Grain growth and grain boundaries in in-plane aligned a-axis oriented YBa 2Cu 3O 7− x films on (100) LaSrGaO 4

Abstract

We have grown in-plane aligned a-axis oriented YBa 2Cu 3O 7− x films on (100) LaSrGaO 4 crystalline substrates by pulsed laser deposition under various deposition conditions. We have found that sizes and shapes of the grains in the films depend critically on the deposition pressures and temperatures. Films with very smooth surfaces (mean roughness of 30–50 Å) 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 across each grain boundary can be modeled as a collection of multiple parallel 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-direction). 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 oriented a-axis films is similar to that of standard c-axis films, with no significant deleterious effects from weak links.