Showing papers on "Dielectric loss published in 1991"

Intrinsic dielectric loss in crystals

Abstract: We review the current theory of intrinsic dielectric loss, that is the loss in a perfect crystal due to anharmonic interaction of a.c. electric field with the phonon system of the crystal. Both ordinary dielectrics and displacive ferroelectrics are considered. The theory predicts dependence of the loss on frequency ω and temperature T. This dependence is very sensitive to the symmetry of the crystal. For ordinary dielectrics, the results are presented and tabulated for all 32 symmetry groups, except for non-symmorphic groups. The existing experimental date are analysed and explained on the basis of the theory.

Dielectric properties of agricultural products-measurements and applications

Abstract: The nature of the variation of dielectric properties with frequency, temperature, and product density is discussed. Techniques for measurement of dielectric properties are briefly reviewed, and graphical data on the dielectric properties of grain and soybeans as functions of moisture content, frequency, temperature, and bulk of density are presented. Applications in the electrical measurement of the moisture content and in the dielectric heating of these materials are discussed. >

Relative permittivity and dielectric loss tangent of substrate materials for high-Tc superconducting film

Abstract: We measure the relative permittivitye r and dielectric loss tangent tanδ of substrate materials for high-T c superconducting films at 18–300 K and at 5–10 GHz using the cavity-resonator method. The materials measured are single crystals of MgO, LaAlO3, YAlO3, LaSrGaO4, NdGaO3, sapphire, and ZrO2 ceramic. Thee r values are 10–30 and become almost constant below about 50 K. The tanδ values decrease with decreasing temperature and are below 1×10−5 at 77 K except for those of NdGaO3 and ZrO2 ceramic. This suggests that the tanδ values of MgO, LaAlO3, YAlO3, LaSrGaO4, and sapphire do not limit the quality factors of microwave passive components fabricated using high-T c superconducting films. It is also demonstrated that the tanδ of the substrate material is strongly affected by impurities.

Dielectric ceramic composition

Abstract: PURPOSE:To obtain a dielectric ceramic composition allowing reduced sorts of additives, achieving a high dielectric constant and a low dielectric loss, each of which has an extremely small voltage dependence and deterioration with time by adding a specified wt.% of Mn-based compound to a main composition consisting of SrTiO3, Bi2O3, and TiO2 as an additive. CONSTITUTION:A dielectric ceramic composition consists of 100wt.% a main composition consisting of 50.0-90.5wt.% SrTiO3, 2.0-29.5wt.% Bi2O3, and 5.6-20.5wt.% TiO2 to which a sort of Mn-based compound is added by 0.05-0.20wt.%. A dielectric ceramic composition obtained by molding and baking this composition achieve a high dielectric constant and a low loss, and the voltage dependence and time change of these properties are extremely reduced.

Lead zirconate titanate films by rapid thermal processing

Abstract: Lead zirconate titanate films have been fabricated by a dc sputtering technique with a post deposition rapid thermal annealing treatment at 650 °C for 10 s. The films exhibited good structural, dielectric, and ferroelectric properties compared to conventional furnace‐annealed films. The measured dielectric constant and loss tangent at 1 kHz were 900 and 0.04 and the remanent polarization and coercive field values were 10 μC/cm2 and 23 kV/cm, respectively. No significant fatigue in polarization was observed in the films up to 1010 cycles of bipolar stress. The films were optically transparent and showed a linear electro‐optic (EO) effect after poling with an EO coefficient of 1.5×10 −11 m/V.

Dielectric permittivity and loss of an aluminum-filled epoxy resin

Abstract: Dielectric behaviour of an epoxy resin filled with 0–30 wt% aluminum powder is reported. Permittivity, loss index and dissipation factor are characterized as a function of temperature in the range 20–150°C and frequency in the range 20 Hz–20 kHz. The filled resin shows a higher permittivity and higher dielectric loss. An interfacial or Maxwell-Wagner-Sillars polarization effect is clearly evident and glass transition temperature is unaffected by the filler.

Ferroelectric Sr0.60Ba0.40Nb2O6 thin films by the sol-gel process: Electrical and optical properties.

