Grain boundaries in high temperature superconducting ceramics

Abstract

The aim of this paper is to review the different types of grain boundaries found in YBa₂Cu₃O_{7− d} superconducting ceramics, which have been investigated over the past decade. A variety of samples covering a wide range of current density J _c 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, J _c is expected and found to decrease with increasing grain boundary (GB) misorientation. From the magnetic behaviour, the critical current density J _c(H) is expected to increase with the number of pinning centres. The properties of the various types of GBs are discussed. All the studies reviewed lead to the conclusion that grain boundaries in YBCO materials cannot be understood without specific information on their local composition, structure and electronic state. They confirm that research on bicrystals is crucial for high-temperature superconductor development.

Acknowledgements

My very special thanks to Michel Gasgnier for his contribution throughout the time of our collaboration and especially now for his positive and constructive criticisms while re-reading the manuscript. My thanks go also to Bernard Lang for his kind and efficient help in correcting my English.