from other sources or by using structure search methods. Because the immediate targetmore » of this work is to assist the design of high dielectric constant polymers, it is initially designed to include the optimized structures, atomization energies, band gaps, and dielectric constants. As a result, it will be progressively expanded by accumulating new materials and including additional properties calculated for the optimized structures provided.« less

Enhancement of dielectric constant at percolation threshold in CaCu3 Ti4 O12 ceramic fabricated by both solid state and sol-gel process

NASA Astrophysics Data System (ADS)

Mukherjee, Rupam; Garcia, Lucia; Lawes, Gavin; Nadgorny, Boris

2014-03-01

We have investigated the large dielectric enhancement at the percolation threshold by introducing metallic RuO2 grains into a matrix of CaCu3Ti4O12 (CCTO). The intrinsic response of the pure CCTO samples prepared by solid state and sol-gel processes results in a dielectric constant on the order of 104 and 103 respectively with low loss. Scanning electron microscopy and energy dispersive x-ray spectroscopy indicate that a difference in the thickness of the copper oxide enriched grain boundary is the main reason for the different dielectric properties between these two samples. Introducing RuO2 metallic fillers in these CCTO samples yields a sharp increase of the dielectric constant at percolation threshold fc, by a factor of 6 and 3 respectively. The temperature dependence of the dielectric constant shows that the dipolar relaxation plays an important role in enhancing dielectric constant in composite systems.

Measurement of complex terahertz dielectric properties of polymers using an improved free-space technique

NASA Astrophysics Data System (ADS)

Chang, Tianying; Zhang, Xiansheng; Yang, Chuanfa; Sun, Zhonglin; Cui, Hong-Liang

2017-04-01

The complex dielectric properties of non-polar solid polymer materials were measured in the terahertz (THz) band by a free-space technique employing a frequency-extended vector network analyzer (VNA), and by THz time-domain spectroscopy (TDS). Mindful of THz wave’s unique characteristics, the free-space method for measurement of material dielectric properties in the microwave band was expanded and improved for application in the THz frequency region. To ascertain the soundness and utility of the proposed method, measurements of the complex dielectric properties of a variety of polymers were carried out, including polytetrafluoroethylene (PTFE, known also by the brand name Teflon), polypropylene (PP), polyethylene (PE), and glass fiber resin (Composite Stone). The free-space method relies on the determination of electromagnetic scattering parameters (S-parameters) of the sample, with the gated-reflect-line (GRL) calibration technique commonly employed using a VNA. Subsequently, based on the S-parameters, the dielectric constant and loss characteristic of the sample were calculated by using a Newtonian iterative algorithm. To verify the calculated results, THz TDS technique, which produced Fresnel parameters such as reflection and transmission coefficients, was also used to independently determine the dielectric properties of these polymer samples, with results satisfactorily corroborating those obtained by the free-space extended microwave technique.

Dielectric properties of CaCu3Ti4O12-silicone resin composites

NASA Astrophysics Data System (ADS)

Babu, Sanjesh; Singh, Kirti; Govindan, Anil

2012-06-01

CaCu3Ti4O12 (CCTO)-silicone resin composites with various CCTO volume fractions were prepared. Relatively high dielectric constant ( ɛ=119) and low loss (tan δ=0.35) of the composites with CCTO volume fraction of 0.9 were observed. Two theoretical models were employed to predict the dielectric constant of these composites; the dielectric constant obtained via the Maxwell-Garnett model was in close agreement with the experimental data. The dielectric constant of CCTO-silicone resin composites showed a weak frequency dependence at the measuring frequency range and the loss tangent apparently decreases with increase in frequency.

Ionomer Design, Synthesis and Characterization for Ion-Conducting Energy Materials

NASA Astrophysics Data System (ADS)

Colby, Ralph H.

2013-03-01

For ionic actuators and battery separators, it is vital to utilize single-ion conductors that avoid the detrimental polarization of other ions; the commonly studied dual-ion conductors simply will not be used in the next generation of materials for these applications. Ab initio quantum chemistry calculations at 0 K in vacuum characterize ion interactions and ion solvation by various functional groups, allowing identification of constituents with weak interactions to be incorporated in ionomers for facile ion transport. Simple ideas for estimating the ion interactions and solvation at practical temperatures and dielectric constants are presented that indicate the rank ordering observed at 0 K in vacuum should be preserved. Hence, such ab initio calculations are useful for screening the plethora of combinations of polymer-ion, counterion and polar functional groups, to decide which are worthy of synthesis for new ionomers. Single-ion conducting ionomers are synthesized based on these calculations, with low glass transition temperatures (facile dynamics) to prepare ion-conducting membranes for ionic actuators and battery separators. Characterization by X-ray scattering, dielectric spectroscopy, NMR and linear viscoelasticity collectively develop a coherent picture of ionic aggregation and both counterion and polymer dynamics. Examples are shown of how ab initio calculations can be used to understand experimental observations of dielectric constant, glass transition temperature and conductivity of polymerized ionic liquids with counterions being either lithium, sodium, fluoride, hydroxide (for batteries) or bulky ionic liquids (for ionic actuators). This work was supported by the Department of Energy under Grant BES-DE-FG02-07ER46409.

Transport and dielectric properties of water and the influence of coarse-graining: Comparing BMW, SPC/E, and TIP3P models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Braun, Daniel; Boresch, Stefan; Steinhauser, Othmar

Long-term molecular dynamics simulations are used to compare the single particle dipole reorientation time, the diffusion constant, the viscosity, and the frequency-dependent dielectric constant of the coarse-grained big multipole water (BMW) model to two common atomistic three-point water models, SPC/E and TIP3P. In particular, the agreement between the calculated viscosity of BMW and the experimental viscosity of water is satisfactory. We also discuss contradictory values for the static dielectric properties reported in the literature. Employing molecular hydrodynamics, we show that the viscosity can be computed from single particle dynamics, circumventing the slow convergence of the standard approaches. Furthermore, our datamore » indicate that the Kivelson relation connecting single particle and collective reorientation time holds true for all systems investigated. Since simulations with coarse-grained force fields often employ extremely large time steps, we also investigate the influence of time step on dynamical properties. We observe a systematic acceleration of system dynamics when increasing the time step. Carefully monitoring energy/temperature conservation is found to be a sufficient criterion for the reliable calculation of dynamical properties. By contrast, recommended criteria based on the ratio of fluctuations of total vs. kinetic energy are not sensitive enough.« less

Protein-ion binding process on finite macromolecular concentration. A Poisson-Boltzmann and Monte Carlo study.

PubMed

de Carvalho, Sidney Jurado; Fenley, Márcia O; da Silva, Fernando Luís Barroso

2008-12-25

Electrostatic interactions are one of the key driving forces for protein-ligands complexation. Different levels for the theoretical modeling of such processes are available on the literature. Most of the studies on the Molecular Biology field are performed within numerical solutions of the Poisson-Boltzmann Equation and the dielectric continuum models framework. In such dielectric continuum models, there are two pivotal questions: (a) how the protein dielectric medium should be modeled, and (b) what protocol should be used when solving this effective Hamiltonian. By means of Monte Carlo (MC) and Poisson-Boltzmann (PB) calculations, we define the applicability of the PB approach with linear and nonlinear responses for macromolecular electrostatic interactions in electrolyte solution, revealing some physical mechanisms and limitations behind it especially due the raise of both macromolecular charge and concentration out of the strong coupling regime. A discrepancy between PB and MC for binding constant shifts is shown and explained in terms of the manner PB approximates the excess chemical potentials of the ligand, and not as a consequence of the nonlinear thermal treatment and/or explicit ion-ion interactions as it could be argued. Our findings also show that the nonlinear PB predictions with a low dielectric response well reproduce the pK shifts calculations carried out with an uniform dielectric model. This confirms and completes previous results obtained by both MC and linear PB calculations.

Poly(vinylidene fluoride) Flexible Nanocomposite Films with Dopamine-Coated Giant Dielectric Ceramic Nanopowders, Ba(Fe0.5Ta0.5)O3, for High Energy-Storage Density at Low Electric Field.

PubMed

Wang, Zhuo; Wang, Tian; Wang, Chun; Xiao, Yujia; Jing, Panpan; Cui, Yongfei; Pu, Yongping

2017-08-30

Ba(Fe 0.5 Ta 0.5 )O 3 /poly(vinylidene fluoride) (BFT/PVDF) flexible nanocomposite films are fabricated by tape casting using dopamine (DA)-modified BFT nanopowders and PVDF as a matrix polymer. After a surface modification of installing a DA layer with a thickness of 5 nm, the interfacial couple interaction between BFT and PVDF is enhanced, resulting in less hole defects at the interface. Then the dielectric constant (ε'), loss tangent (tan δ), and AC conductivity of nanocomposite films are reduced. Meanwhile, the value of the reduced dielectric constant (Δε') and the strength of interfacial polarization (k) are introduced to illustrate the effect of DA on the dielectric behavior of nanocomposite films. Δε' can be used to calculate the magnitude of interfacial polarization, and the strength of the dielectric constant contributed by the interface can be expressed as k. Most importantly, the energy-storage density and energy-storage efficiency of nanocomposite films with a small BFT@DA filler content of 1 vol % at a low electric field of 150 MV/m are enhanced by about 15% and 120%, respectively, after DA modification. The high energy-storage density of 1.81 J/cm 3 is obtained in the sample. This value is much larger than the reported polymer-based nanocomposite films. In addition, the outstanding cycle and bending stability of the nanocomposite films make it a promising candidate for future flexible portable energy devices.

First-principles study of structural and electronic properties of Be0.25Zn0.75S mixed compound

NASA Astrophysics Data System (ADS)

Paliwal, U.; Joshi, K. B.

2018-05-01

In this work the first-principles study of structural and electronic properties of Be0.25Zn0.75S mixed compound is presented. The calculations are performed applying the QUANTUM ESPRESSO code utilizing the Perdew, Becke, Ernzerhof generalized gradient approximation in the framework of density functional theory. Adopting standard optimization strategy, the ground state equilibrium lattice constant and bulk modulus are calculated. After settling the structure the electronic band structure, bandgap and static dielectric constant are evaluated. In absence of any experimental work on this system our findings are compared with the available theoretical calculations which are found to follow well anticipated general trends.

Effect of vacuum-ultraviolet irradiation on the dielectric constant of low-k organosilicate dielectrics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, H.; Shohet, J. L.; Ryan, E. T.

2014-11-17

Vacuum ultraviolet (VUV) irradiation is generated during plasma processing in semiconductor fabrications, while the effect of VUV irradiation on the dielectric constant (k value) of low-k materials is still an open question. To clarify this problem, VUV photons with a range of energies were exposed on low-k organosilicate dielectrics (SiCOH) samples at room temperature. Photon energies equal to or larger than 6.0 eV were found to decrease the k value of SiCOH films. VUV photons with lower energies do not have this effect. This shows the need for thermal heating in traditional ultraviolet (UV) curing since UV light sources do notmore » have sufficient energy to change the dielectric constant of SiCOH and additional energy is required from thermal heating. In addition, 6.2 eV photon irradiation was found to be the most effective in decreasing the dielectric constant of low-k organosilicate films. Fourier Transform Infra-red Spectroscopy shows that these 6.2 eV VUV exposures removed organic porogens. This contributes to the decrease of the dielectric constant. This information provides the range of VUV photon energies that could decrease the dielectric constant of low-k materials most effectively.« less

Synthesis and Characterization of High-Dielectric-Constant Nanographite-Polyurethane Composite

NASA Astrophysics Data System (ADS)

Mishra, Praveen; Bhat, Badekai Ramachandra; Bhattacharya, B.; Mehra, R. M.

2018-05-01

In the face of ever-growing demand for capacitors and energy storage devices, development of high-dielectric-constant materials is of paramount importance. Among various dielectric materials available, polymer dielectrics are preferred for their good processability. We report herein synthesis and characterization of nanographite-polyurethane composite with high dielectric constant. Nanographite showed good dispersibility in the polyurethane matrix. The thermosetting nature of polyurethane gives the composite the ability to withstand higher temperature without melting. The resultant composite was studied for its dielectric constant (ɛ) as a function of frequency. The composite exhibited logarithmic variation of ɛ from 3000 at 100 Hz to 225 at 60 kHz. The material also exhibited stable dissipation factor (tan δ) across the applied frequencies, suggesting its ability to resist current leakage.

The effect of diamic acid additives on the dielectric constant of polyimides

NASA Technical Reports Server (NTRS)

Stoakley, Diane M.; St. Clair, Anne K.

1988-01-01

The effect of six selected diamic acids additives (including 2,2-prime bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride-aniline (An); 4,4-prime-oxydiphthalic anhydride-An, 3,3-prime diaminodiphenyl sulfone-phthalic anhydride (PA); 4,4-prime-oxydianiline-PA; 2,2-bis 4(4-aminophenoxy)phenyl hexafluoropropane-PA; and 2,2-bis 4(3-aminophenoxy)phenyl hexafluoropropane-PA) on the dielectric constants of low-dielectric-constant polyimide resins was evaluated. It was found that the effect of the incorporation of the diamic acids on reducing the dielectric constant of polyimides may be limited as the dielectric constant of the base resin itself becomes very low. The additives were found to lower the resin's values of glass transition temperature, with no effect on thermooxidative stability.

Dielectric constant of liquid alkanes and hydrocarbon mixtures

NASA Technical Reports Server (NTRS)

Sen, A. D.; Anicich, V. G.; Arakelian, T.

1992-01-01

The complex dielectric constants of n-alkanes with two to seven carbon atoms have been measured. The measurements were conducted using a slotted-line technique at 1.2 GHz and at atmospheric pressure. The temperature was varied from the melting point to the boiling point of the respective alkanes. The real part of the dielectric constant was found to decrease with increasing temperature and correlate with the change in the molar volume. An upper limit to all the loss tangents was established at 0.001. The complex dielectric constants of a few mixtures of liquid alkanes were also measured at room temperature. For a pentane-octane mixture the real part of the dielectric constant could be explained by the Clausius-Mosotti theory. For the mixtures of n-hexane-ethylacetate and n-hexane-acetone the real part of the dielectric constants could be explained by the Onsager theory extended to mixtures. The dielectric constant of the n-hexane-acetone mixture displayed deviations from the Onsager theory at the highest fractions of acetone. The dipole moments of ethylacetate and acetone were determined for dilute mixtures using the Onsager theory and were found to be in agreement with their accepted gas-phase values. The loss tangents of the mixtures exhibited a linear relationship with the volume fraction for low concentrations of the polar liquids.

Prediction of electronic and optical properties of ZnAl2Te4 defect chalcopyrite semiconductor: an ab-initio study

NASA Astrophysics Data System (ADS)

Mayengbam, Rishikanta; Tripathy, S. K.; Pandey, B. P.

2018-03-01

In this paper, we have investigated the structural, electronic and optical properties of ZnAl2Te4 defect chalcopyrite semiconductor using generalized gradient approximation (GGA) within density functional theory (DFT). We have calculated the optimized lattice constants (a and c) and compared with the available experimental values. The optimized lattice constants have been used to calculate the energy band gap and found to be 1.57 eV. The partial density of states and total density of states have been discussed in detail. The frequency dependent dielectric constant and refractive index have been calculated and plotted in the energy range 0-13 eV. All the above parameters have been compared with the available experimental and theoretical values and found good agreement between them.

Effect of Solvent Dielectric Constant on the Formation of Large Flat Bilayer Stacks in a Lecithin/Hexadecanol Hydrogel.

PubMed

Nakagawa, Yasuharu; Nakazawa, Hiromitsu; Kato, Satoru

2016-07-12

We investigated the effect of dielectric properties of the aqueous medium on the novel type of hydrogel composed of a crude lecithin mixture (PC70) and hexadecanol (HD), in which charged sheet-like bilayers are kept far apart due to interbilayer repulsive interaction. We used dipropylene glycol (DPG) as a modifier of the dielectric properties and examined its effect on the hydrogel by synchrotron X-ray diffraction, differential scanning calorimetry (DSC), polarized optical microscopy, and freeze-fracture electron microscopy. We found that at a DPG weight fraction in the aqueous medium WDPG ≈ 0.4, the bilayer organization is transformed into unusually large flat bilayer stacks with a regular lamellar spacing of 6.25 nm and consequently disintegration of the hydrogel takes place. Semiquantitative calculation of the interbilayer interaction energy based on the Deyaguin-Landau-Verwey-Overbeek (DLVO) theory suggested that the reduction of the aqueous medium dielectric constant ε by DPG may lower the energy barrier preventing flat bilayers from coming closer together. We inferred that the size of the bilayer sheet increases because the reduction of ε promotes protonation of acidic lipids that work as edge-capping molecules.

A Multi-Objective Optimization Technique to Model the Pareto Front of Organic Dielectric Polymers

NASA Astrophysics Data System (ADS)

Gubernatis, J. E.; Mannodi-Kanakkithodi, A.; Ramprasad, R.; Pilania, G.; Lookman, T.

Multi-objective optimization is an area of decision making that is concerned with mathematical optimization problems involving more than one objective simultaneously. Here we describe two new Monte Carlo methods for this type of optimization in the context of their application to the problem of designing polymers with more desirable dielectric and optical properties. We present results of applying these Monte Carlo methods to a two-objective problem (maximizing the total static band dielectric constant and energy gap) and a three objective problem (maximizing the ionic and electronic contributions to the static band dielectric constant and energy gap) of a 6-block organic polymer. Our objective functions were constructed from high throughput DFT calculations of 4-block polymers, following the method of Sharma et al., Nature Communications 5, 4845 (2014) and Mannodi-Kanakkithodi et al., Scientific Reports, submitted. Our high throughput and Monte Carlo methods of analysis extend to general N-block organic polymers. This work was supported in part by the LDRD DR program of the Los Alamos National Laboratory and in part by a Multidisciplinary University Research Initiative (MURI) Grant from the Office of Naval Research.

Brillouin light scattering studies on the mechanical properties of ultrathin, porous low-K dielectric films

NASA Astrophysics Data System (ADS)

Zhou, Wei; Sooryakumar, R.; King, Sean

2010-03-01

Low K dielectrics have predominantly replaced silicon dioxide as the interlayer dielectric material for interconnects in state of the art integrated circuits. To further reduce interconnect resistance-capacitance (RC) delays, additional reductions in the K for these low-K materials is being pursued by the introduction of controlled levels of porosity. The main challenge for porous low-K dielectrics is the substantial reduction in mechanical properties that is accompanied by the increased pore volume content needed to reduce K. We report on the application of the nondestructive Brillouin light scattering technique to monitor and characterize the mechanical properties of these porous films at thicknesses well below 200 nm that are pertinent to present applications. Observation of longitudinal and transverse standing wave acoustic resonances and the dispersion that accompany their transformation into traveling waves with finite in-plane wave vectors provides for the principal elastic constants that completely characterize the mechanical properties of these porous films. The mode amplitudes of the standing waves, their variation within the film, and the calculated Brillouin intensities account for most aspects of the spectra. The resulting elastic constants are compared with corresponding values obtained from other experimental techniques.

Comparison of all atom, continuum, and linear fitting empirical models for charge screening effect of aqueous medium surrounding a protein molecule

NASA Astrophysics Data System (ADS)

Takahashi, Takuya; Sugiura, Junnnosuke; Nagayama, Kuniaki

2002-05-01

To investigate the role hydration plays in the electrostatic interactions of proteins, the time-averaged electrostatic potential of the B1 domain of protein G in an aqueous solution was calculated with full atomic molecular dynamics simulations that explicitly considers every atom (i.e., an all atom model). This all atom calculated potential was compared with the potential obtained from an electrostatic continuum model calculation. In both cases, the charge-screening effect was fairly well formulated with an effective relative dielectric constant which increased linearly with increasing charge-charge distance. This simulated linear dependence agrees with the experimentally determined linear relation proposed by Pickersgill. Cut-off approximations for Coulomb interactions failed to reproduce this linear relation. Correlation between the all atom model and the continuum models was found to be better than the respective correlation calculated for linear fitting to the two models. This confirms that the continuum model is better at treating the complicated shapes of protein conformations than the simple linear fitting empirical model. We have tried a sigmoid fitting empirical model in addition to the linear one. When weights of all data were treated equally, the sigmoid model, which requires two fitting parameters, fits results of both the all atom and the continuum models less accurately than the linear model which requires only one fitting parameter. When potential values are chosen as weighting factors, the fitting error of the sigmoid model became smaller, and the slope of both linear fitting curves became smaller. This suggests the screening effect of an aqueous medium within a short range, where potential values are relatively large, is smaller than that expected from the linear fitting curve whose slope is almost 4. To investigate the linear increase of the effective relative dielectric constant, the Poisson equation of a low-dielectric sphere in a high-dielectric medium was solved and charges distributed near the molecular surface were indicated as leading to the apparent linearity.

Computation of Dielectric Response in Molecular Solids for High Capacitance Organic Dielectrics.

PubMed

Heitzer, Henry M; Marks, Tobin J; Ratner, Mark A

2016-09-20

The dielectric response of a material is central to numerous processes spanning the fields of chemistry, materials science, biology, and physics. Despite this broad importance across these disciplines, describing the dielectric environment of a molecular system at the level of first-principles theory and computation remains a great challenge and is of importance to understand the behavior of existing systems as well as to guide the design and synthetic realization of new ones. Furthermore, with recent advances in molecular electronics, nanotechnology, and molecular biology, it has become necessary to predict the dielectric properties of molecular systems that are often difficult or impossible to measure experimentally. In these scenarios, it is would be highly desirable to be able to determine dielectric response through efficient, accurate, and chemically informative calculations. A good example of where theoretical modeling of dielectric response would be valuable is in the development of high-capacitance organic gate dielectrics for unconventional electronics such as those that could be fabricated by high-throughput printing techniques. Gate dielectrics are fundamental components of all transistor-based logic circuitry, and the combination high dielectric constant and nanoscopic thickness (i.e., high capacitance) is essential to achieving high switching speeds and low power consumption. Molecule-based dielectrics offer the promise of cheap, flexible, and mass producible electronics when used in conjunction with unconventional organic or inorganic semiconducting materials to fabricate organic field effect transistors (OFETs). The molecular dielectrics developed to date typically have limited dielectric response, which results in low capacitances, translating into poor performance of the resulting OFETs. Furthermore, the development of better performing dielectric materials has been hindered by the current highly empirical and labor-intensive pace of synthetic progress. An accurate and efficient theoretical computational approach could drastically decrease this time by screening potential dielectric materials and providing reliable design rules for future molecular dielectrics. Until recently, accurate calculation of dielectric responses in molecular materials was difficult and highly approximate. Most previous modeling efforts relied on classical formalisms to relate molecular polarizability to macroscopic dielectric properties. These efforts often vastly overestimated polarizability in the subject materials and ignored crucial material properties that can affect dielectric response. Recent advances in first-principles calculations via density functional theory (DFT) with periodic boundary conditions have allowed accurate computation of dielectric properties in molecular materials. In this Account, we outline the methodology used to calculate dielectric properties of molecular materials. We demonstrate the validity of this approach on model systems, capturing the frequency dependence of the dielectric response and achieving quantitative accuracy compared with experiment. This method is then used as a guide to new high-capacitance molecular dielectrics by determining what materials and chemical properties are important in maximizing dielectric response in self-assembled monolayers (SAMs). It will be seen that this technique is a powerful tool for understanding and designing new molecular dielectric systems, the properties of which are fundamental to many scientific areas.

Investigation of dielectric properties of different cake formulations during microwave and infrared-microwave combination baking.

PubMed

Sakiyan, Ozge; Sumnu, Gulum; Sahin, Serpil; Meda, Venkatesh

2007-05-01

Dielectric properties can be used to understand the behavior of food materials during microwave processing. Dielectric properties influence the level of interaction between food and high frequency electromagnetic energy. Dielectric properties are, therefore, important in the design of foods intended for microwave preparation. In this study, it was aimed to determine the variation of dielectric properties of different cake formulations during baking in microwave and infrared-microwave combination oven. In addition, the effects of formulation and temperature on dielectric properties of cake batter were examined. Dielectric constant and loss factor of cake samples were shown to be dependent on formulation, baking time, and temperature. The increase in baking time and temperature decreased dielectric constant and loss factor of all formulations. Fat content was shown to increase dielectric constant and loss factor of cakes.

Dielectric Properties of PANI/CuO Nanocomposites

NASA Astrophysics Data System (ADS)

Ambalagi, Sharanabasamma M.; Devendrappa, Mahalesh; Nagaraja, Sannakki; Sannakki, Basavaraja

2018-02-01

The combustion method is used to prepare the Copper Oxide (CuO) nanoparticles. The nanocomposites of Polyaniline (PANI) by doping with copper oxide nanoparticles have synthesized at 10, 20, 30, 40 and 50 different weight percentages during the in-situ polymerization. The samples of nanocomposite of PANI-CuO were characterized by using X-Ray diffraction (XRD) technique. The physical properties such as dielectric constant, dielectric loss and A C conductivity of the nanocomposites are studied as a function of frequency in the range 5Hz-35MHz at room temperature. It is found that the dielectric constant decreases as the frequency increases. The dielectric constant it remains constant at higher frequencies and it is also observed that in particular frequency both the dielectric constant and dielectric loss are decreased as a weight percentage of CuO increased. In case of AC conductivity it is found that as the frequency increases the AC conductivity remains constant up to 3.56MHz and afterwards it increases as frequency increases. This is due to the increase in charge carriers through the hopping mechanism in the polymer nanocomposites. It is also observed that as a weight percentage of CuO increased the AC conductivity is also increasing at a particular frequency.

Film Thickness Allowance and Waveguide Length in 3-Layer Unidirectional Magneto-Optical TE-TM Mode Converter

NASA Astrophysics Data System (ADS)

Abe, Masanori; Nakagawa, Hidenobu; Gomi, Manabu; Nomura, Shoichiro

1982-01-01

The film thickness allowance and the waveguide length in a 3-layer (substrate/film/air) magneto-optical unidirectional TE-TM mode converter which utilizes the intrinsic birefringence in an anisotropic material are calculated at λ0{=}1.55 μm. The film material should be gyrotropic in order to make the waveguide length short, and the film thickness allowance is relaxed by reducing the ratio of the dielectric constant of the film to that of the substrate. When the waveguide is made of an isotropic gyrotropic film of YIG deposited on an anisotropic substrate (which may be gyrotropic or not), the restriction on the film thickness can in practice be removed, but this requires precise control of the dielectric constant of the film and the substrate instead.

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

PubMed

Wang, Lin; Li, Lin; Alexov, Emil

2015-12-01

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. © 2015 Wiley Periodicals, Inc.

Three-phase Fe3O4/MWNT/PVDF nanocomposites with high dielectric constant for embedded capacitor

NASA Astrophysics Data System (ADS)

Wang, Haiyun; Fu, Qiong; Luo, Jiangqi; Zhao, Dongmei; Luo, Laihui; Li, Weiping

2017-06-01

To get the dielectric material with a high dielectric constant and low dielectric loss, the modified multiwalled carbon nanotube (MWNT-S) and ferroferric oxide (Fe3O4) particles were embedded into polyvinylidene fluoride (PVDF) to fabricate the Fe3O4/MWNT-S/PVDF ternary composites. The maximum dielectric constant of these composites can be up to 3490 at a very low filler fraction, and dielectric loss can be suppressed below 0.5. The small amount of the second filler (Fe3O4) can accelerate the formation of a percolation conductive network and improve the interfacial polarization. Therefore, the excellent dielectric properties can be achieved at low loading of fillers.

Dielectric spectroscopy of Ag-starch nanocomposite films

NASA Astrophysics Data System (ADS)

Meena; Sharma, Annu

2018-04-01

In the present work Ag-starch nanocomposite films were fabricated via chemical reduction route. The formation of Ag nanoparticles was confirmed using transmission electron microscopy (TEM). Further the effect of varying concentration of Ag nanoparticles on the dielectric properties of starch has been studied. The frequency response of dielectric constant (ε‧), dielectric loss (ε″) and dissipation factor tan(δ) has been studied in the frequency range of 100 Hz to 1 MHz. Dielectric data was further analysed using Cole-Cole plots. The dielectric constant of starch was found to be 4.4 which decreased to 2.35 in Ag-starch nanocomposite film containing 0.50 wt% of Ag nanoparticles. Such nanocomposites with low dielectric constant have potential applications in microelectronic technologies.

Comparative study of urea and betaine solutions by dielectric spectroscopy: liquid structures of a protein denaturant and stabilizer.

PubMed

Hayashi, Yoshihito; Katsumoto, Yoichi; Oshige, Ikuya; Omori, Shinji; Yasuda, Akio

2007-10-11

We performed dielectric spectroscopy measurements on aqueous solutions of glycine betaine (N,N,N-trimethylglycine), which is known to be a strong stabilizer of globular proteins, over a wide concentration range (3-62 wt %) and compared the results with our previously published data for aqueous solutions of urea, a representative protein denaturant. The hydration number of betaine (9), calculated on the basis of the reduction in the dielectric relaxation strength of bulk water with addition of betaine, is significantly larger than that of urea (2). Furthermore, the dielectric relaxation time increased with betaine concentration, while that remained nearly constant for the urea-water system over a wide concentration range. This difference between urea and betaine is probably related to their opposite effects on the protein stabilization.

On the Dielectric Constant for Acetanilide: Experimental Measurements and Effect on Energy Transport

NASA Astrophysics Data System (ADS)

Careri, G.; Compatangelo, E.; Christiansen, P. L.; Halding, J.; Skovgaard, O.

1987-01-01

Experimental measurements of the dielectric constant for crystalline acetanilide powder for temperatures ranging from - 140°C to 20°C and for different hydration levels are presented. A Davydov-soliton computer model predicts dramatic changes in the energy transport and storage for typically increased values of the dielectric constant.

The transmembrane gradient of the dielectric constant influences the DPH lifetime distribution.

PubMed

Konopásek, I; Kvasnicka, P; Amler, E; Kotyk, A; Curatola, G

1995-11-06

The fluorescence lifetime distribution of 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-[4-(trimethylamino)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH) in egg-phosphatidylcholine liposomes was measured in normal and heavy water. The lower dielectric constant (by approximately 12%) of heavy water compared with normal water was employed to provide direct evidence that the drop of the dielectric constant along the membrane normal shifts the centers of the distribution of both DPH and TMA-DPH to higher values and sharpens the widths of the distribution. The profile of the dielectric constant along the membrane normal was not found to be a linear gradient (in contrast to [1]) but a more complex function. Presence of cholesterol in liposomes further shifted the center of the distributions to higher value and sharpened them. In addition, it resulted in a more gradient-like profile of the dielectric constant (i.e. linearization) along the normal of the membrane. The effect of the change of dielectric constant on the membrane proteins is discussed.

Wave propagation in and around negative-dielectric-constant discharge plasma

NASA Astrophysics Data System (ADS)

Sakai, Osamu; Iwai, Akinori; Omura, Yoshiharu; Iio, Satoshi; Naito, Teruki

2018-03-01

The modes of wave propagation in media with a negative dielectric constant are not simple, unlike those for electromagnetic waves in media with a positive dielectric constant (where modes propagate inside the media with positive phase velocity since the refractive index is usually positive). Instead, they depend on the permeability sign, either positive or negative, and exhibit completely different features. In this report, we investigated a wave confined on the surface of a negative-dielectric-constant and a positive-permeability plasma medium for which the refractive index is imaginary. The propagation mode is similar to surface plasmon polaritons on the metal containing free electrons, but its frequency band is different due to the significant spatial gradient of the dielectric constant and a different pressure term. We also studied a wave with a negative dielectric constant and negative permeability, where the refractive index is negative. This wave can propagate inside the media, but its phase velocity is negative. It also shares similar qualities with waves in plasmonic devices with negative permeability in the photon range.

Dielectric Properties of PMMA and its Composites with ZrO2

NASA Astrophysics Data System (ADS)

Sannakki, Basavaraja; Anita

The polymer films of PMMA with different thickness and its composites with ZrO2 at various weight percentages but of same thickness have been studied. The determination of its dielectric properties, dielectric loss, a.conductivity and dielectric modulus were carried out using capacitance measurements of the above samples as a function of frequency, over the range 50 Hz - 5 MHz at room temperature. The films of PMMA and its composites have been characterized using X-Ray Diffractometer. The dielectric permittivity of films of PMMA behaves nonlinearly as frequency increases over the range 50-300 Hz, where as above 300 Hz the values of dielectric constant remains constant. But it is observed that the dielectric constant of PMMA increases as thickness of the film increases. In case of composite films of PMMA with ZrO2 the values of dielectric permittivity decreases gradually up to frequency of around 1 KHz and at higher frequencies it remains constant for all the weight percentages of ZrO2. The complex form of dielectric modulus of PMMA is obtained from the experimentally measured data of dielectric constant and dielectric loss values. The relaxation time of the orientation of dipoles is obtained from the peak value of angular frequency through the plots of imaginary part of electrical modulus as function of frequency. The impedance of PMMA polymer increases as thickness of the films increases. The a c conductivity of PMMA film remains constant up to frequency of 1 MHz and above. It shows a nonlinear phenomenon with peak values at frequency 4 MHz. Shape and size of the nanoparticles of composite film of PMMA with ZrO2 was analyzed by Field Emission Scanning Electron Microscope (FESEM).

Native defects in Tl 6SI 4: Density functional calculations

DOE PAGES

Shi, Hongliang; Du, Mao -Hua

2015-05-05

In this study, Tl 6SI 4 is a promising room-temperature semiconductor radiation detection material. Here, we report density functional calculations of native defects and dielectric properties of Tl 6SI 4. Formation energies and defect levels of native point defects and defect complexes are calculated. Donor-acceptor defect complexes are shown to be abundant in Tl 6SI 4. High resistivity can be obtained by Fermi level pinning by native donor and acceptor defects. Deep donors that are detrimental to electron transport are identified and methods to mitigate such problem are discussed. Furthermore, we show that mixed ionic-covalent character of Tl 6SI 4more » gives rise to enhanced Born effective charges and large static dielectric constant, which provides effective screening of charged defects and impurities.« less

The impact of chemical structure and molecular packing on the electronic polarisation of fullerene arrays.

PubMed

Few, Sheridan; Chia, Cleaven; Teo, Daniel; Kirkpatrick, James; Nelson, Jenny

2017-07-19

Electronic polarisation contributes to the electronic landscape as seen by separating charges in organic materials. The nature of electronic polarisation depends on the polarisability, density, and arrangement of polarisable molecules. In this paper, we introduce a microscopic, coarse-grained model in which we treat each molecule as a polarisable site, and use an array of such polarisable dipoles to calculate the electric field and associated energy of any arrangement of charges in the medium. The model incorporates chemical structure via the molecular polarisability and molecular packing patterns via the structure of the array. We use this model to calculate energies of charge pairs undergoing separation in finite fullerene lattices of different chemical and crystal structures. The effective dielectric constants that we estimate from this approach are in good quantitative agreement with those measured experimentally in C 60 and phenyl-C 61 -butyric acid methyl ester (PCBM) films, but we find significant differences in dielectric constant depending on packing and on direction of separation, which we rationalise in terms of density of polarisable fullerene cages in regions of high field. In general, we find lattices containing molecules of more isotropic polarisability tensors exhibit higher dielectric constants. By exploring several model systems we conclude that differences in molecular polarisability (and therefore, chemical structure) appear to be less important than differences in molecular packing and separation direction in determining the energetic landscape for charge separation. We note that the results are relevant for finite lattices, but not necessarily for infinite systems. We propose that the model could be used to design molecular systems for effective electronic screening.

Effect of Zn doping on structural, magnetic and dielectric properties of LaFeO{sub 3} synthesized through sol–gel auto-combustion process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhat, Irshad; Husain, Shahid, E-mail: s.husain@lycos.com; Khan, Wasi

2013-11-15

Graphical abstract: - Highlights: • We have synthesized the samples of LaFe{sub 1−x}Zn{sub x}O{sub 3} (0 ≤ x ≤ 0.3) using sol–gel auto-combustion process. • The doping of Zn{sup 2+} hugely enhances the dielectric constant (ε′) and it shows a colossal value. • The parent compound LaFeO{sub 3} does not show any relaxation peak, but the substitution of Zn at Fe{sup 3+} site brings the relaxation in the system. • The system shows a peak behavior thereby giving the Debye like dipolar relaxation response. - Abstract: We have studied the structural and dielectric properties of nano-crystalline LaFe{sub 1−x}Zn{sub x}O{sub 3}more » (0 ≤ x ≤ 0.3) pervoskite samples synthesized through sol–gel auto-combustion technique. X-ray diffraction and FTIR spectroscopy are used to confirm the single phase characteristics. Microstructural features are investigated using scanning electron microscope and compositional analysis is performed through energy dispersive spectroscopy. The average grain sizes, calculated from the Scherrer formula, lie in the range below 30 nm. The hysteresis (M-H) curves display a weak magnetic order and a shift in the hysteresis loops. Dielectric response has been discussed, in the framework of “universal dielectric response” model. The value of dielectric constant (ε′) increases drastically on Zn doping. The dielectric loss factor (ε″) shows Debye like dipolar relaxation behavior. The observed peaks in loss factor (ε″) are attributed to the fact that a strong correlation between the conduction mechanism and the dielectric behavior exists in ferrites.« less

Giant dielectric constant in titania nanoparticles embedded in conducting polymer matrix.

PubMed

Dey, Ashis; De, Sukanta; De, Amitabha; De, S K

2006-05-01

Complex impedance and dielectric permittivity of titania-polypyrrole nanocomposites have been investigated as a function of frequency and temperature at different compositions. A very large dielectric constant of about 13,000 at room temperature has been observed. The colossal dielectric constant is mainly dominated by interfacial polarization due to Maxwell-Wagner relaxation effect. Two completely separate groups of dielectric relaxation have been observed. The low frequency dielectric relaxation arises from surface defect states of titania nanoparticles. The broad peak at high frequency region is attributed to Maxwell-Wagner type polarization originating from the inhomogeneous property of nanocomposite. An abrupt change in grain boundary conductivity and dielectric relaxation associated with titania was observed at around 150 K. Anomalous behavior in conductivity and dielectric relaxation is qualitatively explained by band tail structure of titania nanoparticle.

Colossal dielectric constant in PrFeO 3 semiconductor ceramics

NASA Astrophysics Data System (ADS)

Prasad, Bandi Vittal; Rao, G. Narsinga; Chen, J. W.; Babu, D. Suresh

2012-02-01

The perovskite PrFeO 3 ceramics were synthesized via sol-gel method. The dielectric properties and impedance spectroscopy (IS) of these ceramics were studied in the frequency range from 100 Hz to 1000 kHz in the temperature range from 80 K to 300 K. These materials exhibited colossal dielectric constant value of ˜10 4 at room temperature. The response is similar to that observed for relaxorferroelectrics. IS data analysis indicates the ceramics to be electrically heterogeneous semiconductor consisting of semiconducting grains with dielectric constant 30 and more resistive grain boundaries with effective dielectric constant ˜10 4. We conclude, therefore that grain boundary effect is the primary source for the high effective permittivity in PrFeO 3 ceramics.

Quantum Calculations on Salt Bridges with Water: Potentials, Structure, and Properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liao, Sing; Green, Michael E.

2011-01-01

Salt bridges are electrostatic links between acidic and basic amino acids in a protein; quantum calculations are used here to determine the energetics and other properties of one form of these species, in the presence of water molecules. The acidic groups are carboxylic acids (aspartic and glutamic acids); proteins have two bases with pK above physiological pH: one, arginine, with a guanidinium basic group, the other lysine, which is a primary amine. Only arginine is modeled here, by ethyl guanidinium, while propionic acid is used as a model for either carboxylic acid. The salt bridges are accompanied by 0-12 watermore » molecules; for each of the 13 systems, the energy-bond distance relation, natural bond orbitals (NBO), frequency calculations allowing thermodynamic corrections to room temperature, and dielectric constant dependence, were all calculated. The water molecules were found to arrange themselves in hydrogen bonded rings anchored to the oxygens of the salt bridge components. This was not surprising in itself, but it was found that the rings lead to a periodicity in the energy, and to a 'water addition' rule. The latter shows that the initial rings, with four oxygen atoms, become five member rings when an additional water molecule becomes available, with the additional water filling in at the bond with the lowest Wiberg index, as calculated using NBO. The dielectric constant dependence is the expected hyperbola, and the fit of the energy to the inverse dielectric constant is determined. There is an energy periodicity related to ring formation upon addition of water molecules. When 10 water molecules have been added, all spaces near the salt bridge are filled, completing the first hydration shell, and a second shell starts to form. The potentials associated with salt bridges depend on their hydration, and potentials assigned without regard to local hydration are likely to cause errors as large as or larger than kBT, thus suggesting a serious problem if these potentials are used in Molecular Dynamics simulations.« less

Lightning arrestor connector lead magnesium niobate qualification pellet test procedures.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tuohig, W.; Mahoney, Patrick A.; Tuttle, Bruce Andrew

2009-02-01

Enhanced knowledge preservation for DOE DP technical component activities has recently received much attention. As part of this recent knowledge preservation effort, improved documentation of the sample preparation and electrical testing procedures for lead magnesium niobate--lead titanate (PMN/PT) qualification pellets was completed. The qualification pellets are fabricated from the same parent powders used to produce PMN/PT lightning arrestor connector (LAC) granules at HWF&T. In our report, the procedures for fired pellet surface preparation, electrode deposition, electrical testing and data recording are described. The dielectric measurements described in our report are an information only test. Technical reasons for selecting the electrodemore » material, electrode size and geometry are presented. The electrical testing is based on measuring the dielectric constant and dissipation factor of the pellet during cooling from 280 C to 220 C. The most important data are the temperature for which the peak dielectric constant occurs (Curie Point temperature) and the peak dielectric constant magnitude. We determined that the peak dielectric constant for our procedure would be that measured at 1 kHz at the Curie Point. Both the peak dielectric constant and the Curie point parameters provide semi-quantitative information concerning the chemical and microstructural homogeneity of the parent material used for the production of PMN/PT granules for LACs. Finally, we have proposed flag limits for the dielectric data for the pellets. Specifically, if the temperature of the peak dielectric constant falls outside the range of 250 C {+-} 30 C we propose that a flag limit be imposed that will initiate communication between production agency and design agency personnel. If the peak dielectric constant measured falls outside the range 25,000 {+-} 10,000 we also propose that a flag limit be imposed.« less

Investigation of structural, electronic, elastic and optical properties of Cd1-x-yZnxHgyTe alloys

NASA Astrophysics Data System (ADS)

Tamer, M.

2016-06-01

Structural, optical and electronic properties and elastic constants of Cd1-x-yZnx HgyTe alloys have been studied by employing the commercial code Castep based on density functional theory. The generalized gradient approximation and local density approximation were utilized as exchange correlation. Using elastic constants for compounds, bulk modulus, band gap, Fermi energy and Kramers-Kronig relations, dielectric constants and the refractive index have been found through calculations. Apart from these, X-ray measurements revealed elastic constants and Vegard's law. It is seen that results obtained from theory and experiments are all in agreement.

Structural, morphological and electrical properties of Sn-substituted Ni-Zn ferrites synthesized by double sintering technique

NASA Astrophysics Data System (ADS)

Ali, M. A.; Uddin, M. M.; Khan, M. N. I.; Chowdhury, F.-U.-Z.; Haque, S. M.

2017-02-01

The Sn-substituted Ni-Zn ferrites, (0.0≤x≤0.30), have been synthesized by the standard double sintering technique from the oxide nanopowders of Ni, Zn, Fe and Sn. The structural and electrical properties have been investigated by the X-ray diffraction (XRD), scanning electron microscopy (SEM), DC resistivity and dielectric measurements. From XRD data, the single cubic spinel phase has been confirmed for x≤0.1, whereas for x>0.1 an extra intermediate phase has been detected along with the cubic spinel phase of Ni-Zn ferrite. The grain size is increased due to Sn substitution in Ni-Zn ferrites. DC resistivity as a function of temperature has been measured by two probe method. The semiconducting nature has been found operative in the samples. The DC resistivity was found to decrease whilst the dielectric constant increased with increasing Sn content in Ni-Zn ferrites. The unusual behavior of the dielectric loss factor of the ferrites was explained by the Rezlescu model. The electrical relaxation of the ferrites has been studied in terms of electric modulus formalism and the time for dielectric relaxation was calculated. The contribution of grain resistance has been studied from the Cole-Cole plot. The suitability to use the as prepared samples in the miniaturized memory devices based capacitive components or energy storage principles are confirmed from the values of dielectric constant.

Thin-film composite materials as a dielectric layer for flexible metal-insulator-metal capacitors.

PubMed

Tiwari, Jitendra N; Meena, Jagan Singh; Wu, Chung-Shu; Tiwari, Rajanish N; Chu, Min-Ching; Chang, Feng-Chih; Ko, Fu-Hsiang

2010-09-24

A new organic-organic nanoscale composite thin-film (NCTF) dielectric has been synthesized by solution deposition of 1-bromoadamantane and triblock copolymer (Pluronic P123, BASF, EO20-PO70-EO20), in which the precursor solution has been achieved with organic additives. We have used a sol-gel process to make a metal-insulator-metal capacitor (MIM) comprising a nanoscale (10 nm-thick) thin-film on a flexible polyimide (PI) substrate at room temperature. Scanning electron microscope and atomic force microscope revealed that the deposited NCTFs were crack-free, uniform, highly resistant to moisture absorption, and well adhered on the Au-Cr/PI. The electrical properties of 1-bromoadamantane-P123 NCTF were characterized by dielectric constant, capacitance, and leakage current measurements. The 1-bromoadamantane-P123 NCTF on the PI substrate showed a low leakage current density of 5.5 x 10(-11) A cm(-2) and good capacitance of 2.4 fF at 1 MHz. In addition, the calculated dielectric constant of 1-bromoadamantane-P123 NCTF was 1.9, making them suitable candidates for use in future flexible electronic devices as a stable intermetal dielectric. The electrical insulating properties of 1-bromoadamantane-P123 NCTF have been improved due to the optimized dipole moments of the van der Waals interactions.

Effect of Fe3O4 addition on dielectric properties of LaFeO3 nano-crystalline materials synthesized by sol-gel method

NASA Astrophysics Data System (ADS)

Laysandra, H.; Triyono, D.

2017-04-01

Dielectric properties of nano-crystalline material LaFeO3.xFe3O4 with x = 0, 0.1, 0.2, 0.3, and 0.4 at.% have been studied by impedance spectroscopy method. LaFeO3 was synthesized by sol-gel method resulting nano-particle. Then, it was mixed with Fe3O4 powder. The mixture powder was pressed to form pellet and then sintered at 1300°C for 1 h to form nano-crystalline of LaFeO3.xFe3O4. X-ray diffraction characterization at room temperature for all samples show two phases i.e. perovskite LaFeO3 (orthorhombic) as a main phase and Fe3O4 (cubic) as second phase. It is found that the crystallite size of main phase increases with addition of Fe3O4 until 0.3 at.%. The electrical properties as a function of temperature (300-500 K) and frequency (100 Hz - 1 MHz) are presented in Nyquist and Bode plots. It is observed that from equivalent circuit and their parameters, dielectrical properties are contributed by grain and grain boundary. The dielectric constant, ε‧ were calculated by parallel plate method and their values reach up to 107 exhibiting typical colossal dielectric constant (CDC) material like behavior.

High dielectric hyperbranched polyaniline materials.

PubMed

Yan, X Z; Goodson, T

2006-08-03

New organic materials for the purpose of high speed capacitor applications are discussed. The effect of the microcrystalline size dependence of different polyaniline polymeric systems on the dielectric constant is investigated. Two different methods are described for the preparation of the polyaniline dielectric materials. By sonication polymerization, the prepared polyaniline with a suggested hyperbranched structure showed much larger microcrystalline domains in comparison to the conventional linear polyaniline. Investigations of the dielectric constant and capacitance at a relatively high frequency (>100 kHz) suggested that the system with the larger microcrystalline domains (hyperbranched) gives rise to a larger dielectric constant. The mechanism of the increased dielectric response at higher frequencies is investigated by EPR spectroscopy, and these results suggest that delocalized polarons may provide a way to enhance the dielectric response at high frequency.

Colossal dielectric constant up to gigahertz at room temperature

NASA Astrophysics Data System (ADS)

Krohns, S.; Lunkenheimer, P.; Kant, Ch.; Pronin, A. V.; Brom, H. B.; Nugroho, A. A.; Diantoro, M.; Loidl, A.

2009-03-01

The applicability of recently discovered materials with extremely high ("colossal") dielectric constants, required for future electronics, suffers from the fact that their dielectric constant ɛ' only is huge in a limited frequency range below about 1 MHz. In the present report, we show that the dielectric properties of a charge-ordered nickelate, La15/8Sr1/8NiO4, surpass those of other materials. Especially, ɛ' retains its colossal magnitude of >10 000 well into the gigahertz range.

Facile synthesis of Ni/NiO@GO nanocomposites and its enhanced dielectric constant

NASA Astrophysics Data System (ADS)

Sarkar, S.; Giri, N.; Mondal, A.; Ray, R.

2018-05-01

Ni/NiO embedded Graphene Oxide (GO): Ni/NiO@GO is synthesized by citric acid assisted Pechini-type method. Structural and morphological characterizations are performed by X-ray powdered diffraction (XRD), field emission scanning electron microscopy (FESEM) and tunneling electron microscopy (TEM). Defects in GO sheets are probed by RAMAN spectroscopy. The temperature variation of dielectric constant (ɛR) and dielectric loss (tan δ) are investigated in the temperature range 300 - 400 K. Decoration of GO with Ni/NiO nanoparticles enhances its ɛR by˜55 times. Moreover, its dielectric constant measured at 5 MHz is found to be˜430 times to that of Ni/NiO along with the reduction of dielectric loss by a factor˜0.5. The enhanced dielectric constant makes the composite Ni/NiO@GO a potential candidate for using in ecologically friendly energy storage devices.

Magnetoelectric Coupling in CuO Nanoparticles for Spintronics Applications

NASA Astrophysics Data System (ADS)

Kaur, Mandeep; Tovstolytkin, Alexandr; Lotey, Gurmeet Singh

2018-05-01

Multiferroic copper oxide (CuO) nanoparticles have been synthesized by colloidal synthesis method. The morphological, structural, magnetic, dielectric and magnetodielectric property has been investigated. The structural study reveals the monoclinic structure of CuO nanoparticles. Transmission electron microscopy images disclose that the size of the CuO nanoparticles is 18 nm and the synthesized nanoparticles are uniform in size and dispersion. Magnetic study tells the weak ferromagnetic character of CuO nanoparticles with coercivity and retentivity value 206 Oe and 0.060 emu/g respectively. Dielectric study confirms that the dielectric constant of CuO nanoparticles is around 1091 at low frequency. The magnetoelectric coupling in the synthesized CuO nanoparticles has been calculated by measuring magnetodielectric coupling coefficient.

Influence of Mn doping on structural, dielectric and optical properties of neodymium orthoferrite

NASA Astrophysics Data System (ADS)

Somvanshi, Anand; Manzoor, Samiya; Husain, Shahid

2018-05-01

We report the study of structural, dielectric and optical properties of nanocrystalline samples of NdFe1-xMnxO3 (x=0, 0.1 and 0.2) synthesized using solid state reaction route. X-ray diffraction (XRD) patterns are recorded to confirm phase purity. These samples conform in orthorhombic crystal symmetry with Pbnm space group. The lattice parameters are determined using Rietveld refinement. The crystallite size is calculated using Scherrer formula and that is found to lie in the range of 40-50 nm. The dielectric constant (ɛ') decreases with the increase in frequency as well as Mn doping concentration. Energy bandgap (Eg) as determined using UV-Vis. absorption spectra, is found to decrease with the increase in Mn doping.

