Showing papers on "Relative permittivity published in 2011"
TL;DR: In this article, the effects of frequency, temperature and microstructure (point defects, grain size and texture) on the ferroelectric properties of several Ferroelectric compositions, including BaTiO3, lead zirconate titanate (PZT), lead-free Na0.5K0.15Nd0.06FeO3.
Abstract: Triangular voltage waveform was employed to distinguish the contributions of dielectric permittivity, electric conductivity and domain switching in current-electric field curves. At the same time, it is shown how those contributions can affect the shape of the electric displacement — electric field loops (D–E loops). The effects of frequency, temperature and microstructure (point defects, grain size and texture) on the ferroelectric properties of several ferroelectric compositions is reported, including: BaTiO3; lead zirconate titanate (PZT); lead-free Na0.5K0.5NbO3; perovskite-like layer structured A2B2O7 with super high Curie point (Tc); Aurivillius phase ferroelectric Bi3.15Nd0.5Ti3O12; and multiferroic Bi0.89La0.05Tb0.06FeO3. This systematic study provides an instructive outline in the measurement of ferroelectric properties and the analysis and interpretation of experimental data.
285 citations
TL;DR: In this article, the results of an experimental investigation on the thermophysical, chemical and dielectric properties of three varieties of date palm wood (Phoenix dactylifera L.) from Biskra oasis in Algeria were reported.
264 citations
TL;DR: Li2WO4 with the phenacite structure has been shown to be chemically compatible with both silver and aluminum powders at 640°C and 660°C, respectively.
Abstract: A new ultra-low-temperature firing microwave dielectric ceramic, Li2WO4 with the phenacite structure, was prepared via solid-state reaction method. The Li2WO4 ceramic can be well sintered at 640°–660°C, with a microwave relative permittivity ∼5.5, a Q×f value about 62 000 GHz, and a negative temperature coefficient of −146 ppm/°C at 15.7 GHz. From an X-ray diffraction analysis, the Li2WO4 ceramic was found to be chemically compatible with both silver and aluminum powders at 640°C. All the results indicate that the Li2WO4 ceramic is a promising candidate for ultra-low temperature cofired ceramic technology, especially for dielectric substrate application.
196 citations
TL;DR: In this paper, a push-pull dipole is synthesized to be compatible with the silicone crosslinking chemistry, allowing for direct grafting to the crosslinker molecules in a one-step film formation process.
Abstract: A novel method is established for permittivity enhancement of a silicone matrix for dielectric elastomer actuators (DEAs) by molecular level modifications of the elastomer matrix. A push-pull dipole is synthesized to be compatible with the silicone crosslinking chemistry, allowing for direct grafting to the crosslinker molecules in a one-step film formation process. This method prevents agglomeration and yields elastomer films that are homogeneous down to the molecular level. The dipole-to-silicone network grafting reaction is studied by FTIR. The chemical, thermal, mechanical and electrical properties of films with dipole contents ranging from 0 wt% to 13.4 wt% were thoroughly characterized. The grafting of dipoles modifies the relative permittivity and the stiffness, resulting in the actuation strain at a given electrical field being improved by a factor of six. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
186 citations
TL;DR: In this article, the dielectric, electrical and structural properties of (1−x) 0.94Bi1/2Na1/ 2TiO3 (BNT)-BT-xKNN with x=0.18 were investigated as potential candidates for high-temperature capacitors with a working temperature far beyond 200°C.
Abstract: The dielectric, electrical and structural properties of (1–x)(0.94Bi1/2Na1/2TiO3–0.06BaTiO3)–xK0.5Na0.5NbO3 (BNT–BT–xKNN) with x=0.09, 0.12, 0.15, and 0.18 were investigated as potential candidates for high-temperature capacitors with a working temperature far beyond 200 °C. Temperature dependent dielectric permittivity (e) showed two local broad maxima that at the optimal composition of KNN (x=0.18) are combined to form a plateau. This then results in a highly temperature-insensitive permittivity up to ∼300 °C at the expense of a small reduction in absolute permittivity values. High-temperature in situ x-ray diffraction study showed pseudocubic symmetry without obvious structural changes, which implies that the dielectric anomalies observed could only be a consequence of a slight change in space group. BNT–BT–0.18KNN showed a permittivity of ∼2150 at the frequency of 1 kHz at 150 °C with a normalized permittivity e/e150 °C varying no more than ±10% from 43 to 319 °C. With very good electrical properties ...
