The influence of carbon impurities on Jc in Ag/Bi(2223) tapes

Silver sheathed tapes based on the oxide compound Bi(2223) have been prepared with critical current densities up to 3.3 · 104 A/cm2 at 77 K and 0 T. These tapes were characterized by measurements of jc vs. B and of jc vs. θ, the angle between the applied magnetic field and the c axis. The presence of carbon impurities in Pb stabilized Ag/Bi(2223) tapes has been detected by means of chemical analysis and of high resolution Auger spectroscopy. A substantial amount of carbon was found on the inside of the superconducting layer of Ag/Bi(2223) tapes. In tapes with jc values varying from 1500 to 2 · 104 A/cm2 at 77 K and 0 T produced by the same sintering and processing steps, jc was found to be maximum for the lowest C content. Auger profile measurements showed a drastic change of the overall C content, ranging from 10 at.% for jc(77K,0T) = 1500 A/cm2 to 2 · 104 A/cm2. The present results show that a low carbon content is a necessary condition for obtaining Bi(2223) tapes with high jc values, the final value depending in addition on the degree of texturing, the amount of foreign phases and the density of the superconducting layer