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Öğe AC susceptibility analysis on MgB2 bulk and Ti-sheathed wire superconductors(Elsevier Sci Ltd, 2014) Çiçek, Özlem; Yetiş, Hakan; Gencer, AliWe report a comparative study for bulk MgB2 superconductors and monofilamentary Ti/MgB2 wires as functions of the boron powder purity, average particle size of magnesium, and applied pressure. The structural and magnetic characterizations of the bulk samples were performed by means of XRD and AC susceptibility measurements, respectively. We found that the applied pressure did not cause any significant change on the onset transition temperature T-c,T-onset and transition width. This is also confirmed by the calculation of the lattice parameters. On the other hand, T-c,T-onset values were measured as 37.3 K, 38.0 K, and 38.6 K for the samples prepared from the precursor boron powders with purities of 95.2%, >= 95%, and >98%, respectively. However Mg-particle size (Mg1: AlfaAesar Mg powder, avg. par. size: -325 mesh, purity: 99.8%; Mg2: SigmaAldrich Mg powder, avg. par. size: 20-230 mesh, purity: 98%) did not affect the T-c,T-onset but increasing the Mg particle size caused a significant broadening at the superconducting transition width for all precursor boron powder purity levels. Magnetization measurements showed that the critical current density of Ti/MgB2 wire prepared from AlfaAesar Mg powder (avg. par. size: -325 mesh) and Aldrich B powder (amorphous, purity >= 95%) is greater than that of prepared by SigmaAldrich Mg powder (avg. par. size: 20-230 mesh) and Pavezyum B powder (amorphous, avg. par. size: 0,3 mu m (max), purity > 98%) as 2.6 x 10(5) A/cm(2) and 1.4 x 10(5) A/cm(2) at T = 10 K and mu H-0 = 0.5 T, respectively. In addition, SigmaAldrich Mg and Pavezyum B wire sample has a lower pinning force, F-p, value at each temperature. (C) 2014 Elsevier Ltd. All rights reserved.Öğe Effect of cooling rates on bare bulk and silver wrapped pellets of Bi-2223 superconductor(Elsevier, 2006) Terzioğlu, Cabir; Öztürk, Özgür; Kılıç, Ahmet; Gencer, Ali; Belenli, İbrahimWe have examined the effect of cooling rates on oxygen content of Bi-2223 phase samples with and without silver sheating. Two sets of samples with and without silver sheating were annealed under identical conditions and cooled with rates of 10 degrees C/h, 25 degrees C/h, 50 degrees C/h, 75 degrees C/h, and 100 degrees C/h. XRD examination of the samples showed that a high percentage of Bi-2223 was obtained. Microstructure examinations were performed by scanning electron microscopy. Resistive and magnetic transitions of the samples were studied. All the reported data were discussed and related.Öğe Fabrication and transport critical current densities of MgB2/Fe/Cu multifilament tapes without any intermediate annealing(Polish Acad Sciences Inst Physics, 2012) Yücel, Ersin; Terzioğlu, Cabir; Varilci, Ahmet; Gencer, Ali; Belenli, İbrahimWe have fabricated superconducting 6 and 7 filaments MgB2/Fe/Cu tapes by ex situ powder-in-tube method using Cu-sheath without any intermediate annealing. Properties of two different multicore MgB2/Fe/Cu tapes annealed at 900 degrees C for 2 h in high purity argon gas atmosphere were compared. The samples were characterized using scanning electron microscope, X-ray diffraction, electron dispersive spectroscopy, optical microscopy, critical transition temperature, transport critical current density, and magnetic measurements. Transport critical current densities of the 6 and 7 filaments tapes were found to be 450 A/cm(2) and 190 A/cm(2) at 20 K, respectively. From X-ray diffraction measurements, lattice parameters a and c were determined. From dc resistivity measurements, the connectivity between grains was investigated by using Rowell's connectivity analysis.Öğe Influence of gold diffusion-doped on phase formation, superconducting and microstructure properties of Bi1.8Pb0.35Sr 1.9Ca2.1Cu3Oy superconductors(Institute of Physics Publishing, 2009) Özgür, Öztürk; Akdoğan, Mustafa; Terzioğlu, Cabir; Gencer, AliWe report on low-field magnetic properties of gold diffusion-doped Bi 1.8Pb0.35Sr1.9Ca2.1Cu 3Oy superconducting bulk samples by performing ac susceptibility measurements. The undoped samples were prepared by the standard solid-state reaction method. Doping of Bi1.8Pb0.35Sr 1.9Ca2.1Cu3Oy was carried out by means of Au-diffusion during sintering from an evaporated gold film on pellets. To investigate the effect of gold-diffusion and diffusion-annealing duration on transport, magnetic and microstructure properties of the superconducting samples we performed magnetoresistivity, scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements. The ac susceptibility as a function of temperature measurements were carried out at different values of the ac magnetic field amplitudes (Hac) in the range between 20A/m and 320 A/m for 211 Hz. The imaginary part of ac susceptibility measurements is used to calculate intergranular critical current density Jc(Tp) using the Bean Model. Jc(Tp) is seen to increase from 60 A cm -2 to 90 A cm-2 with increasing diffusion-annealing time from 10 h to 50 h. The peak temperature, Tp, in the imaginary part of the ac susceptibility is shifted to a lower temperature with decreasing diffusion-annealing duration as well as increasing ac magnetic fields. The force pinning density (?jj (0)) increased with increasing diffusion annealing time. The value of Tc in gold-diffused samples, in comparison with the undoped samples, increased from 100 0.2 K to 104 0.2 K. It was observed that the value of Tc-offset of the gold-doped samples enhanced with further increasing diffusion-annealing duration. XRD patterns and SEM micrographs are used to obtain information about Bi-2223 phase ratio, lattice parameters and grain size of the samples. Gold doping enhanced the formation high-Tc phase and increased the grain size. The possible reasons for the observed improvements in transport, microstructure and magnetic properties due to Au diffusion and diffusion-annealing time were discussed. © 2009 IOP Publishing Ltd.Öğe MgB 2 /Fe Parkur Tipi Bobin Tasarımı ve Üretimi(2016) Belenli, Ibrahim; Gencer, Ali; Karaboğa, Firat; Demirtürk, Emine; Akdoğan, Mustafa; Yetiş, Hakan; Pilten, Emir-
