Yazar "Boudjadja, Y." seçeneğine göre listele

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    Effect of doping by low content of yttrium at Ca and Sr sites of Bi(Pb)-2212 superconducting ceramics
    (Elsevier, 2011) Amira, Abderrezak; Boudjadja, Y.; Saoudel, A.; Varilci, Ahmet; Akdoğan, Mustafa; Terzioğlu, Cabir
    In this work, a comparative study of the effect of doping bylaw content of Y3+ between (Ca site) and out of (Sr site) the CuO2 planes of Bi(Pb)-2212 phase is presented. Ceramics of Bi1.6Pb0.4Sr2Ca1-xYxCu2O8+d (called CY series) and Bi1.6Pb0.4Sr2-xYxCaCu2O8+d (called SY series) with x=0, 0.025, 0.05, 0.075 and 0.1 are elaborated in air by conventional solid state reaction. They are characterized by X-ray diffraction (XRD), Scanning Electronic Microscopy (SEM), density, Vickers microhardness and resistivity measurements. The refinement of cell parameters is done by considering the structural modulation. In comparison with the undoped sample (x=0), the cell parameters a, b and c are reduced by the doping for both series while the b component of the modulation vector increases. A good correlation between the variations of the bulk density and the Vickers microhardness with x is obtained. For both series, the SEM analysis shows that the doped samples exhibit a reduced grain size than that of the undoped one. The variation of resistivity with temperature shows that all samples exhibit a metallic-like character in the normal state. For all doping levels, the CY series presents higher onset critical transition temperature than that of the undoped sample, which is equal to 85.43 K. The opposite is obtained for SY series. The highest value of this temperature is obtained for x=0.075 in the doped samples and is about 92.15 and 79.96 K for CY and SY series, respectively. These values may correspond to a near optimally doped state since the slope (d rho/dT) of resistivity shows a maximum at the same value of x=0.075. For both series, when Y3+ is introduced into the samples, the residual resistivity decreases first for x=0.025 and increases gradually after this value until x=0.1. (C) 2010 Elsevier B.V. All rights reserved.
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    Effect of fluorine doping on phase formation and properties of Bi(Pb)-2223 ceramics
    (Elsevier Science Bv, 2011) Amira, A.; Saoudel, A.; Boudjadja, Y.; Amirouche, L.; Mahamdioua, N.; Varilci, Ahmet; Akdoğan, Mustafa; Terzioğlu, Cabir
    Superconducting ceramics of Bi1.6Pb0.4Sr2Ca2Cu3OyFx (x = 0-0.6) are prepared in air by conventional solid state reaction and characterized. The study shows that the melting point of the samples decreases as fluorine content increases. As a consequence, the grain size increases with the doping level and for x = 0.6, the sample is completely deformed and presents a concave shape making impossible the measurements on it. The Vickers microhardness reaches its maximum for x = 0.2. The analysis of the X-ray diffraction results reveals that all the samples are composed of only Bi(Pb)-2212 and Bi(Pb)-2223 phases. The highest proportion of the high T-c phase (Bi(Pb)-2223) is also observed for x = 0.2 and is about 67.32%. The refinement of cell parameters is done by considering the structural modulation. The results show that the doping leads to a reduction of cell volume as well as the a axis component of modulation. Fran resistivity versus temperature measurements, it is shown that the doped phases exhibit higher onset critical transition temperatures than the undoped one. The residual resistivity increases with fluorine content suggesting that the doping introduces structural defects and disorder into the samples. The obtainal critical current density at 77 K under zero magnetic field also increases with fluorine doping. (C) 2011 Elsevier B.V. All rights reserved.
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    Effect Y substitution on the microstructure, transport and magnetic proprieties of Bi2Sr2Ca1Cu2O8+? superconducting ceramics
    (Walter de Gruyter GmbH, 2016) Menassel, S.; Mosbah, M.-F.; Boudjadja, Y.; Altintas, S.P.; Varilci, A.; Terzioglu, C.
    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+d (Bi-2212) for different values of applied magnetic field. Samples of Bi2Sr2Ca1-xYxCu2O8+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. © 2016 Wroclaw University of Technology.
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    Investigation of Cr addition effect on structural, morphological, electrical and magnetic properties of Bi(Pb)-2212 superconductors
    (Springer, 2023) Menassel, S.; Galluzzi, A.; Boudjadja, Y.; Altıntaş, Sevgi Polat; Terzioğlu, Cabir; Polichetti, M.
    The main purpose of this research work will assess the effect of Cr addition on the properties of Bi1.8Pb0.4Sr2CaCu2O8+d superconducting ceramics. The samples are produced from industrial powders with different amounts of Cr (0, 1, 2, 3, 4, 5, 6 and 7 wt %) by sol-gel synthesis route. The influence of doping element has been determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), electrical resistivity and magnetic characterizations. In particular, the eventual presence of secondary phases as a result of Cr doping on the undoped sample was investigated by using XRD. By means of SEM analysis, the Cr doping influence on the grain morphology of the samples was explored. Contrarily, the T-c,T-on and the T-c,T-off of the samples have been obtained by using electrical resistivity measurements and their behavior as a function of the Cr doping has been discussed. Finally, by performing magnetization analysis versus temperature and magnetic field, the behavior of the critical temperature T-c and of the critical current density J(c) as a proportion of the Cr concentration has been discussed.