Showing papers on "Dielectric published in 1990"

Existence of a Photonic Gap in Periodic Dielectric Structures

Abstract: Using a plane-wave expansion method, we have solved Maxwell's equations for the propagation of electromagnetic waves in a periodic lattice of dielectric spheres (dielectric constant ${\mathrm{\ensuremath{\epsilon}}}_{\mathit{a}}$) in a uniform dielectric background (${\mathrm{\ensuremath{\epsilon}}}_{\mathit{b}}$). Contrary to experiment, we find that fcc dielectric structures do not have a ``photonic band gap'' that extends throughout the Brillouin zone. However, we have determined that dielectric spheres arranged in the diamond structure do possess a full photonic band gap. This gap exists for refractive-index contrasts as low as 2.

Thermal conductivity measurement from 30 to 750 K: the 3ω method

Abstract: An ac technique for measuring the thermal conductivity of dielectric solids between 30 and 750 K is described This technique, the 3ω method, can be applied to bulk amorphous solids and crystals as well as amorphous films tens of microns thick Errors from black‐body radiation are calculated to be less than 2% even at 1000 K Data for a‐SiO2, Pyrex 7740, and Pyroceram 9606 are compared to results obtained by conventional techniques

Freezing of the polarization fluctuations in lead magnesium niobate relaxors

Abstract: The dielectric relaxation of a solid solution of 10‐mol % lead titanate in lead magnesium niobate is found to be similar to the magnetic relaxation in spin‐glass systems.1–3 Based on this analogy, it is proposed that the relaxor ferroelectric is a polar‐glassy system which has thermally activated polarization fluctuations above a static freezing temperature. An activation energy and freezing temperature of 0.0407 eV and 291.5 K, respectively, were found by analyzing the frequency dependence of the temperature of the dielectric maximum using the Vogel–Fulcher relationship.4,5 It has also been shown that a macroscopic polarization is sustained on heating up to this freezing temperature. A coupling between nanometer scale clusters is believed to control the kinetics of the fluctuations and the development of a frustration as the system freezes into states of local equilibrium. The possibility of an orientational freezing associated with the ferroelastic nature of the nanosized polar regions in the rhombohedr...

Calibration of time domain reflectometry for water content measurement using a composite dielectric approach

Abstract: Time domain reflectometry (TDR) has been developed to an operational level for the measurement of soil water content during the past decade. Because it is able to provide fast, precise and nondestructive in situ measurements, it has become an alternative to the neutron scattering method, in particular for monitoring water content under field conditions. One of the major disadvantages of the neutron scattering technique is that, due to the relatively high sensitivity of the signal to factors other than water content, site-specific calibration is usually required. In this paper a calibration curve for the TDR method is presented which is not restricted to specific soil conditions. The calibration is based on the dielectric mixing model of Dobson et al. (1985). Measurements of volumetric water content and dielectric number at eleven different field sites representing a wide range of soil types were used to determine the parameter of the model by weighted nonlinear regression. The uncertainty (root mean square error) of water content values calculated with the optimized calibration curve was estimated not to exceed 0.013 cm3/cm3. This value is comparable to the precision of the thermogravimetric method. From a sensitivity analysis it was determined that the temperature dependence of the TDR signal may have to be corrected to obtain optimum accuracy.

The Dielectric Constant of Water and Debye‐Hückel Limiting Law Slopes

Abstract: Experimental values of the dielectric constant of water suggest that, for temperatures greater than 400 K, the integral in the Kirkwood dielectric‐constant equation, which involves the intermolecular potential function, is a simpler function of temperature and pressure than of temperature and density An equation has been fitted to values of this integral calculated from experimental values of the dielectric constant for temperatures from 23815 K to 82315 K and to pressures of approximately 500 MPa for temperatures greater than 273 K The equation of e thus has explicit variables T, ρ, p and gives a good representation of the available experimental results The quality of representation of the experimental results has been compared to that of previous correlations of the dielectric constant The new equation is applicable through wider regions of independent variables than the previous equations and is capable of sufficient accuracy to provide values of Debye–Huckel limiting law slopes which are as accurate as the experimental results allow Values of Debye‐Huckel limiting‐law slopes are tabulated

