P. C. Jana

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

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...

Synthesis, electrical transport and optical properties of polyaniline-zirconium nanocomposite

Here, we report the synthesis of polyaniline-zirconium nanocomposite by chemical oxidative polymerization of aniline. Structural, thermal, and morphological properties of the samples are characterized by XRD, FTIR, TGA, SEM, and UV-Vis spectroscopy. Crystalline behavior of the nanocomposite has been obtained due to the presence of zirconium nanoparticles in polyaniline. FTIR analysis reveals the formation of polyaniline and changes to the structure of polyaniline due to the presence of zirconium nanoparticles. Granular morphology of the nanocomposite has been obtained from SEM micrographs and its conductivity has been increased due to the incorporation of zirconium nanoparticles. Temperature dependence of the resistivity has been fitted with ln [ρ(T)] ∝ T−1/4 which indicates three dimensional variable range hopping transport mechanism. ac conductivity follows the correlated barrier hopping transport mechanism. Some optical parameters like bandgap (Eg), peak transition energy (E0), and peak broadening para...

Determination of Refractive Index Profile and Mode Index from the Measured Mode Profile of Single-Mode LiNbO3-Diffused Waveguides

Abstract A refractive index profile and a mode index of single-mode LiNbO3 channel waveguides are simultaneously estimated from the measured near-field intensity distributions. A third-order low-pass Butterworth filter is used to filter the measured amplitude and its double derivative to remove high-frequency spatial noise and impulses. The mode index or effective index of the propagating mode is extracted by matching the index change profile equal to zero at the waveguide boundary. The proposed technique is applicable to any slowly varying, single-mode, integrated-optic waveguide for TE and TM modes and for any operating wavelength within the single-mode regime.

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

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...

Effect of samarium nanoparticles on the electrical transport properties of polyaniline

A comprehensive study of the effect of samarium nanoparticles on electrical transport properties of polyaniline has been reported. Samples are prepared by chemical oxidative polymerization of aniline in the presence of samarium nanoparticles and characterized by XRD, FESEM, EDS, HRTEM and UV-Vis spectrometer. When the samarium content in polyaniline matrix increases, energy band gap decreases and conductivity increases by four orders of magnitude. A transformation of negative to positive magnetoconductivity has been observed by incorporating samarium nanoparticles in polyaniline matrix. Two types of activation behavior have been observed from the dielectric relaxation behavior. AC conductivity strongly depends on magnetic field. Although, at present, no theoretical model is found in literature to explain directly the behavior of ac conductivity in the presence of magnetic field, it may be due to the change of grain and interfacial boundary resistances by magnetic field.

Comparison of calculated and measured refractive index profiles of continuous wave ultravoilet written waveguides in LiNbO3 and its analysis by effective index based matrix method

The refractive index profiles of the continuous wave (CW) UV-written waveguides in congruent LiNbO3 crystal are theoretically computed and compared with the evaluated profiles from the measured mode intensity distributions. It has been observed that change in activation energy of Li-indiffusion affects the computed refractive index profiles to a large extent, and the computed and measured profiles match fairly well for 305 nm and 275 nm written waveguides with an activation energy equal to ∼1.3 eV. The calculated refractive index profiles are used in effective index based matrix method (EIMM) to compute the guided mode propagation constants of these waveguides at 632.8 nm transmitting wavelength. For both the writing wavelengths, the waveguides are single mode in nature, which tally with experimental results. The bending losses of the bent waveguides for different bending radii are also computed using a conformal mapping technique along with EIMM. Finally, the behavior of CW UV-written waveguides under an...

Theoretical Estimation of Refractive Index of Continuous Wave UV Induced Waveguide in LiNbO

A theoretical modeling of continuous wave UV laser induced waveguides in congruent LiNbO3 is presented considering temperature dependent absorption coefficients at 305 nm and 275 nm writing wavelengths. The extrapolated empirical relations of absorption coefficient with temperature, extracted from the published experimental data, is used for the purpose. Some of the previously published experimental findings of the fabricated waveguides are justified with this model, which otherwise seem impossible.

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In this work a novel chemical reduction method at room temperature is described to synthesize nanocrystalline ZnS, CdS, ZnxCd1-xS. The method is cheap and cost effective. The grown nanoparticles are characterized by XRD, TEM, EDX, UV-VIS absorption and PL study. CdS formation is supported by the systematic splitting of x-ray diffraction peak at lower angle and the peaks are identified. ZnS peaks are also identified comparing with ICDD data. EDX analysis shows two other phases Zn 0.8 Cd 0.2 S, Zn 0.5 Cd 0.5 S. The particle sizes are in the range 4-8 nm. The band gap changes with change of composition. Also at each composition the band gap is greater compared to bulk band gap. This indicates quantum confinement takes place. The band gap energy of nanoparticles can be tuned to a lower energy by increasing the Cd content, indicating the formation of the alloyed nanoparticles. PL peak shifts towards higher wavelength as Cd content increases. The peak corresponds to transition associated with surface state.

Considering Temperature Dependent Absorption Coefficient

Abstract A semi-analytical technique, effective index-based matrix method (EIMM), has been applied to determine the coupling length of continuous wave UV-written directional coupler for different gaps between the waveguides as well as the pure bending loss and transition loss of S-curved waveguides estimated to optimize the transition length (L) and lateral offset (h). The refractive index profiles of the directional coupler were computed by solving the heat flow equation on the surface of LiNbO3 crystal, and used as input to EIMM.

Composition Dependent Structural and Optical Properties of Nanocrystallites ZnxCd1-xS

Using short-time dynamics and analytical solution of Heisenberg equation of motion for the Hamiltonian of quadratically-coupled optomechanical system for different field modes, we have investigated the existence of higher-order single mode squeezing, sum squeezing and difference squeezing in absence of driving and dissipation. Depth of squeezing increases with order number for higher-order single mode squeezing. Squeezing factor exhibits a series of revival-collapse phenomena for single mode, which becomes more pronounced as order number increases. In case of sum squeezing amounts of squeezing is greater than single mode higher-order squeezing (n = 2). It is also greater than from difference squeezing for same set of interaction parameters. Sum squeezing is prominently better for extracting information regarding squeezing.