Investigation of dielectric and electrical behavior of Mn doped YCrO3 nanoparticles synthesized by the sol gel method

In the present work Mn doped YCrO₃ nanoparticles are synthesized by the sol–gel method. Samples have been characterized by the X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–vis absorption spectroscopy. The optical band gap of Mn doped YCrO₃ nanoparticles increases with increase of doping concentration. The dc resistivity of the prepared samples decreases with increasing temperature. The variation of ac conductivity with frequency has been explained by the Correlated Barrier Hoping (CBH) conduction mechanism. Dielectric permittivity of the samples was studied and it follows the power law ε^/(f)∝Tⁿ, where the temperature exponent n is found to be frequency dependent. The dielectric properties of the samples have been discussed in terms of electric modulus vector. Both activation energies due to dc resistance and dielectric response have been measured for the different samples and it is observed that it increases with the Mn content.     

Electrical and switching properties of NiAlxFe2−xO4 ferrites synthesized by chemical method

Nickel-aluminum ferrite system NiAl_xFe_2−xO₄ has been synthesized by wet chemical co-precipitation method. The samples were studied by means of X-ray diffraction, d.c. electrical resistivity, a.c. electrical resistivity, a.c. conductivity and switching properties. The XRD patterns confirm the cubic spinel structure for all the synthesized samples. The crystallite size calculated from XRD data which confirm the nano-size dimension of the prepared samples. Electrical properties such as a.c. and d.c. resistivities as function of temperature were studied for various Al substitution in nickel ferrite. The dielectric constant and dielectric loss tangent were also studied as a function of frequency. The dielectric constant follows the Maxwell-Wagner interfacial polarization. A.C. conductivity increases with increase in applied frequency. The d.c. resistivity decreases as temperature increases, which indicate that the sample have semi-conducting nature. Verwey hoping mechanism explains the observed variation in resistivity. The activation energy is derived from the temperature variation of resistivity. Electrical switching properties were studied as I-V measurements. The current controlled negative resistance type switching is observed in all the samples. The Al substitution in nickel ferrite decreases the required switching field.     

Dielectric properties of electrolytic solutions

The variation in dielectric properties of water with the addition of ionic salts have been measured using automated frequency domain experimental microwave C-band. The dielectric properties, that is dielectric constant (ε′) and dielectric loss (ε″) of two electrolyte solutions for various concentrations have been measured at 5-GHz frequency at room temperature. It has been observed that for concentration between 0.2 to 1.0 mole the dielectric constant of water is smaller and some larger than that of pure water and dielectric loss increases with increasing concentration of these salts. It has been also observed that the variation in dielectric loss is different, though the ionic concentration of the two salts are equal.     

Al3+掺杂的CuZn铁氧体的结构，电学和磁学特性

采用固相合成反应技术制备纳米Cu_0.5Zn_0.5Fe_2-xAl_xO₂(x=0.0,0.1,0.2,0.3,0.4和0.5)铁氧体材料,研究Al³⁺含量对结构,电学和磁学性质的影响. 采用X射线衍射研究单相立方尖晶石结构. 利用Scherrer公式估算晶粒尺寸. 测定了温度依赖的直流电阻率.结果表明随Al³⁺含量的增加,晶格常数减小,孔隙度增加,饱和磁化强度值降低,Al³⁺对铁氧体的介电常数、介电损耗角的正切值和介质损耗因子等介电性能有明显影响,这可能与空间电荷极化有关.     

Dielectric behavior and PTCR effect in nanocrystallite PMN ferroelectric ceramics

The ac behavior of a nanocrystallite lead magnesium niobate (PMN) ceramic sample was studied over a wide range of temperatures and frequencies. The results revealed a diffuse phase transition and very high dielectric constant at lower frequencies. The high value of the dielectric constant at lower frequencies is shown to be due to barrier layer formation. A positive temperature coefficient of resistivity (PTCR) was observed in the temperature dependence of the ceramic resistivity. The results are explained on the basis of the Heywang and Jonker models. The Schottky barrier formed at grain boundary regions acts as a trap for the electrons available from oxygen vacancies in the ceramics. This provides PTCR characteristics from the transition temperature to about 208°C.     

Dielectric properties of BaTiO3 modified with ZrO2

The dielectric constant and loss tangent of BaTiO₈ with ZrO₂ additives have been studied. The loss tangent was less ranging between 0.16 for pure BaTiO₃ and 0.05 for samples containing 5% ZrO₂. The dielectric constant at Curie temperature decreased with increasing ZrO₂ concentration up to 0.4%. The volume resistivity measurements illustrate a peak value at a certain range of temperatures for each composition.     

