Browsing by Author "Gencer A."

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Changes in mechanical and structural properties of Bi-2212 added MgB2 superconductors
(2016-06-01) Koparan E.; Savaskan B.; Ozturk O.; Kaya S.; Aksoy C.; Wang J.; Speller S.; Grovenor C.; Gencer A.; Yanmaz E.
In the present study, we investigate the effects of Bi2Sr2Ca1Cu2O8+κ (Bi-2212) addition on structural and mechanical properties of bulk MgB2 obtained by hot-press method by means of X-ray diffraction, the Scanning Electron Microscopy and Vickers microhardness measurements. The amount of Bi-2212 was varied between 0 and 10 wt% (0, 2, 4, 6, 8 and 10 wt%) of the total MgB2. All samples were prepared by using elemental magnesium (Mg) powder, amorphous nano boron (B) powder and Bi-2212 powder which are produced by hot-press method. As a result of the hot-press process, the compact pellet samples were manufactured. The microhardness results were analyzed by Meyer’s law, Proportional Sample Resistance Model, Elastic–Plastic Deformation Model, Hays Kendall Approach, and Indentation Induced Cracking (IIC) Model. IIC model was identified as the most appropriate model for samples exhibiting the reverse indentation size effect behavior.
Influence of different boron precursors on superconducting and mechanical properties of MgB 2
(2014-01-01) Safran S.; Kılıç A.; Asikuzun E.; KIlIçarslan E.; Ozturk O.; Gencer A.
The superconducting, structural and mechanical properties of MgB 2 bulk samples have been studied as a function of precursor B powder particle size by means of AC susceptibility, XRD and microhardness measurements, respectively. The in situ processed MgB 2 samples have been prepared by means of conventional solid state reaction method with magnesium powder (99.8 %, 325 mesh) and four different types of boron powders (95.2, >95, 91.9 and 86.7 %) from two sources, Pavezyum and Sigma Aldrich. The XRD measurements showed that the diffraction peaks for our samples belong to the main phase of the MgB 2 diffraction patterns. The highest critical temperature T c = 37.7 K was achieved for the MgB 2 sample which was fabricated by using >95 % purity amorphous boron. Microhardness measurements were performed to investigate the mechanical properties. Load independent hardness, Vickers microhardness, Young's modulus, fracture toughness, and yield strength values were calculated separately for all samples. The results were analyzed by using the Meyer's law, proportional sample resistance model, elastic-plastic deformation model, Hays Kendall approach, and indentation induced cracking (IIC) model. It was found that the IIC model is the most successful model to describe the mechanical properties of our samples. © 2014 Springer Science+Business Media New York.
Influence of gold diffusion-doped on phase formation, superconducting and microstructure properties of Bi1.8Pb0.35Sr 1.9Ca2.1Cu3Oy superconductors
(2009-01-01) Ozturk O.; Akdogan M.; Terzioglu C.; Gencer A.
We 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 (αjj (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.
Magnetocaloric effect in CeCo4B compound
(2008-10-20) Gencer H.; Kervan N.; Gencer A.; Gunes M.; Atalay S.
Polycrystalline CeCo4B compound was prepared by arc melting under argon atmosphere. The magnetic and magnetocaloric properties of CeCo4B were investigated. The magnetic measurements show that CeCo4B is ferrimagnetically ordered. The Curie temperature was determined to be 291 K. It was found that the maximum value of the magnetic entropy change |ΔSm| has reached the highest value of 0.361 J/(kg K) at 1 T. Using the Landau expansion of magnetic free energy and Arrott plots, it was found that the phase transition in CeCo4B is of second order. © 2007 Elsevier B.V. All rights reserved.