Critical current and microstructure in oxide superconductors

Critical current density (J_c) in the presence of a magnetic field is the property that currently limits many applications of the high-critical-temperature oxide superconductors. Poor current transmission at grain boundaries and weak flux pinning are responsible for the low critical current densities observed in bulk materials. Since 1986, substantial progress has been made both in understanding the microstructural factors affecting J_c and in developing practical fabrication methods. Much of the fundamental understanding has been obtained from studies of YBa₂Cu₃O_7-x while the bismuth and thallium-based compounds appear to offer greater potential as the basis for the first practical conductors.