MICROSTRUCTURE AND COMPOSITION OF ELECTROMAGNETICALLY-CHARACTERIZED YBa2Cu3O7-δ GRAIN BOUNDARIES

The electrical character (flux-pinning, Josephson junction, or resistive) of the grain boundaries in approximately twenty flux-grown YBa2Cu3O7-δ bicrystals was determined in previous studies. A selection of these same bicrystals now have been thinned for study by transmission and scanning transmission electron microscopy. High-spatial resolution imaging and analytical techniques reveal microstructural differences among these boundaries that are consistent with their diverse electrical characteristics. The observations offer preliminary insight into some of the features that control the grain boundary superconducting properties and re-emphasize the very fine scale on which the grain boundary electrical character is determined.