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Various advancements have been made in the development of [YBa.sub.2][Cu.sub.3][O.sub.x] (YBCO) second generation HTS conductor scale-up at superpower. These conductors are found to exhibit very high values of the critical current.

Current barriers were investigated in Y-Ba-Cu-O coated conductors using the Rolling Assisted Biaxially Textured Substrate method.

Bubbling of the Ag-sheath and porosity in the superconducting core can be caused by gases such as CO2 and H2O in lengthy Bi-2212 tapes and wires. H2O can be eliminated and CO2 can be lessened during heating through a pre-processing step that consists of vacuum annealing. Porosity can also be countered through an overpressure heat treatment. The shape and size of pores in multifilaments changes during the processing treatment.

An overpressure furnace was utilized to determine the extent in which sheath deformation changes with the total pressure in melt-processed silver-sheathed Bi-2212 tapes. Results show that bubbling in coils are eliminated by processing in total pressure of up to 9 atmospheres with constant oxygen partial pressure. Results also reveal that critical current density rises with the increase of total pressure.

Coupled magneto-optical imaging and local misorientation angle mapping have been used to demonstrate the percolative nature of supercurrent flow in YBa[sub 2]Cu[sub 3]O[sub 7-x](YBCO) coated conductors grown on deformation-textured Ni substrates. Barriers to current flow occur at many YBCO grain boundaries (GBs) which have propagated through the buffer layers from the underlying Ni substrate, and all Ni GBs with misorientation angles >4° initiate percolative current flow. This type of current barrier is characteristic of the conductor form and has been found to exist in samples with J[sub c](0 T,77 K) values >2 MA/cm[sup 2]. Sharpening of the local substrate texture or improving in low-angle GB properties should lead to higher J[sub c] values. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The microstructural and compositional evolution of thick (>1 μm) high temperature superconducting YBa2Cu3O7-x (YBCO) films grown on single crystal SrTiO3 substrates by the metal organic chemical vapor deposition (MOCVD) process was investigated by focused ion beam microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and atomic force microscopy. This study showed that as the MOCVD YBCO film thickness increased above 0.5 μm, defects such as second phase particles, pores, and misaligned grains preferentially nucleated and grew at the YBCO surface. A portion of this defective top layer was eliminated from all the samples using a gas cluster ion beam (GCIB) process that first removed material with a focused argon cluster beam. Next, an oxygen cluster beam was used to smooth the surface and re-oxygenate the YBCO. Comparing the critical current (Ic) measured before and after GCIB processing showed that the Ic remained the same, and even improved, when part of the defective top layer was removed. This microstructural and electromagnetic “dead layer” is believed to be responsible for the overall Ic decrease of MOCVD YBCO films thicker than 0.5 μm. [Copyright &y& Elsevier]