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  • Küçük Resim
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    Comparison of vickers microhardness of undoped and ru doped BSCCO glass ceramic materials
    (Springer, 2018) Öztürk, Özgür; Aşıkuzun, Elif; Taşçı, Ahmet Tolga; Gökçen, Tuğba; Ada, Hakan; Koralay, Haluk; Çavdar, Şükrü
    In this study, effect of substitution ratio on the mechanical and structural properties of Bi1-xRuxPb0.2Sr2CaCu2O10+delta system, that is prepared in the ratios of x = 0.0, 0.025, 0.050, 0.075, is investigated. Samples are prepared with glass ceramic method and sintered at 845 A degrees C. XRD and SEM measurements are performed for structural analyses, and Vickers micro-hardness measurements are carried out at different applied load (0.245 <= F <= 2.940 N) in order to investigate the mechanical performance of the Ru doped Bi1-xRuxPb0.2Sr2CaCu2O10+delta system. Experimental results of Vickers micro-hardness analyses are performed using the Meyer's law, the proportional samples resistance model, the elastic/plastic deformation model, the Hays-Kendall approach and the indentation induced cracking (IIC) model. All analyses results are exhibited reverse indentation size effect behavior. The measured hardness values increase with increasing the applied load. Finally, IIC model is determined as the most successful model describing the mechanical properties of our samples.
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    Evaluation of superconducting features and gap coefficients for electron-phonon couplings properties of MgB2 with multi-walled carbon nanotube addition
    (Springer, 2022) Kaya, N.; Çavdar, Şükrü; Öztürk, Öztürk; Yıldırım, Gürcan; Koralay, Haluk
    In this study, the samples are prepared by solid state reaction method at different weight ratios (0-4%). The characterization of materials produced is conducted with the aid of powder X-ray diffraction (XRD), temperature-dependent electrical resistivities (rho-T) and magnetization (M-H) measurements. Moreover, the change in the scattering/breaking of cooper-pairs in the small homogeneous clusters in the superconducting paths with the addition of multi-walled carbon nanotube is also examined by the energy gap coefficients. All the experimental findings show that the weight ratio of wt 2% is observed to be the optimum addition level. The XRD results indicate that the MgB2 material prepared by the optimum level crystallizes better in hexagonal symmetry. The critical current density is found to increase from 1.0 x 10(4) to 2.3 x 10(4)A cm(-2) depending on the increment in the magnetization values. On the other hand, the addition mechanism is noted to degrade slightly the general electrical features, critical transition temperatures, lattice cell constants and crystallite size of MgB2 material. Regardless, although the carbon nanotube addition seems to be negative effect on some general properties, the fundamental characteristic properties (the crystallinity with smoother crystallographic transition, magnetization values, coupling of adjacent layers, degree of broadening and especially formation of effective nucleation centers for the flux pinning ability) improve seriously at the optimum dopant level. Thus, the MgB2 prepared with the optimum carbon nanotube concentration can exhibit higher performance against the magnetic field and current in larger magnetic field strengths applied.
  • Küçük Resim
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    Microstructural, thermal, and electrical properties of Bi1.7V0.3Sr2Ca2Ca3Ox glass-ceramic superconductor
    (Wiley-V C H Verlag Gmbh, 2004) Kayed, Tarek Said; Çalınlı, N.; Aksu, Erhan; Koralay, Haluk; Günen, A.; Ercan, İsmail; Aktürk, Selçuk; Çavdar, Şükrü
    A glass-ceramic Bi1.7V0.3Sr2Ca2Cu3Ox superconductor was prepared by the melt-quenching method. The compound was characterized by scanning electron microscopy, x-ray diffraction, differential thermal analysis, current-voltage characteristics, transport resistance measurements, and Hall effect measurements. Two main phases (BSCCO 2212 and 2223) were observed in the x-ray data and the values of the lattice parameters quite agree with the known values for 2212 and 2223 phases. The glass transition temperature was found to be 426 degreesC while the activation energy for crystallization of glass has been found to be E-a = 370.5 kJ / mol. This result indicates that the substitution of vanadium increased the activation energy for the BSCCO system. An offset T-c of 80 K was measured and the onset T-c was 100 K. The Hall resistivity rho(H) was found to be almost field-independent at the normal state. A negative Hall coefficient was observed and no sign reversal of rho(H) or RH could be noticed. The mobility and carrier density at different temperatures in the range 140-300 K under different applied magnetic fields up to 1.4 T were also measured and the results are discussed.