Showing papers on "Dielectric loss published in 2007"

High Dielectric Performance of Polymer Composite Films Induced by a Percolating Interparticle Barrier Layer

Abstract: The mechanical flexibility and tunable properties of polymer-based materials make them attractive ones for a lot of applications. Exploring polymer-based dielectrics, such as ones used for capacitors and charge-storage applications, with high dielectric constant (high-j) has recently aroused considerable interest. Especially, motivated by higher function and further miniaturization of electronics, embedding (or integrating) polymer-based capacitors into the inner layers of organic printed circuit boards (PCBs) allows packaging substrate miniaturization and better electrical performance, which is a key for organic-based system-on-package technologies. But as capacitors, the relative dielectric constant j of general polymers (being good insulators) is too low (e.g., j< 5).Thus, a key issue is to substantially raise the dielectric constant of the polymers while retaining low dielectric loss. A few strategies have been developed to raise the j of polymer-based materials. A common approach is to add high-j ceramic fillers (e.g., BaTiO3) into a polymer. High loading of the ceramic fillers in the polymer composite, usually over 50 vol %, can increase j by about ten times relative to the polymer matrix, but dramatically decreases the adhesion of the composite (and increases its porosity) thus deteriorating the adaptability between the composite and the organic circuit boards. Another strategy is to fabricate percolative composite capacitors by using conductive fillers (e.g., metal particles). As the volume fraction f of the fillers increases to the vicinity of the percolation threshold fc, j of the composites can be dramatically enhanced as described by the well-known power law

Interfacial Effect on Dielectric Properties of Polymer Nanocomposites Filled with Core/Shell‐Structured Particles

Abstract: Novel polymer nanocomposites were prepared by solution processing with core/shell structured nanoparticles (carbonaceous shell coating on silver cores) as fillers. The organic carbonaceous shells act as interlayers between the Ag cores as well as with the polymer matrix. It is shown that the electrical properties of the interlayers play a dominative role in determining the dielectric behavior of the nanocomposites. Insulating interlayers reduce the tunnel current between neighboring Ag cores by causing potential barriers, endowing the nanocomposites with stable and high dielectric constants and low dielectric loss. Furthermore, the stable dielectric constants of the nanocomposites could be tuned by adjusting the thickness of the interlayers. Increasing the conductivity of the interlayers lowers the potential barriers, making the dielectric behavior of the nanocomposites more similar to that of conventional percolative composites.

Structural and multiferroic properties of La-modified BiFeO3 ceramics

Abstract: The coexistence of the magnetic and the electrical properties in lanthanum (La)-modified bismuth ferrite (Bi1−xLaxFeO3, x=0.05, 0.1, 0.15, and 0.2) ceramics was studied and compared with those of bismuth ferrite (BiFeO3). The presence of a small secondary phase of BiFeO3 (arises due to excess Bi2O3) was removed on La substitution at the Bi site, as observed in x-ray diffraction (XRD). The effect of La substitution on dielectric constant, loss tangent, and remnant polarization of the samples was studied in a wide range of temperature (77–400K) and frequency (1kHz–1MHz). The variation of magnetization, coercive field, and exchange bias with temperature (2–300K) and La concentration were investigated. These changes in the magnetic parameters with La doping along with those of the electron magnetic resonance parameters measured at 300K and 9.28GHz are understood in terms of increase in the magnetic anisotropy and magnetization. These results also show that stabilization of crystal structure and nonuniformity ...

Dielectric properties and relaxor behavior of rare-earth (La, Sm, Eu, Dy, Y) substituted barium zirconium titanate ceramics

Abstract: Based on the Ti-vacancy defect compensation model, (Ba1−xLnx)Zr0.2Ti0.8−x∕4O3 (Ln=La,Sm,Eu,Dy,Y) ceramics have been fabricated via the conventional solid-state reaction method. The microstructures, dielectric properties, and ferroelectric relaxor behavior of (Ba1−xLnx)Zr0.2Ti0.8−x∕4O3 ceramics have been investigated. The results indicate that rare-earth ions with various ionic radii enter the unit cell to substitute for A-site Ba2+ ions and inhibit the grain growth. The typical ferroelectric relaxor behavior is induced due to the rare-earth ions substitution. The diffuseness of the phase transition and the degree of ferroelectric relaxor behavior are enhanced, the TC is remarkably shifted to lower temperature, and the tunability is suppressed with the increase of x value and substituted ionic radius for (Ba1−xLnx)Zr0.2Ti0.8−x∕4O3 (x=0.005–0.04, Ln=La,Sm,Eu,Dy,Y) ceramics. Tunable ferroelectric materials with moderate dielectric constant and low dielectric loss can be obtained by manipulating the doping am...

