Using additional Y (or Cu) nitrate we had been successful in production of Y-enriched 123 (YBa2Cu3O7-x) as well as Cu-enriched ones. The magnetic Jc at 77K is 106 (B=0) and 105 (B=1 Tesla). A critical issue is the understanding flux pinning in terms of defects in microstructure.Precipitates were observed inside of the 123 crystal as shown in Fig. 1. These precipitated slabs are usually 3 - 10 nm long along c axis of 123 and 101 - 102 nm in the a-b plane, similar to that reported in CVD films. An interesting point is the precipitates found in both Yenriched and Cu-enriched samples have similar size and morphology. It is reasonable to assume those precipitates are the strong pinning centers for the size effect as known in type II superconductors. In the 123 compound the coherent length is about 2∼3 angstrom in the c direction and 16∼30 angstrom in the a-b plane.
Magnetic nanoparticles as efficient bulk pinning centers in type-II superconductors