Cole-cole analysis and electrical conduction mechanism of N{sup +} implanted polycarbonate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chawla, Mahak; Shekhawat, Nidhi; Aggarwal, Sanjeev, E-mail: write2sa@gmail.com

2014-05-14

In this paper, we present the analysis of the dielectric (dielectric constant, dielectric loss, a.c. conductivity) and electrical properties (I–V characteristics) of pristine and nitrogen ion implanted polycarbonate. The samples of polycarbonate were implanted with 100 keV N{sup +} ions with fluence ranging from 1 × 10{sup 15} to 1 × 10{sup 17} ions cm{sup −2}. The dielectric measurements of these samples were performed in the frequency range of 100 kHz to 100 MHz. It has been observed that dielectric constant decreases whereas dielectric loss and a.c. conductivity increases with increasing ion fluence. An analysis of real and imaginary parts of dielectric permittivity has beenmore » elucidated using Cole-Cole plot of the complex permittivity. With the help of Cole-Cole plot, we determined the values of static dielectric constant (ε{sub s}), optical dielectric constant (ε{sub ∞}), spreading factor (α), average relaxation time (τ{sub 0}), and molecular relaxation time (τ). The I–V characteristics were studied using Keithley (6517) electrometer. The electrical conduction behaviour of pristine and implanted polycarbonate specimens has been explained using various models of conduction.« less

Predictive methods of some optoelectronic properties for blends based on quaternized polysulfones

NASA Astrophysics Data System (ADS)

Dobos, Adina Maria; Filimon, Anca

2017-11-01

Blends based on quaternized polysulfones were investigated in terms of optical and electronic properties. By applying the Bicerano formalism the refractive index and dielectric constant were evaluated. Also, the dielectric constant of these blends was studied as a function of temperature and frequency. As the result of the main chain structure and charged groups, an increase in theoretical values of the refractive index and dielectric constant with increasing of the ionic quaternized units content in the polymer blend occurs. Additionally, decrease in the dielectric constant with the increase of frequency and decrease of temperature was observed. Refractive index and dielectric constant values indicate that the analyzed samples are transparent and can be used in obtaining of materials with applications involving a small polarizability. Thus, the results are important in prediction of the special optoelectronic features of new polymers blends to obtain high-performance materials with applications in electronic and biomedical fields.

Analysis of capacitive force acting on a cantilever tip at solid/liquid interfaces

NASA Astrophysics Data System (ADS)

Umeda, Ken-ichi; Kobayashi, Kei; Oyabu, Noriaki; Hirata, Yoshiki; Matsushige, Kazumi; Yamada, Hirofumi

2013-04-01

Dielectric properties of biomolecules or biomembranes are directly related to their structures and biological activities. Capacitance force microscopy based on the cantilever deflection detection is a useful scanning probe technique that can map local dielectric constant. Here we report measurements and analysis of the capacitive force acting on a cantilever tip at solid/liquid interfaces induced by application of an alternating voltage to explore the feasibility of the measurements of local dielectric constant by the voltage modulation technique in aqueous solutions. The results presented here suggest that the local dielectric constant measurements by the conventional voltage modulation technique are basically possible even in polar liquid media. However, the cantilever deflection is not only induced by the electrostatic force, but also by the surface stress, which does not include the local dielectric information. Moreover, since the voltage applied between the tip and sample are divided by the electric double layer and the bulk polar liquid, the capacitive force acting on the apex of the tip are strongly attenuated. For these reasons, the lateral resolution in the local dielectric constant measurements is expected to be deteriorated in polar liquid media depending on the magnitude of dielectric response. Finally, we present the criteria for local dielectric constant measurements with a high lateral resolution in polar liquid media.

Nonlocal continuum electrostatic theory predicts surprisingly small energetic penalties for charge burial in proteins.

PubMed

Bardhan, Jaydeep P

2011-09-14

We study the energetics of burying charges, ion pairs, and ionizable groups in a simple protein model using nonlocal continuum electrostatics. Our primary finding is that the nonlocal response leads to markedly reduced solvent screening, comparable to the use of application-specific protein dielectric constants. Employing the same parameters as used in other nonlocal studies, we find that for a sphere of radius 13.4 Å containing a single +1e charge, the nonlocal solvation free energy varies less than 18 kcal/mol as the charge moves from the surface to the center, whereas the difference in the local Poisson model is ∼35 kcal/mol. Because an ion pair (salt bridge) generates a comparatively more rapidly varying Coulomb potential, energetics for salt bridges are even more significantly reduced in the nonlocal model. By varying the central parameter in nonlocal theory, which is an effective length scale associated with correlations between solvent molecules, nonlocal-model energetics can be varied from the standard local results to essentially zero; however, the existence of the reduction in charge-burial penalties is quite robust to variations in the protein dielectric constant and the correlation length. Finally, as a simple exploratory test of the implications of nonlocal response, we calculate glutamate pK(a) shifts and find that using standard protein parameters (ε(protein) = 2-4), nonlocal results match local-model predictions with much higher dielectric constants. Nonlocality may, therefore, be one factor in resolving discrepancies between measured protein dielectric constants and the model parameters often used to match titration experiments. Nonlocal models may hold significant promise to deepen our understanding of macromolecular electrostatics without substantially increasing computational complexity. © 2011 American Institute of Physics

Off Axis Growth of Strontium Titanate Films with High Dielectric Constant Tuning and Low Loss

NASA Astrophysics Data System (ADS)

Kampangkeaw, Satreerat

2002-03-01

Using off-axis pulsed laser deposition, we have grown strontium titanate (STO) films on neodymium gallate (NGO) and lanthanum aluminate (LAO) substrates. We measured the film dielectric constant and loss tangent as a function of temperature in the 10kHz to 1 MHz frequency range. We found that the loss is less than 0.01 We also obtained a figure of merit from the relative variation of the dielectric constant divided by the loss tangent. The obtained figured of merit at 35K and 1MHz is about 1000 comparable to bulk values. The dielectric constant of these films can be changed by a factor of 4-8 in the presence of a DC electric field up to 5V/μm. The films show significant variations of dielectric properties grown on different substrates at different locations respect to the axis of the plume. The STO films on LAO having high dielectric constant and dielectric tuning were grown in region near the center of the plume. On the other hand, STO on NGO shows this effect only on the films grown far from the plume axis.

Improving dielectric properties of BaTiO3/poly(vinylidene fluoride) composites by employing core-shell structured BaTiO3@Poly(methylmethacrylate) and BaTiO3@Poly(trifluoroethyl methacrylate) nanoparticles

NASA Astrophysics Data System (ADS)

Zhang, Xianhong; Zhao, Sidi; Wang, Fang; Ma, Yuhong; Wang, Li; Chen, Dong; Zhao, Changwen; Yang, Wantai

2017-05-01

Polymer based dielectric composites were fabricated through incorporation of core-shell structured BaTiO3 (BT) nanoparticles into PVDF matrix by means of solution blending. Core-shell structured BT nanoparticles with different shell composition and shell thickness were prepared by grafting methacrylate monomer (MMA or TFEMA) onto the surface of BT nanoparticles via surface initiated atom transfer radical polymerization (SI-ATRP). The content of the grafted polymer and the micro-morphology of the core-shell structured BT nanoparticles were investigated by thermo gravimetric analyses (TGA) and transmission electron microscopy (TEM), respectively. The dielectric properties were measured by broadband dielectric spectroscopy. The results showed that high dielectric constant and low dielectric loss are successfully realized in the polymer based composites. Moreover, the type of the grafted polymer and its content had different effect on the dielectric constant. In detail, the attenuation of dielectric constant was 16.6% for BT@PMMA1/PVDF and 10.7% for BT@PMMA2/PVDF composite in the range of 10 Hz to 100 kHz, in which the grafted content of PMMA was 5.5% and 8.0%, respectively. However, the attenuation of dielectric constant was 5.5% for BT@PTFEMA1/PVDF and 4.0% for BT@PTFEMA2/PVDF composite, in which the grafted content of PTFEMA was 1.5% and 2.0%, respectively. These attractive features of BT@PTFEMA/PVDF composites suggested that dielectric ceramic fillers modified with fluorinated polymer can be used to prepare high performance composites, especially those with low dielectric loss and high dielectric constant.

Molecular dynamics studies of a DNA-binding protein: 2. An evaluation of implicit and explicit solvent models for the molecular dynamics simulation of the Escherichia coli trp repressor.

PubMed Central

Guenot, J.; Kollman, P. A.

1992-01-01

Although aqueous simulations with periodic boundary conditions more accurately describe protein dynamics than in vacuo simulations, these are computationally intensive for most proteins. Trp repressor dynamic simulations with a small water shell surrounding the starting model yield protein trajectories that are markedly improved over gas phase, yet computationally efficient. Explicit water in molecular dynamics simulations maintains surface exposure of protein hydrophilic atoms and burial of hydrophobic atoms by opposing the otherwise asymmetric protein-protein forces. This properly orients protein surface side chains, reduces protein fluctuations, and lowers the overall root mean square deviation from the crystal structure. For simulations with crystallographic waters only, a linear or sigmoidal distance-dependent dielectric yields a much better trajectory than does a constant dielectric model. As more water is added to the starting model, the differences between using distance-dependent and constant dielectric models becomes smaller, although the linear distance-dependent dielectric yields an average structure closer to the crystal structure than does a constant dielectric model. Multiplicative constants greater than one, for the linear distance-dependent dielectric simulations, produced trajectories that are progressively worse in describing trp repressor dynamics. Simulations of bovine pancreatic trypsin were used to ensure that the trp repressor results were not protein dependent and to explore the effect of the nonbonded cutoff on the distance-dependent and constant dielectric simulation models. The nonbonded cutoff markedly affected the constant but not distance-dependent dielectric bovine pancreatic trypsin inhibitor simulations. As with trp repressor, the distance-dependent dielectric model with a shell of water surrounding the protein produced a trajectory in better agreement with the crystal structure than a constant dielectric model, and the physical properties of the trajectory average structure, both with and without a nonbonded cutoff, were comparable. PMID:1304396

Nonintrinsic origin of the colossal dielectric constants in Ca Cu3 Ti4 O12

NASA Astrophysics Data System (ADS)

Lunkenheimer, P.; Fichtl, R.; Ebbinghaus, S. G.; Loidl, A.

2004-11-01

The dielectric properties of CaCu3Ti4O12 , a material showing colossal values of the dielectric constant, were investigated over a broad temperature and frequency range extending up to 1.3GHz . A detailed equivalent-circuit analysis of the results and two crucial experiments, employing different types of contacts and varying the sample thickness were performed. The results provide clear evidence that the apparently high values of the dielectric constant in CaCu3Ti4O12 are nonintrinsic and due to electrode polarization effects. The intrinsic properties of CaCu3Ti4O12 are characterized by charge transport via hopping of localized charge carriers and a relatively high dielectric constant of the order of 100.

Giant dielectric constant dominated by Maxwell-Wagner relaxation in Al{sub 2}O{sub 3}/TiO{sub 2} nanolaminates synthesized by atomic layer deposition.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, W.; Auciello, O.; Premnath, R. N.

2010-01-01

Nanolaminates consisting of Al{sub 2}O{sub 3} and TiO{sub 2} oxide sublayers were synthesized by using atomic layer deposition to produce individual layers with atomic scale thickness control. The sublayer thicknesses were kept constant for each multilayer structure, and were changed from 50 to 0.2 nm for a series of different samples. Giant dielectric constant ({approx}1000) was observed when the sublayer thickness is less than 0.5 nm, which is significantly larger than that of Al{sub 2}O{sub 3} and TiO{sub 2} dielectrics. Detailed investigation revealed that the observed giant dielectric constant is originated from the Maxwell-Wagner type dielectric relaxation.

Assessing the performance of the Tran-Blaha modified Becke-Johnson exchange potential for optical constants of semiconductors in the ultraviolet-visible light region

NASA Astrophysics Data System (ADS)

Nakano, Kousuke; Sakai, Tomohiro

2018-01-01

We report on the performance of density functional theory (DFT) with the Tran-Blaha modified Becke-Johnson exchange potential and the random phase approximation dielectric function for optical constants of semiconductors in the ultraviolet-visible (UV-Vis) light region. We calculate optical bandgaps Eg, refractive indices n, and extinction coefficients k of 70 semiconductors listed in the Handbook of Optical Constants of Solids [(Academic Press, 1985), Vol. 1; (Academic Press, 1991), Vol. 2; and (Academic Press, 1998), Vol. 3] and compare the results with experimental values. The results show that the calculated bandgaps and optical constants agree well with the experimental values to within 0.440 eV for Eg, 0.246-0.299 for n, and 0.207-0.598 for k in root mean squared error (RMSE). The small values of the RMSEs indicate that the optical constants of semiconductors in the UV-Vis region can be quantitatively predicted even by a low-cost DFT calculation of this type.

Physical aspects of colossal dielectric constant material CaCu3Ti4O12 thin films

NASA Astrophysics Data System (ADS)

Deng, Guochu; He, Zhangbin; Muralt, Paul

2009-04-01

The underlying physical mechanism of the so-called colossal dielectric constant phenomenon in CaCu3Ti4O12 (CCTO) thin films were investigated by using semiconductor theories and methods. The semiconductivity of CCTO thin films originated from the acceptor defect at a level ˜90 meV higher than valence band. Two contact types, metal-semiconductor and metal-insulator-semiconductor junctions, were observed and their barrier heights, and impurity concentrations were theoretically calculated. Accordingly, the Schottky barrier height of metal-semiconductor contact is about 0.8 eV, and the diffusion barrier height of metal-insulator-semiconductor contact is about 0.4-0.7 eV. The defect concentrations of both samples are quite similar, of the magnitude of 1019 cm-3, indicating an inherent feature of high defect concentration.

Dielectric and thermal modeling of Vesta's surface

NASA Astrophysics Data System (ADS)

Palmer, E. M.; Heggy, E.; Capria, M. T.; Tosi, F.; Russell, C. T.

2013-09-01

We generate a dielectric model for the surface of Vesta from thermal observations by Dawn's Visible and Infrared (VIR) mapping spectrometer. After retrieving surface temperatures from VIR data, we model thermal inertia, and derive a theoretical temperature map of Vesta's surface at a given UTC. To calculate the real part of the dielectric constant (ɛ') and the loss tangent (tg δ) we use the dielectric properties of basaltic lunar regolith as a first-order analog, assuming surface density and composition consistent with fine basaltic lunar dust. First results indicate that for the majority of the surface, ɛ' ranges from 2.0 to 2.1 from the night to day side respectively, and tg δ ranges from 1.05E-2 to 1.40E-2. While these regions are consistent with a basaltic, desiccated ~55% porous surface, we also find anomalies in the thermal inertia that may correspond to a variation in local surface density relative to the global average, and a consequent variation in the local dielectric properties.

Microstructures and dielectric properties of CaCu3Ti4O12 ceramics via combustion method

NASA Astrophysics Data System (ADS)

Yuan, W. X.; Li, Z. J.

2012-01-01

CaCu3Ti4O12 (CCTO) powder was synthesized by the combustion method. The effect of sintering temperature was studied on dielectric properties of the prepared ceramic samples. They have the dielectric constant of ~31 000 and 80 000 for the grain size of 0.3 and 30-100 μm. It is unusual for CCTO with a grain size of 0.3 μm to have a dielectric constant of ~31 000. Their giant dielectric constant could be explained by a two-step internal-barrier-layer-capacitor model, associated with grain boundaries and domain boundaries. The existence of domain boundaries helped to explain the contradiction of the dielectric mechanisms between polycrystalline and single-crystal CCTO.

Dielectric and Excess Properties of Glycols with Formamide Binary Mixtures at Different Temperatures

NASA Astrophysics Data System (ADS)

Navarkhele, V. V.

2018-07-01

Dielectric constant measurements of glycol-formamide binary solutions with various concentrations have been carried out at different temperatures. The dielectric measurement has been achieved at 100 MHz frequency using a sensor which is based on frequency domain reflectomery technique. The excess dielectric constant, Kirkwood correlation factor and Bruggeman factor has also been reported for the binary mixtures. The results show that the dielectric constant of the mixtures increases with increase in the volume fraction of formamide and decreases with increase in temperature. The study also confirms the presence of intermolecular interaction, hydrogen bonding and orientation of the dipoles in the binary mixtures.

Functionalised graphene sheets as effective high dielectric constant fillers

PubMed Central

2011-01-01

A new functionalised graphene sheet (FGS) filled poly(dimethyl)siloxane insulator nanocomposite has been developed with high dielectric constant, making it well suited for applications in flexible electronics. The dielectric permittivity increased tenfold at 10 Hz and 2 wt.% FGS, while preserving low dielectric losses and good mechanical properties. The presence of functional groups on the graphene sheet surface improved the compatibility nanofiller/polymer at the interface, reducing the polarisation process. This study demonstrates that functionalised graphene sheets are ideal nanofillers for the development of new polymer composites with high dielectric constant values. PACS: 78.20.Ci, 72.80.Tm, 62.23.Kn PMID:21867505

Functionalised graphene sheets as effective high dielectric constant fillers

NASA Astrophysics Data System (ADS)

Romasanta, Laura J.; Hernández, Marianella; López-Manchado, Miguel A.; Verdejo, Raquel

2011-08-01

A new functionalised graphene sheet (FGS) filled poly(dimethyl)siloxane insulator nanocomposite has been developed with high dielectric constant, making it well suited for applications in flexible electronics. The dielectric permittivity increased tenfold at 10 Hz and 2 wt.% FGS, while preserving low dielectric losses and good mechanical properties. The presence of functional groups on the graphene sheet surface improved the compatibility nanofiller/polymer at the interface, reducing the polarisation process. This study demonstrates that functionalised graphene sheets are ideal nanofillers for the development of new polymer composites with high dielectric constant values. PACS: 78.20.Ci, 72.80.Tm, 62.23.Kn

Evaluation of solvation free energies for small molecules with the AMOEBA polarizable force field

PubMed Central

Mohamed, Noor Asidah; Bradshaw, Richard T.

2016-01-01

The effects of electronic polarization in biomolecular interactions will differ depending on the local dielectric constant of the environment, such as in solvent, DNA, proteins, and membranes. Here the performance of the AMOEBA polarizable force field is evaluated under nonaqueous conditions by calculating the solvation free energies of small molecules in four common organic solvents. Results are compared with experimental data and equivalent simulations performed with the GAFF pairwise‐additive force field. Although AMOEBA results give mean errors close to “chemical accuracy,” GAFF performs surprisingly well, with statistically significantly more accurate results than AMOEBA in some solvents. However, for both models, free energies calculated in chloroform show worst agreement to experiment and individual solutes are consistently poor performers, suggesting non‐potential‐specific errors also contribute to inaccuracy. Scope for the improvement of both potentials remains limited by the lack of high quality experimental data across multiple solvents, particularly those of high dielectric constant. © 2016 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc. PMID:27757978

Performance and Self-Consistency of the Generalized Dielectric Dependent Hybrid Functional

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brawand, Nicholas P.; Govoni, Marco; Vörös, Márton

Here, we analyze the performance of the recently proposed screened exchange constant functional (SX) on the GW100 test set, and we discuss results obtained at different levels of self-consistency. The SX functional is a generalization of dielectric dependent hybrid functionals to finite systems; it is nonempirical and depends on the average screening of the exchange interaction. We compare results for ionization potentials obtained with SX to those of CCSD(T) calculations and experiments, and we find excellent agreement, on par with recent state of the art methods based on many body perturbation theory. Applying SX perturbatively to correct PBE eigenvalues yieldsmore » improved results in most cases, except for ionic molecules, for which wave function self-consistency is instead crucial. Calculations where wave functions and the screened exchange constant (α SX) are determined self-consistently, and those where α SX is fixed to the value determined within PBE, yield results of comparable accuracy. Perturbative G 0W 0 corrections of eigenvalues obtained with self-consistent αSX are small on average, for all molecules in the GW100 test set.« less

Performance and Self-Consistency of the Generalized Dielectric Dependent Hybrid Functional

DOE PAGES

Brawand, Nicholas P.; Govoni, Marco; Vörös, Márton; ...

2017-05-24

Here, we analyze the performance of the recently proposed screened exchange constant functional (SX) on the GW100 test set, and we discuss results obtained at different levels of self-consistency. The SX functional is a generalization of dielectric dependent hybrid functionals to finite systems; it is nonempirical and depends on the average screening of the exchange interaction. We compare results for ionization potentials obtained with SX to those of CCSD(T) calculations and experiments, and we find excellent agreement, on par with recent state of the art methods based on many body perturbation theory. Applying SX perturbatively to correct PBE eigenvalues yieldsmore » improved results in most cases, except for ionic molecules, for which wave function self-consistency is instead crucial. Calculations where wave functions and the screened exchange constant (α SX) are determined self-consistently, and those where α SX is fixed to the value determined within PBE, yield results of comparable accuracy. Perturbative G 0W 0 corrections of eigenvalues obtained with self-consistent αSX are small on average, for all molecules in the GW100 test set.« less

Comparison of calculation and experiment implicates significant electrostatic contributions to the binding stability of barnase and barstar.

PubMed

Dong, Feng; Vijayakumar, M; Zhou, Huan-Xiang

2003-07-01

The contributions of electrostatic interactions to the binding stability of barnase and barstar were studied by the Poisson-Boltzmann model with three different protocols: a), the dielectric boundary specified as the van der Waals (vdW) surface of the protein along with a protein dielectric constant (epsilon (p)) of 4; b), the dielectric boundary specified as the molecular (i.e., solvent-exclusion (SE)) surface along with epsilon (p) = 4; and c), "SE + epsilon (p) = 20." The "vdW + epsilon (p) = 4" and "SE + epsilon (p) = 20" protocols predicted an overall electrostatic stabilization whereas the "SE + epsilon (p) = 4" protocol predicted an overall electrostatic destabilization. The "vdW + epsilon (p) = 4" protocol was most consistent with experiment. It quantitatively reproduced the observed effects of 17 mutations neutralizing charged residues lining the binding interface and the measured coupling energies of six charge pairs across the interface and reasonably rationalized the experimental ionic strength and pH dependences of the binding constant. In contrast, the "SE + epsilon (p) = 4" protocol predicted significantly larger coupling energies of charge pairs whereas the "SE + epsilon (p) = 20" protocol did not predict any pH dependence. This study calls for further scrutiny of the different Poisson-Boltzmann protocols and demonstrates potential danger in drawing conclusions on electrostatic contributions based on a particular calculation protocol.

First-principle calculations of crystal structures, electronic structures, and optical properties of RETaO4 (RE = Y, La, Sm, Eu, Dy, Er)

NASA Astrophysics Data System (ADS)

Ma, Zhuang; Zheng, Jiayi; Wang, Song; Gao, Lihong

2018-01-01

It is an effective method to protect components from high power laser damage using high reflective materials. The rare earth tantalates RETaO4 with high dielectric constant suggests that they may have very high reflectivity, according to the relationship between dielectric constant and reflectivity. The crystal structures, electronic structures, and optical properties of RETaO4 (RE=Y, La, Sm, Eu, Dy, Er) have been studied by first-principle calculations. With the increasing atomic number of RE (i.e., the number of 4f electrons), a 4f electron shell moves from the bottom of conduction band to the forbidden gap and then to the valence band. The relationship between the electronic structures and optical properties is explored. The electron transitions among O 2p states, RE 4f states, and Ta 5d states have a key effect on optical properties such as dielectric function, absorption coefficient, and reflectivity. For the series of RETaO4, the appearance of the 4f electronic states will obviously promote the improvement of reflectivity. When the 4f states appear at the middle of the forbidden gap, the reflectivity reaches the maximum. The reflectivity of EuTaO4 at 1064 nm is up to 93.47%, indicating that it has potential applications in the antilaser radiation area.

Improved linearity in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors with nonlinear polarization dielectric

NASA Astrophysics Data System (ADS)

Gao, Tao; Xu, Ruimin; Kong, Yuechan; Zhou, Jianjun; Kong, Cen; Dong, Xun; Chen, Tangsheng

2015-06-01

We demonstrate highly improved linearity in a nonlinear ferroelectric of Pb(Zr0.52Ti0.48)-gated AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT). Distinct double-hump feature in the transconductance-gate voltage (gm-Vg) curve is observed, yielding remarkable enhancement in gate voltage swing as compared to MIS-HEMT with conventional linear gate dielectric. By incorporating the ferroelectric polarization into a self-consistent calculation, it is disclosed that in addition to the common hump corresponding to the onset of electron accumulation, the second hump at high current level is originated from the nonlinear polar nature of ferroelectric, which enhances the gate capacitance by increasing equivalent dielectric constant nonlinearly. This work paves a way for design of high linearity GaN MIS-HEMT by exploiting the nonlinear properties of dielectric.

Three-dimensional function photonic crystals

NASA Astrophysics Data System (ADS)

Zhang, Hai-Feng

2017-11-01

In this paper, the properties of the photonic band gaps (PBGs) of three-dimensional (3D) function photonic crystals (PCs) are theoretically investigated by a modified plane wave expansion (PWE) method, whose equations for computations are deduced. The configuration of 3D function PCs is the dielectric spheres inserted in the air background with simple-cubic (SC) lattices whose dielectric constants are the functions of space coordinates, which can be realized by the electro-optical or optical Kerr effect in the practice. The influences of the parameter for 3D function PCs on the PBGs also are discussed. The calculated results show that the bandwidths and number of PBGs can be tuned with different distributions of function dielectrics. Compared with the conventional 3D dielectric PCs with SC lattices, the larger and more PBGs can be obtained in the 3D function PCs. Those results provide a new way to design the novel practical devices.

Impedance and electric modulus approaches to investigate four origins of giant dielectric constant in CaCu3Ti4O12 ceramics

NASA Astrophysics Data System (ADS)

Yuan, Wen-Xiang

2012-03-01

The frequency dependence of electric modulus of polycrystalline CaCu3Ti4O12 (CCTO) ceramics has been investigated. The experimental data have also been analyzed in the complex plane of impedance and electric modulus, and a suitable equivalent circuit has been proposed to explain the dielectric response. Four dielectric responses are first distinguished in the impedance and modulus spectroscopies. The results are well interpreted in terms of a triple insulating barrier capacitor model. Using this model, these four dielectric relaxations are attributed to the domain, domain-boundary, grain-boundary, and surface layer effects with three Maxwell-Wagner relaxations. Moreover, the values of the resistance and capacitance of bulk CCTO phase, domain-boundary, grain-boundary and surface layer contributions have been calculated directly from the peak characteristics of spectroscopic plots.

Suppression of spin and optical gaps in phosphorene quantum dots

NASA Astrophysics Data System (ADS)

Zhang, Yingjie; Sheng, Weidong

2018-05-01

Electronic structure and optical properties of triangular phosphorene quantum dots have been investigated theoretically. Based on systematic configuration interaction calculations, the ground and excited states of the interacting many-electron system together with its optical absorption spectrum are obtained. For the nanodot with 60 phosphorus atoms in various dielectric environments, it is found that the spin gap of the correlated system surprisingly overlaps its optical gap over a large range of the effective dielectric constant. The overlapping of the spin and optical gaps can be attributed to the fact that the extra correlation energy in the spin singlet almost compensates the exchange energy in the spin triplet in the presence of strong long-range electron-electron interactions. Moreover, both the spin and optical gaps are shown to be greatly suppressed as the screening effect becomes strong. When the dielectric constant decreases below 2.65, it is seen that the spin gap becomes negative and the quantum dot undergoes a phase transition from nonmagnetic to ferromagnetic. Our results are compared with the previous experimental and theoretical works.

Quantitative thickness measurement of polarity-inverted piezoelectric thin-film layer by scanning nonlinear dielectric microscopy

NASA Astrophysics Data System (ADS)

Odagawa, Hiroyuki; Terada, Koshiro; Tanaka, Yohei; Nishikawa, Hiroaki; Yanagitani, Takahiko; Cho, Yasuo

2017-10-01

A quantitative measurement method for a polarity-inverted layer in ferroelectric or piezoelectric thin film is proposed. It is performed nondestructively by scanning nonlinear dielectric microscopy (SNDM). In SNDM, linear and nonlinear dielectric constants are measured using a probe that converts the variation of capacitance related to these constants into the variation of electrical oscillation frequency. In this paper, we describe a principle for determining the layer thickness and some calculation results of the output signal, which are related to the radius of the probe tip and the thickness of the inverted layer. Moreover, we derive an equation that represents the relationship between the output signal and the oscillation frequency of the probe and explain how to determine the thickness from the measured frequency. Experimental results in Sc-doped AlN piezoelectric thin films that have a polarity-inverted layer with a thickness of 1.5 µm fabricated by radio frequency magnetron sputtering showed a fairly good value of 1.38 µm for the thickness of the polarity-inverted layer.

First-Principles Calculations of Structural, Electronic and Optical Properties of Ternary Semiconductor Alloys ZAs x Sb1- x ( Z = B, Al, Ga, In)

NASA Astrophysics Data System (ADS)

Bounab, S.; Bentabet, A.; Bouhadda, Y.; Belgoumri, Gh.; Fenineche, N.

2017-08-01

We have investigated the structural and electronic properties of the BAs x Sb 1- x , AlAs x Sb 1- x , GaAs x Sb 1- x and InAs x Sb 1- x semiconductor alloys using first-principles calculations under the virtual crystal approximation within both the density functional perturbation theory and the pseudopotential approach. In addition the optical properties have been calculated by using empirical methods. The ground state properties such as lattice constants, both bulk modulus and derivative of bulk modulus, energy gap, refractive index and optical dielectric constant have been calculated and discussed. The obtained results are in reasonable agreement with numerous experimental and theoretical data. The compositional dependence of the lattice constant, bulk modulus, energy gap and effective mass of electrons for ternary alloys show deviations from Vegard's law where our results are in agreement with the available data in the literature.

Thermal conductivity and thermal boundary resistance of atomic layer deposited high-k dielectric aluminum oxide, hafnium oxide, and titanium oxide thin films on silicon

NASA Astrophysics Data System (ADS)

Scott, Ethan A.; Gaskins, John T.; King, Sean W.; Hopkins, Patrick E.

2018-05-01

The need for increased control of layer thickness and uniformity as device dimensions shrink has spurred increased use of atomic layer deposition (ALD) for thin film growth. The ability to deposit high dielectric constant (high-k) films via ALD has allowed for their widespread use in a swath of optical, optoelectronic, and electronic devices, including integration into CMOS compatible platforms. As the thickness of these dielectric layers is reduced, the interfacial thermal resistance can dictate the overall thermal resistance of the material stack compared to the resistance due to the finite dielectric layer thickness. Time domain thermoreflectance is used to interrogate both the thermal conductivity and the thermal boundary resistance of aluminum oxide, hafnium oxide, and titanium oxide films on silicon. We calculate a representative design map of effective thermal resistances, including those of the dielectric layers and boundary resistances, as a function of dielectric layer thickness, which will be of great importance in predicting the thermal resistances of current and future devices.

Evolutionary search for new high-k dielectric materials: methodology and applications to hafnia-based oxides.

PubMed

Zeng, Qingfeng; Oganov, Artem R; Lyakhov, Andriy O; Xie, Congwei; Zhang, Xiaodong; Zhang, Jin; Zhu, Qiang; Wei, Bingqing; Grigorenko, Ilya; Zhang, Litong; Cheng, Laifei

2014-02-01

High-k dielectric materials are important as gate oxides in microelectronics and as potential dielectrics for capacitors. In order to enable computational discovery of novel high-k dielectric materials, we propose a fitness model (energy storage density) that includes the dielectric constant, bandgap, and intrinsic breakdown field. This model, used as a fitness function in conjunction with first-principles calculations and the global optimization evolutionary algorithm USPEX, efficiently leads to practically important results. We found a number of high-fitness structures of SiO2 and HfO2, some of which correspond to known phases and some of which are new. The results allow us to propose characteristics (genes) common to high-fitness structures--these are the coordination polyhedra and their degree of distortion. Our variable-composition searches in the HfO2-SiO2 system uncovered several high-fitness states. This hybrid algorithm opens up a new avenue for discovering novel high-k dielectrics with both fixed and variable compositions, and will speed up the process of materials discovery.

Hamaker constants of iron oxide nanoparticles.

PubMed

Faure, Bertrand; Salazar-Alvarez, German; Bergström, Lennart

2011-07-19

The Hamaker constants for iron oxide nanoparticles in various media have been calculated using Lifshitz theory. Expressions for the dielectric responses of three iron oxide phases (magnetite, maghemite, and hematite) were derived from recently published optical data. The nonretarded Hamaker constants for the iron oxide nanoparticles interacting across water, A(1w1) = 33 - 39 zJ, correlate relatively well with previous reports, whereas the calculated values in nonpolar solvents (hexane and toluene), A(131) = 9 - 29 zJ, are much lower than the previous estimates, particularly for magnetite. The magnitude of van der Waals interactions varies significantly between the studied phases (magnetite < maghemite < hematite), which highlights the importance of a thorough characterization of the particles. The contribution of magnetic dispersion interactions for particle sizes in the superparamagnetic regime was found to be negligible. Previous conjectures related to colloidal stability and self-assembly have been revisited on the basis of the new Lifshitz values of the Hamaker constants.

Dielectric and spectroscopic study of binary mixture of Acrylonitrile with Chlorobenzene

NASA Astrophysics Data System (ADS)

Deshmukh, Snehal D.; Pattebahadur, K. L.; Mohod, A. G.; Undre, P. B.; Patil, S. S.; Khirade, P. W.

2018-05-01

In this paper, study of binary mixture of Acrylonitrile (ACN) with Chlorobenzene (CBZ) has been carried out at eleven concentrations at room temperature. The determined Dielectric Constant (ɛ0) Density (ρ) and Refractive index (nD) values of binary mixture are used to calculate the excess properties of mixture over the entire composition range and fitted to the Redlich-Kister equation. From the above parameters, intermolecular interaction and dynamics of molecules of binary mixture at molecular level are discussed. The Conformational analysis of the intermolecular interaction between Acrylonitrile and Chlorobenzene is supported by the FTIR spectra.

Quantum-dot size and thin-film dielectric constant: precision measurement and disparity with simple models.

PubMed

Grinolds, Darcy D W; Brown, Patrick R; Harris, Daniel K; Bulovic, Vladimir; Bawendi, Moungi G

2015-01-14

We study the dielectric constant of lead sulfide quantum dot (QD) films as a function of the volume fraction of QDs by varying the QD size and keeping the ligand constant. We create a reliable QD sizing curve using small-angle X-ray scattering (SAXS), thin-film SAXS to extract a pair-distribution function for QD spacing, and a stacked-capacitor geometry to measure the capacitance of the thin film. Our data support a reduced dielectric constant in nanoparticles.

Effect of Cold Temperature on the Dielectric Constant of Soil

DTIC Science & Technology

2012-04-01

explosive device (IED) threats is ground-penetrating radar ( GPR ). Proper development of GPR technology for this application requires a unique...success or failure of GPR as a detection technique. One soil property of interest to radar engineers is the dielectric constant. Previous...results to temperatures, moisture levels, and frequencies relevant to GPR systems. 2. Dielectric Constant and the Ring-resonator Concept The two

In-situ GPR test for three-dimensional mapping of the dielectric constant in a rock mass

NASA Astrophysics Data System (ADS)

Elkarmoty, Mohamed; Colla, Camilla; Gabrielli, Elena; Papeschi, Paolo; Bonduà, Stefano; Bruno, Roberto

2017-11-01

The Ground Penetrating Radar (GPR) is used to detect subsurface anomalies in several applications. The more the velocity of propagation or the dielectric constant is estimated accurately, the more the detection of anomalies at true subsurface depth can be accurately obtained. Since many GPR applications are performed in rock mass with non-homogeneous discontinuous nature, errors in estimating a bulk velocity of propagation or dielectric constant are possible. This paper presents a new in-situ GPR test for mapping the dielectric constant variability in a rock mass. The main aim is to investigate to what extent the dielectric constant is variable in the micro and macro scale of a typical rock mass and to give attention to GPR users in rock mass mediums. The methodology of this research is based on the insertion of steel rods in a rock mass, thus acting as reflectors. The velocity of propagation can be then modeled, from hyperbolic reflections, in the form of velocity pathways from antenna positions to a buried rod. Each pathway is characterized by discrete points which are assumed in three dimensions as centers of micro cubic rock mass. This allows converting the velocity of propagation into a dielectric constant for mapping and modeling the dielectric constant in a volumetric rock mass using a volumetric data visualization software program (Voxler). In a case study, 6 steel drilling rods were diagonally inserted in a vertical face of a bench in a sandstone quarry. Five equally spaced parallel lines, almost perpendicular to the orientations of the rods, were surveyed by a dual frequency GPR antenna of 200 and 600 MHz. The results show that the dielectric constant is randomly varied within the micro and macro scale either in single radargrams or in the volumetric rock mass. The proposed method can be useful if considered in signal processing software programs, particularly in presence of subsurface utilities with known geometry and dimension, allowing converting double travel time, through portions of a radargram, into more reliable depths using discrete dielectric constant values instead of one value for a whole radargram.

High-gradient compact linear accelerator

DOEpatents

Carder, B.M.

1998-05-26

A high-gradient linear accelerator comprises a solid-state stack in a vacuum of five sets of disc-shaped Blumlein modules each having a center hole through which particles are sequentially accelerated. Each Blumlein module is a sandwich of two outer conductive plates that bracket an inner conductive plate positioned between two dielectric plates with different thicknesses and dielectric constants. A third dielectric core in the shape of a hollow cylinder forms a casing down the series of center holes, and it has a dielectric constant different that the two dielectric plates that sandwich the inner conductive plate. In operation, all the inner conductive plates are charged to the same DC potential relative to the outer conductive plates. Next, all the inner conductive plates are simultaneously shorted to the outer conductive plates at the outer diameters. The signal short will propagate to the inner diameters at two different rates in each Blumlein module. A faster wave propagates quicker to the third dielectric core across the dielectric plates with the closer spacing and lower dielectric constant. When the faster wave reaches the inner extents of the outer and inner conductive plates, it reflects back outward and reverses the field in that segment of the dielectric core. All the field segments in the dielectric core are then in unipolar agreement until the slower wave finally propagates to the third dielectric core across the dielectric plates with the wider spacing and higher dielectric constant. During such unipolar agreement, particles in the core are accelerated with gradients that exceed twenty megavolts per meter. 10 figs.

High-gradient compact linear accelerator

DOEpatents

Carder, Bruce M.

1998-01-01

A high-gradient linear accelerator comprises a solid-state stack in a vacuum of five sets of disc-shaped Blumlein modules each having a center hole through which particles are sequentially accelerated. Each Blumlein module is a sandwich of two outer conductive plates that bracket an inner conductive plate positioned between two dielectric plates with different thicknesses and dielectric constants. A third dielectric core in the shape of a hollow cylinder forms a casing down the series of center holes, and it has a dielectric constant different that the two dielectric plates that sandwich the inner conductive plate. In operation, all the inner conductive plates are charged to the same DC potential relative to the outer conductive plates. Next, all the inner conductive plates are simultaneously shorted to the outer conductive plates at the outer diameters. The signal short will propagate to the inner diameters at two different rates in each Blumlein module. A faster wave propagates quicker to the third dielectric core across the dielectric plates with the closer spacing and lower dielectric constant. When the faster wave reaches the inner extents of the outer and inner conductive plates, it reflects back outward and reverses the field in that segment of the dielectric core. All the field segments in the dielectric core are then in unipolar agreement until the slower wave finally propagates to the third dielectric core across the dielectric plates with the wider spacing and higher dielectric constant. During such unipolar agreement, particles in the core are accelerated with gradients that exceed twenty megavolts per meter.

Dielectric characteristics of CaCu3Ti4O12/P(VDF-TrFE) nanocomposites

NASA Astrophysics Data System (ADS)

Zhang, Lin; Shan, Xiaobing; Wu, Peixuan; Cheng, Z.-Y.

2012-06-01

Composite thin film is highly desirable for the dielectric applications. In order to develop composite thin film, a nanocomposite, in which nanosized CaCu3Ti4O12 (CCTO) particles are used as filler and P(VDF-TrFE) 55/45 mol% copolymer is used as polymer matrix, is investigated. The contents of CCTO in the nanocomposites range from 0% to 50 vol%. The dielectric property of these nanocomposites was characterized at frequencies ranging from 100 Hz to 1 MHz and at temperatures ranging from 200 K to 370 K. A dielectric constant of 62 with a loss of 0.05 was obtained in nanocomposite with 50 vol% CCTO at room temperature at 1 kHz. At the phase transition temperature (˜340 K) of the copolymer, a dielectric constant of 150 with a loss less than 0.1 was obtained in this nanocomposite. It is found that the dielectric loss of the nanocomposites is dominated by the polymer which has a relaxation process. Comparing to composites made using microsized CCTO, the nanocomposites exhibit a much lower dielectric loss and a lower dielectric constant. This indicates that the nanosized CCTO particles have a lower dielectric constant than the microsized CCTO particles.

PLZT capacitor and method to increase the dielectric constant

DOEpatents

Taylor, Ralph S.; Fairchild, Manuel Ray; Balachjandran, Uthamalingam; Lee, Tae H.

2017-12-12

A ceramic-capacitor includes a first electrically-conductive-layer, a second electrically-conductive-layer arranged proximate to the first electrically-conductive-layer, and a dielectric-layer interposed between the first electrically-conductive-layer and the second electrically-conductive-layer. The dielectric-layer is formed of a lead-lanthanum-zirconium-titanate material (PLZT), wherein the PLZT is characterized by a dielectric-constant greater than 125, when measured at 25 degrees Celsius and zero Volts bias, and an excitation frequency of ten-thousand Hertz (10 kHz). A method for increasing a dielectric constant of the lead-lanthanum-zirconium-titanate material (PLZT) includes the steps of depositing PLZT to form a dielectric-layer of a ceramic-capacitor, and heating the ceramic-capacitor to a temperature not greater than 300.degree. C.

Let's Measure the Dielectric Constant of a Piece of Paper!

ERIC Educational Resources Information Center

Karlow, Edwin A.

1991-01-01

Described is a simple circuit with which students can observe the effect of common dielectric materials in a capacitor and measure the dielectric constant of a piece of paper. Discussed are the theory, apparatus construction, and experimental procedures for this activity. (CW)

Increase of dielectric constant in PVDF by incorporating La{sub 1.8}Sr{sub 0.2}NiO{sub 4} into its matrix

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Rajnish, E-mail: rajnish@iitp.ac.in; Goswami, Ashwin M., E-mail: ashwin.nanoplast@gmail.com; Kar, Manoranjan, E-mail: mano-iitg@yahoo.com

2016-05-06

To obtain the material with high dielectric constant and high dielectric strength for the technological applications, nanocomposite of Lanthanum Strontium Nickelete (La{sub 1.8}Sr{sub 0.2}NiO{sub 4}) as nanofiller and polyvinylidene fluoride (PVDF) as polymer matrix has been prepared. The different nanofiler weight concentration varies from 2-8 weight percent. X-ray diffraction technique confirms the phase formation of nanocomposite. Differential scanning calorimeter (DSC) has been employed to study the percentage of crystallinity and Impedance measurement has been carried out to study the dielectric constant. DSC analysis shows decreasing trend of crystallinity whereas impedance analysis gives increasing dielectric constant with increasing La{sub 1.8}Sr{sub 0.2}NiO{submore » 4} concentration in the nanocomposite. Also, these materials can be used as insulator in the transformer as the strength and dielectric behavior of present composite meets the technological requirements.« less

Correlation potential of a test ion near a strongly charged plate.

PubMed

Lu, Bing-Sui; Xing, Xiangjun

2014-03-01

We analytically calculate the correlation potential of a test ion near a strongly charged plate inside a dilute m:-n electrolyte. We do this by calculating the electrostatic Green's function in the presence of a nonlinear background potential, the latter having been obtained using the nonlinear Poisson-Boltzmann theory. We consider the general case where the dielectric constants of the plate and the electrolyte are distinct. The following generic results emerge from our analyses: (1) If the distance to the plate Δz is much larger than a Gouy-Chapman length, the plate surface will behave effectively as an infinitely charged surface, and the dielectric constant of the plate effectively plays no role. (2) If Δz is larger than a Gouy-Chapman length but shorter than a Debye length, the correlation potential can be interpreted in terms of an image charge that is three times larger than the source charge. This behavior is independent of the valences of the ions. (3) The Green's function vanishes inside the plate if the surface charge density is infinitely large; hence the electrostatic potential is constant there. In this respect, a strongly charged plate behaves like a conductor plate. (4) If Δz is smaller than a Gouy-Chapman length, the correlation potential is dominated by the conventional image charge due to the dielectric discontinuity at the interface. (5) If Δz is larger than a Debye length, the leading order behavior of the correlation potential will depend on the valences of the ions in the electrolyte. Furthermore, inside an asymmetric electrolyte, the correlation potential is singly screened, i.e., it undergoes exponential decay with a decay width equal to the Debye length.

Low-Thermal-Expansion Filled Polytetrafluoroethylene

NASA Technical Reports Server (NTRS)

Shapiro, Sanford S.

1989-01-01

PTFE made thermally compatible with aluminum without changing dielectric constant. Manufactured with fillers and pores to reduce coefficient of thermal expansion by factor of 6 to match aluminum. Material retains 2.1 dielectric constant of pure PTFE. Combines filler and micropore concepts. Particles and voids embedded in PTFE matrix function cooperatively. Particles take up compressive stress imposed by contracting PTFE, and voids take up expanding material. Increases dielectric constant, while voids reduce it.

Investigation of structural, electronic, elastic and optical properties of Cd{sub 1-x-y}Zn{sub x}Hg{sub y}Te alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tamer, M., E-mail: mehmet.tamer@zirve.edu.tr

2016-06-15

Structural, optical and electronic properties and elastic constants of Cd1{sub -x-y}Zn{sub x} Hg{sub y}Te alloys have been studied by employing the commercial code Castep based on density functional theory. The generalized gradient approximation and local density approximation were utilized as exchange correlation. Using elastic constants for compounds, bulk modulus, band gap, Fermi energy and Kramers–Kronig relations, dielectric constants and the refractive index have been found through calculations. Apart from these, X-ray measurements revealed elastic constants and Vegard’s law. It is seen that results obtained from theory and experiments are all in agreement.

Study of electrical properties of Sc doped BaFe12O19 ceramic using dielectric, impedance, modulus spectroscopy and AC conductivity

NASA Astrophysics Data System (ADS)

Gupta, Surbhi; Deshpande, S. K.; Sathe, V. G.; Siruguri, V.

2018-04-01

We present dielectric, complex impedance, modulus spectroscopy and AC conductivity studies of the compound BaFe10Sc2O19 as a function of temperature and frequency to understand the conduction mechanism. The variation in complex dielectric constant with frequency and temperature were analyzed on the basis of Maxwell-Wagner-Koop's theory and charge hopping between ferrous and ferric ions. The complex impedance spectroscopy study shows only grain contribution whereas complex modulus plot shows two semicircular arcs which indicate both grain and grain boundary contributions in conduction mechanism. AC conductivity has also been evaluated which follows the Jonscher's law. The activation energy calculated from temperature dependence of DC conductivity comes out to be Ea˜ 0.31eV.

Optical properties of armchair (7, 7) single walled carbon nanotubes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gharbavi, K.; Badehian, H., E-mail: hojatbadehian@gmail.com

2015-07-15

Full potential linearized augmented plane waves method with the generalized gradient approximation for the exchange-correlation potential was applied to calculate the optical properties of (7, 7) single walled carbon nanotubes. The both x and z directions of the incident photons were applied to estimate optical gaps, dielectric function, electron energy loss spectroscopies, optical conductivity, optical extinction, optical refractive index and optical absorption coefficient. The results predict that dielectric function, ε (ω), is anisotropic since it has higher peaks along z-direction than x-direction. The static optical refractive constant were calculated about 1.4 (z-direction) and 1.1 (x- direction). Moreover, the electron energymore » loss spectroscopy showed a sharp π electron plasmon peaks at about 6 eV and 5 eV for z and x-directions respectively. The calculated reflection spectra show that directions perpendicular to the tube axis have further optical reflection. Moreover, z-direction indicates higher peaks at absorption spectra in low range energies. Totally, increasing the diameter of armchair carbon nanotubes cause the optical band gap, static optical refractive constant and optical reflectivity to decrease. On the other hand, increasing the diameter cause the optical absorption and the optical conductivity to increase. Moreover, the sharp peaks being illustrated at optical spectrum are related to the 1D structure of CNTs which confirm the accuracy of the calculations.« less

Substrate Screening Effects in ab initio Many-body Green's Function Calculations of Doped Graphene on SiC

NASA Astrophysics Data System (ADS)

Vigil-Fowler, Derek; Lischner, Johannes; Louie, Steven

2013-03-01

Understanding many-electron interaction effects and the influence of the substrate in graphene-on-substrate systems is of great theoretical and practical interest. Thus far, both model Hamiltonian and ab initio GW calculations for the quasiparticle properties of such systems have employed crude models for the effect of the substrate, often approximating the complicated substrate dielectric matrix by a single constant. We develop a method in which the spatially-dependent dielectric matrix of the substrate (e.g., SiC) is incorporated into that of doped graphene to obtain an accurate total dielectric matrix. We present ab initio GW + cumulant expansion calculations, showing that both the cumulant expansion (to include higher-order electron correlations) and a proper account of the substrate screening are needed to achieve agreement with features seen in ARPES. We discuss how this methodology could be used in other systems. This work was supported by NSF Grant No. DMR10-1006184 and U.S. DOE Contract No. DE-AC02-05CH11231. Computational resources have been provided by the NERSC and NICS. D.V-F. acknowledges funding from the DOD's NDSEG fellowship.

A DFT study on structural, vibrational properties, and quasiparticle band structure of solid nitromethane.

PubMed

Appalakondaiah, S; Vaitheeswaran, G; Lebègue, S

2013-05-14

We report a detailed theoretical study of the structural and vibrational properties of solid nitromethane using first principles density functional calculations. The ground state properties were calculated using a plane wave pseudopotential code with either the local density approximation, the generalized gradient approximation, or with a correction to include van der Waals interactions. Our calculated equilibrium lattice parameters and volume using a dispersion correction are found to be in reasonable agreement with the experimental results. Also, our calculations reproduce the experimental trends in the structural properties at high pressure. We found a discontinuity in the bond length, bond angles, and also a weakening of hydrogen bond strength in the pressure range from 10 to 12 GPa, picturing the structural transition from phase I to phase II. Moreover, we predict the elastic constants of solid nitromethane and find that the corresponding bulk modulus is in good agreement with experiments. The calculated elastic constants show an order of C11> C22 > C33, indicating that the material is more compressible along the c-axis. We also calculated the zone center vibrational frequencies and discuss the internal and external modes of this material under pressure. From this, we found the softening of lattice modes around 8-11 GPa. We have also attempted the quasiparticle band structure of solid nitromethane with the G0W0 approximation and found that nitromethane is an indirect band gap insulator with a value of the band gap of about 7.8 eV with G0W0 approximation. Finally, the optical properties of this material, namely the absorptive and dispersive part of the dielectric function, and the refractive index and absorption spectra are calculated and the contribution of different transition peaks of the absorption spectra are analyzed. The static dielectric constant and refractive indices along the three inequivalent crystallographic directions indicate that this material has a considerable optical anisotropy.

