Yazar "Amira, Abderrezak" seçeneğine göre listele
Listeleniyor 1 - 16 / 16
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe Effect of anionic substitution on the structural and magneto-electrical properties of La-Ca-Mn-O perovskite manganites(Elsevier Science Bv, 2014) Altıntaş, Sevgi Polat; Mahamdioua, Nabil; Amira, Abderrezak; Terzioğlu, CabirThe role of anion substitution of oxygen by fluorine in La0.7Ca0.3MnO3-delta Fx (x=0.0 and 0.6) system has been investigated by means of X-ray powder diffraction, electrical resistivity and magnetization measurements. The oxygen content of the samples, estimated by a redox back titration method, decreases with doping while the lattice parameters and unit cell volume increase slightly. The Curie temperature and the metal-insulator transition temperatures of the samples are also found to increase with doping. The deduced magnetoresistance is slightly higher for the doped sample. (C) 2014 Elsevier B.V. All rights reserved.Öğe 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, CabirIn 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.Öğe Effect of Re doping on structure and magneto-electrical properties of La1.2Re0.2Ca1.6Mn2O7 manganites(Elsevier, 2013) Mahamdioua, Nabil; Amira, Abderrezak; Altıntaş, Sevgi Polat; Varilci, Ahmet; Terzioğlu, CabirIn this paper, the structural and magneto-electrical properties of the double layered La12Re0.2Ca1.6Mn2O7 manganites doped with Re=La, Pr, Eu, Y and Gd are presented. The results show that the decreasing of the ionic radii of the doping element decreases the lattice parameters. The grain size of the samples also decreases in the same order. Except for Pr, the doping decreases the metal-insulator transition temperature (T-MI) and increases the resistivity. The doped samples exhibit higher magnetoresistance (MR) than the undoped one on a large domain of temperature. The highest value is seen for the Eu doped sample and is about 91.96% at 139.4 K and 5 T. This sample exhibits a crossover from positive to negative MR for temperatures greater than T-MI. The obtained minimum of MR is about - 100.7% at 185.4 K. (C) 2013 Elsevier B.V. All rights reserved.Öğe 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 PolatAn 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.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 Effect of ZrO2 addition on microstructure, transport and magnetic properties of Bi2Sr2CaCu2O8+delta system(Springer, 2013) Boussouf, N.; Mosbah, M. -F.; Amira, Abderrezak; Varilci, Ahmet; Altıntaş, Sevgi Polat; Guerioune, MohamedThe influence of zirconium (Zr) addition to the Bi2Sr2CaCu2O8+delta (Bi2212) system on its phase formation, microstructure, transport, and magnetic properties is investigated. Samples have been characterized by means of X-ray diffraction analysis (XRD), scanning electron microscopy equipped with energy dispersive of X-ray analysis (SEM/EDX), and resistivity versus temperature measurement. The results show an increase of the critical temperature of superconductive transition T (c) for x=0.01 and in all the samples containing Zr the Bi2212 phase is the majority. SEM observations show whiskers grains randomly distributed and microstructural change due to the addition of Zr. Resistivity measurement show that the temperature of the onset of transition T (c) increases by 9 K for x=0.005, 0.02, and 5 K for x=0.01 of ZrO2. An improvement of the normal state conductivity is obtained for the lowest content of Zr (x=0.005). In the normal state, all the samples exhibit a metallic behavior except the sample with x=0.01, which exhibit a semiconductor character.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 Influence of Gd-doping in La0.7Ca0.3MnO3 on its structural and magneto-electrical properties(Elsevier Science Bv, 2012) Altıntaş, Sevgi Polat; Amira, Abderrezak; Varilci, Ahmet; Terzioğlu, CabirBulk samples of gadolinium doped manganites with compositional formula La0.7-xGdxCa0.3MnO3 (x=0.0 and 0.1) were prepared by conventional solid state reaction method. After characterizing the samples by X-ray diffraction, scanning electron microscope and energy dispersive X-ray spectrometer, a systematic investigation of electrical and magneto-transport properties has been investigated. The replacement of La ion by Gd results in a decrease of the metal-insulator transition temperature T-MI and the magnetoresistance as well as the resistivity are found to increase. The electrical resistivity in the entire temperature range fit well with the phenomenological percolation model, which is based upon an approach that the system consists of the phase separated ferromagnetic metallic and paramagnetic insulating regions. (C) 2011 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 Microstructural and magneto-transport properties of Bi1.6Pb0.4Sr2Ca1-xGdxCu2O8+delta superconducting ceramics(Elsevier, 2017) Boudjadja, Yazid; Amira, Abderrezak; Mahamdioua, Nabil; Saoudel, A.; Menassel, S.; Varilci, Ahmet; Terzioglu, Cabir; Altıntaş, Sevgi PolatThis study aims to investigate the effect of Gd doping on the phase formation, microstructure, transport and magnetic properties of the Bi(Pb)-2212 system. A series of superconducting