Structure and electrical properties of polyaniline synthesized in presence of low magnetic field

Chemical polymerization of aniline is carried out in the presence of low magnetic field (1 kG and 2 kG). The impact of application of magnetic field externally during polymerization increases the electrical conductivity by two orders of magnitude. This enhanced electrical conductivity depends on ordering of polymer chain, structure, molecular weight, magnetic susceptibility, and thermal characteristics of polyaniline which has been studied and reported.     

Electrical conductivity of Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O ferromagnetic films at low temperatures

The results of experiments on electrical conductivity and magnetic properties of thin cobalt-doped zinc oxide films are reported. The results indicate the predominance of the hoping conduction mechanism at low temperatures and the band mechanism at high temperatures. An increase in the cobalt concentration from 1.5 to 6.3 at % leads to the reduction of the electrical conductivity of the films. The contribution of hopping conduction to the conductivity increases due to a decrease in the crystallinity of the films and localization of a part of electron states upon an increase in the cobalt concentration. For cobalt-containing films, a hysteresis of the magnetic moment as a function of the magnetic field is observed. The dependence of the shape of the magnetization curves on the cobalt concentration is irregular. The paramagnetic contribution to the magnetic susceptibility increases with the cobalt concentration.     

Effect of the Protonation and Chemical Doping of Poly(o-toludine) with Copper Sulfate on the Spectral and Electrical Properties of the Host Polymer

Poly(o-toluidine) (POT) and its samples doped with copper sulfate, a transition metal salt, were synthesized by a chemical oxidative polymerization technique using potassium dichromate as oxidant in aqueous hydrochloric acid medium and chemical doping with copper sulfate. The prepared polymeric samples were characterized by ultraviolet (UV)-visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction, and DC conductivity measurement techniques. The UV-visible spectra of doped polymer displayed peaks indicating the presence of charged particles/polarons and/or formation of conducting POT. The characteristic FTIR peaks of the doped polymer provided information regarding structural changes in the backbone of POT and were consistent with the interaction of the benzenoid groups of the polymer with metal ions. X-ray diffraction patterns of powdered doped polymer showed an amorphous nature, as exhibited by most conducting polymers. The DC conductivity of doped polymer was measured by a two-probe method in the temperature range of 300–400 K; a significant enhancement in DC conductivity was observed with an increase in temperature, showing the semiconductor nature of the synthesized doped polymer.     

Study of DC conductivity and relative magnetic permeability of nanoparticle NiZnFe2O4/PPy composites

The DC conductivity and the relative magnetic permeability have been measured as functions of temperature for five powder samples of nanoparticle ferrites (Ni_xZn_1−xFe₂O₄; x=0, 0.25, 0.5, 0.75 and 1), a pure polypyrrole (PPy) powder sample and many composite samples prepared by mixing different ratios of the ferrites to PPy. By comparing the results it is found that there is an obvious increase in DC conductivity of the ferrite/PPy composite samples compared to the corresponding pure ferrite samples, whereas compared to the pure PPy sample there is a decrease in DC conductivity. On the contrary, the magnetic permeability of the composites is higher than that of the pure PPy sample and lower than that of the pure ferrite samples as was expected.     

Effect of carbon substitution on low magnetic field AC losses in MgB2 single crystals

The DC magnetization and AC magnetic susceptibilities were measured for MgB₂ single crystals, unsubstituted and carbon substituted with the composition of Mg(B_0.94C_0.06)₂. AC magnetic losses were derived from the AC susceptibility data as a function of the AC amplitude and the DC bias magnetic field. From the DC magnetization loops critical current densities were derived as a function of temperature and DC field. Results show that the substitution with carbon decreases critical current densities at low external magnetic fields, in contrast to the well known effect of an increase of the critical current densities at higher magnetic fields.     

Magnetic conducting composites based on polypyrrol and iron oxide nanoparticles synthesized via electrochemistry

In this work, the preparation of a polypyrrol-magnetite composite with good magnetic and electric properties is described. Firstly, the method consists of the electrochemical synthesis of magnetite nanoparticles 20 nm in diameter and narrow size distribution, and secondly, the encapsulation of the nanoparticles in a polymer matrix during its formation by chemical oxidation of the monomer. Particles appear well dispersed in the polymer matrix by transmission electron microscopy (TEM) while no degradation, in terms of nanoparticles size or magnetic properties during the polymer formation, seems to take place as it was revealed by X-ray diffraction and Mössbauer spectroscopy. Saturation magnetization increases with the amount of magnetic material present in the composite, but conductivity decreases in such a way that the amount of magnetic material was optimized to 10% with respect to the monomer to obtain a composite with high electrical conductivity and magnetic response.     

