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    Effect of Tungsten (W) Substitution on the Physical Properties of Bi-(2223) Superconductors
    (Springer, 2014) Turk, Nihal; Gundogmus, Hakan; Akyol, Mustafa; Yakinci, Z. Deniz; Ekicibil, Ahmet; Ozcelik, Bekir
    The superconducting Bi1.6Pb0.4Sr2Ca2Cu3-x W (x) O10+y (x=0.00, 0.05, 0.10, 0.15) bulk samples were prepared by the solid-state reaction method. The effects of W substitution on the BSCCO system have been investigated by the electrical resistivity (rho-T), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), magnetic hysteresis and critical current density measurements. It has been found that the Bi-(2212) low-T (C) phase is formed for all the substitution levels, together with the Bi-(2223) high-T (C) phase. The results obtained from the XRD data show that the Bi-(2223) phase gradually transforms into the Bi-(2212) phase with increasing W substituting for Cu. In addition, from the magnetization measurements at the temperatures below the zero resistance temperatures of the samples, we have observed that a decreasing in magnitude of |M| with the increasing measurement temperature and W concentration. Therefore, the decreasing of |M| related to superconducting volume seems to imply an existence of flux-pinning centers in our samples.
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    Improved superconducting properties of MgB2 thin films fabricated by ultrasonic spray pyrolysis method at high temperature
    (Elsevier Sci Ltd, 2012) Yakinci, M. Eyyuphan; Yakinci, Z. Deniz; Aksan, M. Ali; Balci, Yakup
    High quality MgB2 superconducting thin films have been successfully prepared by 2.4 MHz ultrasonic spray pyrolysis (USP) system on single crystal Al2O3 (001) substrates. The microstructure, electrical and magnetic properties of approximately 500-600 nm thick films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) in conjunction with the energy dispersive X-ray analysis (EDX), resistance versus temperature (R-T) and magnetization measurements (M-H) under different magnetic fields and transport critical current density (J(c)). Films were first heat treated in situ in the spraying chamber with an extra Mg powder during deposition to compensate excess evaporation of Mg from the films and then additionally heat treated in Ar atmosphere at 700 degrees C for a short time. According to the results obtained, orientation on any particular direction for the crystal growth was not seen. Homogeneous, highly dense and highly smooth surface morphology and low resistance have been achieved under optimum conditions. Optimally treated films exhibited relatively high transport critical current density of 2.37 x 10(5) A cm(-2). These results have been also compared with the J(c)(mag) results calculated from the M-H curves. The electrical resistance property of the best samples was obtained to be 39.5 and 37.4 K for T-c and T-zero, respectively. (C) 2012 Elsevier Ltd. All rights reserved.