mustafa akdogan - Academia.edu (original) (raw)

Papers by mustafa akdogan

Journal of Alloys and Compounds, 2017

We report a study on the structural and transport properties of long in situ MgB 2 /Fe wires that... more We report a study on the structural and transport properties of long in situ MgB 2 /Fe wires that are prepared by use of amorphous boron and nano amorphous boron powders with 50e50% weight ratio. The wire samples are fabricated by means of a standard Powder-in-Tube (PIT) method. Transport measurements are applied under high magnetic fields, of up to 9 T, obtained in a Bitter magnet. We find that use of a mixture of the amorphous boron and amorphous nano boron precursor powders at equal amounts is very promising way to fabricate long wires without any degradation in transport engineering J ce values in the presence of low and moderate magnetic fields.

Journal of Alloys and Compounds

IEEE Transactions on Applied Superconductivity

Journal of Physics Condensed Matter, 2002

We have performed a first-principles study of structural, dynamical and dielectric properties of ... more We have performed a first-principles study of structural, dynamical and dielectric properties of chalcopyrite semiconductor CuGaS2. The calculations have been carried out within the local density functional approximation using norm-conserving pseudopotentials and a plane-wave basis. Born effective charge tensors, dielectric permittivity tensors, the phonon frequencies at the Brillouin zone centre and mode oscillator strengths are calculated using density functional perturbation theory. The calculated properties help resolve the source of some of the discrepancies in the experimental literature.

Journal of Superconductivity and Novel Magnetism, 2011

This paper presents the synthesis and characterization of three new Y-based high temperature-supe... more This paper presents the synthesis and characterization of three new Y-based high temperature-superconducting compounds having relatively higher transition temperature T c compared with that of the Y-123, Y-124, and Y-247. The electrical resistivity measurements indicate the onset critical temperatures as high as 98 K. Atomic compositions of these new Y-Ba-Cu-O superconductors are Y2Ba3Cu5.2O x , Y2Ba5Cu9O x , and YBa4Cu5O

Journal of Superconductivity and Novel Magnetism, 2014

ABSTRACT The distribution of nanostructural inhomogeneities, such as areas with high concentratio... more ABSTRACT The distribution of nanostructural inhomogeneities, such as areas with high concentration of B and impurity O, plays one of the key roles on the variation of the critical current density, j c, of MgB2 materials. The effect of O and B redistribution can be enhanced by Ti addition and thus leads to the j c increase. The effect of Ti addition and the mechanism of this effect are discussed based on experiments of MgB2 synthesis under 2 GPa pressure at 800 and 1,050 °C.

Advances in Cryogenic Engineering Materials, 1980

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ABSTRACT A precursor powder with a nominal chemical composition of Bi1.8Pb0.4Ca2.2Sr2Cu3Ox was us... more ABSTRACT A precursor powder with a nominal chemical composition of Bi1.8Pb0.4Ca2.2Sr2Cu3Ox was used to fabricate the multilayered Bi1.8Pb0.4Ca2.2Sr2Cu3Ox/Ag samples (number of layers was 2, 4 and 8) using the powder-in-tube method (PIT). The density of powder increases during the drawing procedure and inside the composite wires of the final diameter is 3.54 mm. By an intermediate rolling, pressing and annealing procedure, the wires were rolled to obtain tapes. The rolling process was not effective in obtaining further substantially increase of the powder density, but greatly improved the orientation of ceramic grains inside the silver sheath. The sample is composed of a highly oriented Bi-2223 phase in the region near to the Ag layer. The eight-layered sample exhibits a rather high Ic value of 110 A. Tc and Jc are enhanced by increasing the number of Ag layers. The formation of the dense oriented structure is near the interface between oxide and the Ag layer. This suggests that Ag plays an important role in the improvement of Jc.

This study reports the effect of annealing time (15 min, 1.5 and 3 h) and temperature (850, 860 a... more This study reports the effect of annealing time (15 min, 1.5 and 3 h) and temperature (850, 860 and 870°C) on the structural and superconducting properties of thin films by means of scanning electron microscopy (SEM), X-Ray analysis (XRD), electron dispersive X-Ray (EDX), resistivity and transport critical current density (J c) measurements. Zero resistivity transition temperatures (T c) of the films produced are estimated from the dc resistivity measurements. In addition, the phase and lattice parameters are determined from XRD patterns when the microstructure, surface morphology and element composition analyses of the samples are investigated by SEM and EDX measurements, respectively. The results indicate that T c values of the films obtained are observed to be in a range of 23-102 K. The T c of the film annealed at 870°C for 3 h is found to be the smallest (23 K) while the film annealed at 860°C for 3 h is noted to obtain the maximum T c value (102 K). On the other hand, the maximum (minimum) J c is found to be about 2068 A/cm 2 (20 A/cm 2) for the film annealed at 860°C for 3 h (870 for 3 h). Moreover, according to the refinement of cell parameters done by considering the structural modulation, the greatest Bi-2223 phase fraction is noticed to belong to the film annealed at 860°C for 3 h. Furthermore, SEM measurements show that the best surface morphology, largest grain size and grain connectivity are observed for that film. Based on these results, T c and J c values of the samples studied are found to depend strongly on the microstructure. As for EDX results, the elements used for the preparation of samples are observed to distribute homogeneously. The aim of this study is not only to investigate the changes of structural and superconducting properties of the films produced in the varied time and temperature but also to determine the best ambient for the film fabrication and show the feasibility of obtaining Bi-2223 film with tailored structure.