Semiconductor-metal transition in FeSi in an ultrahigh magnetic field

We study the conductivity and magnetic susceptibility of single-crystal iron monosilicide in ultrahigh magnetic fields (up to 500 T) at low temperatures. The experimental methods used in measuring the conductivity and magnetic susceptibility are discussed. At 77K we detect a gradual increase in the conductivity of iron monosilicide by more than a factor of 100 as the magnetic field gets stronger. At 4.2K we detect a first-order phase transition in a field of 355 T accompanied by a sudden change in the value of the magnetic moment by 0.95 μ _B per iron atom and a transition to a phase with high conductivity. The results are discussed within the scope of the spin-fluctuation theory. Zh. éksp. Teor. Fiz. 116, 1770–1780 (November 1999)     

DC susceptibility of type-II superconductors in field-cooled processes

The DC susceptibility of oxide superconducting specimens in the field-cooled process has been experimentally found to depend not only on the applied DC magnetic field but also on the size of the specimens. The DC susceptibility is calculated using the critical state model in which the diamagnetism and the flux-pinning effect of superconductors are taken into account. It is shown that the saturated value of the DC susceptibility at sufficiently low temperatures, i.e., the so-called Meissner fraction, decreases with increasing DC field and/or increasing specimen size.     

New polymer electrolyte based on (PVA–PAN) blend for Li-ion battery applications

A polymer blend electrolyte based on polyvinyl alcohol (PVA) and polyacrylonitrile (PAN) was prepared by a simple solvent casting technique in different compositions. The ionic conductivity of polymer blend electrolytes was investigated by varying the PAN content in the PVA matrix. The ionic conductivity of polymer blend electrolyte increased with the increase of PAN content. The effect of lithium salt concentrations was also studied for the polymer blend electrolyte of high ionic conductivity system. A maximum ionic conductivity of 3.76×10⁻³ S/cm was obtained in 3 M LiClO₄ electrolyte solution. The effect of ionic conductivity of polymer blend electrolyte was measured by varying the temperature ranging from 298 to 353 K. Linear sweep voltammetry and DC polarization studies were carried out to find out the stability and lithium transference number of the polymer blend electrolyte. Finally, a prototype cell was assembled with graphite as anode, LiMn₂O₄ as cathode, and polymer blend electrolyte as the electrolyte as well as separator, which showed good compatibility and electrochemical stability up to 4.7 V.     

Semiconductor-metal transition in FeSi in ultrahigh magnetic fields up to 450 T

The magnetic susceptibility and conductivity of single-crystal iron monosilicide are investigated in ultrahigh magnetic fields up to 450 T at a temperature of 77 K. It is found that the conductivity of iron monosilicide increases continuously by two orders of magnitude as the magnetic field increases. The results obtained can be interpreted as a semiconductor-metal transition induced by the magnetic field. The dependence of the conductivity on the magnetic field is described well on the basis of the spin-fluctuation theory. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 4, 326–330 (25 August 1998)     

Influence of the carbon substitution on the critical current density and AC losses in MgB<Subscript>2</Subscript> single crystals

The DC magnetization and AC complex magnetic susceptibilities were measured for MgB₂ single crystals, unsubstituted and carbon substituted with the composition of Mg(B_0.94C_0.05)₂. The measurements were performed in AC and DC magnetic fields oriented parallel to the c-axis of the crystals. From the DC magnetization loops and the AC susceptibility measurements, critical current densities (J _c were derived as a function of temperature and the DC and AC magnetic fields. Results show that the substitution with carbon decreases J _c ) at low magnetic fields, opposite to the well known effect of an increase of J _c at higher fields. AC magnetic losses were derived from the AC susceptibility data as a function of amplitude and the DC bias magnetic field. The AC losses were determined for temperatures of 0.6 and 0.7 of the transition temperature T _c , so close to the boiling points of LH₂ and LNe, potential cooling media for magnesium diboride based composites. The results are analyzed and discussed in the context of the critical state model.     