Abstract: Mesure des proprietes optiques, pyroelectriques, ferroelectriques et electro-optiques. On obtient un indice de refraction optique de 2,31 et un coefficient electro-optique lineaire effectif de 30×30 −12 m/V

Low-frequency dielectric behaviour of mixed Li-Ti ferrites

Abstract: The dielectric constants and dielectric loss tangents of Li-Ti ferrites of different composition were measured at room temperature using a capacitance bridge at low frequencies. It was observed that the lower concentration of titanium ( 0.6 mol. of Ti) titanium dopants, the value of dielectric constant decreased very rapidly. For some compositions, the dielectric loss tangent curves exhibited a maximum at frequencies between 3 and 15 kHz. A qualitative explanation for the observed behaviour is given.

Studies of mixing formulae in the complex plane

Abstract: Remote sensing signal monitoring is considered. Mixing rules that have been introduced to explain the permittivity of mixtures by analytically continuing these to the whole complex plane are discussed. Equipermittivity curves for both the real and imaginary parts of the mixture dielectric constant (the imaginary part of the permittivity is a measure for the dielectric losses) are studied. These form a map on the complex plant, illustrating the nature of a mixing rule better than the classical way of presenting the mixture permittivity as a function of the volume fraction of a component in the mixture. These maps naturally vary for a given mixing rule as the volume fraction is changed, but, in principle, the structure is the same. The resulting illustrations show that certain mixing formulae can be conceived as a continuum that gradually changes from the Maxwell-Garnett formula through Polder-van Santen and coherent potential formulas to the so-called exponential formulas. >

Conducting polymers. V. Electrical conductivity of polymer complexes of bis-2,6-diaminopyridinesulphoxide-copper halides

Abstract: The electrical conductivity of polymer complexes of bis-2,6-diaminopyridinesulphoxide with CuCl2, CuBr2 and CuI2 was measured at different frequencies and temperatures. It was found that the conductivity increases as frequency and/or temperature increases. The dielectric constant, dielectric loss and relaxation time of the polymer complexes were calculated.

Dielectric medium for capacitor of semiconductor device

Abstract: A dielectric medium for the capacitor of a semiconductor device is disclosed. The dielectric material is prepared by replacing Sr and Ba in (Sr, Ba)Nb2 O6 with La, and the replacement is carried out by adding 2 mole % or more of La2 O3 to (Sr,Ba)Nb2 O6, thereby forming a composition (Srx Ba1-x)1-(3/2)y Lay Nb2 O6 (0.25≦x≦0.5, 0.04≦y). According to the present invention, the dielectric medium has the characteristics that the crystal structure is not affected even over the Curie temperature, and that a high dielectric constant and a low dielectric loss coefficient are maintained.

Technical aspects of interfacial phenomena in solid insulating systems

Abstract: HV insulation systems are often composed of different insulating materials. In the contact areas between these materials (interfaces) interfacing polarization may occur, resulting in an increase of both permittivity and loss tangent and, consequently, of dielectric losses. By the interaction of humidity such interfacial phenomena may be enhanced. Other important characteristics of insulating systems such as the treeing strength and the breakdown strength are also lowered by interfaces, especially when humidity has been adsorbed. Microscopic and macroscopic, internal and external interfaces are defined for composite insulation systems. Interfacial phenomena in such systems, for instance made out of fiber glass-reinforced polymeric materials, are described both under dry conditions and in the presence of water. It is demonstrated that the hydrophobic properties of materials improve the dielectric characteristics; this is true for bulk and surface properties. >

Alternating-current electrical properties of random metal-insulator composites

Abstract: The complex a.c. impedance of three different random metal-insulator composites near their percolation threshold has been studied. These three metal-insulator systems include different shapes of nickel particles (filamentary and nodular shapes) in a matrix of polypropylene and silver particles in the matrix of potassium chloride. By using different metal-insulator structures and phases it is possible to elucidate the effect of different metal particle shapes and types of insulator phase on the electrical properties of these composites near their percolation threshold. Electrical properties, including d.c. conductivity, a.c. conductance, capacitance and dielectric loss tangent, of these metal-insulator composites as a function of metal volume fraction and frequency (5 Hz to 13 MHz) are presented. The results are correlated with structural characterization of these composites and are used to examine the applicability of different electrical transport models on these composite materials. The effect of different metal particle shapes on the percolation threshold and the power-law dependent percolation phenomenon is also discussed.

