Electromigration studies of the role of oxygen defects in YBa/sub 2/Cu/sub 3/O/sub 7- delta / grain boundary weak links

Electromigration experiments were used to help establish the role of local basal-plane oxygen disorder in determining the properties of grain-boundary (GB) weak links in YBa/sub 2/Cu/sub 3/O/sub 7- delta / thin films. The response to electromigration currents allows an estimate of the atomic force required to promote chain oxygen disorder in this material. In addition, it was determined that a lesser force is sufficient to promote long-range motion (1-2 mu m) of oxygen defects once they have been created. The activation energy for this process is approximately 0.8 eV. The creation of localized regions of disorder by electromigration in microbridges without GBs shows that these regions have superconductive properties indicative of a filamentary superconductive system shunted by nonsuperconductive ohmic paths. Parallels are drawn between the bulk thin film behavior and the effects due to the presence of GBs. These boundaries can be viewed as limiting the degree of connection between two disordered regions created by the elastic strain gradients caused by the GB.<>