Microstructural homogeneity and electromagnetic connectivity of YBa2Cu3O7-delta grown on rolling-assisted biaxially textured coated conductor substrates

The electromagnetic connectivity and microstructure of three YBa2Cu3O7-delt a (YBCO) films grown on biaxially textured substrates were investigated by magneto optic (MO) imaging and scanning electron microscopy (SEM). The film s were deposited by pulsed laser deposition (PLD) on yttria-stabilized zirc onia (YSZ) and CeO2-buffered, biaxially textured Ni tapes. The transport cr itical current density (J(c)) values of the films were 0.3, 0.6 and 0.7 MA/ cm(2) (77 K, 0 T). MO imaging revealed clearly granular electromagnetic beh avior in the lowest J(c) and one of the higher J(c) samples, but considerab ly better connectivity in the sample with a J(c) value of 0.6 MA/cm(2). Hig h resolution SEM showed a dense and rather featureless microstructure in th e YBCO of the most highly electromagnetically connected sample, whereas por es and/or second phase particles cluttered the YBCO layers of the granular samples. Thus, the granular behavior in these samples appears to be caused by pores and second phase particles that locally obstruct the superconducti ng current in the YBCO layer. Control of these types of defects clearly is important for raising the J(c) value. (C) 2000 Elsevier Science B.V. All ri ghts reserved.