GROWTH-INDUCED COLUMNAR DEFECTS IN YBA2CU3O7-X THIN-FILMS GROWN ON MISCUT MOSAIC LAALO3(001)

Measurements of the critical current density in YBa2Cu3O7-x (YBCO) thi n films grown on deliberately miscut (1.6 degrees) LaAlO3 {001} substr ates that also contain a small mosaic spread of subgrain orientations have shown an anomalous angular dependence of J(c), A strong, magnetic field-dependent peak in J(c) is observed when the magnetic field is o riented between the c-axis (the film normal direction) and the a-b-pla ne; in this orientation flux pinning is normally not strong. Transmiss ion electron microscopy (TEM) has been used to determine the defects w hich are responsible for the flux pinning related to the anomalous J(c ) peak. [001] columnar defects have been observed to penetrate right t hrough the YBCO films. The diameters of the columnar defect regions ar e similar to 3-5 nm, which is near ideal for producing the observed an omalous pinning and high J(c). Numerous stacking faults involving exce ss Cu-O layers have also been observed; these can also serve as effect ive flux pinners. Small-angle planar boundaries perpendicular to the s ubstrate are rarely seen. Images of the YBCO-substrate interface revea l that some of the columnar growth defects initiate at substrate steps /dislocations. The YBCO unit cells grown on the upper and lower terrac es of a substrate step have a relative shift of c/3[001]; thus, the Cu -O planes are broken within a region less than 10 nm from the substrat e, presumably reducing the superconducting order parameter in this reg ion and leading to pinned vortices situated on these sites. Thus, the columnar defects initiated from the interface and the stacking faults are useful for pinning flux through the entire film thickness.