Dielectric and magnetic properties of(Zn,Co) co-doped SnO_2 nanoparticles

Polycrystalline samples of(Zn, Co) co-doped SnO2 nanoparticles were prepared using a co-precipitation method. The influence of(Zn, Co) co-doping on electrical, dielectric, and magnetic properties was studied. All of the(Zn, Co) co-doped SnO2 powder samples have the same tetragonal structure of SnO2. A decrease in the dielectric constant was observed with the increase of Co doping concentration. It was found that the dielectric constant and dielectric loss values decrease, while AC electrical conductivity increases with doping concentration and frequency. Magnetization measurements revealed that the Co doping SnO2 samples exhibits room temperature ferromagnetism. Our results illustrate that(Zn, Co) co-doped SnO2 nanoparticles have an excellent dielectric, magnetic properties, and high electrical conductivity than those reported previously, indicating that these(Zn, Co) co-doped SnO2 materials can be used in the field of the ultrahigh dielectric material, high frequency device, and spintronics.     

Dielectric behaviour of polycrystalline lead germanate

The dielectric behaviour of ferroelectric Lead Germanate (Pb₅Ge₃O₁₁) is reported in the frequency region 60 Hz-100 KHz for various particle size ranges from 40 to 300 μ m. The dielectric constant and conductivity decrease with decreasing particle size. The dielectric anomaly in small particle size unsintered samples disappears at lower frequencies, while at 100 KHz a broad diffuse phase transition is observed for all the samples, irrespective of particle size. A strong dielectric dispersion has been observed in the frequency range 60 Hz–100 KHz. The dielectric constant of sintered samples for the same panicle size range, and the dielectric anomaly which was absent at lower frequencies for unsintered samples re-appears in sintered samples. These results have been explained by assuming a high resistivity surface layer having a lower dielectric constant than the bulk at the boundary of particles.     

DC electrical resistivity for CoxNi5/3−xSb1/3Fe1O4 ferrites

The DC electrical resistivity (p) was studied for Co substituted SbNi ferrites as a function of temperature and composition. The experimental results showed that DC resistivity, Curie temperature and activation energies for electrical conduction increase as Co-ion substitution decreases. The DC electrical conductivity increases as temperature increases. The real part of dielectric constant (e') was found to be inversely proportional to the root mean square value of the electrical resistivity.     

Ionic conductance behaviour of plasticized polymer electrolytes containing different plasticizers

The effect of different plasticizers on the properties of PEO-NH₄F polymer electrolytes has been studied. Aprotic organic solvents like propylene carbonate (PC), ethylene carbonate (EC), γ-butyrolactone (γ-BL), dimethylacetamide (DMA), dimethylformamide (DMF), diethylcarbonate (DEC) and dimethylcarbonate (DMC) having different values of donor number, dielectric constant, viscosity etc. have been used as plasticizers in the present study. The addition of plasticizer has been found to modify the conductivity of polymer electrolytes by increasing the amorphous content as well as by dissociating the ion aggregates present in polymer electrolytes at higher salt concentrations. The conductivity enhancement with different plasticizers has been found to be closely related to the donor number of the plasticizer used rather than its dielectric constant. The increase in conductivity with the addition of plasticizer has further been found to be dependent upon the level of ion association present in the electrolytes. The variation of conductivity as a function of plasticizer concentration and temperature has also been studied and maximum conductivity of ∼ 10⁻³ S /cm at room temperature has been obtained. X-ray diffraction studies show an increase of amorphous content in polymer electrolytes with the addition of plasticizers.     

Dielectric relaxation in polyvinylidenefluoride–polysulfone blends

Dielectric properties of polymer blend of polyvinylidenefluoride (PVDF) and polysulfone (PSF) of different wt. % have been studied to understand the molecular motion and their relaxation behavior in the frequency range of 100 Hz to 10 kHz at different temperatures between 30 and 190 °C. The dielectric constant of the blend decreased with frequency and increased with the increasing temperature and PSF content in the blend. The magnitude of dielectric loss also increased with increase in temperature and PSF content. The observed characteristic has been consistently explained in terms of dipolar motions and the plasticization effect brought about by blending of PSF with PVDF. At constant frequency and temperature, the blend follows a linear relationship between logarithm of their dielectric constant and different ratios of blend. The appearance of a peak for each concentration in dielectric loss suggests the presence of relaxing dipoles in the blend. In addition of PSF with PVDF, the peak shifts toward higher frequency side suggesting the speed up the relaxation process. AC dielectric data is also combined with thermally stimulated depolarization current (TSDC) data which is generally studied for low-frequency dielectric properties of polymers blends so as to produce the results in a wide frequency range. The glass transition temperature (T_g) of the blend was studied by differential scanning calorimetric technique (DSC), the T_g was compared and correlated with TSDC peak. The blend samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) to study the formation of blend and micro structural properties of the materials. The shifting of peak toward lower diffraction angle side confirms the reduction in particle size with increasing amorphous content in the blend.     

