Showing papers on "Dielectric loss published in 2002"

Electromagnetic and absorption properties of some microwave absorbers

Abstract: Electromagnetic properties of a thermoplastic natural rubber (TPNR), a lithium–nickel–zinc (Li–Ni–Zn) ferrite and a TPNR–ferrite composite subjected to transverse electromagnetic (TEM) wave propagation were investigated. The incorporation of the ferrite into the matrix of the TPNR was found to reduce the dielectric loss but the magnetic loss increased. The absorption characteristics of all the samples subjected to a normal incidence of TEM wave were investigated based on a model of a single-layered plane wave absorber backed by a perfect conductor. It is evident from a computer simulation that the ferrite is a narrowband absorber, whereas the polymeric samples show broadband absorption characteristics. Minimal reflection of the microwave power or matching condition occurs when the thickness of the absorbers approximates an odd number multiple of a quarter of the propagating wavelength. This is discussed as due to cancellation of the incident and reflected waves at the surface of the absorbers. The Li–Ni–Z...

Electrical conductivity and dielectric behaviour of nanocrystalline NiFe2O4 spinel

Abstract: Electrical conductivity and dielectric measurements have been performed for nanocrystalline NiFe2O4 spinel for four different average grain sizes, ranging from 8 to 97 nm. The activation energy for the grain and grain boundary conduction and its variation with grain size have been reported in this paper. The conduction mechanism is found to be due to the hopping of both electrons and holes. The high-temperature conductivity shows a change of slope at about 500 K for grain sizes of 8 and 12 nm and this is attributed to the hole hopping in tetrahedral sites of NiFe2O4. Since the activation energy for the dielectric relaxation is found to be almost equal to that of the dc conductivity, the mechanism of electrical conduction must be the same as that of the dielectric polarization. The real part e' of the dielectric constant and the dielectric loss tanδ for the 8 and 12 nm grain size samples are about two orders of magnitude smaller than those of the bulk NiFe2O4. The anomalous frequency dependence of e' has been explained on the basis of hopping of both electrons and holes. The electrical modulus analysis shows the non-Debye nature of the nanocrystalline nickel ferrite.

Thermal noise in interferometric gravitational wave detectors due to dielectric optical coatings

Abstract: We report on thermal noise from the internal friction of dielectric coatings made from alternating layers of Ta2O5 and SiO2 deposited on fused silica substrates. We present calculations of the thermal noise in gravitational wave interferometers due to optical coatings, when the material properties of the coating are different from those of the substrate and the mechanical loss angle in the coating is anisotropic. The loss angle in the coatings for strains parallel to the substrate surface was determined from ringdown experiments. We measured the mechanical quality factor of three fused silica samples with coatings deposited on them. The loss angle, ||(f), of the coating material for strains parallel to the coated surface was found to be 4.2 ± 0.3 × 10−4 for coatings deposited on commercially polished slides, and 1.0 ± 0.3 × 10−4 for a coating deposited on a superpolished disc. Using these numbers, we estimate the effect of coatings on thermal noise in the initial LIGO and Advanced LIGO interferometers. We also find that the corresponding prediction for thermal noise in the 40 m LIGO prototype at Caltech is consistent with the noise data. These results are complemented by results for a different type of coating, presented in a companion paper.

Design Consideration and Performance Analysis of Substrate Integrated Waveguide Components

Abstract: This paper presents a new design scheme and measurement results of circuit discontinuities on the basis of the recently proposed substrate integrated waveguide technology. Design considerations are discussed with respect to H-plane step, post resonator, 90° bend and 90° curvature, which are analyzed using an equivalent rectangular waveguide model. Results show a good agreement between design predictions and practical measurements. Loss properties of the discontinuities are also examined. It is demonstrated that the radiation loss of the new substrate integrated waveguide is smaller as compared to dielectric and conductor losses.