Dielectric properties above the glass transition for a series of epoxide prepolymers

Abstract: Dielectric properties above the glass transition have been investigated for a series of bisphenol-A type epoxide prepolymers (388 ≤ Mw ≤ 2640). Dielectric measurements were performed over a frequency range of 50 Hz–1 MHz using a vertical parallel plate cell which was constructed in the laboratory. The dielectric α-relaxation for each prepolymer fits the empirical model of the Havriliak–Negami equation. The temperature dependence of the dielectric relaxation time τ is described by the Williams–Landel–Ferry (WLF) equation as well as that of the direct current conductivity σ, which can be measured using the same cell. The relationship between τ and σ, σ· τm = const, is derived from experimental results. The exponent m, which depends on the molecular weight of the prepolymer, is considered to correspond to the ratio of the segmental mobility to ionic mobility. The dielectric loss e″ can be used as an indicator of the direct current conduction in the temperatures where the ionic component in e″ becomes much larger than the dipole one.

Application of P(VDF/TrFE) thin films in pyroelectric detectors

Abstract: Copolymer thin films can be cast by coating a thickness of 0.8 μm to 2.5 μm on solid silicon substrates as well as on unrestrained 800 nm thin SiO2/Si3N4 supporting membranes. By poling the P(VDF/TrFE) at about 140 V/μm, a high spontaneous polarization can be obtained without any stretching process. Measurements of dielectric constant, dielectric losses and pyroelectric coefficient confirm the ideal nature of these materials for pyroelectric detectors. Built-up single element detectors distinguish themselves by a high specific detectivity D* of 2 · 108 cm√Hz/W at a frequency of 10 Hz.

Piezoelectric and dielectric properties of some la, mn modified pbtio3 ceramics

Abstract: The piezoelectric and dielectric properties of (Pb1-xLax)(Ti1-yMny)O3 [x = 0.025; 0.15 and y = 0; 0.01] ceramics were investigated. The poling field dependence was determined for the relative dielectric constant, the dielectric loss factor, the piezoelectric coupling factors and the piezoelectric anisotropy.

Dielectric behaviour of GexSe100-x and Ge22Se68M10 (M = Ag, In, Pb, Cd) glassy alloys

Abstract: The present paper reports the temperature and frequency dependence of the dielectric constant and the dielectric loss in binary GexSe100-x and ternary Ge22Se68M10 (M = Ag, In, Pb and Cd) glassy alloys in the audio frequency range (0.12–10 kHz). No dielectric dispersion is observed in GexSe100-x glassy alloys. However, in ternary Ge22Se68M10 alloys, dielectric dispersion is observed except in the case of Ge22Se68Ag10. Among these glasses, maximum dielectric loss is observed in the case of Ge22Se68Cd10, which is explained in terms of increase in the density of defect states on incorporation of Cd in binary Ge-Se alloy.

Broadband microwave dielectric properties of lithium niobate

Abstract: The anisotropic microwave refractive index and loss of lithium niobate, in the 15–140GHz range, are measured using the coherent microwave transient spectroscopy technique. The frequency-dependent complex transmission function of a 5.98 mm thick crystal is studied as a function of the angle between the electric field and the optic axis.

