Toru Tanigawa

Long length oxide template for YBCO coated conductor prepared by surface-oxidation epitaxy method

A 50 m long, biaxially textured NiO buffer layer for epitaxial growth of YBa 2 Cu 3 O 7-δ (YBCO) film has been fabricated on the long cube textured nickel tape using surface-oxidation epitaxy (SOE) method. The SOE-NiO layers were highly {100} (001) textured. The full width at half maximum of 10-14.5° from X-ray o-scan (Δo) was in the range of 10-14.5° through the whole length. The critical current density (J c ) values exceeding 0.3 MA/cm 2 (77 K, 0 T) have been obtained in short samples of YBCO films on NiO/Ni tapes, by using thin MgO cap layer. Thirty meters long Ni-clad Ni-20wt.%Cr (Ni/NiCr) and Ni-clad austenitic stainless steel (Ni/SS) tapes were also prepared for YBCO coated conductors with higher strength and lower magnetism than those of pure nickel tape. Highly {100} (001) textured NiO layers were formed on those textured composite tapes by SOE method as same as on cube textured pure nickel tapes. YBCO films with J c of 0.1 MA/cm 2 (77 K, 0 T) have been obtained on MgO/SOE-NiO layer of short Ni/NiCr composite tape.

Surface-oxidation epitaxy of Ni-clad Ni-20wt%Cr and Ni-clad austenitic stainless steel tapes for Y-Ba-Cu-O coated conductors

We have prepared Ni-clad Ni-20wt%Cr (Ni/NiCr) and Ni-clad austenitic stainless steel (Ni/SS) tapes for YBa/sub 2/Cu/sub 3/O/sub x/ (YBCO) coated conductors with higher strength and lower magnetism than those of pure nickel tape. Highly {100} textured nickel outermost layers on those composite tapes were obtained by cold-rolling and subsequent heat treatment. The surfaces of Ni/NiCr composite tape and Ni/SS composite tape are favorable for epitaxial NiO growth by the surface-oxidation epitaxy (SOE) method. Highly {100} textured NiO layers were formed on those textured composite tapes, as on cube-textured pure nickel tapes. Biaxially textured YBCO films were grown on SOE-NiO layers by the pulsed laser deposition (PLD) method. A thin MgO cap layer deposited on NiO layer improved the surface qualities of NiO, so that the YBCO films with a high critical current density (J/sub c/) of 1.0/spl times/10/sup 5/ A/cm/sup 2/ (77 K, 0 T) have been obtained on SOE-NiO with MgO cap layer on Ni/NiCr composite tape.

Long-length Y-Ba-Cu-O coated conductors produced by surface-oxidation epitaxy method

A 50-m long, biaxially textured NiO buffer layer for epitaxial growth of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//(YBCO) film has been fabricated on a long length cube-textured Ni tape using the surface-oxidation epitaxy (SOE) technique. The thickness of NiO layer was arranged to be around 3 /spl mu/m. The tape manufacturing speed was 15 m/h, The SOE-NiO layer was highly [100] oriented and the full width at half maximum from the X-ray /spl phi/-scan for NiO(111) was varied from 13 to 19 degrees in the whole length. J/sub c/ values exceeding 0.3 MA/cm/sup 2/ at 77 K and self field have been obtained in short samples of YBCO films on NiO/Ni tapes, by using a thin MgO cap layer with the thickness of about 100 nm. Crystal orientation control of YBCO coated conductors by the SOE method is very effective even for the long length Ni tapes.

Development of Twisted Multifilamentary Tape using AgMg Alloy

To improve over-all critical current density (Je) and mechanical properties, and also reduce AC losses, we have developed twisted multifilamentary tapes using AgMg alloy sheath. The alloy-sheathed twisted tape achieved Je of 5.4kA/cm2 at 77K and 0T, with Je uniformity over the whole length. The tape produced about twice higher strength and almost one third of particular AC loss, compared to a silver-sheathed untwisted one. A rate of inter-filament coupling in a tape was evaluated by comparing measured AC loss and calculated one.

Jc distribution in the Bi-2223/Ag-AgMg tapes

Bismuth-based, silver-sheathed tapes are considered to have great possibilities for electric power applications. Remarkable progress in Bi-2223/Ag tapes has been made in the world. We also have been developing Bi-2223/Ag tape since 1989, and we can fabricate 1 km length tape now. One of the important properties for J c of Bi-2223/Ag tape is the distribution in the cross-section of tape, as well as that of longitudinal distribution. We measured J c distribution in the cross-section of tapes that were cut in the constant period from the edge of tape by using laser beam. It was cleared that J c increased periodically toward the center of the tape but J c slightly decreased at the center. We consider that J c distribution in the tape has good correlation with the density of filament. By this result, we succeeded in manufacturing the long Bi-2223/Ag-AgMg tape of J c = 31000 A/cm 2 and J e = 8000 A/cm 2 . Furthermore, we achieved I c = 50 A in Bi-2223/Ag-AgMg twisted long tape.

Fabrication and Properties of Bi-Based Multilayered Wires

In an attempt to moderate magnetic anisotropy of critical current density (Jc) and improve overall Jc, a jelly-roll method and a multi-pipe method were applied to fabricate multilayered wires, which underwent performance tests for Jc temperature dependence, mechanical property and AC loss. A double pancake coil was made on trial, considering the mechanical property of a multilayered tape.