Showing papers on "Dielectric loss published in 2006"

Piezoelectric properties in perovskite 0.948(K0.5Na0.5)NbO3–0.052LiSbO3 lead-free ceramics

Abstract: Lead-free piezoelectric ceramics, with the nominal composition of 0.948(K0.5Na0.5)NbO3–0.052LiSbO3 (KNN-LS5.2), were synthesized by conventional solid-state sintering, and the piezoelectric and electromechanical properties were characterized as a function of temperature. The Curie temperature of the KNN based perovskite material was found to be 368°C with an orthorhombic-tetragonal polymorphic phase transition (TO-T) temperature at approximately ∼35°C. The room temperature dielectric permittivity (e33T∕e0) and loss were found to be 1380 and 2%, respectively, with piezoelectric properties of k33∼62% and d33∼265pC∕N and k31∼30% and d31∼−116pC∕N. The temperature dependence of the properties mimicked the compositional variation seen in the proximity of a morphotropic phase boundary [e.g., lead zirconate titanate (PZT)], with a maxima in the dielectric and piezoelectric properties and a corresponding “softening” of the elastic properties. Unlike that found for PZT-type materials, the modified KNN material exhi...

Microwave Characteristics of (Zr, Sn)TiO4 and BaO‐PbO‐Nd2O3‐TiO2 Dielectric Resonators

Abstract: The microwave characteristics of two dielectric resonator materials were investigated. This research included (Zr, Sn)TiO4, a material having the characteristics of a dielectric constant K= 38, Q= 7000 at 7 GHz, and temperature coefficient of resonant frequency τf, = 0 ppm/°C. The investigation determined the relations between the dielectric loss and micro-structures of this ceramic. Analysis by X-ray microanalyzer made it clear that the addition of Fe2O3 increased the dielectric loss of this ceramic because the Fe ions diffused into the grain. The other material investigated was BaO-PbO-Nd2O3-TiO2, a ceramic having a dielectric constant of K= 88, Q= 5000 at 1 GHz, and τf= 0 ppm/°C. As this ceramic has a very high dielectric constant, it is useful for applications at frequencies <1 GHz.

Perovskite (Na0.5K0.5)1−x(LiSb)xNb1−xO3 lead-free piezoceramics

Abstract: Lead-free potassium sodium niobate piezoelectric ceramics substituted with lithium and antimony (Na0.5K0.5)1−x(LiSb)xNb1−xO3 have been synthesized by conventional solid state sintering method. Compositionally engineered around the orthorhombic-tetragonal polymorphic phase transition, the dielectric and piezoelectric properties were further enhanced with the addition of lithium and antimony substituted into the perovskite structure. The combined effects of lithium and antimony additions resulted in a downward shift in the orthorhombic-tetragonal (TO-T) without significantly reducing TC. The dielectric, piezoelectric, and electromechanical properties were found to be e∕e0>1300, d33>260pC∕N, and kp>50%, while maintaining low dielectric loss. The enhanced polarizability associated with the polymorphic TO-T transition and high TC transition (∼390°C) should provide a wide range of temperature operation.

Sintering and Electrical Properties of Lead-Free Na0.5K0.5NbO3 Piezoelectric Ceramics

Abstract: Lead-free Na0.5K0.5NbO3 (NKN) piezoelectric ceramics were fairly well densified at a relatively low temperature under atmospheric conditions. A relative density of 96%–99% can be achieved by either using high-energy attrition milling or adding 1 mol% oxide additives. It is suggested that ultra-fine starting powders by active milling or oxygen vacancies and even liquid phases from B-site oxide additives mainly lead to improved sintering. Not only were dielectric properties influenced by oxide additives, such as the Curie temperature (Tc) and dielectric loss (D), but also the ferroelectricity was modified. A relatively large remanent polarization was produced, ranging from 16 μC/cm2 for pure NKN to 23 μC/cm2 for ZnO-added NKN samples. The following dielectric and piezoelectric properties were obtained: relative permittivity ɛT33/ɛ0=570–650, planar mode electromechanical coupling factor, kp=32%–44%, and piezoelectric strain constant, d33=92–117 pC/N.

Frequency domain complex permittivity measurements at microwave frequencies

Abstract: Overview of frequency domain measurement techniques of the complex permittivity at microwave frequencies is presented. The methods are divided into two categories: resonant and non-resonant ones. In the first category several methods are discussed such as cavity resonator techniques, dielectric resonator techniques, open resonator techniques and resonators for non-destructive testing. The general theory of measurements of different materials in resonant structures is presented showing mathematical background, sources of uncertainties and theoretical and experimental limits. Methods of measurement of anisotropic materials are presented. In the second category, transmission–reflection techniques are overviewed including transmission line cells as well as free-space techniques.