Dielectric mixtures: electrical properties and modeling

Abstract: A review of the current state of understanding of dielectric mixture properties, and approaches to use numerical calculations for their modeling are presented. It is shown that interfacial polarization can yield different non-Debye dielectric responses depending on the properties of the constituents, their concentrations and geometrical arrangements. Future challenges on the subject are also discussed.

Low-temperature scaling behavior of BaFe 0.5 Nb 0.5 O 3

Abstract: The ferroelectric ceramic ${\mathrm{BaFe}}_{0.5}{\mathrm{Nb}}_{0.5}{\mathrm{O}}_{3}$ (BFN) is synthesized by a solid-state reaction technique. The x-ray-diffraction of the sample at room temperature shows a monoclinic phase. The field dependences of the dielectric response and the conductivity are measured in a frequency range from 10 Hz to 2 MHz and in a temperature range from 93 to 213 K. The frequency dependence of the loss peak is found to obey an Arrhenius law with an activation energy 0.12 eV. An analysis of the real and imaginary parts of the dielectric permittivity with frequency is performed, assuming a distribution of relaxation times as confirmed by Cole-Cole plots as well as the scaling behavior of the dielectric loss. The scaling behavior of the dielectric loss spectra suggests that the distribution of the relaxation times is temperature independent. The frequency-dependent electrical data are also analyzed in the framework of the conductivity and modulus formalisms. Both these formalisms provided qualitative similarities in the relaxation times. We observe that the hopping frequency can be used for a scaling of the conductivity spectra for BFN. All these observations clearly suggest that BFN is a relaxor ferroelectric.

Ferroelectric-relaxor behavior of Ba(Ti0.7Zr0.3)O3 ceramics

Abstract: Ferroelectric-relaxor behavior of Ba(Ti0.7Zr0.3)O3 ceramics is studied in the temperature range from 150 to 450 K. A broad dielectric peak with a high-dielectric maximum exhibits frequency dispersion. The dielectric relaxation rate follows the Vogel–Fulcher relation with E=0.21 eV and TVF=199.6 K. The polarization hysteresis loops were observed with a remnant polarization of 10 μC/cm2 at 175 K. The high-dielectric constant and high-polarization properties are expected to find practical applications at low temperatures.

A three-phase magnetoelectric composite of piezoelectric ceramics, rare-earth iron alloys, and polymer

Abstract: A class of multiferroic, three-phase particulate composites of Tb–Dy–Fe alloy, lead–zirconate–titanate (PZT), and polymer are investigated, in which a small volume fraction f of Tb–Dy–Fe alloy particles are dispersed in a PZT/polymer mixture. The measured dielectric, piezoelectric, and magnetoelectric properties demonstrate that a percolation transition occurs at f∼0.12 in the composites. When f is low (e.g., f<0.07), the composites exhibit piezoelectric and increasing magnetoelectric response. In the critical f range of 0.07

MgO-mixed Ba0.6Sr0.4TiO3 bulk ceramics and thin films for tunable microwave applications

Abstract: The dielectric properties of Ba0.6Sr0.4TiO3 (BST) and 1.0, 20.0, 40.0, and 60.0 wt % MgO-mixed BST bulk ceramics and thin films were investigated for tunable microwave applications. The effects of MgO mixing with BST on BST phase transitions were examined. It is observed that Mg substitution into BST causes a shift in the cubic-tetragonal BST phase transition peak to a lower temperature. Mg-substituted BST and MgO-mixed phases exhibit depressed and broadened BST phase transition peaks, resulting in decreased dielectric constants and dielectric losses at room temperature. BST and 1.0, 20.0, 40.0, and 60.0 wt % MgO-mixed BST thin films (∼0.3 μm thick) were deposited on (100) MgO single-crystal substrates at 750°C in an oxygen ambient pressure of 200 mTorr by pulsed laser deposition. The MgO–BST composite thin films showed a relatively high dielectric Q (=1/tan δ) compared to the pure BST and Mg-substituted BST thin films while retaining useful dielectric tuning.