Band alignment of semiconductors and insulators using dielectric-dependent hybrid functionals: Toward high-throughput evaluation

NASA Astrophysics Data System (ADS)

Hinuma, Yoyo; Kumagai, Yu; Tanaka, Isao; Oba, Fumiyasu

2017-02-01

The band alignment of prototypical semiconductors and insulators is investigated using first-principles calculations. A dielectric-dependent hybrid functional, where the nonlocal Fock exchange mixing is set at the reciprocal of the static electronic dielectric constant and the exchange correlation is otherwise treated as in the Perdew-Burke-Ernzerhof (PBE0) hybrid functional, is used as well as the Heyd-Scuseria-Ernzerhof (HSE06) hybrid and PBE semilocal functionals. In addition, these hybrid functionals are applied non-self-consistently to accelerate calculations. The systems considered include C and Si in the diamond structure, BN, AlP, AlAs, AlSb, GaP, GaAs, InP, ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe in the zinc-blende structure, MgO in the rocksalt structure, and GaN and ZnO in the wurtzite structure. Surface band positions with respect to the vacuum level, i.e., ionization potentials and electron affinities, and band offsets at selected zinc-blende heterointerfaces are evaluated as well as band gaps. The non-self-consistent approach speeds up hybrid functional calculations by an order of magnitude, while it is shown using HSE06 that the resultant band gaps and surface band positions are similar to the self-consistent results. The dielectric-dependent hybrid functional improves the band gaps and surface band positions of wide-gap systems over HSE06. The interfacial band offsets are predicted with a similar degree of precision. Overall, the performance of the dielectric-dependent hybrid functional is comparable to the G W0 approximation based on many-body perturbation theory in the prediction of band gaps and alignments for most systems. The present results demonstrate that the dielectric-dependent hybrid functional, particularly when applied non-self-consistently, is promising for applications to systematic calculations or high-throughput screening that demand both computational efficiency and sufficient accuracy.

A review on data and predictions of water dielectric spectra for calculations of van der Waals surface forces.

PubMed

Wang, Jianlong; Nguyen, Anh V

2017-12-01

Van der Waals forces are one of the important components of intermolecular, colloidal and surface forces governing many phenomena and processes. The latest examples include the colloidal interactions between hydrophobic colloids and interfaces in ambient (non-degassed) water in which dissolved gases and nanobubbles are shown to affect the van der Waals attractions significantly. The advanced computation of van der Waals forces in aqueous systems by the Lifshitz theory requires reliable data for water dielectric spectra. In this paper we review the available predictions of water dielectric spectra for calculating colloidal and surface van der Waals forces. Specifically, the available experimental data for the real and imaginary parts of the complex dielectric function of liquid water in the microwave, IR and UV regions and various corresponding predictions of the water spectra are critically reviewed. The data in the UV region are critical, but the available predictions are still based on the outdated data obtained in 1974 (for frequency only up to 25.5eV). We also reviewed and analysed the experimental data obtained for the UV region in 2000 (for frequency up to 50eV) and 2015 (for frequency up to 100eV). The 1974 and 2000 data require extrapolations to higher frequencies needed for calculating the van der Waals forces but remain inaccurate. Our analysis shows that the latest data of 2015 do not require the extrapolation and can be used to reliably calculate van der Waals forces. The most recent water dielectric spectra gives the (non-retarded) Hamaker constant, A=5.20×10 -20 J, for foam films of liquid water. This review provides the most updated and reliable water dielectric spectra to compute van der Waals forces in aqueous systems. Copyright © 2017 Elsevier B.V. All rights reserved.

Dynamic properties of III-V polytypes from density-functional theory

NASA Astrophysics Data System (ADS)

Benyahia, N.; Zaoui, A.; Madouri, D.; Ferhat, M.

2017-03-01

The recently discovered hexagonal wurtzite phase of several III-V nanowires opens up strong opportunity to engineer optoelectronic and transport properties of III-V materials. Herein, we explore the dynamical and dielectric properties of cubic (3C) and wurtzite (2H) III-V compounds (AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, and InSb). For cubic III-V compounds, our calculated phonon frequencies agree well with neutron diffraction and Raman-scattering measurements. In the case of 2H III-V materials, our calculated phonon modes at the zone-center Γ point are in distinguished agreement with available Raman-spectroscopy measurements of wurtzite GaAs, InP, GaP, and InAs nanowires. Particularly, the "fingerprint" of the wurtzite phase, which is our predicted E2(high) phonon mode, at 261 cm-1(GaAs), 308 cm-1(InP), 358 cm-1(GaP), and 214 cm-1(InAs) matches perfectly the respective Raman values of 258 cm-1, 306.4 cm-1, 353 cm-1, and 213.7 cm-1 for GaAs, InP, GaP, and InAs. Moreover, the dynamic charges and high-frequency dielectric constants are predicted for III-V materials in both cubic (3C) and hexagonal (2H) crystal polytypes. It is found that the dielectric properties of InAs and InSb contrast markedly from those of other 2H III-V compounds. Furthermore, InAs and InSb evidence relative strong anisotropy in their dielectric constants and Born effective charges, whereas GaP evinces the higher Born effective charge anisotropy of 2H III-V compounds.

Quantum chemistry in arbitrary dielectric environments: Theory and implementation of nonequilibrium Poisson boundary conditions and application to compute vertical ionization energies at the air/water interface

NASA Astrophysics Data System (ADS)

Coons, Marc P.; Herbert, John M.

2018-06-01

Widely used continuum solvation models for electronic structure calculations, including popular polarizable continuum models (PCMs), usually assume that the continuum environment is isotropic and characterized by a scalar dielectric constant, ɛ. This assumption is invalid at a liquid/vapor interface or any other anisotropic solvation environment. To address such scenarios, we introduce a more general formalism based on solution of Poisson's equation for a spatially varying dielectric function, ɛ(r). Inspired by nonequilibrium versions of PCMs, we develop a similar formalism within the context of Poisson's equation that includes the out-of-equilibrium dielectric response that accompanies a sudden change in the electron density of the solute, such as that which occurs in a vertical ionization process. A multigrid solver for Poisson's equation is developed to accommodate the large spatial grids necessary to discretize the three-dimensional electron density. We apply this methodology to compute vertical ionization energies (VIEs) of various solutes at the air/water interface and compare them to VIEs computed in bulk water, finding only very small differences between the two environments. VIEs computed using approximately two solvation shells of explicit water molecules are in excellent agreement with experiment for F-(aq), Cl-(aq), neat liquid water, and the hydrated electron, although errors for Li+(aq) and Na+(aq) are somewhat larger. Nonequilibrium corrections modify VIEs by up to 1.2 eV, relative to models based only on the static dielectric constant, and are therefore essential to obtain agreement with experiment. Given that the experiments (liquid microjet photoelectron spectroscopy) may be more sensitive to solutes situated at the air/water interface as compared to those in bulk water, our calculations provide some confidence that these experiments can indeed be interpreted as measurements of VIEs in bulk water.

Quantum chemistry in arbitrary dielectric environments: Theory and implementation of nonequilibrium Poisson boundary conditions and application to compute vertical ionization energies at the air/water interface.

PubMed

Coons, Marc P; Herbert, John M

2018-06-14

Widely used continuum solvation models for electronic structure calculations, including popular polarizable continuum models (PCMs), usually assume that the continuum environment is isotropic and characterized by a scalar dielectric constant, ε. This assumption is invalid at a liquid/vapor interface or any other anisotropic solvation environment. To address such scenarios, we introduce a more general formalism based on solution of Poisson's equation for a spatially varying dielectric function, ε(r). Inspired by nonequilibrium versions of PCMs, we develop a similar formalism within the context of Poisson's equation that includes the out-of-equilibrium dielectric response that accompanies a sudden change in the electron density of the solute, such as that which occurs in a vertical ionization process. A multigrid solver for Poisson's equation is developed to accommodate the large spatial grids necessary to discretize the three-dimensional electron density. We apply this methodology to compute vertical ionization energies (VIEs) of various solutes at the air/water interface and compare them to VIEs computed in bulk water, finding only very small differences between the two environments. VIEs computed using approximately two solvation shells of explicit water molecules are in excellent agreement with experiment for F - (aq), Cl - (aq), neat liquid water, and the hydrated electron, although errors for Li + (aq) and Na + (aq) are somewhat larger. Nonequilibrium corrections modify VIEs by up to 1.2 eV, relative to models based only on the static dielectric constant, and are therefore essential to obtain agreement with experiment. Given that the experiments (liquid microjet photoelectron spectroscopy) may be more sensitive to solutes situated at the air/water interface as compared to those in bulk water, our calculations provide some confidence that these experiments can indeed be interpreted as measurements of VIEs in bulk water.

Correlations of structural, magnetic, and dielectric properties of undoped and doped CaCu3Ti4O12

NASA Astrophysics Data System (ADS)

Krohns, S.; Lu, J.; Lunkenheimer, P.; Brizé, V.; Autret-Lambert, C.; Gervais, M.; Gervais, F.; Bourée, F.; Porcher, É. F.; Loidl, A.

2009-11-01

The present work reports synthesis, as well as a detailed and careful characterization of structural, magnetic, and dielectric properties of differently tempered undoped and doped CaCu3Ti4O12 (CCTO) ceramics. For this purpose, neutron and X-ray powder diffraction, SQUID measurements, and dielectric spectroscopy have been performed. Mn-, Fe-, and Ni-doped CCTO ceramics were investigated in great detail to document the influence of low-level doping with 3d metals on the antiferromagnetic structure and dielectric properties. In the light of possible magnetoelectric coupling in these doped ceramics, the dielectric measurements were also carried out in external magnetic fields up to 7 T. At low temperatures the dielectric constant shows a minor but significant dependence on the applied magnetic field. Undoped CCTO is well-known for its colossal dielectric constant in a broad frequency and temperature range. With the present extended characterization of doped as well as undoped CCTO, we want to address the question why doping with only 1% Mn or 0.5% Fe decreases the room-temperature dielectric constant of CCTO by a factor of ~100 with a concomitant reduction of the conductivity, whereas 0.5% Ni doping changes the dielectric properties only slightly. In addition, diffraction experiments and magnetic investigations were undertaken to check for possible correlations of the magnitude of the colossal dielectric constants with structural details or with magnetic properties like the magnetic ordering, the Curie-Weiss temperatures, or the paramagnetic moment. It is revealed, that while the magnetic ordering temperature and the effective moment of all investigated CCTO ceramics are rather similar, there is a dramatic influence of doping and tempering time on the Curie-Weiss constant.

THE STUDY OF HIGH DIELECTRIC CONSTANT MECHANISM OF La-DOPED Ba0.67Sr0.33TiO3 CERAMICS

NASA Astrophysics Data System (ADS)

Xu, Jing; He, Bo; Liu, Han Xing

It is a common and effective method to enhance the dielectric properties of BST ceramics by adding rare-earth elements. In this paper, it is important to analyze the cause of the high dielectric constant behavior of La-doped BST ceramics. The results show that proper rare earth La dopant (0.2≤x≤0.7) may greatly increase the dielectric constant of BST ceramics, and also improve the temperature stability, evidently. According to the current-voltage (J-V) characteristics, the proper La-doped BST ceramics may reach the better semiconductivity, with the decrease and increase in La doping, the ceramics are insulators. By using the Schottky barrier model and electric microstructure model to find the surface or grain boundary potential barrier height, the width of the depletion layer and grain size do play an important role in impacting the dielectric constant.

Physical properties and solubility parameters of 1-ethyl-3-methylimidazolium based ionic liquids/DMSO mixtures at 298.15 K

NASA Astrophysics Data System (ADS)

Saba, H.; Yumei, Z.; Huaping, W.

2015-12-01

Densities, refractive indices, conductivities and viscosities of binary mixtures of 1-ethyl-3-methylimidazolium-based ionic liquids (ILs) with dimethyl sulfoxide at 298.15 K are reported. Excess molar volumes have been calculated from experimental data and were fitted with Redlich-Kister equation. The density and refractive index were found to increase with increasing concentration in all cases except [EMIM]COOH. The free mobility of ions has found to enhance conductivity and decrease viscosity to varying extent in all mixtures being studied. It has been observed that solubility parameters, dielectric constants and nature of anions of ILs being used play a vital role in determining the subsequent characteristics. As DMSO has high dielectric constant therefore, it was able to form interactions with most of ILs except with [EMIM]COOH due to anomalous nature of anion.

Viking landing sites, remote-sensing observations, and physical properties of Martian surface materials

USGS Publications Warehouse

Moore, H.J.; Jakosky, B.M.

1989-01-01

Important problems that confront future scientific exploration of Mars include the physical properties of Martian surface materials and the geologic processes that formed the materials. The design of landing spacecraft, roving vehicles, and sampling devices and the selection of landing sites, vehicle traverses, and sample sites will be, in part, guided by the physical properties of the materials. Four materials occur in the sample fields of the Viking landers: (1) drift, (2) crusty to cloddy, (3) blocky, and (4) rock. The first three are soillike. Drift materials is weak, loose, and porous. We estimate that it has a dielectric constant near 2.4 and a thermal inertia near 1 ?? 10-3 to 3 ?? 10-3 (cal cm-2 sec 1 2 K-1) because of its low bulk density, fine grain size, and small cohesion. Crusty to cloddy material is expected to have a dielectric constant near 2.8 and a thermal inertia near 4 ?? 10-3 to 7 ?? 10-3 because of its moderate bulk density and cementation of grains. Blocky material should have a dielectric constant near 3.3 and a thermal inertia near 7 ?? 10-3 to 9 ?? 10-3 because of its moderate bulk density and cementation. Common basaltic rocks have dielectric constans near 8 and thermal inertias near 30 ?? 10-3 to 60 ?? 10-3. Comparisons of estimated dielectric constants and thermal inertias of the materials at the landing sites with those obtained remotely by Earth-based radars and Viking Orbiter thermal sensors suggest that the materials at the landing sites are good analogs for materials elsewhere on Mars. Correlation of remotely estimated dielectric constant and thermal inertias indicates two modal values for paired values of dielectric constants and thermal inertias near (A) 2 and 2 ?? 10-3 and (B) 3 and 6 ?? 10-3, respectively. These two modes are comparable to the dielectric constants and thermal inertias for drift and crusty to cloddy material, respectively. Dielectric constants and thermal inertias for blocky material are larger but conistent with values in the northern plains. Our interprertations are compatible with an aeolian origin for drift and similar materials elsewhere on Mars. The postulate that moderate dielectric constants and thermal inertias larger than 3 or 4 ?? 10-3 are produced by cementation of soillike materials is partly consistent with the data. The average dielectric constant and thermal inertia and their correlation with one another suggest that most of the surface of Mars should present few difficulties to future surface exploration, but some surfaces may present difficulties for spacecraft that are not suitably designed. ?? 1989.

Light induced dielectric constant of Alumina doped lead silicate glass based on silica sands

NASA Astrophysics Data System (ADS)

Diantoro, Markus; Natalia, Desi Ayu; Mufti, Nandang; Hidayat, Arif

2016-04-01

Numerous studies on glass ceramic compounds have been conducted intensively. Two major problems to be solved are to simplify the fabrication process by reducing melting temperature as well as improving various properties for various fields of technological application. To control the dielectric constant, the researchers generally use a specific dopant. So far there is no comprehensive study to control the dielectric constant driven by both of dopant and light intensity. In this study it is used Al2O3 dopant to increase the light induced dielectric constant of the glass. The source of silica was taken from local silica sands of Bancar Tuban. The sands were firstly leached using hydrochloric acid to improve the purity of silica which was investigated by means of XRF. Fabricating the glass samples were performed by using melting-glass method. Silica powder was mixed with various ratio of SiO2:Na2CO3:PbO:Al2O3. Subsequently, a mixture of various Al2O3 doped lead silicate glasses were melted at 970°C and directy continued by annealed at 300°C. The samples were investigated by XRD, FTIR, SEM-EDX and measuring dielectric constant was done using dc-capacitance meter with various light intensities. The investigation result of XRD patterns showed that the crystal structures of the samples are amorphous state. The introduction of Al2O3 does not alter the crystal structure, but significantly change the structure of the functional glass bonding PbO-SiO2 which was shown by the FTIR spectra. It was noted that some new peak peaks were exist in the doped samples. Measuring result of dielectricity shows that the dielectric constant of glass increases with the addition of Al2O3. Increasing the light intensity gives rise to increase their dielectric constant in general. A detail observation of the dielectric seen that there are discontinuous step-like of dielectric. Most likely a specific quantization mechanism occurs when glass exposed under light.

Strongly nonlinear composite dielectrics: A perturbation method for finding the potential field and bulk effective properties

NASA Astrophysics Data System (ADS)

Blumenfeld, Raphael; Bergman, David J.

1991-10-01

A class of strongly nonlinear composite dielectrics is studied. We develop a general method to reduce the scalar-potential-field problem to the solution of a set of linear Poisson-type equations in rescaled coordinates. The method is applicable for a large variety of nonlinear materials. For a power-law relation between the displacement and the electric fields, it is used to solve explicitly for the value of the bulk effective dielectric constant ɛe to second order in the fluctuations of its local value. A simlar procedure for the vector potential, whose curl is the displacement field, yields a quantity analogous to the inverse dielectric constant in linear dielectrics. The bulk effective dielectric constant is given by a set of linear integral expressions in the rescaled coordinates and exact bounds for it are derived.

Microwave dielectric properties of boreal forest trees

NASA Technical Reports Server (NTRS)

Xu, G.; Ahern, F.; Brown, J.

1993-01-01

The knowledge of vegetation dielectric behavior is important in studying the scattering properties of the vegetation canopy and radar backscatter modelling. Until now, a limited number of studies have been published on the dielectric properties in the boreal forest context. This paper presents the results of the dielectric constant as a function of depth in the trunks of two common boreal forest species: black spruce and trembling aspen, obtained from field measurements. The microwave penetration depth for the two species is estimated at C, L, and P bands and used to derive the equivalent dielectric constant for the trunk as a whole. The backscatter modelling is carried out in the case of black spruce and the results are compared with the JPL AIRSAR data. The sensitivity of the backscatter coefficient to the dielectric constant is also examined.

Electronic structure and defect properties of selenophosphate Pb2P2Se6 for γ-ray detection

NASA Astrophysics Data System (ADS)

Kontsevoi, Oleg Y.; Im, Jino; Wessels, Bruce W.; Kanatzidis, Mercouri G.; Freeman, Arthur J.

Heavy metal chalco-phosphate Pb2P2Se6 has shown a significant promise as an X-ray and γ-ray detector material. To assess the fundamental physical properties important for its performance as detector, theoretical calculations were performed for the electronic structure, band gaps, electron and hole effective masses, and static dielectric constants. The calculations were based on first-principles density functional theory (DFT) and employ the highly precise full potential linearized augmented plane wave method and the projector augmented wave method and include nonlocal exchange-correlation functionals to overcome the band gap underestimation in DFT calculations. The calculations show that Pb2P2Se6 is an indirect band gap material with the calculated band gap of 2.0 eV, has small effective masses, which could result in a good carrier mobility-lifetime product μτ , and a very high static dielectric constant, which could lead to high mobility of carriers by screening of charged scattering centers. We further investigated a large set of native defects in Pb2P2Se6 to determine the optimal growth conditions for application as γ-ray detectors. The results suggest that the prevalent intrinsic defects are selenium vacancies, followed by lead vacancies, then phosphorus vacancies and antisite defects. The effect of various chemical environments on defect properties was examined and the optimal conditions for material synthesis were suggested. Supported by DHS (Grant No. 2014-DN-077-ARI086-01).

Imaging performance of an isotropic negative dielectric constant slab.

PubMed

Shivanand; Liu, Huikan; Webb, Kevin J

2008-11-01

The influence of material and thickness on the subwavelength imaging performance of a negative dielectric constant slab is studied. Resonance in the plane-wave transfer function produces a high spatial frequency ripple that could be useful in fabricating periodic structures. A cost function based on the plane-wave transfer function provides a useful metric to evaluate the planar slab lens performance, and using this, the optimal slab dielectric constant can be determined.

An improved model for the dielectric constant of sea water at microwave frequencies

NASA Technical Reports Server (NTRS)

Klein, L. A.; Swift, C. T.

1977-01-01

The advent of precision microwave radiometry has placed a stringent requirement on the accuracy with which the dielectric constant of sea water must be known. To this end, measurements of the dielectric constant have been conducted at S-band and L-band with a quoted uncertainty of tenths of a percent. These and earlier results are critically examined, and expressions are developed which will yield computations of brightness temperature having an error of no more than 0.3 K for an undisturbed sea at frequencies lower than X-band. At the higher microwave and millimeter wave frequencies, the accuracy is in question because of uncertainties in the relaxation time and the dielectric constant at infinite frequency.

First principles calculations of optical properties of the armchair SiC nanoribbons with O, F and H termination

NASA Astrophysics Data System (ADS)

Lu, Dao-Bang; Song, Yu-Ling

2018-03-01

Based on density functional theory, we perform first-principles investigations to study the optical properties of the O-, F- and H-terminated SiC nanoribbons with armchair edges (ASiCNRs). By irradiating with an external electromagnetic field, we calculate the dielectric function, reflection spectra, energy loss coefficient and the real part of the conductance. It is demonstrated that the optical constants are sensitive to the low-energy range, different terminal atoms do not make much difference in the shape of the curves of the optical constants for the same-width ASiCNR, and the optical constants of wider nanoribbons usually have higher peaks than that of the narrower ones in low energy range. We hope that our study helps in experimental technology of fabricating high-quality SiC-based nanoscale photoelectric device.

Hadron mass and decays constant predictions of the valence approximation to lattice QCD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weingarten, D.

1993-05-01

A key goal of the lattice formulation of QCD is to reproduce the masses and decay constants of the low-lying baryons and mesons. Lattice QCD mass and decay constant predictions for the real world are supposed to be obtained from masses and decay constants calculated with finite lattice spacing and finite lattice volume by taking the limits of zero spacing and infinite volume. In addition, since the algorithms used for hadron mass and decay constant calculations become progressively slower for small quark masses, results are presently found with quark masses much larger than the expected values of the up andmore » down quark masses. Predictions for the properties of hadrons containing up and down quarks then require a further extrapolation to small quark masses. The author reports here mass and decay constant predictions combining all three extrapolations for Wilson quarks in the valence (quenched) approximation. This approximation may be viewed as replacing the momentum and frequency dependent color dielectric constant arising from quark-antiquark vacuum polarization with its zero-momentum, zero-frequency limit. These calculations used approximately one year of machine time on the GF11 parallel computer running at a sustained rate of between 5 and 7 Gflops.« less

Study of Some Dielectric Properties of Suspensions of Magnesium Particles in Mineral Oil

NASA Technical Reports Server (NTRS)

Altshuller, Aubrey P

1954-01-01

The variation of dielectric constant has been measured as a function of the concentration of magnesium particles; the shape, size, and degree of oxidation of the particles; the temperature; and the frequency of oscillation. The variation of dielectric constant and settling rate was investigated as a function of time. Also investigated were the effects of particle concentration, shape and time on dielectric losses.

Preparation of a Carbon Doped Tissue-Mimicking Material with High Dielectric Properties for Microwave Imaging Application

PubMed Central

Lan, Siang-Wen; Weng, Min-Hang; Yang, Ru-Yuan; Chang, Shoou-Jinn; Chung, Yaoh-Sien; Yu, Tsung-Chih; Wu, Chun-Sen

2016-01-01

In this paper, the oil-in-gelatin based tissue-mimicking materials (TMMs) doped with carbon based materials including carbon nanotube, graphene ink or lignin were prepared. The volume percent for gelatin based mixtures and oil based mixtures were both around 50%, and the doping amounts were 2 wt %, 4 wt %, and 6 wt %. The effect of doping material and amount on the microwave dielectric properties including dielectric constant and conductivity were investigated over an ultra-wide frequency range from 2 GHz to 20 GHz. The coaxial open-ended reflection technology was used to evaluate the microwave dielectric properties. Six measured values in different locations of each sample were averaged and the standard deviations of all the measured dielectric properties, including dielectric constant and conductivity, were less than one, indicating a good uniformity of the prepared samples. Without doping, the dielectric constant was equal to 23 ± 2 approximately. Results showed with doping of carbon based materials that the dielectric constant and conductivity both increased about 5% to 20%, and the increment was dependent on the doping amount. By proper selection of doping amount of the carbon based materials, the prepared material could map the required dielectric properties of special tissues. The proposed materials were suitable for the phantom used in the microwave medical imaging system. PMID:28773678

Effect of Bi doping on morphotropic phase boundary and dielectric properties of PZT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joshi, Shraddha; Acharya, Smita, E-mail: saha275@yahoo.com

2016-05-23

In our present attempt, Pb{sub (1-x)}Bi{sub x}Zr{sub 0.52}Ti{sub 0.48}O{sub 3} [PBZT] {where x = 0, 0.05, 0.1} is synthesized by sol-gel route. Effect of Bi addition on structure, sinterability and dielectric properties are observed. The presence of morphotropic phase boundary (coexistence of tetragonal and rhombohedral symmetry) is confirmed by X-ray diffraction. Enhancement of sinterability after Bi doping is observed through a systematic sintering program. Frequency and temperature dependent dielectric constant are studied. Bi doping in PZT is found to enhance room temperature dielectric constant. However, at high temperature the dielectric constant of pure PZT is more than that of dopedmore » PZT.« less

Dielectric properties of single wall carbon nanotubes-based gelatin phantoms

NASA Astrophysics Data System (ADS)

Altarawneh, M. M.; Alharazneh, G. A.; Al-Madanat, O. Y.

In this work, we report the dielectric properties of Single wall Carbon Nanotubes (SWCNTs)-based phantom that is mainly composed of gelatin and water. The fabricated gelatin-based phantom with desired dielectric properties was fabricated and doped with different concentrations of SWCNTs (e.g., 0%, 0.05%, 0.10%, 0.15%, 0.2%, 0.4% and 0.6%). The dielectric constants (real ɛ‧ and imaginary ɛ‧‧) were measured at different positions for each sample as a function of frequency (0.5-20GHz) and concentrations of SWCNTs and their averages were found. The Cole-Cole plot (ɛ‧ versus ɛ‧‧) was obtained for each concentration of SWCNTs and was used to obtain the static dielectric constant ɛs, the dielectric constant at the high limit of frequency ɛ∞ and the average relaxation time τ. The measurements showed that the fabricated samples are in good homogeneity and the SWCNTs are dispersed well in the samples as an acceptable standard deviation is achieved. The study showed a linear increase in the static dielectric constant ɛs and invariance of the average relaxation time τ and the value of ɛ∞ at room temperature for the investigated concentrations of SWCNTs.

Process and Microstructure to Achieve Ultra-high Dielectric Constant in Ceramic-Polymer Composites.

PubMed

Zhang, Lin; Shan, Xiaobing; Bass, Patrick; Tong, Yang; Rolin, Terry D; Hill, Curtis W; Brewer, Jeffrey C; Tucker, Dennis S; Cheng, Z-Y

2016-10-21

Influences of process conditions on microstructure and dielectric properties of ceramic-polymer composites are systematically studied using CaCu 3 Ti 4 O 12 (CCTO) as filler and P(VDF-TrFE) 55/45 mol.% copolymer as the matrix by combining solution-cast and hot-pressing processes. It is found that the dielectric constant of the composites can be significantly enhanced-up to about 10 times - by using proper processing conditions. The dielectric constant of the composites can reach more than 1,000 over a wide temperature range with a low loss (tan δ ~ 10 -1 ). It is concluded that besides the dense structure of composites, the uniform distribution of the CCTO particles in the matrix plays a key role on the dielectric enhancement. Due to the influence of the CCTO on the microstructure of the polymer matrix, the composites exhibit a weaker temperature dependence of the dielectric constant than the polymer matrix. Based on the results, it is also found that the loss of the composites at low temperatures, including room temperature, is determined by the real dielectric relaxation processes including the relaxation process induced by the mixing.

Process and Microstructure to Achieve Ultra-high Dielectric Constant in Ceramic-Polymer Composites

NASA Astrophysics Data System (ADS)

Zhang, Lin; Shan, Xiaobing; Bass, Patrick; Tong, Yang; Rolin, Terry D.; Hill, Curtis W.; Brewer, Jeffrey C.; Tucker, Dennis S.; Cheng, Z.-Y.

2016-10-01

Influences of process conditions on microstructure and dielectric properties of ceramic-polymer composites are systematically studied using CaCu3Ti4O12 (CCTO) as filler and P(VDF-TrFE) 55/45 mol.% copolymer as the matrix by combining solution-cast and hot-pressing processes. It is found that the dielectric constant of the composites can be significantly enhanced-up to about 10 times - by using proper processing conditions. The dielectric constant of the composites can reach more than 1,000 over a wide temperature range with a low loss (tan δ ~ 10-1). It is concluded that besides the dense structure of composites, the uniform distribution of the CCTO particles in the matrix plays a key role on the dielectric enhancement. Due to the influence of the CCTO on the microstructure of the polymer matrix, the composites exhibit a weaker temperature dependence of the dielectric constant than the polymer matrix. Based on the results, it is also found that the loss of the composites at low temperatures, including room temperature, is determined by the real dielectric relaxation processes including the relaxation process induced by the mixing.

In-situ preparation of hierarchical flower-like TiO2/carbon nanostructures as fillers for polymer composites with enhanced dielectric properties

PubMed Central

Xu, Nuoxin; Zhang, Qilong; Yang, Hui; Xia, Yuting; Jiang, Yongchang

2017-01-01

Novel three-dimensional hierarchical flower-like TiO2/carbon (TiO2/C) nanostructures were in-situ synthesized via a solvothermal method involving calcination of organic precursor under inert atmosphere. The composite films comprised of P (VDF-HFP) and as-prepared hierarchical flower-like TiO2/C were fabricated by a solution casting and hot-pressing approach. The results reveal that loading the fillers with a small amount of carbon is an effective way to improve the dielectric constant and suppress the dielectric loss. In addition, TiO2/C particles with higher carbon contents exhibit superiority in promoting the dielectric constants of composites when compared with their noncarbon counterparts. For instance, the highest dielectric constant (330.6) of the TiO2/C composites is 10 times over that of noncarbon-TiO2-filled ones at the same filler volume fraction, and 32 times over that of pristine P (VDF-HFP). The enhancement in the dielectric constant can be attributed to the formation of a large network, which is composed of local micro-capacitors with carbon particles as electrodes and TiO2 as the dielectric in between. PMID:28262766

Process and Microstructure to Achieve Ultra-high Dielectric Constant in Ceramic-Polymer Composites

PubMed Central

Zhang, Lin; Shan, Xiaobing; Bass, Patrick; Tong, Yang; Rolin, Terry D.; Hill, Curtis W.; Brewer, Jeffrey C.; Tucker, Dennis S.; Cheng, Z.-Y.

2016-01-01

Influences of process conditions on microstructure and dielectric properties of ceramic-polymer composites are systematically studied using CaCu3Ti4O12 (CCTO) as filler and P(VDF-TrFE) 55/45 mol.% copolymer as the matrix by combining solution-cast and hot-pressing processes. It is found that the dielectric constant of the composites can be significantly enhanced–up to about 10 times – by using proper processing conditions. The dielectric constant of the composites can reach more than 1,000 over a wide temperature range with a low loss (tan δ ~ 10−1). It is concluded that besides the dense structure of composites, the uniform distribution of the CCTO particles in the matrix plays a key role on the dielectric enhancement. Due to the influence of the CCTO on the microstructure of the polymer matrix, the composites exhibit a weaker temperature dependence of the dielectric constant than the polymer matrix. Based on the results, it is also found that the loss of the composites at low temperatures, including room temperature, is determined by the real dielectric relaxation processes including the relaxation process induced by the mixing. PMID:27767184

Constant fields and constant gradients in open ionic channels.

PubMed Central

Chen, D P; Barcilon, V; Eisenberg, R S

1992-01-01

Ions enter cells through pores in proteins that are holes in dielectrics. The energy of interaction between ion and charge induced on the dielectric is many kT, and so the dielectric properties of channel and pore are important. We describe ionic movement by (three-dimensional) Nemst-Planck equations (including flux and net charge). Potential is described by Poisson's equation in the pore and Laplace's equation in the channel wall, allowing induced but not permanent charge. Asymptotic expansions are constructed exploiting the long narrow shape of the pore and the relatively high dielectric constant of the pore's contents. The resulting one-dimensional equations can be integrated numerically; they can be analyzed when channels are short or long (compared with the Debye length). Traditional constant field equations are derived if the induced charge is small, e.g., if the channel is short or if the total concentration gradient is zero. A constant gradient of concentration is derived if the channel is long. Plots directly comparable to experiments are given of current vs voltage, reversal potential vs. concentration, and slope conductance vs. concentration. This dielectric theory can easily be tested: its parameters can be determined by traditional constant field measurements. The dielectric theory then predicts current-voltage relations quite different from constant field, usually more linear, when gradients of total concentration are imposed. Numerical analysis shows that the interaction of ion and channel can be described by a mean potential if, but only if, the induced charge is negligible, that is to say, the electric field is spatially constant. Images FIGURE 1 PMID:1376159

Growth, structural, thermal, dielectric and nonlinear optical properties of potassium hexachloro cadmate (IV) a novel single crystal

NASA Astrophysics Data System (ADS)

Umarani, P.; Jagannathan, K.

2018-02-01

The Potassium hexachloro cadmate (IV) (PHC) single crystal was grown from the aqueous of the solution by a controlled evaporation method. Single crystal XRD solved the structure. FTIR is used to identify the functional groups of grown crystal. The UV-Vis-NIR spectrometer was used to find out the UV cut off region and to calculate the optical band gap of the Potassium hexachloro cadmate (IV) single crystal. The EDAX spectrum has been used to identify the compounds present in title compound. The TG-DTA profile shows the thermal stability of the grown crystal of Potassium hexachloro cadmate (IV). The Vicker's hardness measurement was used to calculate the material hardness of the title compound. The dielectric loss and constant varied with frequencies and activation energy is also calculated. The solid state parameters like plasma energy, Penn gap, Fermi energy, electronic polarizability using Penn analysis and Clausius-Mossotti equation were also calculated for the title compound. The Z-scan technique is used to calculate the third order nonlinear susceptibility of a real and imaginary part.

L-band Dielectric Constant Measurements of Seawater (Oral presentation and SMOS Poster)

NASA Technical Reports Server (NTRS)

Lang, Roger H.; Utku, Cuneyt; LeVine, David M.

2003-01-01

This paper describes a resonant cavity technique for the measurement of the dielectric constant of seawater as a function of its salinity. Accurate relationships between salinity and dielectric constant (which determines emissivity) are needed for sensor systems such as SMOS and Aquarius that will monitor salinity from space in the near future. The purpose of the new measurements is to establish the dependence of the dielectric constant of seawater on salinity in contemporary units (e.g. psu) and to take advantage of modern instrumentation to increase the accuracy of these measurements. The measurement device is a brass cylindrical cavity 16cm in diameter and 7cm in height. The seawater is introduced into the cavity through a slender glass tube having an inner diameter of 0.1 mm. By assuming that this small amount of seawater slightly perturbs the internal fields in the cavity, perturbation theory can be employed. A simple formula results relating the real part of the dielectric constant to the change in resonant frequency of the cavity. In a similar manner, the imaginary part of the dielectric constant is related to the change in the cavity s Q. The expected accuracy of the cavity technique is better than 1% for the real part and 1 to 2% for the imaginary part. Presently, measurements of methanol have been made and agree with precision measurements in the literature to within 1% in both real and imaginary parts. Measurements have been made of the dielectric constant of seawater samples from Ocean Scientific in the United Kingdom with salinities of 10, 30, 35 and 38 psu. All measurements were made at room temperature. Plans to make measurements at a range of temperatures and salinities will be discussed.

Analysis of the Dielectric constant of saline-alkali soils and the effect on radar backscattering coefficient: a case study of soda alkaline saline soils in Western Jilin Province using RADARSAT-2 data.

PubMed

Li, Yang-yang; Zhao, Kai; Ren, Jian-hua; Ding, Yan-ling; Wu, Li-li

2014-01-01

Soil salinity is a global problem, especially in developing countries, which affects the environment and productivity of agriculture areas. Salt has a significant effect on the complex dielectric constant of wet soil. However, there is no suitable model to describe the variation in the backscattering coefficient due to changes in soil salinity content. The purpose of this paper is to use backscattering models to understand behaviors of the backscattering coefficient in saline soils based on the analysis of its dielectric constant. The effects of moisture and salinity on the dielectric constant by combined Dobson mixing model and seawater dielectric constant model are analyzed, and the backscattering coefficient is then simulated using the AIEM. Simultaneously, laboratory measurements were performed on ground samples. The frequency effect of the laboratory results was not the same as the simulated results. The frequency dependence of the ionic conductivity of an electrolyte solution is influenced by the ion's components. Finally, the simulated backscattering coefficients measured from the dielectric constant with the AIEM were analyzed using the extracted backscattering coefficient from the RADARSAT-2 image. The results show that RADARSAT-2 is potentially able to measure soil salinity; however, the mixed pixel problem needs to be more thoroughly considered.

Comparison of Calculation and Experiment Implicates Significant Electrostatic Contributions to the Binding Stability of Barnase and Barstar

PubMed Central

Dong, Feng; Vijayakumar, M.; Zhou, Huan-Xiang

2003-01-01

The contributions of electrostatic interactions to the binding stability of barnase and barstar were studied by the Poisson-Boltzmann model with three different protocols: a), the dielectric boundary specified as the van der Waals (vdW) surface of the protein along with a protein dielectric constant (ɛp) of 4; b), the dielectric boundary specified as the molecular (i.e., solvent-exclusion (SE)) surface along with ɛp = 4; and c), “SE + ɛp = 20.” The “vdW + ɛp = 4” and “SE + ɛp = 20” protocols predicted an overall electrostatic stabilization whereas the “SE + ɛp = 4” protocol predicted an overall electrostatic destabilization. The “vdW + ɛp = 4” protocol was most consistent with experiment. It quantitatively reproduced the observed effects of 17 mutations neutralizing charged residues lining the binding interface and the measured coupling energies of six charge pairs across the interface and reasonably rationalized the experimental ionic strength and pH dependences of the binding constant. In contrast, the “SE + ɛp = 4” protocol predicted significantly larger coupling energies of charge pairs whereas the “SE + ɛp = 20” protocol did not predict any pH dependence. This study calls for further scrutiny of the different Poisson-Boltzmann protocols and demonstrates potential danger in drawing conclusions on electrostatic contributions based on a particular calculation protocol. PMID:12829463

Growth, structural, optical, thermal and mechanical properties of cytosinium hydrogen selenite: A novel nonlinear optical single crystal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jaikumar, P.; Sathiskumar, S.; Balakrishnan, T., E-mail: balacrystalgrowth@gmail.com

Highlights: • Growth of bulk single crystals of cytosinium hydrogen selenite (CHS) is reported. • Dielectric constant of CHS is measured as a function of Frequency and temperature. • Lower cut off value of UV–vis-NIR spectrum of CHS crystal is observed at 210 nm. • Meyer’s index value of CHS crystal calculated identifies it as a soft material. • Powder SHG efficiency of CHS is about 1.5 times that of KDP crystal. - Abstract: A novel nonlinear optical single crystal of cytosinium hydrogen selenite was grown from aqueous solution of cytosinium hydrogen selenite by slow solvent evaporation method at roommore » temperature. The structural properties of grown crystal have been studied by single crystal and powder X-ray diffraction analysis. Presence of various functional groups was identified from Fourier transform infrared spectroscopy. The optical transmittance and absorbance spectra were recorded by UV–vis-NIR spectrometer and the grown crystal possesses good transparency in the entire visible region. The dielectric constant and dielectric loss of the crystal were calculated as a function of frequency at different temperatures. The mechanical strength of the cytosinium hydrogen selenite crystal was estimated using Vicker’s microhardness tester. Etch patterns of the cytosinium hydrogen selenite crystal were obtained using distilled water as etchant for different etching time. Second harmonic generation efficiency tested using Nd:YAG laser is about 1.5 times that of KDP.« less

Effect of dipolar moments in domain sizes of lipid bilayers and monolayers

NASA Astrophysics Data System (ADS)

Travesset, A.

2006-08-01

Lipid domains are found in systems such as multicomponent bilayer membranes and single component monolayers at the air-water interface. It was shown by Keller et al. [J. Phys. Chem. 91, 6417 (1987)] that in monolayers, the size of the domains results from balancing the line tension, which favors the formation of a large single circular domain, against the electrostatic cost of assembling the dipolar moments of the lipids. In this paper, we present an exact analytical expression for the electric potential, ion distribution, and electrostatic free energy for different problems consisting of three different slabs with different dielectric constants and Debye lengths, with a circular homogeneous dipolar density in the middle slab. From these solutions, we extend the calculation of domain sizes for monolayers to include the effects of finite ionic strength, dielectric discontinuities (or image charges), and the polarizability of the dipoles and further generalize the calculations to account for domains in lipid bilayers. In monolayers, the size of the domains is dependent on the different dielectric constants but independent of ionic strength. In asymmetric bilayers, where the inner and outer leaflets have different dipolar densities, domains show a strong size dependence with ionic strength, with molecular-sized domains that grow to macroscopic phase separation with increasing ionic strength. We discuss the implications of the results for experiments and briefly consider their relation to other two dimensional systems such as Wigner crystals or heteroepitaxial growth.

Solvent effects on adsorption of CO over CuCl(1 1 1) surface: A density functional theory study

NASA Astrophysics Data System (ADS)

Zhang, Riguang; Ling, Lixia; Wang, Baojun; Huang, Wei

2010-09-01

DFT calculations have been performed to investigate the effect of dielectric responses of the solvent environment on the CO adsorption over CuCl(1 1 1) surface by using COSMO (conductor-like solvent model) model in Dmol 3. Different dielectric constants, including vacuum, liquid paraffin, methylene chloride, methanol and water solution, are considered. The effects of solvent model on the structural parameters, adsorption energies and vibrational frequency of CO adsorption over CuCl(1 1 1) surface have been investigated. The calculation results suggest that solvent effects can improve the stability of CO adsorption and reduce the intensity of C-O bond, which might mean that solvent is in favor of C-O bond activation and improve the reaction activity of oxidative carbonylation in a slurry reactor.

Influence of defects on the absorption edge of InN thin films: The band gap value

NASA Astrophysics Data System (ADS)

Thakur, J. S.; Danylyuk, Y. V.; Haddad, D.; Naik, V. M.; Naik, R.; Auner, G. W.

2007-07-01

We investigate the optical-absorption spectra of InN thin films whose electron density varies from ˜1017tõ1021cm-3 . The low-density films are grown by molecular-beam-epitaxy deposition while highly degenerate films are grown by plasma-source molecular-beam epitaxy. The optical-absorption edge is found to increase from 0.61to1.90eV as the carrier density of the films is increased from low to high density. Since films are polycrystalline and contain various types of defects, we discuss the band gap values by studying the influence of electron degeneracy, electron-electron, electron-ionized impurities, and electron-LO-phonon interaction self-energies on the spectral absorption coefficients of these films. The quasiparticle self-energies of the valence and conduction bands are calculated using dielectric screening within the random-phase approximation. Using one-particle Green’s function analysis, we self-consistently determine the chemical potential for films by coupling equations for the chemical potential and the single-particle scattering rate calculated within the effective-mass approximation for the electron scatterings from ionized impurities and LO phonons. By subtracting the influence of self-energies and chemical potential from the optical-absorption edge energy, we estimate the intrinsic band gap values for the films. We also determine the variations in the calculated band gap values due to the variations in the electron effective mass and static dielectric constant. For the lowest-density film, the estimated band gap energy is ˜0.59eV , while for the highest-density film, it varies from ˜0.60tõ0.68eV depending on the values of electron effective mass and dielectric constant.

The stress system generated by an electromagnetic field in a suspension of drops

NASA Technical Reports Server (NTRS)

Erdogan, M. E.

1982-01-01

The stress generated in a suspension of drops in the presence of a uniform electric field and a pure straining motion, taking into account that the magnetohydrodynamic effects are dominant was calculated. It was found that the stress generated in the suspension depended on the direction of the applied electric field, the dielectric constants, the vicosity coefficients, the conductivities, and the permeabilities of fluids inside and outside the drops. The expression of the particle stress shows that for fluids which are good conductors and poor dielectrics, especially for larger drops, magnetohydrodynamic effects end to reduce the dependence on the direction of the applied electric field.

An optical model for the microwave properties of sea ice

NASA Technical Reports Server (NTRS)

Gloersen, P.; Larabee, J. K.

1981-01-01

The complex refractive index of sea ice is modeled and used to predict the microwave signatures of various sea ice types. Results are shown to correspond well with the observed values of the complex index inferred from dielectic constant and dielectric loss measurements performed in the field, and with observed microwave signatures of sea ice. The success of this modeling procedure vis a vis modeling of the dielectric properties of sea ice constituents used earlier by several others is explained. Multiple layer radiative transfer calculations are used to predict the microwave properties of first-year sea ice with and without snow, and multiyear sea ice.

The method of impedance transformation for electromagnetic waves propagating in one-dimension plasma photonic crystal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yao, Jingfeng; Yuan, Chengxun, E-mail: yuancx@hit.edu.cn, E-mail: zhouzx@hit.edu.cn; Gao, Ruilin

2016-08-15

This study focuses on the transmission of normal-incidence electromagnetic waves in one-dimensional plasma photonic crystals. Using the Maxwell's equations in a medium, a method that is based on the concept of impendence is employed to perform the simulation. The accuracy of the method was evaluated by simulating a one-layer plasma and conventional photonic crystal. In frequency-domain, the transmission and reflection coefficients in the unmagnetized plasma photonic crystal were calculated, and the influence factors on plasma photonic crystals including dielectric constants of dielectric, spatial period, filling factor, plasma frequency, and collision frequency were studied.

Optically controlled dielectric properties of single-walled carbon nanotubes for terahertz wave applications.

PubMed

Smirnov, Serguei; Anoshkin, Ilya V; Demchenko, Petr; Gomon, Daniel; Lioubtchenko, Dmitri V; Khodzitsky, Mikhail; Oberhammer, Joachim

2018-06-21

Materials with tunable dielectric properties are valuable for a wide range of electronic devices, but are often lossy at terahertz frequencies. Here we experimentally report the tuning of the dielectric properties of single-walled carbon nanotubes under light illumination. The effect is demonstrated by measurements of impedance variations at low frequency as well as complex dielectric constant variations in the wide frequency range of 0.1-1 THz by time domain spectroscopy. We show that the dielectric constant is significantly modified for varying light intensities. The effect is also practically applied to phase shifters based on dielectric rod waveguides, loaded with carbon nanotube layers. The carbon nanotubes are used as tunable impedance surface controlled by light illumination, in the frequency range of 75-500 GHz. These results suggest that the effect of dielectric constant tuning with light, accompanied by low transmission losses of the carbon nanotube layer in such an ultra-wide band, may open up new directions for the design and fabrication of novel Terahertz and optoelectronic devices.

Large dielectric constant in zirconia polypyrrole hybrid nanocomposites.

PubMed

Dey, Ashis; De, S K

2007-06-01

Zirconia nanoparticles have been synthesized by a novel two-reverse emulsion technique and combined with polypyrrole (PPY) to form ZrO2-PPY nanocomposites. Complex impedance and dielectric permittivity of ZrO2-PPY nanocomposite have been investigated as a function of frequency and temperature for different compositions. The composite samples are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning and transmission electron microscopy. The composites reveal ordered semiconducting behaviour. Polypyrrole is the major component in electrical transport process of the samples. A very large dielectric constant of about 12,000 at room temperature has been observed. The colossal dielectric constant is mainly dominated by interfacial polarization due to Maxwell-Wagner relaxation effect. Two completely separate groups of dielectric relaxation have been observed. The low frequency dielectric relaxation arises from surface defect states of zirconia nanoparticles. The broad peak at high frequency is due to Maxwell-Wagner type polarization.

Studies on the structural, optical and dielectric properties of samarium coordinated with salicylic acid single crystal

NASA Astrophysics Data System (ADS)

Singh, Harjinder; Slathia, Goldy; Gupta, Rashmi; Bamzai, K. K.

2018-04-01

Samarium coordinated with salicylic acid was successfully grown as a single crystal by low temperature solution technique using mixed solvent of methanol and water in equal ratio. Structural characterization was carried out by single crystal X-ray diffraction analysis and it crystallizes in centrosymmetric space group P121/c1. FTIR and UV-Vis-NIR spectroscopy confirmed the compound formation and help to determine the mode of binding of the ligand to the rare earth-metal ion. Dielectric constant and dielectric loss have been measured over the frequency range 100 Hz - 30MHz. The decrease in dielectric constant with increases in frequency is due to the transition from interfacial polarization to dipolar polarization. The small value of dielectric constant at higher frequency ensures that the crystal is good candidate for NLO devices. Dielectric loss represents the resistive nature of the material.

Core-shell structured polystyrene/BaTiO3 hybrid nanodielectrics prepared by in situ RAFT polymerization: a route to high dielectric constant and low loss materials with weak frequency dependence.

PubMed

Yang, Ke; Huang, Xingyi; Xie, Liyuan; Wu, Chao; Jiang, Pingkai; Tanaka, Toshikatsu

2012-11-23

A novel route to prepare core-shell structured nanocomposites with excellent dielectric performance is reported. This approach involves the grafting of polystyrene (PS) from the surface of BaTiO(3) by an in situ RAFT polymerization. The core-shell structured PS/BaTiO(3) nanocomposites not only show significantly increased dielectric constant and very low dielectric loss, but also have a weak frequency dependence of dielectric properties over a wide range of frequencies. In addition, the dielectric constant of the nanocomposites can also be easily tuned by varying the thickness of the PS shell. Our method is very promising for preparing high-performance nanocomposites used in energy-storage devices. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ferroelectric, elastic, piezoelectric, and dielectric properties of Ba(Ti0.7Zr0.3)O3-x(Ba0.82Ca0.18)TiO3 Pb-free ceramics

NASA Astrophysics Data System (ADS)

Yuan, Ruihao; Xue, Deqing; Zhou, Yumei; Ding, Xiangdong; Sun, Jun; Xue, Dezhen

2017-07-01

We designed and synthesized a pseudo-binary Pb-free system, Ba(Ti0.7Zr0.3)O3-x(Ba0.82Ca0.18)TiO3, by combining a rhombohedral end (with only cubic to rhombohedral ferroelectric phase transition) and a tetragonal end (with only cubic to tetragonal ferroelectric phase transition). The established composition-temperature phase diagram is characterized by a tricritical point type morphotropic phase boundary (MPB), and the MPB composition has better ferroelectric, piezoelectric, and dielectric properties than the compositions deviating from MPB. Moreover, a full set of material constants (including elastic stiffness constants, elastic compliance constants, piezoelectric constants, dielectric constants, and electromechanical coupling factors) of the MPB composition are determined using a resonance method. The good piezoelectric performance of the MPB composition can be ascribed to the high dielectric constants, elastic softening, and large electromechanical coupling factor.

Laser-driven interactions and resultant instabilities in materials with high dielectric constant

NASA Astrophysics Data System (ADS)

Rajpoot, Moolchandra; Dixit, Sanjay

2015-07-01

An analytical investigation of nonlinear interactions resulting in parametric amplification of acoustic wave is made by obtaining the dispersion relation using hydrodynamic model of inhomogeneous plasma by applying large static field at an arbitrary angle with the pump wave. The investigation shows that many early studies have neglected dependence of dielectric constant on deformation of materials but deformation of materials does infect depends on the dielectric constant of medium. Thus we have assumed to high dielectric material like BaTiO3 which resulted in substantially high growth rate of threshold electric field which opens a new dimension to study nonlinear interactions and instabilities.

Dielectric constants of soils at microwave frequencies

NASA Technical Reports Server (NTRS)

Geiger, F. E.; Williams, D.