Electromagnetic and microwave absorbing properties of multi-walled carbon nanotubes/polymer composites

Abstract: The preparation and characterization of CNTs/polymer (PET, PP, PE and varnish) composites were studied for microwave absorption applications in the range of 2–18 GHz. The results indicated the position of reflectivity peak moves to a lower frequency and the loss factors of composites increase with increasing CNTs concentrations. When CNTs concentration was above 4 wt%, there was a sharp increase of loss tangent. 4 wt% CNTs/PET and 8 wt% CNTs/varnish composites had considerable absorbing peak at 7.6 GHz, 15.3 GHz and achieved maximum absorbing value of 17.61 dB, 24.27 dB, respectively. In addition, the frequencies range for absorbing values exceeding 5 dB of CNTs/(PET, PP, varnish) composites are 13 GHz, 10 GHz and 6 GHz, respectively. The microwave absorption of CNTs composites can be mainly attributed to the dielectric loss rather than magnetic loss.

Synthesis, characterization and a.c. conductivity of polypyrrole/Y 2 O 3 composites

Abstract: Conducting polymer composites of polypyrrole/yttrium oxide (PPy/Y2O3) were synthesized byin situ polymerization of pyrrole with Y2O3 using FeCl3 as an oxidant. The Y2O3 is varied in five different weight percentages of PPy in PPy/Y2O3 composites. The synthesized polymer composites are characterized by infrared and X-ray diffraction techniques. The surface morphology of the composite is studied by scanning electron microscopy. The glass transition temperature of the polymer and its composite is discussed by DSC. Electrical conductivity of the compressed pellets depends on the concentration of Y2O3 in PPy. The frequency dependent a.c. conductivity reveals that the Y2O3 concentration in PPy is responsible for the variation of conductivity of the composites. Frequency dependent dielectric constant at room temperature for different composites are due to interfacial space charge (Maxwell Wagner) polarization leading to the large value of dielectric constant. Frequency dependent dielectric loss, as well as variation of dielectric loss as a function of mass percentage of Y2O3 is also presented and discussed.

Synthesis and dielectric properties of novel high-K polymer composites containing in-situ formed silver nanoparticles for embedded capacitor applications

Abstract: Dielectric properties of in-situ formed silver (Ag) incorporated carbon black (CB)/polymer composites were studied. In-situ formed Ag nanoparticles in the Ag/CB/epoxy composites increased the dielectric constant (K) value and decreased the dissipation factor (Df). The remarkably increased dielectric constant of the nanocomposite is due to the piling of charges at the extended interface of the interfacial polarization-based composites. The reduced dielectric loss might be due to the Coulomb blockade effect of the contained Ag nanoparticles, the well-known quantum effect of metal nanoparticles. The size, size distribution and loading level of metal nanoparticles in the nanocomposite were found to have significant influences on the dielectric properties of the nanocomposite system.

Study of room temperature magnetoelectric coupling in Ti substituted bismuth ferrite system

Abstract: Dielectric, magnetic, and magnetoelectric properties of Ti substituted bismuth ferrite (BiFeO3) ceramic synthesized by solid state reaction are reported. Ti substitution for Fe in BiFeO3 increased the room temperature electrical resistivity by approximately six orders of magnitude and also increased the dielectric constant and reduced the loss tangent. The remanent polarization, coercive field, and maximum polarization were 0.081μC∕cm2, 2.571kV∕cm, and 0.658μC∕cm2, respectively at 20kV∕cm. An anomaly in the dielectric constant and loss tangent around Neel temperature was observed. The ferroelectric and magnetic hysteresis loops were measured which are not really saturated in BiFe0.75Ti0.25O3 compound and represented a partial reversal. The magnetoelectric coupling between electric dipoles and magnetic dipoles at room temperature was demonstrated by measuring the effect of magnetic poling on ferroelectric hysteresis loop and the change in the dielectric constant with the external magnetic field.

