Showing papers on "Dielectric loss published in 1989"

Time domain reflection methods for dielectric measurements to 10 GHz

Abstract: Total reflection methods and instrumentation for their use are described for measurements of dielectric permittivity and loss at frequencies to 10 GHz or more. Several cell designs are shown, together with analyses of their performance. Procedures are given for correcting effects of wave propagation in the cells and residual reflections in the cells by bilinear analysis with calibrations using dielectrics of known permittivity. Representative results are presented for highly polar liquids, dilute solutions of polar molecules in nonpolar solvents, electrolyte solutions, and ionic glasses with appreciable ohmic conduction.

Frequency-selective reflection and transmission by a periodic dielectric layer

Abstract: The feasibility of using a periodic dielectric layer, composed of alternating bars having dielectric constants epsilon /sub 1/ and epsilon /sub 2/, as a dichroic surface at millimeter-wave frequencies is examined For oblique incidence, it is found that total transmission and total reflection can be obtained at different frequencies for proper choices of epsilon /sub 1/ and epsilon /sub 2/ and the geometric parameters The frequencies of total reflection and transmission can be estimated from wave phenomena occurring in a layer of uniform dielectric constant equal to the average value in the periodic layers For some of the frequencies of total transmission, the bandwidth for 90% transmission is found to be 40% The bandwidth for 90% reflection is always found to be much narrower, the greatest value obtained being 25% >

Dielectric relaxation in polymeric solids Part 1. A new model for the interpretation of the shape of the dielectric relaxation function

Abstract: A model is proposed which explains the shape of the dielectric relaxation function at the glass transition of polymers. The model is based on the idea that the molecular mobility at the glass transition is controlled by intra- and intermolecular interaction. In addition, a specific model for the local chain dynamics in amorphous polymer systems is used. According to the scaling hypothesis of molecular dynamics the model relates the high frequency dependence of the dielectric loss curve to the local chain dynamics and the low frequency dependence to the intermolecular correlation.

On the relaxation between Debye and nonexponential relaxation in supercooled monohydric alcohols and water: A solution study

Abstract: We examine one of a number of possible classes of exceptions to the usual rule that non‐Arrhenius behavior in supercooled liquids is accompanied by a departure from exponential relaxation kinetics. The exceptions we study are the dielectric relaxations of monohydric alcohols and supercooled water, in which also the dielectric relaxation times may greatly exceed their mechanical relaxation counterparts. This paper gives evidence that the exceptional behavior is due to a clustering or self‐micellization phenomenon by showing how both the relaxation time ratio and Debye relaxation anomalies can be removed by small additions of ionic solutes. These compete with the hydrogen bonding interactions responsible for the clustering. The study, which uses the electrical modulus formalism for data analysis, is restricted by the rapid merging of conductivity and dielectric loss peaks at salt content increases. The relaxation times extracted from a given data set depend on the formalism employed in the data analysis, and the importance of consistency in this respect when comparing mechanical and electrical pheonomena is emphasized. We conclude that comparisons between different responses are most appropriately made in the susceptibility formalism, that the dielectric response in n‐propanol is ∼160 times slower than the mechanical response at ∼130 °C, and that the difference is due to the fact that slowly relaxing hydrogen bonded molecular clusters dominate the dielectric susceptibility, hence also the dielectric relaxation. Using the susceptibility formalism for comparsions, we then infer that in water the dielectric relaxation process is considerably slower than the mechanical relaxation process, and that this fact, as well as the fact that the dielectric relaxation in supercooled water remains exponential while uniquely non‐Arrhenius in temperature dependence, is to be explained by the dominance of the dielectric relaxation process by ‘‘network clusters.’’

Dielectric constants of BeO, MgO, and CaO using the two-terminal method

Abstract: Using fused SiO2, CaF2, and SrF2 samples with accurately known dielectric constants, we have evaluated the accuracy and precision of two-terminal dielectric constant measurements on small single crystals using empirically determined edge corrections. Values of κ′ at 1 MHz of 3.836±0.05 for silica, 6.814±0.07 for CaF2 and 6.463±0.09 for SrF2 indicate an accuracy and precision of 1.0–1.5% for samples having areas of 0.05–1.0 cm2. Dielectric constants of BeO, MgO, and CaO measured by this technique are: BeO, κ′a=6.87 and κ′c=7.74; MgO, κ′= 9.90; and CaO, κ′=11.95 where κ′a and κ′c are the dielectric constants parallel to the a and c axes, respectively. Dielectric loss measurements on CaO in vacuum between 5–400 K at 10–105 Hz indicate significant dispersion at temperatures higher than 300 K, but the effect of the losses on the dielectric constant is less than 1% at 1 MHz and 300 K.

