Yazar "Terzioglu, C." seçeneğine göre listele

Listeleniyor 1 - 6 / 6
  • Küçük Resim
    Öğe
    Effect of Mn Addition on Structural and Superconducting Properties of (Bi, Pb)-2223 Superconducting Ceramics
    (Springer, 2012) Yildirim, G.; Bal, S.; Yucel, E.; Dogruer, M.; Akdogan, M.; Varilci, A.; Terzioglu, C.
    This study deals with the effect of Mn addition on the structural and superconducting properties of Bi1.8Pb0.4Sr2Mn (x) Ca2.2Cu3.0O (y) ceramics with x=0,0.03,0.06,0.15,0.3 and 0.6 by means of X-ray analysis (XRD), scanning electron microscopy (SEM), electron dispersive X-ray (EDX), resistivity, and transport critical current density (J (c)) measurements. Zero-resistivity transition temperatures (T (c)) of the samples produced via the standard solid-state reaction method are estimated from the dc resistivity measurements. Moreover, the phase fraction and lattice parameters are determined from XRD measurements while the microstructure, surface morphology and element composition analyses of the samples are investigated by SEM and EDX measurements, respectively. It is found that T (c) values are obtained to decrease from 109 K to 85 K; likewise, J (c) values are observed to reduce from 3200 A/cm(2) to 125 A/cm(2) with increasing Mn addition. According to the refinement of cell parameters done by considering the structural modulation, the Mn addition is confirmed by both an increase of the lattice parameter a and a decrease of the cell parameter c of the samples in comparison with that of the pure sample (Mn0). SEM measurements show that not only the surface morphology and grain connectivity are seen to degrade but the grain sizes of the samples are found to decrease with the increase of the Mn addition as well. The EDX results reveal that the elements used for the preparation of samples distribute homogeneously and the Mn atoms enter into the crystal structure by replacing Sr and Cu atoms. The possible reasons for the obtained degradation in microstructural and superconducting properties are also interpreted.
  • [ N/A ]
    Öğe
    Fabrication and Transport Critical Current Densities of MgB2/Fe/Cu Multifilament Tapes without Any Intermediate Annealing
    (Polish Acad Sciences Inst Physics, 2012) Yucel, E.; Terzioglu, C.; Varilci, A.; Gencer, A.; Belenli, I.
    We 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.
  • Küçük Resim
    Öğe
    The influence of cooling rates on microstructure and mechanical properties of Bi1,6Pb0,4Sr2Ca2Cu3Oy superconductors
    (Iop Publishing Ltd, 2009) Cetinkara, H. A.; Yilmazlar, M.; Ozturk, O.; Nursoy, M.; Terzioglu, C.
    We investigated the effect of cooling rates on the microstructure and mechanical properties of Bi(1,6)Pb(0,4)Sr(2)Ca(2)Cu(3)Oy superconductors prepared by standard solid state reaction methods. The samples were annealed under identical condition and cooled with different cooling rates. The investigations consisted of Vickers microhardness, SEM and XRD measurements. XRD examination of the samples showed that high percentage of Bi-2212 phase was observed and low-T-c phase increased with increasing the cooling rates. From SEM analysis, flake-like grains were more pronounced with increasing cooling rates. The indentation load versus diagonal length of the samples under different indentation loads in the range of 0.245-2.940 N were presented. We calculated Vickers hardness, Young's modulus, yield strength, fracture toughness values. These mechanical properties of the samples were found to be load and cooling rate dependent. In addition, we calculated the load independent microhardness, Young's modulus, and yield strength and fracture toughness of the samples using different models. The possible reasons for the observed changes in microstructure and mechanical properties of the samples due to cooling rates were discussed.
  • Küçük Resim
    Öğe
    Investigation of mechanical and superconducting properties of iron diffusion-doped Bi-2223 superconductors
    (Springer, 2011) Ozturk, O.; Cetinkara, H. A.; Asikuzun, E.; Akdogan, M.; Yilmazlar, M.; Terzioglu, C.