1972-01-01

A knowledge of the complex dielectric constant of soils is essential in the interpretation of microwave airborne radiometer data of the earth's surface. Measurements were made at 37 GHz on various soils from the Phoenix, Ariz., area. Extensive data have been obtained for dry soil and soil with water content in the range from 0.6 to 35 percent by dry weight. Measurements were made in a two arm microwave bridge and results were corrected for reflections at the sample interfaces by solution of the parallel dielectric plate problem. The maximum dielectric constants are about a factor of 3 lower than those reported for similar soils at X-band frequencies.

An anion substitution route to low loss colossal dielectric CaCu{sub 3}Ti{sub 4}O{sub 12}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Andrew E.; Calvarese, T.G.; Sleight, A.W.

2009-02-15

An anion substitution route was utilized for lowering the dielectric loss in CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) by partial replacement of oxygen by fluorine. This substitution reduced the dielectric loss, and retained a high dielectric constant that was essentially temperature independent from 25 to 200 deg. C. In particular, CaCu{sub 3}Ti{sub 4}O{sub 11.7}F{sub 0.3} exhibited a giant dielectric constant over 6000 and low dielectric loss below 0.075 at 100 kHz within a temperature range of 25-200 deg. C. Fluorine analysis confirmed the presence of fluorine in all samples measured. - Grapical Abstract: An anion substitution route was utilized for loweringmore » the dielectric loss in CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) by partial replacement of oxygen by fluorine. This substitution, confirmed by fluorine analysis, reduced tan {delta}, and retained a high dielectric constant that was essentially temperature independent from 25 to 200 deg. C at 100 kHz.« less

Microwave dielectric behavior of vegetation material

NASA Technical Reports Server (NTRS)

Elrayes, Mohamed A.; Ulaby, Fawwaz T.

1987-01-01

The microwave dielectric behavior of vegetation was examined through the development of theoretical models involving dielectric dispersion by both bound and free water and supported by extensive dielectric measurements conducted over a wide range of conditions. The experimental data were acquired using an open-ended coaxial probe that was developed for sensing the dielectric constant of thin layers of materials, such as leaves, from measurements of the complex reflection coefficient using a network analyzer. The probe system was successfully used to record the spectral variation of the dielectric constant over a wide frequency range extending from 0.5 to 20.4 GHz at numerous temperatures between -40 to +40 C. The vegetation samples were measured over a wide range of moisture conditions. To model the dielectric spectrum of the bound water component of the water included in vegetation, dielectric measurements were made for several sucrose-water solutions as analogs for the situation in vegetation. The results were used in conjunction with the experimental data for leaves to determine some of the constant coefficients in the theoretical models. Two models, both of which provide good fit to the data, are proposed.

Effect of doping ions on the structural defect and the electrical behavior of CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xue, Renzhong; Department of Technology and Physics, Zhengzhou University of Light Industry, Zhengzhou 450002; Zhao, Gaoyang, E-mail: zhaogy@xaut.edu.cn

Graphical abstract: The dielectric constant decreases with Ta doping, increases with Y doping and keeps almost constant with Zr doping compared with that of pure CCTO. - Highlights: • Y and Ta doping cause different defect types and concentration. • Defect influences the grain boundary mobility and results in different grain size. • Y doping increases the dielectric constant and decreases the nonlinear property. • Ta doping decreases the dielectric constant and enhances the nonlinear property. • Zr doped sample has nearly the defect type and dielectric properties as CaCu{sub 3}Ti{sub 4}O{sub 12}. - Abstract: The microstructure, dielectric and electricalmore » properties of CaCu{sub 3}Ti{sub 4−x}R{sub x}O{sub 12} (R = Y, Zr, Ta; x = 0 and 0.005) ceramics were investigated by XRD, Raman spectra, SEM and dielectric spectrum measurements. Positron annihilation measurements have been performed to investigate the influence of doping on the defects. The results show that all samples form a single crystalline phase. Y and Ta doping cause different defect types and increase the defect size and concentration, which influence the mobility of grain boundary and result in the different grain size. Y doping increases the dielectric constant and decreases the nonlinear property while Ta doping lead to an inverse result. Zr-doped sample has nearly the defect type, grain morphology and dielectric properties as pure CaCu{sub 3}Ti{sub 4}O{sub 12}. The effects of microstructure including the grain morphology and the vacancy defects on the mechanism of the dielectric and electric properties by doping are discussed.« less

On the room temperature multiferroic BiFeO3: magnetic, dielectric and thermal properties

NASA Astrophysics Data System (ADS)

Lu, J.; Günther, A.; Schrettle, F.; Mayr, F.; Krohns, S.; Lunkenheimer, P.; Pimenov, A.; Travkin, V. D.; Mukhin, A. A.; Loidl, A.

2010-06-01

Magnetic dc susceptibility between 1.5 and 800 K, ac susceptibility and magnetization, thermodynamic properties, temperature dependence of radio and audio-wave dielectric constants and conductivity, contact-free dielectric constants at mm-wavelengths, as well as ferroelectric polarization are reported for single crystalline BiFeO3. A well developed anomaly in the magnetic susceptibility signals the onset of antiferromagnetic order close to 635 K. Beside this anomaly no further indications of phase or glass transitions are indicated in the magnetic dc and ac susceptibilities down to the lowest temperatures. The heat capacity has been measured from 2 K up to room temperature and significant contributions from magnon excitations have been detected. From the low-temperature heat capacity an anisotropy gap of the magnon modes of the order of 6 meV has been determined. The dielectric constants measured in standard two-point configuration are dominated by Maxwell-Wagner like effects for temperatures T > 300 K and frequencies below 1 MHz. At lower temperatures the temperature dependence of the dielectric constant and loss reveals no anomalies outside the experimental errors, indicating neither phase transitions nor strong spin phonon coupling. The temperature dependence of the dielectric constant was measured contact free at microwave frequencies. At room temperature the dielectric constant has an intrinsic value of 53. The loss is substantial and strongly frequency dependent indicating the predominance of hopping conductivity. Finally, in small thin samples we were able to measure the ferroelectric polarization between 10 and 200 K. The saturation polarization is of the order of 40 μC/cm2, comparable to reports in literature.

Effect of solvents on morphology, magnetic and dielectric properties of (α-Fe2O3@SiO2) core-shell nanoparticles.

PubMed

Joshi, Deepika P; Pant, Geeta; Arora, Neha; Nainwal, Seema

2017-02-01

Present work describes the formation of α-Fe 2 O 3 @SiO 2 core shell structure by systematic layer by layer deposition of silica shell on core iron oxide nanoparticles prepared via various solvents. Sol-gel method has been used to synthesize magnetic core and the dielectric shell. The average crystallite size of iron oxide nanoparticles was calculated ∼20 nm by X-ray diffraction pattern. Morphological study by scanning electron microscopy revealed that the core-shell nanoparticles were spherical in shape and the average size of nanoparticles increased by varying solvent from methanol to ethanol to isopropanol due to different chemical structure and nature of the solvents. It was also observed that the particles prepared by solvent ethanol were more regular and homogeneous as compared to other solvents. Magnetic measurements showed the weak ferromagnetic behaviour of both core α-Fe 2 O 3 and silica-coated iron oxide nanoparticles which remained same irrespective of the solvent chosen. However, magnetization showed dependency on the types of solvent chosen due to the variation in shell thickness. At room temperature, dielectric constant and dielectric loss of silica nanoparticles for all the solvents showed decrement with the increment in frequency. Decrement in the value of dielectric constant and increment in dielectric loss was observed for silica coated iron oxide nanoparticles in comparison of pure silica, due to the presence of metallic core. Homogeneous and regular silica layer prepared by using ethanol as a solvent could serve as protecting layer to shield the magnetic behaviour of iron oxide nanoparticles as well as to provide better thermal insulation over pure α-Fe 2 O 3 nanoparticles.

Effect of SiO2/B2O3 Ratio on the Crystallization Behavior and Dielectric Properties of Barium Strontium Titanate Glass-Ceramics Prepared by Sol-Gel Process

NASA Astrophysics Data System (ADS)

Chen, Yongzhou; Zhang, Yong; Song, Xiaozhen; Shen, Ziqin; Zhang, Tianyuan

2018-05-01

Ferroelectric glass-ceramics, with a basic composition 90 wt.% (Ba0.65Sr0.35)TiO3-10 wt.% (B2O3-nSiO2) (n = 0.5, 1, 3, 5) were synthesized by the sol-gel method and their phase development and dielectric properties were investigated by differential thermal analysis, x-ray diffraction, field emission scanning electron microscopy, dielectric temperature curves and impedance spectroscopy. From the differential thermal analysis, glass transition and crystallization behavior can be observed. From the x-ray diffraction study, two crystalline phases (Ba,Sr)TiO3 and Ba2TiSi2O8 were formed over the entire composition range of the glass-ceramics. In addition, the main crystal phase has undergone a transformation from (Ba,Sr)TiO3 to Ba2TiSi2O8 with the increase of n. A typical structure in which the crystal phase was surrounded by a glassy matrix has been observed in the scanning electron microscope images. As a result of temperature dependent dielectric property measurements, the dielectric constant increased obviously with the increase of n from 0.5 to 1. Further increasing n led to a reduction of the dielectric constant, which is in coincidence with the variation of the intensity of (Ba,Sr)TiO3 phase with n. According to the impedance spectroscopy analysis and the activation energy calculation, the relaxation peak in both Z″ and M″ data should be attributed to the crystal-glass interface, and the change of conduction mechanism with the increase of SiO2/B2O3 ratio may be attributed to the corresponding transition of the main crystal phase.

Possible origin of nonlinear conductivity and large dielectric constant in the commensurate charge-density-wave phase of 1 T -TaS2

NASA Astrophysics Data System (ADS)

Ma, Yongchang; Hou, Yanhui; Lu, Cuimin; Li, Lijun; Petrovic, Cedomir

2018-05-01

The electric field dependence of the dielectric properties and the nonlinear conductance of 1 T -TaS2 below 50 K has been investigated. A large dielectric constant of about 104 is obtained up to 107 Hz, which cannot be attributed to hopping of the localized carriers alone, the collective excitations of the commensurate charge-density-wave must be another contributor. The dielectric spectra disperse slightly in our measured temperature and frequency range. At a moderate dc bias field, the real part of the dielectric constant ɛ1(ω ) decreases. We propose that the separation of bound soliton-antisoliton pairs may be a contributor to the reduction of ɛ1(ω ) and the accompanying nonlinear conductivity with increasing dc bias.

A hollow coaxial cable Fabry-Pérot resonator for liquid dielectric constant measurement

NASA Astrophysics Data System (ADS)

Zhu, Chen; Zhuang, Yiyang; Chen, Yizheng; Huang, Jie

2018-04-01

We report, for the first time, a low-cost and robust homemade hollow coaxial cable Fabry-Pérot resonator (HCC-FPR) for measuring liquid dielectric constant. In the HCC design, the traditional dielectric insulating layer is replaced by air. A metal disk is welded onto the end of the HCC serving as a highly reflective reflector, and an open cavity is engineered on the HCC. After the open cavity is filled with the liquid analyte (e.g., water), the air-liquid interface acts as a highly reflective reflector due to large impedance mismatch. As a result, an HCC-FPR is formed by the two highly reflective reflectors, i.e., the air-liquid interface and the metal disk. We measured the room temperature dielectric constant for ethanol/water mixtures with different concentrations using this homemade HCC-FPR. Monitoring the evaporation of ethanol in ethanol/water mixtures was also conducted to demonstrate the ability of the sensor for continuously monitoring the change in dielectric constant. The results revealed that the HCC-FPR could be a promising evaporation rate detection platform with high performance. Due to its great advantages, such as high robustness, simple configuration, and ease of fabrication, the novel HCC-FPR based liquid dielectric constant sensor is believed to be of high interest in various fields.

A hollow coaxial cable Fabry-Pérot resonator for liquid dielectric constant measurement.

PubMed

Zhu, Chen; Zhuang, Yiyang; Chen, Yizheng; Huang, Jie

2018-04-01

We report, for the first time, a low-cost and robust homemade hollow coaxial cable Fabry-Pérot resonator (HCC-FPR) for measuring liquid dielectric constant. In the HCC design, the traditional dielectric insulating layer is replaced by air. A metal disk is welded onto the end of the HCC serving as a highly reflective reflector, and an open cavity is engineered on the HCC. After the open cavity is filled with the liquid analyte (e.g., water), the air-liquid interface acts as a highly reflective reflector due to large impedance mismatch. As a result, an HCC-FPR is formed by the two highly reflective reflectors, i.e., the air-liquid interface and the metal disk. We measured the room temperature dielectric constant for ethanol/water mixtures with different concentrations using this homemade HCC-FPR. Monitoring the evaporation of ethanol in ethanol/water mixtures was also conducted to demonstrate the ability of the sensor for continuously monitoring the change in dielectric constant. The results revealed that the HCC-FPR could be a promising evaporation rate detection platform with high performance. Due to its great advantages, such as high robustness, simple configuration, and ease of fabrication, the novel HCC-FPR based liquid dielectric constant sensor is believed to be of high interest in various fields.

Wave attenuation and mode dispersion in a waveguide coated with lossy dielectric material

NASA Technical Reports Server (NTRS)

Lee, C. S.; Chuang, S. L.; Lee, S. W.; Lo, Y. T.

1984-01-01

The modal attenuation constants in a cylindrical waveguide coated with a lossy dielectric material are studied as functions of frequency, dielectric constant, and thickness of the dielectric layer. A dielectric material best suited for a large attenuation is suggested. Using Kirchhoff's approximation, the field attenuation in a coated waveguide which is illuminated by a normally incident plane wave is also studied. For a circular guide which has a diameter of two wavelengths and is coated with a thin lossy dielectric layer (omega sub r = 9.1 - j2.3, thickness = 3% of the radius), a 3 dB attenuation is achieved within 16 diameters.

Dielectric relaxation of near-percolated carbon nanofiber polypropylene composites

NASA Astrophysics Data System (ADS)

Paleo, A. J.; Zille, A.; Van Hattum, F. W.; Ares-Pernas, A.; Agostinho Moreira, J.

2017-07-01

In this work, the morphological, structural and dielectric analysis of near-percolated polypropylene (PP) composites containing carbon nanofibers (CNF) processing by melt-mixing are investigated. Whereas the morphological analysis shows that CNF exhibit some tendency to agglomerate within the PP matrix, the structural analysis showed first a general decrease in the intensity of the IR bands as a consequence of the interaction between carbon nanofibers and PP matrix and second an increase of the crystallinity degree of the PP/CNF composites when compared to the pure PP. The dielectric analysis demonstrates enhanced dielectric constants (from 2.97 for neat polymer to 9.7 for 1.9 vol% loaded composites at 200 Hz) and low dielectric losses. Furthermore, the dielectric relaxation for composites with concentrations in the vicinity of percolation is evidenced and well described by the generalized polydispersive Cole-Cole model from which the values of static dielectric constant (εs) , high frequency dielectric constant (ε∞) , distribution of relaxation time (α) and mean relaxation time (τo), are determined, suggesting that this latter analysis constitutes a strong tool for understanding the relationships between microstructure and dielectric properties in this type of polymer composites.

Effects of oxygen deficiency on the transport and dielectric properties of NdSrNbO

NASA Astrophysics Data System (ADS)

Hzez, W.; Benali, A.; Rahmouni, H.; Dhahri, E.; Khirouni, K.; Costa, B. F. O.

2018-06-01

In the present study, Nd0.7Sr0.3NbO3-y (y = 0.1, 0.15, 0.2) compounds were prepared via a solid-solid reaction route. The prepared samples were characterized by electrochemical impedance spectroscopy in order to establish the effects of temperature, frequency, and oxygen vacancies on both the transport and dielectric properties of NdSrNbO. We found that both the electrical and dielectric properties were highly sensitive to the concentration of oxygen vacancies. The conduction mechanism data were explained well according to the Mott model and adiabatic small polaronic hopping model. Electrochemical impedance spectroscopy analysis showed that one relaxation process was present in the Nd0.7Sr0.3NbO2.9 system whereas two relaxation processes were observed in the Nd0.7Sr0.3NbO2.85 and Nd0.7Sr0.3NbO2.8 systems, where the latter behavior indicated the presence of many active regions (due to the contributions of different microstructures). The temperature and frequency dependences of the dielectric constant confirmed the contributions of different polarization mechanisms. In particular, the high dielectric constant values at low frequencies and high temperatures were mainly related to the presence of different Schottky barriers, whereas the low dielectric constant values at high frequencies were essentially related to the intrinsic effect. The constant dielectric values obtained for the samples are greater than those in the NdSrFeO system, which makes them interesting materials for use in applications that require high dielectric constants.

Investigation of different physical aspects such as structural, mechanical, optical properties and Debye temperature of Fe2ScM (M=P and As) semiconductors: A DFT-based first principles study

NASA Astrophysics Data System (ADS)

Ali, Md. Lokman; Rahaman, Md. Zahidur

2018-04-01

By using first principles calculation dependent on the density functional theory (DFT), we have investigated the mechanical, structural properties and the Debye temperature of Fe2ScM (M=P and As) compounds under various pressures up to 60 GPa. The optical properties have been investigated under zero pressure. Our calculated optimized structural parameters of both the materials are in good agreement with other theoretical predictions. The calculated elastic constants show that Fe2ScM (M=P and As) compounds are mechanically stable under external pressure below 60 GPa. From the elastic constants, the shear modulus G, the bulk modulus B, Young’s modulus E, anisotropy factor A and Poisson’s ratio ν are calculated by using the Voigt-Reuss-Hill approximation. The Debye temperature and average sound velocities are also investigated from the obtained elastic constants. The detailed analysis of all optical functions reveals that both compounds are good dielectric material.

Lattice dynamics and thermal conductivity of lithium fluoride via first-principles calculations

NASA Astrophysics Data System (ADS)

Liang, Ting; Chen, Wen-Qi; Hu, Cui-E.; Chen, Xiang-Rong; Chen, Qi-Feng

2018-04-01

The lattice thermal conductivity of lithium fluoride (LiF) is accurately computed from a first-principles approach based on an iterative solution of the Boltzmann transport equation. Real-space finite-difference supercell approach is employed to generate the second- and third-order interatomic force constants. The related physical quantities of LiF are calculated by the second- and third- order potential interactions at 30 K-1000 K. The calculated lattice thermal conductivity 13.89 W/(m K) for LiF at room temperature agrees well with the experimental value, demonstrating that the parameter-free approach can furnish precise descriptions of the lattice thermal conductivity for this material. Besides, the Born effective charges, dielectric constants and phonon spectrum of LiF accord well with the existing data. The lattice thermal conductivities for the iterative solution of BTE are also presented.

Dielectric Properties of BST/(Y 2O 3) x(ZrO 2) 1-x/BST Trilayer Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sahoo, Santosh K.; Misra, D.

2011-01-31

Thin films of Ba1-xSrxTiO3 (BST) are being actively investigated for applications in dynamic random access memories (DRAM) because of their properties such as high dielectric constant, low leakage current, and high dielectric breakdown strength. Various approaches have been used to improve the dielectric properties of BST thin films such as doping, graded compositions, and multilayer structures. We have found that inserting a ZrO2 layer in between two BST layers results in a significant reduction in dielectric constant as well as dielectric loss. In this work the effect of Y2O3 doped ZrO2 on the dielectric properties of BST/ZrO2/BST trilayer structure ismore » studied. The structure Ba0.8Sr0.2TiO3/(Y2O3)x(ZrO2)1-x/Ba0.8Sr0.2TiO3 is deposited by a sol-gel process on platinized Si substrate. The composition (x) of the middle layer is varied while keeping the total thickness of the trilayer film constant. The dielectric constant of the multilayer film decreases with the increase of Y2O3 amount in the film whereas there is a slight variation in dielectric loss. In Y2O3 doped multilayer thin films, the dielectric loss is lower in comparison to other films and also there is good frequency stability in the loss in the measured frequency range and hence very suitable for microwave device applications.« less

Voltage sensor and dielectric material

DOEpatents

Yakymyshyn, Christopher Paul; Yakymyshyn, Pamela Jane; Brubaker, Michael Allen

2006-10-17

A voltage sensor is described that consists of an arrangement of impedance elements. The sensor is optimized to provide an output ratio that is substantially immune to changes in voltage, temperature variations or aging. Also disclosed is a material with a large and stable dielectric constant. The dielectric constant can be tailored to vary with position or direction in the material.

A flexible insulator of a hollow SiO2 sphere and polyimide hybrid for flexible OLEDs.

PubMed

Kim, Min Kyu; Kim, Dong Won; Shin, Dong Wook; Seo, Sang Joon; Chung, Ho Kyoon; Yoo, Ji Beom

2015-01-28

The fabrication of interlayer dielectrics (ILDs) in flexible organic light-emitting diodes (OLEDs) not only requires flexible materials with a low dielectric constant, but also ones that possess the electrical, thermal, chemical, and mechanical properties required for optimal device performance. Porous polymer-silica hybrid materials were prepared to satisfy these requirements. Hollow SiO2 spheres were synthesized using atomic layer deposition (ALD) and a thermal calcination process. The hybrid film, which consists of hollow SiO2 spheres and polyimide, shows a low dielectric constant of 1.98 and excellent thermal stability up to 500 °C. After the bending test for 50 000 cycles, the porous hybrid film exhibits no degradation in its dielectric constant or leakage current. These results indicate that the hybrid film made up of hollow SiO2 spheres and polyimide (PI) is useful as a flexible insulator with a low dielectric constant and high thermal stability for flexible OLEDs.

Flexible, Low-Power Thin-Film Transistors Made of Vapor-Phase Synthesized High-k, Ultrathin Polymer Gate Dielectrics.

PubMed

Choi, Junhwan; Joo, Munkyu; Seong, Hyejeong; Pak, Kwanyong; Park, Hongkeun; Park, Chan Woo; Im, Sung Gap

2017-06-21

A series of high-k, ultrathin copolymer gate dielectrics were synthesized from 2-cyanoethyl acrylate (CEA) and di(ethylene glycol) divinyl ether (DEGDVE) monomers by a free radical polymerization via a one-step, vapor-phase, initiated chemical vapor deposition (iCVD) method. The chemical composition of the copolymers was systematically optimized by tuning the input ratio of the vaporized CEA and DEGDVE monomers to achieve a high dielectric constant (k) as well as excellent dielectric strength. Interestingly, DEGDVE was nonhomopolymerizable but it was able to form a copolymer with other kinds of monomers. Utilizing this interesting property of the DEGDVE cross-linker, the dielectric constant of the copolymer film could be maximized with minimum incorporation of the cross-linker moiety. To our knowledge, this is the first report on the synthesis of a cyanide-containing polymer in the vapor phase, where a high-purity polymer film with a maximized dielectric constant was achieved. The dielectric film with the optimized composition showed a dielectric constant greater than 6 and extremely low leakage current densities (<3 × 10 -8 A/cm 2 in the range of ±2 MV/cm), with a thickness of only 20 nm, which is an outstanding thickness for down-scalable cyanide polymer dielectrics. With this high-k dielectric layer, organic thin-film transistors (OTFTs) and oxide TFTs were fabricated, which showed hysteresis-free transfer characteristics with an operating voltage of less than 3 V. Furthermore, the flexible OTFTs retained their low gate leakage current and ideal TFT characteristics even under 2% applied tensile strain, which makes them some of the most flexible OTFTs reported to date. We believe that these ultrathin, high-k organic dielectric films with excellent mechanical flexibility will play a crucial role in future soft electronics.

New Parameters for Higher Accuracy in the Computation of Binding Free Energy Differences upon Alanine Scanning Mutagenesis on Protein-Protein Interfaces.

PubMed

Simões, Inês C M; Costa, Inês P D; Coimbra, João T S; Ramos, Maria J; Fernandes, Pedro A

2017-01-23

Knowing how proteins make stable complexes enables the development of inhibitors to preclude protein-protein (P:P) binding. The identification of the specific interfacial residues that mostly contribute to protein binding, denominated as hot spots, is thus critical. Here, we refine an in silico alanine scanning mutagenesis protocol, based on a residue-dependent dielectric constant version of the Molecular Mechanics/Poisson-Boltzmann Surface Area method. We have used a large data set of structurally diverse P:P complexes to redefine the residue-dependent dielectric constants used in the determination of binding free energies. The accuracy of the method was validated through comparison with experimental data, considering the per-residue P:P binding free energy (ΔΔG binding ) differences upon alanine mutation. Different protocols were tested, i.e., a geometry optimization protocol and three molecular dynamics (MD) protocols: (1) one using explicit water molecules, (2) another with an implicit solvation model, and (3) a third where we have carried out an accelerated MD with explicit water molecules. Using a set of protein dielectric constants (within the range from 1 to 20) we showed that the dielectric constants of 7 for nonpolar and polar residues and 11 for charged residues (and histidine) provide optimal ΔΔG binding predictions. An overall mean unsigned error (MUE) of 1.4 kcal mol -1 relative to the experiment was achieved in 210 mutations only with geometry optimization, which was further reduced with MD simulations (MUE of 1.1 kcal mol -1 for the MD employing explicit solvent). This recalibrated method allows for a better computational identification of hot spots, avoiding expensive and time-consuming experiments or thermodynamic integration/ free energy perturbation/ uBAR calculations, and will hopefully help new drug discovery campaigns in their quest of searching spots of interest for binding small drug-like molecules at P:P interfaces.

Dielectric properties of carbon nanotubes/epoxy composites.

PubMed

Peng, Jin-Ping; Zhang, Hui; Tang, Long-Cheng; Jia, Yu; Zhang, Zhong

2013-02-01

Material with high dielectric properties possesses the effect of energy storage and electric field homogenization, which plays an important role in the electrical and electronics domain, especially in the capacitor, electrical machinery and cable realm. In this paper, epoxy-based nanocomposites with high dielectric constant were fabricated by adding pristine and ozone functionalized multi-wall carbon nanotubes (MWCNTs). In the process-related aspect, the favorable technological parameter was obtained via reasonable arrangement and consideration of the dispersing methods including high-speed stirring and three-roller mill. As a result, a uniform dispersion status of MWCNTs in matrix has been guaranteed, which was observed by scanning and transmission electron microscopy. Meanwhile, the influence of different MWCNTs contents and diverse frequencies on the dielectric properties was compared. It was found that the dielectric constant of nano-composites decreased gradually with the increasing of frequency (10(3)-10(6) Hz). Moreover, as the content of MWCNTs increasing, the dielectric constant reached to a maximum of about 1,328 at 10(3) Hz when the pristine MWCNTs content was 0.5 wt.%. Accordingly, the DC conductivity results could interpret the peak value phenomenon by percolation threshold of MWCNTs. In addition, at the fixed content, the dielectric constant of epoxy-based nano-composites with ozone functionalized MWCNTs was lower than that of pristine ones.

Quantitative evaluation of the piezoelectric response of unpoled ferroelectric ceramics from elastic and dielectric measurements: Tetragonal BaTiO3

NASA Astrophysics Data System (ADS)

Cordero, F.

2018-03-01

A method is proposed for evaluating the potential piezoelectric response, that a ferroelectric material would exhibit after full poling, from elastic and dielectric measurements of the unpoled ceramic material. The method is based on the observation that the softening in a ferroelectric phase with respect to the paraelectric phase is of piezoelectric origin, and is tested on BaTiO3. The angular averages of the piezoelectric softening in unpoled ceramics are calculated for ferroelectric phases of different symmetries. The expression of the orientational average with the piezoelectric and dielectric constants of single crystal tetragonal BaTiO3 from the literature reproduces well the softening of the Young's modulus of unpoled ceramic BaTiO3, after a correction for the porosity. The agreement is good in the temperature region sufficiently far from the Curie temperature and from the transition to the orthorhombic phase, where the effect of fluctuations should be negligible, but deviations are found outside this region, and possible reasons for this are discussed. This validates the determination of the piezoelectric response by means of purely elastic measurements on unpoled samples. The method is indirect and, for quantitative assessments, requires the knowledge of the dielectric tensor. On the other hand, it does not require poling of the sample, and therefore is insensitive to inaccuracies from incomplete poling, and can even be used with materials that cannot be poled, for example, due to excessive electrical conductivity. While the proposed example of the Young's modulus of a ceramic provides an orientational average of all the single crystal piezoelectric constants, a Resonant Ultrasound Spectroscopy measurement of a single unpoled ceramic sample through the ferroelectric transition can in principle measure all the piezoelectric constants, together with the elastic ones.

A theory of electrical conductivity, dielectric constant, and electromagnetic interference shielding for lightweight graphene composite foams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xia, Xiaodong; Department of Mechanical and Aerospace Engineering, Rutgers University, New Brunswick, New Jersey 08903; Wang, Yang

This work was driven by the need to understand the electromagnetic interference (EMI) shielding effectiveness (SE) of light weight, flexible, and high performance graphene composite foams, but as EMI SE of a material depends on its electrical conductivity, dielectric permittivity, and magnetic permeability, the investigation of these three properties also became a priority. In this paper, we first present a continuum theory to determine these three electromagnetic properties, and then use the obtained properties to evaluate the EMI SE of the foam. A two-scale composite model is conceived to evaluate these three properties, with the large one being the skeleton-voidmore » composite and the small one being the graphene-polymer composite that serves as the skeleton of the foam. To evaluate the properties of the skeleton, the effective-medium approach is taken as the starting point. Subsequently, the effect of an imperfect interface and the contributions of electron tunneling to the interfacial conductivity and Maxwell-Wagner-Sillars polarization mechanism to the dielectric constant are also implemented. The derived skeleton properties are then utilized on the large scale to determine the three properties of the composite foam at a given porosity. Then a uniform plane electromagnetic wave is considered to evaluate the EMI SE of the foam. It is demonstrated that the electrical conductivity, dielectric constant, and EMI SE of the foam calculated from the developed theory are in general agreement with the reported experimental data of graphene/PDMS composite foams. The theory is further proven to be valid for the EMI SE of solid graphene/epoxy and solid carbon nanotube/epoxy nanocomposites. It is also shown that, among the three electromagnetic properties, electrical conductivity has the strongest influence on the EMI shielding effectiveness.« less

Structural elucidation and magnetic behavior evaluation of Cu-Cr doped BaCo-X hexagonal ferrites

NASA Astrophysics Data System (ADS)

Azhar Khan, Muhammad; Hussain, Farhat; Rashid, Muhammad; Mahmood, Asif; Ramay, Shahid M.; Majeed, Abdul

2018-04-01

Ba2-xCuxCo2CryFe28-yO46 (x = 0.0, 0.1, 0.2, 0.3, 0.4, y = 0.0, 0.2, 0.4, 0.6, 0.8) X-type hexagonal ferrites were synthesized via micro-emulsion route. The techniques which were applied to characterize the prepared samples are as follows: X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Dielectric measurements and vibrating sample magnetometer (VSM). The structural parameters i.e. lattice constant (a, c), cell volume (V), X-ray density, bulk density and crystallite size of all the prepared samples were obtained using XRD analysis. The lattice parameters 'a' and 'c' increase from 5.875 Å to 5.934 Å and 83.367 Å to 83.990 Å respectively. The crystallite size of investigated samples lies in the range of 28-32 nm. The magnetic properties of all samples have been calculated by vibrating sample magnetometer (VSM) analysis. The increase in coercivity (Hc) was observed with the increase of doping contents. It was observed that the coercivity (Hc) of all prepared samples is inversely related to the crystalline size which reflects that all materials are super-paramagnetic. The dielectric parameters i.e. dielectric constant, dielectric loss, tangent loss etc were obtained in the frequency range of 1 MHz-3 GHz and followed the Maxwell-Wagner's model. The significant variation the dielectric parameters are observed with increasing frequency. The maximum Q value is obtained at ∼2 GHz due to which these materials are used for high frequency multilayer chip inductors.

Colossal dielectric and electromechanical responses in self-assembled polymeric nanocomposites

NASA Astrophysics Data System (ADS)

Huang, Cheng; Zhang, Q. M.; Li, Jiang Yu; Rabeony, Manese

2005-10-01

An electroactive polymer nanocomposite, in which high dielectric constant copper phthalocyanine oligomer (o-CuPc) nanoparticles are incorporated into the block polyurethane (PU) matrix by the combination of "top down" and "bottom up" approaches, was realized. Such an approach enables the nanocomposite to exhibit colossal dielectric and electromechanical responses with very low volume fraction of the high dielectric constant o-CuPc nanofillers (˜3.5%) in the composite. In contrast, a simple blend of o-CuPc and PU composite with much higher o-CuPc content (˜16% of o-CuPc) shows much lower dielectric and electromechanical responses.

The Effect of Multi Wall Carbon Nanotubes on Some Physical Properties of Epoxy Matrix

NASA Astrophysics Data System (ADS)

Al-Saadi, Tagreed M.; hammed Aleabi, Suad; Al-Obodi, Entisar E.; Abdul-Jabbar Abbas, Hadeel

2018-05-01

This research involves using epoxy resin as a matrix for making a composite material, while the multi wall carbon nanotubes (MWNCTs) is used as a reinforcing material with different fractions (0.0,0.02, 0.04, 0.06) of the matrix weight. The mechanical ( hardness ), electrical ( dielectric constant, dielectric loss factor, dielectric strength, electrical conductivity ), and thermal properties (thermal conductivity ) were studied. The results showed the increase of hardness, thermal conductivity, electrical conductivity and break down strength with the increase of MWCNT concentration, but the behavior of dielectric loss factor and dielectric constant is opposite that.

Main regularities of SERS on semiconductors and dielectrics

NASA Astrophysics Data System (ADS)

Chelibanov, V. P.; Polubotko, A. M.

2018-04-01

The paper demonstrates that the reason of SERS on dielectrics and semiconductors is the enhancement of the electric field in the regions of the tops of the surface roughness with a very large positive curvature. The enhancement in many ways depends on the dielectric constant of the substrate and is stronger for a larger dielectric constant. The theoretical result points out that on dielectrics and semiconductors it is weaker than on metals. Experimentally it is demonstrated that there are forbidden lines on hydroquinone, adsorbed on TiO2 , which indicate on the existence of strong quadrupole light-molecule interaction in such systems.

The electromagnetic radiation from simple sources in the presence of a homogeneous dielectric sphere

NASA Technical Reports Server (NTRS)

Mason, V. B.

1973-01-01

In this research, the effect of a homogeneous dielectric sphere on the electromagnetic radiation from simple sources is treated as a boundary value problem, and the solution is obtained by the technique of dyadic Green's functions. Exact representations of the electric fields in the various regions due to a source located inside, outside, or on the surface of a dielectric sphere are formulated. Particular attention is given to the effect of sphere size, source location, dielectric constant, and dielectric loss on the radiation patterns and directivity of small spheres (less than 5 wavelengths in diameter) using the Huygens' source excitation. The computed results are found to closely agree with those measured for waveguide-excited plexiglas spheres. Radiation patterns for an extended Huygens' source and for curved electric dipoles located on the sphere's surface are also presented. The resonance phenomenon associated with the dielectric sphere is studied in terms of the modal representation of the radiated fields. It is found that when the sphere is excited at certain frequencies, much of the energy is radiated into the sidelobes. The addition of a moderate amount of dielectric loss, however, quickly attenuates this resonance effect. A computer program which may be used to calculate the directivity and radiation pattern of a Huygens' source located inside or on the surface of a lossy dielectric sphere is listed.

Spatially resolved dielectric constant of confined water and its connection to the non-local nature of bulk water

NASA Astrophysics Data System (ADS)

Schaaf, Christian; Gekle, Stephan

2016-08-01

We use molecular dynamics simulations to compute the spatially resolved static dielectric constant of water in cylindrical and spherical nanopores as occurring, e.g., in protein water pockets or carbon nanotubes. For this, we derive a linear-response formalism which correctly takes into account the dielectric boundary conditions in the considered geometries. We find that in cylindrical confinement, the axial component behaves similar as the local density akin to what is known near planar interfaces. The radial dielectric constant shows some oscillatory features when approaching the surface if their radius is larger than about 2 nm. Most importantly, however, the radial component exhibits pronounced oscillations at the center of the cavity. These surprising features are traced back quantitatively to the non-local dielectric nature of bulk water.

Broadband dielectric spectroscopy on single-crystalline and ceramic CaCu3Ti4O12

NASA Astrophysics Data System (ADS)

Krohns, S.; Lunkenheimer, P.; Ebbinghaus, S. G.; Loidl, A.

2007-07-01

The authors present dielectric measurements of the colossal dielectric constant material CaCu3Ti4O12 extending up to 1.3GHz also covering so far only rarely investigated single-crystalline samples. Special emphasis is put on the second relaxation reported in several works on polycrystals, which the authors detect also in single crystals. For polycrystalline samples, the authors provide a recipe to achieve values of the dielectric constant as high as in single crystals.

Polymer Nanocomposite Materials with High Dielectric Permittivity and Low Dielectric Loss Properties

NASA Astrophysics Data System (ADS)

Toor, Anju

Materials with high dielectric permittivity have drawn increasing interests in recent years for their important applications in capacitors, actuators, and high energy density pulsed power. Particularly, polymer-based dielectrics are excellent candidates, owing to their properties such as high breakdown strength, low dielectric loss, flexibility and easy processing. To enhance the dielectric permittivity of polymer materials, typically, high dielectric constant filler materials are added to the polymer. Previously, ferroelectric and conductive fillers have been mainly used. However, such systems suffered from various limitations. For example, composites based on ferroelectric materials like barium titanate, exhibited high dielectric loss, and poor saturation voltages. Conductive fillers are used in the form of powder aggregates, and they may show 10-100 times enhancement in dielectric constant, however these nanoparticle aggregates cause the dielectric loss to be significant. Also, agglomerates limit the volume fraction of fillers in polymer and hence, the ability to achieve superior dielectric constants. Thus, the aggregation of nanoparticles is a significant challenge to their use to improve the dielectric permittivity. We propose the use of ligand-coated metal nanoparticle fillers to enhance the dielectric properties of the host polymer while minimizing dielectric loss by preventing nanoparticle agglomeration. The focus is on obtaining uniform dispersion of nanoparticles with no agglomeration by utilizing appropriate ligands/surface functionalizations on the gold nanoparticle surface. Use of ligand coated metal nanoparticles will enhance the dielectric constant while minimizing dielectric loss, even with the particles closely packed in the polymer matrix. Novel combinations of materials, which use 5 nm diameter metal nanoparticles embedded inside high breakdown strength polymer materials are evaluated. High breakdown strength polymer materials are chosen to allow further exploration of these materials for energy storage applications. In summary, two novel nanocomposite materials are designed and synthesized, one involving polyvinylidene fluoride (PVDF) as the host polymer for potential applications in energy storage and the other with SU-8 for microelectronic applications. Scanning elec- tron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy and ultramicrotoming techniques were used for the material characterization of the nanocomposite materials. A homogeneous dispersion of gold nanoparticles with low particle agglomeration has been achieved. Fabricated nanoparticle polymer composite films showed the absence of voids and cracks. Also, no evidence of macro-phase separation of nanoparticles from the polymer phase was observed. This is important because nanoparticle agglomeration and phase separation from the polymer usually results in poor processability of films and a high defect density. Dielectric characterization of the nanocomposite materials showed enhancement in the dielectric constant over the base polymer values and low dielectric loss values were observed.

The fluid mechanics of continuous flow electrophoresis

NASA Technical Reports Server (NTRS)

Saville, D. A.

1990-01-01

The overall objective is to establish theoretically and confirm experimentally the ultimate capabilities of continuous flow electrophoresis chambers operating in an environment essentially free of particle sedimentation and buoyancy. The efforts are devoted to: (1) studying the effects of particle concentration on sample conductivity and dielectric constant. The dielectric constant and conductivity were identified as playing crucial roles in the behavior of the sample and on the resolving power and throughput of continuous flow devices; and (2) improving the extant mathematical models to predict flow fields and particle trajectories in continuous flow electrophoresis. A dielectric spectrometer was designed and built to measure the complex dielectric constant of a colloidal dispersion as a function of frequency between 500 Hz and 200 kHz. The real part of the signal can be related to the sample's conductivity and the imaginary part to its dielectric constant. Measurements of the dielectric constants of several different dispersions disclosed that the dielectric constants of dilute systems of the sort encountered in particle electrophoresis are much larger than would be expected based on the extant theory. Experiments were carried out to show that, in many cases, this behavior is due to the presence of a filamentary structure of small hairs on the particle surface. A technique for producing electrokinetically ideal synthetic latex particles by heat treating was developed. Given the ubiquitous nature of hairy surfaces with both cells and synthetic particles, it was deemed necessary to develop a theory to explain their behavior. A theory for electrophoretic mobility of hairy particles was developed. Finally, the extant computer programs for predicting the structure of electro-osmotically driven flows were extended to encompass flow channels with variable wall mobilities.

Temperature and pressure effects on capacitance probe cryogenic liquid level measurement accuracy

NASA Technical Reports Server (NTRS)

Edwards, Lawrence G.; Haberbusch, Mark

1993-01-01

The inaccuracies of liquid nitrogen and liquid hydrogen level measurements by use of a coaxial capacitance probe were investigated as a function of fluid temperatures and pressures. Significant liquid level measurement errors were found to occur due to the changes in the fluids dielectric constants which develop over the operating temperature and pressure ranges of the cryogenic storage tanks. The level measurement inaccuracies can be reduced by using fluid dielectric correction factors based on measured fluid temperatures and pressures. The errors in the corrected liquid level measurements were estimated based on the reported calibration errors of the temperature and pressure measurement systems. Experimental liquid nitrogen (LN2) and liquid hydrogen (LH2) level measurements were obtained using the calibrated capacitance probe equations and also by the dielectric constant correction factor method. The liquid levels obtained by the capacitance probe for the two methods were compared with the liquid level estimated from the fluid temperature profiles. Results show that the dielectric constant corrected liquid levels agreed within 0.5 percent of the temperature profile estimated liquid level. The uncorrected dielectric constant capacitance liquid level measurements deviated from the temperature profile level by more than 5 percent. This paper identifies the magnitude of liquid level measurement error that can occur for LN2 and LH2 fluids due to temperature and pressure effects on the dielectric constants over the tank storage conditions from 5 to 40 psia. A method of reducing the level measurement errors by using dielectric constant correction factors based on fluid temperature and pressure measurements is derived. The improved accuracy by use of the correction factors is experimentally verified by comparing liquid levels derived from fluid temperature profiles.

Effect of NiO and Light Intensity on Dielectric Constant of SiO2-B2O3-Bi2O3-Na2CO3 Glass Based on Silica Gel of Natural Sands

NASA Astrophysics Data System (ADS)

Diantoro, M.; Muniroh, Z.; Zaini, B.; Mustikasari, A. A.; Nasikhudin; Hidayat, A.; Taufiq, A.; Sunaryono; Mufti, N.

2017-05-01

The use of silica in various fields is significantly increasing. One common application is silica based functional glass which has naturally show specific dielectric, optical, and magnetic properties. Many studies have been performing to explore the influence of dopant, composition, and other processing parameters as well as employing various characterization. In the previous work, we report the use of silica from silica sands. To reduce the melting temperature, we used silica sol-gel beside the utilization of some oxides such as B2O3, Na2CO3, and Bi3O3. We also used NiO as dopant explore the glass properties. We have prepared a series of sample with the composition of 50SiO2-25B2O3-(6.5-x) Bi3O3-18.5 Na2CO3-xNiO (x = 0, 1, 2, 3 and 4 wt%). After weighting process, the composition was blended, then heated to 450 °C for 120 minutes and then raised at 950 °C for 60 minutes in the crucible. Then samples of glass separated from the crucible and in the characterization of the structure using the DTA, XRD, SEM-EDAX and FTIR and measuring dielectric constant using a capacitance meter. The increase of NiO dopant resulted in increasing the dielectric constant of glass. On the other hand, the dielectric constant gradually decreases with the increase of light intensity. One can be noted that the applied intensity give rise to the step-like decrease of the dielectric constant. Whereas, the increasing magnetic field indicate the increase of dielectric constant.

Poly(methyl methacrylate) as a self-assembled gate dielectric for graphene field-effect transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sanne, A.; Movva, H. C. P.; Kang, S.

We investigate poly(methyl methacrylate) (PMMA) as a low thermal budget organic gate dielectric for graphene field effect-transistors (GFETs) based on a simple process flow. We show that high temperature baking steps above the glass transition temperature (∼130 °C) can leave a self-assembled, thin PMMA film on graphene, where we get a gate dielectric almost for “free” without additional atomic layer deposition type steps. Electrical characterization of GFETs with PMMA as a gate dielectric yields a dielectric constant of k = 3.0. GFETs with thinner PMMA dielectrics have a lower dielectric constant due to decreased polarization arising from neutralization of dipoles and charged carriersmore » as baking temperatures increase. The leakage through PMMA gate dielectric increases with decreasing dielectric thickness and increasing electric field. Unlike conventional high-k gate dielectrics, such low-k organic gate dielectrics are potentially attractive for devices such as the proposed Bilayer pseudoSpin Field-Effect Transistor or flexible high speed graphene electronics.« less

Optical and microwave dielectric properties of pulsed laser deposited Na{sub 0.5}Bi{sub 0.5}TiO{sub 3} thin film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joseph, Andrews; Goud, J. Pundareekam; Raju, K. C. James

2016-05-23

Optical properties of pulsed laser deposited (PLD) sodium bismuth titanate thin films (NBT), are investigated at wavelengths of 190-2500 nm. Microwave dielectric properties were investigated using the Split Post Dielectric Resonator (SPDR) technique. At 10 GHz, the NBT films have a dielectric constant of 205 and loss tangent of 0.0373 at room temperature. The optical spectra analysis reveals that NBT thin films have an optical band gap E{sub g}=3.55 eV and it has a dielectric constant of 3.37 at 1000 nm with dielectric loss of 0.299. Hence, NBT is a promising candidate for photonic device applications.

Like-Charge Guanidinium Pairing between Ligand and Receptor: An Unusual Interaction for Drug Discovery and Design?

PubMed

Yang, Yang; Xu, Zhijian; Zhang, Zhengyan; Yang, Zhuo; Liu, Yingtao; Wang, Jinan; Cai, Tingting; Li, Shujin; Chen, Kaixian; Shi, Jiye; Zhu, Weiliang

2015-09-10

A database survey in this study revealed for the first time that there are 227 counterintuitive like-charge guanidinium pairings (Gdm(+)-Arg pairings) between ligands and receptors in the Protein Data Bank, implying the potential guanidinium-arginine binding between guanidine-containing drugs and their target proteins. Furthermore, there are 145 guanidine-containing molecules in the DrugBank, showing the prevalence of guanidinium groups in drugs. It has also been reported that the introduction of a guanidinium group forming Gdm(+)-Arg pairing improved the potency of the drug by more than 8-fold in a typical case. On the basis of the survey, six ligand-protein complexes with typical Gdm(+)-Arg pairings were chosen for QM/MM calculations. The calculations at the B97-D/6-311++g(d,p) level revealed that the interaction could be as strong as -1.0 to -2.5 kcal/mol in DMSO and water, comparable to common intermolecular interactions. The calculations also unveiled that the Gdm(+)-Arg pairing interactions change from repulsive to attractive with the increase of dielectric constant, suggesting that the dielectric constant has a general stabilization effect on the Gdm(+)-Arg pairing. This study suggested that the like-charge guanidinium pairing interaction could be used not only for tuning the physical and chemical properties of drug leads but also for improving ligand binding affinity.

Accurate Measurements of the Dielectric Constant of Seawater at L Band

NASA Technical Reports Server (NTRS)

Lang, Roger; Zhou, Yiwen; Utku, Cuneyt; Le Vine, David

2016-01-01

This paper describes measurements of the dielectric constant of seawater at a frequency of 1.413 GHz, the center of the protected band (i.e., passive use only) used in the measurement of sea surface salinity from space. The objective of the measurements is to accurately determine the complex dielectric constant of seawater as a function of salinity and temperature. A resonant cylindrical microwave cavity in transmission mode has been employed to make the measurements. The measurements are made using standard seawater at salinities of 30, 33, 35, and 38 practical salinity units over a range of temperatures from 0 degree C to 35 degree C in 5 degree C intervals. Repeated measurements have been made at each temperature and salinity. Mean values and standard deviations are then computed. The total error budget indicates that the real and imaginary parts of the dielectric constant have a combined standard uncertainty of about 0.3 over the range of salinities and temperatures considered. The measurements are compared with the dielectric constants obtained from the model functions of Klein and Swift and those of Meissner and Wentz. The biggest differences occur at low and high temperatures.

Dielectric characteristics of Mn-doped LaTiO3+δ ceramics

NASA Astrophysics Data System (ADS)

Chen, Yan; Cui, Yimin

A series of ceramic composites of Mn-doped La1- x MnxTiO3+ δ and LaMnxTi1- x O3+ δ (x = 0.1, 0.2) were synthesized by conventional solid-state reaction method. The low-frequency complex dielectric properties of the composites were investigated as functions of temperature (77 K <= T <= 360 K) and frequency (100 Hz <= f <= 1 MHz), respectively. The dielectric constant of A-site doped samples is higher than that of B-site doped samples. The loss tangent of low doped samples is much less than that of high doped samples. The A-site doped composites exhibit intrinsic dielectric response with a dielectric constant of 40 in the temperature below 250 K. Interestingly, the dielectric constants of B-site doped ceramics increase slightly in the temperature range from 77 to 360 K. And it is clearly observed that extraordinarily high dielectric loss tangent ( 6) appear at low frequency (100 Hz) in LaMn0.2Ti0.8O3+ δ , which is 8 times larger than that of LaMn0.1Ti0.9O3+ δ , which indicates that the doped content can affect the intrinsic dielectric characteristics significantly.

Investigation of structural, optical and electrical properties of Co3O4 nanoparticles

NASA Astrophysics Data System (ADS)

Bhargava, Richa; Khan, Shakeel; Ahmad, Naseem; Ansari, Mohd Mohsin Nizam

2018-05-01

In the current work, we report the synthesis of Cobalt oxide (Co3O4) NPs (NPs) by co-precipitation method. The structural analysis was confirmed by using X-ray diffractometer (XRD) which shows that the Co3O4 NPs have cubic phase. The average crystallite size and the lattice parameter were calculated for Co3O4 NPs. The functional groups of the as-synthesized sample were examined by Fourier transform infrared spectroscopy (FTIR). The optical band gap of Co3O4 NPs was estimated by using UV diffuse reflectance spectroscopy and the Band gap was evaluated by using Tauc relation. The temperature dependence of dielectric constant and dielectric loss were studied over a range of temperature 50-300 °C. The DC electrical resistivity of Co3O4 NPs shows a semiconducting behaviour and the value of activation energy was calculated by using Arrhenius equation.

Low percolation transitions in carbon nanotube networks dispersed in a polymer matrix: dielectric properties, simulations and experiments.

PubMed

Simoes, Ricardo; Silva, Jaime; Vaia, Richard; Sencadas, Vítor; Costa, Pedro; Gomes, João; Lanceros-Méndez, Senentxu

2009-01-21

The low concentration behaviour and the increase of the dielectric constant in carbon nanotubes/polymer nanocomposites near the percolation threshold are still not well understood. In this work, a numerical model has been developed which focuses on the effect of the inclusion of conductive fillers in a dielectric polymer matrix on the dielectric constant and the dielectric strength. Experiments have been carried out in carbon nanotubes/poly(vinylidene fluoride) nanocomposites in order to compare to the simulation results. This work shows how the critical concentration is related to the formation of capacitor networks and that these networks give rise to high variations in the electrical properties of the composites. Based on numerical studies, the dependence of the percolation transition on the preparation of the nanocomposite is discussed. Finally, based on numerical and experimental results, both ours and from other authors, the causes of anomalous percolation behaviour of the dielectric constant are identified.

Dielectric properties of doping-free NaMn{sub 7}O{sub 12}: Origin of the observed colossal dielectric constant

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cabassi, R.; Bolzoni, F.; Gauzzi, A.

