The large cross-sectional aspect ratio of YBCO coated conductors leads to a large magnetization loss in an AC transverse magnetic field. In this work, the magnetization loss of a multifilamentary YBCO coated conductor was studied experimentally. A 100 mm length of striated multifilamentary YBCO coated conductor was prepared where the conductor and filaments were 10 mm wide and 0.4 mm wide, respectively. Striations in the sample were accomplished by laser ablation. The magnetization loss of this striated conductor as well as a reference non-striated conductor was measured in AC transverse magnetic fields normal to the conductor at various frequencies. The measured magnetization loss of the 100 mm striated conductor was less than 9% of the measured loss of the non-striated conductor at f = 11.3 Hz and H/Hcc = 8.8 (Hcc = Ic/πwc; Ic: critical current, wc: conductor width). Even though the coupling loss component increases the magnetization loss in the striated conductor, the AC loss reduction by striation is still apparent even at 171.0 Hz. The transverse resistance between filaments estimated by a four-probe measurement was 38 µΩ for 1 m at 80 K. The coupling length estimated using this transverse resistance is much longer than the sample length even at 171.0 Hz, suggesting that the filaments in the striated conductor are far from ‘completely coupled’ or ‘saturated’.

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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...