Showing papers on "Dielectric loss published in 1990"

Low‐temperature dielectric properties of candidate substrates for high‐temperature superconductors: LaAlO3 and ZrO2 : 9.5 mol % Y2O3

Abstract: The effects of temperature (4–400 K), hydrostatic pressure and frequency on the dielectric constant, e’, and dielectric loss of single crystals of LaAlO3 and cubic yttria(9.5 mol %)‐stabilized zirconia (ZrO2) were investigated. Both crystals are relatively low‐loss, low‐dispersion dielectrics in the temperature range (T<150 K) of most interest for high‐temperature superconductors. The pressure results make it possible to evaluate the various contributions to the temperature dependence of e’. It is found that this dependence is dominated by the change of polarizability with volume. The dielectric properties of the two crystals are compared with those of other candidate substrate materials.

Quasi-TEM analysis of multilayered, multiconductor coplanar structures with dielectric and magnetic anisotropy including substrate losses

Abstract: A quasi-TEM (transverse electromagnetic) analysis of multiconductor planar lines embedded in a layered structure involving lossy iso/anisotropic electric and/or magnetic materials is achieved. Conditions under which a quasi-TEM assumption is valid are theoretically determined. An efficient spectral-domain analysis is used to determine the complex capacitance and inductance matrices characterizing the transmission system. computation of the inductance matrix is reduced to the computation of an equivalent capacitance matrix when media characterized for a fully general permeability tensor are present. It is also shown that most actual monolithic microwave integrated circuit (MMIC) microstrip-type structures (where semiconductor substrates are present) and possible future applications including lossy magnetic materials can be analyzed by using the simple quasi-TEM model. The validity of the results has been verified by comparison with full-wave theoretical and experimental data on microstrip lines on magnetic substrates and slow-wave structures. >

Dielectric and pyroelectric properties of the morphotropic phase boundary lead barium niobate (PBN) single crystals at low temperature (10-300 K)

Abstract: Low‐temperature (10–300 K) dielectric and pyroelectric properties of morphotropic‐phase‐boundary lead‐barium‐niobate tungsten‐bronze ferroelectric single crystals have been investigated. Strong ‘‘Debye‐like’’ dielectric dispersion, along a nonpolar direction (perpendicular to the polarization direction), has been observed and characterized by dielectric spectrum techniques. A direct charge measurement method has been used to study the low‐temperature pyroelectric properties in polar and nonpolar directions. A ‘‘frozen‐in’’ polarization component in a nonpolar direction is also reported. The low‐temperature relaxation effects are explained by the internal reorientation polarization perturbation and a thermally agitated local dipole fluctuation model.

The method of lines for the analysis of lossy planar waveguides

Abstract: The method of lines is extended to calculate the losses of waveguide structures. Ohmic losses in metallizations (with frequency-dependent, extremely high dielectric constants) and dielectric losses are simultaneously considered. Despite the high ratios of the dielectric constants of the metallizations and the dielectrics, the analysis and numerical treatment are carried out accurately. Using nonequidistant discretizations the results are computed efficiently, and an approximate value of the propagation constant close to the exact value is found by extrapolation. The phase constant deviates less than 0.5%. The attenuation may deviate up to 2%. The advantages of the method of lines are a small computation time and, due to the analytical solutions of the fields in one direction, a very good approach to the fields inside the strip as well as to the strong fields directly adjacent at the edges. The results for a single microstrip line are shown and compared with those of other authors. >

Relaxations in thermosets. 7. Dielectric effects during the curing and postcuring of an epoxide by mixed amines

Abstract: The dielectric permittivity and loss during the curing of diglycidyl ether of Bisphenol A with a 0.3:0.7 (mole:mole) mixture of diaminodiphenylmethane and diaminodiphenyl sulfone have been measured from their sol to gel to glass formation regions and the effects of physical aging on their sub-T g relaxations investigated. The permittivity monotonically decreases with the curing, but the loss initially decreases, then increases to a peak value, and finally reaches extremely low values characteristic of a glassy state

Critical behaviour in (BPI)x(BP)1−x

Abstract: Measurements of dielectric constant, dielectric loss and pyroelectric coefficient as a function of temperature have been performed in Betaine Phosphite (BPI), Betaine Phosphate (BP), and mixed crystals of (BPI)x(BP)1−x for x=0.05; 0.15; 0.30 and 0.60. The behaviour observed for the mixed compounds has a good resemblance to that of structural glasses.