Dielectric relaxation and deuteron NMR of water in polyimide films

Abstract: Polyimide films containing up to 3.2 wt. % water (H2 O or D2 O) have been studied by dielectric relaxation (DR) and 2H nuclear magnetic resonance (NMR) spectroscopies. Dielectric loss measurements show the presence of a double peak near 200 K due to water, with two components designated as γ1 and γ2 . The γ2 peak, which appears at the lower temperature, is only present for the interior portion of thick (>25 μm) films and rapidly decreases as the moisture content decreases. Correspondingly, deuteron NMR measurements show the presence of narrow and broad lines, which are correlated, respectively, with the γ1 and γ2 DR peaks. The spin‐spin relaxation time T2, is much longer for the narrow line than for the broad line. The γ1 DR peak and the narrow NMR line are attributed to sites where isolated water molecules are only loosely coupled to the polymer chains. The γ2 and broad NMR lines involve small clusters of water molecules with associated nuclear magnetic dipole‐dipole coupling. Additional measurements on polyimides containing methanol and acetic acid absorbents are also reported.

Low Temperature Properties of Microwave Dielectrics

Abstract: Temperature dependences of resonant frequency and dielectric loss tangent were measured at the temperature range from 20 to 300 K for three kinds of microwave dielectrics, (Zr, Sn)TiO4, Ba(Zr, Zn, Ta)O3, and Ba(Sn, Mg, Ta)O3. The deviations of resonant frequencies from 20 to 300 K for these materials were less than 1200 ppm, which is equivalent to 4.3 ppm/°C of the temperature coefficient. The dielectric loss tangents of (Zr, Sn)TiO4 materials showed a remarkable difference when they were made of the raw materials of different purities. These low temperature characteristics are discussed in connection with the anharmonic terms in the crystal's Hamiltonian.

Low temperature synthesis and dielectric properties of ceramics derived from amorphous barium titanate gels and crystalline powders

Abstract: Water-soluble titanyl acylate precursor, prepared by molecular modification of titanium(IV) isopropoxide, was used with inexpensive water-soluble barium acetate for the synthesis of high purity BaTiO3 The amorphous gels obtained under acidic conditions were calcined at 1000°C to obtain high purity, crystalline BaTiO3 pwders (sol-gel process) The same precursors were used under alkaline conditions (pH 13) to precipitate crystalline, ultrafine (less than 100 nm) BaTiO3 powders diretly at temperatures below 100°C (sol-precipitation process) On sintering at 1350°C, relatively dense (85%–90%) ceramic bodies with good dielectric properties were obtained from gels calcined at temperatures above 1000°C Sol-precipitated powders were calcined (950–1000°C), compacted and sintered (1350°C) to obtain dense (92%–96%) ceramic bodies without using any sintering additives The room temperature dielectric constant (at 1 KHz) of these ceramics was about 1000 with a dielectric loss (tan δ) of 001 Mechanisms for the evolution of crystalline BaTiO3 in the sol-gel and the sol-precipitation processes are proposed and discussed in the context of microstructure and dielectric properties

Propagation of terahertz bandwidth electrical pulses on YBa2Cu3O7−δ transmission lines on lanthanum aluminate

Abstract: We study the propagation of terahertz bandwidth electrical pulses on high critical current density c‐axis oriented YBa2Cu3O7−δ (YBCO) coplanar transmission lines deposited epitaxially on the low dielectric loss substrate lanthanum aluminate (LaAlO3). The losses on the YBCO transmission line are lower than on an equivalent gold line on the same substrate at temperatures below 50 K. At higher temperatures, absorption and dispersion of the ultrashort electrical pulses are observed in reasonable agreement with Mattis–Bardeen theory.

