Variation Of Dielectric Properties Research Articles

Preparation and Characterization of Pb(Zr,Ti)O3 films prepared by a modified sol-gel route

ABSTRACTPb(Zr0.53Ti0.47)O3 (PZT) films have been fabricated on stainless steel substrates by a Polyvinylpirrolidone (PVP) modified sol-gel route. The single layer of about 0.26 μm was achieved by using the PVP-modified PZT sol, and Crack-free PZT films with thickness of up to 2.37 μm were fabricated by repeating the deposition process. The variations in crystallite orientation, microstructure, dielectric and ferroelectric properties of PZT films were investigated as a function of film thickness. Our results indicate that PZT films prepared on stainless steel substrates maintain good dielectric and ferroelectric properties.

Bone dielectric property variation as a function of mineralization at microwave frequencies.

A critical need exists for new imaging tools to more accurately characterize bone quality beyond the conventional modalities of dual energy X-ray absorptiometry (DXA), ultrasound speed of sound, and broadband attenuation measurements. In this paper we investigate the microwave dielectric properties of ex vivo trabecular bone with respect to bulk density measures. We exploit a variation in our tomographic imaging system in conjunction with a new soft prior regularization scheme that allows us to accurately recover the dielectric properties of small, regularly shaped and previously spatially defined volumes. We studied six excised porcine bone samples from which we extracted cylindrically shaped trabecular specimens from the femoral heads and carefully demarrowed each preparation. The samples were subsequently treated in an acid bath to incrementally remove volumes of hydroxyapatite, and we tested them with both the microwave measurement system and a micro-CT scanner. The measurements were performed at five density levels for each sample. The results show a strong correlation between both the permittivity and conductivity and bone volume fraction and suggest that microwave imaging may be a good candidate for evaluating overall bone health.

Microwave Imaging and Emerging Applications

Microwave Imaging and Emerging Applications

MWCNTs/SiO2 Composite System: Carrier Transmission, Twin-Percolation and Dielectric Properties

We synthesize composite systems of multi-wall carbon nanotubes (MWCNTs)/SiO2 by using the sol-gel method. The dielectric properties of the systems with different-concentration MWCNTs are studied. In our MWCNTs/SiO2 inorganic systems, the twin-percolation phenomenon exists when the concentrations of MWCNTs are 5–10% and 15–20%. The permittivity and conductivity have jumping changes. The twin-percolation phenomenon is attributed to the special transfer mechanism of MWCNTs in the system, determined by hopping and migrating electrons. Variations of dielectric properties and conductance of the MWCNTs/SiO2 systems are conformed to the percolation theory. The special percolation phenomenon and electric properties of MWCNTs/SiO2 can help us comprehend the conductivity mechanism of the MWCNTs/SiO2 systems effectively, and promote the development of a high performance function composite system.

Raman scattering, electronic structure and microwave dielectric properties of Ba([Mg 1− xZn x] 1/3Ta 2/3)O 3 ceramics

Effects of Zn substitution for Mg on the crystal structure, lattice vibrations and microwave dielectric properties of Ba(Mg 1/3,Ta 2/3)O 3 (BMT) ceramics were investigated. Raman scattering spectra for Ba([Mg 1− x Zn x ] 1/3Ta 2/3)O 3 (BMZT) ceramics, with x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0, were measured at room temperature. The Raman result shows a dominance of 1:2 ordered structure at all Zn substitution contents. All Raman modes shift to lower frequencies with increasing Zn substitution. Higher Qf value correlates well with narrower width of the breathing Raman mode A 1g(4) and larger relative intensity of 1:2 long-range-ordered mode E g(2) in BMZT solid solution. First-principle calculation was performed to investigate the electronic structure of 1:2 ordered BMT and Ba(Zn 1/3,Ta 2/3)O 3 (BZT). Covalent bond between Zn and O in BZT is much stronger than that between Mg and O in BMT due to the Zn 3 d orbital. Zn substitution for Mg leads to longer and weaker Ta–O bonds, which may be one reason for the variation of Raman spectroscopy and microwave dielectric properties of BMZT system.