2006-07-15

The semiconducting NaMn{sub 7}O{sub 12} is a doping-free compound with several coexistent properties such as orbital ordering, charge ordering, and magnetic orderings of different types. We investigated its dielectric response by means of frequency impedance measurements in the range from 20 Hz to 1 MHz. Standard measurements on metallized samples exhibit an apparent colossal dielectric constant (CDC) with an {epsilon}{sub R} value of several thousands at low frequencies, but a careful equivalent circuit analysis allows one to ascribe the observed CDC to the effect of a depletion layer on the metal-semiconductor junctions. We bypass this effect by means of amore » nonstandard technique employing mica linings: the resulting dielectric behavior exhibits the presence of the charge ordering transition at T{sub CO}=176 K and shows a net bulk dielectric constant value {epsilon}{sub R}{approx_equal}68 at room temperature.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mahesh, P., E-mail: pamu@iitg.ernet.in; Subhash, T., E-mail: pamu@iitg.ernet.in; Pamu, D., E-mail: pamu@iitg.ernet.in

We report the dielectric properties of (K{sub 0.5}Na{sub 0.5})NbO{sub 3} ceramics doped with x wt% of Dy{sub 2}O{sub 3} (x= 0.0-1.5 wt%) using the broadband dielectric spectroscopy. The X-ray diffraction studies showed the formation of perovskite structure signifying that Dy{sub 2}O{sub 3} diffuse into the KNN lattice. Samples doped with x > 0.5 wt% exhibit smaller grain size and lower relative densities. The dielectric properties of KNN ceramics doped with Dy{sub 2}O{sub 3} are enhanced by increasing the Dy{sup 3+} content; among the compositions studied, x = 0.5 wt% exhibited the highest dielectric constant and lowest loss at 1MHz overmore » the temperature range of 30°C to 400°C. All the samples exhibit maximum dielectric constant at the Curie temperature (∼ 326°C) and a small peak in the dielectric constant at around 165°C is due to a structural phase transition.« less

Origin of the colossal dielectric permittivity and magnetocapacitance in LuFe2O4

NASA Astrophysics Data System (ADS)

Ren, P.; Yang, Z.; Zhu, W. G.; Huan, C. H. A.; Wang, L.

2011-04-01

We report the detailed study on the colossal dielectric constant and magnetocapacitance of LuFe2O4. The experimental results indicate that the large dielectric constant of LuFe2O4 is originated from two sources, (1) Maxwell Wagner-type contributions of depletion layers at grain boundaries and the interfaces between sample and contacts, (2) AC response of the constant phase element in the bulk. A detailed equivalent circuit analysis indicates that the conductivity variation can be responsible for the observed "magnetocapacitance."

The p- T phase diagram of KNbO 3 by a dielectric constant measurement

NASA Astrophysics Data System (ADS)

Kobayashi, Y.; Endo, S.; Deguchi, K.; Ming, L. C.; Zou, G.

2001-11-01

A dielectric constant measurement was carried out on perovskite-type ferroelectrics KNbO 3 over a wide range of temperature under high pressure. The temperature- and pressure-dependence of the dielectric constant clarified that all temperatures of the transitions from the ferroelectric rhombohedral to orthorhombic, to tetragonal and then to the paraelectric cubic phase, decrease with increasing pressure. These results indicate that the orthorhombic-tetragonal transition takes place at 8.5 GPa and the tetragonal-cubic transition at 11 GPa, at room temperature.

Fluoro-polymer functionalized graphene for flexible ferroelectric polymer-based high-k nanocomposites with suppressed dielectric loss and low percolation threshold.

PubMed

Yang, Ke; Huang, Xingyi; Fang, Lijun; He, Jinliang; Jiang, Pingkai

2014-12-21

Flexible nanodielectric materials with high dielectric constant and low dielectric loss have huge potential applications in the modern electronic and electric industry. Graphene sheets (GS) and reduced-graphene oxide (RGO) are promising fillers for preparing flexible polymer-based nanodielectric materials because of their unique two-dimensional structure and excellent electrical and mechanical properties. However, the easy aggregation of GS/RGO significantly limits the potential of graphene in enhancing the dielectric constant of polymer composites. In addition, the poor filler/matrix nanoscale interfacial adhesion also causes difficulties in suppressing the dielectric loss of the composites. In this work, using a facile and environmentally friendly approach, polydopamine coated RGO (PDA-RGO) and fluoro-polymer functionalized RGO (PF-PDA-RGO) were prepared. Compared with the RGO prepared by the conventional methods [i.e. hydrazine reduced-graphene oxide (H-RGO)] and PDA-RGO, the resulting PF-PDA-RGO nanosheets exhibit excellent dispersion in the ferroelectric polymer matrix [i.e. poly(vinylidene fluoride-co-hexafluoro propylene), P(VDF-HFP)] and strong interfacial adhesion with the matrix, leading to a low percolation threshold (fc = 1.06 vol%) and excellent flexibility for the corresponding nanocomposites. Among the three nanocomposites, the P(VDF-HFP)/PF-PDA-RGO nanocomposites exhibited the optimum performance (i.e. simultaneously having high dielectric constant and low dielectric loss). For instance, at 1000 Hz, the P(VDF-HFP) nanocomposite sample with 1.0 vol% PF-PDA-RGO has a dielectric constant of 107.9 and a dielectric loss of 0.070, showing good potential for dielectric applications. Our strategy provides a new pathway to prepare high performance flexible nanodielectric materials.

Origin of the colossal dielectric response of Pr0.6 Ca0.4 Mn O3

NASA Astrophysics Data System (ADS)

Biškup, N.; de Andrés, A.; Martinez, J. L.; Perca, C.

2005-07-01

We report the detailed study of dielectric response of Pr0.6Ca0.4MnO3 (PCMO), a member of the manganite family showing colossal magnetoresistance. Measurements have been performed on four polycrystalline samples and four single crystals, allowing us to compare and extract the essence of dielectric response in the material. High-frequency dielectric function is found to be ɛHF=30 , as expected for the perovskite material. Dielectric relaxation is found in the frequency window of 20Hzto1MHz at temperatures of 50-200K that yields to colossal low-frequency dielectric function, i.e., the static dielectric constant. The static dielectric constant is always colossal, but varies considerably in different samples from ɛ(0)=103to105 . The measured data can be simulated very well by blocking (surface barrier) capacitance in series with sample resistance. This indicates that the large dielectric constant in PCMO arises from the Schottky barriers at electrical contacts. Measurements in magnetic field and with dc bias support this interpretation. Colossal magnetocapacitance observed in the title compound is thus attributed to extrinsic effects. Weak anomaly at the charge ordering temperature can also be attributed to interplay of sample and contact resistance. We comment on our results in the framework of related studies by other groups.

Mid-infrared plasmonic resonances exploiting heavily-doped Ge on Si

NASA Astrophysics Data System (ADS)

Biagioni, P.; Sakat, E.; Baldassarre, L.; Calandrini, E.; Samarelli, A.; Gallacher, K.; Frigerio, J.; Isella, G.; Paul, D. J.; Ortolani, M.

2015-03-01

We address the behavior of mid-infrared localized plasmon resonances in elongated germanium antennas integrated on silicon substrates. Calculations based on Mie theory and on the experimentally retrieved dielectric constant allow us to study the tunability and the figures of merit of plasmon resonances in heavily-doped germanium and to preliminarily compare them with those of the most established plasmonic material, gold.

Structure and performance of dielectric films based on self-assembled nanocrystals with a high dielectric constant.

PubMed

Huang, Limin; Liu, Shuangyi; Van Tassell, Barry J; Liu, Xiaohua; Byro, Andrew; Zhang, Henan; Leland, Eli S; Akins, Daniel L; Steingart, Daniel A; Li, Jackie; O'Brien, Stephen

2013-10-18

Self-assembled films built from nanoparticles with a high dielectric constant are attractive as a foundation for new dielectric media with increased efficiency and range of operation, due to the ability to exploit nanofabrication techniques and emergent electrical properties originating from the nanoscale. However, because the building block is a discrete one-dimensional unit, it becomes a challenge to capture potential enhancements in dielectric performance in two or three dimensions, frequently due to surface effects or the presence of discontinuities. This is a recurring theme in nanoparticle film technology when applied to the realm of thin film semiconductor and device electronics. We present the use of chemically synthesized (Ba,Sr)TiO3 nanocrystals, and a novel deposition-polymerization technique, as a means to fabricate the dielectric layer. The effective dielectric constant of the film is tunable according to nanoparticle size, and effective film dielectric constants of up to 34 are enabled. Wide area and multilayer dielectrics of up to 8 cm(2) and 190 nF are reported, for which the building block is an 8 nm nanocrystal. We describe models for assessing dielectric performance, and distinct methods for improving the dielectric constant of a nanocrystal thin film. The approach relies on evaporatively driven assembly of perovskite nanocrystals with uniform size distributions in a tunable 7-30 nm size range, coupled with the use of low molecular weight monomer/polymer precursor chemistry that can infiltrate the porous nanocrystal thin film network post assembly. The intercrystal void space (low k dielectric volume fraction) is minimized, while simultaneously promoting intercrystal connectivity and maximizing volume fraction of the high k dielectric component. Furfuryl alcohol, which has good affinity to the surface of (Ba,Sr)TiO3 nanocrystals and miscibility with a range of solvents, is demonstrated to be ideal for the production of nanocomposites. The nanocrystal/furfuryl alcohol dispersions are suitable for the fabrication of thin films by chemical deposition techniques, including spin-coating, printing or a spraying process. To demonstrate the application of this technique to device fabrication, a multilayer capacitor with capacitance of 0.83 nF mm(-2) at 1 MHz is presented.

An empirical model for the complex dielectric permittivity of soils as a function of water content

NASA Technical Reports Server (NTRS)

Wang, J. R.; Chmugge, T. J.

1978-01-01

The recent measurements on the dielectric properties of soils shows that the variation of dielectric constant with moisture content depends on soil types. The observed dielectric constant increases only slowly with moisture content up to a transition point. Beyond the transition it increases rapidly with moisture content. The moisture value of transition region was found to be higher for high clay content soils than for sandy soils. Many mixing formulas were compared with, and were found incompatible with, the measured dielectric variations of soil-water mixtures. A simple empirical model was proposed to describe the dielectric behavior of ths soil-water mixtures. The relationship between transition moisture and wilting point provides a means of estimating soil dielectric properties on the basis of texture information.

Effect of the addition of B{sub 2}O{sub 3} and BaO-B{sub 2}O{sub 3}-SiO{sub 2} glasses on the microstructure and dielectric properties of giant dielectric constant material CaCu{sub 3}Ti{sub 4}O{sub 12}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shri Prakash, B.; Varma, K.B.R.

2007-06-15

The effect of the addition of glassy phases on the microstructure and dielectric properties of CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) ceramics was investigated. Both single-component (B{sub 2}O{sub 3}) and multi-component (30 wt% BaO-60 wt% B{sub 2}O{sub 3}-10 wt% SiO{sub 2} (BBS)) glass systems were chosen to study their effect on the density, microstructure and dielectric properties of CCTO. Addition of an optimum amount of B{sub 2}O{sub 3} glass facilitated grain growth and an increase in dielectric constant. However, further increase in the B{sub 2}O{sub 3} content resulted in its segregation at the grain boundaries associated with a reduction in themore » grain size. In contrast, BBS glass addition resulted in well-faceted grains and increase in the dielectric constant and decrease in the dielectric loss. An internal barrier layer capacitance (IBLC) model was invoked to correlate the dielectric constant with the grain size in these samples. - Graphical abstract: Scanning electron micrograph of 30 wt% BaO-60 wt% B{sub 2}O{sub 3}-10 wt% SiO{sub 2} (BBS) glass-added CaCu{sub 3}Ti{sub 4}O{sub 12} ceramic on sintering.« less

Temperature and size-dependent Hamaker constants for metal nanoparticles

NASA Astrophysics Data System (ADS)

Jiang, K.; Pinchuk, P.

2016-08-01

Theoretical values of the Hamaker constant have been calculated for metal nanoparticles using Lifshitz theory. The theory describes the Hamaker constant in terms of the permittivity of the interacting bodies. Metal nanoparticles exhibit an internal size effect that alters the dielectric permittivity of the particle when its size falls below the mean free path of the conducting electrons. This size dependence of the permittivity leads to size-dependence of the Hamaker constant for metal nanoparticles. Additionally, the electron damping and the plasma frequency used to model the permittivity of the particle exhibit temperature-dependence, which lead to temperature dependence of the Hamaker constant. In this work, both the size and temperature dependence for gold, silver, copper, and aluminum nanoparticles is demonstrated. The results of this study might be of interest for studying the colloidal stability of nanoparticles in solution.

Temperature and size-dependent Hamaker constants for metal nanoparticles.

PubMed

Jiang, K; Pinchuk, P

2016-08-26

Theoretical values of the Hamaker constant have been calculated for metal nanoparticles using Lifshitz theory. The theory describes the Hamaker constant in terms of the permittivity of the interacting bodies. Metal nanoparticles exhibit an internal size effect that alters the dielectric permittivity of the particle when its size falls below the mean free path of the conducting electrons. This size dependence of the permittivity leads to size-dependence of the Hamaker constant for metal nanoparticles. Additionally, the electron damping and the plasma frequency used to model the permittivity of the particle exhibit temperature-dependence, which lead to temperature dependence of the Hamaker constant. In this work, both the size and temperature dependence for gold, silver, copper, and aluminum nanoparticles is demonstrated. The results of this study might be of interest for studying the colloidal stability of nanoparticles in solution.

An Improved Dielectric Constant Cell for Use in Student and Research Laboratories.

ERIC Educational Resources Information Center

Thompson, H. Bradford.; Walmsley, Judith A.

1979-01-01

Describes the latest stage in the design of an economical dielectric constant cell, tested in both instructional and research applications, that is suitable for student laboratories and for precision research measurements. (BT)

Advanced concepts for transformers pressboard dielectric constant and mechanical strength

NASA Astrophysics Data System (ADS)

1982-03-01

Of the numerous electrical considerations in a material, the value of the dielectric constant serves as an important criterion in designing proper insulation systems. Ways to reduce the dielectric constant of solid (fibrous) insulating materials were investigated. A literature search was made on cellulosic and synthetic fibers and also additives which offered the potential for dielectric constant reduction of the solid insulation. Sample board structures were produced in the laboratory and tested for electrical, mechanical and chemical characteristics. Electrical tests determined the suitability of the material at transformer test and operating conditions. The mechanical tests established the physical characteristics of the modified board structures. Chemical tests checked the conductivity of the aqueous extract, acidity, and ash content. Further, compatibility with transformer oil and some aging tests were performed. An actual computer transformer design was made based on one of the modified board structures and the reduction in core steel and transformer losses were shown.

Microstructural, optical and electrical transport properties of Cd-doped SnO2 nanoparticles

NASA Astrophysics Data System (ADS)

Ahmad, Naseem; Khan, Shakeel; Mohsin Nizam Ansari, Mohd

2018-03-01

We have successfully investigated the structural, optical and dielectric properties of Cd assimilated SnO2 nanoparticles synthesized via very convenient precipitation route. The structural properties were studied by x-ray diffraction method (XRD) and Fourier Transform Infrared (FTIR) Spectroscopy. As-synthesized samples in the form of powder were examined for its morphology and average particle size by Transmission electron microscopy (TEM). The optical properties were studied by diffuse reflectance spectroscopy. Dielectric properties such that complex dielectric constant and ac conductivity were investigated by LCR meter. Average crystallite size calculated by XRD and average particle size obtained from TEM were found to be consistent and below 50 nm for all samples. The optical band gap of as-synthesized powder samples from absorption study was found in the range of 3.76 to 3.97 eV. The grain boundary parameters such that Rgb, Cgb and τ were evaluated using impedance spectroscopy.

Substantial optical dielectric enhancement by volume compression in LiAsSe 2

DOE PAGES

Zheng, Fan; Brehm, John A.; Young, Steve M.; ...

2016-05-15

Based on first-principles calculations, we predict a substantial increase in the optical dielectric function of LiAsSemore » $$_2$$ under pressure. We find that the optical dielectric constant is enhanced threefold under volume compression. This enhancement is mainly due to the dimerization strength reduction of the one-dimensional (1D) As--Se chains in LiAsSe$$_2$$, which significantly alters the wavefunction phase mismatch between two neighboring chains and changes the transition intensity. By developing a tight-binding model of the interacting 1D chains, the essential features of the low-energy electronic structure of LiAsSe$$_2$$ are captured. In conclusion, our findings are important for understanding the fundamental physics of LiAsSe$$_2$$ and provide a feasible way to enhance the material optical response that can be applied to light harvesting for energy applications.« less

Solvent effects on the excited-state double proton transfer mechanism in the 7-azaindole dimer: a TDDFT study with the polarizable continuum model.

PubMed

Yu, Xue-Fang; Yamazaki, Shohei; Taketsugu, Tetsuya

2017-08-30

Solvent effects on the excited-state double proton transfer (ESDPT) mechanism in the 7-azaindole (7AI) dimer were investigated using the time-dependent density functional theory (TDDFT) method. Excited-state potential energy profiles along the reaction paths in a locally excited (LE) state and a charge transfer (CT) state were calculated using the polarizable continuum model (PCM) to include the solvent effect. A series of non-polar and polar solvents with different dielectric constants were used to examine the polarity effect on the ESDPT mechanism. The present results suggest that in a non-polar solvent and a polar solvent with a small dielectric constant, ESDPT follows a concerted mechanism, similar to the case in the gas phase. In a polar solvent with a relatively large dielectric constant, however, ESDPT is likely to follow a stepwise mechanism via a stable zwitterionic intermediate in the LE state on the adiabatic potential energy surface, although inclusion of zero-point vibrational energy (ZPE) corrections again suggests the concerted mechanism. In the meantime, the stepwise reaction path involving the CT state with neutral intermediates is also examined, and is found to be less competitive than the concerted or stepwise path in the LE state in both non-polar and polar solvents. The present study provides a new insight into the experimental controversy of the ESDPT mechanism of the 7AI dimer in a solution.

MCCE2: improving protein pKa calculations with extensive side chain rotamer sampling.

PubMed

Song, Yifan; Mao, Junjun; Gunner, M R

2009-11-15

Multiconformation continuum electrostatics (MCCE) explores different conformational degrees of freedom in Monte Carlo calculations of protein residue and ligand pK(a)s. Explicit changes in side chain conformations throughout a titration create a position dependent, heterogeneous dielectric response giving a more accurate picture of coupled ionization and position changes. The MCCE2 methods for choosing a group of input heavy atom and proton positions are described. The pK(a)s calculated with different isosteric conformers, heavy atom rotamers and proton positions, with different degrees of optimization are tested against a curated group of 305 experimental pK(a)s in 33 proteins. QUICK calculations, with rotation around Asn and Gln termini, sampling His tautomers and torsion minimum hydroxyls yield an RMSD of 1.34 with 84% of the errors being <1.5 pH units. FULL calculations adding heavy atom rotamers and side chain optimization yield an RMSD of 0.90 with 90% of the errors <1.5 pH unit. Good results are also found for pK(a)s in the membrane protein bacteriorhodopsin. The inclusion of extra side chain positions distorts the dielectric boundary and also biases the calculated pK(a)s by creating more neutral than ionized conformers. Methods for correcting these errors are introduced. Calculations are compared with multiple X-ray and NMR derived structures in 36 soluble proteins. Calculations with X-ray structures give significantly better pK(a)s. Results with the default protein dielectric constant of 4 are as good as those using a value of 8. The MCCE2 program can be downloaded from http://www.sci.ccny.cuny.edu/~mcce. 2009 Wiley Periodicals, Inc.

Combinatorial Investigation of ZrO2-Based Dielectric Materials for Dynamic Random-Access Memory Capacitors

NASA Astrophysics Data System (ADS)

Kiyota, Yuji; Itaka, Kenji; Iwashita, Yuta; Adachi, Tetsuya; Chikyow, Toyohiro; Ogura, Atsushi

2011-06-01

We investigated zirconia (ZrO2)-based material libraries in search of new dielectric materials for dynamic random-access memory (DRAM) by combinatorial-pulsed laser deposition (combi-PLD). We found that the substitution of yttrium (Y) to Zr sites in the ZrO2 system suppressed the leakage current effectively. The metal-insulator-metal (MIM) capacitor property of this system showed a leakage current density of less than 5×10-7 A/cm2 and the dielectric constant was 20. Moreover, the addition of titanium (Ti) or tantalum (Ta) to this system caused the dielectric constant to increase to ˜25 within the allowed leakage level of 5×10-7 A/cm2. Therefore, Zr-Y-Ti-O and Zr-Y-Ta-O systems have good potentials for use as new materials with high dielectric constants of DRAM capacitors instead of silicon dioxides (SiO2).

Vibrational, DFT, thermal and dielectric studies on 3-nitrophenol-1,3,5-triazine-2,4,6-triamine (2/1).

PubMed

Sangeetha, V; Govindarajan, M; Kanagathara, N; Marchewka, M K; Gunasekaran, S; Anbalagan, G

2014-01-24

A new organic-organic salt, 3-nitrophenol-1,3,5-triazine-2,4,6-triamine (2/1) (3-NPM) has been synthesized by slow evaporation technique at room temperature. Single crystal X-ray diffraction analysis reveals that 3-NPM crystallizes in orthorhombic system with centrosymmetric space group Pbca and the lattice parameters are a=15.5150(6) Å, b=12.9137(6) Å, c=17.8323(6) Å, α=β=γ=90° and V=3572.8(2)(Å)(3). The geometry, fundamental vibrational frequencies are interpreted with the aid of structure optimization and normal coordinate force field calculations based on density functional theory (DFT) B3LYP/6-311G(d,p) method. IR and Raman spectra of 3-NPM have been recorded and analyzed. The complete vibrational assignments are made on the basis of potential energy distribution (PED). The electric dipole moment, polarizability and the first order hyperpolarizability values of the 3-NPM have been calculated. (1)H and (13)C NMR chemical shifts are calculated by using the gauge independent atomic orbital (GIAO) method with B3LYP method with 6-311G (d,p) basis set. Moreover, molecular electrostatic potential (MEP) and thermodynamic properties are performed. Mulliken and Natural charges of the title molecule are also calculated and interpreted. Thermal decomposition behavior of 3-NPM has been studied by means of thermogravimetric analysis. The dielectric measurements on the powdered sample have been carried out and the variation of dielectric constant and dielectric loss at different frequencies of the applied field has been studied and the results are discussed in detail. Copyright © 2013 Elsevier B.V. All rights reserved.

Vibrational, DFT, thermal and dielectric studies on 3-nitrophenol-1,3,5-triazine-2,4,6-triamine (2/1)

NASA Astrophysics Data System (ADS)

Sangeetha, V.; Govindarajan, M.; Kanagathara, N.; Marchewka, M. K.; Gunasekaran, S.; Anbalagan, G.

2014-01-01

A new organic-organic salt, 3-nitrophenol-1,3,5-triazine-2,4,6-triamine (2/1) (3-NPM) has been synthesized by slow evaporation technique at room temperature. Single crystal X-ray diffraction analysis reveals that 3-NPM crystallizes in orthorhombic system with centrosymmetric space group Pbca and the lattice parameters are a = 15.5150(6) Å, b = 12.9137(6) Å, c = 17.8323(6) Å, α = β = γ = 90° and V = 3572.8(2) (Å)3. The geometry, fundamental vibrational frequencies are interpreted with the aid of structure optimization and normal coordinate force field calculations based on density functional theory (DFT) B3LYP/6-311G(d,p) method. IR and Raman spectra of 3-NPM have been recorded and analyzed. The complete vibrational assignments are made on the basis of potential energy distribution (PED). The electric dipole moment, polarizability and the first order hyperpolarizability values of the 3-NPM have been calculated. 1H and 13C NMR chemical shifts are calculated by using the gauge independent atomic orbital (GIAO) method with B3LYP method with 6-311G (d,p) basis set. Moreover, molecular electrostatic potential (MEP) and thermodynamic properties are performed. Mulliken and Natural charges of the title molecule are also calculated and interpreted. Thermal decomposition behavior of 3-NPM has been studied by means of thermogravimetric analysis. The dielectric measurements on the powdered sample have been carried out and the variation of dielectric constant and dielectric loss at different frequencies of the applied field has been studied and the results are discussed in detail.

Effects of Cr/Zn Substitutions on Dielectric Properties of CaCu{sub 3}Ti{sub 4}O{sub 12}(CCTO) Ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rajmi, R.; Yahya, A. K.; Deni, M. S. M.

2010-07-07

Effects of Zn and Cr substitutions on dielectric properties of CaCu{sub 3-x}Zn{sub x}Ti{sub 4-y}Cr{sub y}O{sub 12} ceramics are reported. Dielectric measurements at room temperature for un-substituted CaCu{sub 3-x}Zn{sub x}Ti{sub 4-y}Cr{sub y}O{sub 12}(x = 0, y = 0) between 10{sup 2}-10{sup 6} Hz showed dielectric constant of 2.7x10{sup 4} at 10{sup 2} Hz. Substitution of Zn for Cu in CaCu{sub 3-x}Zn{sub xTi{sub 4{sub -{sub yCr{sub yO{sub 1{sub 2}}}}}}}(y = 0, x = 0.10, 0.50)caused dielectric constant to drop with increasing x. Cr substitution at Ti-site in CaCu{sub 3-x}Zn{sub xTi{sub 4{sub -{sub yCr{sub yO{sub 1{sub 2}}}}}}}(x = 0, x = 0,) alsomore » caused decrease in dielectric constant. However, at x = 0.50, the dielectric constant at low frequency was enhanced compared to the un-substituted sample. Our results indicate that Cu and Ti sites play an important role in the formation of Internal Barrier Layer Capacitance (IBLC) in CCTO.« less

Reversible dielectric property degradation in moisture-contaminated fiber-reinforced laminates

NASA Astrophysics Data System (ADS)

Rodriguez, Luis A.; García, Carla; Fittipaldi, Mauro; Grace, Landon R.

2016-03-01

The potential for recovery of dielectric properties of three water-contaminated fiber-reinforced laminates is investigated using a split-post dielectric resonant technique at X-band (10 GHz). The three material systems investigated are bismaleimide (BMI) reinforced with an eight-harness satin weave quartz fabric, an epoxy resin reinforced with an eight- harness satin weave glass fabric (style 7781), and the same epoxy reinforced with a four-harness woven glass fabric (style 4180). A direct correlation between moisture content, dielectric constant, and loss tangent was observed during moisture absorption by immersion in distilled water at 25 °C for five equivalent samples of each material system. This trend is observed through at least 0.72% water content by weight for all three systems. The absorption of water into the BMI, 7781 epoxy, and 4180 epoxy laminates resulted in a 4.66%, 3.35%, and 4.01% increase in dielectric constant for a 0.679%, 0.608%, and 0.719% increase in water content by weight, respectively. Likewise, a significant increase was noticed in loss tangent for each material. The same water content is responsible for a 228%, 71.4%, and 64.1% increase in loss tangent, respectively. Subsequent to full desorption through drying at elevated temperature, the dielectric constant and loss tangent of each laminate exhibited minimal change from the dry, pre-absorption state. The dielectric constant and loss tangent change after the absorption and desorption cycle, relative to the initial state, was 0.144 % and 2.63% in the BMI, 0.084% and 1.71% in the style 7781 epoxy, and 0.003% and 4.51% in the style 4180 epoxy at near-zero moisture content. The similarity of dielectric constant and loss tangent in samples prior to absorption and after desorption suggests that any chemical or morphological changes induced by the presence of water have not caused irreversible changes in the dielectric properties of the laminates.

Magnetically tunable liquid dielectric with giant dielectric permittivity based on core-shell superparamagnetic iron oxide.

PubMed

Vinayasree, S; Nitha, T S; Tiwary, C S; Ajayan, P M; Joy, P A; Anantharaman, M R

2018-06-29

A liquid dielectric based on a core-shell architecture having a superparamagnetic iron oxide core and a shell of silicon dioxide was synthesized. The frequency dependence of dielectric properties was evaluated for different concentrations of iron oxide. The dependence of magnetic field on the dielectric properties was also studied. Aqueous ferrofluid exhibited a giant dielectric constant of 6.4 × 10 5 at 0.1 MHz at a concentration of 0.2 vol% and the loss tangent was 3. The large rise in dielectric constant at room temperature is modelled and explained using percolation theory and Maxwell-Wagner-Sillars type polarization. The ferrofluid is presumed to consist of nanocapacitor networks which are wired in series along the lateral direction and parallel along longitudinal direction. On the application of an external magnetic field, the chain formation and its alignment results in the variation of dielectric permittivity.

Role of annealing temperatures on structure polymorphism, linear and nonlinear optical properties of nanostructure lead dioxide thin films

NASA Astrophysics Data System (ADS)

Zeyada, H. M.; Makhlouf, M. M.

2016-04-01

The powder of as synthesized lead dioxide (PbO2) has polycrystalline structure β-PbO2 phase of tetragonal crystal system. It becomes nanocrystallites α-PbO2 phase with orthorhombic crystal system upon thermal deposition to form thin films. Annealing temperatures increase nanocrystallites size from 28 to 46 nm. The optical properties of α-PbO2 phase were calculated from absolute values of transmittance and reflectance at nearly normal incidence of light by spectrophotometer measurements. The refractive and extinction indices were determined and showed a response to annealing temperatures. The absorption coefficient of α-PbO2 films is >106 cm-1 in UV region of spectra. Analysis of the absorption coefficient spectra near optical edge showed indirect allowed transition. Annealing temperature decreases the value of indirect energy gap for α-PbO2 films. The dispersion parameters such as single oscillator energy, dispersion energy, dielectric constant at high frequency and lattice dielectric constant were calculated and its variations with annealing temperatures are reported. The nonlinear refractive index (n2), third-order nonlinear susceptibility (χ(3)) and nonlinear absorption coefficient (βc) were determined. It was found that χ(3), n2 and β increase with increasing photon energy and decrease with increasing annealing temperature. The pristine film of α-PbO2 has higher values of nonlinear optical constants than for annealed films; therefore it is suitable for applications in manufacturing nonlinear optical devices.

First principles study of optical properties of molybdenum disulfide: From bulk to monolayer

NASA Astrophysics Data System (ADS)

Hieu, Nguyen N.; Ilyasov, Victor V.; Vu, Tuan V.; Poklonski, Nikolai A.; Phuc, Huynh V.; Phuong, Le T. T.; Hoi, Bui D.; Nguyen, Chuong V.

2018-03-01

In this paper, we theoretically study the optical properties of both bulk and monolayer MoS2 using first-principles calculations. The optical characters such as: dielectric function, optical reflectivity, and electron energy-loss spectrum of MoS2 are observed in the energy region from 0 to 15 eV. At equilibrium state the dielectric constant in the parallel E∥ x and perpendicular E∥ z directions are of 15.01 and 8.92 for bulk while they are 4.95 and 2.92 for monolayer MoS2, respectively. In the case of bulk MoS2, the obtained computational results for both real and imaginary parts of the dielectric constant are in good agreement with the previous experimental data. In the energy range from 0 to 6 eV, the dielectric functions have highly anisotropic, whereas they become isotropic when the energy is larger than 7 eV. For the adsorption spectra and optical reflectivity, both the collective plasmon resonance and (π + σ) electron plasmon peaks are observed, in which the transition in E∥ x direction is accordant with the experiment data more than the transition in E∥ z direction is. The refractive index, extinction index, and electron energy-loss spectrum are also investigated. The observed prominent peak at 23.1 eV in the energy-loss spectra is in good agreement with experiment value. Our results may provide a useful potential application for the MoS2 structures in electronic and optoelectronic devices.

Electrical conduction mechanism and dielectric characterization of MnTPPCl thin films

NASA Astrophysics Data System (ADS)

Meikhail, M. S.; Oraby, A. H.; El-Nahass, M. M.; Zeyada, H. M.; Al-Muntaser, A. A.

2018-06-01

The AC conductivity and dielectric properties of MnTPPCl sandwich structure as Au/MnTPPCl/Au were studied. The conductivity of the MnTPPCl thin films have been interpreted by the correlated barrier hopping (CBH) model. The dominant conduction process have found to be the single polaron hopping conduction. The values of the hopping distance, Rω, barrier height, W, and the localized-state density, N, are estimated at different frequencies. The behavior of dielectric constant and dielectric loss was discussed as a function of temperature and frequency. The dielectric constant was described in terms of polarization mechanism in materials. The spectral behavior of dielectric loss is interpreted on the basis of the Giuntini et al. model [1]. The value of WM is obtained as 0.32 eV. A non-Debye relaxation phenomenon was observed from the dielectric relaxation mechanism.

Synthesis of Derivatives of Alpha, Omega Difunctional Perfluoroaliphatic Compounds for Low Dielectric Constant Resins

DTIC Science & Technology

1992-03-06

coupling reactions of perfluoroalkyl iodides with certain aryl iodides have been studied. Simple trial tests were carried out between perfluorooctyl iodide...omega Difunctional Perfluoroaliphatic Compounds for Low Dielectric Constant Resins by Robert L. Soulen Department of Chemistry Southwestern University...Difunctional Perfluoroaliphatic Compounds for Low Dielectric Resins 12 PERSONAL AUTHOR(S) Robert L. Soulen 1Ja TYPE OF REPORT 73b TIME COVERED FI DATE OF

Dielectric constants of soils at microwave frequencies-2

NASA Technical Reports Server (NTRS)

Wang, J.; Schmugge, T.; Williams, D.

1978-01-01

The dielectric constants of several soil samples were measured at frequencies of 5 and 19 GHz using the infinite transmission line method. The results of these measurements are presented and discussed with respect to soil types and texture structures. A comparison is made with other measurements at 1.4 GHz. At all three frequencies, the dependence of dielectric constant on soil moisture can be approximated by two straight lines. At low moisture, the slope is less than at high moisture level. The intersection of the two lines is believed to be a function of soil texture.

Role of dielectric constant in electrohydrodynamics of conducting fluids

NASA Technical Reports Server (NTRS)

Rhodes, Percy H.; Snyder, Robert S.; Roberts, Glyn O.

1994-01-01

Electrohydrodynamic sample distortion during continuous flow electrophoresis is an experiment to be conducted during the second International Microgravity Laboratory (IML-2) in July 1994. The specific objective of this experiment is the distortion caused by the difference in dielectric constant between the sample and surrounding buffer. Although the role of sample conductivity in electrohydrodynamic has been the subject of both flight and ground experiments, the separate role of dielectric constant, independent of sample conductivity, has not been measured. This paper describes some of the laboratory research and model development that will support the flight experiment on IML-2.

Remote Sensing of Salinity: The Dielectric Constant of Sea Water

NASA Technical Reports Server (NTRS)

LeVine, David M.; Lang, R.; Utku, C.; Tarkocin, Y.

2011-01-01

Global monitoring of sea surface salinity from space requires an accurate model for the dielectric constant of sea water as a function of salinity and temperature to characterize the emissivity of the surface. Measurements are being made at 1.413 GHz, the center frequency of the Aquarius radiometers, using a resonant cavity and the perturbation method. The cavity is operated in a transmission mode and immersed in a liquid bath to control temperature. Multiple measurements are made at each temperature and salinity. Error budgets indicate a relative accuracy for both real and imaginary parts of the dielectric constant of about 1%.

Microclimate, Water Potential, Transpiration, and Bole Dielectric Constant of Coniferous and Deciduous Tree Species in the Continental Boreal Ecotone of Central Alaska

NASA Technical Reports Server (NTRS)

Zimmermann, R.; McDonald, K.; Way, J.; Oren, R.

1994-01-01

Tree canopy microclimate, xylem water flux and xylem dielectric constant have been monitored in situ since June 1993 in two adjacent natural forest stands in central Alaska. The deciduous stand represents a mature balsam poplar site on the Tanana River floodplain, while the coniferous stand consists of mature white spruce with some black spruce mixed in. During solstice in June and later in summer, diurnal changes of xylem water potential were measured to investigate the occurrence and magnitude of tree transpiration and dielectric constant changes in stems.

Solid electrolytes

DOEpatents

Abraham, Kuzhikalail M.; Alamgir, Mohamed

1993-06-15

This invention pertains to Li ion (Li.sup.+) conductive solid polymer electrolytes composed of solvates of Li salts immobilized (encapsulated) in a solid organic polymer matrix. In particular, this invention relates to solid polymer electrolytes derived by immobilizing complexes (solvates) formed between a Li salt such as LiAsF.sub.6, LiCF.sub.3 SO.sub.3 or LiClO.sub.4 and a mixture of aprotic organic solvents having high dielectric constants such as ethylene carbonate (EC) (dielectric constant=89.6) and propylene carbonate (PC) (dielectric constant=64.4) in a polymer matrix such as polyacrylonitrile, poly(tetraethylene glycol diacrylate), or poly(vinyl pyrrolidinone).

Solvent Dependence of Double Proton Transfer in the Formic Acid-Formamidine Complex: Path Integral Molecular Dynamics Investigation.

PubMed

Kungwan, Nawee; Ngaojampa, Chanisorn; Ogata, Yudai; Kawatsu, Tsutomu; Oba, Yuki; Kawashima, Yukio; Tachikawa, Masanori

2017-10-05

Solvent dependence of double proton transfer in the formic acid-formamidine (FA-FN) complex at room temperature was investigated by means of ab initio path integral molecular dynamics (AIPIMD) simulation with taking nuclear quantum and thermal effects into account. The conductor-like screening model (COSMO) was applied for solvent effect. In comparison with gas phase, double proton delocalization between two heavy atoms (O and N) in FA-FN were observed with reduced proton transfer barrier height in low dielectric constant medium (<4.8). For dielectric constant medium at 4.8, the chance of finding these two protons are more pronounced due to the solvent effect which completely washes out the proton transfer barrier. In the case of higher dielectric constant medium (>4.8), the ionic species becomes more stable than the neutral ones and the formate anion and formamidium cation are thermodynamically stable. For ab initio molecular dynamics simulation, in low dielectric constant medium (<4.8) a reduction of proton transfer barrier with solvent effect is found to be less pronounced than the AIPIMD due to the absence of nuclear quantum effect. Moreover, the motions of FA-FN complex are significantly different with increasing dielectric constant medium. Such a difference is revealed in detail by the principal component analysis.

Non-polarizable force field of water based on the dielectric constant: TIP4P/ε.

PubMed

Fuentes-Azcatl, Raúl; Alejandre, José

2014-02-06

The static dielectric constant at room temperature and the temperature of maximum density are used as target properties to develop, by molecular dynamics simulations, the TIP4P/ε force field of water. The TIP4P parameters are used as a starting point. The key step, to determine simultaneously both properties, is to perform simulations at 240 K where a molecular dipole moment of minimum density is found. The minimum is shifted to larger values of μ as the distance between the oxygen atom and site M, lOM, decreases. First, the parameters that define the dipole moment are adjusted to reproduce the experimental dielectric constant and then the Lennard-Jones parameters are varied to match the temperature of maximum density. The minimum on density at 240 K allows understanding why reported TIP4P models fail to reproduce the temperature of maximum density, the dielectric constant, or both properties. The new model reproduces some of the thermodynamic and transport anomalies of water. Additionally, the dielectric constant, thermodynamics, and dynamical and structural properties at different temperatures and pressures are in excellent agreement with experimental data. The computational cost of the new model is the same as that of the TIP4P.

Non-trivial behavior of the low temperature maximum of dielectric constant and location of the end critical point in Na0.5Bi0.5TiO3-0.06BaTiO3 lead free relaxor ferroelectrics crystals detected by acoustic emission

NASA Astrophysics Data System (ADS)

Dul'kin, Evgeniy; Tiagunova, Jenia; Mojaev, Evgeny; Roth, Michael

2018-01-01

[001] lead free relaxor ferroelectrics crystals of Na0.5Bi0.5TiO3-0.06BaTiO3 were studied by means of dielectric and acoustic emission methods in the temperature range of 25-240 °C and under a dc bias electric field up to 0.4 kV/cm. A temperature maximum of the dielectric constant was found near 170 °C, as well as the acoustic emission bursts pointed out to both the depolarization temperature near 120 °C and the temperature, corresponding to the maximum of dielectric constant, near 170 °C. While the depolarization temperature increased linearly, the temperature of the dielectric constant maximum was shown to exhibit a V-shape behavior under an electric field: it initially decreases, reaches a sharp minimum at some small threshold electric field of 0.15 kV/cm, and then starts to increase similar to the Curie temperature of the normal ferroelectrics, as the field enhances. Acoustic emission bursts, accompanying the depolarization temperature, weakened with the enhancing field, whereas the ones accompanying the temperature of the dielectric constant maximum exhibited two maxima: near 0.1 kV/cm and near 0.3 kV/cm. The meaning of these two acoustic emission maxima is discussed.

Porosity in plasma enhanced chemical vapor deposited SiCOH dielectrics: A comparative study

NASA Astrophysics Data System (ADS)

Grill, A.; Patel, V.; Rodbell, K. P.; Huang, E.; Baklanov, M. R.; Mogilnikov, K. P.; Toney, M.; Kim, H.-C.

2003-09-01

The low dielectric constant (k) of plasma enhanced chemical vapor deposited SiCOH films has been attributed to porosity in the films. We have shown previously that the dielectric constant of such materials can be extended from the typical k values of 2.7-2.9 to ultralow-k values of k=2.0. The reduction in the dielectric constants has been achieved by enhancing the porosity in the films through the addition of an organic material to the SiCOH precursor and annealing the films to remove the thermally less-stable organic fractions. In order to confirm the relation between dielectric constant and film porosity the latter has been evaluated for SiCOH films with k values from 2.8 to 2.05 using positron annihilation spectroscopy, positron annihilation lifetime spectroscopy, small angle x-ray scattering, specular x-ray reflectivity, and ellipsometric porosimetry measurements. It has been found that the SiCOH films with k=2.8 had no detectable porosity, however the porosity increased with decreasing dielectric constant reaching values of 28%-39% for k values of 2.05. The degree of porosity and the pore size determined by the dissimilar techniques agreed within reasonable limits, especially when one takes into account the small pore size in these films and the different assumptions used by the different techniques. The pore size increases with decreasing k, however the diameter remains below 5 nm for k=2.05, most of the pores being smaller than 2.5 nm.

Thin film colossal dielectric constant oxide La2-xSrxNiO4: Synthesis, dielectric relaxation measurements, and electrode effects

NASA Astrophysics Data System (ADS)

Podpirka, Adrian; Ramanathan, Shriram

2011-01-01

We have successfully synthesized the colossal dielectric constant oxide La2-xSrxNiO4 in thin film form by reactive cosputtering from metallic targets and careful annealing protocols. Composition and phase purity was determined through energy dispersive spectra and x-ray diffraction, respectively. The dielectric constant exceeds values of over 20 000 up to 1 kHz and the activation energy for the frequency-independent conductivity plateau was extracted to be approximately 155 meV from 300 to 473 K, both in agreement with measurements conducted on bulk single crystals. However, unlike in single crystals, we observe early onset of relaxation in thin films indicating the crucial role of grain boundaries in influencing the dielectric response. ac conductivity at varying temperatures is analyzed within the framework of the universal dielectric law leading to an exponent of approximately 0.3, dependent on the electrode material. Impedance spectroscopy with electrodes of different work function (Pt, Pd, and Ag) was further carried out as a function of temperature and applied bias to provide mechanistic insights into the nature of the dielectric response.

Effect of calcination temperature on microstructure, dielectric, magnetic and optical properties of Ba0.7La0.3Fe11.7Co0.3O19 hexaferrites

NASA Astrophysics Data System (ADS)

Kaur, Talwinder; Kaur, Barjinder; Bhat, Bilal H.; Kumar, Sachin; Srivastava, A. K.

2015-01-01

M-type barium hexaferrite Ba0.7La0.3Fe11.7Co0.3O19 (BaLCM) powder, synthesized using sol gel auto combustion method, heat treated at 700, 900, 1100 and 1200 °C. X ray diffraction (XRD) powder patterns of heat treated samples show the formation of pure phase of M-type hexaferrite after 700 °C. Thermo gravimetric analysis (TGA) reveals that the weight loss of BaLCM becomes constant after 680 °C. The presence of two prominent peaks, at 432 cm-1 and 586 cm-1 in Fourier Transform Infrared Spectroscopy (FT-IR) spectra, gives the idea of formation of M-type hexaferrites. The M-H curve obtained from Vibrating Sample Magnetometer (VSM) were used to calculate saturation magnetization (MS), retentivity (Mr), squareness ration (SR) and coercivity (Hc). The maximum value of coercivity (5602 Oe) is found at 900 °C. The band gap dependency on temperature was studied using UV-vis NIR spectroscopy. The dielectric constant has been found to be high at low frequency but it decreases with increase in frequency. Such kind of dielectric behavior is explained on the basis of Koop's phenomenological theory and Maxwell Wagner theory.

Light Assisted IN-VIVO Microwave Sensing for Electrical Characterization of Prokaryotes

NASA Astrophysics Data System (ADS)

Sharma, Rajveer; Daya, K. S.; Tirumalai, Prem Saran

2012-11-01

This paper reports an in vivo characterization technique to characterize dielectric properties of living tissues and bio-molecules at microwave frequency using cavity perturbation technique, where a slot ring resonant sensor has been used, that works at 8 GHz and has been designed to enumerate the effective dielectric constant of Spirulina platensis and chlorophyll molecule. Observed value of the dielectric constant of Spirulina platensis was 8 ± 0.04 in the absence of light and 14.575 ± 0.145 in the presence of light. Molecular polarizability of chl a molecule was 5.07 ± 0.05 × 104 Å3. Experimentally calculated local electric field actually experienced by chl a molecule was 14.197 ± 0.003 V/m for applied field of 9.79 V/m across the slot ring, dipole moment of chl a molecule was 2.175 ± 0.005 × 105 Debye and total polarisation produced due to these molecules was 1.545 ± 0.005 C/m2. Observed relaxation time of chl a molecule was 8.09 ± 0.18 × 10-9s. The proposed sensing method can be an alternate to spectral characterisation technique, generally used to characterize light sensitive bio-molecules and can also be extended to characterize light sensitive bio-molecules in plant cells.

Effects of synthesis techniques on chemical composition, microstructure and dielectric properties of Mg-doped calcium titanate

NASA Astrophysics Data System (ADS)

Jongprateep, Oratai; Sato, Nicha

2018-04-01

Calcium titanate (CaTiO3) has been recognized as a material for fabrication of dielectric components, owing to its moderate dielectric constant and excellent microwave response. Enhancement of dielectric properties of the material can be achieved through doping, compositional and microstructural control. This study, therefore, aimed at investigating effects of powder synthesis techniques on compositions, microstructure, and dielectric properties of Mg-doped CaTiO3. Solution combustion and solid-state reaction were powder synthesis techniques employed in preparation of undoped CaTiO3 and CaTiO3 doped with 5-20 at% Mg. Compositional analysis revealed that powder synthesis techniques did not exhibit a significant effect on formation of secondary phases. When Mg concentration did not exceed 5 at%, the powders prepared by both techniques contained only a single phase. An increase of MgO secondary phase was observed as Mg concentrations increased from 10 to 20 at%. Experimental results, on the contrary, revealed that powder synthesis techniques contributed to significant differences in microstructure. Solution combustion technique produced powders with finer particle sizes, which consequently led to finer grain sizes and density enhancement. High-density specimens with fine microstructure generally exhibit improved dielectric properties. Dielectric measurements revealed that dielectric constants of all samples ranged between 231 and 327 at 1 MHz, and that superior dielectric constants were observed in samples prepared by the solution combustion technique.

High-k 3D-barium titanate foam/phenolphthalein poly(ether sulfone)/cyanate ester composites with frequency-stable dielectric properties and extremely low dielectric loss under reduced concentration of ceramics

NASA Astrophysics Data System (ADS)

Zheng, Longhui; Yuan, Li; Guan, Qingbao; Liang, Guozheng; Gu, Aijuan

2018-01-01

Higher dielectric constant, lower dielectric loss and better frequency stability have been the developing trends for high dielectric constant (high-k) materials. Herein, new composites have been developed through building unique structure by using hyperbranched polysiloxane modified 3D-barium titanate foam (BTF) (BTF@HSi) as the functional fillers and phenolphthalein poly(ether sulfone) (cPES)/cyanate ester (CE) blend as the resin matrix. For BTF@HSi/cPES/CE composite with 34.1 vol% BTF, its dielectric constant at 100 Hz is as high as 162 and dielectric loss is only 0.007; moreover, the dielectric properties of BTF@HSi/cPES/CE composites exhibit excellent frequency stability. To reveal the mechanism behind these attractive performances of BTF@HSi/cPES/CE composites, three kinds of composites (BTF/CE, BTF/cPES/CE, BTF@HSi/CE) were prepared, their structure and integrated performances were intensively investigated and compared with those of BTF@HSi/cPES/CE composites. Results show that the surface modification of BTF is good for preparing composites with improved thermal stability; while introducing flexible cPES to CE is beneficial to fabricate composites with good quality through effectively blocking cracks caused by the stress concentration, and then endowing the composites with good dielectric properties at reduced concentration of ceramics.

Cavity resonator for dielectric measurements of high-ɛ, low loss materials, demonstrated with barium strontium zirconium titanate ceramics

NASA Astrophysics Data System (ADS)

Marksteiner, Quinn R.; Treiman, Michael B.; Chen, Ching-Fong; Haynes, William B.; Reiten, M. T.; Dalmas, Dale; Pulliam, Elias

2017-06-01

A resonant cavity method is presented which can measure loss tangents and dielectric constants for materials with dielectric constant from 150 to 10 000 and above. This practical and accurate technique is demonstrated by measuring barium strontium zirconium titanate bulk ferroelectric ceramic blocks. Above the Curie temperature, in the paraelectric state, barium strontium zirconium titanate has a sufficiently low loss that a series of resonant modes are supported in the cavity. At each mode frequency, the dielectric constant and loss tangent are obtained. The results are consistent with low frequency measurements and computer simulations. A quick method of analyzing the raw data using the 2D static electromagnetic modeling code SuperFish and an estimate of uncertainties are presented.

Dielectric response of Anderson and pseudogapped insulators

NASA Astrophysics Data System (ADS)

Feigel’man, M. V.; Ivanov, D. A.; Cuevas, E.

2018-05-01

Using a combination of analytic and numerical methods, we study the polarizability of a (non-interacting) Anderson insulator in one-, two-, and three-dimensions and demonstrate that, in a wide range of parameters, it scales proportionally to the square of the localization length, contrary to earlier claims based on the effective-medium approximation. We further analyze the effect of electron–electron interactions on the dielectric constant in quasi-1D, quasi-2D and 3D materials with large localization length, including both Coulomb repulsion and phonon-mediated attraction. The phonon-mediated attraction (in the pseudogapped state on the insulating side of the superconductor-insulator transition) produces a correction to the dielectric constant, which may be detected from a linear response of a dielectric constant to an external magnetic field.

Optical and electronic properties of SO2 molecule adsorbed on Si-doped (8, 0) boron nitride nanotube

NASA Astrophysics Data System (ADS)

Guo, Shuang-Shuang; Wei, Xiu-Mei; Zhang, Jian-Min; Zhu, Gang-Qiang; Guo, Wan-Jin

2016-09-01

The study of the optical properties of pristine BNNT, Si-doped BNNTs and SO2 molecule adsorption on Si-doped BNNTs is that, to our knowledge, few relevant research have ever been found. In this paper, the adsorption behaviors of Sulfur dioxide (SO2) molecule on Si-doped Boron nitride nanotubes (BNNTs) are investigated applying the first-principles calculations. The main contribution of this paper is that the foremost investigation for the optical properties of the pristine BNNT, Si-doped BNNTs and SO2 adsorption on Si-doped BNNTs. Additionally, the electronic properties and the structural properties are also presented. In our calculations of optical properties, the dielectric constant, the refractive index and the absorption coefficient are obtained. Comparing the pristine BNNT, our results indicate that, the blue-shifts (in the main peaks of the dielectric constant of SiB -BNNT and SO2-SiB -BNNT), and the red-shifts (in the main peaks of the refractive index of SiN -BNNT and SO2-SiN -BNNT) are appeared. Under these conditions, Si-doped BNNT and Si-doped BNNT with SO2 adsorption, the gaps are reduced both for the speculated optical band gaps and the electronic structure band gaps.

