A review was presented of the various types of grain boundary found in YBa2Cu3O7−d superconducting ceramics. A variety of samples covering a wide range of current density Jc values were examined, including classical bulk ceramics, melt-textured bulk ceramics, bulk and thin film bicrystals with specific orientations, thin films and single crystals. From electronic coupling, Jc was expected and found to decrease with increasing grain boundary misorientation. From the magnetic behaviour, the critical current density Jc(H) was expected to increase with the number of pinning centres. The properties of the various types of grain boundaries were considered. All of the studies led to the conclusion that grain boundaries in YBCO materials could not be understood without specific information on their local composition, structure and electronic state. They confirmed that research on bicrystals was crucial for high-temperature superconductor development.

Grain Boundaries in High Temperature Superconducting Ceramics. J.Ayache: Philosophical Magazine, 2006, 86[15], 2193-239