Showing papers by "Ajit Kumar Meikap published in 2010"

Synthesis of copper chloride and cobalt chloride doped polyanilines and their magnetic and alternating-current transport properties

Abstract: Polyaniline (PANI) was synthesized by the well-known oxidative polymerization of aniline with ammonium peroxodisulfate as the oxidant. The morphological, structural, thermal, optical, magnetic, and electrical properties were characterized with scanning electron microscopy, X-ray diffraction, Fourier transform infrared, thermogravimetric analysis, differential scanning calorimetry, ultraviolet–visible spectroscopy, room-temperature magnetic measurements, and low-temperature electrical transport measurements by the standard four-probe method. Greater thermal stability and crystallinity were observed in doped PANI versus pure PANI. Magnetic measurements showed that the magnetic susceptibility was field-dependent. Positive and negative susceptibility values were observed. This may have been due to the interactions of magnetic ions among interchains or intrachains of the polymer matrix. The alternating-current (ac) conductivity was measured in the temperature range of 77–300 K in the frequency range of 20 Hz to 1 MHz. The frequency-dependent real part of the complex ac conductivity was found to follow the universal dielectric response: σ′(f) ∝ fs [where σ′(f) is the frequency-dependent total conductivity, f is the frequency, and s is the frequency exponent] The trend in the variation of the frequency exponent with temperature corroborated the fact that correlated barrier hopping was the dominant charge-transport mechanism for PANI–CoCl2. An anomalous dependence on temperature of the frequency exponent was observed for PANI–CuCl2. This anomalous behavior could not be explained in terms of existing theories. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Synthesis of La0.67Sr0.33MnO3 and polyaniline nanocomposite with its electrical and magneto-transport properties

Abstract: We have synthesized composite of polyaniline nanotubes with lanthanum strontium manganite (La0.67Sr0.33MnO3) (LSMO) nanoparticles. Scanning electron microscopy, x-ray diffraction, Fourier transform infrared, and thermogravimetric analysis scans are done for morphological, structural, and thermal characterization of polyaniline-LSMO nanocomposite. Room temperature hysteresis loop shows ferromagnetic behavior of polyaniline-LSMO nanocomposite but with very low saturation magnetization. Overall pattern of temperature dependence of resistivity for polyaniline has been best-fitted with the form ln[ρ(T)]∝T−1/2. This may be attributed to quasi-one dimensional hopping and also tunneling between mesoscopic ferromagnetic metallic islands. Total resistivity due to grain and grain boundary reduces by application of magnetic field. Remarkable increase (∼73%) in magnetoresistance (MR) is obtained in these polymer coated LSMO compared to the without coated counterpart (16%). The MR% is found to increase with the increas...

Characterization and electrical transport properties of polyaniline and multiwall carbon nanotube composites

Abstract: Polyaniline/multiwalled carbon nanotube (PANI/MWNT) composites were prepared by in situ polymerization Scanning electron microscope, X-ray diffraction, Fourier transform infrared, Uv-Visible spectroscopy, Fluorescence spectrophotometry were done to characterize the PANI/MWNT composites Thermal stability was measured by thermogravimetry analysis The thermal stability of PANI/MWNT composites becomes higher than PANI Electrical transport properties of different PANI/MWNT composites were investigated in the temperature range 77 ≤ T ≤ 300 K with and without magnetic field up to 1 T The dc resistivity of PANI/MWNT composites shows different behavior compared to the sample without MWNT The room temperature dc magnetoconductivity of the samples is negative; however, its sign changes to positive by lowering the temperature, which has been explained by hopping type charge transport © 2010 Wiley Periodicals, Inc J Polym Sci Part B: Polym Phys 48: 1767–1775, 2010

Synthesis, magnetic, optical, and electrical transport properties of the nanocomposites of polyaniline with some rare earth chlorides

Abstract: Nanocomposites of polyaniline with some rare earth chlorides like neodymium chloride, europium chloride, and dysprosium chloride were synthesized by chemical oxidative polymerization of aniline. Morphological, structural, thermal, optical, magnetic, and electrical properties of the samples were characterized by scanning electron microscope, x-ray diffractometer, Fourier transform infrared spectrometer, thermogravimetric analyzer, differentiating scanning calorimeter, optical absorption spectroscopy, room temperature magnetic susceptibility measurement, and low temperature electrical transport measurement. Nanocomposites were thermally more stable than pure polyaniline and they were more crystalline than pure polyaniline. Magnetic susceptibilities of the samples were field dependent. Three-dimensional variable range hopping charge transport mechanism was followed by the samples. The dc magnetoconductivity of the composites can be explained in terms of forward interference effect and wave function shrinkage...