dc Electrical Degradation of Perovskite-Type Titanates: I, Ceramics

Abstract: The rate of the resistance degradation of doped SrTiO3 ceramics is investigated as a function of various external and material parameters. The effects of the mutually interrelated parameters dc voltage, dc electric field, and thickness of the dielectric are described by power laws. Electron microscopic potential contrast studies show a Maxwell-Wagner polarization leading to a concentration of the electric field at the grain boundaries during the degradation. Based on this finding, the voltage step per grain boundary, ΔΘgb, is introduced as a rate-determining parameter which allows an explanation of the influence of the grain size on the degradation rate as well as the difference in the power laws for ceramic and single-crystal samples.

Dipole glass and ferroelectricity in random-site electric dipole systems

Abstract: This review covers recent experimental and theoretical investigations into cooperative phenomena in crystals containing off-center ions. These phenomena have attracted much attention in recent years because of a general interest in disordered systems, in particular in spin glasses, whose electrical analog is the dipole glass. Specific features of the dipole glass state in alkali halide crystals with off-center ions are discussed and compared with spin glasses. Experimental studies performed in recent years have demonstrated that off-center ions in highly polarizable crystals can at certain concentrations induce ferroelectric domains with regions of macroscopic spontaneous polarization. The physical causes of this phenomenon are examined and some physical properties of crystals exhibiting such an impurity-induced phase transition are analyzed. Primary emphasis is placed on the range of low impurity concentrations, where system properties differ substantially from predictions of mean-field theory.

Principles of electronic ceramics

Abstract: Quantum mechanics and the band theory of solids semiconductors ionic and defect conductors linear dielectrics nonlinear dielectrics magnetic ceramics photonic ceramics optical waveguides electro-optical ceramics glass and crystalline lasers ceramic superconductors.

Optical matter : crystallization and binding in intense optical fields

Abstract: Properly fashioned electromagnetic fields coupled to microscopic dielectric objects can be used to create arrays of extended crystalline and noncrystalline structures. Organization can be achieved in two ways: In the first, dielectric matter is transported in direct response to the externally applied standing wave optical fields. In the second, the external optical fields induce interactions between dielectric objects that can also result in the creation of complex structures. In either case, these new ordered structures, whose existence depends on the presence of both light and polarizable matter, are referred to as optical matter.

Dielectric behavior of single crystals near the (1−X) Pb(Mg1/3Nb2/3)O3-(x) PbTiO3 morphotropic phase boundary

Abstract: Single crystals in the lead magnesium niobate-lead titanate-(1−x) Pb(Mg1/3 Nb2/3)O3-(x) PbTiO3 solid solution system were grown using a flux growth technique. Crystals over the compositional range of 0.3 ≤ ′ ≤ 0.4 being near the rhombohedra1 (pseudo-cubic)-tetragonal morphotropic phase boundary were characterized. The dielectric behavior along the pseudo cubic [111] and [100] directions were measured as a function of temperature and frequency. The effect of poling was also examined.

Scaling in the relaxation of supercooled liquids.

Abstract: We have measured the dielectric susceptibility of several glass-forming liquids over 13 decades of frequency. The primary relaxation for all the liquids, over the entire frequency and temperature range studied, can be collapsed onto a single scaling curve with only two parameters, peak position and width. This curve is different from any of the theoretical forms suggested in the literature. The relaxation evolves smoothly from Debye behavior at high temperature

Device modeling of ferroelectric capacitors

Abstract: A physically based methodology is developed for modeling the behavior of electrical circuits containing nonideal ferroelectric capacitors. The methodology is illustrated by modeling the discrete ferroelectric capacitor as a stacked dielectric structure, with switching ferroelectric and nonswitching dielectric layers. Electrical properties of a modified Sawyer–Tower circuit are predicted by the model. Distortions of hysteresis loops due to resistive losses as a function of input signal frequency are accurately predicted by the model. The effect of signal amplitude variations predicted by the model also agree with experimental data. The model is used as a diagnostic tool to demonstrate that cycling degradation, at least for the sample investigated, cannot be modeled by the formation of nonswitching dielectric layer(s) or the formation of conductive regions near the electrodes, but is consistent with a spatially uniform reduction in the number of switching dipoles.

