IN-SITU LOW-PRESSURE OXYGEN ANNEALING OF YBA2CU3O7-DELTA SINGLE-LAYER AND MULTILAYER SYSTEMS

Optimized NdGaO3/YBa2Cu3O7-delta multilayers grown by various techniques usually suffer from reduced superconducting transition temperatures due to oxygen deficiency in the superconducting layer. We examined different post-deposition processes for in-situ and ex-situ oxygen treatment of sputter-deposited YBa2Cu3O7-delta single- and NdGaO3/YBa2Cu3O7-delta bilayers. The only procedure which reproducibly recovered the superconducting properties for YBCO films covered with a dense NdGaO3 top layer, was found to be a low-pressure procedure (typically <250 Pa) at the temperature of the structural transition from the tetragonal (non-superconducting) to the orthorhombic (superconducting) perovskite structure in activated oxygen. Furthermore, this procedure is advantageous for single-layer YB CO or other YBCO multilayer systems. The optimum condition for the oxygen treatment was determined to be 200 Pa and 540 degrees C, yielding transition temperatures T-c greater than or equal to 90 K and values for the ratio of the resistivities at 300 K and 100 K of 3.2.