Effect of Yb-substitution on thermally activated flux creep in the Bi_2Sr_2Ca_1Cu_(2-x)Yb_xO_y superconductors

摘要

In the present work, Bi_2Sr_2Ca_1Cu_2-_xYb_xO_y (x = 0.0, 0.05, 0.1, and 0.25) superconductors were prepared by a polymer matrix route technique, and subsequently used as feed in a laser induced directional solidification (LFZ) process. The X-ray diffraction, DC magnetization and mag-netoresistance measurements were studied. All samples consist mainly of the Bi-2212 phase which indicates the performed process is adequate. However, some impurity phases like CaCuO_2 were also detected. We have calculated the hole number using the relation given by Presland, and particle size, L_(hkl), using the XRD patterns results. From M-T results, the superconducting transition temperatures, T_c, of the samples were found 93, 90, 87, and 85 K, respectively. The activation energies, irreversibility fields (H_(irr)), upper critical fields (H_(c2)) and coherence lengths at 0 K (ξ(0)) were calculated from the resistivity versus temperature (R-T) curves, under DC magnetic fields up to 5 T. The thermally activated flux creep model has been studied in order to calculate the flux pinning energies. The results indicated that Hc2(0) varied from 132 to 30 T and the flux pinning energies varied from 650 to 400 meV at 0 T, with the content of Yb.