HIGH-QUALITY THIN-FILMS OF YBA2CU3O7 BY POSTANNEALING AT LOW OXYGEN PARTIAL-PRESSURE

Thin films of YBa2Cu3O7 were made by coevaporation and post-annealing at two sets of temperature and oxygen partial pressure (850-degrees-C and 1 atm of oxygen, and 750-degrees-C and 29 Pa of oxygen). The films were deposited on (100) LaAlO3 substrates. The shape of the resistance versus temperature curves for samples annealed as above are similar, but the room temperature resistance of the sample annealed at high temperature is a factor of 1.7 higher, and the critical current density at 77 K is a factor of 3 lower. Samples annealed at low temperature and low oxygen partial pressure are much smoother, and have a significantly sharper RF eddy-current transition. The improved properties of samples annealed at low oxygen partial pressure may be related to the proximity of the conditions used to this superconductor's thermodynamic stability line.