Structural, magnetic and electrical properties of Al 3+ substituted Ni–Zn ferrite nanoparticles

Nanocrystalline ferrite materials having the general formula Ni 0.7Zn 0.3Fe 2− x Al x O 4 (0.0 ≤ x ≤ 0.5) have been synthesized by citrate-gel auto combustion method and characterized using X-ray diffraction (XRD), energy dispersive X-ray (EDX), field emission scanning electron microscopy (FE-SEM), dc magnetization, dielectric and impedance spectroscopy measurements. XRD studies confirm that all the samples show single phase cubic spinel structure. The crystallite size of Ni 0.7Zn 0.3Fe 2− x Al x O 4 (0.0 ≤ x ≤ 0.5) nanoparticles calculated using the Debye–Scherrer formula was found in the range of 13–17 nm. The value of lattice parameter ‘ a’ is found to decrease with increasing Al 3+ content. EDX patterns confirm the compositional formation of the synthesized samples. FE-SEM micrographs show that all the samples have nano-crystalline behavior and particles show spherical shape. The variation of dielectric properties ɛ′, ɛ″, and tan δ with frequency shows the dispersion behavior which is explained in the light of Maxwell–Wagner type of interfacial polarization in accordance with the Koop's phenomenological theory. The dc magnetization studies infer that magnetic moment of Ni 0.7Zn 0.3Fe 2− x Al x O 4 (0.0 ≤ x ≤ 0.5) nanoparticles was found to decrease with Al doping. Impedance spectroscopy techniques have been used to investigate the effect of grain and grain boundary on the electrical properties of the synthesized compounds.

Nd:YAG laser irradiation effects on electrical properties of polycrystalline Li 0.5Fe 2.5O 4

The polycrystalline spinel structured Li 0.5Fe 2.5O 4 ferrite have been prepared by conventional double sintering ceramic method. The samples were palletized and irradiated by Nd:YAG laser with different laser fluencies and characterized by infrared spectroscopy and DC electrical resistivity in order to obtain phase, crystal structure and conduction mechanism in pristine and irradiated samples. The infrared spectroscopy is employed to study the local symmetry and conduction mechanism in crystalline solids before and after irradiation. The DC electrical resistivity measured by two-probe technique from room temperature to beyond Curie temperature with steps of 10 K increases after laser irradiation. Variation of dielectric properties like dielectric constant and dielectric loss tangent is also measured as a function of temperature. A significant reduction in the values of dielectric constant and dielectric loss tangent has been observed with the increase of laser dose.

Structural and electrical properties of Cu doped NiFe 2O 4 nanoparticles prepared through modified citrate gel method

Nanoparticles of polycrystalline NiFe 2− x Cu x O 4 (0.0≤ x≤0.05) ferrites were prepared through the modified citrate-gel method. The samples were obtained as dried gel after the successful chemical reaction of their respective metal nitrate solutions in the midst of citric acid as catalyst. X-ray diffraction (XRD) and selective area electron diffraction (SAED) confirmed the single phase nature of all the samples with an average particle size of 19.8 (±1). Fourier transformation infrared spectroscopy (FTIR) shows the presence of two broad vibrational bands between 400 and 1000 cm −1 corresponding to the tetrahedral and the octahedral sites. The variation of dielectric properties ( ε′, ε″, tan δ) and ac conductivity ( σ ac), with frequency reveals that the dispersion is due to the Maxwell–Wagner type of interfacial polarization in general and due to hopping of charges between Fe +2 and Fe +3 as well as between Ni +2 and Ni +3 ions at B-sites. The complex impedance spectroscopy has been used to study the effect of grain and grain boundary on the electrical properties of all the ferrite nanoparticles.

Effect of Gd 3+ doping on magnetic, electric and dielectric properties of MgGd xFe 2− xO 4 ferrites processed by solid state reaction technique

MgGd x Fe 2− x O 4 ( x = 0.0, 0.05, 0.1 and 0.15) ferrites, with improved dc resistivity, initial permeability, saturation magnetization, and extremely low relative loss factor, have been synthesized by solid state reaction technique. The microstructures, electric, dielectric and magnetic properties have been investigated by means of X-ray diffraction, Keithley 2611 system, impedance analyzer and VSM respectively. The addition of Gadolinium in Mg ferrite has been shown to play a crucial role in enhancing the electric, dielectric and magnetic properties. The dc resistivity is increased by two orders of magnitude as compared to Mg ferrite. Saturation magnetization has been increased by two times and remnant magnetization has been increased by more than three times due to the doping of Gd 3+ ions in Mg ferrite. The relative loss factor was found to have very low values and is of the order of 10 −4–10 −5 in the frequency range 0.1–30 MHz. The variations of electric, dielectric and magnetic properties of the samples have been studied as a function of frequency and Gd 3+ ions concentration measured at room temperature. High resistivity and improved magnetic properties can be correlated with better compositional stoichiometry and the replacement of Fe 3+ ions by Gd 3+ ions. The mechanisms responsible to these results have been discussed in this paper.

Application of variable frequency technique on electrical dehydration of water-in-oil emulsion

Although the concept of optimum frequency had been proposed many years due to the various dielectrics, electrical and rheological properties of the water-in-oil (W/O) emulsion, the frequency of the pulsed DC electrical field was still kept constant during the electrical dehydration process in most of the industry application up to now. Taking into consideration of the increment of the droplets’ diameter and variation of various dielectric and rheological properties of the dispersion system during the dehydration process, the dehydration efficiency of pulsed DC electrical field with changing frequency during the dehydration process was investigated in this paper. The results showed that with appropriate combination of the frequencies, the dehydration efficiency of the pulsed DC electrical field can be significantly improved.

