GRAIN-GROWTH AND GRAIN-BOUNDARIES IN INPLANE ALIGNED A-AXIS ORIENTED YBA2CU3O7-X FILMS ON (100)LASRGAO4

We have grown in-plane aligned a-axis oriented YBa2Cu3O7-x films on (1 00) LaSrGaO4 crystalline substrates by pulsed laser deposition under v arious deposition conditions. We have found that sizes and shapes of t he grains in the films depend critically on the deposition pressures a nd temperatures. Films with very smooth surfaces (mean roughness of 30 -50 Angstrom) and densely packed grains were achieved by utilizing low oxygen deposition pressure (40-60 mTorr). Critical current density (J (c)) depends on the granular nature of the films and the transport acr oss each grain boundary can be modeled as a collection of multiple par allel narrow conductive paths. Though limited by the grain boundaries, J(c) is still relatively high (> 10(6) A/cm(2) at 60 K, in the b-dire ction). Measurements in fields up to 6 T indicate that the behavior of J(c) versus B along the b- and c-directions in these in-plane oriente d a-axis films is similar to that of standard c-axis films, with no si gnificant deleterious effects from weak links.