bulks with a nominal composition of Bi1.6Pb0.4Sr2Ca1-xGdxCu2O8+delta with x= 0, 0.05, 0.10 and 0.15 are synthesized by the solid state synthesis route. The formed samples are characterized by means of X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), electrical transport and magnetic measurements. The experiment results reveal that all the samples doped are composed of Bi-2212 phase and traces of Bi-2201 secondary phase when compared to the undoped sample. The refinement of cell parameters shows that the doping reduces the cell volume of the samples. The texture degree decreases with doping while the degree of orthorhombicity increases. Quantitative EDS analysis confirms that Gd atoms are successfully introduced into crystalline structure. The SEM micrographs show randomly distributed grains with a flake-like shape. The highest value of onset critical transition temperatures is obtained for x= 0.10 and is about 90.22 K, which correlates well with the observed slope of resistivity and the hole concentration of the CuO2 layers. Magnetic hysteresis loops suggest that the diamagnetism, remanant magnetization and lower critical field are better for x= 0.10. Based on the enhancements of both grain boundary weak-links and flux pinning centers, improvement of the critical current densities and flux pinning density is obtained with this kind of doping.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 Structural and magneto-transport properties of copper doped double layered manganites La1.4Ca1.6Mn2O7(Springer, 2013) Mahamdioua, Nabil; Amira, Abderrezak; Altıntaş, Serpil Polat; Saoudel, A.; Boudjadja, Yazid; Varilci, Ahmet; Terzioğlu, CabirSamples of La1.4Ca1.6Mn2-xCuxO7 with 0 <= x <= 0.075 were prepared by a solid state reaction and characterized. The cell parameters and volume increase with increasing doped content in all the samples. The metal-insulator (MI) transition was observed in all the samples except for x = 0.075. The doping increases the MI transition temperature and resistivity. The application of a magnetic field increases the transition temperature. It can be referred to the suppression of the ferromagnetic-insulator state around it. The magnetoresistance (MR) of the undoped and 0.025 Cu-doped samples is observed on a wide range of temperatures (3.5-283 K). The undoped one exhibits a maximum value of 39.7 % at 5.07 K under 5 T. The 0.025 Cu-doped one exhibits a maximum value of 40.65 % at 44 K in the same magnetic field. No MR effect is shown for the 0.05 doped sample. The 0.075 doped sample exhibits a small negative MR behavior and a second peak of resistivity at a very low temperature.Öğe Structural and magnetotransport properties of the Y doped A-site deficient double layered manganites La1.2-x square 0.2YxCa1.6Mn2O7(Academic Press Inc Elsevier Science, 2016) Mahamdioua, Nabil; Amira, Abderrezak; Altıntaş, Sevgi Polat; Varilci, Ahmet; Terzioğlu, CabirWe present structural, magnetic and electrical properties of the polycrystalline A-site-deficient yttrium doped double layered manganites La(1.2-)x square 0.2YxCa1.6Mn2O7 (x=0.2, 0.3 and 0.4) prepared by a solid state reaction method. The samples crystallize in the tetragonal structure with the space group I4/mmm. Doping with Y decreases the cell parameters and causes a decrease of the metal-insulator transition temperature. The same evolution with doping is also seen for the deduced Curie temperature from susceptibility curves which present a clear paramagnetic-ferromagnetic transition. The significant positive intrinsic magnetoresistance, shown in all samples, reaches 85% at 122 K under 7 T for 0.3 doped sample and can be attributed to the suppression of spin fluctuations via aligning the spins under external magnetic field, while the extrinsic one is attributed to the inter-grain spin-polarized tunneling across the grain boundaries. The simulation of the resistivity curves in the entire temperature range show that the percolation model is suitable to fit our results. The applied magnetic field increases the density of states near the Fermi level, which is in accordance with the observed decrease of resistivity. (C) 2016 Elsevier Inc. All rights reserved.Öğe Structural characterization and magneto electrical behavior of Sm Doped La0.7Ca0.3MnO3 manganites(Springer, 2013) Altıntaş, Serpil Polat; Amira, Abderrezak; Terzioğlu, CabirThe La0.7-xSmxCa0.3MnO3 with x = 0.0 and 0.1 compounds were fabricated by compositional solid state reaction method and investigated for their structural and magnetoelectrical properties. The samples are characterized structurally by X-ray diffraction, scanning electron microscope, and energy dispersive X-ray spectrometer. The electrical and magnetotransport properties of bulk samples have been investigated in the temperature range 5-300 K and a magnetic field up to 7 T. The metal-insulator transition temperature, T-MI, decreased with samarium (Sm) doping and also it is increased slightly with the application of magnetic field. The results of Sm doped LCMO compound showed that the maximum magneto resistance (MR) is about 54 % and it appears near the transition temperature.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.
