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    The Effect of K Substitution on Magnetoresistivity and Activation Energy of Bi-2212 System
    (Springer, 2015) Ozcelik, B.; Yalaz, E.; Yakinci, M. E.; Sotelo, A.; Madre, M. A.
    In the present work, magnetoresistivity performance of polycrystalline Bi2Sr2Ca1-x K (x) Cu-2 O (8+y) superconductor with x=0.0,0.05,0.075, and 0.1 has been studied by change of flux pinning mechanism, using magnetoresistivity measurements. The samples were prepared using a polymer solution technique. The effects of K substitution for Ca on the irreversibility field, upper critical magnetic field, coherence length, and activation energies have been investigated. The magnetoresistivity of the samples has been measured under applied magnetic fields ranging from 0 to 9 T. Broadening of superconducting transition is observed under magnetic field, explained on the basis of thermally activated flux flow (TAFF) model. The upper critical magnetic field H (C2)(0) and the coherence length (zeta(0)) at T = 0 K were calculated using the resistivity data and from H (C2)(0) ,respectively. H (C2)(0) and xi(0) values have been calculated as 62, 72, 75, and 53 T and 23, 21, 20, and 25 for the 0.0, 0.05, 0.075, and 0.10 K doped samples, respectively. TAFF model has been studied in order to calculate the flux pinning energies. In particular, the flux pinning energies of Bi2Sr2Ca1-x K (x) Cu-2 O (8+y) where x = 0.075 are calculated as 0.0147 eV for 9 T and 0.29 eV for 0 T.
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    Relationship Between Annealing Time and Magnetic Properties in Bi-2212 Textured Composites
    (Springer, 2013) Ozcelik, B.; Ozkurt, B.; Yakinci, M. E.; Sotelo, A.; Madre, M. A.
    In this study, we report the physical and magnetic properties of Bi2Sr2CaCu2O (x) textured materials prepared by a LFZ melting technique and annealed for different times (60, 72, 96 and 120 h). SEM images of the annealed samples for 96 and 120 hours indicate very good alignment with the longitudinal rod axis. In all cases, X-ray diffraction patterns show that the Bi-2212 phase is the major one. The magnetization measurements have been carried out as a function of the magnetic field up to 9 kOe. J (c) values of the samples were calculated by using the Bean model. The results indicate that the different annealing time has no significant effects on the T (c) values but, significant change on the critical current values of samples, J (c), has been obtained for sample annealed at 96 hours. We also found that the maximum critical density of J (c) is 5.5x10(5) A/cm(2) at 10 K for the 96 hours annealed sample.