Abshact-YB~Cu30x (YBCO) films have been deposited on buffered metal substrates by metal organic chemical-vapor deposition (MOCVD). Nickel alloy substrates with biaxirdlytextured yttria-stabilized zirconia (YSZ) buffer layers deposited by ion-beam-assisted deposition (IBAD) were used. A liquidstatic precursor delivery system was designed, constructed, and used in the MOCVD facility at Intermagnetics for the reported work. At 77 & under self-field conditions, we achieved a critical current (Q of 97.5 A in YBCO film grown by MOCVD on an IBAD substrate. This ICcorresponds to a critical current density of 1.3 MA/cm2 and 130 A/cm width of tape.

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Short and long periods of sintering of short single-core (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O 10+x tapes have been studied. Comparisons are made between three batches of these tapes with the same thermomechanical deformation and sintering conditions but with the starting precursor powders having undergone different processing. It is found that the volume density of the macroscopic pinning force in fields up to 1 T is greater for a particular sintering period. Resistivity measurements further show that the pinning activation energy also reaches a higher value for the same chosen sintering period. SEM images of the surfaces indicate that better core morphology and density can be achieved with this particular sintering period. Prolonged sintering leads to greater porosity while short-duration sintering inhibits grain growth and thus is of no assistance in the healing of cracks induced during the intermediate deformation between sintering periods.

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The effect of sintering periods for monocore (Bi, Pb)2Sr2Ca2Cu3O10+x (Bi-2223) tapes on microstructure and critical current density (Jc) have been studied. The results show that long sintering periods (of duration ≥100 h) give better grain growth, but greater misalignment. Prolonged sintering also necessitates the increase in porosity of the core due to random grain growth, increasing the chance of penetrating into the silver matrix and oxide core interface. Critical currents for long sintering periods are found to be lower in comparison with those obtained for slightly shorter sintering periods. The increase in frequency of intermediate cold uniaxial pressing between sintering periods assists grain alignment. However, when the sintering period is further reduced by increasing the frequency of intermediate deformation, it is found that microcracks are unable to heal as there is not enough time for grain regrowth. The tapes made using “three-to-four-sinter-period” (each period ∼60 h) show superior electrical transport properties which are attributable to the fact that their oxide core is more dense and better aligned relative to the “two-sinter-period” (each period ≥100 h) tapes and contain less cracks relative to the “five-to-six-sinter-period” (each period ∼40 h) tapes.

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Isothermal melt processing (IMP) has been used to produce phase-pure, high critical current density (J,) Bi-2212 tapes at temperatures as low as 780°C. Bi-2212 tapes processed by IMP have yielded J, values up to 250 kA/cm2 (I, = 345 A) at liquid helium temperatures. Small test coils have been produced with 9, values up to 150 kA/cm2. The effects of the oxidation rate, processing temperature, and time spent in the partial melt on the superconducting properties and microstructure were investigated. Optimal superconducting properties result from the interplay of these parameters such that the grain size of the Bi-2212 phase in the polycrytalline core is allowed to coarsen and align itself with the silver sheath to form a well-connected superconductor. Deviations from optimal conditions result in either too little coarsening to form a well-aligned structure or instabilities in the coarsening process that lead to the formation of large secondary phases which disrupt connectivity..