Microstructural studies on YBCO film bicrystals with large single facet grain boundaries grown by liquid phase epitaxy

In order to understand the intrinsic dependence of intergranular Jc on the misorientation angle, a large, single-faceted grain boundary (GB) that is atomically smooth is necessary. Growth of YBCO film on MgO bicrystal substrates by liquid phase epitaxy (LPE) was applied to obtain large single-faceted GBs. Plan-view and cross sectional TEM observations confirmed that the GBs are straight and a single facet with 10-30 µm dimension can be easily found. High-resolution electron microscopic studies on these GBs showed that GBs with misorientation angles of 4°, 8°, 12°, 16° and 45° are single facets at the atomic scale, but 24° and 36° GBs are faceted at a scale, of a few nanometres. Shear structures at stacking faults observed at asymmetric low-angle GB may result in a Cu-rich GBs, so the stacking fault becomes insulting and is a strong barrier for current flow. A possible relationship between the dependence of Jc on misorientation angles and microstructures are discussed for LPE bicrystals.