Ac Resistivity Research Articles

Electrical and morphological properties of magnetocaloric nano ZnNi ferrite

A series of Zn1–xNixFe2O4 nano ferrite (with x=0, 0.2, 0.4, 0.6, 0.8, and 1) compositions were synthesized using the combustion technique. The powder samples were characterized by XRD. The X-ray analysis showed that the samples were single phase spinel cubic structure. The AC resistivity decreases by increasing the frequency from 1kHz to 10kHz. As the frequency of the applied field increases the hopping of charge carrier also increase, thereby decreasing the resistivity. A shift in dielectric maximum is observed toward higher temperature with increasing the Ni content from 536K to 560K at 1kHz. The HRTEM (high resolution TEM) images of four compositions have lattice spacing which confirms the crystalline nature of the samples. The surface morphology SEM of the sample consists of some grains with relatively homogenies distribution with an average size varying from 0.85 to 0.92μm. The values for entropy change in this work are still small but are significally higher than the values that have been reported for iron oxide nanoparticle. The magnetic entropy change was calculated from measurements of M (H, T) where H is the magnetic field and T is the temperature. The maximum value of entropy change (∆S) obtained near Curie temperature which makes these material candidates for magnetocaloric applications.

Dielectric and electrical properties of Cr substituted Mg ferrites

The spinel ferrites MgCrxFe2-xO4 (0.0 ? × ?1.0) were prepared through the solid state reaction using conventional ceramic method at 1300°C in air. The homogeneous phase of the ferrite samples was observed from the X-ray diffraction study. Lattice parameter of the samples was found to decrease with increasing Cr concentration in the system obeying Vegard’s law. The ac electrical resistivity, measured as a function of temperature, decreases with the increase of temperature indicating the semiconducting nature of all the samples. The activation energies were calculated and found to decrease with increasing Cr content. The lower activation energies are associated with higher electrical conductivity. With the increase of temperature, dielectric constant (e`) and dielectric loss tangent are observed to be increased; while with the increase of frequency, dielectric constant (e`) and dielectric loss tangent decrease for all the samples.Journal of Bangladesh Academy of Sciences, Vol. 39, No. 1, 1-12, 2015

Study of the electric properties of palm fiber-reinforced acrylonitrile butadiene styrene composites

The electrical properties like AC conductivity, AC resistivity, and dielectric constant of the palm fiber-reinforced acrylonitrile butadiene styrene composites were investigated using impedance analyzer at room and variable temperatures. Palm fiber was collected from 10 trees of different age group from Comilla region in Bangladesh. Three sets of samples were prepared for three different wt (%) (5%, 10%, and 20%) of fiber contents using Injection Moulding Machine. Each set has 10 composite samples in which first five of them are made with 11 to 20 years-aged palm fiber and latter five of them are made with 5 to 10 years-aged palm fiber. The AC electric conductivity increases with the increase of frequency, wt (%) of palm fiber in the PF-ABS composites, and with the increase of temperature. The AC resistivity decreases with the increase of frequency, with the wt (%) of fiber content in the PF-ABS composites and with the increase of temperature. Moreover, the comparison between the PF-ABS composites with 11 to 20 years-aged palm tree shows better result than 5 to 10 years-aged palm tree. The dielectric constant of the composites decreases with the increase of frequency. With the addition of palm fiber content in composites, dielectric constant increases. The dielectric constant also increased with the increase of temperature.

RESISTIVITY MEASUREMENT TECHNIQUES FOR COMPOSITE MATERIALS

In this article, the theoretical concepts and the experimental techniques for measurements of the volume and surface resistivity of carbon fibre reinforced polymer (CFRP) composite materials have been explained. The purpose of these measurements is to investigate the potential of composite materials as lightning arrestors for an aircraft. In particular, the AC resistivity method and the Delta mode of measurement have been described in detail. A few measurements were carried out using an indigenously designed and fabricated collinear four-probe resistivity measurement tool, for which factors dependent on the dimensions of the samples have to be incorporated, as per the ASTM F390-11 standards. The validity of the two-probe and four-probe methods is also analyzed, along with techniques to minimize errors in measurements. Conductivity measurements on uni-directional laminates have been made in the longitudinal (fibre) direction as well as perpendicular to it, indicating a marked difference in the relative magnitudes. When investigating the potential of materials as lightning arrestors, a very high surface conductivity is desired so that lightning currents (even of the order of kA) pass along the exterior of the aircraft, without penetrating the underlying structure. The effects of the addition of copper nanotubes (CNT) and copper mesh have also been studied. The instruments involved in these experiments have been automated based on the IEEE – 488.2 protocols. The software to program them was developed using Labview. Measurements have also been performed on standard samples to test the accuracy of the data. Currents ranging from 0.1 to 100mA were passed, to deduce the current-dependency of the surface resistivity of these materials.

