Low magnetic field superconducting phase diagram of the high- T sub C YBa sub 2 Cu sub 3 ) sub (9-delta).

The low magnetic field phase diagram of the high-T sub c superconductor YBa sub 2 Cu sub 3 O sub (9-delta) with delta~2.1 has been determined in fields to 5000 0e. The lower critical field is about 300 Oe near T=0 and less than 100 0e at liquid nitrogen temperature. The mixed phase shows significant relaxation and field cooling effects.