Critical Current Densities JC(H,T) and Current-Voltage Characteristics in Melt Processed Bi-2212 with and without Preferential Orientation

ABSTRACTIn contrast to sintered Bi2Sr2Ca1Cu2Oy (Bi-2212), melt processed material exhibits nonzero intergrain supercurrents at T < 77 K. By means of partial melting and long term annealing we achieved nonoriertted material with Jc(77) - 3500 A/cm2 (1μV/cm criterion) and Tc = 96 K. Zone melting leads to well textured bulk material with the c-axis of the crystallites oriented perpendicular to the pulling direction R, and thus to an anisotropie critical current density. The anisotropy factor is between 2 and 5. At low temperatures the melt textured ceramic exhibits higher critical currents than the nonoriented material. This is not true at high temperatures, since the latter has a higher critical temperature.At 77 K and small fields both oriented and nonoriented ceramics exhibit no transition in their current-voltage characteristics, but obey the power law E = Eo(j/jo(H)) α(H) over a large range in E (10”−3-10”−3 V/cm). Measurements on the textured ceramic with magnetic fields parallel and perpendicular to the pulling direction demonstrate that the superconducting properties of these materials are only affected by the field components parallel to the c-axes of the crystallites. For fields parallel to the pulling direction the measured values of α(H), Jo(H) and of the reversible magnetization Mrev can be attributed to the misorientation of the Bi-2212 platelets which is in average about 14°.