Nanostructural-property relations in complex lead perovskites

Abstract: From transmission electron microscopy studies on several complex lead perovskite compounds Pb(B'B'')O3, and their solid solutions a classification can be obtained based on B-cation order. This classification divides the complex lead perovskites into three subgroups; random occupation or disordered, nanoscale or short coherent long-range order and long coherent long-range order of B-site cations. A correlation between the nanoscale B-site order and relaxor on glassy ferroelectric behavior is found in these lead perovskites. An hypothesis is suggested which relates 0-3 polar connectivity to 0-3 order-disorder connectivity. This hypothesis is discussed with relation to present theories [G. A. Smolenskii: J. Phys. Soc. Jpn. (1970) Suppl., p. 26, L. E. Cross: Ferroelectrics 76 (1987) 241, T. L. Renieke and K. L. Ngai: Solid State Commun. 18 (1973) 1543] and reported experimental results of the perovskite relaxor ferroelectrics.

Energy Storage in Ceramic Dielectrics

Abstract: Historically, multilayer ceramic capacitors (MLC's) have not been considered for energy storage applications for two primary reasons. First, physically large ceramic capacitors were very expensive and, second, total energy density obtainable was not nearly so high as in electrolytic capacitor types. More recently, the fabrication technology for MLC's has improved significantly, permitting both significantly higher energy density and significantly lower costs. Simultaneously, in many applications, total energy storage has become smaller, and the secondary requirements of very low effective series resistance and effective series inductance (which, together, determine how efficiently the energy may be stored and recovered) have become more important. It is therefore desirable to reexamine energy storage in ceramics for contemporary commercial and near-commercial dielectrics. Stored energy is proportional to voltage squared only in the case of paraelectric insulators, because only they have capacitance that is independent of bias voltage. High dielectric constant materials, however, are ferroics (that is ferroelectric and/or antiferroelectric) and display significant variation of effective dielectric constant with bias voltage. The common ferroelectric materials, whether based upon barium titanate or lead manganese niobate (PMN), in the high-field limit, exhibit an energy storage which increases linearly with bias voltage. Mixed phase, ferroelectric plus antiferroelectric, dielectrics from the lead lanthanum zirconate titanate (PLZT) system, as predicted theoretically, show the best energy density at low to moderate fields. Surprisingly, maximum energy storage is not obtained in high dielectric constant materials but in those materials which display intermediate dielectric constant and the highest ultimate breakdown voltages.

Dielectric properties and influence of conductivity in soils at one to fifty megahertz

Abstract: A series of laboratory experiments were performed in order to systematically explore the dielectric response of soils to a frequency range of 1 to 50 MHz. A network analyzer and a coaxial-transmission-line type of dielectric probe were used to measure the complex (both real and imaginary) dielectric response of moist soils. The dielectric probe was placed in a modified Tempe cell in which the moisture content of the soil under investigation could be varied. Both the real and imaginary components of the dielectric permittivity of the moist soils investigated are greatest at 1 MHz and monotonically decrease with frequency. The variation in the dielectric constant among these soils is also greatest at 1 MHz and decreases with increasing frequency. The soils that have a large imaginary dielectric constant also have the largest real dielectric constant dispersion. The loss tangent for a given soil is relatively independent of moisture content over a wide range of soil moisture conditions. At low water contents, both the real and imaginary dielectric values begin to drop rapidly with decreasing water content. There is a significant temperature dependence present in the dielectric response of moist soils, which changes markedly with frequency. Ionic conductivity is the predominant mechanism causing the imaginary dielectric response and can account for many features of the observed dielectric response. A Looyenga-type mixing model incorporating ionic conductivity can account for the frequency dependence of the dielectric constant of soils

Structure of electrorheological fluids.

