Grain boundaries and interfaces in Y-Ba-Cu-O films laser deposited on single-crystal MgO

Y-Ba-Cu-O thin films were deposited on [001] MgO using pulsed laser deposition. The films are granular with the c axis normal to the surface and the a-b axes locked into several preferred orientations. The grain sizes range from a few hundred to a few thousand nanometers. The misorientation of the Y-Ba-Cu-O grains with respect to the MgO could be predicted by a modified version of the coincident site lattice theory, where near coincidence as opposed to exact coincidence is sought. The resulting boundaries between adjacent Y-Ba-Cu-O grains were found to be dominated by four types of low-energy boundaries, namely, low-angle, special crystallographic, near special crystallographic, and high-angle noncrystallographic boundaries. The critical current observed in this material is as high as 5×105 A cm-2 at 77 K and is believed to be a result of clean, low-energy boundaries with a high density of connected Cu-O-Cu bonds in adjacent Y-Ba-Cu-O grains. © 1990 The American Physical Society.