Evidence for local composition variations within YBa2Cu3O7−δ grain boundaries

Abstract
The composition variations associated with grain boundaries in bulk sintered YBa2Cu3O7−δ have been investigated by means of energy‐dispersive x‐ray microanalysis in a high spatial resolution scanning transmission electron microscope. A series of composition profiles indicates that considerable variations in composition occur on a very local scale both parallel and perpendicular to these grain boundaries. The regular, oscillatory (period ∼25 nm) nature of the composition variations observed along a grain boundary suggests that these heterogeneities may be an intrinsic feature of the boundary. Some possible implications of these observations for percolative conduction mechanisms are discussed briefly.