Influence of insulation morphology, impurities and oxidation on some electric properties of cables

Abstract: It is shown that the AC breakdown strength and dielectric loss of unaged and field-aged transmission and distribution cables vary with insulation crystallinity, contamination, and oxidation. It is also shown that the influence of these parameters is particularly important near the conductor shield and varies with aging. The influence of curing on cable properties is briefly discussed. The sample preparation, crystallinity, impurity, oxidation, AC breakdown, and dielectric loss measurements are described. >

Study on the pyroelectric properties of TGS-PVDF composites

Abstract: TGS-PVDF composite has been prepared in our laboratory and its dielectric and pyroelectric properties were analyzed. The dielectric constants, dielectric losses and pyroelectric coefficients of this composite with different component proportions have been measured, and their variations with temperature were observed. In addition, the figure of merit M has also been calculated. The D* value of the pyroelectric devices made from this composite even reach (5–7) × 107 cm · Hz1/2 · W−1 . The results have shown that TGS-PVDF composite has bright prospects in applications as a pyroelectric composite material.

The microstructure developments and electrical properties of calcium-modified barium titanate ceramics

Abstract: The microstructure and electrical behaviour of calcium-modified BaTiO3 ceramics of compositions (a) (Ba1-x Ca x )TiO3, (b) Ba(Ti1-x Ca x )O3-x and (c) (Ba1-x/2Ca x/2) (Ti1-x/2Ca x/2) O33-x/2 have been investigated. These characteristics are observed to vary systematically with the cationic ratio, α = (Ba + Ca)/Ti, rather than the amount (x-value) and sites that Ca2+ ions are supposed to occupy. A large uniform grain microstructure and normal dielectric behaviour are obtained for α ≤ 1.01 samples (groups I and II), whereas an ultra-fine grain microstructure and diffuse phase transformation (DPT) characteristics are observed for α ≥ 1.08 samples (groups III). The latter is proposed to be the suppression of tetragonal to cubic transformation due to the formation of second phase. When the sintering atmosphere is changed from air to H2/N2 mixture, the electrical resistivity decreases and dielectric loss increases tremendously for α = 0.99 samples (groups I), whereas the high electrical resistivity and low dielectric loss characteristics are preserved for α ≥ 1.01 samples (groups II and III). The mechanism by which the cationic ratio improves the resistance of the materials to a reducing atmosphere is proposed to be the formation of hexagonal BaTiO3-δ phase which consumes the oxygen vacancies generated.

Complex permittivity in ionically conducting solids: a hopping model

Abstract: Using both the correlated barrier hopping model accounting for the dielectric losses and the Anderson and Stuart model describing the potential barrier in ionically conducting glasses, the calculation of the dielectric processes in ionic solids is extended to the complex permittivity and the results are compared with the behaviour described by the empirical Cole-Davidson function. Experimental results for the ac conductivity obtained on Na 2 O-3SiO 2 glass are fitted by the theoretical behaviour predicted by this model.

Size-dependent dielectric response of small metal particles.

Abstract: The complex dielectric function of small metal particles is size dependent at microwave and radio frequencies. This was measured for particle diameters between 10 nm and 10 \ensuremath{\mu}m. In contrast to bulk electromagnetic response, the real part of the dielectric function in the small particles is positive and goes through a maximum. In addition, the temperature dependence of the loss index was found to change from positive to negative behavior near 1 \ensuremath{\mu}m.

A method of measuring the vibration level dependence of impedance-type equivalent circuit constants

Abstract: In piezoelectric transducers with high electromechanical coupling and finite dielectric loss angle, the mechanical quality factor of the transducer resonating under the short-circuit condition of the electric terminal is usually lower than that under the open-circuit condition. This fact is well explained by the impedance-type improved equivalent circuit including the effect of dielectric loss. This circuit is available for design of high power ultrasonic devices. A method of measuring the vibration level dependence of the impedance-type circuit constants is described and some experimental results are shown.

A.c. conduction through MIM sandwich samples of evaporated thin films of V2O5 and V2O5/B2O3

Abstract: The a.c. electrical properties of evaporated V2O5 and co-evaporated V2O5/B2O3 films have been investigated. The conductivity in both types of film follows the theory of Elliott for single polaron hopping. The behaviour of capacitance, tangent of loss angle and dielectric loss agrees with the model proposed by Goswami and Goswami. The co-evaporated films of V2O5/B2O3 show better dielectric properties than simple V2O5 with increasing content of B2O3. Because of their hygroscopic character, the films with B2O3 content larger than 40% are observed to be unstable in the atmosphere.