Secondary phases in (001)RBa2Cu3O7-delta epitaxial thin films

The composition and orientation of secondary phases in epitaxial (001)RBa2C u3O7-delta thin films grown by MOCVD were investigated by HREM, XRD, SEM, a nd other techniques. The observed secondary phases often did not correspond to those expected from equilibrium phase diagrams of bulk R-Ba-Cu-O system s. No evidence was found for the presence of R2BaCuO5 or BaCuO2, which are the equilibrium phases with bulk RBa2Cu3O7-delta. In contrast, inclusions o f well-oriented R2CuO4 (R = Gd), R2O3 (R = Lu, Ho, Y), R2Cu2O5 (R = Lu), Ba 2CuO3, and BaCu3O4 were observed, depending on the films' stoichiometry. It is concluded that the formation of coherent or semicoherent interfaces bet ween embedded inclusions and the surrounding matrix is critical for a stabi lization of otherwise nonequilibrium oxide phases in epitaxial films. The c rystal structure of unstable-in-bulk cuprate BaCu3O4 was determined using e lectron nanodiffraction of the films' cross sections.