Dielectric properties of Mn-substituted Ni–Zn ferrites

Abstract: The dielectric properties of MnxNi0.5−xZn0.5Fe2O4 ferrites with x varying from 0.05 to 0.4 synthesized by the citrate precursor method have been investigated as a function of frequency, temperature, composition, and sintering temperature. An increase in the dielectric constant is observed with the increase in Mn concentration except for x=0.3. Dispersion in the dielectric constant with frequency in the range of 100 Hz–1 MHz is observed. Resonance peaks were observed in tan δ∈ versus frequency curves for all samples. A shift in the resonance frequency towards higher frequency is observed with increase in temperature. The peak height also increases with increase in temperature. Possible mechanisms contributing to these processes have been discussed. From the temperature variation of the dielectric relaxation, activation energies for various samples have been calculated and compared with those obtained from dc resistivity.

Structure-property relationships in pure and acceptor-doped Ba1-xSrxTiO3 thin films for tunable microwave device applications

Abstract: The influence of low concentration (1 mol %) Mg doping on the structural, microstructural, surface morphological, and dielectric properties of Ba1−xSrxTiO3 (BST) thin films has been measured and analyzed. The films were fabricated on MgO and Pt–Si substrates via the metalorganic solution deposition technique using carboxylate–alkoxide precursors and postdeposition annealed at 800 °C (film/MgO substrates) and 750 °C (film/Pt–Si substrates). The structure, microstructure, surface morphology, and film/substrate compositional quality were analyzed by glancing angle x-ray diffraction, field emission scanning microscopy, atomic force microscopy, and Auger electron spectroscopy studies. Dielectric properties of unpatterned films were measured at 10 GHz using a coupled, tuned split dielectric resonator system, and at 100 kHz using metal–insulator–metal capacitors. The Mg-doped BST films exhibited improved dielectric and insulating properties compared to the undoped Ba0.6Sr0.4TiO3 thin films. The improved dielectric properties, low leakage current, and good dielectric tunability of the low level Mg-doped BST thin films merits strong potential for utilization in tunable microwave devices.

Anomalous broad dielectric relaxation in Bi 1.5 Zn 1.0 Nb 1.5 O 7 pyrochlore

Abstract: The complex dielectric response of ${\mathrm{Bi}}_{1.5}{\mathrm{Zn}}_{1.0}{\mathrm{Nb}}_{1.5}{\mathrm{O}}_{7}$ cubic pyrochlore ceramics was investigated between 100 Hz and 100 THz by a combination of low-frequency capacitance bridges, a high-frequency coaxial technique, time domain transmission THz spectroscopy, and infrared spectroscopy. The data obtained between 10 K and 400 K revealed glasslike dielectric behavior: dielectric relaxation is observed over a wide frequency and temperature range, and the dielectric permittivity and loss maxima shift to higher temperature values by almost 200 K with increasing measuring frequency. The distribution of relaxation frequencies broadens on cooling and can be described by a uniform distribution. The high-frequency end of the distribution at $\ensuremath{\sim}{10}^{11} \mathrm{Hz}$ is almost temperature independent and its low-frequency end obeys the Arrhenius Law with an activation energy of $\ensuremath{\sim}0.2 \mathrm{eV}.$ The relaxation is assigned to the local hopping of atoms in the A and O' positions of the pyrochlore structure among several local potential minima. The barrier height for hopping is distributed between 0 and 0.2 eV. Such an anomalously broad distribution may have its origin in the inhomogeneous distribution of ${\mathrm{Zn}}^{2+}$ atoms and vacancies on ${\mathrm{Bi}}^{3+}$ sites, which gives rise to random fields and nonperiodic interatomic potential. Frequency independent dielectric losses $(1/f$ noise) are observed at low temperatures, which seems to be a universal behavior of disordered systems at low temperatures.