A comparative study of the electrical and the magnetic properties and Mössbauer studies of normal and hot pressed MgxMn1−xFe2O4 ferrites

Modifying the proportion of the base composition by substituting with suitable dopants and improving the preparation conditions is expected to change the performance of ferrites. In the present study, Mg_xMn_1−xFe₂O₄ series of ferrites were prepared by, the conventional ceramic technique and the hot-pressed ceramic technique. Hot pressing of Mg–Mn ferrites results in an improvement of their magnetic and micro-structural properties as it controls simultaneously grain growth and porosity. Hot pressing of the Mg–Mn ferrites, however, results in a deterioration of their DC resistivity. The cation distribution has been studied by X-ray analysis and magnetisation. The variation of the saturation magnetisation and Curie temperature with increasing concentration of the Mg²⁺ ions can be explained on the basis of cation distribution and Neel's two sub-lattice models. The observed Mössbauer spectra show two hyperfine split sextets with an absence of magnetic relaxation indicating an absence of domain wall oscillations. The variations of the internal magnetic field have been qualitatively explained by taking into account, the predominant super-transferred hyperfine interactions (STHI).     

Structural,magnetic and electrical properties of Co1−xZnxFe2O4 synthesized by co-precipitation method

Nanoparticles of Co_1−xZn_xFe₂O₄ with stoichiometric proportion (x) varying from 0.0 to 0.6 were prepared by the chemical co-precipitation method. The samples were sintered at 600 °C for 2 h and were characterized by X-ray diffraction (XRD), low field AC magnetic susceptibility, DC electrical resistivity and dielectric constant measurements. From the analysis of XRD patterns, the nanocrystalline ferrite had been obtained at pH=12.5–13 and reaction time of 45 min. The particle size was calculated from the most intense peak (3 1 1) using the Scherrer formula. The size of precipitated particles lies within the range 12–16 nm, obtained at reaction temperature of 70 °C. The Curie temperature was obtained from AC magnetic susceptibility measurements in the range 77–850 K. It is observed that Curie temperature decreases with the increase of Zn concentration. DC electrical resistivity measurements were carried out by two-probe method from 370 to 580 K. Temperature-dependent DC electrical resistivity decreases with increase in temperature ensuring the semiconductor nature of the samples. DC electrical resistivity results are discussed in terms of polaron hopping model. Activation energy calculated from the DC electrical resistivity versus temperature for all the samples ranges from 0.658 to 0.849 eV. The drift mobility increases by increasing temperature due to decrease in DC electrical resisitivity. The dielectric constants are studied as a function of frequency in the range 100 Hz–1 MHz at room temperature. The dielectric constant decreases with increasing frequency for all the samples and follow the Maxwell–Wagner's interfacial polarization.     

The effect of zinc concentration on vacancies jump rate, diffusion coefficient and jump length in Cu-Zn ferrite

Samples with the chemical formula Cu_1−xZn_xFe₂O₄ (x=0.2, 0.4, 0.6, 0.8 and 1) were prepared by the standard ceramic method. The dielectric constant and dielectric loss tangent were studied as a function of vacancy jump rate. The results show that the dielectric constant and dielectric loss tangent decrease with increasing vacancy jump rate. In addition, the electron jump length in the octahedral sites was studied as a function of zinc concentration. The increase in jump length with Zn concentration has been attributed to the substitution of Fe⁺³ for Zn²⁺ at the A-sites, which increases the B-B interaction. The increase of diffusion coefficient with increasing Zn concentration was reinforced by the increase of jump rate.     

Influence of the plasma parameters and nitrogen addition on the electrical characteristics of DLC films deposited by inductively coupled plasma deposition

This work has been based on studies of the plasma parameters influence and nitrogen addition over on the electrical characteristics of diamond-like carbon (DLC) films deposited by inductively coupled plasma deposition (ICP) system. For these studies, it was used a mixture of methane with different flows of nitrogen, two different pressure processes and three different coil powers. The nitrogenated DLC films, had presented a great variation in their electric and structural properties with the nitrogen variation in the plasma. With the nitrogen addition, an increase in its dielectric constant of 1.7-7.4 to concentration of the 40% of the nitrogen has occurred. For high nitrogen concentrations (80% of nitrogen), the dielectric constant decreases (of 7.4 for 5.0). The resistivity of the films decreases with the nitrogen concentration increase (1.2 × 10⁹ Ω cm). Attributing semiconductors characteristics to DLC films. With the increase of nitrogen concentration, the sp³ hybridization increases, too. These characteristics were excellent for innumerable applications in electronic devices.     