176 citations
TL;DR: In this paper, the authors compared the crystal structure measured in situ as a function of an applied electric field with the in situ X-ray experiment, and showed that small additions of BZT led to an irreversible phase transition into a ferroelectric phase with remanent polarization and a reduced relative permittivity.
Abstract: Morphotropic phase boundary (Bi1/2Na1/2)TiO3–(Bi1/2K1/2)TiO3 (BNT–BKT), was modified with increasing additions of Bi(Zn1/2Ti1/2)O3 (BZT). Microstructure, electric-field-induced strain and polarization, dielectric permittivity, and temperature-dependent piezoelectric coefficient were investigated and compared with crystal structure measured in situ as a function of applied electric field. Furthermore, permittivity and piezoelectric coefficient were characterized as a function of electric field. For small additions of BZT, an applied electric field leads to an irreversible phase transition into a ferroelectric phase with remanent polarization and a reduced relative permittivity. Increasing the content of BZT increased the threshold field for the transition. For additions of more than 2 mol% BZT, the piezoelectric coefficient dropped, permittivity remained almost constant, and a high normalized strain of up to 500 pm/V was observed. However, no field-dependent structural change was evidenced by the in situ X-ray experiment.
118 citations
TL;DR: In this article, the authors reported a nature indefinite permittivity in crystalline graphite that exhibits negative group refraction at ultraviolet region and a hyperbolic equifrequency contour was obtained from ellipsometry data at 254 nm.
Abstract: In this work, we report a nature indefinite permittivity in crystalline graphite that exhibits negative group refraction at ultraviolet region. A hyperbolic equifrequency contour was obtained from ellipsometry data at 254 nm and an all angle negative refraction was verified experimentally. The indefinite permittivity is attributed to extremely strong anisotropy in the crystal structure and the hybrid electronic transitions. This result not only explores a route toward natural negative-index materials, but also holds a promise for ultraviolet hyperlens, which may lead to a breakthrough in nanolithography for the next generation of electronics.
102 citations
TL;DR: In this paper, the Li2(M2+)2Mo3O12 and Li3(M3+)Mo 3O12 (M=Zn, Ca, Al, and In) lyonsite-related structures were prepared using a solid-state reaction method.
Abstract: In this work, the Li2(M2+)2Mo3O12 and Li3(M3+)Mo3O12 (M=Zn, Ca, Al, and In) lyonsite-related structures were prepared using a solid-state reaction method. Single-phase lyonsite materials were formed for the following compositions Li2Zn2Mo3O12, Li3AlMo3O12, and Li3InMo3O12 ceramics. Whereas, the Li2Ca2Mo3O12 batched compositions produced Li2MoO4 and CaMoO4 phases. All the four ceramics did not react with Ag and Al powders at their optimal sintering temperatures, which will permit the possibility of cofired electrodes with these metallurgies. The Li2Zn2Mo3O12 ceramic can be sintered at 630°C with a relative permittivity of 11.1, a Q×f value of ∼70 000 GHz, and a temperature coefficient of −90 ppm/°C at 14.6 GHz. The Li3AlMo3O12 ceramic sintered at 570°C has a relative permittivity of 9.5, a Q×f value of ∼50 000 GHz, and a temperature coefficient of −73 ppm/°C at 14.1 GHz. The Li3InMo3O12 ceramic sintered at 630°C has a relative permittivity of 9.8, a Q×f value of ∼36 000 GHz, and a temperature coefficient of −73 ppm/°C at 15.0 GHz. These ceramics are a good candidate for the expanding family of ultra-low temperature cofired ceramic technologies, for filter and substrate applications at the high-frequency range.
