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Öğe Cation size mismatch effect in (La1-yREy)(1.4)Ca1.6Mn2O7 perovskite manganites(Elsevier Science Sa, 2019) Koç, Nevin Soylu; Altıntaş, Sevgi Polat; Mahamdioua, Nabil; Terzioğlu, CabirThe size variance (sigma(2)) that indicates random disorder of cations distributed over the A or B-site, has significant influence on the basic quantities on perovskite manganites. In this study, we investigate the effect of A-site variance (sigma(2)(A)) in double layered perovskite manganites. In order to understand how the magneto-electrical properties of layered perovskite type RE2-2xCa1+2xMn2O7 change with sigma(2)(A), we have prepared a series of four samples with optimal doping (x = 0.3) and fixed mean A-cation radius ( = 1.3353 angstrom). A-site disorder is varied by use of different rare earth combinations by co-doping of La with Gd, Sm, Nd and Pr. Based on structural analysis by Rietveld profile fitting, all the samples crystallize in Sr3Ti2O7-type tetragonal phase (space group I4/mmm). As sigma(2)(A) increases, paramagnetic (PM) to ferromagnetic (FM) transition temperature shows a linear decrease. However, metal-insulator transition temperature shows a linear correlation with sigma(2). (C) 2019 Elsevier B.V. All rights reserved.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 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 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 Investigation of hole-doping effect on structural, magnetic properties and magnetoresistance via Gd-site substitution by Pb in the layered manganite La0.1Gd0.2-xPbxCa1.2Sr0.6Mn2O7 (0 <= x <= 0.2)(Springer, 2023) Belguet, Radjia; Mahamdioua, Nabil; Meriche, Faiza; Alonso, Jose A.; Martinez, Jose L.; Altıntaş, Sevgi Polat; Terzioğlu, CabirIn this work, the hole-doping double-layered manganites with formula La1:0Gd(0.2-x)PbxCa1.2Sr0.6Mn2O7 (x = 0, 0.1, and 0.2) are prepared by the solidstate reaction route and experimentally characterized. The samples' crystallization into a tetragonal structure with an I4/mmm space group was confirmed by Rietveld refinement results of the XRD diffraction patterns using the FullProf software. The results were thoroughly studied after it was discovered that the cell parameters were decreasing. The structure was granular and porous, with grains that resembled spheres, according to micrographs obtained using a scanning electron microscope (SEM). Fourier-transform infrared (FTIR) analysis shows that our samples' characteristic vibrational bands are present. The entire temperature range of 0 to 300 K was used to evaluate electrical resistivity both in the absence and in the presence of an applied magnetic field. The increase in bandwidth, which is determined from the Rietveld refinement results, is found to explain why the rho(T) lowers with increasing Pb concentrations for a given temperature. The calculated magnetoresistance (MR%) for sample with x = 0.1 fell to 24.62% at 8 K for x = 0.2 from a maximum value of 30.01% at 5 K under 1 T of applied magnetic field. These values give our samples the opportunity to be good candidates in temperature and magnetic sensors in the cryogenic domains at low magnetic field. Residual resistivity, weak localization, electronelectron, and/or electron-phonon combinations fit the resistivity curves well in the low temperature region. The resistivity curves' fitting revealed that the adiabatic tiny polaron hopping model and Mott's 3D variable range hopping mechanism (3D-VRH) are both effective at controlling electrical conduction above T-MI and below Debye temperature, respectively. Based on Mott's 3D-VRH model, the density of states near the Fermi level (DOS), mean hopping distance Rh, and mean hopping energy E-h of the charge carriers have been carried out and discussed. On the basis of measurements of magnetization, inverse susceptibility, and loop hysteresis, the samples' magnetic properties are thoroughly described and discussed. The samples show a magnetic phase change from the ferromagnetic to the paramagnetic phase at Curie temperature T-C. Griffith phase temperature was determined to be above T-C based on the inverse of susceptibility's temperature dependency.