Grain Boundaries and Jc in High-Tc Oxide Superconductors

Abstract

In metallic superconductors, grain boundaries are effective pinners of magnetic flux and, as such, are partially responsible for high critical current densities achievable in those materials. However, in the high-critical-temperature oxide superconductors, grain boundaries have been identified as the source of problems leading to the low critical current densities exhibited by bulk-sintered material. The very short superconducting coherence lengths of the oxides make their electrical and magnetic properties exceedingly sensitive to microstructural inhomogeneities, thus placing stringent requirements on the quality of grain boundaries. Recent studies of grain boundary chemistry and its effects on critical current density have shed some light on the problem.