Abstract: Electrorheological (ER) fluids are colloidal suspensions of highly polarizable particles in a nonpolarizable solvent. In a strong electric field, the behavior of the fluid is dominated by the dipolar interactions between the colloidal particles. We address problems of structure formation and long-time relaxation in an ER fluid. When a high electric field is applied to a fluid, dielectric columns oriented parallel to the field rapidly form. The relaxation of these columns is a much slower process. We calculate the shape of the columns formed and the time scale for the relaxation of the columnar structure.

The influence of microstructure on the properties of ferroelectric ceramics

Abstract: The domain twinning in ferroelectric ceramics is dependent on grain size. In fine grained ceramic a simple lamellar structure allows two- dimensional stress relief, in coarse grained ceramic a banded lamellar structure takes away homogeneous stress in three dimensions. The different domain configurations and internal stresses lead to different dielectric properties and to different hysteresis curves. Inhomogeneous grains of BaTiO3 with some CdBi2Nb2O9 have a core with a normal domain pattern and a shell without domains at room temperature. Core and shell have different transition temperatures. The macroscopic dielectric constant therefore has very high values in a very broad temperature range. Ceramics which are properly prepared in order to have oriented grains exhibit properties which come near to the properties of single crystals.

Ferroelectric materials for 64 Mb and 256 Mb DRAMs

Abstract: The authors have studied the feasibility of using ferroelectric materials as the capacitor dielectric in the one-transistor memory cells for 64-Mb and 256-Mb DRAMs. They have performed an intensive literature search and analysis. They discuss the crystal structure of the materials reviewed, their hysteresis curve, temperature dependence of the spontaneous polarization, leakage current, dielectric breakdown, reliability, ageing, and fatigue. The authors examine the charge storage capacity in a 1-T DRAM cell and analyze a number of ferroelectric materials for their potential use as the dielectric in 64-Mb and 256-Mb DRAM capacitors, focusing on projected requirements for the electrical parameters and preferred material characteristics. Of the materials examined, those that appear to hold the greatest promise for 64-Mb and 256-Mb DRAMs are the paraelectric phase compositions of (Pb,La)TiO/sub 3/ (PLT) and (Pb,La)(Zr,Ti)O/sub 3/ (PLZT). Pb(Mg,Nb)O/sub 3/ (PMN) is also attractive because it is paraelectric, but it may not be able to achieve the required charge densities when deposited as a thin film. >

Water treeing in polyethylene cables

Abstract: Water tree growth in polyethylene cable insulation is discussed. The characteristics of water trees, the effect of aging parameters on water tree growth, and the possible mechanisms of growth are considered, emphasizing vented tree development in polyethylene insulating materials. The morphology of water trees, the characteristics of the tree-infested dielectric cable, and test methods and measures to reduce water treeing are discussed. >

The effective microwave surface impedance of high Tc thin films

Abstract: The dependence of the effective surface impedance Zeff=Reff+iXeff of superconducting thin films on the film thickness d, on the magnetic field penetration depth λ, and on the dielectric properties of the substrate material is investigated theoretically by means of impedance transformations. It was found that the effective surface resistance Reff can be expressed by RSf(d/λ)+Rtrans where RS is the intrinsic surface resistance of the superconductor. The function f(d/λ) describes the altered current density distribution in the film. Rtrans arises from power transmission through the film. It depends on d and λ as well as on the dielectric properties of the substrate material and is significantly altered in the case of a resonant background. The effective surface reactance Xeff of a superconducting thin film can be expressed by XS cosh(d/λ) where XS=ωμ0λ is the intrinsic surface reactance. Measurements of Zeff at 87 GHz have been performed for YBa2Cu3O7−δ thin films grown epitaxially by laser ablation on SrTiO...

A treatment by the FD‐TD method of the dispersive characteristics associated with electronic polarization

Abstract: In this article, the formulation of dispersive characteristics associated with an electronic polarization is discussed. The formulation is appropriate for use in the finite-difference-time-domain (FD-TD) method and is based on the equation of polarization. The validity of the formulation is verified by comparing the calculated complex dielectric constant with analytical values.