The effect of PECVD plasma decomposition on the wettability and dielectric constant changes in silicon modified DLC films for potential MEMS and low stiction applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ogwu, A. A.; Okpalugo, T. I. T.; Nanotechnology Institute, School of Electrical and Mechanical Engineering, University of Ulster, Northern Ireland

We have carried out investigations aimed at understanding the mechanism responsible for a water contact angle increase of up to ten degrees and a decrease in dielectric constant in silicon modified hydrogenated amorphous carbon films compared to unmodified hydrogenated amorphous carbon films. Our investigations based on surface chemical constituent analysis using Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), SIMS, FTIR, contact angle / surface energy measurements and spectroscopic ellipsometry suggests the presence of hydrophobic chemical entities on the surface of the films. This observation is consistent with earlier theoretical plasma chemistry predictions and observed Raman peak shifts in the films. Thesemore » surface hydrophobic entities also have a lower polarizability than the bonds in the un-modified films thereby reducing the dielectric constant of the silicon modified films measured by spectroscopic ellipsometry. Ellipsometric dielectric constant measurement is directly related to the surface energy through Hamaker's constant. Our current finding is expected to be of benefit to understanding stiction, friction and lubrication in areas that range from nano-tribology to microfluidics.« less

The effect of PECVD plasma decomposition on the wettability and dielectric constant changes in silicon modified DLC films for potential MEMS and low stiction applications

NASA Astrophysics Data System (ADS)

Ogwu, A. A.; Okpalugo, T. I. T.; McLaughlin, J. A. D.

2012-09-01

We have carried out investigations aimed at understanding the mechanism responsible for a water contact angle increase of up to ten degrees and a decrease in dielectric constant in silicon modified hydrogenated amorphous carbon films compared to unmodified hydrogenated amorphous carbon films. Our investigations based on surface chemical constituent analysis using Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), SIMS, FTIR, contact angle / surface energy measurements and spectroscopic ellipsometry suggests the presence of hydrophobic chemical entities on the surface of the films. This observation is consistent with earlier theoretical plasma chemistry predictions and observed Raman peak shifts in the films. These surface hydrophobic entities also have a lower polarizability than the bonds in the un-modified films thereby reducing the dielectric constant of the silicon modified films measured by spectroscopic ellipsometry. Ellipsometric dielectric constant measurement is directly related to the surface energy through Hamaker's constant. Our current finding is expected to be of benefit to understanding stiction, friction and lubrication in areas that range from nano-tribology to microfluidics.

Effect of soil texture on the microwave emission from soils

NASA Technical Reports Server (NTRS)

Schmugge, T. J.

1980-01-01

The intensity brightness temperature of the microwave emission from the soil is determined primarily by its dielectric properties. The large difference between the dielectric constant of water and that of dry soil produces a strong dependence of the soil's dielectric constant on its moisture content. This dependence is effected by the texture of the soil because the water molecules close to the particle surface are tightly bound and do not contribute significantly to the dielectric properties. Since this surface area is a function of the particle size distribution (soil texture), being larger for clay soils with small particles, and smaller for sandy soils with larger particles; the dielectric properties will depend on soil texture. Laboratory measurements of the dielectric constant for soils are summarized. The dependence of the microwave emission on texture is demonstrated by measurements of brightness temperature from an aircraft platform for a wide range of soil textures. It is concluded that the effect of soil texture differences on the observed values can be normalized by expressing the soil moisture values as a percent field capacity for the soil.

New dielectric elastomers with improved properties for energy harvesting and actuation

NASA Astrophysics Data System (ADS)

Stiubianu, George; Bele, Adrian; Tugui, Codrin; Musteata, Valentina

2015-02-01

New materials with large value for dielectric constant were obtained by using siloxane and chemically modified lignin. The modified lignin does not act as a stiffening filler material for the siloxane but acts as bulk filler, preserving the softness and low value of Young's modulus specific for silicones. The measured values for dielectric constant compare positively with the ones for previously tested dielectric elastomers based on siloxane rubber or acrylic rubber loaded with ceramic nanoparticles. The new materials use the well-known silicone chemistry and lignin which is available worldwide in large amounts as a by-product of pulp and paper industry, making its manufacturing affordable. The prepared dielectric elastomers were tested for possible applications for wave, wind and kinetic body motion energy harvesting. Siloxane, lignin, dielectric

Effect of cobalt doping on structural and dielectric properties of nanocrystalline LaCrO3

NASA Astrophysics Data System (ADS)

Zarrin, Naima; Husain, Shahid

2018-05-01

Pure and Co doped Lanthanum chromite (LaCrO3) nanoparticles, LaCr1-xCoxO3 (0≤x≤0.3), have been synthesized through sol-gel process and their structural, morphological and dielectric properties have been studied. X ray diffraction patterns reveal that the samples are in single phase having orthorhombic structure with Pnma space group. Structural parameters are refined by Rietveld refinement using Fullprof software. Lattice parameters and unit cell volume are found to decrease with increase in Co doping. Crystallite size is calculated using Scherrer equation and is also found to decrease with increase in Co concentration. Surface morphology is examined using SEM-EDX analysis, which confirms the formation of regular and homogeneous samples without any impurities. The value of dielectric constant (ɛ') decreases with the increase in frequency while it enhances with the increase in Co concentration. The log (ɛ'×f) versus log (f) graphs have been plotted to verify the universal dielectric response (UDR) model. All the samples follow UDR model in the low frequency range.

Water-separated ion pairs cause the slow dielectric mode of magnesium sulfate solutions

NASA Astrophysics Data System (ADS)

Mamatkulov, Shavkat I.; Rinne, Klaus F.; Buchner, Richard; Netz, Roland R.; Bonthuis, Douwe Jan

2018-06-01

We compare the dielectric spectra of aqueous MgSO4 and Na2SO4 solutions calculated from classical molecular dynamics simulations with experimental data, using an optimized thermodynamically consistent sulfate force field. Both the concentration-dependent shift of the static dielectric constant and the spectral shape match the experimental results very well for Na2SO4 solutions. For MgSO4 solutions, the simulations qualitatively reproduce the experimental observation of a slow mode, the origin of which we trace back to the ion-pair relaxation contribution via spectral decomposition. The radial distribution functions show that Mg2+ and SO42 - ions form extensive water-separated—and thus strongly dipolar—ion pairs, the orientational relaxation of which provides a simple physical explanation for the prominent slow dielectric mode in MgSO4 solutions. Remarkably, the Mg2+-SO42 - ion-pair relaxation extends all the way into the THz range, which we rationalize by the vibrational relaxation of tightly bound water-separated ion pairs. Thus, the relaxation of divalent ion pairs can give rise to widely separated orientational and vibrational spectroscopic features.

Key optoelectronic properties of Diiodo-bis(carbamide)-zinc(II): An experimental and computational investigation

NASA Astrophysics Data System (ADS)

Shkir, Mohd.; Irfan, Ahmad; AlFaify, S.; Ganesh, V.; Arora, M.; Muhammad, Shabbir; Al-Sehemi, Abdullah G.; Yahia, I. S.

2018-03-01

Large size single crystals of Diiodo-bis(carbamide)-zinc(II) [ZnI2. 2[CO(NH2)2] were grown successfully for the first time by slow evaporation techniques at room temperature within the evaporation time of two weeks. The single phase and high crystalline nature of the grown crystals was confirmed by X-ray diffraction analysis. Quantum chemically the geometrical parameters were found in good correlation with experimental values calculated at B3LYP/6-31G* (LANL2DZ), B2LYPD/6-31G* (LANL2DZ), M062X/6-31G* (LANL2DZ) and MP2/6-31G* (LANL2DZ) level of theories. Additionally, the experimental vibrational modes also have shown a good agreement with calculated ones. The optical transparency and band gap were calculated and found to be ∼80% and 4.706 eV, respectively. The calculated value of HOMO-LUMO gap was found in correlation with experimental energy gap. The electronic properties were investigated by shedding light on the frontier molecular orbitals, partial density of states (PDOS), and total density of states (TDOS). The mechanical and dielectric studies show that the grown crystals possess quite good mechanical strength and dielectric constant. The dielectric loss revealed that the grown crystal contains low defects. The total ac electrical conductivity was increased with frequency and the frequency components confirm the sudden hoping mechanism in the grown crystal.

Off Axis Growth of Strontium Titanate Films with High Dielectric Constant Tuning and Low Loss

DTIC Science & Technology

2003-04-03

80309, U.S.A. ABSTRACT We have measured the nonlinear dielectric properties of strontium titanate (STO) thin films grown on neodymium gallate (NGO...and lanthanum aluminate (LAO) substrates. The films prepared by off-axis pulsed laser deposition were characterized by their dielectric constant and...performed on the films prepared with the off axis growth. EXPERIMENTAL Pulsed laser deposition (PLD) was used to deposit STO films on lanthanum

Assessing the performance of the MM/PBSA and MM/GBSA methods. 1. The accuracy of binding free energy calculations based on molecular dynamics simulations.

PubMed

Hou, Tingjun; Wang, Junmei; Li, Youyong; Wang, Wei

2011-01-24

The Molecular Mechanics/Poisson-Boltzmann Surface Area (MM/PBSA) and the Molecular Mechanics/Generalized Born Surface Area (MM/GBSA) methods calculate binding free energies for macromolecules by combining molecular mechanics calculations and continuum solvation models. To systematically evaluate the performance of these methods, we report here an extensive study of 59 ligands interacting with six different proteins. First, we explored the effects of the length of the molecular dynamics (MD) simulation, ranging from 400 to 4800 ps, and the solute dielectric constant (1, 2, or 4) on the binding free energies predicted by MM/PBSA. The following three important conclusions could be observed: (1) MD simulation length has an obvious impact on the predictions, and longer MD simulation is not always necessary to achieve better predictions. (2) The predictions are quite sensitive to the solute dielectric constant, and this parameter should be carefully determined according to the characteristics of the protein/ligand binding interface. (3) Conformational entropy often show large fluctuations in MD trajectories, and a large number of snapshots are necessary to achieve stable predictions. Next, we evaluated the accuracy of the binding free energies calculated by three Generalized Born (GB) models. We found that the GB model developed by Onufriev and Case was the most successful model in ranking the binding affinities of the studied inhibitors. Finally, we evaluated the performance of MM/GBSA and MM/PBSA in predicting binding free energies. Our results showed that MM/PBSA performed better in calculating absolute, but not necessarily relative, binding free energies than MM/GBSA. Considering its computational efficiency, MM/GBSA can serve as a powerful tool in drug design, where correct ranking of inhibitors is often emphasized.

Preparation of dielectric coating of variable dielectric constant by plasma polymerization

NASA Technical Reports Server (NTRS)

Hudis, M.; Wydeven, T. (Inventor)

1979-01-01

A plasma polymerization process for the deposition of a dielectric polymer coating on a substrate comprising disposing of the substrate in a closed reactor between two temperature controlled electrodes connected to a power supply is presented. A vacuum is maintained within the closed reactor, causing a monomer gas or gas mixture of a monomer and diluent to flow into the reactor, generating a plasma between the electrodes. The vacuum varies and controls the dielectric constant of the polymer coating being deposited by regulating the gas total and partial pressure, the electric field strength and frequency, and the current density.

Crystal structure study of dielectric oxynitride perovskites La{sub 1−x}Sr{sub x}TiO{sub 2+x}N{sub 1−x} (x=0, 0.2)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Habu, Daiki; Masubuchi, Yuji; Torii, Shuki

As is the case with SrTaO{sub 2}N, both cis-ordering of nitride anions and octahedral titling are also preferable in La{sub 1−x}Sr{sub x}TiO{sub 2+x}N{sub 1−x} (x=0, 0.2) oxynitride perovskites. A larger dielectric constant of ε{sub r}≈5.0×10{sup 3} was estimated for the pure oxynitride with x=0.2, compared with ε{sub r}≈750 for the product with x=0, by extrapolating the ε{sub r} values obtained from powders mixed with paraffin at various mixing ratios. The crystal structure of x=0.2 with larger tolerance factor than x=0 increased the octahedral tilting, which contributes to the increased dielectric constant. The increased dielectric constant supports the exchange mechanism formore » the dielectric property between two kinds of –Ti–N– helical coils (clockwise and anticlockwise) derived from the above cis-ordering of nitride anions. - Graphical abstract: Very large dielectric constant values were estimated for La{sub 1−x}Sr{sub x}TiO{sub 2+x}N{sub 1−x}; ε{sub r}≈5.0×10{sup 3} in x=0.2 and ε{sub r}≈750 in x=0. - Highlights: • Cis-configuration of nitride anions was confirmed in La{sub 1−x}Sr{sub x}TiO{sub 2+x}N{sub 1−x} (x=0, 0.2). • Dielectric constant values were estimated to be 750 for x=0 and 5.0×10{sup 3} for x=0.2, respectively. • The large dielectric property is to the exchange mechanism between clockwise and anticlockwise –Ti–N– coil motifs.« less

Independence of the effective dielectric constant of an electrolytic solution on the ionic distribution in the linear Poisson-Nernst-Planck model.

PubMed

Alexe-Ionescu, A L; Barbero, G; Lelidis, I

2014-08-28

We consider the influence of the spatial dependence of the ions distribution on the effective dielectric constant of an electrolytic solution. We show that in the linear version of the Poisson-Nernst-Planck model, the effective dielectric constant of the solution has to be considered independent of any ionic distribution induced by the external field. This result follows from the fact that, in the linear approximation of the Poisson-Nernst-Planck model, the redistribution of the ions in the solvent due to the external field gives rise to a variation of the dielectric constant that is of the first order in the effective potential, and therefore it has to be neglected in the Poisson's equation that relates the actual electric potential across the electrolytic cell to the bulk density of ions. The analysis is performed in the case where the electrodes are perfectly blocking and the adsorption at the electrodes is negligible, and in the absence of any ion dissociation-recombination effect.

Electronic polarizability of light crude oil from optical and dielectric studies

NASA Astrophysics Data System (ADS)

George, A. K.; Singh, R. N.

2017-07-01

In the present paper we report the temperature dependence of density, refractive indices and dielectric constant of three samples of crude oils. The API gravity number estimated from the temperature dependent density studies revealed that the three samples fall in the category of light oil. The measured data of refractive index and the density are used to evaluate the polarizability of these fluids. Molar refractive index and the molar volume are evaluated through Lorentz-Lorenz equation. The function of the refractive index, FRI , divided by the mass density ρ, is a constant approximately equal to one-third and is invariant with temperature for all the samples. The measured values of the dielectric constant decrease linearly with increasing temperature for all the samples. The dielectric constant estimated from the refractive index measurements using Lorentz-Lorentz equation agrees well with the measured values. The results are promising since all the three measured properties complement each other and offer a simple and reliable method for estimating crude oil properties, in the absence of sufficient data.

Sensor and Methodology for Dielectric Analysis of Vegetal Oils Submitted to Thermal Stress

PubMed Central

Stevan, Sergio Luiz; Paiter, Leandro; Ricardo Galvão, José; Vieira Roque, Daniely; Sidinei Chaves, Eduardo

2015-01-01

Vegetable oils used in frying food represent a social problem as its destination. The residual oil can be recycled and returned to the production line, as biodiesel, as soap, or as putty. The state of the residual oil is determined according to their physicochemical characteristics whose values define its economically viable destination. However, the physicochemical analysis requires high costs, time and general cost of transporting. This study presents the use of a capacitive sensor and a quick and inexpensive method to correlate the physicochemical variables to the dielectric constant of the material undergoing oil samples to thermal cycling. The proposed method allows reducing costs in the characterization of residual oil and the reduction in analysis time. In addition, the method allows an assessment of the quality of the vegetable oil during use. The experimental results show the increasing of the dielectric constant with the temperature, which facilitates measurement and classification of the dielectric constant at considerably higher temperatures. The results also confirm a definitive degradation in used oil and a correlation between the dielectric constant of the sample with the results of the physicochemical analysis (iodine value, acid value, viscosity and refractive index). PMID:26501293

Sensor and methodology for dielectric analysis of vegetal oils submitted to thermal stress.

PubMed

Stevan, Sergio Luiz; Paiter, Leandro; Galvão, José Ricardo; Roque, Daniely Vieira; Chaves, Eduardo Sidinei

2015-10-16

Vegetable oils used in frying food represent a social problem as its destination. The residual oil can be recycled and returned to the production line, as biodiesel, as soap, or as putty. The state of the residual oil is determined according to their physicochemical characteristics whose values define its economically viable destination. However, the physicochemical analysis requires high costs, time and general cost of transporting. This study presents the use of a capacitive sensor and a quick and inexpensive method to correlate the physicochemical variables to the dielectric constant of the material undergoing oil samples to thermal cycling. The proposed method allows reducing costs in the characterization of residual oil and the reduction in analysis time. In addition, the method allows an assessment of the quality of the vegetable oil during use. The experimental results show the increasing of the dielectric constant with the temperature, which facilitates measurement and classification of the dielectric constant at considerably higher temperatures. The results also confirm a definitive degradation in used oil and a correlation between the dielectric constant of the sample with the results of the physicochemical analysis (iodine value, acid value, viscosity and refractive index).

Enhanced dielectric and electrical properties of annealed PVDF thin film

NASA Astrophysics Data System (ADS)

Arshad, A. N.; Rozana, M. D.; Wahid, M. H. M.; Mahmood, M. K. A.; Sarip, M. N.; Habibah, Z.; Rusop, M.

2018-05-01

Poly (vinylideneflouride) (PVDF) thin films were annealed at various annealing temperatures ranging from 70°C to 170°C. This study demonstrates that PVDF thin films annealed at temperature of 70°C (AN70) showed significant enhancement in their dielectric constant (14) at frequency of 1 kHz in comparison to un-annealed PVDF (UN-PVDF), dielectric constant (10) at the same measured frequency. As the annealing temperature was increased from 90°C (AN90) to 150°C (AN150), the dielectric constant value of PVDF thin films was observed to decrease gradually to 11. AN70 also revealed low tangent loss (tan δ) value at similar frequency. With respect to its resistivity properties, the values were found to increase from 1.98×104 Ω.cm to 3.24×104 Ω.cm for AN70 and UN-PVDF films respectively. The improved in dielectric constant, with low tangent loss and high resistivity value suggests that 70°C is the favorable annealing temperature for PVDF thin films. Hence, AN70 is a promising film to be utilized for application in electronic devices such as low frequency capacitor.

Giant dielectric response and low dielectric loss in Al{sub 2}O{sub 3} grafted CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rajabtabar-Darvishi, A.; Center for Surface and Nanoanalytics; Bayati, R., E-mail: reza.bayati@intel.com, E-mail: mbayati@ncsu.edu, E-mail: wdfei@hit.edu.cn

2015-03-07

This study sheds light on the effect of alumina on dielectric constant and dielectric loss of novel CaCu{sub 3}Ti{sub 4}O{sub 12} composite ceramics. Alumina, at several concentrations, was deposited on the surface of CaCu{sub 3}Ti{sub 4}O{sub 12} particles via sol-gel technique. The dielectric constant significantly increased for all frequencies and the dielectric loss substantially decreased for low and intermediate frequencies. These observations were attributed to the change in characteristics of grains and grain boundaries. It was found that the insulating properties of the grain boundaries are improved following the addition of Al{sub 2}O{sub 3}. The relative density of CaCu{sub 3}Ti{submore » 4}O{sub 12}/Al{sub 2}O{sub 3} composite ceramics decreased compared to the pure CaCu{sub 3}Ti{sub 4}O{sub 12} and the grain size was greatly changed with the alumina content affecting the dielectric properties. With the addition of alumina into CaCu{sub 3}Ti{sub 4}O{sub 12}, tighter interfaces formed. The 6%- and 10%-alumina ceramics showed the minimum dielectric loss and the maximum dielectric constant, respectively. Both the dielectric constant and loss tangent decreased in the 20%-alumina ceramic due to the formation of CuO secondary phase. It was revealed that Al serves as an electron acceptor decreasing the electron concentration, if Al{sup 3+} ions substitute for Ti{sup 4+} ions, and as an electron donor increasing the electron concentration, if Al{sup 3+} ions substitute for Ca{sup 2+} ions. We established a processing-microstructure-properties paradigm which opens new avenues for novel applications of CaCu{sub 3}Ti{sub 4}O{sub 12}/Al{sub 2}O{sub 3} composite ceramics.« less

Microwave assisted synthesis and characterization of barium titanate nanoparticles for multi layered ceramic capacitor applications.

PubMed

Thirumalai, Sundararajan; Shanmugavel, Balasivanandha Prabu

2011-01-01

Barium titanate is a common ferroelectric electro-ceramic material having high dielectric constant, with photorefractive effect and piezoelectric properties. In this research work, nano-scale barium titanate powders were synthesized by microwave assisted mechano-chemical route. Suitable precursors were ball milled for 20 hours. TGA studies were performed to study the thermal stability of the powders. The powders were characterized by XRD, SEM and EDX Analysis. Microwave and Conventional heating were performed at 1000 degrees C. The overall heating schedule was reduced by 8 hours in microwave heating thereby reducing the energy and time requirement. The nano-scale, impurity-free and defect-free microstructure was clearly evident from the SEM micrograph and EDX patterns. LCR meter was used to measure the dielectric constant and dielectric loss values at various frequencies. Microwave heated powders showed superior dielectric constant value with low dielectric loss which is highly essential for the fabrication of Multi Layered Ceramic Capacitors.

Relationship between BaTiO₃ nanowire aspect ratio and the dielectric permittivity of nanocomposites.

PubMed

Tang, Haixiong; Zhou, Zhi; Sodano, Henry A

2014-04-23

The aspect ratio of barium titanate (BaTiO3) nanowires is demonstrated to be successfully controlled by adjusting the temperature of the hydrothermal growth from 150 to 240 °C, corresponding to aspect ratios from 9.3 to 45.8, respectively. Polyvinylidene fluoride (PVDF) nanocomposites are formed from the various aspect ratio nanowires and the relationship between the dielectric constant of the nanocomposite and the aspect ratio of the fillers is quantified. It was found that the dielectric constant of the nanocomposite increases with the aspect ratio of the nanowires. Nanocomposites with 30 vol % BaTiO3 nanowires and an aspect ratio of 45.8 can reach a dielectric constant of 44.3, which is 30.7% higher than samples with an aspect ratio of 9.3 and 352% larger than the polymer matrix. These results demonstrate that using high-aspect-ratio nanowires is an effective way to control and improve the dielectric performance of nanocomposites for future capacitor applications.

Influence of applied electric field annealing on the microwave properties of (Ba0.5Sr0.5)TiO3 thin films

NASA Astrophysics Data System (ADS)

Cho, Kwang-Hwan; Lee, Chil-Hyoung; Kang, Chong-Yun; Yoon, Seok-Jin; Lee, Young-Pak

2007-04-01

The effect of heat treatment in electric field on the structure and dielectric properties at microwave range of rf magnetron sputtering derived (Ba0.5Sr0.5)TiO3 thin films have been studied. It has been demonstrated that postannealing in the proper electric field can increase the dielectric constant and the tunability. The increased out-of-plane lattice constant in the electric-annealed films indicated the formation of small polar regions with tetragonal structure, which are responsible for the increased dielectric constant and tunability. It was proposed that the segregation of Ti3+ ions caused by electric annealing could induce the formation of BaTiO3-like regions, which are ferroelectric at room temperature. And in dielectric loss, as the Ti-O bonding lengths increase, the energy scattering on the ferroelectric mode also increases. So, the value of dielectric loss is slightly increased.

General expressions for the coupling coefficient, quality and filling factors for a cavity with an insert using energy coupled mode theory.

PubMed

Elnaggar, Sameh Y; Tervo, Richard; Mattar, Saba M

2014-05-01

A cavity (CV) with a dielectric resonator (DR) insert forms an excellent probe for the use in electron paramagnetic resonance (EPR) spectrometers. The probe's coupling coefficient, κ, the quality factor, Q, and the filling factor, η are vital in assessing the EPR spectrometer's performance. Coupled mode theory (CMT) is used to derive general expressions for these parameters. For large permittivity the dominating factor in κ is the ratio of the DR and CV cross sectional areas rather than the dielectric constant. Thus in some cases, resonators with low dielectric constant can couple much stronger with the cavity than do resonators with a high dielectric constant. When the DR and CV frequencies are degenerate, the coupled η is the average of the two uncoupled ones. In practical EPR probes the coupled η is approximately half of that of the DR. The Q of the coupled system generally depends on the eigenvectors, uncoupled frequencies (ω1,ω2) and the individual quality factors (Q1,Q2). It is calculated for different probe configurations and found to agree with the corresponding HFSS® simulations. Provided there is a large difference between the Q1, Q2 pair and the frequencies of DR and CV are degenerate, Q is approximately equal to double the minimum of Q1 and Q2. In general, the signal enhancement ratio, Iwithinsert/Iempty, is obtained from Q and η. For low loss DRs it only depends on η1/η2. However, when the DR has a low Q, the uncoupled Qs are also needed. In EPR spectroscopy it is desirable to excite only a single mode. The separation between the modes, Φ, is calculated as a function of κ and Q. It is found to be significantly greater than five times the average bandwidth. Thus for practical probes, it is possible to excite one of the coupled modes without exciting the other. The CMT expressions derived in this article are quite general and are in excellent agreement with the lumped circuit approach and finite numerical simulations. Hence they can also be applied to a loop-gap resonator in a cavity. For the design effective EPR probes, one needs to consider the κ, Q and η parameters. Copyright © 2014 Elsevier Inc. All rights reserved.

General expressions for the coupling coefficient, quality and filling factors for a cavity with an insert using energy coupled mode theory

NASA Astrophysics Data System (ADS)

Elnaggar, Sameh Y.; Tervo, Richard; Mattar, Saba M.

2014-05-01

A cavity (CV) with a dielectric resonator (DR) insert forms an excellent probe for the use in electron paramagnetic resonance (EPR) spectrometers. The probe’s coupling coefficient, κ, the quality factor, Q, and the filling factor, η are vital in assessing the EPR spectrometer’s performance. Coupled mode theory (CMT) is used to derive general expressions for these parameters. For large permittivity the dominating factor in κ is the ratio of the DR and CV cross sectional areas rather than the dielectric constant. Thus in some cases, resonators with low dielectric constant can couple much stronger with the cavity than do resonators with a high dielectric constant. When the DR and CV frequencies are degenerate, the coupled η is the average of the two uncoupled ones. In practical EPR probes the coupled η is approximately half of that of the DR. The Q of the coupled system generally depends on the eigenvectors, uncoupled frequencies (ω1, ω2) and the individual quality factors (Q1, Q2). It is calculated for different probe configurations and found to agree with the corresponding HFSS® simulations. Provided there is a large difference between the Q1, Q2 pair and the frequencies of DR and CV are degenerate, Q is approximately equal to double the minimum of Q1 and Q2. In general, the signal enhancement ratio, I/Iempty, is obtained from Q and η. For low loss DRs it only depends on η1/η2. However, when the DR has a low Q, the uncoupled Qs are also needed. In EPR spectroscopy it is desirable to excite only a single mode. The separation between the modes, Φ, is calculated as a function of κ and Q. It is found to be significantly greater than five times the average bandwidth. Thus for practical probes, it is possible to excite one of the coupled modes without exciting the other. The CMT expressions derived in this article are quite general and are in excellent agreement with the lumped circuit approach and finite numerical simulations. Hence they can also be applied to a loop-gap resonator in a cavity. For the design effective EPR probes, one needs to consider the κ, Q and η parameters.

Surface Plasmon Waves on Thin Metal Films.

NASA Astrophysics Data System (ADS)

Craig, Alan Ellsworth

Surface-plasmon polaritons propagating on thin metal films bounded by dielectrics of nearly equal refractive indexes comprise two bound modes. Calculations indicate that, while the modes are degenerate on thick films, both the real and the imaginary components of the propagation constants for the modes split into two branches on successively thinner films. Considering these non-degenerate modes, the mode exhibiting a symmetric (antisymmetric) transverse profile of the longitudinally polarized electric field component, has propagation constant components both of which increase (decrease) with decreasing film thickness. Theoretical propagation constant eigenvalue (PCE) curves have been plotted which delineate this dependence of both propagation constant components on film thickness. By means of a retroreflecting, hemispherical glass coupler in an attenuated total reflection (ATR) configuration, light of wavelength 632.8 nm coupled to the modes of thin silver films deposited on polished glass substrates. Lorentzian lineshape dips in the plots of reflectance vs. angle of incidence indicate the presence of the plasmon modes. The real and imaginary components of the propagation constraints (i.e., the propagation constant and loss coefficient) were calculated from the angular positions and widths of the ATR resonances recorded. Films of several thicknesses were probed. Results which support the theoretically predicted curves were reported.

Grain size effect on the giant dielectric constant of CaCu3Ti4O12 nanoceramics prepared by mechanosynthesis and spark plasma sintering

NASA Astrophysics Data System (ADS)

Ahmad, Mohamad M.; Yamada, Koji

2014-04-01

In the present work, CaCu3Ti4O12 (CCTO) nanoceramics with different grain sizes were prepared by spark plasma sintering (SPS) at different temperatures (SPS-800, SPS-900, SPS-975, and SPS-1050) of the mechanosynthesized nano-powder. Structural and microstructural properties were studied by XRD and field-emission scanning electron microscope measurements. The grain size of CCTO nanoceramics increases from 80 nm to ˜200 nm for the ceramics sintered at 800 °C and 975 °C, respectively. Further increase of SPS temperature to 1050 °C leads to micro-sized ceramics of 2-3 μm. The electrical and dielectric properties of the investigated ceramics were studied by impedance spectroscopy. Giant dielectric constant was observed in CCTO nanoceramics. The dielectric constant increases with increasing the grain size of the nanoceramics with values of 8.3 × 103, 2.4 × 104, and 3.2 × 104 for SPS-800, SPS-900, and SPS-975, respectively. For the micro-sized SPS-1050 ceramics, the dielectric constant dropped to 2.14 × 104. The dielectric behavior is interpreted within the internal barrier layer capacitance picture due to the electrical inhomogeneity of the ceramics. Besides the resistive grain boundaries that are usually observed in CCTO ceramics, domain boundaries appear as a second source of internal layers in the current nanoceramics.

Cast dielectric composite linear accelerator

DOEpatents

Sanders, David M [Livermore, CA; Sampayan, Stephen [Manteca, CA; Slenes, Kirk [Albuquerque, NM; Stoller, H M [Albuquerque, NM

2009-11-10

A linear accelerator having cast dielectric composite layers integrally formed with conductor electrodes in a solventless fabrication process, with the cast dielectric composite preferably having a nanoparticle filler in an organic polymer such as a thermosetting resin. By incorporating this cast dielectric composite the dielectric constant of critical insulating layers of the transmission lines of the accelerator are increased while simultaneously maintaining high dielectric strengths for the accelerator.

THE STRUCTURE, MAGNETISM AND CONDUCTIVITY OF Li3V2(PO4)3: A THEORETICAL AND EXPERIMENTAL STUDY

NASA Astrophysics Data System (ADS)

Lin, Zhi-Ping; Zhao, Yu-Jun; Zhao, Yan-Ming

2013-10-01

In this paper, we present a combination of first-principles and experimental investigations on the structural, magnetic and electronic properties of monoclinic Li3V2(PO4)3. The change of dielectric constant indicates that the structural phase transition appear around the temperature 120°C. The first-principles calculation and magnetic measurement display that Li3V2(PO4)3 is a compound with weak ferromagnetism, with Curie constant of C = 0.004 and Curie temperature of 140 K. The experimental and theoretical results demonstrated that the Li3V2(PO4)3 is a typical semiconductor.

Enhanced dielectric properties of Fe-substituted TiO2 nanoparticles

NASA Astrophysics Data System (ADS)

Ali, T.; Ahmed, Ateeq; Naseem siddique, M.; Tripathi, P.

2018-04-01

We report the structural and dielectric properties Ti1-xFexO2 (0.00 < x < 0.10) nanoparticles (NPs) synthesized by sol-gel method. The synthesized material has been characterized by soft X-ray absorption spectroscopy (SXAS) in order to investigate the fine structure and electronic valence state. SXAS analysis reveals that Fe-ions exist only in 3+ valance state in all the samples. The dielectric properties were studied by the use of LCR impedance spectroscopy. The dielectric constants, dielectric loss and A.C. conductivity have been determined as a function of frequency and composition of iron. At higher frequencies, the materials exhibited high AC Conductivity and low dielectric constant. The above theory could be explained by 'Maxwell Wagner Model' and may provide a new insight to fabricate nanomaterials having possible electrical application.

Heat treatment effects on dielectric properties of SRFe{sub 12}O{sub 19} hexaferrite prepared by an SHS route

DOE Office of Scientific and Technical Information (OSTI.GOV)

Panchal, Nital R.; Jotania, Rajshree B., E-mail: natal_panchal@yahoo.co.in, E-mail: rbjotania@gmail.com

2011-07-01

The M-type Strontium Hexaferrite SRFe{sub 12}O{sub 19} particles were prepared by a Self propagating High temperature Synthesis (SHS) route. Precursors were heated under two different conditions: microwave heating for 30 minutes and sintered at 950 deg C for 4 hrs. The dielectric properties: dielectric constant ({epsilon}{sup '}), dielectric loss (tan {delta} ) and ac conductivity ({sigma}{sub ac}) were measured at room temperature in the frequency range from 100 Hz to 2 MHz. The samples present a non-linear behavior for the dielectric constant at 1 kHz, 100 kHz and 2 MHz. The dielectric properties of prepared Strontium Hexaferrite samples were discussedmore » in view of applications as a material for microwave devices, permanent magnets and high density magnetic recording media. (author)« less

Stiff, strong, yet tough free-standing dielectric films of graphene nanosheets-polyurethane nanocomposites with very high dielectric constant and loss

NASA Astrophysics Data System (ADS)

Jan, Rahim; Habib, Amir; Gul, Iftikhar Hussain

2016-01-01

In this study, graphene nanosheets (GNS) prepared through a liquid exfoliation technique are dispersed in thermoplastic polyurethane (TPU) at a volume fraction (Vf) of up to 0.19. Then, the electrical and mechanical properties of the obtained composites are characterized. The dielectric spectroscopy shows an excessive variation in dielectric constant (1.1 to 3.53 × 107) and dielectric tangent loss (0.03 to 2515) with varying Vf over the frequency range of 25 kHz to 5 MHz. A considerable enhancement in electrical conductivity (DC) is found, from 3.87 × 10-10 S/m (base polymer) to 53.5 S/m for the 0.19 Vf GNS-TPU nanocomposite. The GNS-TPU composites are mechanically robust, with a considerable increase in stiffness (˜4-fold) and strength (almost twice), maintaining its ductility up to 0.09 Vf GNS. The high dielectric constant at lower frequencies is attributed to the well-established Maxwell-Wagner polarization effect, whereas the high dielectric tangent loss is due to leakage currents as a physical conducting network is formed at high filler loadings. The layered structure, high aspect ratio, and improved dispersion of GNS are the main reasons for the improvement in both the dielectric characteristics and the mechanical properties of the host polymer. [Figure not available: see fulltext.

Influence of rare earth ion doping (Ce and Dy) on electrical and magnetic properties of cobalt ferrites

NASA Astrophysics Data System (ADS)

Hashim, Mohd.; Raghasudha, M.; Meena, Sher Singh; Shah, Jyoti; Shirsath, Sagar E.; Kumar, Shalendra; Ravinder, D.; Bhatt, Pramod; Alimuddin; Kumar, Ravi; Kotnala, R. K.

2018-03-01

Ce and Dy substituted Cobalt ferrites with the chemical composition CoCexDyxFe2-2xO4 (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) were synthesized through the chemical route, citrate-gel auto-combustion method. The structural characterization was carried out with the help of XRD Rieveld analysis, SEM and EDAX analysis. Formation of spinel cubic structure of the ferrites was confirmed by XRD analysis. SEM and EDAX results show that the particles are homogeneous with slight agglomeration without any impurity pickup. The effect of RE ion doping (Ce and Dy) on the dielectric, magnetic and impedance studies was systematically investigated by LCR meter, Vibrating Sample Magnetometer and Impedance analyzer respectively at room temperature in the frequency range of 10 Hz-10 MHz. Various dielectric parameters viz., dielectric constant, dielectric loss and ac conductivity were measured. The dielectric constant of all the ferrite compositions shows normal dielectric dispersion of ferrites with frequency. Impedance analysis confirms that the conduction in present ferrites is majorly due to the grain boundary mechanism. Ferrite sample with x = 0.03 show high dielectric constant, low dielectric loss and hence can be utilized in high frequency electromagnetic devices. Magnetization measurements indicate that with increase in Ce and Dy content in cobalt ferrites, the magnetization values decreased and coercivity has increased.

Metamaterial Behavior of Polymer Nanocomposites Based on Polypropylene/Multi-Walled Carbon Nanotubes Fabricated by Means of Ultrasound-Assisted Extrusion

PubMed Central

Pérez-Medina, Juan C.; Waldo-Mendoza, Miguel A.; Cruz-Delgado, Víctor J.; Quiñones-Jurado, Zoe V.; González-Morones, Pablo; Ziolo, Ronald F.; Martínez-Colunga, Juan G.; Soriano-Corral, Florentino; Avila-Orta, Carlos A.

2016-01-01

Metamaterial behavior of polymer nanocomposites (NCs) based on isotactic polypropylene (iPP) and multi-walled carbon nanotubes (MWCNTs) was investigated based on the observation of a negative dielectric constant (ε′). It is demonstrated that as the dielectric constant switches from negative to positive, the plasma frequency (ωp) depends strongly on the ultrasound-assisted fabrication method, as well as on the melt flow index of the iPP. NCs were fabricated using ultrasound-assisted extrusion methods with 10 wt % loadings of MWCNTs in iPPs with different melt flow indices (MFI). AC electrical conductivity (σ(AC)) as a function of frequency was determined to complement the electrical classification of the NCs, which were previously designated as insulating (I), static-dissipative (SD), and conductive (C) materials. It was found that the SD and C materials can also be classified as metamaterials (M). This type of behavior emerges from the negative dielectric constant observed at low frequencies although, at certain frequencies, the dielectric constant becomes positive. Our method of fabrication allows for the preparation of metamaterials with tunable ωp. iPP pure samples show only positive dielectric constants. Electrical conductivity increases in all cases with the addition of MWCNTs with the largest increases observed for samples with the highest MFI. A relationship between MFI and the fabrication method, with respect to electrical properties, is reported. PMID:28774042

Giant voltage-induced deformation of a dielectric elastomer under a constant pressure

NASA Astrophysics Data System (ADS)

Godaba, Hareesh; Foo, Choon Chiang; Zhang, Zhi Qian; Khoo, Boo Cheong; Zhu, Jian

2014-09-01

Dielectric elastomer actuators coupled with liquid have recently been developed as soft pumps, soft lenses, Braille displays, etc. In this paper, we investigate the performance of a dielectric elastomer actuator, which is coupled with water. The experiments demonstrate that the membrane of a dielectric elastomer can achieve a giant voltage-induced area strain of 1165%, when subject to a constant pressure. Both theory and experiment show that the pressure plays an important role in determining the electromechanical behaviour. The experiments also suggest that the dielectric elastomer actuators, when coupled with liquid, may suffer mechanical instability and collapse after a large amount of liquid is enclosed by the membrane. This failure mode needs to be taken into account in designing soft actuators.

Simulation of Charged Systems in Heterogeneous Dielectric Media via a True Energy Functional

NASA Astrophysics Data System (ADS)

Jadhao, Vikram; Solis, Francisco J.; de la Cruz, Monica Olvera

2012-11-01

For charged systems in heterogeneous dielectric media, a key obstacle for molecular dynamics (MD) simulations is the need to solve the Poisson equation in the media. This obstacle can be bypassed using MD methods that treat the local polarization charge density as a dynamic variable, but such approaches require access to a true free energy functional, one that evaluates to the equilibrium electrostatic energy at its minimum. In this Letter, we derive the needed functional. As an application, we develop a Car-Parrinello MD method for the simulation of free charges present near a spherical emulsion droplet separating two immiscible liquids with different dielectric constants. Our results show the presence of nonmonotonic ionic profiles in the dielectric with a lower dielectric constant.

Effect of crystal structure on strontium titanate thin films and their dielectric properties

NASA Astrophysics Data System (ADS)

Kampangkeaw, Satreerat

Strontium titanate (SrTiO3 or STO) has application in radio and microwave-frequency tunable capacitor devices particularly at low temperatures due to its high dielectric constant, low loss and the electric field tunability of its dielectric constant. The main goal of improving the performance in these devices is to increase the tunability and decrease the dielectric loss at the same time, especially at microwave frequencies. Thin films of STO however, show dramatic differences compared to the bulk. The dielectric constant of bulk STO increases nonlinearly from 300 at room temperature to 30000 at 4 K and the loss range is 10-3--10 -4. On the other hand. STO thin films, while showing a dielectric constant close to 300 at room temperature, typically reach a maximum between 1000 and 10000 in the 30 K to 100 K range before decreasing, and the high-loss range is 10-2--10-3. We have grown strontium titanate thin films using a pulsed laser deposition technique on substrates selected to have a small lattice mismatch between the film and substrate. Neodymium gallate (NdGaO3 or NGO) and lanthanum aluminate (LaAlO3 or LAO) substrates were good candidates due to only 1--2% mismatching. Film capacitor devices were fabricated with 25 micron gap separation. 1.5 mm total gap length and an overall 1 x 2 mm dimension using standard lithography and gold metal evaporative techniques. Their nonlinear dielectric constant and loss tangent were measured at low frequencies and also at 2 GHz, and from room temperature down to 4 K. The resulting films show significant variations of dielectric properties with position on the substrates with respect to the deposition plume axis. In the presence of DC electric fields up to +/-4 V/mum, STO films show improved dielectric tunability and low loss in regions far from the plume axis. We found that the films grown on NCO have lower dielectric loss than those on LAO due to a closer match of the NCO lattice to that of STO. We investigated the possible causes that make dielectric behavior in STO thin films different from the bulk. We characterized such film structures as lattice parameters, out-of-plane grain size, in-plane grain size, thickness, roughness, strains, and defects using ellipsometry, atomic force microscopy, and a high-resolution X-ray diffractometry. In plane grain size and percentage of defects were found to play a major role on the dielectric performance of the films.

Dielectric spectroscopy of Dy2O3 doped (K0.5Na0.5)NbO3 piezoelectric ceramics

NASA Astrophysics Data System (ADS)

Mahesh, P.; Subhash, T.; Pamu, D.

2014-06-01

We report the dielectric properties of ( K 0.5 Na 0.5 ) NbO 3 ceramics doped with x wt% of Dy 2 O 3 (x= 0.0-1.5 wt%) using the broadband dielectric spectroscopy. The X-ray diffraction studies showed the formation of perovskite structure signifying that Dy 2 O 3 diffuse into the KNN lattice. Samples doped with x > 0.5 wt% exhibit smaller grain size and lower relative densities. The dielectric properties of KNN ceramics doped with Dy 2 O 3 are enhanced by increasing the Dy 3+ content; among the compositions studied, x = 0.5 wt% exhibited the highest dielectric constant and lowest loss at 1MHz over the temperature range of 30°C to 400°C. All the samples exhibit maximum dielectric constant at the Curie temperature (˜ 326°C) and a small peak in the dielectric constant at around 165°C is due to a structural phase transition. At the request of all authors, and by agreement with the Proceedings Editors, a corrected version of this article was published on 19 June 2014. The full text of the Corrigendum is attached to the corrected article PDF file.

The measurement of the dielectric constant of concrete pipes and clay pipes

NASA Astrophysics Data System (ADS)

McGraw, David

To optimize the effectiveness of the rehabilitation of underground utilities, taking in consideration limitation of available resources, there is a need for a cost effective and efficient sensing systems capable of providing effective, in real time and in situ, measurement of infrastructural characteristics. To carry out accurate non-destructive condition assessment of buried and above ground infrastructure such as sewers, bridges, pavements and dams, an advanced ultra-wideband (UWB) based radar was developed at Trenchless Technology Centre (TTC) and Centre for Applied Physics Studies (CAPS) at Louisiana Tech University (LTU). One of the major issues in designing the FCC compliant UWB radar was the contribution of the pipe wall, presence of complex soil types and moderate-to-high moisture levels on penetration depth of the electromagnetic (EM) energy. The electrical properties of the materials involved in designing the UWB radar exhibit a significant variation as a result of the moisture content, mineral content, bulk density, temperature and frequency of the electromagnetic signal propagating through it. Since no measurements of frequency dependence of the dielectric permittivity and conductivities of the pipe wall material in the FCC approved frequency range exist, in this thesis, the dielectric constant of concrete and clay pipes are measured over a microwave frequency range from 1 Ghz to 10 Ghz including the effects of moisture and chloride content. A high performance software package called MU-EPSLN(TM) was used for the calculations. Data reduction routines to calculate the complex permeability and permittivity of materials as well as other parameters are also provided. The results obtained in this work will be used to improve the accuracy of the numerical simulations and the performances of the UWB radar system.

A Finite Element Solution of Lateral Periodic Poisson–Boltzmann Model for Membrane Channel Proteins

PubMed Central

Xu, Jingjie; Lu, Benzhuo

2018-01-01

Membrane channel proteins control the diffusion of ions across biological membranes. They are closely related to the processes of various organizational mechanisms, such as: cardiac impulse, muscle contraction and hormone secretion. Introducing a membrane region into implicit solvation models extends the ability of the Poisson–Boltzmann (PB) equation to handle membrane proteins. The use of lateral periodic boundary conditions can properly simulate the discrete distribution of membrane proteins on the membrane plane and avoid boundary effects, which are caused by the finite box size in the traditional PB calculations. In this work, we: (1) develop a first finite element solver (FEPB) to solve the PB equation with a two-dimensional periodicity for membrane channel proteins, with different numerical treatments of the singular charges distributions in the channel protein; (2) add the membrane as a dielectric slab in the PB model, and use an improved mesh construction method to automatically identify the membrane channel/pore region even with a tilt angle relative to the z-axis; and (3) add a non-polar solvation energy term to complete the estimation of the total solvation energy of a membrane protein. A mesh resolution of about 0.25 Å (cubic grid space)/0.36 Å (tetrahedron edge length) is found to be most accurate in linear finite element calculation of the PB solvation energy. Computational studies are performed on a few exemplary molecules. The results indicate that all factors, the membrane thickness, the length of periodic box, membrane dielectric constant, pore region dielectric constant, and ionic strength, have individually considerable influence on the solvation energy of a channel protein. This demonstrates the necessity to treat all of those effects in the PB model for membrane protein simulations. PMID:29495644

A Finite Element Solution of Lateral Periodic Poisson-Boltzmann Model for Membrane Channel Proteins.

PubMed

Ji, Nan; Liu, Tiantian; Xu, Jingjie; Shen, Longzhu Q; Lu, Benzhuo

2018-02-28

Membrane channel proteins control the diffusion of ions across biological membranes. They are closely related to the processes of various organizational mechanisms, such as: cardiac impulse, muscle contraction and hormone secretion. Introducing a membrane region into implicit solvation models extends the ability of the Poisson-Boltzmann (PB) equation to handle membrane proteins. The use of lateral periodic boundary conditions can properly simulate the discrete distribution of membrane proteins on the membrane plane and avoid boundary effects, which are caused by the finite box size in the traditional PB calculations. In this work, we: (1) develop a first finite element solver (FEPB) to solve the PB equation with a two-dimensional periodicity for membrane channel proteins, with different numerical treatments of the singular charges distributions in the channel protein; (2) add the membrane as a dielectric slab in the PB model, and use an improved mesh construction method to automatically identify the membrane channel/pore region even with a tilt angle relative to the z -axis; and (3) add a non-polar solvation energy term to complete the estimation of the total solvation energy of a membrane protein. A mesh resolution of about 0.25 Å (cubic grid space)/0.36 Å (tetrahedron edge length) is found to be most accurate in linear finite element calculation of the PB solvation energy. Computational studies are performed on a few exemplary molecules. The results indicate that all factors, the membrane thickness, the length of periodic box, membrane dielectric constant, pore region dielectric constant, and ionic strength, have individually considerable influence on the solvation energy of a channel protein. This demonstrates the necessity to treat all of those effects in the PB model for membrane protein simulations.

Effect of Mn doping on the temperature-dependent anomalous giant dielectric behavior of CaCu3Ti4O12

NASA Astrophysics Data System (ADS)

Kim, C. H.; Jang, Y. H.; Seo, S. J.; Song, C. H.; Son, J. Y.; Yang, Y. S.; Cho, J. H.

2012-06-01

We report dielectric properties and dielectric relaxation behaviors of Mn-substituted CaCu3Ti4O12 (CCTO) on Cu sites. While CCTO exhibits the giant dielectric constant and low dielectric loss in a wide temperature range, drastic suppression of the dielectric constant in Mn-doped CCTO (CCMTO) samples have been observed in temperature and frequency dependencies of dielectric properties with two possible origins as Mn doping increases. The observed suppression of dielectric response in the low Mn doping differs from the heavy doping of Mn in CCMTO samples. The low-Mn-doped CCMTO samples (x=0.01 and 0.02) show that the relaxation time and the activation energy Ea were slightly reduced due to a decreased contribution from the density of the dipolar effect. However, in heavily doped CCMTO samples (x=0.03, 0.04, and 0.05), the dielectric response, relaxation time, and Ea were significantly decreased, suggesting Mn doping plays a significant role in the destruction of the intrinsic dipolar effect.

Solvent dependent triphenylamine based D-(pi-A)n type dye molecules and optical properties.

PubMed

Li, Xiaochuan; Son, Young-A; Kim, Young-Sung; Kim, Sung-Hoon; Kun, Jun; Shin, Jong-Il

2012-02-01

D-(pi-A)n type dyes of triphenylamine derivatives were synthesized and their absorption and luminescence in different solvents were examined to investigate solvent dependent properties observed for their emissions in solvents with different dielectric constants. The emission wavelengths showed a dramatic blue shift with increasing solvent polarity. The results of molecular orbital calculations by computer simulation, based on Material Studio suite of programs, were found to reasonably account for the spectral properties. Relative levels of HOMO and LUMO were measured and calculated and all derivatives exhibited strong solid fluorescence with distinctively different FWHMs.

Classification of Solvents according to Interaction Mechanisms.

ERIC Educational Resources Information Center

Ahmed, Wasi

1979-01-01

Presented is a model for solvent effects based on the observation that the excitation energy of all-trans-N-Retinylidenmethyl-n-butylammonium iodide is directly related to the dielectric constant of a series of aromatic and aliphatic solvents as the dielectric constant (e) ranges from 2 to 10.5. (BT)

Investigation of multiferroic behavior on flakes-like BiFeO{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sheikh, Javed R.; Gaikwad, Vishwajit M.; Acharya, Smita A., E-mail: saha275@yahoo.com

2016-05-23

In present work, multiferroic BiFeO{sub 3} was synthesized by hydrothermal route. The rhombohedral structure was confirmed X-ray diffraction pattern and data fitted with Reitveld refinement using Full-Prof software suite. SEM micrograph shows flake like morphology. Frequency and temperature dependence of dielectric constant and dielectric loss were studied and detected enhancement in dielectric constant. The magnetic measurement indicates antiferromagnetic nature of BFO. P-E curve shows ferroelectic hysteresis loop with remanent polarization (2Pr) 0.3518 µC/cm{sup 2}. The dielectric anomaly observed near T{sub N} can be assigned to magnetoelectric coupling which is useful in device application.

