Browsing by Author "Belenli I."

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Effect of Gd addition on the activation energies of Bi-2223 superconductor
(2011-02-01) Erdem M.; Özturk O.; Yucel E.; Altintas S.P.; Varilci A.; Terziolu C.; Belenli I.
We have investigated the effect of addition of Gd in Bi 1.8Pb0.35Sr1.9Ca2.1Cu 3GdxOy 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 (Hirr), upper critical fields (Hc2) and coherence lengths at 0 K (ξ(0)) were calculated from the resistivity versus temperature (RT) curves under DC magnetic fields up to 7 T. The superconducting transition temperature, Tc, and activation energy, U0, 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. Hirr and Hc2 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. © 2010 Elsevier B.V. All rights reserved.
The effect of Au diffusion on some physical properties of Bi1.8Pb0.35Sr1.9Ca2.1Cu 3Oy superconductors
(2009-03-05) Terzioglu C.; Ozturk O.; Belenli I.
We have investigated the effect of the gold diffusion on the crystal structure and superconducting properties of Bi-2223 superconducting samples employing X-ray diffraction (XRD), scanning electron microscopy (SEM), critical transition temperature, critical current density, and room temperature resistivity measurements. Doping of Bi-2223 was carried out by means of gold diffusion from an evaporated gold film on pellets during sintering. XRD patterns and SEM micrographs are used to obtain information about Bi-2223 phase ratio, lattice parameters and grain size, respectively. Au doping of the samples increased the critical transition temperature and the critical current density from 100 ± 0.2 to 104 ± 0.2 K and from 40 to 125 A cm-2, in comparison with those of undoped samples. The gold diffusion in Bi1.8Pb0.35Sr1.9Ca2.1Cu 3Oy has been studied over the temperature range of 500-830 °C using the technique of successive removal of thin layers and measurement of the sample's conductivity at room temperature. The temperature dependence of the Au diffusion coefficient in the range of 500-830 °C was described by the relation D = 5 × 10-4 exp (-1.09 eV/kBT). The possible reasons for the observed improvements in microstructure and superconducting properties due to Au diffusion were discussed. © 2008 Elsevier B.V. All rights reserved.
The influence of Gd addition on microstructure and transport properties of Bi-2223
(2008-10-01) Terzioglu C.; Aydin H.; Ozturk O.; Bekiroglu E.; Belenli I.
We have investigated the effect of addition of Gd in Bi 1.8Pb0.35Sr1.9Ca2.1Cu 3GdxOy superconductor with x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5. The samples were prepared by standard solid-state reaction methods. The investigation consisted of X-ray diffraction (XRD), scanning electron microscopy (SEM), de electrical resistivity, hole concentration and transport critical current density measurements. Transport measurements indicated that the superconducting transition temperature, transport critical current density and hole concentration values of the samples strongly depend on the Gd addition. The values of Tc, and Jc of the samples decreased with the increase in Gd addition. When Gd addition ratio was increased, surface morphology and grain connectivity of the samples were observed to degrade from SEM investigations and phase ratio of the high-Tc (Bi-2223) phase to the low-Tc (Bi-2212) phase decreased (XRD measurements). The possible reasons for the observed degradation in superconducting and microstructure properties of Bi-2223 due to Gd addition were discussed. © 2008 Elsevier B.V. All rights reserved.
Variation of mechanical properties of Cr doped Bi-2212 superconductors
(2013-09-01) Dogruer M.; Yildirim G.; Ozturk O.; Belenli I.; Terzioglu C.
This study shows the influence of Cr inclusions on the mechanical properties of Bi1.8Sr2.0Crx Ca 1.1Cu2.1Oy (Bi-2212) superconducting samples (x=0, 0.1, 0.3, 0.5, 0.7, and 1) prepared by conventional solid-state reaction route with the aid of the microhardness (Hv) measurements. Moreover, some characteristics such as Vickers microhardness, Young's (elastic) modulus (E) and yield strength (Y), being responsible for the potential technological and industrial applications, are theoretically evaluated from the microhardness curves belonging to the samples and compared with each other. It is found that the load dependent microhardness values decrease nonlinearly as the applied load enhances until 2 N beyond, which the curves shift to the saturation region, confirming that all the samples exhibit the indentation size effect (ISE) nature. Further, the elastic modulus and yield strength values observed reduce with the enhancement of the applied load and Cr inclusions in the Bi-2212 matrix. The experimental findings are also analyzed by Meyer's law, proportional sample resistance model (PSR), modified proportional sample resistance model (MPRS), elastic/plastic deformation model (EPD), and Hays-Kendall (HK) approach. According to the results obtained, the load independent microhardness values calculated by EPD, PSR, and MPSR models are far from the values of the plateau region; however, the HK approach is the most suitable model for the microhardness calculations of the samples prepared in this study. © 2013 Springer Science+Business Media New York.