Processing and Characterization of BaTi4O9

Abstract: BaTi4O9 powder prepared by calcining BaCO3 and TiO2 powders was sintered to over 97% of theoretical density. Less than 5% Ba2Ti9O20 occurred as a second phase in “pure” BaTi4O9, and Al2O3 impurities from processing formed isolated hollandite (∼BaAl2Ti6O16) grains, which were identified by fringes in bright-field TEM images. For pure BaTi4O9 at 1 MHz, a dielectric loss (tan δ) of 5 × 10−4 and dielectric constant of 39 were recorded. Hollandite impurities were found to increase tan δ by 2 orders of magnitude, whereas firing in oxygen decreased tan δ by an order of magnitude.

Two cylindrical obstacles in a rectangular waveguide-resonances and filter applications

Abstract: Two metallic or lossy dielectric cylinders placed in one cross section of a rectangular waveguide are investigated by the orthogonal expansion method. Resonances are shown by frequency responses of the transmission coefficient. They are discussed by patterns of the magnetic field and diagrams of the Poynting vector. Physical explanations of the resonances are given. The structure may be used as a filter element. With two small dielectric posts, a frequency characteristic with two stopbands can be obtained. Center frequencies are tunable by moving the posts. Using one large metallic and one small dielectric post, a tunable passband characteristic can be realized. >

Application of microwave dielectric loss heating effects for the rapid and convenient synthesis of intercalation compounds

Abstract: Intercalation compounds of α-VO(PO4)·2H2O with pyridine, 4-methylpyridine, and 4-phenylpyridine have been synthesised two orders of magnitude more quickly using microwave dielectric loss heating effects than with conventional thermal methods; the samples retain a high degree of crystallinity and are therefore readily characterised by powder X-ray crystallographic techniques.

Dielectric constants of chrysoberyl, spinel, phenacite, and forsterite and the oxide additivity rule

Abstract: The dielectric constants and dielectric loss values of BeAl2O4 (chrysoberyl), MgAl2O4 (spinel), Be2SiO4 (phenacite), and Mg2SiO4 (forsterite) were measured at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: chrysoberyl, κ′ a =9.436, κ′ b =9.071, κ′ c =8.269; spinel, κ′ a =8.18; phenacite, κ′ a =6.28, κ′ c =6.06; and forsterite, κ′ a =6.867, κ′ b =7.392, κ′ c =6.739. The agreement between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of oxide polarizabilities according to αD(M2M′X4) = 2αD(MX)+αD(M′X2) is ~ 1.0%.

Correlation of electrical properties and internal friction in mixed conduction glasses containing ionic and electronic conduction (1) Fe2O3-Na2O-P2O5 glasses

Abstract: The electrical properties and internal friction in (40−x)Fe2O3·xNa20.60P2O5 glasses were measured. Two or three peak on internal friction were observed in the temperature range of −100 to 300° C at a frequency of about 1 Hz. The peak area of internal friction could be explained quantitatively by the additivity law of diffusion of Na+ ion and hopping of electrons which are carriers similar to those of dielectric loss. Activation energy, peak temperature of dielectric loss and internal friction showed almost the same value. Both relaxation phenomena have the same mechanism which is due to the diffusion of Na+ion and the hopping of electrons between Fe2+ ⇌ Fe3+. The high-temperature peak is assumed to result from the interaction between protons or alkali ions and non-bridging oxygen.

Dielectric properties of SrTiO3 single crystals subjected to high electric fields and later irradiated with X-rays orγ-rays

Abstract: The dielectric constant (K), loss (tanδ), and hence conductivity (σ) of SrTiO3 single crystals have been measured in the frequency region 102–107 Hz and in the temperature range 30°–350° C. Quenching, subjecting the crystals to high electric fields (a.c. or d.c.) and X-ray orγ-ray irradiation, or a combination of these treatments, is found to bring about interesting changes in these properties. An attempt is made to understand the results.

Synergism on electromagnetic inductance (EMI)‐shielding in metal‐ and ferroelectric‐particle filled polymers

Abstract: In this paper the electromagnetic inductance (EMI)-shielding of metal-and ferroelectric-particle filled polymers is described. The composite, containing only metallic fillers, has a shielding effectiveness comparable to conventional products. The addition of a few percent of ferroelectric material to this composite enhances the shielding behavior by several orders of magnitude—without increasing its electrical conductivity. In this three component composite the shielding effectiveness reaches a maximum close to the ferroelectric/paraelectric transition temperature. The synergetic effect, obtained by the addition of ferroelectrical particles, is related to the high dielectric losses of ferroelectric material close to its transition temperature.