86 citations
TL;DR: In this article, a new L-shaped chiral structure working in microwave and optical frequency bands has been designed and simulated, and the results show that the exceptionally strong optical activity is found for the L-shape chiral structures.
Abstract: A new L-shaped chiral structure working in microwave and optical frequency bands has been designed and simulated. The circular dichroism, ellipticity angle, polarization azimuth rotation angle, and efiective parameters of this structure, including relative permittivity, relative permeability, chiral parameter and refractive index, are retrieved from simulated transmission and re∞ection spectra. The results show that the exceptionally strong optical activity is found for the L-shaped chiral structure. Because of the large chiral parameter of this structure, negative refractive index of one circularly polarized wave can be obtained without simultaneously negative permittivity and negative permeability.
84 citations
TL;DR: In this article, the impedance and dielectric properties of Ag/Al2O3 composites are investigated experimentally in the frequency range from 100 MHz to 1 GHz, and equivalent circuit analysis and numerical simulations are carried out.
Abstract: The impedance and dielectric properties of Ag/Al2O3 composites are investigated experimentally in the frequency range from 100 MHz to 1 GHz. Besides, equivalent circuit analysis and numerical simulations were carried out. For the composites with sufficiently high silver loading, current paths were formed and negative permittivity appeared. The negative permittivity can be well described by lossy Drude model. Moreover, the negative permittivity sample manifests inductive characteristic and shunt inductors are added to its equivalent circuit. Numerical simulations show that the interconnection of silver particles results in negative permittivity, hence the serious attenuation of electromagnetic waves.
83 citations
20 Oct 2011
TL;DR: In this article, a review of techniques used for measurements of permittivity and permeability of materials for quasi-static electromagnetic field is presented, where the authors focus on the measurement of material properties.
Abstract: The review of techniques used for measurements of permittivity and permeability of materials for quasi-static electromagnetic field.
TL;DR: In this paper, negative capacitors are used to create superluminal waveguides for broadband leaky-wave antennas, which cancels part of the dielectric constant within the waveguide to provide a broadband relative permittivity between 0 and 1.
Abstract: Non-Foster circuits such as negative capacitors can be used to create superluminal waveguides for broadband leaky-wave antennas. The negative capacitors effectively cancel part of the dielectric constant within the waveguide to provide a broadband relative permittivity between 0 and 1. When used as a leaky-wave antenna, the beam angle is independent of frequency over a broad bandwidth because the waveguide provides a frequency-independent phase velocity greater than the vacuum speed of light. Thus, this approach eliminates beam squint, which is a primary drawback of passive leaky-wave antenna designs. Simulation results using ideal negative capacitors are presented, and the effects of causality are analyzed.
TL;DR: In this article, the ECH 2 O EC-5 and 5TE sensors were evaluated with coarse sand and silty clay loam soil samples, and the performance of the correction functions for the 5TE sensor was evaluated using coarse-grained soil samples.
Abstract: The measurement accuracy of low-cost electromagnetic soil water content sensors is often deteriorated by temperature and soil bulk electrical conductivity effects. This study aimed to quantify these effects for the ECH 2 O EC-5 and 5TE sensors and to derive and test correction functions. In a first experiment, the temperature of eight reference liquids with permittivity ranging from 7 to 42 was varied from 5 to 40°C. Both sensor types showed an underestimation of permittivity for low temperature (5–25°C) and an overestimation for high temperature (25–40°C). Next, NaCl was added to increase the conductivity of the reference liquids (up to ∼2.5 dS m −1 for a permittivity of 26–42, up to ∼1.5 dS m −1 for a permittivity of 22–26). The permittivity measured with both sensors showed a strong and complicated dependence on electrical conductivity, with both under- and overestimation of permittivity. Using these experimental data, we derived empirical correction functions. The performance of the correction functions for the 5TE sensor was evaluated using coarse sand and silty clay loam soil samples. After correcting for temperature effects, the measured permittivity corresponded well with theoretical predictions from a dielectric mixing model for soil with low electrical conductivity. The conductivity correction function also improved the accuracy of the soil moisture measurements, but only within the validity range of this function. Finally, both temperature and electrical conductivity of the silty clay loam were varied and a sequential application of both correction functions also resulted in permittivity measurements that corresponded well with model predictions.