Dipolar correlations and the dielectric permittivity of water.

Abstract: The static dielectric properties of liquid and solid water are investigated within linear response theory in the context of ab initio molecular dynamics. Using maximally localized Wannier functions to treat the macroscopic polarization we formulate a first-principles, parameter-free, generalization of Kirkwood's phenomenological theory. Our calculated static permittivity is in good agreement with experiment. Two effects of the hydrogen bonds, i.e., a significant increase of the average local moment and a local alignment of the molecular dipoles, contribute in almost equal measure to the unusually large dielectric constant of water.

Effects of pore shape and porosity on the properties of porous PZT 95/5 ceramics

Abstract: Porous lead zirconate titanate (PZT 95/5) ferroelectric ceramics were prepared by sintering compacts consisting of PZT and pore formers. The piezoelectric, dielectric and ferroelectric properties of porous PZT ceramics were investigated as a function of pore shape and porosity. Piezoelectric coefficient ( d 33 ), dielectric constant ( ɛ 33 ) and remnant polarization ( P r ) decreased with an increase in porosity, and the porous PZT ceramics with spherical pores exhibited better properties than that with irregular pores. Furthermore, the electrical conductivities of PZT ceramics were investigated to explain the phenomena that porous PZT ceramics exhibited lower dielectric loss (tan δ ) than dense PZT ceramics in the temperature range from 250 to 500 °C.

Growth and electrical properties of large size Pb(In1∕2Nb1∕2)O3–Pb(Mg1∕3Nb2∕3)O3–PbTiO3 crystals prepared by the vertical Bridgman technique

Abstract: Relaxor-based ferroelectric single crystals Pb(In1∕2Nb1∕2)O3–Pb(Mg1∕3Nb2∕3)O3–PbTiO3 (PIMNT) have been grown directly from their melt using the vertical Bridgman method, and their boules have reached the size of ϕ45×80mm. The as-grown PIMNT28/40/32 crystals on the (001) cuts exhibit a dielectric constant e∼5200, dielectric loss tanδ∼0.50%, piezoelectric strain constant d33∼1700–2200pC∕N, electromechanical coupling factors kt∼0.61 and k33∼0.92, coercive field Ec∼10.88kV∕cm, remanent polarization Pr∼46μC∕cm2, Curie temperature TC∼192°C, and rhombohedral to tetragonal phase transition temperature Trt∼119°C. Moreover, their piezoelectric properties show good thermal stability under the heat treatment at 105°C.

Metal–Dielectric Slot-Waveguide Structures for the Propagation of Surface Plasmon Polaritons at 1.55 $\mu{\hbox {m}}$

Abstract: We present a deep-subwavelength-size metal slot-waveguide structure which can efficiently propagate surface plasmon polaritons (SPPs) at 1.55 mum within a high-index material. Through a systematic design analysis, we investigate the intrinsic tradeoffs and suggest solutions to substantially increase the propagation length of SPPs combining high-index dielectrics and metal structures. By studying several metal/dielectric geometries, we have found that the slot-waveguide size can be significantly decreased by the use of high-index materials without compromising the overall propagation losses. Our analysis also indicates that the device size-scaling is ultimately limited by a cutoff thickness for the metal film in which the slot is defined. For film thicknesses below cutoff, radiation modes exist which leak out of the guiding region. For certain operating frequencies, the radiant energy leaks out into both free space modes as well as surface plasmons guided along the top/bottom metal surfaces of the device. We have shown that, by using a silicon filling, the cutoff thickness of a 100-nm-wide slot waveguide can be as small as 90 nm, compared with 750 nm for the unfilled reference structures. In addition, we have demonstrated that by the use of SiO2 gap regions surrounding the Si dielectric core in a 200times400-nm silver slot region (partially filled metal slot), we can considerably reduce the overall propagation losses to less than 0.14 dB/mum, corresponding to a propagation length of approximately 50 mum

Comparing calorimetric and dielectric polarization modes in viscous 2-ethyl-1-hexanol.

