PRECIPITATES IN YBA2CU3O7-DELTA THIN-FILMS ANNEALED AT LOW-OXYGEN PARTIAL-PRESSURE

We have studied the precipitates in YBa2Cu3O7-delta(YBCO) thin films g rown by the BaF2 process in p(O2)= 4 Torr and 700-degrees-C. While sto ichiometric films result in BaCuO2 surface precipitates, we have found Y2Cu2O5 precipitates embedded in the matrix of the same film. Off sto ichiometric films with Ba/Y < 1.5 have a precipitate-free surface but with higher abundance of Y2Cu2O5 in the film matrix. The estimated den sities of the two precipitates favor a stoichiometric YBCO film matrix . This behavior is not explainable in terms of phase equilibria and is attributed to kinetic effects. The electrical properties of the films degrade as the Ba/Y ratio deviates from 2.00.