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 Non-adiabatic small-polaron and 3D-Mott's variable range conductions above 100 K in Pb-substituted double-layered manganites LaSm0.4Ca1.6-xPbxMn2O7(Pergamon-Elsevier Science Ltd, 2022) Denbri, Fatih; Mahamdioua, Nabil; Meriche, Faiza; Altıntaş, Sevgi Polat; Terzioğlu, CabirIn this study, the role of Pb substitution on the microstructural and magneto-transport properties of the double layered manganites LaSm0.4Ca1.6-xPbxMn2O7 (x = 0, 0.1 and 0.2), prepared by the solid-state reaction method, was investigated. On the samples, X-Ray Diffraction, Scanning Electron Microscopy and resistivity as a function of temperature measurements were performed. XRD measurements revealed that the samples crystallized in a tetragonal phase with an I4/mmm space group and that the lattice parameters increased with increasing Pb content. SEM measurements indicated the granular character and the average grain sizes ranged between 0.5 and 4 mu m for all the samples. The temperature dependence of resistivity of all the samples shows insulating-like behavior for the studied range of temperature (T > 100 K). The maximum magnetoresistance (MR%) value was found to be 31.95% at 100 K for the sample with x = 0, while it was 11% and 8% for the samples with x = 0.1 and 0.2, respectively. The resistivity curves are found to be well described by the Adiabatic Small Polaron Model in the range and Mott's 3D Variable Range Hopping model in the range. The density of states near the Fermi level (DOS), mean hopping distance, and mean hopping energy values were computed in the range, and the role of Pb substitution on these parameters was discussed as well.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 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-electrical properties of bi(2-x)sm(x)sr(2)cacu(2)o(8+delta)high t(c)superconductor prepared by pechini method(Springer, 2020) Mimouni, Mourad; Mahboub, Mohammed Sadok; Mahamdioua, Nabil; Mosbah, Mohamed Faycal; Rihia, Ghani; Zeroual, Soria; Ghougali, Mebrouk; Altıntaş, Sevgi PolatPolycrystalline superconducting samples of Bi(2-x)Sm(x)Sr(2)CaCu(2)O(8+delta)were synthesized using Pechini method with different doping Sm concentrations (x = 0.0, 0.05, and 0.10) and investigated. FTIR spectroscopy showed that our final samples are totally free of organic elements. Le Bail refinement revealed that they were crystallized in the Bi-2212 phase. A small amount of the omnipresent Bi-2201 phase appeared as an impurity phase in all samples, whereas a small amount of Bi-2223 appeared only in the case ofx = 0.5. In one hand, the Sm doping decreases the cell parameters, and in other hand, it leads to a transformation into a pseudo-tetragonal structure in the case ofx = 0.10.The modulation was found to be incommensurate and increases with Sm content. The magneto-electrical resistivity curves show a transition to the superconductor state. The critical temperature T(C)decreases with the Sm doping, whereas the activation energy U(0)increased from 53.4 meV to 68.9 meV.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, electrical, magnetic and magnetotransport properties of La0.7Ca0.18Ba0.12Mn0.95Sn0.05O3 manganite prepared with different quenching processes(Springer Heidelberg, 2023) Belal, Ibtihal; Meriche, Faiza; Mahamdioua, Nabil; Denbri, Fatih; Altıntaş, Sevgi Polat; Terzioğlu, CabirStructural, microstructural, magnetic, electrical and magneto-transport properties of La0.7Ca0.18Ba0.12Mn0.95Sn0.05O3 manganite powders, prepared by the solid state method, were investigated. Two quenching processes were performed on the samples: quenching in air and quenching to 77 K in liquid nitrogen. X-ray diffraction patterns refinement revealed that the samples crystallized in the orthorhombic structure. The scanning electron microscopy micrographs presented granular characters. The magnetization vs temperature plot showed a paramagnetic-ferromagnetic transition. The inverse susceptibility chi(-1)(T) deviation from the Curie-Weiss law revealed the existence of the phase above T-C in the nitrogen-quenched sample. The hysteresis cycles reveal that the samples are ferromagnetic at 1.8 K and paramagnetic at 300 K. The resistivity curves exhibit a ferromagnetic-metallic to paramagnetic-insulating transition. The magnetoresistance increased slightly in the sample quenched to 77 K in N-2.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.
