Grain boundaries in high temperature superconducting ceramics

International audienceThe aim of this paper is to review the different types of grain boundaries found in YBa2Cu3O7-d superconducting ceramics which have been investigated over the past decade. A variety of samples covering a wide range of current density Jc values are 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 is expected and found to decrease with increasing grain boundary (GB) misorientation. From the magnetic behaviour, the critical current density Jc(H) is expected to increase with the number of pinning centres. The properties of the various types of GB's are discussed. All the studies reviewed lead to the conclusion that grain boundaries in YBCO materials cannot be understood without specific information about their local composition, structure and electronic state. They confirm that research on bicrystals is crucial for high-temperature superconductor development