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  • Küçük Resim
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    Effect of Gd addition on the activation energies of Bi-2223 superconductor
    (Elsevier Science Bv, 2011) Erdem, M.; Öztürk, Özgür; Yücel, E.; Altıntaş, Sevgi Polat; Varilci, Ahmet; Terzioğlu, Cabir; Belenli, İbrahim
    We have investigated the effect of addition of Gd in Bi1.8Pb0.35Sr1.9Ca2.1Cu3GdxOy superconductor with x=0, 0.1, 0.2, 0.3, 0.4 and 0.5. The samples were prepared using the standard solid-state reaction method. The activation energies, irreversibility fields (H-irr), upper critical fields (H-c2) and coherence lengths at 0 K (xi(0)) were calculated from the resistivity versus temperature (R-T) curves under DC magnetic fields up to 7 T. The superconducting transition temperature, T-c, and activation energy, U-0, were found to decrease with increase in Gd concentration and with increase in applied magnetic field. The offset transition temperature of the pure (Gd00) sample without applied magnetic field is 108 K, whereas for Gd05 sample, the offset transition temperature drops to 5 K with 7 T applied magnetic field. The activation energy of the Gd00 sample without applied magnetic field is 34,980 K, and for Gd05 sample with 7 T applied field it is 98 K. H-irr and H-c2 values also decrease with increase in Gd addition. The possible reasons for the observed degradation in microstructural and superconducting properties due to Gd addition were discussed. (C) 2010 Elsevier B.V. All rights reserved.
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    The effect of the number of Ag layers on some physical properties of Bi1.8Pb0.4Ca2.2Sr2Cu3Ox
    (Springer, 2012) Akdoğan, Mustafa; Erdem, M.; Terzioğlu, Cabir; Belenli, İbrahim
    Bi1.8Pb0.4Ca2.2Sr2Cu3Ox/Ag multilayered samples with 2, 4 and 8 layers are prepared by powder in tube (PIT) method and the effect of multilayering with Ag on the superconducting and the microstructural properties of Bi1.8Pb0.4Ca2.2Sr2Cu3Ox is studied. The investigations consist of XRD, SEM, EDS, magnetoresistivity, and I-V measurements. In the magnetoresistivity measurements, magnetic fields up to 0.5 T are applied both parallel and perpendicular to the current flow direction. The superconducting and microstructure properties of the samples are enhanced as the number of Ag layers are increased. The samples are composed of a highly oriented Bi-2223 phase in the regions near the Ag layers. The formation of the dense oriented structure is near the interface between oxide and the Ag layer. T-c and J(c) values are enhanced from 107 to 109 K and from 240 to 600 A/cm(2) by increasing the number of Ag layers, respectively. The results suggest that Ag plays an important role in the improvement of superconducting properties. The possible mechanisms of the enhancement of superconducting properties due to Ag layering are discussed.
  • Küçük Resim
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    Investigation of indentation size effect (ISE) and micro-mechanical properties of Lu added Bi2Sr2CaCu2Oy ceramic superconductors
    (Springer, 2013) Öztürk, Özgür; Erdem, M.; Aşıkuzun, Elif; Yıldız, O.; Yıldırım, Gürcan; Varilci, Ahmet; Terzioğlu, Cabir
    In this study, we investigated the effect of the Lutetium (Lu) addition on microstructure and mechanical properties of the Bi-2212 superconductors annealed at 840 degrees C for 50 h. The samples were prepared by the widely used conventional solid-state reaction method. For comparison, undoped sample was prepared in the same conditions. The prepared samples were characterized using X-ray powder diffraction (XRD), scanning electron microscope (SEM), and microhardness measurements (H-v). The volume fraction and lattice parameters were determined from the XRD measurements. The microstructure, surface morphology and orientation of the grains were investigated by SEM. In this study we have focused on microhardness measurements to investigate the mechanical properties. Vickers microhardness, load independent hardness, Young's modulus, fracture toughness and yield strength values were calculated separately for doped and undoped samples. Experimental results of hardness measurements were analyzed using the Meyer's law, proportional sample resistance (PSR) model, modified proportional sample resistance (MPRS) model, Elastic-Plastic deformation model (EPD), and Hays-Kendall (HK) approach. Finally, the Hays-Kendall (HK) approach was determined as the most successful model describing the mechanical properties of our samples. Moreover, lattice parameter c and volume fraction of Bi-2212 phase decreased with increasing Lu content. SEM measurements show that not only the surface morphology and grain connectivity were obtained to degrade but also the grain sizes of the samples were found to decrease with the increase of the Lu addition, as well.