Dielectric studies on struvite urinary crystals, a gateway to the new treatment modality for urolithiasis

Struvite or magnesium ammonium phosphate hexahydrate (MAPH) are biological crystals, found in the kidney, which are formed due to the infection caused by urea splitting bacteria in the urinary tract. The struvite crystals observe different morphologies and were developed using single diffusion gel growth technique. The crystalline nature and its composition were studied from different characterization techniques like X-ray Diffraction (XRD) and FTIR. The dielectric behavior of the developed crystal was studied by varying temperature and at different frequencies. The parameters like dielectric constant, dielectric loss, ac conductivity, ac resistivity, impedance and admittance of the struvite crystals were calculated. The studies proved that the dielectric loss or dissipation heat is high in lower frequencies at normal body temperature, which develops a plasma state in the stones and in turn leads to the disintegration of urinary stones. The dielectric nature of the stones leads to the dielectric therapy, which will be a gateway for future treatment modality for urolithiasis.

Structural, magnetic and dielectric investigations in antimony doped nano-phased nickel-zinc ferrites

Nanocrystalline Ni–Zn–Sb ferrites synthesized by hydrothermal method are reported. Influence of Sb5+ ions on structural, magnetic and dielectric properties of ferrites is studied. Phase identification, lattice parameter and crystallite size studies are carried out using by X-ray diffraction (XRD). Addition of dopant resulted for decrease in lattice parameter. Crystallite size gets reduced from 62nm to 38nm with doping of Antimony. Crystallite size and porosity exhibit similar trends with doping. Morphological study is carried out by Field Emission Scanning Electron Microscopy (FESEM). Strong FTIR absorption bands at 400–600cm−1 confirm the formation of ferrite structure. Increase of porosity is attributed to the grain size. Doping with Antimony results for decrease in saturation magnetization and increase in coercivity. An initial increase of saturation magnetization for x=0.1 is attributed to the unusually high density. Reversed trend of coercivity with crystallite size are observed. Higher value of dielectric constant ε′(ω) is attributed to the formation of excess of Fe2+ ions caused by aliovalent doping of Sb5+ ions. Variation of dielectric constant infers hopping type of conductivity mechanism. The dielectric loss factor tanδ attains lower values of ~10−2. High ac resistivity ρ(ω) of 108Ωcm is witnessed for antimony doped ferrites. Higher saturation magnetization and enhanced dielectric response directs for a possible utility as microwave oscillators and switches.

Electrical properties of silver-intercalated hafnium disulfide in DC and AC electric fields

The temperature dependences of the direct-current (dc) and alternating-current (ac) resistivities of silver intercalated compounds Ag x HfS 2 have been measured using impedance spectroscopy over a wide frequency range at different temperatures for the first time. The dc conductivity has an activation behavior and increases with increasing silver content in the samples. The results of the ac measurements have demonstrated that the ac conductivity has a frequency dispersion described by “the universal dynamic response.” It has been shown that the relaxation processes in an ac field are accelerated when the silver content in the sample and temperature increase.

Competing magnetic phases and field-induced dynamics in DyRuAsO

Analysis of neutron diffraction, dc magnetization, ac magnetic susceptibility, heat capacity, and electrical resistivity for DyRuAsO in an applied magnetic field are presented at temperatures near and below those at which the structural distortion (${T}_{S}=25$ K) and subsequent magnetic ordering (${T}_{N}=10.5$ K) take place. Powder neutron diffraction is used to determine the antiferromagnetic order of Dy moments of magnitude 7.6(1)${\ensuremath{\mu}}_{B}$ in the absence of a magnetic field, and demonstrate the reorientation of the moments into a ferromagnetic configuration upon application of a magnetic field. Dy magnetism is identified as the driving force for the structural distortion. The magnetic structure of analogous TbRuAsO is also reported. Competition between the two magnetically ordered states in DyRuAsO is found to produce unusual physical properties in applied magnetic fields at low temperature. An additional phase transition near ${T}^{*}=3$ K is observed in heat capacity and other properties in fields $\ensuremath{\gtrsim}3$ T. Magnetic fields of this magnitude also induce spin-glass-like behavior including thermal and magnetic hysteresis, divergence of zero-field-cooled and field-cooled magnetization, frequency dependent anomalies in ac magnetic susceptibility, and slow relaxation of the magnetization. This is remarkable since DyRuAsO is a stoichiometric material with no disorder detected by neutron diffraction, and suggests analogies with spin-ice compounds and related materials with strong geometric frustration.

