DEGRADATION OF THIN-FILMS OF YBA2CU3O7 BY ANNEALING IN AIR AND IN VACUUM

The degradation of epitaxial thin films of YBa2Cu3O7 has been studied as a function of annealing temperature in air and in vacuum; some samp les had an evaporated overlayer of CaF2. Degradation was monitored by the measurement of electrical properties after consecutive 30-min anne aling treatments. The room-temperature resistance registered significa nt increases for all samples after annealing at temperatures above abo ut 200 degrees C; the critical current density at 77 K was degraded fo r annealing temperatures greater than or equal to 400 degrees C in air , and greater than or equal to 200-250 degrees C in vacuum. By anneali ng in oxygen at 550 degrees C, electrical properties were restored in degraded bare YBCO samples annealed in vacuum, but not for those annea led in