Metalorganic chemical vapor deposition (MOCVD) is a well-developed deposition process that shows great promise for scaling up the production of high-temperature superconductors (HTSs) to quickly fabricate useful lengths of superconducting tapes and wires.The primary advantage of MOCVD is its potential for high tape throughput, a key factor in determining the cost of second-generation HTS tapes.This article details progress in long-length HTS tape fabrication, high-throughput processing, and techniques to improve critical current levels in high magnetic fields.

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Coupled magneto-optical imaging and local misorientation angle mapping have been used to demonstrate the percolative nature of supercurrent flow in YBa 2 Cu 3 O 7Ϫx ͑YBCO͒ coated conductors grown on deformation-textured Ni substrates. Barriers to current flow occur at many YBCO grain boundaries ͑GBs͒ which have propagated through the buffer layers from the underlying Ni substrate, and all Ni GBs with misorientation angles Ͼ4°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 c (0 T,77 K) values Ͼ2 MA/cm 2 . Sharpening of the local substrate texture or improving in low-angle GB properties should lead to higher J c values. © 2000 American Institute of Physics. ͓S0003-6951͑00͒00341-7͔High critical current density (J c ) conductors capable of operating in fields of several tesla at liquid-nitrogen temperature are critical to large-scale applications of hightemperature superconductors. Coated conductors ͑CCs͒ with biaxially textured YBa 2 Cu 3 O x ͑YBCO͒ respond to this need. [1][2][3] One widely employed approach today uses deformation texturing of a metal substrate, generally pure Ni, on which buffer layers and YBCO are grown. 1,2 Such architectures permit J c (0 T,77 K) values 1,2 Ͼ1 MA/cm 2 , but many samples have lower values. Here we couple magneto-optical imaging and local misorientation angle mapping to show that many such barriers to current flow occur at YBCO grain boundaries ͑GBs͒ which have propagated through the buffer layers from the Ni GBs in the underlying substrate. All Ni GBs with misorientation angles Ͼ4°were found to initiate percolative current flow. Since typical deformation-textured substrates have many GBs misoriented in the range of 5°-10°, this study shows that it will be very valuable for CC technology to further enhance substrate texture and/or to improve low-angle GB properties.Magneto-optical ͑MO͒ imaging, light microscopy, and backscattered electron Kikuchi pattern ͑BEKP͒ analysis of the local texture were conducted on a series of four CC samples grown on deformation-textured Ni substratres with in-plane and out-of-plane full width at half maxima of 6.6°-7.4°and 5.8°-8.7°, respectively, as measured by x-ray pole figures. The buffer and YBCO layers were deposited by pulsed-laser deposition ͑PLD͒ with architecture YBCO/CeO 2 /yttria-stabilized zirconia ͑YSZ͒/CeO 2 /Ni and thickness of 300-1200/100/500/100 nm for the respective oxide layers. The thickness of the YBCO layer varied from sample to sample without obvious differences in the properties measured by MO imaging and ac susceptibility. A 0.6-m-thick YBCO sample had a high transport J c (0 T,77 K) of 1.2 MA/cm 2 . The remaining samples were taken directly to other characterizations.A representative MO image of the granular fluxpenetration network obtained using standard imaging procedures 4,5 is shown in Fig. 1. This network is common to CCs with varying constructions from multiple sources. Among the variations are deformation-textured s...

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We report on the thickness and angular dependence of the critical current density J c (H, θ), the irreversibility field H irr , and the bulk pinning force F p (H) of a metal-organic chemical vapour deposition (MOCVD) grown YBa 2 Cu 3 O 7−x (YBCO) coated conductor, which contains ∼17 vol% of ∼10 nm sized (Y, Sm) 2 O 3 precipitates with an average spacing of ∼10-15 nm. Some surface porosity and amorphous second-phase particles on the scale of ∼0.5-1 μm appear to reduce the current-carrying cross-section, which controls the magnitude of J c but not the vortex pinning. We observed an enhanced H irr ∼ 9 T at 77 K along the c-axis which, like the shape of J c (H) and F p (H), was independent of thickness as the sample was milled down to ∼0.16 μm. Angular-dependent measurements of J c showed the usual excess vortex pinning along the c-axis and along the ab-plane, but with a background that could only be fitted with an unusually small anisotropy parameter of 3, which, like the high H irr and the thickness-independent shape of F p (H), we ascribe to strong vortex pinning centre interactions. Together, these measurements show very different behaviour from most pulsed-laser-deposited films, which exhibit strong thickness-dependent properties. We ascribe the present different results to the dense array of small, insulating precipitates, which act as strong pinning centres and produce strong three-dimensional (3D) vortex pinning, because their separation of 10-15 nm is always much smaller than the film thickness.

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About 17 vol. % of ϳ10 nm sized ͑Y,Sm͒ 2 O 3 precipitates have been developed in a metal-organic chemical vapor deposition grown Sm-doped YBa 2 Cu 3 O 7−␦ coated conductor. The precipitate spacing of ϳ15 nm suggests strong vortex-precipitate pinning interactions, which are evidenced by a shift in the peak in the flux pinning force curve, an enhanced irreversibility field exceeding 8 T at 77 K, and a lack of temperature scaling of the flux pinning force over the temperature range of 65-82 K.

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