Browsing by Author "Safran S."

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Ac Susceptibility Measurements and Mechanical Performance of Bulk MgB2
(2015-07-24) Ozturk O.; Asikuzun E.; Kaya S.; Erdem M.; Safran S.; Kilic A.; Terzioglu C.
The effects of Ar ambient pressure (vacuum and 0, 10, and 20 B) and annealing times (0.5 and 1 h) on microstructural, superconducting, and mechanical properties of bulk superconducting MgB2 are investigated. The samples are produced using the solid-state reaction method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements are performed for determination of the crystal structure and surface morphology of MgB2 samples, respectively. The superconducting properties are studied by AC magnetic susceptibility measurements. Microhardness analyses are made using the Vickers microhardness test for determination of mechanical properties of all samples. Increasing the Ar pressure decreases the lattice parameters and hence the average grain size. Increasing the annealing time results in larger lattice parameters and larger grain formation. The susceptibility measurements revealed a two-step transition which is reminiscent of granular superconductors. The intra-grain transition temperature is determined to be 38.4 K for all samples. The inter-grain transition temperature of 37.2 K is obtained for samples produced under Ar ambient pressure. The samples produced under Ar ambient pressure have better superconducting properties than the ones produced in vacuum. Increasing the annealing time under vacuum further decreases the superconducting properties probably due to Mg loss.
Characterization of the CoFe2O4/Cu displacement effect in the Y123 superconductor matrix on critical properties
(2020-11-01) Safran S.; Bulut F.; Nefrow A.R.A.; Ada H.; Ozturk O.
In this study, CoFe2O4 (x = 0, 5, 10 and 20 wt%) doped YBa2Cu3−x(CoFe2O4)xO7−δ bulk samples were produced using solid state reaction (SSR) method and sol–gel(SG) methods. Oxide-form and acetate-form powders were preferred for SSR method and SG method, respectively. The heat treatment of the produced samples was carried out in two stages. Firstly, the samples were annealed at 950 °C for 24 h, after which they were kept in oxygen at 500 °C for 5 h and allowed to be cooled down to room temperature. Characterization of all samples was performed using methods such as X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, temperature-dependent resistance measurement (R–T) and Vickers microhardness analysis. Superconducting behavior was observed in all the produced samples, but as a result of the addition, a decrease was observed with the increase of the doping ratio at the critical transition temperature. As a result of the characterization, it is concluded that the doping ions can be replaced with Cu atoms in Y123 structure. In addition, doping led to significant changes in Vickers microhardness results.
Comparison of the Dopant Effect and Sample Preparation Method on Y-123 Superconductors
(2021-11-01) Ozturk O.; Nefrow A.R.A.; Bulut F.; Kurnaz S.; Safran S.
The detailed comparison of the effects of Co and CoFe2O4 dopants and preparation methods (solid-state reaction method and sol–gel methods) have been studied on structural, electrical, superconducting, and mechanical properties of Y123 bulk superconductors. The doping amounts of Co and CoFe2O4 were chosen up to 0.10 wt. %. X-ray powder diffraction (XRD) method, temperature-dependent resistance measurement (R-T), and Vickers microhardness analyses were performed to characterize prepared samples. XRD analysis showed that all samples have Pmmm symmetry of orthorhombic crystal structure; intensities and width of the diffraction lines were affected by doping material, but, independent of the preparation method. Although all samples crystallize in orthorhombic structure and exhibit superconductivity behavior, with increasing doping rate the critical transition temperatures of the samples showed a significant decrease and broadened to superconducting temperature transition width. This is more evident in CoFe2O4-doped Y-123 samples produced by sol–gel method. As the applied force increased, it was observed that the microhardness values of the Co-doped samples increased while the CoFe2O4-doped samples decreased, regardless of the sample preparation method.
Effect of re-pelletization on structural, mechanical and superconducting properties of BSCCO superconductors
(2017-01-01) Safran S.; Kılıç A.; Ozturk O.
We have examined the effect of re-pelletization on structural, mechanical and superconducting properties of high temperature superconducting (HTS) bulk samples using Bi1.85Pb0.35Sr2Ca2Cu3Oy stoichiometry. Conventional solid state reaction method is used for preparation of three different bulk samples. XRD measurement of the samples shows that a high percentage of high-Tc phase is determined. Superconducting critical transition temperature of the samples have been obtained from the curves of ρ-T and χ-T. Vickers micro-hardness are also calculated for all samples. Re-pelletization has a positive effect on structural, mechanical and superconducting properties of bulk samples.
Examination of pairing mechanism, orbital hybridization, stabilization and magnetization behavior of Tb/Y and Zn/Cu partially substituted Y-123 Superconductors
(2022-11-30) Ozturk O.; Guducu G.; Safran S.; Yildirim G.
The effect of homovalent Tb/Y and Zn/Cu substitution on electrical, superconducting, structural, and magnetic features of Y-123 ceramic materials is extensively examined by powder X-ray diffraction, electrical resistivity, scanning electron microscopy, energy dispersive X-ray spectrometry, DC magnetization VSM measurements and related calculations. Y1−xTbxBa2Cu3O7-ɤ and YBa2(Cu1−xZnx)3O7-ɤ samples are prepared with four different molar percentages (0.0 ≤x ≤ 0.15) using the sol-gel technique. DC magnetization data and the Bean model are used to evaluate change in critical current densities with an applied magnetic field. Energy-dispersive X-ray spectrometry measurements indicate that materials are exactly produced in the desired stoichiometric ratios. Moreover, all the experimental findings show that the fundamental characteristic properties are observed to decrease with replacement mechanism. The degradation mechanism with partial substitution is thoroughly explained scientifically in the basic contents for the first time. The role of Tb/Y and Zn/Cu partial substitution on the oxygen concentration level in unit cell, ordering degree in the Cu-O ribbons, lattice cell parameters, grain size, and the number of holes in the σ antibonding in-plane Cu-O bonds are also discussed in detail. Additionally, beginning of weak-interaction problems between adjacent superconductive layers, formation of microscopic structural faults and decoupling of superconducting grains are noted to be the negative effect of substitution mechanism. Regardless, it is observed that Tb-doped samples possessing more uniform surface morphologies with better surface texture and connection quality between particles show much higher magnetization behavior and superconducting properties. All in all, this study developing a scientific methodology about why fundamental characteristic features change with the partial replacements of Tb/Y and Zn/Cu in crystal systems seems a pioneering investigation to construct novel and feasible application fields for the Y-123 ceramic compounds.
