CRITICAL CURRENT-DENSITY IN QUENCHED OXYGEN DEFICIENT YBA2CU3O7-DELTA

The critical current density J(c) was determined magnetically in polycrystalline sintered specimens of YBa2Cu3O7-delta as a function of magnetic field and temperature for 0.02 less-than-or-equal-to delta less-than-or-equal-to 0.31. The critical temperature of these quenched specimens decreases almost linearly with increasing-delta. The highest J(c) values at all temperatures and fields are found in the specimen with delta almost-equal-to 0. However, when taking into account that the thermodynamic critical field H(c) decreases quite strongly with increasing delta it is concluded that the density of pinning centers increases as the oxygen deficiency increases. Low temperature equilibrations (keeping constant stoichiometry) significantly affect J(c) values.