ABSTRACT In order to investigate the role of Fe doping and diffusion-annealing duration on the me... more ABSTRACT In order to investigate the role of Fe doping and diffusion-annealing duration on the mechanical and superconducting properties of Bi-Pb-Sr-Ca-Cu-O, Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy superconductors were prepared by standard solid-state reaction methods. Doping of Bi-2223 was carried out by means of iron diffusion during sintering from an evaporated iron film on pellets. The investigations consist of SEM, dc resistivity and hardness measurements. These measurements indicated that the Fe doping and diffusion-annealing time increased the Tc, Jc, Vickers hardness (H0), Young's modulus(E), yield strength(Y), fracture toughness(KIC) values and improved the grain connectivity. The mechanical properties of the samples were found to be load dependent and on the diffusion-annealing time. In addition, we calculated the load independent H0, E, Y, and KIC of the samples. Possible reasons for the observed improvements in the superconducting and mechanical properties due to Fe diffusion are discussed.

Cryogenics, 2014

ABSTRACT The synthesis and characterization of bulk MgB2 superconductors doped with various amoun... more ABSTRACT The synthesis and characterization of bulk MgB2 superconductors doped with various amounts of organic compound C15H12O2 are reported. We prepared MgB2 + C15H12O2 samples by means of wet-mixing process in ethyl toluene. A high JcJc value 3.6 × 105 A/cm2 in self field was achieved at 20 K for 5 wt % C15H12O2 doped MgB2 sample. The thermal and microstructural analysis of the doped samples revealed the existence of significant differences in their granular structures. The results were interpreted in terms of the additive effects of C15H12O2. Our findings suggested that C15H12O2 promises to be an appropriate material to improve JcJc in a wide magnetic field range at low dopant levels.

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2011

This study presents the identification of a title compound, p-biphenyloxycarbonylphenyl acrylate ... more This study presents the identification of a title compound, p-biphenyloxycarbonylphenyl acrylate by means of experimental and theoretical evidences. The spectroscopic properties of the compound were experimentally investigated by Fourier transformation-infrared spectra (in the region 400-4000 cm −1) and nuclear magnetic resonance (NMR) chemical shifts (with a frequency of 400 MHz). Moreover, the optimized molecular structures, vibrational frequencies including infrared intensities and Raman activities, corresponding vibrational spectra interpreted with the aid of normal coordinate analysis based on scaled density functional force field, thermodynamic properties, atomic charges and ultraviolet-visible (UV-vis) spectra were analyzed utilizing ab initio Hartree-Fock (HF) and Density Functional Theory (B3LYP) methods at 6-31G(d,p) calculation level. It was found that the vibrational frequencies and chemical shifts obtained were shown to have a good agreement with available experimental results. We not only simulated frontier molecular orbitals (FMO) and molecular electrostatic potential (MEP) but also evaluated the transition state and energy band gap clearly.

Physica C: Superconductivity, 2011

... 272â€“276, e179 (2004). [49] NR Khasanova, EV Antipov, Physica C 246, 241 (1995). [50] A. Ami... more ... 272â€“276, e179 (2004). [49] NR Khasanova, EV Antipov, Physica C 246, 241 (1995). [50] A. Amira, F. BouaÃ¯cha, N. Boussouf, MF Mosbah, Solid State Sci. 12, 699 (2010). 12 [51] SA Halim, SA Khawaldeh, SB Mohammed, H. Azhan, Mater. Chem. Phys. 61, 251 (1999). ...

