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    Effect of Eu doping on structural and magneto-electrical properties of La0.7Ca0.3MnO3 manganites
    (Elsevier Science Sa, 2011) Altıntaş, Sevgi Polat; Amira, A.; Mahamdioua, N.; Varilci, Ahmet; Terzioğlu, Cabir
    We have investigated the influence of europium (Eu) doping on structural and magneto-electrical properties of La0.7Ca0.3MnO3 compounds. In order to analyze the physical mechanism of a spin disorder system and study their relative evolutions, two samples of nominal compositions (La0.7-xEux)Ca0.3MnO3 (x = 0.0 and 0.1) have been elaborated and characterized. In addition to structural changes seen by this kind of doping, the magnetoresistance (MR) and resistivity are increased while the metal-insulator transition temperature is decreased. Comparing the experimental data with the theoretical models shows that in the metal-ferromagnetic region, the electrical behaviour of both samples is quite well described by a theory based on Kondo-like spin dependent scattering, electron-electron scattering, electron-phonon and electron-magnon scatterings. For the high temperature paramagnetic insulating regime, the adiabatic small polaron hopping model is found to fit well the experimental curves. (c) 2011 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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    Improved magnetoresistance in Sm0.7-xCexSr0.3MnO3 manganites prepared by a sol-gel route
    (Springer/Plenum Publishers, 2021) Lakhal, E.; Amira, A.; Chihoub, R.; Soylu, Nevin; Altıntaş, Sevgi Polat; Varilci, Ahmet; Terzioğlu, Cabir
    In this work, manganite ceramics of Sm0.7-xCexSr0.3MnO3 (0 <= x <= 0.3) are prepared by a citrate sol-gel chemical route and characterized. The structure of the obtained samples is refined in the orthorhombic system with the Pnma space group. The doping causes a change in the lattice parameters leading to a decrease in the cell volume. It also increases slightly the grain size of the crystallites. The temperature dependence of resistivity reveals a metal-insulator transition for all samples. The doping shifts the temperature of this transition towards high values. The extracted magnetoresistance for a 5 T magnetic field is enhanced by doping. The highest obtained value increases from 66.70% for x = 0 to 97.96% for x = 0.3.
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    Substitution effect of Sr2+ by Ca2+ on structure and superconducting properties of Bi2Sr1.6La0.4CuO6+? (Bi-2201) ceramics
    (Elsevier B.V., 2018) S., Boudjaoui; Amira, A.; Mahamdioua, N.; Altıntaş, Sevgi; Varilci, Ahmet; Terzioğlu, Cabir
    In this work, the effect of Ca2+ iso-valence substitution for Sr2+ on properties of Bi2Sr1.6La0.4CuO6+? superconductors is presented. Samples series with nominal composition of Bi2Sr1.6-xCaxLa0.4CuO6+? (x= 0, 0.2, 0.4, 0.6 and 0.8) are prepared by a solid-state reaction method. When Ca content is increased, the X-ray diffraction technique shows that the cell parameters a and c decrease, while b one is almost constant. The scanning electron microscopy analysis reveals that the substitution has no significant effect on the porosity and the grain size of the samples. The physical properties of the samples are studied by the analysis of the magneto-resistivity curves measured under magnetic fields in the range 0-1 T. As Ca is added, the results show that the high temperature transition appears and is pushed up to 94.87 K for x=0.8. The substitution also improves the bulk onset critical transition temperature, the transition width, the residual resistivity, the activation energy of vortices and the irreversibility field. The best results are seen for x=0.4 of Ca content. © 2017 Elsevier B.V.