Abstract: Dielectric relaxation and dynamic heat capacity measurements are compared for 2-ethyl-1-hexanol near its glass transition temperature Tg in order to further clarify the origin of the prominent Debye-type loss peak observed in many monohydroxy alcohols and other hydrogen-bonding liquids. While the dielectric spectrum e″ displays two distinct polarization processes that are separated by a factor of 2000 in terms of the peak frequency, the heat capacity cp″ shows only a single peak. The dielectric process with lower amplitude and higher peak frequency coincides with the calorimetric signal, whereas the large dielectric Debye signal is not associated with calorimetric modes. The authors conclude that the Debye process corresponds to a transition among states which differ in energy only in the case of an external electric field.

Electrical properties of polyethylene/aluminum nanocomposites

Abstract: Understanding electrical properties of polymer nanocomposites is of great significance in order to diagnose and analyze physical and chemical behaviors of the composites as well as their own dielectric properties and can provide valuable data for improving the characteristics of the nanocomposites. In this work, the solution compounding method was used to prepare the polyethylene (PE)/aluminum (Al) nanocomposites. The dielectric permittivity and loss tangent of the PE/Al nanocomposites with different nanofiller loadings were investigated in the broad frequency range from 0.1 Hz to 10 MHz and the direct current (dc) conductivity and the dielectric breakdown strength of the PE/Al nanocomposites were also studied. The research results have shown that the dielectric permittivity shows different behaviors in the low and high frequency range. The permittivity values of the nanocomposites with the nanofiller loading levels of 0−48 wt % are found to show no percolative characteristics in the low frequency range b...

Percolative conductor/polymer composite films with significant dielectric properties

Abstract: A percolative film with conductive acetylene black introduced into β-polyvinylidene fluoride was prepared by dip-coating method. Percolation theory was employed to explain the dielectric behavior of polymer/conductor composite films. Experimental results showed that the dielectric constant of polymer/conductor composite films can reach 56 and the dielectric loss is below 0.15 when acetylene black concentration is in the neighborhood of percolation threshold (fc). The experimental results are in good agreement with classic percolation power law, with fc≈1.3% and exponent q≈0.53. Such composite films have a potential to become capacitors and can be easily fabricated due to its flexibility.

Dielectric properties of M-type barium hexaferrite prepared by co-precipitation

Abstract: Highly stoichiometric and phase pure barium hexaferrite has been synthesized by co-precipitation as well as a solid-state preparative method using high purity nitrates, oxides and carbonates of iron(III), barium(II) and ammonium hydroxide. The isochronal and isothermally measured complex permittivity and dielectric loss tangents over 1 MHz–1 GHz in frequency remained relatively stable until a sintering temperature between 1100 and 1300 °C. A high value of relative permittivity of 32 and low loss tangent of 0.0329 indicate suitable high frequency characteristics for barium hexaferrite. The measured apparent densities before and after each firing cycle showed a monotonic increase. The crystal structure determined from X-ray diffraction studies confirmed the presence of single phase belonging to the theoretical space group P63/mmc with calculated cell parameters of a = b = 5.895 A and c = 23.199 A. In addition the DTA hexaferrite formation temperature was found to be 1050 °C.

Compositional dependence of phase structure and electrical properties in (K0.42Na0.58)NbO3-LiSbO3 lead-free ceramics

Abstract: (1−x)(K0.42Na0.58)NbO3-xLiSbO3 [(1−x)KNN-xLS] lead-free piezoelectric ceramics were prepared by the conventional mixed oxide method. The compositional dependence of the phase structure and the electrical properties of the ceramics were studied. A morphotropic phase boundary (MPB) between the orthorhombic and tetragonal phases was identified in the composition range of 0.04

Phase transitional behavior and electrical properties of lead-free (K0.44Na0.52Li0.04)(Nb0.96−xTaxSb0.04)O3 piezoelectric ceramics

Abstract: Lead-free (K0.44Na0.52Li0.04)(Nb0.96−xTaxSb0.04)O3 piezoelectric ceramics have been synthesized by conventional solid state sintering process. Two morphotropic phase boundaries (MPBs) respectively corresponding to the orthorhombic to tetragonal and tetragonal to pseudocubic phases are observed with increasing x. The ceramics with x=0.20 between the two MPBs show significantly enhanced electrical properties, which are as follows: piezoelectric constant d33=252pC∕N, planar coupling coefficient kp=0.42, dielectric constant er=1503, and dielectric loss tanδ=0.025, and they show good stability. Lead-free superthin buzzer disks have been prepared by using piezoceramic membrane with x=0.20. (K0.44Na0.52Li0.04)(Nb0.96−xTaxSb0.04)O3 ceramics are very promising as lead-free replacements for lead zirconate titanate.

