Superconductivity above 90 K in Y-Ba-Cu-O Compounds and Their Critical Current Densities at 77 K

Y0.4Ba0.6Cu1O3-y was found to consist of a mostly single orthorhombic phase and exhibit superconductivity with onset at 93 K, midpoint at 92 K and zero resistance (offset) at 90 K. As the ratio of Y0.4Ba0.6 to Cu increases from 1.0 to 2.0, the volume fraction of other unidentified phases increases and the offset T c decreases to below 77 K at 2.0 through 85 K at 1.5, even though the high onset T c remains constant. Critical current densities at 77 K and zero applied field for the Y-Ba-Cu oxides are as low as about 10 A/cm2 and hence the high T c oxides are concluded to be an extremely soft superconductor.