Experimental and theoretical approaches for electrical, magnetic, micromechanical, and structural characterization of BSCCO ceramic superconductors
(2018-07-01) Safran S.; Ozturk H.; Bulut F.; Ozturk O.
This study investigates how the preparation and re-pelletization of BSCCO ceramic superconductors affects their structural, magnetic, electrical, and mechanical properties. Samples were prepared using conventional methods including the dry solid state (SS) reaction and wet ammonium nitrate (AN) precipitation, with three variations prepared for each technique. The fabricated samples were then characterized with X-ray powder diffraction (XRD) and scanning electron microscopy. The density, resistance vs. temperature characteristics, AC susceptibility vs. temperature characteristics, and magnetic hysteresis properties were measured. In addition, Vicker's microhardness was measured and revealed that all six samples exhibit the reverse indentation size effect (RISE). Microhardness modeling was also conducted. Calculations with Meyer's law, the Hays and Kendall model, and the proportional sample resistance model indicate that the samples are far from the plateau region, whereas the indentation-induced cracking model was consistent with the experimental results. The elastic modulus, Young's modulus, yield strength, and brittleness index were also calculated for each sample.
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.
Mechanical, microstructural and magnetic properties of the bulk BSCCO superconductor prepared by two different methods
(2015-04-01) Safran S.; Kılıç A.; Kılıçarslan E.; Ozturk H.; Alp M.; Asikuzun E.; Ozturk O.
BSCCO bulk samples have been prepared by solid-state reaction and ammonium nitrate precipitation methods with Bi1.65Pb0.35Sr2Ca2Cu3O10±y stoichiometry. Structural, mechanical and magnetic characterizations of the samples were performed by the X-ray powder diffraction (XRD), the scanning electron microscopy (SEM), Microhardness measurements, AC susceptibility measurements. The XRD patterns showed that the diffraction peaks for our samples belong to the two main phase, namely 2223 and 2212 of the BSCCO. In this study we have focused on microhardness measurements to investigate the mechanical properties. Vickers microhardness, Young’s modulus and yield strength values were calculated separately for all samples. In addition to these, we calculated the load independent hardness values of samples. Experimental results of hardness measurements were analyzed using the Meyer’s law, proportional sample resistance (PSR) model, Elastic–Plastic deformation model (EPD) and indentation induced cracking (IIC) model. The critical transition temperature, phase purity, lattice parameter, surface morphology and crystallinity of the prepared bulk samples were compared with each other.
Superconducting and mechanical properties of the bulk Bi(pb)SCCO system prepared via solid state and ammonium nitrate precipitation methods
(2015-05-26) Safran S.; Kiliçarslan E.; Ozturk H.; Alp M.; Akdogan M.; Asikuzun E.; Ozturk O.; Kiliç A.
We have investigated the effect of preparation method on superconducting and mechanical properties of Bi(Pb)-2223 bulk samples using Bi1.85Pb0.35Sr2Ca2Cu3O10±y stoichiometry. Solid-state reaction and ammonium nitrate precipitation methods have been used for fabrication of the bulk samples. In addition, the effect of annealing time on BSCCO samples have been studied. Structural, electrical, magnetic and microhardness analyses of samples are performed by the X-ray powder diffraction (XRD), the Scanning Electron Microscopy (SEM), DC resistivity, AC susceptibility and Vickers microhardness test. The critical transition temperature, phase purity, surface morphology and crystallinity of the prepared bulk samples are compared with each other. Elasticity (E), brittleness (Bi), fracture toughness (KIC) and yield strength (Y) values are also determined according to annealing time, applied load and production parameters of materials.
The influence of re-pelletization and heat treatment on physical, superconducting, magnetic and micro-mechanical properties of bulk BSCCO samples prepared by ammonium nitrate precipitation method
(2017-12-01) Safran S.; Ozturk H.; Bulut F.; Ozturk O.
The influence of re-pelletization and annealing time on the structural, magnetic, electrical and mechanical properties of Bi-based high temperature bulk superconductor have been investigated. All samples used in this study have been prepared by a wet technique denoted as ammonium nitrate precipitation method. The samples have been characterized by X-ray powder diffraction (XRD), Scanning Electron Microscopy (SEM), resistance vs. temperature (R-T), magnetic hysteresis (M-H) and hardness vs. applied load (Hv-F) measurements. Bi-2223 and Bi-2212 peaks as major phases have been observed with small amounts of impurities from XRD results. The microstructures of most samples show a plate-like granular form. The grain sizes have been investigated by SEM and XRD. The critical transition temperature (Tc) has been obtained from resistivity measurements in the range of 99–110 K, depending on the annealing time and re-pelletization. The calculated maximum critical current density (Jc), using Beans’ model, is around 12,000 A/cm2 at 10 K ∼ 0.2 T. Moreover, all prepared samples exhibit reverse indentation size effect (RISE) behavior and hardness increased with re-pelletization according to results obtained from mechanical measurements.