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Öğe The effect of TlF3 substitution on the weak links behaviour and AC susceptibility of Bi1.8-xTlxPb0.35Sr2Ca2Cu3OyF3x superconductors(Elsevier Sci Ltd, 2018) Saoudel, Abdelmalek; Amira, Abderrezzak; Boudjadja, Yazid; Mahamdioua, Nabil; Varilci, AhmetWe have studied the thallium fluoride (TlF3) doping and AC field dependence of the weak links behaviour and AC susceptibility of Bi1.8-xTlxPb0.35Sr2Ca2Cu3OyF3x superconductors with range of x = 0, 0.05, 0.10 and 0.15. The estimated value of the peak temperature (T-p) from the derivative of the resistivity curve (dp/dT) is increased with TlF3 doping at 0 and 0.5 teslaand attest on both intragranular and weak links transition, while the full width at half maximum (FWHM) value is decreased. The susceptibility measurements chi'(chi '') show that as the magnetic field increases the intra and intergranular AC loss peaks shift to lower temperature with broadening. It was found that the onset temperature of diamagnetism T-c is increased with TlF3 doping. However, the intergranular peak temperature T-pj decreased with increasing magnetic field and TlF3 amount. This behaviour was explained by the poor connectivity between the grains caused by the presence of weak links or secondary phases. The calculated volume fraction of the grains (f(g)) was found to improve with increasing TlF3 doping and AC magnetic field. Furthermore, the estimated values of the maximum of the extracted matrix susceptibility (chi ''(m,max)) by using a critical state model proved that the intergranular losses are minimized with TlF3 doping. On the other hand, the obtained results shown that the coupling between the grains is rather weak than the coupling within the grains and attested of the improvement of superconducting parameters in the doped samples.Öğe Effect of yttrium doping on structural and electrical properties of Bi2Sr1.9Ca0.1-xYxCu2O7+delta (Bi-2202) cuprate ceramics(Elsevier Science Bv, 2016) Boudjadja, Yazid; Amira, Abderrezak; Saoudel, Abdelmalek; Mahamdioua, Nabil; Varilci, Ahmet; Terzioğlu, Cabir; Altıntaş, Sevgi PolatIn this work, we report on the effect of Y3+ doping on structural, mechanical and electrical properties of Bi-2202 phase. Samples of Bi2Sr1.9Ca0.1-xYxCu2O7+delta with x=0, 0.025, 0.05, 0.075 and 0.10 are elaborated in air by conventional solid state reaction and characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM) combined with EDS spectroscopy, density, Vickers microhardness and resistivity measurements. A good correlation between the variations of the bulk density and the Vickers microhardness with doping is obtained. The SEM photograph shows that the samples are composed of grains with a flat shape that characterizes the Bi-based cuprates. Quantitative EDS analysis confirms the reduction of Ca content and the increase of Y content when xis increased. The variation of resistivity with temperature shows that only samples with x=0, 0.025 and 0.05 present an onset transition to the superconducting state. The higher onset transition temperature is obtained for x= 0.025 and is about 93.62 K. The transition is wide and is realized in two steps confirming then the presence of the low T-c Bi-2201 phase in the samples. For x=0.075 and 0.10, a transition to a semiconducting state is seen at low temperatures. Some physical parameters are extracted from these curves and discussed. (C) 2016 SECV. Published by Elsevier Espana, S.L.U.Öğe 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, CabirIn 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.Öğe Magneto-conductive mechanisms in the La-site doped double-layered La1.4Ca1.6Mn2O7 manganites(Elsevier Science Bv, 2016) Mahamdioua, Nabil; Amira, Abderrezak; Boudjadja, Yazıd; Saoudel, Abdelmalek; Altıntaş, Sevgi Polat; Varilci, Ahmet; Terzioğlu, CabirMagneto-conductive mechanisms and properties of La1.2Re0.2Ca1.6Mn2O7 (Re = La, Pr, Y, Gd and Eu) have been investigated. In the low temperature range, combining residual resistivity, weak localization effect, electron electron and electron phonon interactions in a model, fit well the resistivity curves of undoped, Pr-doped and Y-doped samples. The Gd-doped and Eu-doped ones require the introduction of the small polaron metallic conduction. In the high temperature range, 3D-Mott's variable range hopping (3D-VRH) is the best model to fit resistivity of the undoped, Pr-doped and Y-doped samples, while Effros-Shklovskii model (ES-VRH) is the best one for Gd-doped and Eu-doped samples. In the entire temperature range, the percolation model fit well the resistivity. Using 3D-VRH model, the density of state (DOS) decreases with doping by Gd and Eu, whereas mean hopping distance R-h(T) and mean hopping energy E-h(T) increase. This may explain the resistivity increase and the crossover to the ES-VRH model. Values of R-h(T) vary between 1.811 and 1.030 nm, which allow us to suggest 3D-VRH as the best model fitting current results. E-h(T) values range from 0.1157 to 0.2635 eV. The DOS increases as increasing magnetic field while R-h(T) and E-h(T) decrease, which is in agreement with the observed decrease of resistivity.Öğe 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 PolatIn 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.Öğe Structural and electrical properties of cerium doped Bi(Pb)-2212 phases(Elsevier, 2014) Boudjadja, Yazid; Amira, Abderrezak; Saoudel, Abdelmalek; Varilci, Ahmet; Altıntaş, Sevgi Polat; Terzioğlu, CabirIn this work, a comparative study on the effect of doping by low content cerium at Ca site of Bi(Pb)-2212 phases is presented. Superconducting ceramics of nominal compositions Bi2Sr2Ca1-xCexCu2O8+delta (called CC series) and Bi1.6Pb0.4Sr2Ca1-xCexCu2O8 + delta (called PCC series) with x=0, 0.025, 0.05, 0.075 and 0.1 are successfully synthesized in air by conventional solid state reaction. They are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and resistivity measurements. In both series, the doping reduces the cell volume of samples. SEM photographs show that the samples are composed of grains with a flat shape that characterizes Bi-based cuprates. Quantitative EDS analysis confirms the reduction of Ca content and the increase of Ce 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 PCC series present highest onset critical transition temperatures. The highest value of 90.84 K is obtained for x=0.075 of Ce content, a result which is in line with that obtained in Y doped series. Also, samples of PCC series are more homogeneous. The residual resistivity increases with cerium content in both series, suggesting that doping introduces structural defects and disorder into the samples. (c) 2014 Elsevier By. All rights reserved.Öğe 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 PolatIn 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.Öğe 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, CabirWe 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.