High-speed droplet actuation on single-plate electrode arrays.

PubMed

Banerjee, Arghya Narayan; Qian, Shizhi; Joo, Sang Woo

2011-10-15

This paper reports a droplet-based microfluidic device composed of patterned co-planar electrodes in an all-in-a-single-plate arrangement and coated with dielectric layers for electrowetting-on-dielectric (EWOD) actuation of discrete droplets. The co-planar arrangement is preferred over conventional two-plate electrowetting devices because it provides simpler manufacturing process, reduced viscous drag, and easier liquid-handling procedures. These advantages lead to more versatile and efficient microfluidic devices capable of generating higher droplet speed and can incorporate various other droplet manipulation functions into the system for biological, sensing, and other microfluidic applications. We have designed, fabricated, and tested the devices using an insulating layer with materials having relatively high dielectric constant (SiO(2)) and compared the results with polymer coatings (Cytop) with low dielectric constant. Results show that the device with high dielectric layer generates more reproducible droplet transfer over a longer distance with a 25% reduction in the actuation voltage with respect to the polymer coatings, leading to more energy efficient microfluidic applications. We can generate droplet speeds as high as 26 cm/s using materials with high dielectric constant such as SiO(2). Copyright © 2011. Published by Elsevier Inc.

First-principles study on leakage current caused by oxygen vacancies at HfO2/SiO2/Si interface

NASA Astrophysics Data System (ADS)

Takagi, Kensuke; Ono, Tomoya

2018-06-01

The relationship between the position of oxygen vacancies in HfO2/SiO2/Si gate stacks and the leakage current is studied by first-principles electronic-structure and electron-conduction calculations. We find that the increase in the leakage current due to the creation of oxygen vacancies in the HfO2 layer is much larger than that in the SiO2 interlayer. According to previous first-principles total energy calculations, the formation energy of oxygen vacancies is smaller in the SiO2 interlayer than that in the HfO2 layer under the same conditions. Therefore, oxygen vacancies will be attracted from the SiO2 interlayer to minimize the energy, thermodynamically justifying the scavenging technique. Thus, the scavenging process efficiently improves the dielectric constant of HfO2-based gate stacks without increasing the number of oxygen vacancies, which cause the dielectric breakdown.

Dielectric response of crystalline tris(acetylacetonato)cobalt(III) films grown on Si substrate for low- k dielectric applications

NASA Astrophysics Data System (ADS)

Dakhel, A. A.; Ali-Mohamed, A. Y.

2008-01-01

Thin films of the complex tris(acetylacetonato)cobalt(III) [abb. Co(acac) 3] were deposited in vacuum on glass and p-Si substrates for optical and dielectric studies. The samples were characterised by X-ray diffraction and fluorescence methods as well as optical absorption spectroscopy. The prepared films show a polycrystalline of monoclinic P2 1/ c structure. The optical absorption spectrum of the prepared film was not exactly fit to that of the molecular one. The energy of the optical absorption onset of the Co(acac) 3 film was calculated by using usual solid-state methods. For electrical measurements on the complex as insulator, samples in the form of metal-insulator-semiconductor (MIS) structure were prepared and characterised by measurement of the capacitance as a function of gate voltage at 1 MHz. The frequency dependence of the complex dielectric constant of the complex was studied in the frequency range (1-1000 kHz) in the temperature range (294-323 K). The experimental results were analysed in the framework of Debye single relaxation model. Generally, the present study shows that a film of complex Co(acac) 3 grown on Si substrate is a promising candidate for low- k dielectric applications, it displays low- k value around 1.7 at high frequencies.

Frequency Dependent Electrical and Dielectric Properties of Au/P3HT:PCBM:F4-TCNQ/n-Si Schottky Barrier Diode

NASA Astrophysics Data System (ADS)

Taşçıoğlu, İ.; Tüzün Özmen, Ö.; Şağban, H. M.; Yağlıoğlu, E.; Altındal, Ş.

2017-04-01

In this study, poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester: 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (P3HT:PCBM:F4-TCNQ) organic film was deposited on n-type silicon (n-Si) substrate by spin coating method. The electrical and dielectric analysis of Au/P3HT:PCBM:F4-TCNQ/n-Si Schottky barrier diode was conducted by means of capacitance-voltage ( C- V) and conductance-voltage ( G/ ω- V) measurements in the frequency range of 10 kHz-2 MHz. The C- V- f plots exhibit fairly large frequency dispersion due to excess capacitance caused by the presence of interface states ( N ss). The values of N ss located in semiconductor bandgap at the organic film/semiconductor interface were calculated by Hill-Coleman method. Experimental results show that dielectric constant ( ɛ') and dielectric loss ( ɛ″) decrease with increasing frequency, whereas loss tangent (tan δ) remains nearly the same. The decrease in ɛ' and ɛ″ was interpreted by the theory of dielectric relaxation due to interfacial polarization. It is also observed that ac electrical conductivity ( σ ac) and electric modulus ( M' and M″) increase with increasing frequency.

Microstructure and dielectric properties of silver-barium titanate nanocomplex materials by wet chemical approach

NASA Astrophysics Data System (ADS)

Ueno, Shintaro; Sakamoto, Yasunao; Nakashima, Kouichi; Wada, Satoshi

2014-09-01

To develop ceramic capacitors with a high effective dielectric constant, we attempted to fabricate BaTiO3 (BT) complexes with embedded Ag nanoparticles by wet chemical processes. Ag nanoparticle-adsorbed dendritic BT particles, Ag-BT hybrid particles, were synthesized from the sol-gel-derived precursor gel powders containing Ag, Ba, and Ti by hydrothermal treatment. These particles were pressed with BT fillers and TiO2 precursor nanoparticles into green compacts, and then, the green compacts were chemically converted into the Ag/BT nanocomplex compacts in Ba(OH)2 aqueous solution under the hydrothermal condition at 160 °C. The effective dielectric constant of the resultant Ag/BT nanocomplexes increases with an increase in Ag content. The maximal effective dielectric constant of approximately 900 was recorded for the nanocomplex with the Ag content of 10.7 vol %.

Giant dielectric constant in CaCu3Ti4O12-MgB2 composites near the percolation threshold

NASA Astrophysics Data System (ADS)

Mukherjee, Rupam; Fernandez, Lucia; Lawes, Gavin; Nadgorny, Boris

2013-03-01

We have investigated the enhancement of the dielectric constant K in CaCu3Ti4O12 (CCTO)-MgB2 composite near the percolation threshold. To optimize the dielectric properties of pure CCTO we have sintered the samples at variuos temperatures. We will present the results of the measurements of K in a broad frequency for pure CCTO for the samples sintered at 1100°C and 500°C. Commercially available MgB2 powder was mixed with different weight fractions of CCTO and the pressure of 1GPa was applied to form composite pellets. Near the percolation threshold PC, CCTO/MgB2 composite system exhibit a dramatic increase of the dielectric constant K by several orders of magnitude, compared to pure CCTO. We will also discuss the magnetic field dependence of the capacitance of CCTO composite powders.

Effect of organic flux on the colossal dielectric constant of CaCu3Ti4O12 (CCTO)

NASA Astrophysics Data System (ADS)

Razdan, Vishnu; Singh, Abhishek; Arnold, Brad; Choa, Fow-Sen; Kelly, Lisa; Singh, N. B.

2015-05-01

We have used low temperature organics to achieve orientation of the grains of Ca2/3Cu3Ti4O12 (CCTO) compound to increase the resistivity. During the past fifteen years CCTO has been studied extensively for its performance as a dielectric capacitor. We have synthesized and grown large grains of pure Ca2/3Cu3Ti4O12 and doped compound, and studied the dielectric constant and resistivity. The grains were aligned by using a naphthalene-camphor eutectic. CCTO was mixed in the organic melt and oriented by the directional solidification method. This material has different characteristics than pure processed CCTO material. The effect of solidification conditions and its effect on the morphology and the dielectric constant, resistivity and loss tan delta of pure and doped CCTO are described in this article.

Predicting water-to-cyclohexane partitioning of the SAMPL5 molecules using dielectric balancing of force fields.

PubMed

Paranahewage, S Shanaka; Gierhart, Cassidy S; Fennell, Christopher J

2016-11-01

Alchemical transformation of solutes using classical fixed-charge force fields is a popular strategy for assessing the free energy of transfer in different environments. Accurate estimations of transfer between phases with significantly different polarities can be difficult because of the static nature of the force fields. Here, we report on an application of such calculations in the SAMPL5 experiment that also involves an effort in balancing solute and solvent interactions via their expected static dielectric constants. This strategy performs well with respect to predictive accuracy and correlation with unknown experimental values. We follow this by performing a series of retrospective investigations which highlight the potential importance of proper balancing in these systems, and we use a null hypothesis analysis to explore potential biases in the comparisons with experiment. The collective findings indicate that considerations of force field compatibility through dielectric behavior is a potential strategy for future improvements in transfer processes between disparate environments.

FIRST PRINCIPLES STUDY ON ELECTRONIC AND OPTICAL PROPERTIES OF Al-DOPED γ-Ge3N4

NASA Astrophysics Data System (ADS)

Ding, Y. C.; Xiang, A. P.; Zhu, X. H.; Luo, J.; Hu, X. F.

2012-12-01

First principles study of the structural, electronic and optical properties of Al-doped γ-Ge3N4 with different concentration has been reported using the pseudo-potential plane wave method within the generalized gradient approximation (GGA). The binding energy and the formation energy suggest that Aluminum (Al) impurities prefer to substitute Ge at octahedral sites. Different doping concentrations are considered and the corresponding density of states (DOS) are analyzed. Calculated DOS indicates that there are holes in the top of the valance band after doping, meaning a p-type doping. We study the complex dielectric function, the absorption coefficient, and the electron energy loss spectra. It is demonstrated that for the low Al concentration, the material exhibits the dielectric behavior and for the high Al concentration, the material has possibilities to exhibit some metallic behavior. The γ-Ge3N4 doped with Al has a much higher static dielectric constant than undoped γ-Ge3N4, implying its potential applications in electronics and optics.

Structural, electrical, magnetic and magnetoelectric properties of composites

NASA Astrophysics Data System (ADS)

Rani, Renu; Juneja, J. K.; Singh, Sangeeta; Prakash, Chandra; Raina, K. K.

2013-11-01

The magnetoelectric (ME) composites with composition (y)Ni0.8Zn0.2Fe2O4+(1-y) Ba0.90Sr0.10Zr0.04Ti0.96O3 ((y)NZF+(1-y)BSZT) (where y=0.00-0.15 in wt%) were prepared by the conventional solid state reaction route. The existence of both phases was confirmed by the X-Ray diffraction technique and the lattice parameters for all samples were calculated. The dielectric properties such as dielectric constant and dielectric loss were measured as a function of temperature at different frequencies. P-E hysteresis loops and M-H hysteresis loops confirm the ferroelectric and ferrimagnetic nature of the composite samples. M-H loops for electrically poled and un-poled samples were compared to prove ME evidences. Variation of ME coefficient (α) with dc magnetic field was also studied for all composite samples. The maximum value of α (1.6 mV/cm Oe) was observed for y=0.10 at 750 Oe.

Improved linearity in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors with nonlinear polarization dielectric

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Tao; Science and Technology on Monolithic Integrated Circuits and Modules Laboratory, Nanjing Electronic Devices Institute, Nanjing 210016; Xu, Ruimin

2015-06-15

We demonstrate highly improved linearity in a nonlinear ferroelectric of Pb(Zr{sub 0.52}Ti{sub 0.48})-gated AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT). Distinct double-hump feature in the transconductance-gate voltage (g{sub m}-V{sub g}) curve is observed, yielding remarkable enhancement in gate voltage swing as compared to MIS-HEMT with conventional linear gate dielectric. By incorporating the ferroelectric polarization into a self-consistent calculation, it is disclosed that in addition to the common hump corresponding to the onset of electron accumulation, the second hump at high current level is originated from the nonlinear polar nature of ferroelectric, which enhances the gate capacitance by increasing equivalent dielectricmore » constant nonlinearly. This work paves a way for design of high linearity GaN MIS-HEMT by exploiting the nonlinear properties of dielectric.« less

Large change in dielectric constant of CaCu3Ti4O12 under violet laser

NASA Astrophysics Data System (ADS)

Masingboon, C.; Thongbai, P.; King, P. D. C.; Maensiri, S.; Meevasana, W.

2013-03-01

This work reports the influence of light illumination on the dielectric constant of CaCu3Ti4O12 (CCTO) polycrystals which exhibit giant dielectric constant. When the CCTO samples were exposed to 405-nm laser light, the enhancement in capacitance as high as 22% was observed for the first time, suggesting application of light-sensitive capacitance devices. To understand this change better microscopically, we also performed electronic-structure measurements using photoemission spectroscopy, and measured the electrical conductivity of the CCTO samples under different conditions of light exposure and oxygen partial pressure. All these measurements suggest that this large change is driven by oxygen vacancy induced by the irradiation.

Self-assembly and structural relaxation in a model ionomer melt

DOE PAGES

Goswami, Monojoy; Borreguero, Jose M.; Sumpter, Bobby G.

2015-02-26

Molecular dynamics simulations are used to understand the self-assembly and structural relaxation in ionomer melts containing less than 10% degree of ionization on the backbone. We study the self-assembly of charged sites and counterions that show structural ordering and agglomeration with a range of structures that can be achieved by changing the dielectric constant of the medium. The intermediate scattering function shows a decoupling of charge and counterion relaxation at longer length scales for only high dielectric constant and at shorter length scales for all dielectric constants. Finally, the slow structural decay of counterions in the strongly correlated ionomer systemmore » closely resembles transport properties of semi-flexible polymers.« less

New dielectric ceramics Pb(Cd)BiM/sup IV/SbO/sub 7/ (M/sup IV/ = Ti, Zr, Sn) with the pyrochlore structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lambachri, A.; Monier, M.; Mercurio, J.P.

1988-04-01

Dielectric ceramics have been obtained by natural sintering of pyrochlore phases with general formula Pb(Cd)BiM/sup IV/SbO/sub 7/ (M/sup IV/ = Ti, Zr, Sn). Low frequency dielectric characteristics have been studied with respect to the processing conditions: sintering without additive and in the presence of some low melting compounds (PbO, Pb/sub 5/Ge/sub 3/O/sub 11/, Bi/sub 12/PbO/sub 19/ and Bi/sub 12/CdO/sub 19/). The dielectric constants of these ceramics lie between 30 and 60, the dielectric losses range from 10 to 30.10/sup -4/ and the temperature coefficient of the dielectric constants (20 - 100/sup 0/C) can be tailored by means of additives inmore » the +- 30 ppm K/sup -1/ range.« less

Nanocomposites of polyimide and mixed oxide nanoparticles for high performance nanohybrid gate dielectrics in flexible thin film transistors

NASA Astrophysics Data System (ADS)

Kim, Ju Hyun; Hwang, Byeong-Ung; Kim, Do-Il; Kim, Jin Soo; Seol, Young Gug; Kim, Tae Woong; Lee, Nae-Eung

2017-05-01

Organic gate dielectrics in thin film transistors (TFTs) for flexible display have advantages of high flexibility yet have the disadvantage of low dielectric constant (low- k). To supplement low- k characteristics of organic gate dielectrics, an organic/inorganic nanocomposite insulator loaded with high- k inorganic oxide nanoparticles (NPs) has been investigated but high loading of high- k NPs in polymer matrix is essential. Herein, compositing of over-coated polyimide (PI) on self-assembled (SA) layer of mixed HfO2 and ZrO2 NPs as inorganic fillers was used to make dielectric constant higher and leakage characteristics lower. A flexible TFT with lower the threshold voltage and high current on/off ratio could be fabricated by using the hybrid gate dielectric structure of the nanocomposite with SA layer of mixed NPs on ultrathin atomic-layer deposited Al2O3. [Figure not available: see fulltext.

Short range ferromagnetic, magneto-electric, and magneto-dielectric effect in ceramic Co{sub 3}TeO{sub 6}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Harishchandra, E-mail: singh85harish@gmail.com, E-mail: singh85harish@rrcat.gov.in; Ghosh, Haranath; Indus Synchrotrons Utilization Division, Raja Ramanna Center for Advanced Technology, Indore 452013

2016-01-28

We report observation of magneto-electric and magneto-dielectric couplings along with short range ferromagnetic order in ceramic Cobalt Tellurate (Co{sub 3}TeO{sub 6}, CTO) using magnetic, structural, dielectric, pyroelectric, and polarization studies. DC magnetization along with dielectric constant measurements indicate a coupling between magnetic order and electrical polarization. A strong anomaly in the dielectric constant at ∼17.4 K in zero magnetic field indicates spontaneous electric polarization, consistent with a recent neutron diffraction study. Observation of weak short range ferromagnetic order at lower temperatures is attributed to the Griffiths-like ferromagnetism. Furthermore, magnetic field dependence of the ferroelectric transition follows earlier theoretical predictions, applicable tomore » single crystal CTO. Finally, combined dielectric, pyroelectric, and polarization measurements suggest that the ground state of CTO may possess spontaneous symmetry breaking in the absence of magnetic field.« less

Automated Microwave Dielectric Constant Measurement

DTIC Science & Technology

1987-03-01

IJSWC TR 86-46 AD.-A 184 182 AUTOMATED MICROWAVE DIELECTRIC CONSTANT MEASUREMENT SYTIEM BY B. C. GLANCY A. KRALL PESEARCH AND TECHNOLOGY DEPARTMENT...NO0. NO. ACCESSION NO. Silver Spring, Maryland 20903-500061152N ZROO1 ZRO131 R1AA29 11. TITLE (Include Security Classification) AUTOMATED MICROWAVE ...constants as a funct on of microwave frequency has been simplified using an automated testing apparatus. This automated procedure is based on the use of a

Review of Slow-Wave Structures

NASA Technical Reports Server (NTRS)

Wallett, Thomas M.; Qureshi, A. Haq

1994-01-01

The majority of recent theoretical and experimental reports published in the literature dealing with helical slow-wave structures focus on the dispersion characteristics and their effects due to the finite helix wire thickness and attenuation, dielectric loading, metal loading, and the introduction of plasma. In many papers, an effective dielectric constant is used to take into account helix wire dimensions and conductivity losses, while the propagation constant of the signal and the interaction impedance of the structure are found to depend on the surface resistivity of the helix. Also, various dielectric supporting rods are simulated by one or several uniform cylinders having an effective dielectric constant, while metal vane loading and plasma effects are incorporated in the effective dielectric constant. The papers dealing with coupled cavities and folded or loaded wave guides describe equivalent circuit models, efficiency enhancement, and the prediction of instabilities for these structures. Equivalent circuit models of various structures are found using computer software programs SUPERFISH and TOUCHSTONE. Efficiency enhancement in tubes is achieved through dynamic velocity and phase adjusted tapers using computer techniques. The stability threshold of unwanted antisymmetric and higher order modes is predicted using SOS and MAGIC codes and the dependence of higher order modes on beam conductance, section length, and effective Q of a cavity is shown.

Surface Plasmon Resonance Evaluation of Colloidal Metal Aerogel Filters

NASA Technical Reports Server (NTRS)

Smith, David D.; Sibille, Laurent; Cronise, Raymond J.; Noever, David A.

1997-01-01

Surface plasmon resonance imaging has in the past been applied to the characterization of thin films. In this study we apply the surface plasmon technique not to determine macroscopic spatial variations but rather to determine average microscopic information. Specifically, we deduce the dielectric properties of the surrounding gel matrix and information concerning the dynamics of the gelation process from the visible absorption characteristics of colloidal metal nanoparticles contained in aerogel pores. We have fabricated aerogels containing gold and silver nanoparticles. Because the dielectric constant of the metal particles is linked to that of the host matrix at the surface plasmon resonance, any change 'in the dielectric constant of the material surrounding the metal nanoparticles results in a shift in the surface plasmon wavelength. During gelation the surface plasmon resonance shifts to the red as the average or effective dielectric constant of the matrix increases. Conversely, formation of an aerogel or xerogel through supercritical extraction or evaporation of the solvent produces a blue shift in the resonance indicating a decrease in the dielectric constant of the matrix. From the magnitude of this shift we deduce the average fraction of air and of silica in contact with the metal particles. The surface area of metal available for catalytic gas reaction may thus be determined.

Dielectric and modulus analysis of the photoabsorber Cu2SnS3

NASA Astrophysics Data System (ADS)

Lahlali, S.; Essaleh, L.; Belaqziz, M.; Chehouani, H.; Alimoussa, A.; Djessas, K.; Viallet, B.; Gauffier, J. L.; Cayez, S.

2017-12-01

Dielectric properties of the ternary semiconductor compound Cu2SnS3 is studied for the first time in the high temperature range from 300 °C to 440 °C with the frequency range 1 kHz to 1 MHz. The dielectric constant ε ‧ and dielectric loss tan (δ) were observed to increase with temperature and decrease rapidly with frequency to remains constant at high frequencies. The variation of the dielectric loss Ln (ε ") with L n (ω) was found to follow the empirical law, ε " = B ω m (T). The dielectric data were analyzed using complex electrical modulus M* at various temperatures. The activation energy responsible for the relaxation is estimated from the analysis of the modulus spectra. The value of the hopping barrier potential is estimated from the dielectric loss and compared with the value previously obtained from ac-conductivity. These results are critical for understanding the behavior of based polycrystalline family of Cu2SnS3 for absorber materials in solar-cells.

Effect of solution combusted TiO2 nanopowder within commercial BaTiO3 dielectric layer on the photoelectric properties for AC powder electroluminescence devices.

PubMed

Park, Sung; Choi, Gil Rak; Kim, Youn Cheol; Lee, Jae Chun; Lee, Ju Hyeon

2013-05-01

A unique synthesis method was developed, which is called solution combustion method (SCM). TiO2 nanopowder was synthesized by this method. This SCM TiO2 nanopowder (-35 nm) was added to the dielectric layer of AC powder electroluminescence (EL) device. The dielectric layer was made of commercial BaTiO3 powder (-1.2 microm) and binding polymer. 0, 5, 10 and 15 wt% of SCM TiO2 nanopowder was added to the dielectric layer during fabrication of AC powder EL device respectively. Dielectric constant of these four kinds of dielectric layers was measured. The brightness and current density of AC powder EL device were also measured. When 10 wt% of SCM TiO2 nanopowder was added, dielectric constant and brightness were increased by 30% and 101% respectively. Furthermore, the current density was decreased by 71%. This means that the brightness was double and the power consumption was one third.

γ-rays irradiation effects on dielectric properties of Ti/Au/GaAsN Schottky diodes with 1.2%N

NASA Astrophysics Data System (ADS)

Teffahi, A.; Hamri, D.; Djeghlouf, A.; Abboun Abid, M.; Saidane, A.; Al Saqri, N.; Felix, J. F.; Henini, M.

2018-06-01

Dielectric properties of As grown and irradiated Ti /Au/GaAsN Schottky diodes with 1.2%N are investigated using capacitance/conductance-voltage measurements in 90-290 K temperature range and 50-2000 kHz frequency range. Extracted parameters are interface state density, series resistance, dielectric constant, dielectric loss, tangent loss and ac conductivity. It is shown that exposure to γ-rays irradiation leads to reduction in effective trap density believed to result from radiation-induced traps annulations. An increase in series resistance is attributed to a net doping reduction. Dielectric constant (ε') shows usual step-like transitions with corresponding relaxation peaks in dielectric loss. These peaks shift towards lower temperature as frequency decrease. Temperature dependant ac conductivity followed an Arrhenius relation with activation energy of 153 meV in the 200-290 K temperature range witch correspond to As vacancy. The results indicate that γ-rays irradiation improves the dielectric and electrical properties of the diode due to the defect annealing effect.

Material with high dielectric constant, low dielectric loss, and good mechanical and thermal properties produced using multi-wall carbon nanotubes wrapped with poly(ether sulphone) in a poly(ether ether ketone) matrix

NASA Astrophysics Data System (ADS)

Zhang, Shuling; Wang, Hongsong; Wang, Guibin; Jiang, Zhenhua

2012-07-01

A material with high dielectric constant, low dielectric loss, and good mechanical and thermal properties was produced using multi-wall carbon nanotubes (MWCNTs) wrapped with poly(ether sulphone) (PES) dispersed in a poly(ether ether ketone) (PEEK) matrix. The material was fabricated using melt-blending, and MWCNT/PEEK composites show different degrees of improvement in the measured dielectric, mechanical, and thermal properties as compared to pure PEEK. This is attributed to the high conductivity of MWCNTs, the effect of wrapping MWCNTs with PES, the good dispersion of the wrapped MWCNTs in PEEK, and the strong interfacial adhesion between the wrapped MWCNTs and the PEEK.

Dielectric properties of benzylamine in 1,2,6-hexanetriol mixture using time domain reflectometry technique

NASA Astrophysics Data System (ADS)

Swami, M. B.; Hudge, P. G.; Pawar, V. P.

The dielectric properties of binary mixtures of benzylamine-1,2,6-hexantriol mixtures at different volume fractions of 1,2,6-hexanetriol have been measured using Time Domain Reflectometry (TDR) technique in the frequency range of 10 MHz to 30 GHz. Complex permittivity spectra were fitted using Havriliak-Negami equation. By using least square fit method the dielectric parameters such as static dielectric constant (ɛ0), dielectric constant at high frequency (ɛ∞), relaxation time τ (ps) and relaxation distribution parameter (β) were extracted from complex permittivity spectra at 25∘C. The intramolecular interaction of different molecules has been discussed using the Kirkwood correlation factor, Bruggeman factor. The Kirkwood correlation factor (gf) and effective Kirkwood correlation factor (geff) indicate the dipole ordering of the binary mixtures.

Holmium hafnate: An emerging electronic device material

NASA Astrophysics Data System (ADS)

Pavunny, Shojan P.; Sharma, Yogesh; Kooriyattil, Sudheendran; Dugu, Sita; Katiyar, Rajesh K.; Scott, James F.; Katiyar, Ram S.

2015-03-01

We report structural, optical, charge transport, and temperature properties as well as the frequency dependence of the dielectric constant of Ho2Hf2O7 (HHO) which make this material desirable as an alternative high-k dielectric for future silicon technology devices. A high dielectric constant of ˜20 and very low dielectric loss of ˜0.1% are temperature and voltage independent at 100 kHz near ambient conditions. The Pt/HHO/Pt capacitor exhibits exceptionally low Schottky emission-based leakage currents. In combination with the large observed bandgap Eg of 5.6 eV, determined by diffuse reflectance spectroscopy, our results reveal fundamental physics and materials science of the HHO metal oxide and its potential application as a high-k dielectric for the next generation of complementary metal-oxide-semiconductor devices.

Dielectric response of a nondegenerate electron gas in semiconductor nanocrystallites

NASA Astrophysics Data System (ADS)

van Faassen, E.

1998-12-01

We investigate the low-frequency dielectric response of a dilute electron gas in a small spherical semiconductor particle. The flow of the electrons is described by hydrodynamic equations which incorporate the electrostatic interactions between the electrons in a self-consistent fashion. In the low-frequency regime, the dielectric loss is small and proportional to the frequency, despite substantial field penetration into the semiconductor. The loss remains small even for high doping levels due to effective cancellation between field-induced drift and diffusion. The model is used to estimate the complex dielectric constant of a system of weakly conducting nanosized semiconductor particles. The most prominent manifestation of spatial dispersion is that photoinduced changes in the real and imaginary parts of the dielectric constant are positive and of comparable magnitude.

Electromagnetic mixing laws: A supersymmetric approach

NASA Astrophysics Data System (ADS)

Niez, J. J.

2010-02-01

In this article we address the old problem of finding the effective dielectric constant of materials described either by a local random dielectric constant, or by a set of non-overlapping spherical inclusions randomly dispersed in a host. We use a unified theoretical framework, such that all the most important Electromagnetic Mixing Laws (EML) can be recovered as the first iterative step of a family of results, thus opening the way to future improvements through the refinements of the approximation schemes. When the material is described by a set of immersed inclusions characterized by their spatial correlation functions, we exhibit an EML which, being featured by a minimal approximation scheme, does not come from the multiple scattering paradigm. It is made of a pure Hori-Yonezawa formula, corrected by a power series of the inclusion density. The coefficients of the latter, which are given as sums of standard diagrams, are recast into electromagnetic quantities which calculation is amenable numerically thanks to codes available on the web. The methods used and developed in this work are generic and can be used in a large variety of areas ranging from mechanics to thermodynamics.

Inelastic scattering of electrons at real metal surfaces

NASA Astrophysics Data System (ADS)

Ding, Z.-J.

1997-04-01

A theory is presented to calculate the electron inelastic scattering cross section for a moving electron near the surface region at an arbitrary takeoff angle. The theory is based on using a bulk plasmon-pole approximation to derive the numerically computable expression of the electron self-energy in the random-phase approximation for a surface system, through the use of experimental optical constants. It is shown that the wave-vector-dependent surface dielectric function satisfies the surface sum rules in this scheme. The theory provides a detailed knowledge of electron self-energy depending on the kinetic energy, distance from surface, and velocity vector of an electron moving in any metal of a known dielectric constant, accommodating the formulation to practical situation in surface electron spectroscopies. Numerical computations of the energy-loss cross section have been made for Si and Au. The contribution to the total differential scattering cross section from each component is analyzed. The depth dependence informs us in detail how the bulk excitation mode changes to a surface excitation mode with an electron approaching the surface from the interior of a medium.

Synthesis and physicochemical properties of bis(L-asparaginato) zinc(II): A promising new semiorganic crystal with high laser damage threshold for shorter wavelength generation

NASA Astrophysics Data System (ADS)

Subhashini, R.; Arjunan, S.

2018-05-01

An exceedingly apparent nonlinear semiorganic optical crystals of bis(L-asparaginato)zinc(II) [BLAZ], was synthesized by a traditional slow evaporation solution growth technique. The cell parameters were estimated from single crystal X-ray diffraction analysis. Spectroscopic study substantiates the presence of functional groups. The UV spectrum shows the sustenance of wide transparency window and several optical constants, such as extinction coefficient (K), refractive index, optical conductivity and electric susceptibility with real and imaginary parts of dielectric constant were calculated using the transmittance data. The fluorescence emission spectrum of the crystal pronounces red emission. The laser induced surface damage threshold of the crystal was measured using Nd:YAG laser. The output intensity of second harmonic generation was estimated using the Kurtz and Perry powder method. The hardness stability was investigated by Vickers microhardness test. The decomposition and thermal stability of the compound were scrutinized by TGA-DSC studies. Dielectric studies were carried out to anatomize the electrical properties of the crystal. SEM analysis reveals the existence of minute crystallites on the growth surface.

Effect of strain on the electronic structure and optical properties of germanium

NASA Astrophysics Data System (ADS)

Wen, Shumin; Zhao, Chunwang; Li, Jijun; Hou, Qingyu

2018-05-01

The effects of biaxial strain parallel to the (001) plane on the electronic structures and optical properties of Ge are calculated using the first-principles plane-wave pseudopotential method based on density functional theory. The screened-exchange local-density approximation function was used to obtain more reliable band structures, while strain was changed from ‑4% to +4%. The results show that the bandgap of Ge decreases with the increase of strain. Ge becomes a direct-bandgap semiconductor when the tensile strain reaches to 2%, which is in good agreement with the experimental results. The density of electron states of strained Ge becomes more localized. The tensile strain can increase the static dielectric constant distinctly, whereas the compressive strain can decrease the static dielectric constant slightly. The strain makes the absorption band edge move toward low energy. Both the tensile strain and compressive strain can significantly increase the reflectivity in the range from 7 eV to 14 eV. The tensile strain can decrease the optical conductivity, but the compressive strain can increase the optical conductivity significantly.

Structural and optical characterization of PVA:KMnO4 based solid polymer electrolyte

NASA Astrophysics Data System (ADS)

Abdullah, Omed Gh.; Aziz, Shujahadeen B.; Rasheed, Mariwan A.

Solid polymer electrolyte films of polyvinyl alcohol (PVA) doped with a different weight percent of potassium permanganate (KMnO4) were prepared by standard solution cast method. XRD and FTIR techniques were performed for structural study. Complex formation between the PVA polymer and KMnO4 salt was confirmed by Fourier transform infrared (FTIR) spectroscopy. The description of crystalline nature of the solid polymer electrolyte films has been confirmed by XRD analysis. The UV-Visible absorption spectra were analyzed in terms of absorption formula for non-crystalline materials. The fundamental optical parameters such as optical band gap energy, refractive index, optical conductivity, and dielectric constants have been investigated and showed a clear dependence on the KMnO4 concentration. The observed value of optical band gap energy for pure PVA is about 6.27 eV and decreases to a value 3.12 eV for the film sample formed with 4 wt% KMnO4 salt. The calculated values of refractive index and the dielectric constants of the polymer electrolyte films increase with increasing KMnO4 content.

Estimation of Complex Permittivity of Composite Multilayer Material at Microwave Frequency Using Waveguide Measurements

NASA Technical Reports Server (NTRS)

Deshpande, Manohar D.; Dudley, Kenneth

2003-01-01

A simple method is presented to estimate the complex dielectric constants of individual layers of a multilayer composite material. Using the MatLab Optimization Tools simple MatLab scripts are written to search for electric properties of individual layers so as to match the measured and calculated S-parameters. A single layer composite material formed by using materials such as Bakelite, Nomex Felt, Fiber Glass, Woven Composite B and G, Nano Material #0, Cork, Garlock, of different thicknesses are tested using the present approach. Assuming the thicknesses of samples unknown, the present approach is shown to work well in estimating the dielectric constants and the thicknesses. A number of two layer composite materials formed by various combinations of above individual materials are tested using the present approach. However, the present approach could not provide estimate values close to their true values when the thicknesses of individual layers were assumed to be unknown. This is attributed to the difficulty in modelling the presence of airgaps between the layers while doing the measurement of S-parameters. A few examples of three layer composites are also presented.

Tetragonal (K, Na)NbO3 based lead-free single crystal: Growth, full tensor properties, and their orientation dependence

NASA Astrophysics Data System (ADS)

Zheng, Limei; Wang, Junjun; Liu, Xuedong; Yang, Liya; Lu, Xiaoyan; Li, Yanran; Huo, Da; Lü, Weiming; Yang, Bin; Cao, Wenwu

2017-10-01

A Li and Ta modified (K, Na)NbO3 lead-free single crystal with a large size (13 × 10 × 20 mm3) has been grown by using the top-seeded solution growth method. The large size allows us to carry out an extensive study on this tetragonal crystal. We have measured a complete set of elastic, dielectric, and piezoelectric constants for the [001]C poled crystal with the single domain state. The crystal exhibits high shear piezoelectricity with d15 = 518 pC/N and k15 = 0.733, showing excellent potential in shear electro-sonic energy transformation devices. It is found that the high shear piezoelectricity originates from the vicinity of orthorhombic-tetragonal phase transition, which favors polarization rotation greatly. The orientation dependence of longitudinal dielectric, piezoelectric, and elastic constants and electromechanical coupling factor in the 3-dimentional space were calculated based on the single domain dataset. We believe that this work is of great importance for both fundamental studies and device designs for lead-free materials.

Phosphoryl Transfer Reaction in RNA in Alkaline Conditions.

PubMed

Bertran, Joan; Oliva, Antoni; Branchadell, Vicenç; Acosta-Silva, Carles

2018-06-25

In this work we have studied the phosphoryl transfer reaction in RNA in alkaline conditions by theoretically exploring the influence of several solvents. The calculations have been carried out using the M06-2X functional while the solvents are taken as a continuum using the SMD method. The main results are that the O2'-P-O5' angle in the reactants, the free activation energies and the reaction mechanism are clearly dependent on the dielectric constant of the environment, thus showing that the electrostatic term is determining for this chemical system with two negative charges. Our study seems to indicate that water, the solvent with the greatest dielectric constant, would be the one that mostly increases the reaction rate. As this is not the case in enzymatic catalysis, one has to conclude that, in the case of proteins as well as in the case of ribozymes, the enzymatic catalysis is not mainly due to the solvent reaction field, but to local electrical fields due to the enzyme preorganization. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Use of Ground Penetrating Radar at the FAA's National Airport Pavement Test Facility

NASA Astrophysics Data System (ADS)

Injun, Song

2015-04-01

The Federal Aviation Administration (FAA) in the United States has used a ground-coupled Ground Penetrating Radar (GPR) at the National Airport Pavement Test Facility (NAPTF) since 2005. One of the primary objectives of the testing at the facility is to provide full-scale pavement response and failure information for use in airplane landing gear design and configuration studies. During the traffic testing at the facility, a GSSI GPR system was used to develop new procedures for monitoring Hot Mix Asphalt (HMA) pavement density changes that is directly related to pavement failure. After reviewing current setups for data acquisition software and procedures for identifying different pavement layers, dielectric constant and pavement thickness were selected as dominant parameters controlling HMA properties provided by GPR. A new methodology showing HMA density changes in terms of dielectric constant variations, called dielectric sweep test, was developed and applied in full-scale pavement test. The dielectric constant changes were successfully monitored with increasing airplane traffic numbers. The changes were compared to pavement performance data (permanent deformation). The measured dielectric constants based on the known HMA thicknesses were also compared with computed dielectric constants using an equation from ASTM D4748-98 Standard Test Method for Determining the Thickness of Bound Pavement Layers Using Short-Pulse Radar. Six inches diameter cylindrical cores were taken after construction and traffic testing for the HMA layer bulk specific gravity. The measured bulk specific gravity was also compared to monitor HMA density changes caused by aircraft traffic conditions. Additionally this presentation will review the applications of the FAA's ground-coupled GPR on embedded rebar identification in concrete pavement, sewer pipes in soil, and gage identifications in 3D plots.

THE ONSET OF ELECTRICAL BREAKDOWN IN DUST LAYERS: II. EFFECTIVE DIELECTRIC CONSTANT AND LOCAL FIELD ENHANCEMENT

EPA Science Inventory

Part 1 of the work has shown that electrical breakdown in dust layers obeys Paschen's Law, but occurs at applied field values which appear too small to initiate the breakdown. In this paper the authors show how an effective dielectric constant characterizing the dust layer can be...

Process for lowering the dielectric constant of polyimides using diamic acid additives

NASA Technical Reports Server (NTRS)

Stoakley, Diane M. (Inventor); St.clair, Anne K. (Inventor)

1990-01-01

Linear aromatic polyimides with low dielectric constants are produced by adding a diamic acid additive to the polyamic acid resin formed by the condensation of an aromatic dianhydride with an aromatic diamine. The resulting modified polyimide is a better electrical insulator than state-of-the-art commercially available polyimides.

Microwave dielectric measurements of erythrocyte suspensions.

PubMed Central

Bao, J Z; Davis, C C; Swicord, M L

1994-01-01

Complex dielectric constants of human erythrocyte suspensions over a frequency range from 45 MHz to 26.5 GHz and a temperature range from 5 to 40 degrees C have been determined with the open-ended coaxial probe technique using an automated vector network analyzer (HP 8510). The spectra show two separate major dispersions (beta and gamma) and a much smaller dispersion between them. The two major dispersions are analyzed with a dispersion equation containing two Cole-Cole functions by means of a complex nonlinear least squares technique. The parameters of the equation at different temperatures have been determined. The low frequency behavior of the spectra suggests that the dielectric constant of the cell membrane increases when the temperature is above 35 degrees C. The real part of the dielectric constant at approximately 3.4 GHz remains almost constant when the temperature changes. The dispersion shifts with temperature in the manner of a thermally activated process, and the thermal activation enthalpies for the beta- and gamma-dispersions are 9.87 +/- 0.42 kcal/mol and 4.80 +/- 0.06 kcal/mol, respectively. PMID:8075351

Effects of BOX engineering on analogue/RF and circuit performance of InGaAs-OI-Si MOSFET

NASA Astrophysics Data System (ADS)

Maity, Subir Kr.; Pandit, Soumya

2017-11-01

InGaAs is an attractive choice as alternate channel material in n-channel metal oxide semiconductor transistor for high-performance applications. However, electrostatic integrity of such device is poor. In this paper, we present a comprehensive technology computer-aided design simulation-based study of the effect of scaling the thickness of the buried oxide (BOX) region and varying the dielectric constant of BOX material on the electrostatic integrity, analogue/radio frequency (RF) performance and circuit performance of InGaAs-on-Insulator device. Device with thin BOX layer gives better drain-induced barrier lowering performance which enhances output resistance. The carrier mobility remains almost constant with thinning of BOX layer up to certain value. By lowering the dielectric constant of the BOX material, it is further possible to improve the analogue and RF performance. Effect of BOX thickness scaling and role of BOX dielectric material on gain-frequency response of common source amplifier is also studied. It is observed that frequency response of the amplifier improves for thin BOX and with low dielectric constant-based material.

Effect of N2 Plasma Annealing on Properties of Fluorine Doped Silicon Dioxide Films with Low Dielectric Constant for Ultra-Large-Scale Integrated Circuits

NASA Astrophysics Data System (ADS)

Zhang, Wei; Wang, Peng-Fei; Ding, Shi-Jin; Wang, Ji-Tao; William, Wei Lee

2002-06-01

The influence of N2 plasma annealing on the properties of fluorine doped silicon oxide (SiOF) films is investigated. The stability of the dielectric constant of SiOF film is remarkably improved by the N2 plasma annealing. After enduring a moisture absorption test for six hours in a chamber with 60% humidity at 50°C, the dielectric constant variation of the annealed SiOF films is only 1.5%, while the variation for those SiOF films without annealing is 15.5%. Fourier transform infrared spectroscopic results show that the absorption peaks of Si-OH and H-OH of SiOF films are reduced after the N2 plasma annealing because the annealing can wipe off some unstable Si-F2 bonds in SiOF films. These unstable Si-F2 bonds are suitable to react with water, resulting in the degradation of SiOF film properties. Therefore, the N2 plasma annealing meliorates the properties of SiOF films with low dielectric constant.

Application of the compensated Arrhenius formalism to fluidity data of polar organic liquids.

PubMed

Petrowsky, Matt; Fleshman, Allison M; Frech, Roger

2013-03-14

The temperature dependence of viscosity (the reciprocal of fluidity) in polar liquids has been studied for over a century, but the available theoretical models have serious limitations. Consequently, the viscosity is often described with empirical equations using adjustable fitting parameters that offer no insight into the molecular mechanism of transport. We have previously reported a novel approach called the compensated Arrhenius formalism (CAF) to describe ionic conductivity, self-diffusion, and dielectric relaxation in terms of molecular and system properties. Here the CAF is applied to fluidity data of pure n-acetates, 2-ketones, n-nitriles, and n-alcohols over the temperature range 5-85 °C. The fluidity is represented as an Arrhenius-like expression that includes a static dielectric constant dependence in the exponential prefactor. The dielectric constant dependence results from the dependence of mass and charge transport on the molecular dipole moment and the solvent dipole density. The CAF is the only self-consistent description of fluid transport in polar liquids written solely in terms of molecular and system parameters. A scaling procedure is used to calculate the activation energy for transport. We find that the activation energies for fluidity of the aprotic liquids are comparable in value, whereas a higher average E(a) value is observed for the n-alcohol data. Finally, we contrast the molecular description of transport presented here with the conventional hydrodynamic model.

Perturbation-iteration theory for analyzing microwave striplines

NASA Technical Reports Server (NTRS)

Kretch, B. E.

1985-01-01

A perturbation-iteration technique is presented for determining the propagation constant and characteristic impedance of an unshielded microstrip transmission line. The method converges to the correct solution with a few iterations at each frequency and is equivalent to a full wave analysis. The perturbation-iteration method gives a direct solution for the propagation constant without having to find the roots of a transcendental dispersion equation. The theory is presented in detail along with numerical results for the effective dielectric constant and characteristic impedance for a wide range of substrate dielectric constants, stripline dimensions, and frequencies.

Piezoelectric ceramics with high dielectric constants for ultrasonic medical transducers.

PubMed

Hosono, Yasuharu; Yamashita, Yohachi

2005-10-01

Complex system ceramics Pb(Sc(1/2)Nb(1/2))O3-Pb(Mg(1/3)Nb(2/3))O3-Pb(Ni(1/2)Nb(1/2))O3-(Pb0.965,Sr0.035) (Zr,Ti)O3 (PSN-PMN-PNN-PSZT abbreviated PSMNZT) have been synthesized by the conventional technique, and dielectric and piezoelectric properties of the ceramics have been investigated for ultrasonic medical transducers. High capacitances of the transducers are desired in order to match the electrical impedance between the transducers and the coaxial cable in array probes. Although piezoelectric ceramics that have high dielectric constants (epsilon33t/epsilon0 > 5000, k'33 < 70%) are produced in many foundries, the dielectric constants are insufficient. However, we have reported that low molecular mass B-site ions in the lead-perovskite structures are important in realizing better dielectric and piezoelectric properties. We focused on the complex system ceramics PSMNZT that consists of light B-site elements. The maximum dielectric constant, epsilon33T/epsilon0 = 7, 200, was confirmed in the ceramics, where k'33 = 69%, d33 = 940 pC/N, and T(c) = 135 degrees C were obtained. Moreover, pulse-echo characteristics were simulated using the Mason model. The PSMNZT ceramic probe showed echo amplitude about 5.5 dB higher than that of the conventional PZT ceramic probe (PZT-5H type). In this paper, the electrical properties of the PSMNZT ceramics and the simulation results for pulse-echo characteristics of the phased-array probes are introduced.

Synchrotron radiation x-ray photoelectron spectroscopy study on the interface chemistry of high-k PrxAl2-xO3 (x=0-2) dielectrics on TiN for dynamic random access memory applications

NASA Astrophysics Data System (ADS)

Schroeder, T.; Lupina, G.; Sohal, R.; Lippert, G.; Wenger, Ch.; Seifarth, O.; Tallarida, M.; Schmeisser, D.

2007-07-01

Engineered dielectrics combined with compatible metal electrodes are important materials science approaches to scale three-dimensional trench dynamic random access memory (DRAM) cells. Highly insulating dielectrics with high dielectric constants were engineered in this study on TiN metal electrodes by partly substituting Al in the wide band gap insulator Al2O3 by Pr cations. High quality PrAlO3 metal-insulator-metal capacitors were processed with a dielectric constant of 19, three times higher than in the case of Al2O3 reference cells. As a parasitic low dielectric constant interface layer between PrAlO3 and TiN limits the total performance gain, a systematic nondestructive synchrotron x-ray photoelectron spectroscopy study on the interface chemistry of PrxAl2-xO3 (x =0-2) dielectrics on TiN layers was applied to unveil its chemical origin. The interface layer results from the decreasing chemical reactivity of PrxAl2-xO3 dielectrics with increasing Pr content x to reduce native Ti oxide compounds present on unprotected TiN films. Accordingly, PrAlO3 based DRAM capacitors require strict control of the surface chemistry of the TiN electrode, a parameter furthermore of importance to engineer the band offsets of PrxAl2-xO3/TiN heterojunctions.

Synthesis, morphological, electromechanical characterization of (CaMgFex)Fe1-xTi3O12-δ/PDMS nanocomposite thin films for energy storage application

NASA Astrophysics Data System (ADS)

Tripathy, Ashis; Sharma, Priyaranjan; Sahoo, Narayan

2018-03-01

At the present time, flexible and stretchable electronics has intended to use the new cutting-edge technologies for advanced electronic application. Currently, Polymers are being employed for such applications but they are not effective due to their low dielectric constant. To enhance the dielectric properties of polymer for energy storage application, it is necessary to add ceramic material of high dielectric constant to synthesize a polymer-ceramic composite. Therefore, a novel attempt has been made to enhance the dielectric properties of the Polydimethylsiloxane (PDMS) polymer by adding (CaMgFex)Fe1-xTi3O12-δ(0 90%), which can make it a potential material for advanced flexible electronic devices, energy storage and biomedical applications.

K-Band Latching Switches

NASA Technical Reports Server (NTRS)

Piotrowski, W. S.; Raue, J. E.

1984-01-01

Design, development, and tests are described for two single-pole-double-throw latching waveguide ferrite switches: a K-band switch in WR-42 waveguide and a Ka-band switch in WR-28 waveguide. Both switches have structurally simple junctions, mechanically interlocked without the use of bonding materials; they are impervious to the effects of thermal, shock, and vibration stresses. Ferrite material for the Ka-band switch with a proper combination of magnetic and dielectric properties was available and resulted in excellent low loss, wideband performance. The high power handling requirement of the K-band switch limited the choice of ferrite to nickel-zinc compositions with adequate magnetic properties, but with too low relative dielectric constant. The relative dielectric constant determines the junction dimensions for given frequency responses. In this case the too low value unavoidably leads to a larger than optimum junction volume, increasing the insertion loss and restricting the operating bandwidth. Efforts to overcome the materials-related difficulties through the design of a composite junction with increased effective dielectric properties efforts to modify the relative dielectric constant of nickel-zinc ferrite are examined.

A Facile Strategy to Enhance the Dielectric and Mechanical Properties of MWCNTs/PVDF Composites with the Aid of MMA-co-GMA Copolymer

PubMed Central

Song, Shixin; Xia, Shan; Jiang, Shangkun; Lv, Xue; Sun, Shulin; Li, Quanming

2018-01-01

A facile strategy is adopted to prepare carboxylic functionalized multiwalled carbon nanotube (c-MWCNT) modified high dielectric constant (high-k) poly(vinylidene fluoride) (PVDF) composites with the aid of methyl methacrylate-co-glycidyl methacrylate copolymer (MG). The MG is miscible with PVDF and the epoxy groups of the copolymer can react with the carboxylic groups of c-MWCNT, which induce the uniform dispersion of c-MWCNT and a form insulator layer on the surface of c-MWCNT. The c-MWCNTs/MG/PVDF composites with 8 vol % c-MWCNT present excellent dielectric properties with high dielectric constant (~448) and low dielectric loss (~2.36) at the frequency of 1 KHz, the dielectric loss is much lower than the c-MWCNT/PVDF composites without MG. The obvious improvement in dielectric properties ascribes to the existence of MG, which impede the direct contact of c-MWCNTs and PVDF and avoid the formation of conductive network. Therefore, we propose a practical and simple strategy for preparing composites with excellent dielectric properties, which are promising for applications in electronics devices. PMID:29495491

A Facile Strategy to Enhance the Dielectric and Mechanical Properties of MWCNTs/PVDF Composites with the Aid of MMA-co-GMA Copolymer.

PubMed

Song, Shixin; Xia, Shan; Jiang, Shangkun; Lv, Xue; Sun, Shulin; Li, Quanming

2018-02-27

A facile strategy is adopted to prepare carboxylic functionalized multiwalled carbon nanotube (c-MWCNT) modified high dielectric constant (high- k ) poly(vinylidene fluoride) (PVDF) composites with the aid of methyl methacrylate-co-glycidyl methacrylate copolymer (MG). The MG is miscible with PVDF and the epoxy groups of the copolymer can react with the carboxylic groups of c-MWCNT, which induce the uniform dispersion of c-MWCNT and a form insulator layer on the surface of c-MWCNT. The c-MWCNTs/MG/PVDF composites with 8 vol % c-MWCNT present excellent dielectric properties with high dielectric constant (~448) and low dielectric loss (~2.36) at the frequency of 1 KHz, the dielectric loss is much lower than the c-MWCNT/PVDF composites without MG. The obvious improvement in dielectric properties ascribes to the existence of MG, which impede the direct contact of c-MWCNTs and PVDF and avoid the formation of conductive network. Therefore, we propose a practical and simple strategy for preparing composites with excellent dielectric properties, which are promising for applications in electronics devices.

