EFFECTS OF REDUCING AND OXIDIZING THERMAL TREATMENTS ON THE TRANSPORT CRITICAL CURRENT-DENSITY IN EPITAXIAL BI2SR3-XCAXCU2O8+Y FILMS

We have studied the effects of oxidizing and reducing thermal treatments on the critical current density in epitaxial Bi2Sr3-xCaxCu2O8+y films. Reducing treatments, while increasing the transition temperature up to 94 K, reduces the critical current density relative to the as-grown value in the whole range of reduced temperatures. On the contrary, oxidizing treatments, while decreasing the transition temperature, increases the critical current density. Such effects are shown to be fully reversible under a final air annealing. Such effects are attributed to a decrease of the Bi2Sr3-xCaxCu2O8+y anisotropy which occurs in connection with the increase of the oxygen content in the compound.