A representative group of boundaries and planar defects in this oxide was reviewed in order to relate their geometry, energy and cleanliness to the critical current densities across them. A considerable amount of evidence showed that not all high-angle boundaries had deleterious effects upon current transport, and exhibited weak-link behavior. Various high-angle but low-energy boundaries (such as off  = 13,  = 17,  = 5 and 45 [001] tilt, and 90), grown under many-to-one epitaxy conditions, were found to support high critical currents. It was found that a geometric description was helpful in predicting the energy of a boundary. Energies and thermodynamic boundary-wetting were useful criteria for explaining why some boundaries were clean and some were preferred sites of precipitation and areas of non-stoichiometry. But, as well as boundary geometry and energy, the processing conditions could influence precipitation and composition deviation at the boundary. Because of their minimal lattice distortions and resultant low boundary energies, translational boundaries, stacking faults, and twin boundaries were all atomically clean.

S.W.Chan: Materials Science Forum, 1996, 207-209, 797-800