Papers by Keyword: Dielectric Constant

Abstract: Conductive particle fillers could improve the dielectric properties of the polymer matrix. By solvent casting method, different volume fraction of nanosilver particles were added into the PVDF film to prepare Ag/PVDF composite film so as to increase the dielectric properties of the materials. SEM was used to analyze the microstructure of the films. SEM images show that nanoAg filler particles were uniformly distributed throughout the whole matrix of the composite films. Dielectric property tests show that with the increase of nanoAg content, the dielectric constants of the composites increase first and decrease later while the dielectric losses decrease first and increase later. In the case of the optimal 17vol% Ag content, the dielectric constant of the composite film is the highest (14.5 at 100 Hz) with lower dielectric loss, and the energy storage density is relatively high (0.340 J·cm⁻³).

Abstract: (y) Li_0.5Ni_0.7Zn_0.05Fe₂O₄ + (1-y) Ba_0.5Sr_0.5TiO₃ magnetoelectric composites with y = 0.1, 0.3 and 0.5 were prepared by a conventional standard double sintering ceramic technique. X-ray diffraction analysis confirmed the phase formation of ferrite, ferroelectric and their composites. logρ_dc Vs 1/T graphs reveal that the dc resistivity decreases with increasing temperature exhibiting semiconductor behavior. The plots of logσ_ac Vs logω² are almost linear indicating that the conductivity increases with increase in frequency i.e. conductivity in the composites is due to small poloron hopping. Dielectric constant (έ) and dielectric loss (tan δ) were studied as a function of frequency in the range 100Hz–1MHz which reveal the normal dielectric behavior except the composite with y = 0.1and as a function of temperature at four fixed frequencies (i.e. 100Hz, 1KHz, 10KHz, 100KHz). ME voltage coefficient decreases with increase in ferrite content and was observed to be maximum of about 7.495 mV/cmOe for S₁ i.e. (0.1) Li_0.5Ni_0.7Zn_0.05Fe₂O₄ + (0.9) Ba_0.5Sr_0.5TiO₃ composite.

Abstract: Polydiacetylenes are a type of highly conjugated polymers, and highly polar species are obtained when these polymers contain donor-acceptor azobenzene entities. In this paper the synthesis, characterization and evaluation of the dielectric constant of two polydiacetylenes containing azobenzenes as pendant groups are discussed. The Azobenzene chromophores are covalently bonded to the main chain, and their polarity is defined by an electro-donor (amine) and an electro-acceptor group (nitro or chlorine) bonded to the ends of a conjugated azobenzene structure. Both polymers were processed into plates of 1cm diameter x 0.674 mm thickness using a thermo mechanic technique. Their dielectric constants were evaluated respect to the temperature in a range of frequency of 110 MHz-1.32 GHz, from room temperature to close to their respective T_g. The dielectric constant for the polymer containing the nitro group was higher than it for polymer containing the chloride atom at all temperatures. It is discussed in terms of the ability to nitro and chloride to attract electronic density.

Abstract: Single phase polycrystalline with = 0, 0.01 and 0.02 were synthesized by conventional solid state reaction method. The X-ray diffraction shows that the ceramic samples has hexagonal Wurtzite structure with a space group of p6₃mc and average crystallite size in the range 52 - 88 nm. The dielectric and electrical properties were studied within the temperature range 30 °C to 500 °C under air atmosphere as function of frequency (10 kHz). The electrical properties of grain interior and grain boundary have been studied by using the impedance spectroscopy and follow the non-Debye relaxation process. It was observed that the AC conductivity of ceramic samples following the Universal power law within the frequency range 1kHz to 1 MHz. The activation energy of Pure is 0.29 eV was calculated by using the Arrhenius-relation with in temperature range 300 - 500 °C, which is increased to (0.40 eV ) when = 0.02 of at 10 kHz . The peaks attributed at 1415 cm^-1 () and 1413 cm^-1 () in FT-IR measurement of are due to Ca-O stretching from the calcite phase of CaCO₃, which is not observed in Pure ZnO confirms the presence of Ca in ZnO lattice. Keywords: , FT-IR, Impedance spectroscopy, ac conductivity, Dielectric constant.

Abstract: In this paper, the electrical properties of materials were evaluated using a microstrip patch sensor. The sensor was designed for the operating frequency in range of 1.5 to 3 GHz on a DiClad 880 substrate with the permittivity of 2.2. The resonant frequency of the design sensor ,as well as the magnitude of the reflection spectra S₁₁, were analyzed and then simulated three-dimensional finite element modeling when,. The result shows that the increase of the dielectric constant (ε_r) and conductivity (σ) of the material under test (MUT) led to the significant change of the resonant frequency. Thus, the resonant frequency may be used to evaluate the moisture content of the agricultural products.

