Recent results on the weak link problem in bulk polycrystalline REBa2Cu3O7

In this paper the authors summarize some of our recent work associated with weak link identification in bulk polycrystalline samples of REBa2Cu3O7. The authors continue to find evidence for weak links within grains, although seeing evidence for increased coupling lengths as the temperature decreases. STEM studies of composition variations at grain boundaries indicate in general that the relative concentrations of Cu and O are increased and decreased, respectively. The authors also observe regions, however, where no composition perturbations are measurable. In attempting to explain why grain boundaries act as weak links, the authors briefly note an early proposal that easy flux shear occurs at grain boundaries but develop in more detail a microbridge model for current flow across boundaries