Third Harmonic Distortion of Dielectric Resonator Materials

Abstract: Microwave dielectric materials must have a low third harmonic distortion when they are used for high-power applications. This is because the third harmonic distortion produces a third-order intermodulation distortion which generates interference between signals. In this paper, the measurement results of the third harmonic distortion levels for three types of dielectric resonator materials, (Zr, Sn)TiO4, MgTiO3-CaTiO3 and BaO-PbO-Nd2O3-TiO2, are reported and the equations derived to combine the distortion level and the fourth anharmonic term in the crystal's Hamiltonian. The measured distortion levels have a strong correlation with dielectric loss tangents of the materials. This relationship is also explained in connection with the anharmonic terms in the crystal's Hamiltonian.

Dielectric and Pyroelectric Properties of Cadmium Niobate Ceramics

Abstract: The low-temperature dielectric and pyroelectric properties of pyrochlore Cd2Nb2O7 ceramics have been investigated over the temperature range from 10 to 300 K. Dielectric data confirmed that two ferroelectric transitions occurred in the Cd2Nb2O7 ceramics at temperatures near 80 and 192 K. The higher-temperature ferroelectric transition is complex, with evidence for three separate transitions occurring within a narrow temperature range. The temperature and frequency dependencies of the dielectric constant were consistent with both second-order (diffuse) and improper ferroelectric (ferroelastic) effects. Pyroelectric data also confirmed the multiple-transition behavior, with anomalies in the pyroelectric coefficient at temperatures corresponding to the onset of the diffuse ferroelectric transition and the ferroelastic effect. Dielectric loss data (analyzed by both Arrhenius and Cole-Cole formalisms) indicated the presence of three separate relaxation-type dielectric loss mechanisms in this temperature range. Unambiguous explanations for the observed dielectric and pyroelectric phenomena could not be made, but domain effects are believed to be responsible for at least part of the complex nature of the ferroelectric transitions in this material.

Application of the many-body theory of Dissado and Hill to the complex permittivity of 1,2,4-butanetriol at pressures to 1 GPa

Abstract: The dielectric relaxation of 1,2,4-butanetriol in its supercooled liquid state has been studied at pressures up to 1 GPa. The frequency of the applied field is varied within the range from 1 mHz to 10 MHz. The automated and computer controlled dielectric spectroscopy measuring system is presented in detail. It is found that neither the dielectric relaxation spectra nor the static susceptibility can be accurately described within the theoretical framework which only considers the behaviour of non-interacting dipoles. Instead, the dielectric loss is described by the many-body correlated cluster theory of Dissado and Hill (1983). A relationship between the correlation parameters and the static susceptibility is discussed. The results are compared with previous findings on the homologues glycerol and 1,2,6-hexanetriol.

Simultaneous dielectric and dynamic mechanical analysis of thermosetting polymers

Abstract: This work presents a new method to measure simultaneously the dielectric loss factor and viscosity of thermosetting polymers during various cure cycles. A microdielectric sensor was mounted in the bottom plate of a parallel plate rheometer. Three types of high performance laminating resins were investigated. During non-isothermal curing, dipole peaks were found to correspond to softening/devitrification, the maximum in the loss factor followed the same heating rate dependence as the minimum in the viscosity, and dipole peaks were observed to correlate with vitrification when the cure temperature was below the ultimate glass transition temperature of the resin.

Dielectric Behavior of the Relaxor Pb(Mg1/3Nb2/3)O3—PbTiO3 Solid‐Solution System in the Microwave Region

Abstract: Dielectric behavior of the relaxor ferroelectric Pb(Mg1/3Nb2/3)O3—PbTiO3 solid-solution system was studied from—50° to 200°C in the 100 to 12 × 109 Hz frequency region, and a broad dielectric relaxation was measured for compositions throughout the system. The relative microwave permittivity of the composition 0.9Pb(Mg1/3Nb2/3)O3·0.1 PbTiO3 decreased by 1 order of magnitude from the 1-MHz value of 11800, and similar decreases were observed for other compositions in the system. Dielectric loss (tan δ) values ranged from 0.5 to 1.0 at microwave frequency. The temperature of the broad dielectric constant maximum shifts toward higher values with increased frequency.