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    Effect Y substitution on the microstructure, transport and magnetic proprieties of Bi2Sr2Ca1Cu2O8+delta superconducting ceramics
    (De Gruyter Open Ltd, 2016) Menassel, Salem; Mosbah, F.M.; Boudjadja, Yasin; Altıntaş, Sevgi Polat; Varilci, Ahmet; Terzioğlu, Cabir
    In high Tc superconductors (HTSC) the activation energy gives information about the pinning properties of a sample under applied magnetic field. Pinning of vortices determines the critical current density Jc which is of great importance for practical applications of HTSC. Instead of magnetic measurements, the activation energy may be calculated from resistivity measurements realized under magnetic field. This kind of measurement has been made in this work for yttrium doped samples of Bi2Sr2CaCu2O8+delta (Bi-2212) for different values of applied magnetic field. Samples of Bi(2)Sr(2)Ca(1-x)Y(x)Cu(2)O(8+)d (x = 0, 0.025, 0.1, 0.25) were prepared by a sol-gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive analysis of X-ray. The measurements of resistivity were made using a classical four probe method and DC current. The magnetic field was applied with a constant amplitude of 0 T, 1 T, 2 T and 3 T. The obtained results show that the activation energy decreases with introduction of yttrium, but has a relative maximum when x is equal 0.1. The decrease of the activation energy is explained by the granular nature of the samples which promotes 3D transition to 2D of the vortex lattice.
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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.