Dielectric spectroscopy – yesterday, today and tomorrow

Abstract: Dielectric spectroscopy is an old experimental tool which has dramatically developed in the last two decades. It covers nowadays the extraordinary spectral range from 10−6 to 1012 Hz. This enables researchers to make sound contributions to contemporary problems in modern physics. Two examples will be briefly presented: the scaling behavior of the glass transition and the dynamics of molecules in confined space. In a brief outlook novel perspectives of dielectric techniques will be discussed, e.g. non-resonant dielectric hole-burning spectroscopy, dielectric thermal expansion spectroscopy or dielectric measurements using an atomic force microscope.

Study of CaO–WO3–P2O5 glass system by dielectric properties, IR spectra and differential thermal analysis

Abstract: Dielectric constant e ′ , loss tan δ and ac conductivity σ ac of 40CaO– x WO 3 –(60− x )P 2 O 5 (with 0⩽ x ⩽15) glasses are studied over a range of frequencies and temperature. The dielectric breakdown strength of these glasses is also determined at room temperature. The values of dielectric parameters, viz., e ′ , tan δ and σ ac of CaO–P 2 O 5 glasses are found to decrease with the introduction of WO 3 up to 3 mol% and increase with further increase in the concentration of WO 3 ; the probable reasons for such an increase are identified and explained with the aid of IR spectra and differential thermal analysis of these glasses. The variation of tan δ with temperature at different frequencies of CaO–P 2 O 5 glasses has exhibited dielectric relaxation effects with decreasing relaxation intensity with increase in the concentration of WO 3 from 0 to 3 mol%; such relaxation effects seem to have been absent in glasses containing WO 3 beyond 3 mol%. The relaxation phenomenon has been analysed by a pseudo-Cole–Cole plot method and the possible mechanism responsible for such relaxation effects has been suggested.

Dielectric properties and high tunability of Ba(Ti0.7Zr0.3)O3 ceramics under dc electric field

Abstract: The effect of dc electric field (E) on the dielectric properties of Ba(Ti0.7Zr0.3)O3 ceramics with an obvious ferroelectric-relaxor behavior (Tm∼229 K, 10 kHz) is reported. The dielectric constant is greatly suppressed and a low loss is obtained under dc electric fields (⩽40 kV/cm). The low loss (tan δ∼0.002) and high tunability (∼45%) were obtained for the Ba(Ti0.7Zr0.3)O3 ceramics around 300 K, indicating that it is a promising candidate for tunable materials at room temperature. The field dependence of the temperature (Tm) of the dielectric constant maximum follows the ΔTm∼E2/3 relation, indicating a second-order phase-transition-like behavior.

Structural and dielectric studies of BaFe0.5Nb0.5O3

Abstract: Ferroelectric BaFe0.5Nb0.5O3 (BFN) ceramic is synthesized by the solid-state reaction technique for the first time. The x-ray diffraction of the sample at room temperature shows a monoclinic phase. Dielectric studies of the sample show a frequency dependence of the temperatures at which the dielectric permittivity (real and imaginary) peaks. The temperature variations of the real and imaginary components of the dielectric permittivity show broad maxima. There is evidence for Vogel-Fulcher-type relaxational freezing. The analysis of the real and imaginary parts of the dielectric permittivity with frequency has been performed assuming a distribution of relaxation times as confirmed by Cole-Cole plots as well as the scaling behaviour of the dielectric loss. All these observations clearly suggest that BFN is a relaxor ferroelectric. The Mossbauer spectrum of the sample at room temperature shows a symmetric doublet, with the iron being trivalent.

Characterization of liquid crystal polymer for high frequency system-in-a-package applications

Abstract: Liquid crystal polymer (LCP) is a promising substrate for electronics packaging. In this paper, the high frequency characteristics of LCP were investigated using a microstrip ring resonator to verify the possibility of applying the material in RF packaging. The relative dielectric constant and the loss tangent have been measured. The radiation loss of the ring is considered to accurately determine the loss tangent. A GaAs MMIC switch circuit was fabricated using LCP as substrate to demonstrate the application of this material for system-in-a-package. From the high frequency measurements, it is shown that LCP has low dielectric constant and low loss tangent in the frequency range from 1 GHz to 35 GHz. It is also found that LCP can be used in system-in-a-package applications.