Electrical properties of ceramic/polymer composites

Abstract: Three types of ceramic/polymer composites were prepared and their electrical, dielectric and pyroelectric properties analyzed. The composite PZT5/VDF-TrFE shows a significantly higher pyroelectric figure of merit than PZT (VDF=vinylidine fluoride, TrFE=trifluoroethylene). The dielectric loss of the ceramic/polymer composites is observed to be dominated by those of the polymer, whereas the ceramic phase has a significant contribution on the steady-state electrical conduction and low-frequency dielectric loss at high temperatures. >

Phase Transitions in Leucite: Dielectric Properties and Transition Mechanism

Abstract: To investigate the mechanisms for the cubic-tetragonal phase transition in leucite (KAlSi2O6), the frequency dependence of the dielectric constant (ɛ′), and of the electric conductivity (σ), have been measured as a function of temperature. The dielectric loss function, tan δ, contains two main features: (i) a classical Debye peak, with activation energy of 0.77 eV, ascribed to hopping of K-atoms between their channel (W) sites, via the vacant side-channel (S) sites; (ii) a heavily-overdamped relaxational mode which softens when the crystal is cooled towards the phase transition temperature. The latter relaxational mode shows a critical behaviour, and is thus directly correlated with the transition mechanism. As it is only the potassium ions that could relax at frequencies well below the optical phonon branches, it appears that their movement is relaxational (i.e. heavily overdamped) rather than phonon-like. At temperatures above the transition point, the relaxation of K+ in an electric field is analysed in terms of collective motions within tetragonal domains. Direct evidence for the existence of such domains follows from the presence of diffuse intensity in single-crystal X-ray diffraction experiments.

The dielectric properties of aluminium nitride substrates for microelectronics packaging

Abstract: The dielectric behaviour of sintered polycrystalline aluminium nitride substrates has been examined over the frequency range 500 Hz to 10 MHz and correlated with composition and microstructure. For pure, white AlN at 20 ° C both the permittivity (ɛ′) and dielectric loss (ɛ″) are frequency independent giving ɛ′ = 9.2±0.05 and tan δ = (2.1±0.1) × 10−3. The permittivity is less than for pure alumina substrates (ɛ′ = 10.2) but tan δ compares favourably, with that (1.4 × 10−3) of alumina, which though used more widely has a thermal conductivity some eight times less than that of AlN. The addition of impurities, particularly iron, to give opaque black AlN causes large, frequency dependent increases in ɛ″; at 500 Hz the loss is seven times that of pure white AlN and is two times greater above 100 kHz. The temperature coefficient of permittivity [(ɛ′ − 1)(ɛ′ + 2)]−1 [∂ɛ/∂T]p between −180 and +180 ° C for pure white AlN is 1.05×10−5 K−1 which is similar to the value of 9×10−6 K−1 for pure Al2O3. For impure black AlN the coefficient below 20 ° C is the same but above 20 ° C there is a rapid, non-linear increase of ɛ′ with temperature. Below 180 ° C for pure white AlN and 20 ° C for impure black AlN the values of temperature coefficient are frequency independent at least up to 200 kHz.

Epitaxial Growth of EuBa2Cu3O7-yFilms on YAlO3Single Crystals

Abstract: Epitaxial growth of 1-2-3 superconductor films is reported on a new substrate material that possesses desirable dielectric properties. Magnetron-sputtered EuBa2Cu3O7-y films on YAlO3(001) show excellent properties with a Tc of 91 K. Films are epitaxially grown with the c-axis oriented normal to the surface, and the a- and b-axes ordered in the plane. The high-frequency (50 GHz) surface resistance of a film is 2 mΩ at 30 K. The dielectric constant of YAlO3 is 16. The dielectric loss tangent at 10 GHz is as low as 7.3×10-5 at 300 K and 2×10-6 at 40 K. YAlO3-based films have considerable potential for high-frequency application.

Comparison between frequency-dependent specific heat and dielectric relaxation of glycerol and propylene glycol

Abstract: The recently developed technique of the frequency-dependent specific heat in the linear-response regime has given useful information on the glass transition, which is supplementary to that obtained by other techniques such as dielectric, ultrasonics, and dynamic light scattering. Previous comparisons of these spectroscopies by Birge and others have reported that the shape of the dielectric loss curves are significantly different from the specific-heat results in glycerol. This has led to speculation of the existence of modes of relaxation that carry entropy but have a very small dipole moment. In this work, we analyze the original glycerol dielectric relaxation data of Howell as well as the dielectric results of Davidson and Cole. We find that the dielectric and specific-heat results for glycerol are in reasonable agreement for both the fractional exponent \ensuremath{\beta} of the Kohlrausch-Williams-Watts function and the temperature dependence of loss peak frequencies. The analysis has also been carried out for propylene glycol. However, in this case we find a difference in the values of \ensuremath{\beta} for the dielectric and specific-heat results. The dielectric loss peaks are significantly narrower than the peaks from specific-heat spectroscopy.