Dielectric behavior of a metal-polymer composite with low percolation threshold

Abstract: Stainless steel fiber (SSF)/poly(vinylidene fluoride) composite is prepared via simple blending and hot pressing route. The dependence of the dielectric properties of the composite on both volume fraction of the fillers and frequency is investigated. The percolation threshold of the composite, 9.4vol% (0.094 volume fraction), is much lower than that of the common two phase metal particle-polymer composite. A dielectric constant of 427 is observed at 50Hz with 10vol% of SSF. Large enhancements of the ac conductivity and loss tangent are also observed near the percolation threshold. The dielectric properties are explained by percolation theory while the dielectric anomalies are attributed to the high slenderness ratio of the SSF fillers.

Measurements of Permittivity, Dielectric Loss Tangent, and Resistivity of Float-Zone Silicon at Microwave Frequencies

Abstract: The complex permittivity and resistivity of float-zone high-resistivity silicon were measured at microwave frequencies for temperatures from 10 up to 400 K employing dielectric-resonator and composite dielectric-resonator techniques. At temperatures below 25 K, where all free carriers are frozen out, loss-tangent values of the order of 2times10-4 were measured, suggesting the existence of hopping conductivity or surface charge carrier conductivity in this temperature range. Use of a composite dielectric-resonator technique enabled the measurement of materials having higher dielectric losses (or lower resistivities) with respect to the dielectric-resonator technique. The real part of permittivity of silicon proved to be frequency independent. Dielectric losses of high-resistivity silicon at microwave frequencies are mainly associated with conductivity and their behavior versus temperature can be satisfactory described by dc conductivity models, except at very low temperatures

Effect of cobalt substitution on the properties of nickel-copper ferrite

Abstract: Cobalt-substituted nickel–copper ferrite samples having the chemical formula Ni0.95−xCoxCu0.05Fe2O4, where x varies as 0.01, 0.02 and 0.03, were prepared by the standard double sintering ceramic technique. The formation of the ferrite phase was confirmed by x-ray diffraction (XRD) studies. Resistivity and thermo-emf variation with temperature were studied in the temperature range from room temperature to 773 K as a function of cobalt content. As the cobalt content increases, the resistivity of the ferrites decreases. AC conductivity measurements made in the frequency range 100 Hz–1 MHz show that conduction in these ferrites is due to small polaron hopping. The dielectric constant and loss tangent (tanδ) were measured at room temperature as a function of frequency in the range 20 Hz to 1 MHz. The room-temperature dielectric measurements show dispersion behaviour with increasing frequency. To understand the conduction mechanism, complex impedance measurements were carried out. The variation in saturation magnetization (Ms) with variation of cobalt content is also studied.

Microwave dielectric losses caused by lattice defects

Abstract: Dielectric loss tangent at microwave frequency is mainly determined by the anharmonic terms in the crystal's potential energy. In addition, there is a kind of lattice defect that increases the dielectric loss tangent seriously. This paper presents the experimental results for two materials; the system Ba(Zn,Ta)O 3 -BaZrO 3 and (Zr,Sn)TiO 4 . The dielectric loss tangents of the system Ba(Zn,Ta)O 3 -BaZrO 3 increases seriously when the B-site ions distribute disorderedly in the crystal. The doping of oxygen vacancies and acceptor ions in (Zr,Sn)TiO 4 increase tan δ by the way they increase the gradient and intercept of linear frequency dependency of tan δ. These experimental results are reasonably explained by Schlomann's theory. He predicted that the dielectric loss tangent increases when the ions are distributed disorderedly in a way that they break the periodic arrangement of charges in the crystal, and that the increase of tan δ is negligible if the disordered charge distribution maintains the charge neutrality within a short range of the lattice constant in the crystal.

Ferroelectric-dielectric tunable composites

Abstract: The dielectric response of ferroelectric-dielectric composites is theoretically addressed. Dielectric permittivity, tunability (relative change of the permittivity driven by dc electric field), and loss tangent are evaluated for various composite models. The analytical results for small dielectric concentration and relative tunability are obtained in terms of the traditional electrostatic consideration. The results for large tunability are obtained numerically. A method is proposed for the evaluation of the tunability and loss at large concentrations of the dielectric. The basic idea of the method is to reformulate the effective medium approach in terms of electrical energies stored and dissipated in the composite. The important practical conclusion of the paper is that, for random ferroelectric-dielectric composite, the addition of small amounts of a linear dielectric into the tunable ferroelectric results in an increase of the tunability of the mixture. The loss tangent of such composites is shown to be virtually unaffected by the addition of moderate amounts of the low-loss dielectric. The experimental data for (Ba,Sr)TiO3 based composites are analyzed in terms of the theory developed and shown to be in a reasonable agreement with the theoretical results. (c) 2006 American Institute of Physics.