AC and DC electrical transport studies of (Fe, Co) codoped ZnO nanoparticles

The authors have presented microstructural, ac- and dc-electrical properties, and magnetic and optical studies of Zn1-xFex/2Cox/2O (x = 0.1 and 0.2) semiconducting nanoparticles, prepared through low temperature chemical “pyrophoric reaction process.” Structural characterizations confirm the formation of single phase (at a calcination temperature of 300 °C), chemically homogeneous, nanometric sample (∼7 nm). Electrical studies on those samples have been carried out using an ac impedance spectroscopy and dc resistivity technique. Temperature dependent relaxation processes have been investigated by studying complex impedance spectroscopy. The authors have also estimated activation energy from both ac and dc resistivity data of those nanoparticles. Magnetic data clearly reveal the presence of some sort of magnetic behavior, even up to room temperature, in the x = 0.2 sample, whereas for x = 0.1 sample, there in no such magnetic behavior. This feature has been explained through magnetic polaron percolation theory. The authors have also estimated semiconducting band gap of those nanoparticles using recorded absorbance spectra.

Effects of Oxygen Doping on the Transport Properties of Hg<sub>0.82</sub>Re<sub>0.18</sub>Ba<sub>2</sub>Ca<sub>2</sub>Cu<sub>3</sub>O<sub>8+d</sub> Superconducting Polycrystals

Hg0.82Re0.18Ba2Ca2Cu3O8+dpolycrystalline ceramic samples were prepared using a solid-vapour reaction technique. First, the ceramic precursor was prepared from a mixture of Ba2Ca2Cu3Oxand ReO2powders in a molar ratio of 1:0.18. The precursor material was annealed under three different partial pressures of oxygen that consisted of a mixture of oxygen/argon in the following ratios: 5/95 (sample A), 10/90 (sample B) and 15/85 (sample C). Secondly, the precursors prepared at different O2partial pressures were blended with HgO at a molar relationship of 1:0.82. The synthesis was carried out at 865 °C for 72 h. Moreover, analyses using X-ray powder diffraction, Scanning Electron Microscopy (SEM), and Energy Dispersion X-ray spectroscopy (EDS) were performed. These results demonstrated a similarity in the grain morphology within the samples. Using SEM images, a histogram of grain-boundary size was produced where the average junction size is represented by a gamma density distribution function. Finally, the samples were submitted to ac electrical resistivity ρ (T) under a low applied magnetic field (up to 400 Oe). Samples cut into bars approximately 7 × 1 × 1 mm3in size were studied using a four-probe technique. The zero-resistance critical temperatures (Tcj) were determined from ρ (T) curves. The results are compared and qualitatively explained in the framework of flux trapping by superconducting grains. In our opinion, the oxygen partial pressure has a strong influence on the grain junctions and causes island structures that form defects at the grain boundaries.

Corrosion current density prediction in reinforced concrete by imperialist competitive algorithm.

This study attempted to predict corrosion current density in concrete using artificial neural networks (ANN) combined with imperialist competitive algorithm (ICA) used to optimize weights of ANN. For that reason, temperature, AC resistivity over the steel bar, AC resistivity remote from the steel bar, and the DC resistivity over the steel bar are considered as input parameters and corrosion current density as output parameter. The ICA–ANN model has been compared with the genetic algorithm to evaluate its accuracy in three phases of training, testing, and prediction. The results showed that the ICA–ANN model enjoys more ability, flexibility, and accuracy.

Magnetic and superconducting properties of Ir-doped EuFe2As2

The magnetic and superconducting properties of 14% Ir-doped EuFeAs are studied by means of dc and ac magnetic susceptibilities, electrical resistivity, specific heat and Eu and Fe Mössbauer spectroscopy (MS) measurements. Doping of Ir in EuFeAs suppresses the Fe spin density wave transition and in turn gives rise to high temperature superconductivity below 22.5 K with a reentrant feature at lower temperature. Magnetization and Eu Mössbauer data indicate that the Eu spins order magnetically below 18 K. Fe MS studies show a line broadening in the absorption spectra below 18 K due to transferred hyperfine field from the magnetically ordered Eu sublattices. A pronounced λ-shape peak in the specific heat supports a second-order phase transition of Eu magnetic ordering with a strong ferromagnetic component, as confirmed by the magnetic field dependences of the transition. For a single crystal, the in-plane resistivity and out-of-plane susceptibility () show superconducting transitions with zero resistance and diamagnetism, respectively. But the in-plane susceptibility () does not show any diamagnetic shielding against external fields. The observed non-zero resistance in the temperature range 10–17.5 K, below the superconducting transition temperature, suggests the possible existence of a spontaneous vortex state in this superconductor.