Synthesis,characterization, conductivity and sensor application study of polypyrrole/silver doped nickel oxide nanocomposites

Conducting polymer composites of polypyrrole (PPy) and silver doped nickel oxide (Ag-NiO) nanocomposites were synthesised by in situ polymerisation of pyrrole with different contents of Ag-NiO nanoparticles. The formation of nanocomposites were studied by Fourier transform infrared (FTIR) and UV–vis spectroscopy, field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and AC and DC conductivity measurements. The sensitivity of ammonia gas through the nanocomposite was analysed with respect to different contents of nanoparticles. Spectroscopic studies showed the shift in the absorption bands of polymer nanocomposite than that of pure PPy indicating the strong interaction between the nanoparticles and polymer chain. FESEM revealed the uniform dispersion of nanoparticles with spherically shaped metal oxide particles in PPy matrix. The XRD pattern indicated a decrease in amorphous domain of PPy with increase in loading of nanoparticles. The higher thermal stability and glass transition temperature of polymer nanocomposites than that of pure PPy were revealed from the TGA and DSC respectively. The dielectric properties, DC and AC conductivity of nanocomposites were much higher than PPy and these electrical properties increases with the loading of nanoparticles. The nanocomposites showed an enhancement in sensitivity towards ammonia gas detection than PPy.     

Magnetization and actuation of polymeric microstructures with magnetic nanoparticles for application in microfluidics

An increasing number of lab-on-a-chip devices require advanced fluid manipulations. We intend to address this requirement by incorporating polymeric responsive materials on the walls of the microfluidic channels of such devices. In this paper we present a magnetic polymer made from commercially available functionalized magnetic nanoparticles and PDMS. Loadings of this polymer up to 5% volume of magnetic material were achieved. We report on the Young's modulus of this material and describe its magnetization behavior with a combination of inter-particle interaction and particle cluster demagnetization effects. The magnetic polymer can have a magnetic susceptibility up to 0.5 and by curing in a magnetic field, a magnetic anisotropy of a factor 2 in susceptibility can be created. Finally, a finite element model simulation is performed to quantify the amplitude of motion of a microstructure made of this magnetic polymer, and the local magnetic actuation with a current running in a micro-fabricated wire is discussed.     

Finite element analysis of AC loss in non-twisted Bi-2223 tape carrying AC transport current and/or exposed to DC or AC external magnetic field

AC losses in Bi-2223 superconducting tapes carrying AC transport current and/or exposed to DC or AC magnetic field are calculated with a numerical model based on the finite element method. Superconducting property is given by the E–J characteristic represented by a power law using equivalent conductivity. First, transport loss and magnetization loss are calculated numerically and compared with measured values. The calculated losses almost agree with the measured losses. Frequency dependencies of calculated and measured transport losses are compared with each other. Next, the influence of DC external magnetic field on the transport loss is studied. DC external magnetic field reduces n that is an exponent in the power law connecting resistivity and current density. The numerically calculated transport loss increases with increasing DC magnetic field. Finally, the total loss of superconducting tape carrying AC transport current in AC magnetic field is calculated. In the perpendicular magnetic field, the calculated total loss is lager than the sum of the transport loss and the magnetization loss, while they almost agree with each other in the parallel magnetic field.     

Anomalous properties of new organic conductors: Comparison of bromanil,chloranil, and tetracyanoquinodimethane (TCNQ) salts of tetramethyltetrathiafulvalene (TMTTF)

Structural, conductivity, magnetic susceptibility, optical, infrared, and Raman data are reported for two new highly conducting organic solids, the bromanil and chloranil salts of TMTTF (tetramethyltetrathiafulvalene). These compounds are shown to have the two basic features essential to an organic metal: segregated stacks of planar, polarizable organic molecules and incomplete charge transfer. Nevertheless, their properties are strikingly different than, for example, those of the TMTTF salt of TCNQ (tetracyanoquinodimethane). The properties of the latter are typical of TCNQ-containing organic metals, with the conductivity and magnetic susceptibility $\text{both}$ becoming thermally activated below a (presumably) Peierls transition. In TMTTF-bromanil, on the other hand, the conductivity is already activated at room temperature, well above the transition (～75K) in the susceptibility. This behavior is not characteristic of a simple quasi-one-dimensional metal. Rather it indicates a magnetic semiconductor with appreciable Coulomb interactions, which undergoes a spin-Peierls-like transition at lower temperatures. The reason why the effects of Coulomb interactions are more dramatically manifested in these compounds is not understood.     