Thermodynamic linkage between the binding of protons and inhibitors to HIV-1 protease.

PubMed Central

Trylska, J.; Antosiewicz, J.; Geller, M.; Hodge, C. N.; Klabe, R. M.; Head, M. S.; Gilson, M. K.

1999-01-01

The aspartyl dyad of free HIV-1 protease has apparent pK(a)s of approximately 3 and approximately 6, but recent NMR studies indicate that the aspartyl dyad is fixed in the doubly protonated form over a wide pH range when cyclic urea inhibitors are bound, and in the monoprotonated form when the inhibitor KNI-272 is bound. We present computations and measurements related to these changes in protonation and to the thermodynamic linkage between protonation and inhibition. The Poisson-Boltzmann model of electrostatics is used to compute the apparent pK(a)s of the aspartyl dyad in the free enzyme and in complexes with four different inhibitors. The calculations are done with two parameter sets. One assigns epsilon = 4 to the solute interior and uses a detailed model of ionization; the other uses epsilon = 20 for the solute interior and a simplified representation of ionization. For the free enzyme, both parameter sets agree well with previously measured apparent pK(a)s of approximately 3 and approximately 6. However, the calculations with an internal dielectric constant of 4 reproduce the large pKa shifts upon binding of inhibitors, but the calculations with an internal dielectric constant of 20 do not. This observation has implications for the accurate calculation of pK(a)s in complex protein environments. Because binding of a cyclic urea inhibitor shifts the pK(a)s of the aspartyl dyad, changing the pH is expected to change its apparent binding affinity. However, we find experimentally that the affinity is independent of pH from 5.5 to 7.0. Possible explanations for this discrepancy are discussed. PMID:10210196

High-dielectric-constant polymers as high-energy-density (HED) field effect actuator and capacitor materials

NASA Astrophysics Data System (ADS)

Huang, Cheng; Zhang, Qiming

2004-07-01

The development of high dielectric constant polymers as active materials in high-performance devices is one of the challenges in polymeric electronics and opto-electronics such as flexible thin-film capacitors, memory devices and microactuators for deformable micromirror technology. A group of poly(vinylidene fluoridetrifluoroethylene) P(VDF-TrFE) based high-dielectric-constant fluoroterpolymers have been developed, which have high room-temperature dielectric constant (K>60) and very high strain level and high energy density. The longitudinal and transverse strain of these materials can reach about -7% and 4.5%, respectively, and the elastic energy density is around 1.1 J/cm^3 under a high electric field of 150 MV/m. The influence on the electromechanical properties of copolymerizing poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) with a third monomer, chlorofluoroethylene (CFE), was investigated. It was found that increasing the CFE content from 0 to 8.5% slowly converts the ferroelectric structure of the copolymer to a relaxor ferroelectric system. This allows for a greatly decreased polarization and dielectric hysteresis and a much higher strain. Above 8.5%, increased CFE content substantially degrades the bulk crystallinity and the Young's modulus. These terpolymers have the potential to achieve above 10 J/cm^3 whole capacity energy density, which makes them good candidates for applications in pulse power capacitors. An all-polymer percolative composite by the combination of conductive polyaniline particles (K>10^5) within a fluoroterpolymer matrix, is introduced which exhibits very high dielectric constant (>7,000). The experimental results show that the dielectric behavior of this new class of percolative composites follows the prediction of the percolation theory and the analysis of the conductive percolation phenomena. The very high dielectric constant of the all-polymer composites which are also very flexible and possess elastic modulus not very much different from that of the insulation polymer matrix makes it possible to induce a high electromechanical response under a much reduced electric field (a strain of 2.65% with an elastic energy density of 0.18 J/cm^3 can be achieved under a low field of 16 MV/m). Data analysis also suggests that in these composites, the non-uniform local field distribution as well as interface effects can significantly enhance the strain responses. Furthermore, the experimental data as well as the data analysis indicate that the conduction loss in these composites will not affect the strain hysteresis. Flexible high dielectric constant electroactive polymers provide potential applications in high-energy-density (HED) energy storage and conversion systems such as lightweight field effect actuators and capacitors.

A molecular dynamics simulation study of chloroform

NASA Astrophysics Data System (ADS)

Tironi, Ilario G.; van Gunsteren, Wilfred F.

Three different chloroform models have been investigated using molecular dynamics computer simulation. The thermodynamic, structural and dynamic properties of the various models were investigated in detail. In particular, the potential energies, diffusion coefficients and rotational correlation times obtained for each model are compared with experiment. It is found that the theory of rotational Brownian motion fails in describing the rotational diffusion of chloroform. The force field of Dietz and Heinzinger was found to give good overall agreement with experiment. An extended investigation of this chloroform model has been performed. Values are reported for the isothermal compressibility, the thermal expansion coefficient and the constant volume heat capacity. The values agree well with experiment. The static and frequency dependent dielectric permittivity were computed from a 1·2 ns simulation conducted under reaction field boundary conditions. Considering the fact that the model is rigid with fixed partial charges, the static dielectric constant and Debye relaxation time compare well with experiment. From the same simulation the shear viscosity was computed using the off-diagonal elements of the pressure tensor, both via an Einstein type relation and via a Green-Kubo equation. The calculated viscosities show good agreement with experimental values. The excess Helmholtz energy is calculated using the thermodynamic integration technique and simulations of 50 and 80 ps. The value obtained for the excess Helmholtz energy matches the theoretical value within a few per cent.

Study of dielectric phenomenon for P3HT: PCBM blend

NASA Astrophysics Data System (ADS)

Kumar, Sunil; Kumar, Manoj; Rathi, Sonika; Singh, Amarjeet

2017-05-01

In this present work we prepared the film sample of blend (P3HT (poly (3-hexylthiophene-2, 5-diyl)): PCBM ([6,6]-phenyl C61-butyric acid methyl ester)), P3HT and PCBM solution on ITO substrate by drop cast method. Capacitance and tangent loss (tan δ) were measured and dielectric constants έ and dielectric loss ɛ″ were deduced from them as function frequency at room temperature. Blend samples show strong frequency dependence as compared to pristine P3HT and pristine PCBM sample. The high dielectric constant in blend films at low frequency was attributed to characteristic slow relaxation process in polymers along with polarization of isolated grains in the blend sample.

Super Dielectric Materials

PubMed Central

Fromille, Samuel; Phillips, Jonathan

2014-01-01

Evidence is provided here that a class of materials with dielectric constants greater than 105 at low frequency (<10−2 Hz), herein called super dielectric materials (SDM), can be generated readily from common, inexpensive materials. Specifically it is demonstrated that high surface area alumina powders, loaded to the incipient wetness point with a solution of boric acid dissolved in water, have dielectric constants, near 0 Hz, greater than 4 × 108 in all cases, a remarkable increase over the best dielectric constants previously measured for energy storage capabilities, ca. 1 × 104. It is postulated that any porous, electrically insulating material (e.g., high surface area powders of silica, titania, etc.), filled with a liquid containing a high concentration of ionic species will potentially be an SDM. Capacitors created with the first generated SDM dielectrics (alumina with boric acid solution), herein called New Paradigm Super (NPS) capacitors display typical electrostatic capacitive behavior, such as increasing capacitance with decreasing thickness, and can be cycled, but are limited to a maximum effective operating voltage of about 0.8 V. A simple theory is presented: Water containing relatively high concentrations of dissolved ions saturates all, or virtually all, the pores (average diameter 500 Å) of the alumina. In an applied field the positive ionic species migrate to the cathode end, and the negative ions to the anode end of each drop. This creates giant dipoles with high charge, hence leading to high dielectric constant behavior. At about 0.8 V, water begins to break down, creating enough ionic species to “short” the individual water droplets. Potentially NPS capacitor stacks can surpass “supercapacitors” in volumetric energy density. PMID:28788298

Super Dielectric Materials.

PubMed

Fromille, Samuel; Phillips, Jonathan

2014-12-22

Evidence is provided here that a class of materials with dielectric constants greater than 10⁵ at low frequency (<10 -2 Hz), herein called super dielectric materials (SDM), can be generated readily from common, inexpensive materials. Specifically it is demonstrated that high surface area alumina powders, loaded to the incipient wetness point with a solution of boric acid dissolved in water, have dielectric constants, near 0 Hz, greater than 4 × 10⁸ in all cases, a remarkable increase over the best dielectric constants previously measured for energy storage capabilities, ca. 1 × 10⁴. It is postulated that any porous, electrically insulating material (e.g., high surface area powders of silica, titania, etc. ), filled with a liquid containing a high concentration of ionic species will potentially be an SDM. Capacitors created with the first generated SDM dielectrics (alumina with boric acid solution), herein called New Paradigm Super (NPS) capacitors display typical electrostatic capacitive behavior, such as increasing capacitance with decreasing thickness, and can be cycled, but are limited to a maximum effective operating voltage of about 0.8 V. A simple theory is presented: Water containing relatively high concentrations of dissolved ions saturates all, or virtually all, the pores (average diameter 500 Å) of the alumina. In an applied field the positive ionic species migrate to the cathode end, and the negative ions to the anode end of each drop. This creates giant dipoles with high charge, hence leading to high dielectric constant behavior. At about 0.8 V, water begins to break down, creating enough ionic species to "short" the individual water droplets. Potentially NPS capacitor stacks can surpass "supercapacitors" in volumetric energy density.

Study on the dielectric properties of Al2O3/TiO2 sub-nanometric laminates: effect of the bottom electrode and the total thickness

NASA Astrophysics Data System (ADS)

Ben Elbahri, M.; Kahouli, A.; Mercey, B.; Lebedev, O.; Donner, W.; Lüders, U.

2018-02-01

Dielectrics based on amorphous sub-nanometric laminates of TiO2 and Al2O3 are subject to elevated dielectric losses and leakage currents, in large parts due to the extremely thin individual layer thickness chosen for the creation of the Maxwell-Wagner relaxation and therefore the high apparent dielectric constants. The optimization of performances of the laminate itself being strongly limited by this contradiction concerning its internal structure, we will show in this study that modifications of the dielectric stack of capacitors based on these sub-nanometric laminates can positively influence the dielectric losses and the leakage, as for example the nature of the electrodes, the introduction of thick insulating layers at the laminate/electrode interfaces and the modification of the total laminate thickness. The optimization of the dielectric stack leads to the demonstration of a capacitor with an apparent dielectric constant of 90, combined with low dielectric loss (tan δ) of 7 · 10-2 and with leakage currents smaller than 1  ×  10-6 A cm-2 at 10 MV m-1.

Temperature dependent x-ray diffraction and dielectric studies of multiferroic GaFeO{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Rajeev; Mall, Ashish Kumar, E-mail: ashishm@iitk.ac.in; Gupta, Rajeev

2016-05-06

Polycrystalline GaFeO{sub 3} (GFO) samples were synthesized by sol-gel method. The structural and dielectric properties of GaFeO{sub 3} ceramic have been investigated by a combination of XRD and permittivity measurement. The X-ray diffraction spectra shows single phase orthorhombically distorted perovskite structure with Pc2{sub 1}n symmetry over a wide range of temperature 300 K to 600 K, with no evidence of any phase transition. Refined lattice parameters (a, b, c and V) increases with increasing temperature. Temperature dependent dielectric properties were investigated in the frequency range from 100Hz–5MHz. Impedance spectroscopy study on the sample showed that the dielectric constant and acmore » conductivity with frequency increases on increasing the temperature. Cole-Cole plots suggest that the response from grain is dominant at low temperature whereas grain boundary response overcomes as temperature increases. The relaxation activation energy (calculated from Cole-Cole plots) value is found to be 0.32 eV for the grain boundary. We believe that the oxygen ion vacancies play an important role in conduction processes at higher temperatures.« less

The Canadian Experiment for Freeze/Thaw in 2012 or 2013 CanEx-FT12 or FT13

NASA Technical Reports Server (NTRS)

Belair, Stephane; Bernier, Monique; Colliander, Andreas; Jackson, Thomas; McDonald, Kyle; Walker, Anne

2011-01-01

General objectives of the experiment are: Pre-launch Calibration/Validation of SMAP Freeze/Thaw products and retrieval algorithms and rehearsal for Soil Moisture Active-Passive (SMAP) post launch validation. The basis of the radar freeze-thaw measurement is the large shift in dielectric constant and backscatter (dB) between predominantly frozen & thawed conditions. The Dielectric constant of liquid water varies with frequency, whereas that of pure ice is constant

Full four-component relativistic calculations of the one-bond 77Se-13C spin-spin coupling constants in the series of selenium heterocycles and their parent open-chain selenides.

PubMed

Rusakov, Yury Yu; Rusakova, Irina L; Krivdin, Leonid B

2014-05-01

Four-component relativistic calculations of (77)Se-(13)C spin-spin coupling constants have been performed in the series of selenium heterocycles and their parent open-chain selenides. It has been found that relativistic effects play an essential role in the selenium-carbon coupling mechanism and could result in a contribution of as much as 15-25% of the total values of the one-bond selenium-carbon spin-spin coupling constants. In the overall contribution of the relativistic effects to the total values of (1)J(Se,C), the scalar relativistic corrections (negative in sign) by far dominate over the spin-orbit ones (positive in sign), the latter being of less than 5%, as compared to the former (ca 20%). A combination of nonrelativistic second-order polarization propagator approach (CC2) with the four-component relativistic density functional theory scheme is recommended as a versatile tool for the calculation of (1)J(Se,C). Solvent effects in the values of (1)J(Se,C) calculated within the polarizable continuum model for the solvents with different dielectric constants (ε 2.2-78.4) are next to negligible decreasing negative (1)J(Se,C) in absolute value by only about 1 Hz. The use of the locally dense basis set approach applied herewith for the calculation of (77)Se-(13)C spin-spin coupling constants is fully justified resulting in a dramatic decrease in computational cost with only 0.1-0.2-Hz loss of accuracy. Copyright © 2014 John Wiley & Sons, Ltd.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saha, J.; Chaudhary, S.; Majumdar, P.

We report a study on potential multiferroic characteristics of Yttrium Iron Garnet (YIG). The emergence of ferroelectricity in YIG is in debate but we provide evidence for strong magneto-electric coupling above room temperature from dielectric constant measurement with and without magnetic field. We find that the apparent pseudo-ferroelectric crossover temperature in YIG varies with frequency. For higher frequency the transition shifts towards higher temperature. This is indicative of relaxor behavior. We have also measured the dielectric constant in the presence of external magnetic field at high temperature that confirms interdependence of magnetic and dielectric properties.

An Analysis of the Tensor Dielectric Constant of Sea Ice at Microwave Frequencies.

DTIC Science & Technology

1985-10-01

36.8 > t a -43.2 0 C (5) is convenient. The above equations for p in the range t > -22.9 0 C were first published by Frankenstein and Garner [12). III...Em 0 (6) for the mean electric field propagating in the medium. Here ko is the free space propagation constant, K. the quasi-static dielectric tensor...C. Essen- " tially identical results were found for the real part of the dielectric con- stant whether the polarization of the electric field was

Electrical and magnetic properties of rock and soil

USGS Publications Warehouse

Scott, J.H.

1983-01-01

Field and laboratory measurements have been made to determine the electrical conductivity, dielectric constant, and magnetic permeability of rock and soil in areas of interest in studies of electromagnetic pulse propagation. Conductivity is determined by making field measurements of apparent resisitivity at very low frequencies (0-20 cps), and interpreting the true resistivity of layers at various depths by curve-matching methods. Interpreted resistivity values are converted to corresponding conductivity values which are assumed to be applicable at 10^2 cps, an assumption which is considered valid because the conductivity of rock and soil is nearly constant at frequencies below 10^2 cps. Conductivity is estimated at higher frequencies (up to 10^6 cps) by using statistical correlations of three parameters obtained from laboratory measurements of rock and soil samples: conductivity at 10^2 cps, frequency and conductivity measured over the range 10^2 to 10^6 cps. Conductivity may also be estimated in this frequency range by using field measurements of water content and correlations of laboratory sample measurements of the three parameters: water content, frequency, and conductivity measured over the range 10^2 to 10^6 cps. This method is less accurate because nonrandom variation of ion concentration in natural pore water introduces error. Dielectric constant is estimated in a similar manner from field-derived conductivity values applicable at 10^2 cps and statistical correlations of three parameters obtained from laboratory measurements of samples: conductivity measured at 10^2 cps, frequency, and dielectric constant measured over the frequency range 10^2 to 10^6 cps. Dielectric constant may also be estimated from field measurements of water content and correlations of laboratory sample measurements of the three parameters: water content, frequency, and dielectric constant measured from 10^2 to 10^6 cps, but again, this method is less accurate because of variation of ion concentration of pore water. Special laboratory procedures are used to measure conductivity and dielectric constant of rock and soil samples. Electrode polarization errors are minimized by using an electrode system that is electrochemically reversible-with ions in pore water.

Linear, non-linear and thermal properties of single crystal of LHMHCl

NASA Astrophysics Data System (ADS)

Kulshrestha, Shobha; Shrivastava, A. K.

2018-05-01

The single crystal of amino acid of L-histidine monohydrochloride was grown by slow evaporation technique at room temperature. High optical quality and appropriate size of crystals were grown under optimized growth conditions. The grown crystals were transparent. Crystals are characterized with different characterizations such as Solubility test, UV-Visible, optical band gap (Eg). With the help of optical data to be calculate absorption coefficient (α), extinction coefficient (k), refractive index (n), dielectric constant (ɛ). These optical constants are shows favorable conditions for photonics devices. Second harmonic generation (NLO) test show the green light emission which is confirm that crystal have properties for laser application. Thermal stability of grown crystal is confirmed by TG/DTA.

Accurate L-Band Measurements of the Dielectric Constant of Seawater

NASA Technical Reports Server (NTRS)

Lang, R.H.; Utku, C.; Tarkocin, Y.; Vine, D.M. Le

2007-01-01

A new temperature controlled microwave cavity system to measure the complex dielectric constant of seawater at 1.413 GHz is discussed. The system is being developed to measure seawater for temperatures from O C to 30 C and salinities from 10 to 40 psu, The paper discusses the construction of the measurement system and initial stability tests.

Utilizing Calibrated GPS Reflected Signals to Estimate Soil Reflectivity and Dielectric Constant: Results from SMEX02

NASA Technical Reports Server (NTRS)

Katzberg, Stephen J.; Torres, Omar; Grant, Michael S.; Masters, Dallas

2006-01-01

Extensive reflected GPS data was collected using a GPS reflectometer installed on an HC130 aircraft during the Soil Moisture Experiment 2002 (SMEX02) near Ames, Iowa. At the same time, widespread surface truth data was acquired in the form of point soil moisture profiles, areal sampling of near-surface soil moisture, total green biomass and precipitation history, among others. Previously, there have been no reported efforts to calibrate reflected GPS data sets acquired over land. This paper reports the results of two approaches to calibration of the data that yield consistent results. It is shown that estimating the strength of the reflected signals by either (1) assuming an approximately specular surface reflection or (2) inferring the surface slope probability density and associated normalization constants give essentially the same results for the conditions encountered in SMEX02. The corrected data is converted to surface reflectivity and then to dielectric constant as a test of the calibration approaches. Utilizing the extensive in-situ soil moisture related data this paper also presents the results of comparing the GPS-inferred relative dielectric constant with the Wang-Schmugge model frequently used to relate volume moisture content to dielectric constant. It is shown that the calibrated GPS reflectivity estimates follow the expected dependence of permittivity with volume moisture, but with the following qualification: The soil moisture value governing the reflectivity appears to come from only the top 1-2 centimeters of soil, a result consistent with results found for other microwave techniques operating at L-band. Nevertheless, the experimentally derived dielectric constant is generally lower than predicted. Possible explanations are presented to explain this result.

Time and voltage dependences of nanoscale dielectric constant modulation on indium tin oxide films

NASA Astrophysics Data System (ADS)

Li, Liang; Hao, Haoyue; Zhao, Hua

2017-01-01

The modulation of indium tin oxide (ITO) films through surface charge accumulation plays an important role in many different applications. In order to elaborately study the modulation, we measured the dielectric constant of the modulated layer through examining the excitation of surface plasmon polaritons. Charges were pumped on the surfaces of ITO films through applying high voltage in appropriate directions. Experiments unveiled that the dielectric constant of the modulated layer had large variation along with the nanoscale charge accumulation. Corresponding numerical results were worked out through combining Drude model and Mayadas-Shatzkes model. Based on the above results, we deduced the time and voltage dependences of accumulated charge density, which revealed a long-time charge accumulation process.

Significantly improved dielectric performances of nanocomposites via loading two-dimensional core-shell structure Bi2Te3@SiO2 nanosheets

NASA Astrophysics Data System (ADS)

Chen, Jianwen; Wang, Xiucai; Yu, Xinmei; Fan, Yun; Duan, Zhikui; Jiang, Yewen; Yang, Faquan; Zhou, Yuexia

2018-07-01

Polymer/semiconductor-insulator nanocomposites can display high dielectric constants with a relatively low dissipation factor under low electric fields, and thus seem to promising for high energy density capacitors. Here, a novel nanocomposite films is developed by loading two-dimensional (2D) core-shell structure Bi2Te3@SiO2 nanosheets in the poly (vinylidene fluoride-hexafluoro propylene) (P(VDF-HFP)) polymer matrix. The 2D Bi2Te3 nanosheets were prepared through simple microwave-assisted method. The experimental results suggesting that the SiO2 shell layer between the fillers and polymer matrix could effectively improve the dielectric constant, dielectric loss, AC conductivity, and breakdown strength of composites films. The composite films load with 10 vol.% 2D Bi2Te3@SiO2 nanosheets exhibits a high dielectric constant of 70.3 at 1 kHz and relatively low dielectric loss of 0.058 at 1 kHz. The finite element simulation of electric field and electric current density distribution revealed that the SiO2 shell layer between the fillers and polymer matrix could effectively improve the energy loss, local electric field strength, and breakdown strength of composite films. Therefore, this work will provide a promising route to achieve high-performance capacitors.

Nonlinear dielectric effects in liquids: a guided tour

NASA Astrophysics Data System (ADS)

Richert, Ranko

2017-09-01

Dielectric relaxation measurements probe how the polarization of a material responds to the application of an external electric field, providing information on structure and dynamics of the sample. In the limit of small fields and thus linear response, such experiments reveal the properties of the material in the same thermodynamic state it would have in the absence of the external field. At sufficiently high fields, reversible changes in enthalpy and entropy of the system occur even at constant temperature, and these will in turn alter the polarization responses. The resulting nonlinear dielectric effects feature field induced suppressions (saturation) and enhancements (chemical effect) of the amplitudes, as well as time constant shifts towards faster (energy absorption) and slower (entropy reduction) dynamics. This review focuses on the effects of high electric fields that are reversible and observed at constant temperature for single component glass-forming liquids. The experimental challenges involved in nonlinear dielectric experiments, the approaches to separating and identifying the different sources of nonlinear behavior, and the current understanding of how high electric fields affect dielectric materials will be discussed. Covering studies from Debye’s initial approach to the present state-of-the-art, it will be emphasized what insight can be gained from the nonlinear responses that are not available from dielectric relaxation results obtained in the linear regime.

Development of Dielectric Material with Ceramic Matrix Composite (CMC) Produced from Kaolinite and CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yin, Wong Swee; Hassan, Jumiah; Hashim, Mansor

Ceramic matrix composites (CMC) combine reinforcing ceramic phases, CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) with a ceramic matrix, kaolinite to create materials with new and superior properties. 10% and 20% CCTO were prepared by using a conventional solid state reaction method. CMC samples were pre-sintered at 800 deg. C and sintered at 1000 deg. C. The dielectric properties of samples were measured using HP 4192A LF Impedance Analyzer. Microstructures of the samples were observed using an optical microscope. XRD was used to determine the crystalline structure of the samples. The AFM showed the morphology of the samples. The results showed thatmore » the dielectric constant and dielectric loss factor of both samples are frequency dependent. At 10 Hz, the dielectric constant is 10{sup 11} for both samples. The CMC samples were independent with temperature with low dielectric constant in the frequency range of 10{sup 4}-10{sup 6} Hz. Since the CMC samples consist of different amount of kaolinite, so each sample exhibit different defect mechanism. Different reaction may occur for different composition of material. The effects of processing conditions on the microstructure and electrical properties of CMC are also discussed.« less

Dielectric Studies of Samarium Modified (Pb)(Zr, Ti, Fe, Nb)O3 Ceramic System

NASA Astrophysics Data System (ADS)

Singh, Pratibha; Singh, Sangeeta; Juneja, J. K.; Prakash, Chandra; Raina, K. K.

Here we report the investigations on Sm-substituted PZTFN (Pb1-xSmxZr0.588Ti0.392Fe0.01Nb0.01O3) (where x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) polycrystalline solid solutions fabricated by solid-state reaction method. XRD analysis shows all the samples to be single phase with tetragonal structure. Dielectric measurements were carried out in the temperature range 30°C-400°C at different frequencies in the range 100 Hz to 100 kHz. From the temperature variation of dielectric constant (ɛ), Curie temperature (TC) was determined which was found to decrease with increasing x. The room temperature dielectric constant (ɛRT) initially increases with increasing x and then starts decreasing. Dielectric loss improves with Sm-doping.

Dielectric Relaxation of CaCu3Ti4O12 synthesized from a pyrolysis method

NASA Astrophysics Data System (ADS)

Liu, Jianjun; Mei, W. N.; Smith, R. W.; Hardy, J. R.

2006-03-01

Giant dielectric constant material CaCu3Ti4O12 has been synthesized by using a pyrolysis method. A stable solution was made by dissolving calcium nitrate, copper nitrate, and titanium isopropoxide in 2-methoxyethanol; the solution was then heated at 500 and 700 ^oC for 2 hours to obtain a pure phase of CaCu3Ti4O12. The frequency and temperature dependences of dielectric permittivity were examined in the ranges of 10-1˜10^6 Hz and -150˜200 ^oC. We found that the dielectric properties of the sample were the same as those made from solid state reaction. Specifically, there is a Debye-like relaxation at low temperature and its giant dielectric constant about 11000 is independent of the temperature and frequency over a wide range.

Ferroelectric and paraelectric Ba0.5Sr0.5TiO3 film structure distortions at room temperature and their effects on tunable microwave properties

NASA Astrophysics Data System (ADS)

Alldredge, L. M. B.; Chang, Wontae; Qadri, Syed B.; Kirchoefer, Steven W.; Pond, Jeffrey M.

2007-05-01

Sputter-deposited Ba0.5Sr0.5TiO3 films on (001) MgO were characterized for their dielectric properties with different lattice structures. With varying Ar :O2 ratios during deposition, the films showed either in-plane (ca) tetragonal distortions, significantly affecting the dielectric constant and tunability. The dielectric constant exhibited clear hysteresis with dc bias at room temperature, indicating that the films were ferroelectric. The relationship between the dielectric properties and the distortions was the reverse of that observed in films deposited by pulsed laser deposition. The anisotropic in-plane dielectric behavior can be understood by relating polarization to film distortions and to the presence of permanent dipoles.

Flexible Dielectric Nanocomposites with Ultrawide Zero-Temperature Coefficient Windows for Electrical Energy Storage and Conversion under Extreme Conditions.

PubMed

Shehzad, Khurram; Xu, Yang; Gao, Chao; Li, Hanying; Dang, Zhi-Min; Hasan, Tawfique; Luo, Jack; Duan, Xiangfeng

2017-03-01

Polymer dielectrics offer key advantages over their ceramic counterparts such as flexibility, scalability, low cost, and high breakdown voltages. However, a major drawback that limits more widespread application of polymer dielectrics is their temperature-dependent dielectric properties. Achieving dielectric constants with low/zero-temperature coefficient (L/0TC) over a broad temperature range is essential for applications in diverse technologies. Here, we report a hybrid filler strategy to produce polymer composites with an ultrawide L/0TC window of dielectric constant, as well as a significantly enhanced dielectric value, maximum energy storage density, thermal conductivity, and stability. By creating a series of percolative polymer composites, we demonstrated hybrid carbon filler based composites can exhibit a zero-temperature coefficient window of 200 °C (from -50 to 150 °C), the widest 0TC window for all polymer composite dielectrics reported to date. We further show the electric and dielectric temperature coefficient of the composites is highly stable against stretching and bending, even under AC electric field with frequency up to 1 MHz. We envision that our method will push the functional limits of polymer dielectrics for flexible electronics in extreme conditions such as in hybrid vehicles, aerospace, power electronics, and oil/gas exploration.

Microwave properties of solid CO2. [for Mars surface study

NASA Technical Reports Server (NTRS)

Simpson, R. A.; Howard, H. T.; Fair, B. C.

1980-01-01

Measurements over the range of 2.2 to 12.0 GHz show that CO2 snow is a slightly lossy dielectric whose constant varies with density following the Rayleigh formula to 1.27 g/cu cm. It is independent of frequency and does not vary with temperature in the 113 to 183 K range; frequency independence and agreement with the Rayleigh fit are obtained from measurements on dry block ice. The dielectric constant of solid CO2 in block form is lower than that of solid water ice or solid rock; in powder form, the constant for CO2 is also lower than that of H2O (snow) or soils. These measurements may be useful in limiting the interpretations of the Viking radio reflection experiment; a radio value of 3.0 for the dielectric constant near the North Pole would be strong evidence against the presence of cm thicknesses of CO2 in that region.

Microwave characterization of slotline on high resistivity silicon for antenna feed network

NASA Technical Reports Server (NTRS)

Simons, Rainee N.; Taub, Susan R.; Lee, Richard Q.; Young, Paul G.

1993-01-01

Conventional silicon wafers have low resistivity and consequently unacceptably high value of dielectric attenuation constant. Microwave circuits for phased array antenna systems fabricated on these wafers therefore have low efficiency. By choosing a silicon substrate with sufficiently high resistivity it is possible to make the dielectric attenuation constant of the interconnecting microwave transmission lines approach those of GaAs or InP. In order for this to be possible, the transmission lines must be characterized. In this presentation, the effective dielectric constant (epsilon sub eff) and attenuation constant (alpha) of a slotline on high resistivity (5000 to 10 000 ohm-cm) silicon wafer will be discussed. The epsilon sub eff and alpha are determined from the measured resonant frequencies and the corresponding insertion loss of a slotline ring resonator. The results for slotline will be compared with microstrip line and coplanar waveguide.

Effects of Cryogenic Temperatures on Spacecraft Internal Dielectric Discharges

NASA Technical Reports Server (NTRS)

Ferguson, Dale c.; Schneider, Todd A.; Vaughn, Jason A.

2009-01-01

Abstract Most calculations of internal dielectric charging on spacecraft use tabulated values of material surface and bulk conductivities, dielectric constants, and dielectric breakdown strengths. Many of these properties are functions of temperature, and the temperature dependences are not well known. At cryogenic temperatures, where it is well known that material conductivities decrease dramatically, it is an open question as to the timescales over which buried charge will dissipate and prevent the eventual potentially disastrous discharges of dielectrics. In this paper, measurements of dielectric charging and discharging for cable insulation materials at cryogenic temperatures (approx. 90 K) are presented using a broad spectrum electron source at the NASA Marshall Space Flight Center. The measurements were performed for the James Webb Space Telescope (JWST), which will orbit at the Earth-Sun L2 point, and parts of which will be perennially at temperatures as low as 40 K. Results of these measurements seem to show that Radiation Induced Conductivity (RIC) under cryogenic conditions at L2 will not be sufficient to allow charges to bleed off of some typical cable insulation materials even over the projected JWST lifetime of a dozen years or more. After the charging and discharging measurements are presented, comparisons are made between the material conductivities that can be inferred from the measured discharges and conductivities calculated from widely used formulae. Furthermore, the measurement-inferred conductivities are compared with extrapolations of recent measurements of materials RIC and dark conductivities performed with the charge-storage method at Utah State University. Implications of the present measurements are also given for other spacecraft that may operate at cryogenic temperatures, such as probes of the outer planets or the permanently dark cratered areas on the moon. The present results will also be of interest to those who must design or operate spacecraft in more moderate cold conditions. Finally, techniques involving shielding and/or selective use of somewhat conductive insulators are presented to prevent arc-inducing charge buildup even under cryogenic conditions.

Dielectric properties and microstructure of sintered BaTiO3 fabricated by using mixed 150-nm and 80-nm powders with various additives

NASA Astrophysics Data System (ADS)

Oh, Min Wook; Kang, Jae Won; Yeo, Dong Hun; Shin, Hyo Soon; Jeong, Dae Yong

2015-04-01

Recently, the use of small-sized BaTiO3 particles for ultra-thin MLCC research has increased as a method for minimizing the dielectric layer's thickness in thick film process. However, when particles smaller than 100 nm are used, the reduced particle size leads to a reduced dielectric constant. The use of nanoparticles, therefore, requires an increase in the amount of additive used due to the increase in the specific surface area, thus increasing the production cost. In this study, a novel method of coating 150-nm and 80-nm BaTiO3 powders with additives and mixing them together was employed, taking advantage of the effect obtained through the use of BaTiO3 particles smaller than 100 nm, to conveniently obtain the desired dielectric constant and thermal characteristics. Also, the microstructure and the dielectric properties were evaluated. The additives Dy, Mn, Mg, Si, and Cr were coated on a 150-nm powder, and the additives Dy, Mn, Mg, and Si were coated on 80-nm powder, followed by mixing at a ratio of 1:1. As a result, the microstructure revealed grain formation according to the liquid-phase additive Si; additionally, densification was well realized. However, non-reducibility was not obtained, and the material became a semiconductor. When the amount of added Mn in the 150-nm powder was increased to 0.2 and 0.3 mol%, insignificant changes in the microstructure were observed, and the bulk density after mixing was found to have increased drastically in comparison to that before mixing. Also, non-reducibility was obtained for certain conditions. The dielectric property was found to be consistent with the densification and the grain size. The mixed composition #1-0.3 had a dielectric constant over 2000, and the result somewhat satisfied the dielectric constant temperature dependency for X6S.

Effect of chromium substitution on the dielectric properties of mixed Ni-Zn ferrite prepared by WOWS sol–gel technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ashtar, M.; Munir, A.; Anis-ur-Rehman, M.

2016-07-15

Graphical abstract: Variation of AC conductivity (σ{sub AC}) as a function of natural log of angular frequency (lnω) for Ni{sub 0.5}Zn{sub 0.5}Fe{sub 2-x}Cr{sub x}O{sub 4} nanoferrites at room temperature. - Highlights: • Cr doped mixed Ni-Zn ferrites were successfully synthesized by a newly developed WOWS sol gel technique. • The specific surface area and specific surface area to volume ratio increased with decrease in particle size. • The resonance peaks appeared in dielectric loss graphs, shifting towards low frequency with the increase in Cr concentration. • The prepared samples have the lowest values of the dielectric constant. • The dielectricmore » constant were observed to be inversely proportional to square root of the AC resistivity. - Abstract: Cr{sup +3} doped Ni-Zn nanoferrite samples with composition Ni{sub 0.5}Zn{sub 0.5}Fe{sub 2-x}Cr{sub x}O{sub 4}(x = 0.1, 0.2, 0.3, 0.4) were synthesized With Out Water and Surfactant (WOWS) sol-gel technique. The structural, morphological and dielectric properties of the samples were investigated. The lattice constant, crystallite size, theoretical density and porosity of each sample were obtained from X-ray diffraction (XRD) data. The specific surface area and specific surface area to volume ratio increased with the decrease in the size of Cr{sup +3} doped Ni-Zn ferrite nanoparticles, as the concentration of Cr{sup +3} increased. The SEM analysis revealed that the particles were of nano size and of spherical shape. The dielectric parameters such as dielectric constant (ε′) and dielectric loss (tanδ) of all the samples as a function of frequency at room temperature were measured. The AC conductivity (σ{sub AC}) was determined from the dielectric parameters, which showed increasing trend with the rise in frequency.« less

Microwave Propagation in Dielectric Fluids.

ERIC Educational Resources Information Center

Lonc, W. P.

1980-01-01

Describes an undergraduate experiment designed to verify quantitatively the effect of a dielectric fluid's dielectric constant on the observed wavelength of microwave radiation propagating through the fluid. The fluid used is castor oil, and results agree with the expected behavior within 5 percent. (Author/CS)

The Cotton-Mouton effect of liquid water. Part I: The dielectric continuum model

NASA Astrophysics Data System (ADS)

Ruud, Kenneth; Helgaker, Trygve; Rizzo, Antonio; Coriani, Sonia; Mikkelsen, Kurt V.

1997-07-01

We present a gauge-origin independent method for calculating the electric-field dependence of the molecular magnetizability—that is, the hypermagnetizability, related to the Cotton-Mouton Effect (CME)—of solvated molecules. In our approach, the solvated molecule is placed in a spherical cavity surrounded by a linear, homogeneous, and polarizable dielectric medium. We apply the model to investigate the dielectric-medium effects on the CME of liquid water. The effects of electron correlation, molecular geometry, and the surrounding dielectric continuum on the hypermagnetizability and the CME are investigated. The change induced in the hypermagnetizability anisotropy by the dielectric medium is the dominating effect, being almost twice as large as the correlation contribution. The combined effect of electron correlation and the dielectric continuum leads to a doubling of the hypermagnetizability anisotropy when going from the SCF gas phase value (Δη=17.89 a.u.) to the value obtained for the MCSCF wave function in the dielectric medium (Δη=39.74 a.u.). The effects of change in geometry are shown to be small. Our result for the static Cotton-Mouton constant averaged in the temperature range 283.15 K to 293.15 K, mC=15.2×10-20 G-2 cm3 mol-1, differs from experiment still by the sign and by a factor of almost 8. The major reason for this discrepancy is the neglect of short-range interactions such as hydrogen bonding and van der Waals interactions not accounted for by the continuum model.

Surface Plasmon Polariton Resonance of Gold, Silver, and Copper Studied in the Kretschmann Geometry: Dependence on Wavelength, Angle of Incidence, and Film Thickness

NASA Astrophysics Data System (ADS)

Takagi, Kentaro; Nair, Selvakumar V.; Watanabe, Ryosuke; Seto, Keisuke; Kobayashi, Takayoshi; Tokunaga, Eiji

2017-12-01

Surface plasmon polariton (SPP) resonance spectra for noble metals (Au, Ag, and Cu) were comprehensively studied in the Kretschmann attenuated total reflection (ATR) geometry, in the wavelength (λ) range from 300 to 1000 nm with the angle of incidence (θ) ranging from 45 to 60° and the film thickness (d) ranging from 41 to 76 nm. The experimental plasmon resonance spectra were reproduced by a calculation that included the broadening effects as follows: (1) the imaginary part of the bulk dielectric constant, (2) the thickness-dependent radiative coupling of the SPP at the metal-air interface to the prism, (3) the lack of conservation of the wavevector parallel to the interface kx(k||) caused by the surface roughness, (4) scanning λ at a fixed θ (changing both energy and kx at the same time) over the SPP dispersion relation. For Au and Ag, the experimental results were in good agreement with the calculated results using the bulk dielectric constants, showing no film thickness dependence of the plasmon resonance energy. A method to extract the true width of the plasmon resonance from raw ATR spectra is proposed and the results are rigorously compared with those expected from the bulk dielectric function given in the literature. For Au and Ag, the width increases with energy, in agreement with that expected from the relaxation of bulk free electrons including the electron-electron interaction, but there is clear evidence of extra broadening, which is more significant for thinner films, possibly due to relaxation pathways intrinsic to plasmons near the interface. For Cu, the visibility of the plasmon resonance critically depends on the evaporation conditions, and low pressures and fast deposition rates are required. Otherwise, scattering from the surface roughness causes considerable broadening of the plasmon resonance, resulting in an apparently fixed resonance energy without clear incident angle dependence. For Cu, the observed plasmon dispersion agrees well with that expected from the bulk dielectric function even with nominal oxidation of the surface, but the widths at long wavelengths are much larger than those theoretically expected.

Ion-dipole interactions in concentrated organic electrolytes.

PubMed

Chagnes, Alexandre; Nicolis, Stamatios; Carré, Bernard; Willmann, Patrick; Lemordant, Daniel

2003-06-16

An algorithm is proposed for calculating the energy of ion-dipole interactions in concentrated organic electrolytes. The ion-dipole interactions increase with increasing salt concentration and must be taken into account when the activation energy for the conductivity is calculated. In this case, the contribution of ion-dipole interactions to the activation energy for this transport process is of the same order of magnitude as the contribution of ion-ion interactions. The ion-dipole interaction energy was calculated for a cell of eight ions, alternatingly anions and cations, placed on the vertices of an expanded cubic lattice whose parameter is related to the mean interionic distance (pseudolattice theory). The solvent dipoles were introduced randomly into the cell by assuming a randomness compacity of 0.58. The energy of the dipole assembly in the cell was minimized by using a Newton-Raphson numerical method. The dielectric field gradient around ions was taken into account by a distance parameter and a dielectric constant of epsilon = 3 at the surfaces of the ions. A fair agreement between experimental and calculated activation energy has been found for systems composed of gamma-butyrolactone (BL) as solvent and lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) as salts.

Organic/Inorganic Nano-hybrids with High Dielectric Constant for Organic Thin Film Transistor Applications

NASA Astrophysics Data System (ADS)

Yu, Yang-Yen; Jiang, Ai-Hua; Lee, Wen-Ya

2016-11-01

The organic material soluble polyimide (PI) and organic-inorganic hybrid PI-barium titanate (BaTiO3) nanoparticle dielectric materials (IBX, where X is the concentration of BaTiO3 nanoparticles in a PI matrix) were successfully synthesized through a sol-gel process. The effects of various BaTiO3 contents on the hybrid film performance and performance optimization were investigated. Furthermore, pentacene-based organic thin film transistors (OTFTs) with PI-BaTiO3/polymethylmethacrylate or cyclic olefin copolymer (COC)-modified gate dielectrics were fabricated and examined. The hybrid materials showed effective dispersion of BaTiO3 nanoparticles in the PI matrix and favorable thermal properties. X-ray diffraction patterns revealed that the BaTiO3 nanoparticles had a perovskite structure. The hybrid films exhibited high formability and planarity. The IBX hybrid dielectric films exhibited tunable insulating properties such as the dielectric constant value and capacitance in ranges of 4.0-8.6 and 9.2-17.5 nF cm-2, respectively. Adding the modified layer caused the decrease of dielectric constant values and capacitances. The modified dielectric layer without cross-linking displayed a hydrophobic surface. The electrical characteristics of the pentacene-based OTFTs were enhanced after the surface modification. The optimal condition for the dielectric layer was 10 wt% hybrid film with the COC-modified layer; moreover, the device exhibited a threshold voltage of 0.12 V, field-effect mobility of 4.32 × 10-1 cm2 V-1 s-1, and on/off current of 8.4 × 107.

On the theory of dielectric spectroscopy of protein solutions

NASA Astrophysics Data System (ADS)

Matyushov, Dmitry V.

2012-08-01

We present a theory of the dielectric response of solutions containing large solutes, of the nanometer size, in a molecular solvent. It combines the molecular dipole moment of the solute with the polarization of a large subensemble of solvent molecules at the solute-solvent interface. The goal of the theory is two-fold: (i) to formulate the problem of the dielectric response avoiding the reliance on the cavity-field susceptibility of dielectric theories and (ii) to separate the non-additive polarization of the interface, jointly produced by the external field of the laboratory experiment and the solute, from specific solute-solvent interactions contributing to the dielectric signal. The theory is applied to experimentally reported frequency-dependent dielectric spectra of lysozyme in solution. The analysis of the data in the broad range of frequencies up to 700 GHz shows that the cavity-field susceptibility, critical for the theory formulation, is consistent with the prediction of Maxwell’s electrostatics in the frequency range of 10-200 GHz, but deviates from it outside this range. In particular, it becomes much smaller than the Maxwell result, and shifts to negative values, at small frequencies. The latter observation implies a dia-electric response, or negative dielectrophoresis, of hydrated lysozyme. It also implies that the effective protein dipole recorded by dielectric spectroscopy is much smaller than the value calculated from the protein’s charge distribution. We suggest an empirical equation that describes both the increment of the static dielectric constant and the decrement of the Debye water peak with increasing protein concentration. It gives fair agreement with broad-band dispersion and loss spectra of protein solutions, but misses the δ-dispersion region.

Thermodynamic properties of PbTe, PbSe, and PbS: a first-principles study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yi; Ke, Xuezhi; Chen, Changfeng

2009-01-01

The recent discovery of novel lead chalcogenide-based thermoelectric materials has attracted great interest. These materials exhibit low thermal conductivity which is closely related to their lattice dynamics and thermodynamic properties. In this paper, we report a systematic study of electronic structures and lattice dynamics of the lead chalcogenides PbX (X=Te, Se, S) using first-principles density functional theory calculations and a direct force-constant method. We calculate the struc- tural parameters, elastic moduli, electronic band structures, dielectric constants, and Born effective charges. Moreover, we determine phonon dispersions, phonon density of states, and phonon softening modes in these materials. Based on the resultsmore » of these calculations, we further employ quasihar- monic approximation to calculate the heat capacity, internal energy, and vibrational entropy. The obtained results are in good agreement with experimental data. Lattice thermal conductivities are evaluated in terms of the Gruneisen parameters. The mode Gruneisen parameters are calculated to explain the anharmonicity in these materials. The effect of the spin-orbit interaction is found to be negligible in determining the thermodynamic properties of PbTe, PbSe, and PbS.« less

Impedance analysis and dielectric response of anatase TiO2 nanoparticles codoped with Mn and Co ions

NASA Astrophysics Data System (ADS)

Kumar, Anand; Kashyap, Manish K.; Sabharwal, Namita; Kumar, Sarvesh; Kumar, Ashok; Kumar, Parmod; Asokan, K.

2017-11-01

In order to elucidate the effect of transition metal (TM) doping, the impedance and dielectric responses of Co and/or Mn-doped TiO2 nanocrystalline powder samples with 3% doping concentration synthesized via sol gel technique, have been analyzed. X-ray diffraction (XRD) analysis confirms the formation of tetragonal TiO2 anatase phase for all studied samples without any extra impurity phase peaks. The variation in the grain size measured from field emission scanning electron microscope (FESEM) measurements for all the samples are in accordance with the change in crystallite size as obtained from XRD. The DC resistivity for pure TiO2 nanoparticles is the highest while codoped samples exhibit low resistivity. The temperature dependent dielectric constant and dielectric loss possess step like enhancement and show the relaxation behavior. At room temperature, the dielectric function and dielectric loss decrease rapidly with increase in frequency and become almost constant at the higher frequencies. Such a decrease in dielectric loss is suitable for energy storage devices.

Dielectric Properties of Ca0.7Bi0.3Ti0.7Cr0.3O3 (CBTC)-CaCu3Ti4O12 (CCTO) Composite

NASA Astrophysics Data System (ADS)

Mallmann, E. J. J.; Silva, M. A. S.; Sombra, A. S. B.; Botelho, M. A.; Mazzetto, S. E.; de Menezes, A. S.; Almeida, A. F. L.; Fechine, P. B. A.

2015-01-01

The main object of this work is to study two materials with giant dielectric constants: CaCu3Ti4O12 (CCTO) and Ca0.7Bi0.3Ti0.7Cr0.3O3 (CBTC). CBTC1- x -CCTO x composites were also obtained to create a new dielectric material with dielectric properties between these two phases. Structural properties were studied by x-ray powder diffraction (XRPD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy and dielectric measurements. CCTO showed a cubic phase and CBTC an orthorhombic phase. An interesting result was that the dielectric constant ( K) did not follow the rule of the mixture of Lichtnecker, and this happened due to the presence of other phases of its crystalline structure, which decreases the value of K when compared to the predicted values of Lichtnecker. It was also found that the dielectric properties of the composite are very promising for use in microelectronics, according to the miniaturization factor, which is crucial for those applications.

Charge renormalization and inversion of a highly charged lipid bilayer: effects of dielectric discontinuities and charge correlations.

PubMed

Taheri-Araghi, Sattar; Ha, Bae-Yeun

2005-08-01

We reexamine the problem of charge renormalization and inversion of a highly charged surface of a low dielectric constant immersed in ionic solutions. To be specific, we consider an asymmetrically charged lipid bilayer, in which only one layer is negatively charged. In particular, we study how dielectric discontinuities and charge correlations (among lipid charges and condensed counterions) influence the effective charge of the surface. When counterions are monovalent (e.g., Na+), our mean-field approach implies that dielectric discontinuities can enhance counterion condensation. A simple scaling picture shows how the effects of dielectric discontinuities and surface-charge distributions are intertwined: Dielectric discontinuities diminish condensation if the backbone charge is uniformly smeared out while counterions are localized in space; they can, however, enhance condensation when the backbone charge is discrete. In the presence of asymmetric salts such as CaCl2 , we find that the correlation effect, treated at the Gaussian level, is more pronounced when the surface has a lower dielectric constant, inverting the sign of the charge at a smaller value of Ca2+ concentration.

Lead free dielectric ceramic with stable relative permittivity of 0.90(Na0.50Bi0.50Ti)O3-0.10AgNbO3

NASA Astrophysics Data System (ADS)

Verma, Anita; Yadav, Arun Kumar; Kumar, Sunil; Sen, Somaditya

2018-04-01

Structural, dielectric and ferroelectric properties in perovskite 0.90(Na0.50Bi0.50Ti)03-0.10AgNb03 polycrystalline powders prepared by sol-gel method are discussed. Diffuse phase transition and new type of dielectric anomaly was observed with highly steady capacitive properties in the 135-450 °C temperature range. This compound shows remarkable dielectric with dielectric constant ɛr 1000 with a variation of ± 7% and tan δ = 0.004 0.25 in 135- 450 °C temperature. In addition, it also showed excellent ferroelectric properties with saturation polarization Ps = 13.5 μC/cm2, remnant polarization of Pr = 7.6 μC/cm2 and a low coercive field Ec = 36 kV/cm at room temperature. Stable dielectric constant (ɛr) and low dielectric loss (tan δ) in a wide temperature range observed for the titled composition makes it an interesting candidate for potential use in fast growing "high-temperature electronics" industry applications.

Molten salt synthesis of nanocrystalline phase of high dielectric constant material CaCu3Ti4O12.

PubMed

Prakash, B Shri; Varma, K B R

2008-11-01

Nanocrystalline powders of giant dielectric constant material, CaCu3Ti4O12 (CCTO), have been prepared successfully by the molten salt synthesis (MSS) using KCl at 750 degrees C/10 h, which is significantly lower than the calcination temperature (approximately 1000 degrees C) that is employed to obtain phase pure CCTO in the conventional solid-state reaction route. The water washed molten salt synthesized powder, characterized by X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), and Transmission electron microscopy (TEM) confirmed to be a phase pure CCTO associated with approximately 150 nm sized crystallites of nearly spherical shape. The decrease in the formation temperature/duration of CCTO in MSS method was attributed to an increase in the diffusion rate or a decrease in the diffusion length of reacting ions in the molten salt medium. As a consequence of liquid phase sintering, pellets of as-synthesized KCl containing CCTO powder exhibited higher sinterability and grain size than that of KCl free CCTO samples prepared by both MSS method and conventional solid-state reaction route. The grain size and the dielectric constant of KCl containing CCTO ceramics increased with increasing sintering temperature (900 degrees C-1050 degrees C). Indeed the dielectric constants of these ceramics were higher than that of KCl free CCTO samples prepared by both MSS method and those obtained via the solid-state reaction route and sintered at the same temperature. Internal barrier layer capacitance (IBLC) model was invoked to correlate the observed dielectric constant with the grain size in these samples.