Effect of slow cooling rates on the superconducting characteristics of YBa2Cu3O7−x

We describe an oxygen annealing procedure to obtain bulk YBa2Cu3O7−x samples with zero electrical resistance states at 105 K, a narrow transition width of ∼1 K, and Jc values in excess of 200 A cm−2 at 77 K. It is suggested that enhanced superconducting characteristics result from incorporating very slow cooling rates (0.1 K/min) during oxygen annealing which possibly maximizes the occupancy of 0, 1/2, 0 oxygen sites and leads to a near‐perfect ordering of vacancies at 1/2, 0, 0 sites in the orthorhombic unit cell of YBa2Cu3O7−x.