A method of optical implementation of frequency encoded all optical logic gates based on multiphoton processes in non linear material

Abstract: A novel frequency encoded all optical logic gates are proposed exploiting multiphoton processes in non linear optical medium. In the frequency encoding of the information the ‘0’ is represented by a frequency ω and ‘1’ is represented by another frequency 2ω. The gates proposed are NOT, OR, AND, NAND and NOR among which NAND and NOR are universal. Using these gates one can generate other important gates and logical function generating all optical devices. Two main three-photon processes, second harmonic generation (SHG) and parametric light generation (PLG) are used to implement the gates and the corresponding appropriate non linear material is LiB3O5 (LBO) which has wide operating and transparency range in the wavelength 350–3,200 nm. The source of optical frequency encoded signal may be derived from an external cavity diode laser generating a wavelength 1,560 nm for ω (‘0’ state of information) and its second harmonic 780 nm for 2ω (‘1’ state of information).

Electrical Conductivity, Magnetoconductivity and Dielectric Behaviour of (Mg,Ni)-Ferrite below Room Temperature

Abstract: We report a comprehensive study of electrical transport properties of stoichiometric (Mg,Ni)-ferrite in the temperature range 77 ≤ T ≤ 300K, applying magnetic field upto 1T in the frequency range 20 Hz-1 MHz. After ball milling of MgO, NiO and ?-Fe2O3 and annealing at 1473K, a (Mg,Ni)-ferrite phase is obtained. The temperature dependency of dc resistivity indicates the prevalence of a simple hopping type charge transport in all the investigated samples. The activation energy decreases by annealing the samples by 1473K. The dc magnetoresistivity of the samples is positive, which has been explained by using wave function shrinkage model. The frequency dependence of conductivity has been described by power law and the frequency exponent ‘s’ is found to be anomalous temperature dependent for ball milling and annealing samples. The real part of the dielectric permittivity at a fixed frequency was found to follow the power law ?/(f,T) ? Tn. The magnitude of the temperature exponent ‘n’ strongly depends on milling time and also on annealing temperature. The dielectric permittivity increases with milling and also with annealing. An analysis of the complex impedance by an ideal equivalent circuit indicates that the grain boundary contribution is dominating over the grain contribution in conduction process.

Alternate current conductivity and dielectric properties of nonstoichiometric nanocrystalline Mg–Zn ferrite below room temperature

Abstract: Nanocrystalline Mg–Zn ferrite is prepared by ball milling the stoichiometric powder mixture of MgO, ZnO and α-Fe 2 O 3 . The ternary Mg–Zn ferrite phase may not be obtained by heat treatment of the stoichiometric powder mixture of the oxides. The particle size of ferrite phase in the ball milled samples remains almost unaltered (∼3 nm) and that of in annealed samples increases up to ∼330 nm. Alternate current conductivity and dielectric properties of nanocrystalline Mg–Zn ferrite in the temperature range 77≤ T ≤300 K, applying magnetic field up to 1 T in the frequency range 20 Hz–1 MHz, are being reported. The frequency dependence of conductivity has been described by power law σ′( f , T )∝ f s and the frequency exponent ‘ s ’ is found to be anomalous temperature dependent. A detailed analysis of the temperature dependence of the universal dielectric response parameter ‘ s ’ revealed that the correlated barrier hopping is the dominating charge transport mechanism. The real part of the dielectric permittivity at a fixed frequency was found to follow the power law e ′( f , T )∝ T n and the magnitude of the temperature exponent ‘ n ’ strongly decreases with increasing frequency. The dielectric permittivity shows a large degree of dispersion at low frequency, but rapid polarization at high frequencies, which can be interpreted by the Maxwell-Wagner capacitor model. The temperature dependence of resistance due to grain and grain boundary contribution exhibits two activation regions. The observed positive ac conductivity may be due to the change of grain and grain boundary resistances caused by the magnetic field.

Direct Current Electrical Transport and Magneto Transport Properties of Polyaniline Nanocomposites

Abstract: Polyaniline nanocomposites were prepared by in-situ polymerization with hydrochloric acid (HCl), Copper Chloride (CuCl2) and multiwall Carbon Nanotube (MWCNT). The samples were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM). Direct current electrical conductivity was measured within a temperature range 77≤T≤300K in presence and in absence of a magnetic field up to 1Tesla. The dc transport properties of the samples follow the variable range hopping (VRH) theory. The magnetoconductivity of the samples have been explained by wave function shrinkage model and forward interference model.