    The mechanical and superconducting properties of the Fe diffusion-doped (Bi-Pb)-2223 superconductor have been investigated. First, iron was evaporated on Bi-2223 superconductor and then the Fe layered superconductor was annealed at 830 A degrees C for 10, 30 and 60 h. Static Vickers hardness, dc electrical resistivity, X-ray diffraction and scanning electron microcopy have been carried out to assess the effects of Fe doping. These measurements indicates that Fe doping, in comparison with the undoped samples, increased the critical transition temperature, and improved formation of high T (c) phase, while decreasing the number and size of voids. Moreover, both microhardness and grain size were also enhanced by increasing the amount of diffusion. The values of microhardness were found to be load dependent. In addition, we have investigated the indentation size effect (ISE) behavior using some models such as the Kick's law, modified proportional specimen resistance (MPRS) model and the Hays- Kendall (HK) approach. Among them, both HK and MPRS models are successful. In this study, the possible reasons of noticed improvement on mechanical and physical properties due to iron diffusion are discussed.
  • Küçük Resim
    Öğe
    Role of diffusion-annealing temperature on the microstructural and superconducting properties of Cu-doped MgB2 superconductors
    (Springer, 2012) Dogruer, M.; Yildirim, G.; Yucel, E.; Terzioglu, C.
    This study deals with not only investigate the effect of the copper diffusion on the microstructural and superconducting properties of MgB2 superconducting samples employing dc resistivity as a function of temperature, scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements but also calculate the diffusion coefficient and the activation energy of copper for the first time. Electrical-resistivity measurements indicate that both the room-temperature resistivity value and zero resistivity transition temperatures (T (c) ) increase with increasing the diffusion-annealing temperature from 650 to 850 A degrees C. SEM measurements show that not only the surface morphology and grain connectivity improve but also the grain size of the samples increases with the increase in the diffusion-annealing temperature up to 850 A degrees C. As for the XRD results, all the samples contain the MgB2 phase only and exhibit the polycrystalline superconducting phase with more intensity of diffraction lines, leading to the increasement in the lattice parameter a and c. Additionally, the diffusion coefficient is observed to increase from 6.81 x 10(-8) to 4.69 x 10(-7) cm(2) s(-1) as the diffusion-annealing temperature increases, confirming that the Cu diffusion at lower temperatures is much less significant. Temperature dependence of the Cu diffusion coefficient is described with the aid of the Arrhenius relation D = 3.75 x 10(-3) exp (-1.15 +/- A 0.10 eV/k (B) T) and the corresponding activation energy of copper in MgB2 system is found to be about 1.15 eV. The possible reasons for the observed improvement in microstructural and superconducting properties of the samples due to Cu diffusion are also discussed.
  • Küçük Resim
    Öğe
    Vickers hardness measurements and some physical properties of Pr2O3 doped Bi-2212 superconductors
    (Springer, 2012) Asikuzun, E.; Ozturk, O.; Cetinkara, H. A.; Yildirim, G.; Varilci, A.; Yilmazlar, M.; Terzioglu, C.
    This study deals with the effect of Pr2O3 addition on the structural, superconducting and mechanical properties of Bi-2212 superconductor by means of X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), electron dispersive X-ray (EDX), Vickers microhardness and resistivity measurements. The samples studied are prepared using the standard solid-state reaction method. Onset transition temperatures (T (c) (onset) ) of the samples are estimated from the dc resistivity measurements. Furthermore, the phase ratio and lattice parameters a and c 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. Additionally, vickers microhardness, elastic modulus, yield strength and fracture toughness values of the samples are deduced from microhardness measurements. It is found that T (c) (onset) values of the samples increase from 87 to 97 K with the Pr2O3 addition. According to the refinement of cell parameters done by considering the structural modulation, the doping is confirmed by both an increase of the lattice parameter a and a decrease of the cell parameter c of the samples in comparison with that of the pure sample. As for SEM measurements, it is obtained that the surface morphology and grain connectivity degrade with the increase of the Pr2O3 addition. Moreover, EDX images show that the elements used for the preparation of samples distribute homogeneously and the Pr atoms enter into the crystal structure by replacing Sr atoms. To sum up, the Pr2O3 addition is found to suppress the mechanical, microstructural and superconducting properties of the Bi-2212 superconductor.