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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 of yttrium doping on magneto-transport properties of Bi(Pb)-2212 superconductors
    (Springer, 2013) Boudjadja, Yazid; Amira, Abderrezak; Saoudel, Amira; Amirouche, L.; Mahamdioua, Namir; Varilci, Ahmet; Altıntaş, Sevgi Polat
    An analysis of the temperature dependence of resistivity results under magnetic fields (0-7 T) is presented for yttrium doped Bi1.6Pb0.4Sr2Ca1-x Y (x) Cu2O8+delta and Bi1.6Pb0.4Sr2-x Y (x) CaCu2O8+delta (x=0 and 0.075) superconductors. The experimental methodology is mainly based on DC measurements in the range temperature of 10-300 K. The activation energy (U (0)) is calculated using the Arrhenius law (rho(T)=rho (0)exp(-U (0)/K (B) T)). The irreversibility fields (mu (0) H (irr)) and upper critical fields (mu (0) H (c2)) are extracted using the previously proposed methods. The study shows that the highest values of these parameters are seen for the doped sample at the Ca site, suggesting that the flux lines are effectively pinned in this compound when compared to the others. The calculated physical parameters such penetration depth (lambda(0)) and coherence length (xi(0)) are also in good agreement with values previously published for this phase. The upper critical field has a maximum value when the hole concentration per CuO2 unit (P) is around 0.179.
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    On the effect of carbon nano-tubes addition on structure and superconducting properties of Bi(Pb)-2223 phase
    (Springer, 2013) Saoudel, Abdelmalek; Amira, Abderrezak; Boudjadja, Yazid; Amirouche, L.; Mahamdioua, Nabil; Varilci, Ahmet; Altıntaş, Sevgi Polat
    In this work, a series of ceramic samples of Bi1.6Pb0.4Sr2Ca2Cu3O (y) (Bi(Pb)-2223) added with different amounts (0, 0.2 and 0.4 wt%) of carbon nano-tubes (CNT) are prepared from commercial powders and characterized. The study shows that the volume fraction of the Bi(Pb)-2223 phase decreases with CNT content while the grain size of the samples increases. The obtained cell parameters as well as the onset critical transition temperature are independent of this kind of addition. Also, it has been concluded that CNT addition makes the grains of the samples more connected. The measured magnetization in FC and ZFC modes indicates that CNT addition makes the grains of the samples more connected even if the irreversibility line is decreased. The variation of the residual resistivity and metalicity with CNT content suggests that the addition introduces disorder and defects into the samples. Also, the added samples present broad transitions to the superconducting state when compared to the pure one; this result may be associated to the increase of the volume fraction of the secondary phases. The activation energies, upper critical fields H (c2)(0) and coherence lengths xi(0) are extracted from the magneto-resistivity curves and their evolutions with CNT content are discussed.
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    Structural and electrical properties of fluorine doped (Bi, Pb)-1212 ceramics
    (Springer, 2013) Amirouche, L.; Amira, Abderrezak; Saoudel, Abdelmalek; Boudjadja, Yazid; Mahamdioua, Nabil; Varilci, Ahmet; Altıntaş, Sevgi Polat
    In the aim to test the effect of fluorine doping on structural and electrical properties of semiconducting Bi(Pb)-1212 phase, bulk samples with nominal composition of Bi0.4Pb0.35Sr2Y0.8Ca0.2Cu2.05O (y) F (x) with x=0,0.2,0.4 and 0.6 are prepared in air by solid state reaction method and characterized. Similarly to other Bi-based cuprates, the scanning electron microscopy shows that fluorine doping increases the grain size of the samples. The obtained X-ray diffraction patterns are indexed in P4/mmm space group. A slight increase of cell volume by doping is revealed, a result which is in line with that seen in Y-123 compounds. Even if the resistivity decreases with fluorine content, all compounds exhibit a semiconducting behavior. The conduction mechanism obeys well to the two dimensional variable range hopping (2D-VRH) model from room temperature down to approximately 40 K. The analysis of the fitting results suggests that the improvement of electrical conduction could be due to a delocalization of charge carriers.
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    Study of the thermo-magnetic fluctuations in carbon nano-tubes added Bi-2223 superconductors
    (Elsevier, 2013) Saoudel, Abdelmalek; Amira, Abderrezak; Boudjadja, Yazid; Mahamdioua, Nabil; Amirouche, L.; Varilci, Ahmet; Altıntaş, Sevgi Polat; Terzioğlu, Cabir
    We have investigated the effect of addition of carbon nano-tubes (CNT) on the properties of Bi1.6Pb0.4Sr2Ca2Cu3Oy superconductors. The samples are prepared from commercial powders with addition of 0.1 wt% of CNT. They are characterized by XRD, SEM and magneto-resistivity in the transition region. As it was reported for CNT added Y-123 compounds, the refined cell parameters are practically independent of this kind of addition. Under applied magnetic field, a large broadening of resistive transition is observed. The dissipative behavior of resistivity can be explained using the well known expression, rho=rho(0)(T/T-g-1)(S). The modified vortex-glass to liquid transition theory is used to calculate the values of the glass-transition temperature T-g and the temperature and magnetic field dependent activation energy U-0(B,T). These parameters are seen to decrease with CNT addition and applied magnetic field. Also, we have found that the undoped sample proves a better transition width, residual resistivity (rho(0)) and a higher onset critical transition temperature of about 117.75 K. Also, the appearance of a double resistive transition for both samples is a confirmation of the existence of a secondary phase which plays the role of the weak links at the grain boundaries. (C) 2013 Elsevier B.V. All rights reserved.