Physics and Chemistry of Crystalline Lithium Niobate

Abstract: Introduction Physico-chemical properties of lithium metaniobate: Phase diagram for the Li^O2-0-Nb^O 2O^O5 system Crystal structure of lithium metaniobate Crystal-chemical features of metaniobates of alkali metals Phase formation in LN Crystals Methods of obtaining single crystals of lithium niobate Peculiarities of growth of LN single crystals Synthesis of the charge and preparation of the melt Choice of the optimum conditions for growth Growth conditions for LN crystals of a constant radius High-temperature annealing and formation of single-domains in crystal The Stepanov technique Electric phenomena arising in crystallization of LN Defect structure of single-crystal lithium niobate: Morphology and macro-defects Point defects in LN Formation of F centres in LN crystals Twinning in LN crystals The domain structure of lithium metaniobate crystals: Ferroelectric domains in lithium metaniobate Selective etching of LN crystals Growth domain structure Formation of a stationary domain structure Depolarisation mechanisms of lithium metaniobate crystals The influence of temperature gradients on domain formation in the process of crystal growth and annealing The effect of annealing on the near-surface domain structure The regular domain structure in LN crystals Electrical properties of lithium metaniobate: Electric conductivity Dielectric properties Thermal diffusion in lithium niobate crystals Relaxation phenomena in lithium niobate crystals Electric fields in lithium niobate crystals Electric effect and relaxation polarization of lithium niobate Thermionic emission of lithium niobate single crystals Effective ion charges and spontaneous electric moment of lithium niobate Optical and electro-optical properties of lithium metaniobate single crystals Optical properties of lithium metaniobate Electro-optical effect in dielectric crystals Phenomenological theory of the electro-optical effect Establishment of electro-optic coefficients Specific features of lithium niobate crystals applications in electro-optical devices Nonlinear optical properties of lithium niobate: Elements of nonlinear optics Methods used to establish nonlinear coefficients Relationship of birefringence and phase-matching temperature to lithium niobate crystal composition Criteria for nonlinear-optical quality of crystals Enhancement of SHG in lithium niobate crystals with periodic laminar ferroelectric domains Photoelectrical and photo-refractive properties: Model representations of the photo-refractive effect Occurrence of optical distortion in lithium niobate crystals exposed to cw laser radiation Occurence of optical distortion in lithium niobate exposed to pulsed laser radiation Laser-induced physical effects in lithium niobate Photo-induced distortion of the crystal structure in lithium niobate Optical inhomogeneity of crystals and methods of its investigation Nature of optical inhomogeneity Electrically induced optical inhomogeneity of crystals Doping and heat treatment effects on crystal optical inhomogeneity Methods used to observe optical inhomogeneities in lithium niobate crystals Conclusions References Index

Electrical characteristics of ultrathin oxynitride gate dielectric prepared by rapid thermal oxidation of Si in N2O

Abstract: This letter presents a unique process to grow high quality ultrathin (∼60 A) gate dielectrics using N2O (nitrous oxide) gas Compared with conventional rapid thermally grown oxide in the O2, the new oxynitride dielectrics show very large charge‐to‐breakdown (at +50 mA/cm2, 850 C/cm2 for oxynitride compared to 95 C/cm2 for the control thermal oxide) and less charge trapping under constant current stress Significantly reduced interface state generation was also observed under constant current stress and x‐ray radiation A secondary‐ion mass spectroscopy depth profile indicates a nitrogen‐rich layer at the Si/SiO2 interface, which can explain the improved integrity of oxynitride dielectric

Specific-heat spectroscopy and dielectric susceptibility measurements of salol at the glass transition.

Abstract: We compare specific-heat-spectroscopy and dielectric susceptibility measurements of salol (phenyl salicylate) near the glass transition. The specific-heat-spectroscopy measurements cover 5 decades in frequency; the dielectric susceptibility measurements cover 13 decades. Over their common range, both probes measure the same characteristic relaxation time. In contrast to the viscosity measurements of salol reported in the literature, the characteristic relaxation time measured by these techniques shows non-Arrhenius behavior near ${\mathit{T}}_{\mathit{g}}$. The Vogel-Fulcher divergence temperature is consistent with the Kauzmann temperature. As is seen in other glass formers, the relaxation widths broaden rapidly with decreasing temperature.