Enhanced dielectric properties of polypropylene based composite using Bi2S3 nanorod filler

AbstractA novel two-phase composite system using polypropylene (PP) as matrix and semiconductor bismuth sulfide (Bi2S3) as filler, was prepared by a simple process. Surfactant KH550 was chosen to modify the interface between inorganic fillers and organic PP matrix. The variations of dielectric properties of the Bi2S3/PP composites with the volume fraction of Bi2S3, frequency and temperature were discussed. The results reveal a percolative behavior of the composites with the threshold of 0.08. The composite is demonstrated to have good dielectric properties. The thermal stability of dielectric property and high breakdown strength of the composites show their potential application in film capacitor.

Structural, Electrical and Magnetic Properties of Nanocrystalline Mg-Co Ferrites Prepared by Co-Precipitation

Mg-Co nano crystalline ferrites having general formula Mg1-xCoxFe2O4 (x=0, 0.05, 0.1, 0.15, 0.2, 0.25) were prepared by co-precipitation method. X-ray powder diffraction (XRD) patterns of the prepared samples show the formation single spinel phase. The crystallite size, lattice parameters and porosity of samples were calculated by XRD data analysis as function of cobalt concentration. The crystallite size for each sample was calculated using the Scherrer formula considering the most intense (3 1 1) peak lies in the range 27-35 nm. The lattice parameters increased with increase of cobalt concentration. It is because of the fact that cobalt has greater ionic radius then magnesium. The dielectric constant, dielectric loss tangent and ac electrical conductivity of the prepared samples is also measure. The observed variation in electrical and dielectric properties is explained on the basis of cations distribution among tetrahedral (A) and octahedral (B) sites. The variance in saturation magnetization, remanence magnetization and magnetic moment was also measured from BH curve of samples.

Effect of MgWO 4 content on properties of Ba 0.5Sr 0.5TiO 3 composite ceramics for tunable microwave applications

xMgWO 4–(1 − x) Ba 0.5Sr 0.5TiO 3 ( x = 0.0, 5.0, 15.0, 25.0 and 35.0 wt%) composite ceramics were prepared via solid state reaction processing. Their structural and dielectric properties were systematically characterized. A significant increase in grain size was observed with increasing MgWO 4 content, which was accompanied by obvious variations in dielectric properties of the composite ceramics. It is found that the permittivity peaks of the samples gradually shifted to low temperatures with increasing MgWO 4 content. At the same time, tunabilities of the composite ceramics decreased, but their Q values increased. The sample with 35 wt% MgWO 4 possesses a high tunability of 16.8% (∼10 kHz), a low permittivity of 65 and an appropriate Q value of 309 (∼4.303 GHz), which meet the requirements of high power and impedance matching, thus making it a promising candidate for applications as electrically tunable microwave devices.

A study of the relationship between the rheo-dielectric effect and the elasticity of viscoelastic materials

Dielectrostriction is a rheo-dielectric phenomenon that relates the variation of dielectric properties of a material to deformation. For an initially isotropic material, two independent material parameters, called the strain-dielectric coefficients, α1 and α2, are required to describe dielectrostriction in terms of strain. Deformation affects a material’s dielectric properties in two ways: (a) by introducing anisotropy in the material, which is characterized by α1, and (b) by changing the volume density of the polarizable species, which is associated with (13α1+α2). Purely viscous fluids remain isotropic during any flow-induced deformation, and therefore the coefficient α1 is always zero. In this paper, the dielectrostriction effect is studied in viscoelastic materials that are formulated to possess different degrees of elasticity. A special planar capacitance sensor rosette was employed to measure the coefficients α1 and α2 for these viscoelastic materials. The relationship between the material’s elasticity and the coefficient α1 is discussed, together with some potential applications based on this relationship in the conclusion.

Optical constants detection in tin dioxide nano-size layers by surface plasmon resonance investigation

Optical constants of tin dioxide nano-size layers were detected using surface plasmons resonance research technique. Squared reflectance indexes difference as well as the ones with s- and p-polarized light are measured simultaneously. Obtained in the work the refraction coefficient of the tin dioxide film gives the possibility to judge about the structural perfection of the layer and confirms that the film has significant porosity, which is created during the decomposition of the polymer materials used as structuring additives. It is shown that the resonance condition for surface plasmons may be destroyed through the interaction of surface plasmons with surface roughness potential of the film (medium dielectric properties variation).