Abstract: Thin films of zirconium oxide (ZrO₂) were deposited by DC magnetron sputtering of metallic target of zirconium on to quartz and p-Si (100) substrates at various oxygen partial pressures in the range 2x10^-2 - 6x10^-2 Pa. The crystallinity, surface morphology and optical absorption of the films were influenced by the oxygen partial pressure. X-ray photoelectron spectroscopic studies revealed that the films formed at oxygen partial pressure of 4x10^-2 Pa were of stoichiometric ZrO₂. X-ray diffraction profiles indicated that the grown films were of nanocrystalline with crystallite size increased from 5 nm to 9 nm with increase of oxygen partial pressure from 2x10^-2 Pa to 6x10^-2 Pa. The optical band gap of the films increased from 5.65 to 5.80 eV and the refractive index increased from 2.02 to 2.08 with the increase of oxygen partial pressure from 2x10^-2 to 6x10^-2 Pa respectively. The fabricated MOS structure with the configuration of Al/ZrO₂/p-Si showed the dielectric constant of 22 and leakage current density of 1x10^-6 A/cm².

Abstract: Olivine structured LiNi_1-xZn_xPO₄ (x=0, 0.05, 0.10, 0.15, 0.20) have been prepared by a polyol method using 1, 2 propanediol as a polyol medium. The XRD results of pure and Zn doped LiNiPO₄ sample authenticate the orthorhombic crystal structure with high crystalline nature. The crystallite size is calculated from the Debye Scherer formula and it is found in the range of 55-65nm and 49-55nm for undoped and doped samples respectively. The thermal properties of LiNi_1-xZn_xPO₄ were investigated by thermo gravimetric analysis (TG) and differential thermal analysis. Laser Raman studies confirm that the dopant is entered in to the LiNiPO₄ lattice. Morphology of the samples is analyzed through SEM analysis. The higher electrical conductivity is calculated for LiNi_0.85Zn_0.15PO₄ sample compared with other concentrations of dopant and it is found to be 1.08×10^-7 S cm^-1 at ambient temperature. Dielectric and Modulus studies are also discussed through impedance spectroscopy.

Abstract: Polyimide (PI) was chosen as the matrix of the composite, barium titanate/polyimide (BT/PI) nanocomposite films were prepared by in situ polymerization. In order to improve the dispersion and the physical-chemical properties of BT surface, barium titanate was modified by Al₂O₃ coating and modified BT/PI nanocomposite films were prepared. The prepared modified BT was characterized by X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM), and the dielectric properties of the composites were characterized in detail. It was shown that surface modification with Al₂O₃ is the chemical process and there were new substances forming. When BT was modified by 10 wt% Al₂O₃, the dielectric constant of the composite film was 18.96 (10³ Hz), the loss tangent 0.005, breakdown strength 70 MV·m^-1, energy storage density 0.41 J·cm^-3. The dielectric constant of BT modified by Al₂O₃ is decreased while the dielectric strength of the modified BT/PI composite film is increased.

Abstract: Magnesium titanate based dielectric materials are used for producing type-I capacitors. A common way of obtaining this material is a solid-state reaction. The process of sintering can be enhanced if mechanical activation preceedes. In this work starting powders of magnesium carbonate (MgCO₃) and titanium dioxide (TiO₂) with a rutile crystal modification were weighed to attain a 1:1 molar MgCO₃:TiO₂. Mechanical activation of the starting mixture was performed by high energy ball milling using ZrO balls and vessels with ball to powder mass ratio 40:1. The observed grinding times were 15, 30, 60 and 120 minutes. The isothermal sintering of compacted powders was conducted at 1100°C during 30, 60 and 180 minutes. For specimens synthesized in such a manner, microwave dielectric properties were measured, quality factor Q and the dielectric constant (ε_r) in function of frequency. The measurements of electrical resistivity, capacitance and loss tangent of samples were measured in the frequency range from 500 Hz to 5 MHz frequencies with a HIOKI 3532-50 LCR HiTESTER device at a constant voltage mode (amplitude 0.5 V of sinusoidal signal applied to the specimens).

Abstract: Boron nitride (BN) powder was modified by silane coupling agent, and a series of cyanate ester resin composites containing the modified BN were prepared. The effect of volume fraction of BN on the thermal conductivity, electrical insulation properties of these composites was investigated. Results show that addition of a little of BN powder can improve thermal conductivity of the composites effectively, while the composites still retain the relatively good electrical insulation and low dielectric constant. When the volume fraction of BN was 23.6%, the thermal conductivity of composite increased to 1.33 W/(m·K), which is 4.6 times that of pure resin.