Physica B: Condensed Matter, 2007

ABSTRACT We have investigated the effect of the partial substitution of Ca by Sm in the Bi-2223 s... more ABSTRACT We have investigated the effect of the partial substitution of Ca by Sm in the Bi-2223 superconducting samples prepared by standard solid-state reaction method. Our investigations consisted of DC electrical resistivity, AC susceptibility, X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements. We measured the critical transition temperatures, activation energies and irreversibility lines from the resistivity versus temperature curves under DC magnetic fields in the range of 0 and 0.6 T. The superconducting transition temperature, T, and activation energy, U0, were found to decrease with increasing Sm concentration and with increasing applied magnetic field. Increasing the Sm content shifted the irreversibility temperature to lower values. The AC susceptibility measurements were carried out at 80 A/m field strength and f=211Hz frequency. XRD patterns and SEM micrographs are given to provide information about Bi-2223 and Bi-2212 phases and their grain size. The possible reasons for the observed degradation in microstructural and superconducting properties due to Sm substitution were discussed.

Physica B: Condensed Matter, 2010

ABSTRACT The aim of the present study is to investigate the effect of diffusion-doped silver on s... more ABSTRACT The aim of the present study is to investigate the effect of diffusion-doped silver on some physical properties of Bi1.8Pb0.4Ca2.2Sr2Cu3Ox superconducting samples and to calculate the diffusion coefficient and the activation energy of silver. The present work consists of three parts: (a) optimization of annealing temperature, (b) the effect of Ag diffusion-doped on microstructure and superconducting properties of Bi(Pb)CaSrCuO, and (c) calculation of diffusion coefficient of silver. First, to investigate the optimum annealing temperature we prepared Bi1.8Pb0.4Ca2.2Sr2Cu3Ox ceramic superconductors annealed at 830, 835, 840, 845, and 850°C using the solid state reaction method. The investigations consist of XRD, SEM, dc resistivity, and transport critical current density measurements. The highest Tc and Jc values were observed for the sample annealed at 840°C for 48h (B840). Large grain size, denser surface, and high volume fraction of the high-Tc phase were obtained for the sample B840. The diffusion doping of Bi1.8Pb0.4Ca2.2Sr2Cu3Ox by silver increased the critical current density from 123 to 696A/cm2 and the transition critical temperature by about 3K compared with the undoped sample. Ag-doping increased the amount of high-Tc phase and improved the surface morphology. It also caused an increase of the lattice parameter c by an amount of 0.15%. The temperature dependence of the silver diffusion coefficient in the range 600–800°C is described by D=2.9×10−4exp(−1.05eV/kBT). Possible reasons for the observed improvement in the structural and superconducting properties of the samples due to silver diffusion are discussed.

Physica B: Condensed Matter, 2011

... [14] S. Uthayakumar, E. Srinivasan, R. Jayavel, C. Subramanian, Physica C 383 (2002) 122. [15... more ... [14] S. Uthayakumar, E. Srinivasan, R. Jayavel, C. Subramanian, Physica C 383 (2002) 122. [15] G. Ilonca, TR Yang, AV Pop, G. Stiufiuc, R. Stiufiuc, C. Lung, Physica C 388-389 (2003) 425. ... 431 (2007) 49. [20] PM Sarun, S. Vinu, R. Shabna, A. Biju, U. Syamaprasad, Mater. Lett. ...

Gold (Au) diffusion in superconducting Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy was investigated over the tempe... more Gold (Au) diffusion in superconducting Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy was investigated over the temperature range 500-800 C by the EDXRF technique. It is found that the Au diffusion coefficient decreases as the diffusion-annealing temperature decreases. The temperature dependences of Au diffusion coefficient in grains and over grain boundaries are described by the relations D1=6.7 x 10-5exp(-1.19eV/kBT) and D2=9.7 x 10-4exp(-1.09eV/kBT), respectively. The diffusion doping of Bi-2223 by Au causes a significant increase of the lattice parameter c by about 0.19%. For the Au-diffused samples, transport measurements indicated the Tc increased from 100 to 104K and the Jc increased from 40 to 125Acm-2, in comparison with those of undoped samples. From SEM and XRD measurements it is observed that Au doping of the sample also improved the surface morphology and increased the ratio of the high-Tc phase to the low-Tc phase. The possible reasons for the observed improvement due to Au diffusion are ...

Journal of Superconductivity and Novel Magnetism, 2012

ABSTRACT This study reports the effects of oxygenation on new high-T c cuprates having the struct... more ABSTRACT This study reports the effects of oxygenation on new high-T c cuprates having the structure of RE3Ba5Cu8O18 (RE=Y, Sm and Nd) and T c (on) values of 96.5–97.5 K. The measurements have shown that excess oxygenation has no important contribution to the T c (on) values, but it improves T c (off) values significantly. From these three systems, RE = Nd is the most sensitive one to the oxygenation. Its T c (off) value increases by 13 K (from 78 K to 91.1 K) with post-annealing.