Synthesis and properties of multiferroic La-modified BiFeO3 ceramics

Abstract: Multiferroic Bi(1−x)LaxFeO3 was synthesized by a modified Pechini approach. Optimal conditions for the synthesis of single-phase Bi(1−x)LaxFeO3 powder were reported. A conventional sintering process was used to fabricate Bi(1−x)LaxFeO3 ceramics. Ferroelectric and magnetic loops measured at room temperature indicate the coexistence of ferroelectricity and magnetism. The La modification of BiFeO3 has a beneficial effect on the ferroelectric and magnetic properties. The ceramic samples show a stable dielectric constant and quite low dielectric loss between 100 Hz and 10 MHz. The piezoelectric constants of Bi(1−x)LaxFeO3 ceramics were first reported.

Electric field dependent dielectric properties and high tunability of BaZrxTi1−xO3 relaxor ferroelectrics

Abstract: This letter reports the E-field tunable behavior of the environmental friendly lead-free perovskite BaZrxTi1−xO3 (x=050 and 060) relaxor ceramics in the temperature range from 300to30K dc electric field dependence of dielectric behavior of the ceramics has been studied The results have been analyzed in relation to tunability (%) and K factor of the tunable dielectric materials It is shown that manipulating the Zr:Ti concentration in BaZrxTi1−xO3 ceramics and optimizing the applied dc bias field the properties for specific applications in tunable filters, phase shifters, antennas, etc, can be tailored in the temperature range from 100to300K

Dielectric properties of mixed Li–Ni–Cd ferrites

Abstract: Ferrites with the general formula Li0.5Ni0.75−x/2Cdx/2Fe2O4 (where x = 0, 0.1, 0.3, 0.5, 0.7 and 0.9) were prepared by the standard double sintering ceramic method. X-ray diffraction analysis confirmed the single phase spinel structure of the samples. The variation of saturation magnetization (Ms) was studied as a function of Cd content. The dielectric constant (e') and dielectric loss tangent (tanδ) were measured at room temperature as a function of frequency in the range 100 Hz–1 MHz. These parameters decrease with increasing frequency for all of the samples. The compositional variation of e' and ρDC show an inverse trend of variation with each other.

Nonlinear Dielectric Response and Thermodynamic Heterogeneity in Liquids

Abstract: If large amplitude time-dependent fields (e.g., dielectric, magnetic, mechanical) are applied to a sample that displays relaxational modes, some energy of the external field is absorbed by the slow degrees of freedom. The weak coupling of these modes to the phonon bath leads to long persistence times of the resulting higher fictive temperature. Assuming heterogeneities regarding dielectric and thermal relaxation times, extremely strong nonlinear dielectric effects are predicted and experimentally verified. For glycerol at T = 213 K, the dielectric loss measured at 280 kV/cm increases by more than 6% over its low-field value. This nonlinearity shows a characteristic frequency dependence and implies that dielectric and thermal time constants are locally correlated in viscous liquids.

Decrease of dielectric loss in CaCu3Ti4O12 ceramics by La doping

Abstract: We have developed a novel route to reduce the dielectric loss of CaCu3Ti4O12 (CCTO) material based on the internal-barrier-layer-capacitance (IBLC) model. By the partial La-for-Ca substitution the dielectric loss was suppressed re-markably while the giant dielectric constant still remains. The sample of Ca0.8La0.2Cu3Ti4O12 exhibits a high dielectric con- stant over 3000 and a low dissipation factor below 0.015 at 10 kHz from 180 K to 300 K. The impedance spectroscopy analysis confirms that the decrease of dielectric loss is mainly due to the increase of conductivity in the CCTO grain/subgrain. Our result is expected to be able to promote practical applications. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

B-site donor and acceptor doped Aurivillius phase Bi3NbTiO9 ceramics

Abstract: The electrical properties of B-site donor and acceptor doped Aurivillius phase Bi 3 NbTiO 9 -based ceramics have been investigated. The effect of donor and acceptor doping on the dielectric constant, coercive field, dc conductivity and piezoelectric constant are presented. The band gap of Bi 3 NbTiO 9 (BNTO) is about 3.4 ± 0.2 eV, determined from high-temperature dc conductivity measurements. All of the ceramics are ferroelectrics with high Curie points (∼900 °C). In acceptor doped ceramics, a low-temperature peak in the dielectric loss tangent is explained in terms of a Debye-type relaxation that results from an oxygen ion-jump mechanism. The activation energy for the relaxation is calculated as 0.93 ± 0.05 eV. The reduction of the piezoelectric constant below 500 °C is produced by depolarization, which is produced by the switching of thermally unstable non-180° domain walls.