Electrical Properties of Tissue

Abstract: This chapter discusses the electrical and dielectric properties of tissue, covering the frequency range from d.c. to over 10 GHz. The electrical character of tissues over a wide range of frequencies may be described by using the two properties relative permittivity, ∈′ (the charge) and conductivity, σ (current densities set up in response to an applied electric field of unit amplitude). From both of these, the complex relative permittivity, ∈*, can be defined by the equation ij , characterize the effect in terms of the charge generated for unit applied stress under short circuit conditions.

Theoretical model of the frequency and temperature dependence of the complex dielectric constant of ferroelectric liquid crystals near the smectic-C * -smectic-A phase transition

Abstract: Using the generalized Landau model [Phys. Rev. A 36, 1484 (1987)], the temperature and frequency dependence of the complex dielectric constant of the ferroelectric smectic-${\mathit{C}}^{\mathrm{*}}$ (Sm-${\mathit{C}}^{\mathrm{*}}$) phase and the corresponding smectic-A (Sm-A) phase is calculated. It is demonstrated how the dielectric response of the Sm-${\mathit{C}}^{\mathrm{*}}$ phase generally consists of four modes---two high-frequency polarization modes and two modes of lower frequency that are connected to the reorientation of the director, commonly denoted the soft mode and the Goldstone mode. In the Sm-A phase only two modes are present---one doubly degenerate soft mode and one doubly degenerate polarization mode. The temperature dependences of the dielectric strengths and relaxation frequencies of the modes in question are calculated, and simplified expressions of these quantities are given. The most important feature of the generalized Landau model is the presence of a biquadratic coupling between tilt and polarization in the free-energy density of the system and we show how the general thermodynamic and dielectric properties of the system depend on the strength of this coupling. Comparing the results of the calculations with existing data, we finally conclude that the model provides a description of the Sm-${\mathit{C}}^{\mathrm{*}}$--Sm-A transition that takes all experimentally known features of the dielectric properties of the system into account in a qualitatively correct way.

Amorphous copolymers of perfluoro-2,2-dimethyl-1,3-dioxole

Abstract: Amorphous copolymers of perfluoro-2,2-dimethyl-1,3-dioxole with at least one fluoro comonomer selected from one or more of ten defined classes having a recited minimum mole proportion of perfluoro-2,2-dimethyl-1,3-dioxole, in no event less than 65%, have high glass transition temperatures of 140° C. or higher, low indices of refraction, and good physical properties, and low dielectric constants, which make them suitable for cladding optical fibers as well as for many electronics applications, including the manufacture of substrates for circuit boards. They all are soluble at room temperature in perfluoro(2-butyltetrahydrofuran), which makes it practical to apply them as coatings from solution.

The Role of Excess Magnesium Oxide or Lead Oxide in Determining the Microstructure and Properties of Lead Magnesium Niobate

Abstract: Near-phase pure perovskite lead magnesium niobate (PMN) with MgO or PbO additives was produced by reacting PbO with MgNb2O6 at 800°C and sintering at 1200°C. Dense ceramics were characterized by scanning electron microscopy, X-ray diffraction, and dielectric measurements. The microstructural studies showed that excess MgO exists as micrometer spherical particles either in the grain boundary as a discrete particle or in the perovskite grain as an inclusion. The pyrochlore phase exists in large isolated grains in the microstructure. The 10 mol% MgO excess composition had a peak dielectric constant of 19 500 at 100 Hz, which suggests very “clean” or uninhibiting grain boundaries. The excess addition of PbO did not improve the yield of perovskite PMN phase and decreased the dielectric constant. PMN grain boundaries are the dominant path of fracture. This paper, to a certain degree, explores the chemistry and characteristics of these grain boundaries.