Grain size effect on the dielectric behavior of nanostructured Ni0.5Zn0.5Fe2O4

Abstract: The dielectric properties of nanocrystalline Ni0.5Zn0.5Fe2O4 spinel ferrite with various grain sizes, obtained by mechanically milling, have been studied using impedance measurements in the frequency range from 1 Hz to 10 MHz and in the temperature range from 300 to 823 K. The effect of milling, frequency, and temperature on the dielectric properties of nanocrystalline Ni-Zn ferrite is discussed. The real part of dielectric constant (e′) for the 14 nm grain size sample is found to be about an order of magnitude smaller than that of the bulk nickel zinc ferrite. The anomalous frequency dependence of e′ has been explained on the basis of hopping of both electrons and holes. The unusual increase in dielectric loss with milling is because of the increase in electrical conductivity due to oxygen vacancies introduced upon milling. The electrical modulus has been fitted to a stretched exponential function and the results clearly reveal the presence of the non-Debye type of dielectric relaxation in this material....

Super mode propagation in low index medium

Abstract: We investigate a novel waveguide geometry consisting of a high dielectric medium adjacent to a metal plane with a thin low dielectric spacer. The mechanism of operation is explained and simulation results are presented.

Measurement of Dielectric Constant and Loss Factor of the Dielectric Material at Microwave Frequencies

Abstract: A new technique to evaluate the dielectric constant and loss factor of a homogeneous dielectric material using rectangular shaped perturb cavity has been developed. The values of S-parameters are measured experimentally by placing the sample in the center of the cavity resonator. Sample under test is fabricated in the form of a cylinder. The real and imaginary part of the permittivity can be then calculated from the shift in the resonance frequency and Q-factor. The results of a Teflon sample are also tabulated.

Enhanced electric field tunable dielectric properties of BaZrxTi1−xO3 relaxor ferroelectrics

Abstract: The environmental friendly lead-free perovskite BaZrxTi1−xO3 (x=0.35, 0.40, and 0.45) relaxor ceramics are developed for the tunable microwave device applications such as tunable filters, phase shifters, antennas, etc. Electric field dependence of dielectric behavior of the ceramic samples has been studied in the temperature range from 300to15K for the tunable dielectric devices. The results have been analyzed in relation to tunability (%) and K factor of the tunable dielectric materials. Very high tunability (∼93%) as well as extremely high K factor (∼468) has been achieved by manipulating the Zr:Ti concentration in BaZrxTi1−xO3 ceramics.

The fabrication and material properties of compositionally multilayered Ba1−xSrxTiO3 thin films for realization of temperature insensitive tunable phase shifter devices

Abstract: Compositionally layered BaxSr1−xTiO3 (Ba0.60Sr0.40TiO3–Ba0.75Sr0.25TiO3–Ba0.90Sr0.10TiO3) 220nm thin film heterostructures were fabricated on Pt coated high resistivity Si substrates via the metal organic solution deposition technique (MOSD). Optimization of the material design was achieved by evaluating two integration schemes, namely, the single- and multianneal process protocols. Materials characterization demonstrated that both film process protocols resulted in smooth, dense, crack-free films with a single phase perovskite structure. Rutherford backscattering spectroscopy revealed compositionally distinct layers and severe elemental interdiffusion for the films fabricated via the multianneal and single-anneal process protocols, respectively. The retention of the compositional layering subsequent to film crystallization deemed the multianneal processed BaxSr1−xTiO3 (BST) film suitable for evaluation of dielectric properties. The dielectric properties were compared to both paraelectric uniform composit...

Influence of thermal annealing on the dielectric properties and electrical relaxation behaviour in nanostructured CoFe2O4 ferrite

Abstract: Nanocrystalline cobalt ferrite particles with the grain size of 8 nm were synthesized by using the co-precipitation technique and subsequently heat treated to obtain larger grain sizes. The effect of grain size, cation distribution, frequency and temperature on their dielectric properties has been studied. The dielectric constant (e') of 8 nm grains is found to be an order of magnitude higher and the dielectric loss (tanδ) is an order of magnitude smaller compared to those of the micron-size particles. The dielectric relaxation is found to be non-Debye in nature with the activation energy decreasing with thermal annealing due to structural perfection.