Chemical and physical investigations on the charge transfer interaction of organic donors with iodine and its application as non-traditional organic conductors

The iso-leucine-iodide and methionine-iodide charge-transfer complexes were prepared and characterized using different spectroscopic techniques. The iodide charge-transfer complexes were synthesized by grinding KI-I2-amino acid with 1:1:1M ratio in presence of few drops of methanol solvent. The structures of both solid amino acid iodide charge-transfer complexes are discussed with the help of the obtained results of the infrared and Raman laser spectra, Uv–vis. electronic spectra and thermal analyses. The electrical properties (AC resistivity and dielectric constant) of both complexes were investigated. The positron annihilation Doppler broadening (PADB) spectroscopies were also used to probe the structural changes of both complexes. The PADB line-shape parameters (S and W) were found to be dependent on the structure, electronic configuration of the charge transfer complex. The PADB technique is a powerful tool to probe the structural features of the KI-I2-amino acid complexes.

On the effect of SHI irradiation on dielectric properties of Y3+xFe5−xO12 (x=0.0–0.6) system

The present work aims to investigate the pre- and post-effect of 50 MeV Li3+ ion irradiation at a fluence of 5×1013 ions/cm2 on the dielectric properties of Y3+xFe5−xO12, x=0.0, 0.2, 0.4 and 0.6, garnet system over broad temperature, 300–673 K, and frequency, 100 Hz–13 MHz, ranges. Thermal variation of ac resistivity measurements suggests that the mechanism responsible for conduction in the system is polaron hopping. The observed modifications in dielectric properties after swift heavy ion irradiation are mainly due to the modifications of the metal–insulator contacts due to radiation damage-induced disorder and irradiation-induced point/cluster of defects in the material and also compressive strain generated in the lattice structure. The electric modulus presentation and the complex impedance spectral analysis have been employed to study the relaxation process. The YFeO3 phase is found to be irradiation hard phase as compared with the garnet phase.

Structural, Magnetic and Electrical Properties of Cu-Mg Ferrites

Cu1-xMgxFe2O4 ferrites with (x = 0.2, 0.4, 0.6, 0.8 and 1.0) has been synthesized by double sintering ceramic technique at 11500C for 2hr and investigated for their structure, microstructure, complex permeability behaviour, DC and AC resistivity, dielectric constant measurements. X-ray analysis indicated the formation of single-phase cubic spinel structure for all samples and the lattice parameter was found to decrease with increasing Mg content. Grain size was found to decrease from 34.36 to 4.16 mm with the increase of Mg contents. The real part of initial permeability (??) remained constant up to certain lower range of frequency after it decreased slightly to lower value of permeability at which imaginary part of permeability (?²) showed a maximum value. The decrease of ?? is observed with the increase of Mg content which is attributed to a decrease of grain size. DC electrical resistivity and dielectric constant decreased with increasing Mg content and AC resistivity decreased with increasing frequency, exhibiting normal ferrimagnetic behaviour. The observed variation of electrical and dielectric properties has been explained on the basis of the electronic hopping frequency between Fe2+ and Fe3+ ions in present samples. Keywords: Ferrites; XRD; Micrographs; Complex permeability; DC resistivity. © 2014 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved. doi: http://dx.doi.org/10.3329/jsr.v6i2.17351 J. Sci. Res. 6 (2), 205-215 (2014)

Impact of Co doping on magnetic and electrical properties of La0.5Ca0.5Mn1−xCoxO3 (0≤x≤0.05) manganites

