Upcoming Conference
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TEM, scanning tunneling microscopy, and high-energy and resolution x-ray diffraction were employed. The pinning sites in question included those which were introduced by controlled precipitation or artificial methods (e.g., fission-induced defects). Some of mechanisms suggested for the pinning sites for the precipitation were very fine scale 2-D modulations of composition in Bi(Pb)-2212, Nd clusters in Nd-123, and the small oxygen deficient regions in YBCO single crystals. Despite detailed microstructural characterization, presentations discussions clearly reflected an incomplete understanding of vortex pinning in these high Tc superconductors. For instance, the pinning centers in the coated Y-123 thick films and in Nd-123 single crystals are unclear. In addition, while it is known that the irreversibility line in Bi-2212 is significantly improved with lead doping, the direct mechanism, possibly planar compositional modulation or improved electronic coupling along the c-axis, has not been demonstrated. Thus, this subject is expected to be a topic of extensive discussions in future meetings. Another interesting theoretical presentation concerned the ever
important question of current transport across grain boundaries in Y-123. Here, a model was developed for current transport across the (001) tilt boundary which took into account grain-boundary-area reduction due to edge dislocation cores, which form the boundary, as well as reduced Tc of the surrounding area via elastic strain associated with the cores. Although the model obviously simplified the structures of the boundary by using only primary dislocations to describe the boundary misorientations and by neglecting the often observed meandering boundaries or secondary dislocations, the predicted pseudo-exponential reduction of the critical current Jc with misorientation angle agreed well with the experimental self-field Jc(0) results obtained for the artificially produced bi-crystal grain boundaries in YBCO thin films. In spite of the necessary simplifications of the boundary structures, this appears to represent an important step toward understanding the reduction in Jc at grain boundaries in high Tc superconductors. Nearly a decade has passed since the advent of high-temperature superconductivity. Discovery of new materials and
development of fundamental insight has occurred and continues to occur frequently. In contrast, the progress toward industrialization of the technology has been steadily accelerating. Understanding of crystal growth mechanisms for both thin film and bulk /wire crystals have been deepened, and similarities in thermodynamics, kinetics, and performances of the film and bulk HTS materials especially on processing and crystal growth were well discussed in this workshop, which will help further developments of processes for HTS commercialization. The consensus of the workshop attendees was that most larger-scale applications will require more years to realize, however, and that consistent technological advancement will require worldwide collab
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