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  • Küçük Resim
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    Effect of annealing period on the resistive transitions and AC losses in a Bi1.6Pb0.4Sr2Ca3Cu4O12 superconductor fabricated by a wet technique
    (Elsevier Science Sa, 2000) Nezir, S; Celebi, S; Altunbas, M
    We estimated the irreversibility lines from the resistive-superconducting transition in DC magnetic fields up to 1 T for the Bi1.6Pb0.4Sr2Ca3Cu4O12 superconducting samples prepared by liquid ammonium nitrate with the same heat treatment but 25 h and 200 h of annealing time. Increasing the annealing time from 25 h to 200 h at 840 degrees C shifted the irreversibility temperature to a higher temperature. A non-linear Arrhenius plot of the resistive tail has been found. The activation energy obtainable from Arrhenius plots seems to be non-linear temperature dependent. The peak temperature T-p, in the imaginary part of the AC susceptibility seems to be shifted to a higher temperature by nearly the same amount as the shift in irreversibility temperature with increasing annealing time. Temperature variation of the critical current density extracted from the theoretical calculation of matrix susceptibility and irreversibility line obey the same power law dependence of (1 - T/T-c)(n), where n = 2.7 and 2.5 for the 25-h and 200-h samples, respectively. (C) 2000 Elsevier Science S.A. All rights reserved.
  • Küçük Resim
    Öğe
    Superconducting and Vickers hardness properties of ZnO-added YBCO polycrystalline superconductors
    (Wiley-V C H Verlag Gmbh, 2004) Kolemen, U; Celebi, S; Karal, H; Ozturk, A; Cevik, U; Nezir, S; Gorur, O
    The effects of ZnO addition on the microstructure and mechanical properties of the YBCO have been investigated through XRD, SEM, EDX, ac susceptibility measurements and the standard Vickers micro-hardness testing method. We have prepared the samples by a conventional solid-state reaction method and used an additive method for the YBCO system (0, 0.5 and 1 wt% of ZnO). The orthorhombic strain Delta = (b - a)/(b + a) increases as the Zn content increases, where a and b are the relevant lattice parameters of the samples. The superconducting transition temperatures and hardness depend on the Zn content of the samples. The hardness is found to be load dependent. From the relation between applied load F and the square of the impression diagonal, d(2), the true hardness, H-0, and the dissipative portion of the indentation load F-0, were derived from the slope and the intercept (at d(2) = 0) of the straight line, respectively. The hardness was increased while the transition temperature decreased with the amount of ZnO addition to YBCO.