TL;DR: In this article, a grafting of conducting polymer (poly-aniline) to the elastomer backbone, leading to molecular composites, was performed to enhance the relative permittivity of the dielectric elastomers.
Abstract: Strain sensors based on dielectric elastomer capacitors function by the direct coupling of mechanical deformations with the capacitance. The coupling can be improved by enhancing the relative permittivity of the dielectric elastomer. Here, this is carried out through the grafting of conducting polymer (poly-aniline) to the elastomer backbone, leading to molecular composites. An enhancement in capacitance response of 46 times is observed. This could help to extend the possible range of miniaturization towards even smaller device features.
TL;DR: In this paper, the dielectric response of all samples was studied by means of broadband dielectoric spectroscopy, over a wide temperature (from 30°C to 160°C) and frequency (from 10 −1 ǫ to 10ÂMHz) range.
Abstract: Ceramic–polymer composites incorporating ferroelectric and piezoelectric crystal particles, randomly distributed within the polymer matrix represent a novel class of materials. Composites including ferroelectric and/or piezoelectric particles are expected to exhibit functional properties because of the varying polarization of the ceramic particles. In the present study polymer matrix/ZnO/BaTiO 3 composites were prepared, in different filler concentrations. The dielectric response of all samples was studied by means of broadband dielectric spectroscopy, over a wide temperature (from 30 °C to 160 °C) and frequency (from 10 −1 Hz to 10 MHz) range. Experimental data were analyzed by means of dielectric permittivity and electric modulus formalisms. Dielectric permittivity and loss are increasing with ceramic filler and diminishing rapidly with frequency. The functionality of the composite systems is related to the abrupt variation of the real part of permittivity, in the vicinity of the characteristic Curie temperature of BaTiO 3 , and to the relaxing polarization of the ZnO particles.
TL;DR: In this paper, a citrate gel auto-combustion route was used to produce ferrites with the general formula Cu 1− x Zn x FeMnO 4 (where 0 ≤ x ≤ 1).
TL;DR: In this article, the 1-3 type porous PZT ceramics with high porosity were fabricated by freeze-casting process and all samples possessed high piezoelectric coefficient (d33).
Abstract: Porous PZT ceramics have drawn an increasing amount of interest in recent years due to their superior properties compared with the dense material. However, researchers have usually dedicated effort to 0–3 and 3–3 type porous PZT ceramics and little attention has been focused on 1–3 type. The 1–3 type porous PZT ceramics with high porosity were fabricated in this study by freeze-casting process. All samples possessed high piezoelectric coefficient (d33) with high porosity owing to the special one-dimensional ordered porous structure along the poling direction. The d33 values increased by either improving the pore channel orientation level or decreasing pore size. The relative permittivity improved only with the enhancement of pore channel orientation level. The acoustic impedances ranged from 1.45 to 1.35 MRayls which could match well with those of biological tissue or water; therefore, this material would be beneficial in hydrophone applications.
TL;DR: In this paper, the structural morphology of the Ni1−xCoxFe2O4 nanoparticles was carried out using scanning electron microscopy (SEM) and the results showed the spherical shaped nanoparticles varying in the range of 16−40nm.
TL;DR: In this article, the effect of non-uniform permittivity profiles on the impedance of a film with a uniform permitivity and a resistivity that varies along its thickness according to a power-law is investigated.
Abstract: A recent proposed model showed that the impedance of a film with a uniform permittivity and a resistivity that varies along its thickness according to a power-law is in the form of a constant phase element (CPE). This model is further considered in order to assess the effect of non-uniform permittivity profiles. It is shown that a power-law permittivity profile is also compatible with a CPE behavior when resistivity and permittivity vary in opposite ways along the film thickness. This work shows that, for important classes of materials which show CPE behavior, relaxation of the assumption of a uniform permittivity does not alter the conclusions developed in the earlier work, and the formula relating film properties to CPE parameters is shown to apply.
