Study of structure-processing-property relations in copper oxide based high (Tc) superconductors. Progress report, July 1992--June 1993

摘要

Objective is investigation of critical current limiting processes in bulk superconductors. Since the grain boundaries play a key role here, we focus on the electrical characterization of single grain boundaries. Electrical contact to thin polished sections is established with thermosonic wire bonding. Laser cutting is used to isolate a single grain boundary. Results on YBa(sub 2)Cu(sub 3)O(sub x) showed that two different types of grain boundaries are present. Most grain boundaries showed current voltage characteristics typical for flux pinning effect and no or little change in low magnetic fields. However, Josephson effect could also be found in some grain boundaries exhibiting a remarkable decrease of I(sub c) in low magnetic fields. Both types could be found in the same sample. Additionally we are working on Bi(sub 2)Sr(sub 2)CaCu(sub 2)O(sub x) thick films grown on silver foil on MgO substrates. The films showed metallic behaviour and (Tc)=80K. Preliminary results showed that the grain boundaries are of the flux pinning type.