多自旋态离子Co替代诱导La2/3Ca1/3MnO3体系的输运反常

利用具有多自旋态的Co离子进行Mn位替代,制备了La_2/3Ca_1/3Mn_1-xCo_xO₃ (0≤x≤0.15) 系列样品并研究了体系的结构和输运特性.结果表明,在替代范围内,样品呈现很好的单相结构,各晶格参数随替代量的增大而减小;Co替代导致体系出现电输运反常,具体表现为在居里温度T_C以下电阻-温度曲线的二次金属-绝缘转 关键词： Mn位替代 双峰现象 自旋结构 磁电阻效应     

Structural, magnetic and electrical properties of NiCuZn ferrites prepared by microwave sintering method suitable for MLCI applications

Polycrystalline NiCuZn soft ferrites with stoichiometric iron were prepared by a novel microwave sintering method. The powders were calcined, compacted and sintered at 950 °C for 30 min in a microwave sintering furnace. X-ray diffraction patterns confirm the formation of single phase cubic spinel structure. The grain size was estimated using SEM micrographs. The lattice constant is found to increase with increase in zinc concentration. The sintered ferrites have been investigated for their physical, magnetic and electrical properties such as bulk density, X-ray density, porosity, anisotropy constant, initial permeability, saturation magnetization, DC resistivity, dielectric constant and dielectric loss as a function of zinc concentration. Permeability, saturation magnetization, dielectric constant and dielectric loss were found to increase while DC resistivity was found to decrease with the replacement of Zn with Ni. The present series of ferrites are found to posses properties that are suitable for the core materials in multilayer chip inductors.     

Dielectric properties of short sisal/coir hybrid fibre reinforced natural rubber composites

The dielectric properties, such as dielectric constant, volume resistivity and dielectric loss factor, of sisal/coir hybrid fibre reinforced natural rubber composites have been studied as a function of fibre loading, fibre ratio, frequency, chemical modification of fibres and the presence of a bonding agent. The dielectric constant values have been found to be higher for fibre filled systems than pure natural rubber. This has been attributed to the polarization exerted by the incorporation of fibres into the matrix. Dielectric constant values were observed to be decreased with increase in frequency due to the decreased interfacial and orientation polarization at higher frequencies. Whereas dielectric constant increases with fibre loading because of the increment in number of polar groups after the addition of hydrophilic lignocellulosic fibres. The volume resistivity of the composites was found to be decreased with fibre loading and a percolation threshold has been obtained at 15.6% volume of fibres. Fibre treatment, such as alkali, acetylation, benzoylation, peroxide and permanganate, were carried out to improve the adhesion between fibres and matrix. The dielectric constant values were lower for systems consisting of fibres subjected to chemical treatments due to the increased hydrophobicity of fibres. The addition of a two-component dry bonding agent consisting of hexamethylene tetramine and resorcinol, used for the improvement of interfacial adhesion between the matrix and fibres, reduced the dielectric constant of the composites. When the weight percentage of sisal fibre was increased in the total fibre content of the hybrid composites, the dielectric constant was found to increase. The added fibres and different chemical treatments for them increased the dielectric dissipation factor. A dielectric relaxation has been observed at a frequency of 5 MHz.     

The influence of Co doping on the dielectric, ferroelectric and ferromagnetic properties of Ba0.70Sr0.30TiO3 thin films

Ba_0.70Sr_0.30TiO₃ (BST) thin films doped by Co (BSTC) are fabricated by sol-gel method on a Pt/Ti/SiO₂/Si substrate. A strong correlation is observed among the microstructure, dielectric, ferroelectric, ferromagnetic properties and Co concentration. The dielectric constant of BST thin films can be tailored from 343 to 119 by manipulating the Co concentration. The dielectric loss of BSTC thin films are still kept below 0.020 and the tunability is above 30% at a dc-applied electric field of 500 kV/cm. With increasing Co doping up to 10 mol%, the coexistence of ferromagnetism and ferroelectrics is found. Suitable dielectric constant, low-dielectric loss, and high tunability of this kind of thin films can be useful for potential tunable applications.     

Electrical conductivity and dielectric properties of SiO<Subscript>2</Subscript> nanoparticles dispersed in conducting polymer matrix

Electrical and dielectric properties of conducting polypyrrole–wide band gap silica (PPY–SiO₂) nanocomposites have been investigated as a function of temperature and frequency for different concentrations of polypyrrole. The average grain size of the nanocomposites is in the range of 40–80 nm. Impedance spectra reveal two distorted semicircles corresponding to grain and grain boundary effects. The magnitude of conductivity and its temperature variation are significantly different from polypyrrole and silica. A very large dielectric constant of about 4800 at 30 kHz and at room temperature has been observed for the highest concentration of silica. Inhomogeneous behavior of nanocomposites gives rise to high dielectric constant.