TL;DR: A polymer composite was prepared by embedding fillers made of self-passivated aluminum particles in two kind of sizes, micrometer size and nanometer size with different volume proportions into polyvinylidene fluoride matrix and the thermal conductivity and dielectric properties of the composite were studied.
Abstract: A polymer composite was prepared by embedding fillers made of self-passivated aluminum particles in two kind of sizes, micrometer size and nanometer size with different volume proportions into polyvinylidene fluoride matrix. The thermal conductivity and dielectric properties of the composite were studied. The results showed that the thermal conductivity of composites was significantly increased to 3.258 W∕mK when the volume proportion of micrometer size Al particles to nanometer size Al particles is at 20:1, also the relative permittivity was about 75.8 at 1 MHz. The effective simulation model values were in good accordance with experimental results.
TL;DR: Methodology to compute the relative static dielectric permittivity and dielectic relaxation time of molecular liquids is reviewed and explicit formulas are given for the external field method in the case of simulations using a spherical cutoff.
Abstract: Methodology to compute the relative static dielectric permittivity and dielectric relaxation time of molecular liquids is reviewed and explicit formulas are given for the external field method in the case of simulations using a spherical cutoff, in which the background dielectric permittivity (ecs) can be larger than one, in combination with a Poisson-Boltzmann reaction-field approximation for long-range electrostatic interactions. The external field method is simple to implement and computationally efficient. It is particularly suitable for polarizable molecular models with zero permanent dipole moment and for coarse-grained molecular models with ecs > 1. The dielectric permittivities and relaxation times of water (H2O), dimethylsulfoxide (DMSO), methanol (MeOH), and chloroform (CHCl3), which range from 2 to 80 and from 5 ps to 50 ps, respectively, were calculated as an illustration.
TL;DR: The present mini review is focused on introducing the generalized Stern theory of an EDL, which takes into account the orientational ordering of water molecules, and introduces two Langevin models for spatial variation of the relative permittivity for point-like and finite sized ions.
Abstract: The interaction between a charged metal implant surface and a surrounding body fluid (electrolyte solution) leads to ion redistribution and thus to formation of an electrical double layer (EDL). The physical properties of the EDL contribute essentially to the formation of the complex implant-biosystem interface. Study of the EDL began in 1879 by Hermann von Helmholtz and still today remains a scientific challenge. The present mini review is focused on introducing the generalized Stern theory of an EDL, which takes into account the orientational ordering of water molecules. To ascertain the plausibility of the generalized Stern models described, we follow the classical model of Stern and introduce two Langevin models for spatial variation of the relative permittivity for point-like and finite sized ions. We attempt to uncover the subtle interplay between water ordering and finite sized ions and their impact on the electric potential near the charged implant surface. Two complementary effects appear to account for the spatial dependency of the relative permittivity near the charged implant surface — the dipole moment vectors of water molecules are predominantly oriented towards the surface and water molecules are depleted due to the accumulation of counterions. At the end the expressions for relative permittivity in both Langevin models were generalized by also taking into account the cavity and reaction field.
TL;DR: In this article, the relative permittivity of water from 100 Hz to 1 MHz was studied and it was shown that there is a frequency where this parameter is independent of temperature, and called this the isopermitive point.
TL;DR: In this paper, the effects of nano-BaTiO3 particles on the dielectric, thermophysical (thermal conductivity) and mechanical properties of EVM composites were investigated.