In this study, structural, magnetic and electrical properties of polycrystalline La0.5Ca0.5Mn1−xCoxO3 (x=0, 0.005, 0.0075, 0.01, 0.025 and 0.05) samples have been investigated using ac susceptibility, magnetization and resistivity measurements. Rietveld refinement of X-ray diffraction patterns indicates an orthorhombic structure with Pnma space group for all samples. No structural transition is observed due to Co doping. Magnetic studies show that the magnetization and real parts of ac susceptibility (χ′(T)) increase initially by increasing x up to x=0.025 and decrease by further increase in x, up to x=0.05. The notable point of this study is the ability of a 0.5% of Co doping to induce insulator–metal transition in the insulating undoped sample at low temperatures. Also, we report a feature of thermal hysteresis behavior in La0.5Ca0.5Mn1−xCoxO3 series, which is the inverted thermal hysteresis loop for 0.0075≤x≤0.05 samples. In the Co doping level range of 0≤x<0.0075, χ′(T) and resistivity (ρ(T)) curves show counterclockwise (CCW) and clockwise (CW) thermal hysteresis, respectively. On the other hand samples with 0.0075≤x<0.05 Co doping level exhibit CW thermal hysteresis in χ′(T) and CCW one in ρ(T) curves. The thermal hysteresis behavior is attributed to the interfacial elastic energy in the boundary among the phases with different magnetic states. Magnetic instability is reported for x=0 and 0.005 samples and possible reasons for these behaviors are discussed.

Observation of magnetoelectric effect in Cr2O3/Pt/Co thin film system

We investigate the magnetic, electric, and magnetoelectric properties of a Cr2O3 thin film system that was deposited by radiofrequency magnetron sputtering. The temperature dependence of the magnetic susceptibility of our Cr2O3 film is similar to that of bulk Cr2O3, which indicates a small oxygen non-stoichiometry in the film. The Cr2O3 film exhibits high AC resistivity (∼109 Ω cm) and low leakage current (4.0 × 10−5 A/cm2 at E = 80 kV/cm). Finally, we demonstrate magnetoelectric switching of the exchange bias using the Cr2O3/Pt/Co all-thin-film system. By changing the direction of the electric field during the magnetoelectric field cooling process, the exchange bias field was changed symmetrically from −160 Oe to +160 Oe, which represents the switching of the antiferromagnetic domain of Cr2O3.

Composition‐dependent electrical and dielectric properties of polyaniline/graphene composites produced by in situ polymerization technique

Polyaniline (Pani)/Graphene nanocomposites with different compositions were prepared by in situ polymerization of aniline in presence of graphene oxide. Two types of Pani/graphene composites were prepared, composite‐1: where graphite powder as procured is used for preparation of composites, composite‐2: graphite powder is subjected ball milling for further reduction of graphite particles size and then used for preparation of composites. DC and AC resistivity of these composites have been found to be composition dependent. In fact composite‐2 exhibit lower resistivity compared to composite‐1 at same composition. However, both composites show frequency‐independent AC resistivity but frequency‐dependent dielectric constant and loss. POLYM. COMPOS. 36:445–453, 2015. © 2014 Society of Plastics Engineers

Antiferromagnetic cluster spin-glass behavior in Pr117Co54.5Sn115.2 – A compound with a giant unit cell

The magnetic properties of Pr117Co54.5Sn115.2 – a member of a family of materials with a giant unit cell – have been investigated by dc magnetization, ac magnetic susceptibility, specific heat, and electrical resistivity measurements. A magnetic glassy state at freezing temperature of ∼11K was determined from the magnetic susceptibility and specific heat data. The glassy state in Pr117Co54.5Sn115.2 is not the conventional spin glass with randomly oriented magnetic moments, but it is related to clusters of atoms that exist in the complex crystal lattice of the material. Furthermore, the glassy state coexists with short range antiferromagnetic order, leading to the development of antiferromagnetic clusters. A weak anomaly in the specific heat data centered around 11K supports the formation of magnetic cluster glass state in Pr117Co54.5Sn115.2. Semiconductor-like resistivity with a negative temperature coefficient from 2 to 300K is also observed in Pr117Co54.5Sn115.2.

Synthesis and characterization of gel-grown cobalt tartrate crystals

Crystals of cobalt tartrate are grown from the gel using chemical reaction method. The functional groups are found from Fourier transform infra red spectroscopy (FTIR). The OH stretching mode owing to water, carbonyl group, CH stretching modes and metal–oxygen stretching are identified. The unit cell dimensions, interaxial angles and unit cell volume are found from powder X-ray diffraction studies (XRD) which show the orthorhombic nature of the crystal. The magnetic study is used to find the magnetic susceptibility and magnetic moment of the grown crystal. It reveals the magnetic nature of the crystal. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) are done to find the thermal properties of the crystal which manifest the water of hydration in the crystal. The variation of dielectric constant with respect to the applied frequency shows the polarization property of the crystal. The AC conductivity is increased proportionally with increase in frequency. The reverse nature is found for the AC resistivity. The nature of the composition of the crystals affects the dielectric properties.