Loss mechanisms and high power piezoelectrics

Abstract: Heat generation is one of the significant problems in piezoelectrics for high power density applications. In this paper, we review the loss mechanisms in piezoelectrics first, followed by the heat generation processes for various drive conditions. Heat generation at off-resonance is caused mainly by dielectric loss tan δ′ (i.e., P-E hysteresis loss), not by mechanical loss, while the heat generation at resonance is mainly attributed to mechanical loss tan ′. Then, practical high power materials developed at Penn State is introduced, which exhibit the vibration velocity more than 1 m/s, leading to the power density capability 10 times of the commercially available “hard” PZTs. We propose a internal bias field model to explain the low loss and high power origin of these materials. Finally, using a low temperature sinterable “hard” PZT, we demonstrated a high power multilayer piezoelectric transformers

Decrease of dielectric loss in giant dielectric constant CaCu3 Ti4 O12 ceramics by adding CaTiO3

Abstract: CaCu3 Ti4 O12– x CaTiO3 ceramics ( x = 0 , 0.1 , 0.2 , 0.3 , 0.4 and 0.5) was studied by X-ray diffraction, scanning electron microscope and dielectric measurements. It was indicated that some CaTiO3 entered the boundaries of CaCu3 Ti4 O12 grains and/or subgrains. Dielectric measurement showed that the addition of CaTiO3 lowered the dielectric loss remarkably, especially at low frequencies, while the giant dielectric constant still remained. At room temperature, the dissipation factor of the x = 0.5 sample was decreased to ∼ 0.02 over the frequency range from 50 to 2000 Hz, and the dielectric constant was kept to be 4000. We explain this phenomenon in terms of internal barrier layer capacitance model by using the impedance spectroscopy analysis.

Influence of the relaxation of Maxwell-Wagner-Sillars polarization and dc conductivity on the dielectric behaviors of nylon 1010

Abstract: The effects of dc conductivity and Maxwell-Wagner-Sillars (MWS) polarization on the dielectric behaviors of nylon 1010 have been investigated by means of dielectric relaxation spectroscopy. The experimental dielectric data were analyzed within the formalisms of dielectric permittivity, complex electric modulus, and complex impedance. The results were discussed in terms of dc conductivity, MWS polarization, electrode polarization, and conductivity relaxation. The results revealed that the charge carrier transport is governed by the motion of the polymer chains. There was a transition temperature located between 100 and 110°C in the conductivity relaxation process, showing two different mechanisms for charge carrier movement. The change of charge carrier movement mechanisms was due to the motion of the polymeric chains in the interphase between amorphous and crystalline regions taking place at this temperature.

Dielectric relaxation in SrFe1∕2Nb1∕2O3

Abstract: The strontium iron niobate SrFe1∕2Nb1∕2O3 ceramic is synthesized by a solid-state reaction technique. The x-ray diffraction of the sample at room temperature shows a monoclinic phase. The dielectric permittivity and the loss tangent of the sample are measured in a frequency range from 50Hzto2MHz and in a temperature range from 143to473K. The frequency dependence of the loss peak is found to obey an Arrhenius law with an activation energy of 0.272eV. An analysis of the loss factor with frequency is performed by using the scaling behavior of the dielectric loss spectra. The scaling behavior of the dielectric loss spectra shows its temperature-independent nature. The relaxation mechanism is discussed in the framework of conductivity and impedance spectroscopy. The variation of dielectric constant with temperature is explained considering the space-charge polarization.

Effect of sintering conditions on the dielectric properties of CaCu3Ti4O12 and La2/3Cu3Ti4O12 ceramics : A comparative study

Abstract: The microstructural and dielectric properties of La2/3Cu3Ti4O12 (LCTO) ceramics were found to be less sensitive to the sintering conditions. In contrast, these had imprinting effects on the dielectric characteristics of CaCu3Ti4O12 (CCTO) ceramics. The dielectric constant of CCTO increased drastically with increase in sintering temperature and duration as a consequence of significant change in the microstructural and compositional heterogeneity, while the increase was nominal in the case of LCTO ceramics. The dielectric behavior of both the ceramics was explained based on the Maxwell–Wagner relaxation arising mostly from the interfaces between grains and the grain boundaries.