Dielectric losses in a polymer-dispersed liquid crystal film

Abstract: We have measured the dielectric response of PDLC films containing liquid crystal droplets of E7 in a polymethylmethacrylate (PMMA) matrix as a function of frequency (0-10KHz) and temperature (25°C-11O°C). The liquid crystal composition of the films was varied from 0% to 60%. A principal objective of this study was to understand the dissipation mechanisms in these systems in an effort to control and reduce them. In the light of the experimental results, we discuss the primary dissipation mechanisms, including both DC and AC losses. The major contribution to the losses in these materials comes from the liquid crystal conductivity. Quantitative interpretation of the results can be clouded by a number of factors including incomplete phase separation of the liquid crystal and polymer, percolation effects and a frequency-dependent conductivity due to charge-carrier depletion in the liquid crystal droplets. Using simple two-phase composite formuli to model the dielectric behavior, the contributions of the real and imaginary parts of the dielectric constant to the field inside a droplet are discussed. The model agrees quantitatively with capacitance experiments, indicating that for frequencies below 100 Hz the field inside of a droplet is strongly modified by charge built up at the droplet/polymer interface.

Dielectric relaxator behaviour of the system Sr1−xLaxTi1−xCoxO3 (x ⩽ 0.40)

Abstract: The dielectric behaviour of the valence-compensated solid solution Sr1−x La x Ti1−x CoxO3 (x=0.05, 0.10, 0.20, 0.30 and 0.40) has been studied as a function of temperature and frequency. Compositions withx=0.20, 0.30 and 0.40 exhibit high values of dielectric constant. This high dielectric constant is due partly to the presence of interfacial polarization, and partly to the formation of grain-boundary barrier layers in these materials. The presence of barrier layers is shown by complex plane impedance analysis.

Crystallizable, low dielectric constant, low dielectric loss composition

Abstract: A variable TCE composition for making dielectric layers having low dielectric constant and low dielectric loss, the composition comprising an admixture of finely divided solids comprising amorphous crystallizable glass, amorphous borosilicate frit, ceramic expansion control additive, and crystallization control additive. The dielectric layers are useful in circuits especially for high density and high frequency applications.

A complete description of the dispersion relation for thin metal film plasmon-polaritons

Abstract: A versatile numerical method is used to solve the plasmon-polariton dispersion relation for a planar thin-metal-film geometry. A complete description of the variation of effective-mode index and propagation length with metal thickness and cover index is presented for all four modes. The spatial distribution of these modes is calculated explicitly. The effects of a nonideal metal film and of dielectric loss in the cover material is considered. >

The high voltage design of superconducting power transmission systems

Abstract: The special problems that arise when designing a superconducting system are examined. These are: (1) that the voltage and current levels chosen must permit economic integration into existing transmission and generation facilities; (2) the mechanical design of components that get cold must permit relatively large absolute contraction and possibly differential contraction without damage that may affect successful operation, and cool-down and warm-up cycles throughout the life of the system should not cause deterioration of the dielectric insulation; and (3) the dielectric losses of the insulation must be carefully controlled in AC systems. Basic research on cryogenic dielectrics is briefly reviewed, and 11 projects around the world that have engaged or are engaging in electrical insulation testing of prototype cables are described. The development of accessories is discussed. >

Dielectric properties of hydrothermally grown gallium orthophosphate single crystals

Abstract: GaPO4 single crystals of the low-temperature form were hydrothermally grown in 4M H3PO4 solution at 180 ° C. Single crystals 5.0×5.2×3.7mm3 in size could be grown in a silica glass vessel of 10 mm inner diameter. The dielectric properties of grown crystals were measured with the electric field parallel (E ∥c) and perpendicular (E ⊥c) to thec-axis. The values of dielectric constant (ie2800-01) ofE ∥c andE ⊥c are about 10.3 and 7.8, respectively, at frequencies from 10 kHz to 1 MHz, and these are nearly independent of frequency at room temperature. However, these values increase with temperature in the temperature range about 310 to 500 K and in the frequency region below 1 MHz. Dielectric loss (ie2800-02) increases with increasing temperature at around 300 K (E ∥c) and 310 K (E ⊥c). From the log σ (conductivity) against 1/T plot in the intrinsic region at higher temperatures, the values of activation energy (E) for conduction are calculated to be about 0.17 and 0.33eV, forE ∥c andE ⊥c, respectively.

