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    Improvement of superconducting properties of (Bi, Pb)-2223phase by TlF3 doping
    (Elsevier Science Bv, 2016) Saoudel, Abdelmalek; Amira, Abderrezak; Mahamdioua, Nebil; Boudjadja, Yasin; Varilci, Ahmet; Altıntaş, Sevgi Polat; Terzioğlu, Cabir
    In this work, the superconducting properties of thallium fluoride (TlF3)doped Bi1.8-xTlxPb0.35Sr2Ca2Cu3 OyF3x(x=0-0.15)compounds are presented. The X-ray diffraction analysis shows that the proportion of (Bi, Pb)-2223phase is higher than the secondary (Bi, Pb)-2212 one in all samples and its highest value is about 82.74% for x=0.05. From the resistivity curves, the highest values of the onset critical transition temperature (T-c.on), the offset critical transition temperature (T-c.off) are seen for x=0.10. The calculation of activation energy (U-0) in the TAFF (thermally activation flux flow) region proves the positive effect of TlF3 doping on the dissipative behavior of energy near T-c.off. Flux pinning strength is enhanced by increasing TlF3 content up to x=0.10, and decreased by the application of a magnetic field. The other superconducting parameters like T(H-c2), T(H-irr), xi(0) and mu H-0(c2)(0) are also improved significantly by doping. The obtained results of Ac susceptibility measurements show that the onset temperature of diamagnetism is improved by TlF3 doping, in accordance with the resistivity results. (C) 2016 Elsevier B.V. All rights reserved.
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    Magnetoresistive properties of cerium doped La0.7Ca0.3MnO3 manganites
    (Elsevier B.V., 2016) Chihoub, Ra; Amira, Abdul; Mahamdioua, Nebil; Altıntaş, Sevgi Polat; Varilci, Ahmet; Terzioğlu, Cabir
    In this work, the effect of doping by tetravalent Ce4+on the structural and magnetoresistive properties of La0.7-xCexCa0.3MnO3 polycrystalline manganites is presented. Samples with x=0, 0.1, 0.2 and 0.3 are prepared by solid state reaction method and characterized. For all doping levels, the X ray diffraction (XRD) analysis shows that the doping element is not completely soluble in the manganite. The cell parameters values, which decrease with Ce content, are refined in the orthorhombic system by taking into account the unreacted CeO2 phase. The observation by scanning electron microscopy (SEM) reveals a change in the morphology of the grains and the porosity of the samples by doping. The temperature dependence of magnetization curves shows a transition from paramagnetic to ferromagnetic state in all samples. A decrease of the Curie temperature Tc with doping is revealed. The resistivity of the samples increases with Ce content and shows a clear metal to insulator transition when measured as a function of temperature. The doping also decreases the temperature Tp of this transition, in accordance with the evolution of Tc values. The calculated magnetoresistance (MR) for a magnetic field of 5T increases gradually from 39.52% for x=0 to 66.18% for x=0.3. © 2016 Elsevier B.V. All rights reserved.