High-resolution analytical microscopy of YBa2Cu3O7-δ grain boundaries

Abstract

Grain boundaries are generally considered to be the microstructural entity which is responsible for the weak-link behavior that limits the transport critical current densities (Jct) of the high temperature oxide superconductors to values which are unacceptable for most applications. However, the mechanism by which grain boundaries suppress Jct has yet to be identified. This issue is particularly challenging because the microstructural features which affect Jct may be as small as the superconducting coherence length (< 1 nm for the high-temperature superconductors). Electron microscopy studies, nevertheless, have suggested a number of possible microstructural origins for the weak-link behavior. Among the candidates are: the strains associated with grain boundary dislocations; segregated impurity atoms layers of second phase; and local (within ∼ 5 nm) composition changes at grain boundaries which involve a reduction in the oxygen atom fraction.