Nonequilibrium paramagnetic susceptibility of gallium impurity centers in lead telluride

The temperature dependences of the resistance and magnetic susceptibility are studied in gallium-doped lead telluride, which is characterized by a delayed photoconductivity effect, under various illumination conditions. After a sample is illuminated at low temperatures, the magnetic susceptibility is diamagnetic in the region of metallic delayed conductivity (for T<=0 K). In the region of thermodynamic equilibrium (T<70 K), where conductivity is activational, the magnetic susceptibility is likewise diamagnetic and essentially equals the low-temperature value. A paramagnetic susceptibility peak is observed in the transitional region (T∼50–70 K), where the conductivity is of a nonequilibrium character but the carriers are still nondegenerate. This peak increases in magnitude with the rate of measurements in the indicated temperature range. In addition, a paramagnetic variation of the susceptibility following the Curie law is observed with uncontrollable (weak) illumination from the cryostat cap at low temperatures (T<25 K). The interpretation of the observed dependences is based on notions of variable valence of gallium in lead telluride, while the appearance of a paramagnetic susceptibility peak is attributed to the presence of shallow localized levels of gallium in a trivalent state. Zh. éksp. Teor. Fiz. 114, 1859–1867 (November 1998)     

Structural and electrical characterizations of 50:50 PVA:starch blend complexed with ammonium thiocyanate

The present work deals with the preparation and characterization of polymer blend electrolyte films. Glutaraldehyde is used as a cross-linker to cross-link polymers polyvinyl alcohol (PVA) and starch for the proper film formation. Structural characterizations such as X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) have been performed. X-ray diffraction is done to investigate the amorphous nature of the sample. FTIR study confirms about the complexation of salt with the polymer and interaction of thiocyanate ion with the polymer matrix. Electrical characterizations were done using impedance spectroscopy. DC and AC ionic conductivity was obtained at varying salt concentration in the films which shows maximum ionic conductivity of the polymer electrolyte containing 30 wt% of salt content. The AC conductivity behaviour of the polymer electrolyte follows Jonscher’s power law. Dielectric parameters such as dielectric constant, dielectric loss and loss tangent have been determined. Relaxation time is obtained and decreases to lower value with the increase in the salt concentration in the polymer electrolyte.     

Semiconductor-metal transition in defect lithium cobaltite

The magnetic susceptibility, electrical conductivity, and x-ray photoelectron and x-ray absorption spectra of defect lithium cobaltites of the general formula Li_{1 ? x} CoO₂ are investigated. It is found that, for lithium cobaltites with x > 0.25, the magnetic susceptibility increases abruptly and the conductivity type changes at T ～ 150 K. The assumption is made that the semiconductor-metal transition in defect lithium cobaltite is caused by the increase in the diffusion mobility of lithium ions with an increase in the temperature when there is a correlation between spatial distributions of lithium vacancies and “electron” holes.     

Alternating current electrical conductivity of high-density polyethylene-carbon nanofiber composites

High-density polyethylene (HDPE)-carbon nanofiber (CNF) composites with good dispersion of fillers in the polymer matrix were melt-compounded in a Haake mixer. The dependences of the alternating current conductivity of such nanocomposites on the filler content, temperature, and DC bias were investigated. The results showed that the electrical conducting behavior of HDPE-CNF nanocomposites can be well characterized by the direct current conductivity ( s_DC \sigma_{{{\rm DC}}}^{} , characteristic frequency (f_c) and critical exponent (s . It was found that s_DC \sigma_{{{\rm DC}}}^{} of percolating HDPE-CNF nanocomposites increases with increasing filler concentration and follows the scaling law of percolation theory. Increasing temperature caused a reduction of s_DC \sigma_{{{\rm DC}}}^{} , leading to the occurrence of positive-temperature-coefficient effect near the melting temperature of HDPE matrix. Application of DC bias led to an increase of s_DC \sigma_{{{\rm DC}}}^{} due to the creation of additional conducting paths within the polymer composites. The characteristic frequency generally followed the same tendency as s_DC \sigma_{{{\rm DC}}}^{} . The s values of percolating composites were slightly higher than those predicted by the percolation theory, indicating the presence of tunneling or hopping conduction in these composites.     

MAGNETIC AND ELECTRICAL PROPERTIES OF TWO POLYANILINE FAMILIES:PANI-H3PO4 and PANI-C4H6O6

We report a comparative study between two kinds of polyaniline, PANI-H₃PO₄ and PANI-C₄H₆O₆. We have measured the temperature dependence of the dc-conductivity σ_dc(T) and magnetic susceptibility χ_T(T). The structure of polyaniline was characterized by F ourier transform infrared technique, electron-spin-resonance and X-ray diffraction. Polyanil ine synthesized with phosphoric and tartaric acids leads to high magnetic suscep tibility χ_T(at T=295 K)≈10^-4 emu/mol.2rings. The dc-conductivity of both kinds of PANI shows a semiconductor behavior and follows the quasi one-dimensional variable-range-hopping model. A compa rison of the magnetic susceptibility shows greater electron localization in PANI-C₄H₆O₆, which is in agreement with the lower conductivity at room temper ature for PANI-C₄H₆O₆.