Dielectric ceramic composition and a multilayer ceramic capacitor and a method of manufacturing a multilayer ceramic capacitor

Abstract: A low temperature sintering dielectric ceramic composition, which exhibits high dielectric constant, low dielectric loss, high electrical resistivity, high mechanical strength and narrow grain size distribution, is disclosed. The ceramic composition is a binary system comprising lead magnesium niobate (Pb(Mg1/3 Nb2/3)O3) and copper oxide, or a ternary system comprising lead magnesium niobate (Pb(Mg1/3 Nb2/3)O3), lead titanate (PbTiO3) and copper oxide. A multilayer ceramic capacitor comprising internal copper electrodes and ceramic dielectric layers consisting of the dielectric ceramic composition is also disclosed. A method of readily manufacturing the multilayer ceramic capacitor with copper internal electrodes is also disclosed. This fabrication method comprises a stop of forming a multilayer laminate by the green tape multilayer laminating method using dielectric ceramic tapes and a conductor paste containing CuO as its main component; a step of heat-treatment for decomposing and removing organic binder in air (binder removing process); a step of reducing CuO in the internal electrode layers to copper by heat-treatment in a mixed gas atmosphere of nitrogen and hydrogen (reduction process); and a step of sintering the multilayer laminate in a nitrogen atmosphere (sintering process).

Transient analysis of distortion and coupling in lossy coupled microstrips

Abstract: The transient response of lossy coupled microstrips is studied using the spectral-domain approach (SDA) to rigorously compute the dielectric losses. The dielectric loss coefficient is computed using the SDA with a complex dielectric constant, and results are compared with those obtained by the formula advanced by M.V. Schneider (1969) using a finite-difference approximation for the partial derivative. Transient coupling is formulated in the frequency domain by an even/odd mode approach, showing how differences in either the modal loss coefficients or modal propagation constants can be responsible for coupling between lines. Results for pulse distortion on a semiconductor substrate are presented, showing how losses reduce the signal amplitude without significantly distorting the shape. >

Dielectric properties of sol-gel derived lead magnesium niobate ceramics

Abstract: Lead magnesium niobate (PMN) was prepared by a sol-gel technique. The gel calcined at 850°C for 2hr resulted in > 98% of perovskite phase. About 98% of the theoretical density was achieved for pellets sintered at 1200°C for 4hr. The room temperature dielectric constant of the pellets sintered at 1250°C for 4hr showed a maximum value of 11686 at 1 KHz. The dielectric constant increased with increasing grain size of the samples sintered at various temperatures.

Structural and dielectric studies of GdAsO4

Abstract: Determination par diffraction RX des parametres cristallins. Mesure de la constante dielectrique et de la perte dielectrique en fonction de la frequence (10 2 a 10 4 Hz) et de la temperature (25 a 200 o C)

Electrical conduction and dielectric behaviour of the oxidic spinel Li0.5+0.5xCr0.3TixFe2.2−1.5XO4

Abstract: The electrical conductivity of polycrystalline lithium-chromium ferrites substituted successively with Ti4+ was studied as a function of composition and temperature. The resistivity increased with composition and all the samples exhibited a change in slope in the resistivity-temperature curve. Two different regions with a large variation in activation energies were found. The dielectric constant and loss factor for different compositions were measured in the frequency range of 10kHz to 10 MHz. The dielectric permittivity showed a dispersion with frequency for all the samples. Peaks were observed for the samples with 0.4 ⩽ x ⩽ 0.8. The possible mechanisms involved are discussed.

Millimeter wave complex refractive index, complex dielectric permittivity and loss tangent of high purity and compensated silicon

Abstract: Single-crystal high-resistivity (11000- Omega -cm) boron-doped silicon was found to exhibit the lowest absorption loss at room temperature (25 degrees C) in the entire millimeter-wave region. The millimeter-wave absorption coefficient values for the compensated silicon are at least one order of magnitude less than values obtained with undoped pure silicon. At 140 GHz, the loss tangent value of the compensated silicon is as low as 40 mu rad. The study of the dielectric properties of silicon as a function of resistivity reveals that the low-frequency free-carrier absorption present in all silicon (and other semiconductors) vanishes with increasing resistivity. The dispersive Fourier transform spectroscopic technique was utilized for the measurements. >

Theoretical increase in radiation efficiency of a small dipole antenna made with a high temperature superconductor

Abstract: An electrically small wire dipole antenna with a shunted stub matching network has been analyzed to determine the improvement in radiation efficiency that can be achieved by making the metallic components from high-temperature superconducting (high T/sub c/ or HTS) material. The analysis shows that significantly higher radiation efficiencies can be obtained with HTS material only if the dielectric losses are kept to very low values. A loss tangent of less than 10/sup -4/ is necessary for any dielectric materials in the transmission lines and support structures for the antenna; a loss tangent of at least 10/sup -5/ is desirable, particularly if the dipole length is 0.1 wavelength or less. >