The microstructure of sub-grain boundaries in single-domain melt-textured composites was studied by means of transmission electron microscopy. It was found that sub-grain boundaries had a strong tendency to develop parallel to the (100), (010) and {110} planes, while the form of the dislocation networks was controlled by the properties of the constituent dislocations. In the case of YBa2Cu3O7, which presented an unique glide plane, (001), the boundaries stabilized on {110} planes were accommodated by dislocations with lines running along the c-axis. The occurrence of the unusual line direction was explained in terms of a line-energy anisotropy on the (001) plane. In NdBa2Cu3O7, with (100), (010) and {110} glide planes in addition to (001), c-axis oriented dislocations were also found to be stabilized on (100)/(010)-faced boundaries. For arbitrary sub-grain boundary configurations, the form of the dislocation networks could be parametrized by using the generalized Frank formula; thus permitting the calculation of dislocation densities. As well as the underlying dislocation networks, the sub-grain boundaries could develop mesostructures such as faceting and stepped interfaces which accommodated the deviations from low-index planes. The manner in which these defects affected transport critical currents was explained on the basis of a simple geometrical model. As the form of dislocation networks was governed by intrinsic material parameters, the present results could be extended to other large-scale materials in which a strong incidence of low-angle grain boundaries was expected.

Subgrain Boundary Structure in Melt-Textured RBa2Cu3O7 (R = Y, Nd) - Limitation of Critical Currents Versus Flux Pinning. F.Sandiumenge, N.Vilalta, J.Rabier, X.Obradors: Physical Review B, 2001, 64[18], 184515 (10pp)