Linear stability analysis of thin leaky dielectric films subjected to electric fields

Abstract: An intriguing process, known as lithographically induced self-assembly (LISA), is initiated by positioning a template parallel to a flat silicon wafer-coated with a thin polymeric film and then raising the temperature above the glass transition/melting temperature of the film. Electric fields exert a force on charges induced at the polymer–air interface, placing the film in tension. The static equilibrium that results is unstable to disturbances with wavelengths for which the electrostatic force overcomes the surface tension. Flow ensues, generating a pattern in the film with periodicity reflecting the characteristic length of the instability. Though the initiation of the process as outlined above is generally accepted, the forces guiding the evolution of the film into the remarkably periodic microstructures observed are not. Our goal here is to create a sound understanding of the mechanism through quantitative modeling to facilitate the conversion of these microstructures into nano-structures. Given the apparent importance of conductivity in the film we adopt the “leaky dielectric model”, which also allows for re-distribution of charges on the interfaces, and undertake a linear stability analysis to explore the effects of various process parameters, particularly the conductivity and the film thickness. The linear stability analysis with the leaky dielectric model for the polymer film yields growth exponents and characteristic wavenumbers much larger than that for the perfect dielectric model. The differences are striking in that the slightest conductivity increases the growth exponent by a factor of 2–20 and decreases the fastest growing wavelength by a factor of 2–4.

Dielectric properties of random and 〈100〉 oriented SrTiO3 and (Ba,Sr)TiO3 thin films fabricated on 〈100〉 nickel tapes

Abstract: Properties are presented for random and enhanced 〈100〉 orientation SrTiO3 and BaxSr1−xTiO3 (x=0.33, 0.50, and 0.67) films fabricated on base-metal 〈100〉 Ni tapes using a chemical solution deposition approach. Films were crystallized in a reducing atmosphere, which prevented Ni oxidation, but permitted growth of SrTiO3 and BaxSr1−xTiO3 films with dielectric loss tan δ between 0.003 and 0.015. For randomly oriented BaxSr1−xTiO3 (x=0, 0.33, 0.5, and 0.67) films, zero-field 100 kHz dielectric constants ranged from 250 to 420. Films with enhanced 〈100〉 orientation exhibited zero-field dielectric constants of 980 to 1500, three times higher than random films. Development of such high dielectric constants on Ni suggests a future method for inexpensive, high performance base-metal electrode capacitor fabrication.

Influence of grain size and structural changes on the electrical properties of nanocrystalline zinc ferrite

Abstract: The electrical conductivity and dielectric properties of nanocrystalline zinc ferrite with various grain sizes ranging from 7 to 115 nm have been studied over a wide frequency range 1 Hz–15 MHz by impedance measurements in the temperature range of 300–650 K. The effect of grain size on the conductivity has been investigated by nonlinear least-squares fitting of the impedance data. The conduction mechanism is found to be due to the hopping of both electrons and holes. The activation energies have been obtained from Arrhenius plots of the grain and the grain boundary conductions and their values are characteristic of the hopping of charge carriers. As the grain size decreases, the conductivity also decreases along with a small increase in the activation energy. The real part e′ of the dielectric constant exhibits anomalous behavior, except for the 115 nm grain size sample, which has been accounted for based on the presence of both types of charge carriers. The dielectric loss factor also decreases as the gr...