A Comparison of Dielectric Properties of Palm Oil with Mineral and Synthetic Types Insulating Liquid under Temperature Variation

Mineral oil is known to have a low biodegradability level and high susceptibility to the fire. These conditions motivate many researchers to look for alternative sources for insulating oil. One of the alternative liquid is palm oil. To verify the suitability of using palm oil as an insulating liquid, it is important to make dielectric properties comparison with the commonly used insulating liquid. This paper presents comparison of temperature effect on dielectric properties of palm oil with mineral type insulating liquid and silicone oil. The measured parameters were breakdown voltage, dissipation factor (tan δ), and dielectric constant. Breakdown voltage measurement was performed in accordance with IEC 156 standard, whereas, the dissipation factor and dielectric constant measurement were conducted based on IEC 60247 standard test methods. The results showed that variations of dielectric properties of palm oil to the temperature change, in general, have the same tendency with those of commonly used insulating liquids i.e. mineral oil and silicone oil. Breakdown voltages and dissipation factors of all tested oils were increased, while their dielectric constants were slightly decreased with the increase of temperature.

Study of dielectric and impedance properties of Mn ferrites

The paper reports on the effect of Al substitution on the structural and electrical properties of bulk ferrite series of basic composition MnFe 2−2 x Al 2 x O 4 (0.0≤ x≤0.5) synthesized using solid state reaction method. XRD analysis confirms that all the samples exhibit single phase cubic spinel structure excluding presence of any secondary phase. The dielectric constant shows a normal behaviour with frequency, whereas the loss tangent exhibits an anomalous behaviour with frequency for all compositions. Variation of dielectric properties and ac conductivity with frequency reveals that the dispersion is due to Maxwell–Wagner type of interfacial polarization in general and hopping of charge between Fe +2 and Fe +3 as well as between Mn +2 and Mn +3 ions at octahedral sites. The complex impedance plane spectra shows the presence of two semicircles up to x=0.2, and only one semicircle for the higher values of x. The analysis of the data shows that the resistive and capacitive properties of the Mn ferrite are mainly due to processes associated with grain and grain boundaries.

Structural, Magnetic, and Electrical Properties of Al3+ Substituted CuZn-ferrites

Nanocrystalline Cu0.5Zn0.5AlxFe2−xO2 (x=0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) ferrite materials were synthesized using standard solid state reaction technique. The effects of Al3+ contents on the structural, electrical, and magnetic properties were investigated. Single phase cubic spinel structure was revealed by X-ray diffraction analysis. The crystallite size was evaluated considering the most intense diffraction peak (311) using Scherrer formula. Lattice constant decreased, whereas porosity increased with the increase in Al3+ concentration. The value of saturation magnetization decreased with increasing aluminum contents. Temperature dependent value of direct current electrical resistivity has been determined. It is observed that the substitution of Al3+ has significant impact on the dielectric constant, tangent of dielectric loss angle and dielectric loss factor. The variation in dielectric properties was attributed to space charge polarization.

Variation in structural and dielectric properties of co-precipitated nanoparticles strontium ferrites due to value of pH

Nanoparticles of strontium ferrites with nominal composition SrFe 12O 19 were prepared by co-precipitation method, by decreasing pH from 13 to 8 with a regular step of 1. The secondary phase of α-Fe 2O 3 was increased with the decrease in pH. The crystallite size estimated from X-rays diffraction data was in the range 52–70 nm, which is much smaller than that already reported. Most of the particles formed had hexagonal structure, as observed by the scanning electron microscopy. Particle size and dielectric loss were increased where as dc electrical resistivity and dielectric constant were decreased with decrease in pH. The results show that the material synthesized with higher pH is phase pure and is potentially more suitable for high frequency applications.

High performance CaCu 3Ti 4O 12/cyanate ester composites with excellent dielectric properties and thermal resistance

High performance composites based on CaCu 3Ti 4O 12 (CCTO) and cyanate ester (CE) were successfully developed with desirable dielectric properties (high dielectric constant and low dissipation factor), outstanding thermal resistance and decreased curing temperature for embedded capacitors. CCTO was treated by γ-aminopropyl triethoxy silane, coded as CCTO(KH550), to investigate the interfacial effects on properties of composites. The addition of CCTO or CCTO(KH550) can significantly reduce the whole curing temperature of CE, while CCTO exhibits a higher catalytic capability than CCTO(KH550). Compared with cured CE resin, two kinds of composites exhibit greatly improved thermal resistance and real permittivity, meanwhile the dissipation factor is still very low. Because the interfacial polarization leads to the dependence of dielectric properties on the frequency and temperature, the improvement of interfacial adhesion for composites is beneficial to reduce the variation of dielectric properties with temperature and frequency, and thus improve the reliability of dielectric materials in applications.