A comparison of grain boundary topography and dislocation network structure in bulk-scale [001] tilt bicrystals of Bi 2Sr 2CaCu 2O 8+ x and YBa 2Cu 3O 7−δ

Abstract

The facet topography and grain boundary dislocation content of the grain boundaries in nominally [001] tilt bicrystals of Bi 2Sr 2Ca 1Cu 2O 8+ x (2212) and YBa 2Cu 3O 7−δ (YBCO) are described and compared. Bicrystals with misorientation angles ranging from 8° to 15° were studied by polarized light microscopy, diffraction-contrast transmission electron microscopy (TEM) and high-resolution TEM. On the micron length scale of light microscopy, all of the boundaries appeared to be of pure tilt character and to form facets with dimensions on the order of fifty and several hundred micrometers in YBCO and 2212, respectively. However, TEM studies revealed a distinctly different characteristic pattern of faceting on the 100 nm length scale. In 2212, a rather irregular arrangement of nominally pure symmetrical [001] tilt facets and [001] twist facets is suggested. Very regular saw-tooth shaped arrangements of just two types of tilt facets predominate in YBCO. The nanoscale topography and structure of the tilt boundary facets show similarities in the two materials. Boundaries in both materials tend to facet further onto symmetric tilt planes on the nanoscale. This preference is most pronounced in 2212. A single set of partial edge dislocations and their associated stacking faults comprises the grain boundary dislocation network structure of the symmetric segments in both materials. Thus, the boundaries show nanoscale similarities, mesoscale (∼100 nm) differences, and a number of different possible microstructural sources for the heterogeneous electrical character that is indicated by their electromagnetic properties.