Nanometer silicon carbide powder synthesis and its dielectric behavior in the GHz range

Abstract: In this paper, the dielectric properties of nano-sized SiC powders have been investigated in the GHz frequency range. The polytypes of SiC have been changed from β type (3C) to α type (12H and 21R) by varying the aluminum contents and the reaction atmospheres. The β-SiC powder has much higher relative permittivity ( e ′ r =30∼50) and loss tangent ( tgδ =∼0.7) than α-SiC powders. Though the doping of Al and N decrease the resistivity of SiC to the order of 10 2 Ω cm, the pivotal factor on the dielectric behaviors is ion jump and dipole relaxation, namely the reorientation of lattice defect pairs (V Si –V C , Si C –C si ). The conductivity of SiC has little effect on the dielectric behaviors.

Dielectric Relaxation Time and Relaxation Time Distribution of Alcohol−Water Mixtures

Abstract: Complex permittivity was measured in the frequency range from 10 MHz to 20 GHz at 25 °C for water mixtures of 22 aliphatic alcohols. The molecular structures of these alcohols systematically changed with the number of carbon atoms and hydroxyl groups, and their positions in the molecules. The asymmetric shape of the frequency dependence of the dielectric loss for the primary relaxation process was observed for each mixture. The broadness of the asymmetric dielectric loss depends on the water content, and the broadest dielectric loss was observed in the water mole fraction range of 0.65 < xw < 0.85. There is a strong correlation between the broadness of dielectric loss and the number of carbon atoms in the alcohol molecule. Deviations of observed relaxation times from those estimated for ideal mixtures depend on the number of carbon atoms except for the mixtures of water and alcohols with large alkyl groups, which form a micelle-like structure. These experimental results are interpreted on the basis of a m...

Characterization of low dielectric constant polyaniline thin film synthesized by ac plasma polymerization technique

Abstract: Polyaniline thin films were prepared by ac plasma polymerization technique. Capacitance, dielectric loss, dielectric constant and ac conductivity of these films were investigated in the frequency range from 100 Hz to 1 MHz and in the temperature range from 300 to 373 K. Capacitance and dielectric loss decreased with frequency and increased with temperature. This type of behaviour was found to be in good agreement with an existing model. The ac conductivity σ(ω) was found to vary as ωs with the index s≤1. Annealing of polyaniline thin films in high vacuum at 373 K for 1 h was found to reduce the dielectric loss. FTIR studies reveal that the aromatic ring is retained in the polyaniline thin films, which enhances the thermal stability of the polymer films.

Dielectric Ceramics with Tungsten-bronze Structure in the BaO–Nd2O3–TiO2–Nb2O5 System

Abstract: Some tungsten-bronze compounds in the BaO–Nd2O3–TiO2–Nb2O5 system were prepared and characterized. Ba4Nd2Ti4Nb6O30 and Ba5NdTi3Nb7O30 had the filled tetragonal tungsten-bronze structure, and Ba3Nd3Ti5Nb5O30 consisted of the tetragonal tungsten-bronze major phase and a minor amount of secondary phase BaNd2Ti3O10. These compounds had significant relaxor behaviors, and the Curie temperatures (at 1 MHz) were 0 and 55 °C for Ba3Nd3Ti5Nb5O30 and Ba5NdTi3Nb7O30 ceramics, respectively. A high dielectric constant (213) combined with low dielectric loss (0.004 at 1 MHz) was obtained in Ba3Nd3Ti5Nb5O30 ceramics. In addition, the solid-solution range of BapNd6−pTi8−pNb2+pO30 was 3 < p ≤ 6.

Tunable dielectric compositions including low loss glass

Abstract: Tunable dielectric materials including an electronically tunable dielectric ceramic and a low loss glass additive are disclosed. The tunable dielectric may comprise a ferroelectric perskovite material such as barium strontium titanate. The glass additive may comprise boron, barium, calcium, lithium, manganese, silicon, zinc and/or aluminum-containing glasses having dielectric losses of less than 0.003 at 2 GHz. The materials may further include other additives such as non-tunable metal oxides and silicates. The low loss glass additive enables the materials to be sintered at relatively low temperatures while providing improved properties such as low microwave losses and high breakdown strengths.