Abstract: This paper reports on the effects of nano-BaTiO3 particles on the dielectric, thermophysical (thermal conductivity) and mechanical properties of ethylene-vinyl acetate (EVM) elastomer/BaTiO3 microcomposites. The EVM composites with nano-, micro- and nano/micro hybrid BaTiO3 fillers have been prepared by melt compounding. The results showed that the addition of nano-BaTiO3 particles to micro- BaTiO3/EVM composites could lead to an enhancement in permittivity, thermal conductivity and mechanical strength when compared with the micro-BaTiO3/EVM composites with the same total filler content, whereas the dielectric strength did not show significant difference and the dielectric loss tangent increased slightly. The Maxwell-Garnett effective medium model was used to analyze the BaTiO3 concentration dependence of relative permittivity of the composites.
TL;DR: In this article, a preformed La2NiMnO6 (LNMO) was annealed in air, oxygen, or N2 atmosphere and characterized by powder x-ray diffraction (XRD), neutron diffraction, superconducting quantum interference device magnetometry, and dielectric analysis.
Abstract: La2NiMnO6 (LNMO) was prepared by a combustion method followed by heating at high temperature. Subsequently, the preformed LNMO was annealed in air, oxygen, or N2 atmosphere and characterized by powder x-ray diffraction (XRD), neutron diffraction, superconducting quantum interference device magnetometry, and dielectric analysis. Structural studies by XRD and neutron diffraction revealed the coexistence of partially cation disordered monoclinic (31%) and rhombohedral (69%) phases in the sample annealed in air. However, the sample annealed in oxygen shows about 50:50% of monoclinic and rhombohedral phases. Relaxor-like behavior with relative permittivity of the order of 104 was observed in the sample annealed in air, while relative permittivity decreases to about 200 in samples annealed in oxygen atmosphere. The magnetic properties indicate a well-defined ferromagnetic phase in the oxygen-annealed sample compared to a feeble ferromagnetic signature in the air-annealed one. The dielectric and ferromagnetism of LNMO samples have been related to formation and annihilation of oxygen vacancies.
TL;DR: In this paper, an electrostatic-based vibration energy scavenging scheme using a two-layer configuration made of a high permittivity material and a low layer of variable thickness is presented.
TL;DR: Impedance spectroscopy was applied to determine glucose concentration in the interstitial fluid for its potential use in diabetic monitoring and changes within the physiological range of glucose were small and appeared to be within the measurement error.
TL;DR: In this article, the authors used rotation and seeding with a previously prepared material to tune the crystallization of the zeolitic imidazolate framework ZIF-20.
Abstract: The crystallization of the zeolitic imidazolate framework ZIF-20 has been tuned from the point of view of crystal size and aggregation by using rotation and seeding with a previously prepared material. In addition, the activation of ZIF-20 by solvent extraction has been found to be in correlation with the relative permittivity of the solvent. High permittivity solvents (acetone and methanol) extract more guest dimethylformamide but amorphize the structure, while those with low permittivity (n-pentane and chloroform) preserve the crystallinity of ZIF-20. The dispersion in commercial polysulfone of the small synthesized ZIF-20 particles obtained with low aggregation results in an improved O2-selective mixed matrix membrane (O2 permeability and O2/N2 selectivity being 1.0 (±0.0) Barrer and 6.7 (±0.5), respectively).
TL;DR: In this article, the effect of acceptor dopant concentration on the mobility of ferroelectric domain walls was studied in PbZr0.52Ti0.48O3 (PZT) films.
Abstract: Mn-doped PbZr0.52Ti0.48O3 (PZT) films were utilized to study the effect of acceptor dopant concentration on the mobility of ferroelectric domain walls. For chemical solution deposited PZT films between ∼0.5–2μm in thickness doped with 1–2mol.% Mn, the low field relative permittivity remained between 900 and 1000. With increasing Mn concentration, a threshold field developed in the ac field dependence of the relative permittivity. Furthermore, both the reversible and irreversible Rayleigh constants decreased. These observations are consistent with the possibility that MnTi’–VO•• (or MnTi’’–VO••) defect dipoles act as strong pinning centers.
TL;DR: In this paper, the 0.3Li2TiO3-0.7Li(Zn0.5Ti1.5)O4 ceramic was prepared via the conventional solid state reaction route, and the phase composition, microstructure, and sintering behavior were investigated.