Kazuomi Kakimoto

Reel to reel continuous formation of Y-123 coated conductors by IBAD and PLD method

Continuous deposition of Y-123 tapes was performed by ion-beam-assisted deposition (IBAD) and pulsed laser deposition (PLD) method. YSZ template films were deposited by IBAD on Ni-based alloy tapes with tape shifting speeds of 0.1-0.3 m/h. They were uniformly coated with an in-plane mosaic spread of 12-13 degrees in 5 m length. In order to overcome the low deposition rate of the IBAD process, large area ion sources with inductively coupled discharge plasma were applied. Y-123 films were deposited by PLD on the YSZ templates with a tape shifting speed of 1.0 m/h. The degradation of Y-123 targets for the PLD process was effectively restricted by combined motion of rapid rotation and linear shifting. I/sub c/ of 84.0 A and J/sub c/ of 0.76MA/cm/sup 2/ were obtained at 77 K, 0 T in the length of 1.0 m when the in-plane mosaic spread for the Y-123 film was 7 degrees. I/sub c/ of 35.0 A and J/sub c/ of 0.25MA/cm/sup 2/ were obtained in a 4.6 m long sample at the length of 4.0 m, when the in-plane mosaic spread for the Y-123 film was 11 degrees.

Fabrication of long-Y123 coated conductors by combination of IBAD and PLD

Abstract Continuous deposition of Gd 2 Zr 2 O 7 films were carried out on 10 mm width Hastelloy tapes by ion-beam-assisted deposition (IBAD). They were uniformly deposited with the in-plane mosaic spread (Δ φ ) of 10–14° in the 50 m long and of 16–18° in the 60 m long, at a production rate of 0.5–1.0 m/h. The 6 cm sample with the I c value of 141 A and the J c value of 1.25 MA/cm 2 were obtained by 6 repeated depositions using pulsed laser deposition (PLD). Continuous deposition of Y-123 films were performed by PLD on long IBAD template tapes at a tape speed of 4.0 m/h. The I c value of 40 A and the J c value of 0.8 MA/cm 2 were obtained at the length of 30 m. Furthermore, the 46 m YBCO coated tape with the I c value of 74 A and the n value of 32 was formed uniformly.

Development of long Y-123 coated conductors by ion-beam-assisted-deposition and the pulsed-laser-deposition method

100 m class Y-123 coated conductors were produced by using reel-to-reel vacuum ion-beam-assisted-deposition (IBAD) and pulsed-laser-deposition (PLD) apparatuses. 100 m long IBAD-Gd2Zr2O7 template films were uniformly and routinely obtained on non-textured Ni-alloy tapes, with FWHM of Δ below 10°. Y-123 films with FWHM of Δ below 7° were formed on them by PLD. End-to-end Ic of 38 A and Jc of 0.76 MA cm−2 (77 K, self-field) were obtained in a 100 m long sample. For further texture improvement, secondary buffer layers of CeO2 and Gd2Zr2O7 grown by PLD on IBAD-Gd2Zr2O7 template films were studied. Δ of 3° and Jc of 2.9 MA cm−2 were obtained in a 0.1 m long Y-123 film and Jc improved to 1.6 MA cm−2 for an 80 m long Y-123 tape by using the CeO2 buffer layers.

Critical current properties in HTS tapes

Abstract The author’s recent studies on the critical current properties in Bi-2223 multifilamentary tapes as well as YBCO coated IBAD tapes have been reviewed. Extended electric field vs. current density ( E – J ) characteristics were studied over wide range of temperature, T , magnetic field, B , and angle, θ . Based on the analysis of statistic J c distribution and scaling, we derived an analytical expression for J as a function of E , T , B , and θ . This method allows us to describe and extrapolate the nonlinear E – J characteristics even in extremely low E region and/or high B region based on rather simple measurements.

Fabrication and transport characteristics of long length Y-123 coated conductors processed by IBAD and PLD

Tapes of 30-m length high-J/sub c/ Y-123 were processed by using ion-beam-assisted deposition (IBAD) and pulsed-laser deposition (PLD). Biaxially textured Gd/sub 2/Zr/sub 2/O/sub 7/ buffer layers up to 60-m length were fabricated by IBAD with production speed of 0.5 - 1.0 m/h. Y-123 films were processed on them by PLD with production speed of 1.0 - 4.0 m/h. A 30-m Y-123 film was obtained with uniform thickness of 0.5 /spl mu/m and /spl Delta//spl phi/ of 8 - 11/spl deg/. I/sub c/ of 49 A (J/sub c/ = 0.99 MA/cm/sup 2/) was obtained in 10-m length part end-to-end, whose I-V curve had high n-value of 46. The 30-m length end-to-end I/sub c/ value was 40 A (J/sub c/ = 0.8 MA/cm/sup 2/), where I/sub c/ times length reached 1200 Am.

Temperature and RE elemental dependence for ZrO2-RE2O3 oxide film growth by IBAD method

Abstract Biaxially aligned growth was studied by dual-ion-beam sputtering method for ZrO 2 –RE 2 O 3 oxide films on polycrystalline Ni-based alloy substrates. Cube-textured (all axes aligned with a 〈1 0 0〉 axis substrate normal) films were obtained by low energy (∼200 eV) Ar + ion bombardment. The optimized growth temperature increased with the richer combined ratio for RE 2 O 3 . Several pyrochlore type oxides (RE 2 Zr 2 O 7 ) were found to have sharp textures at the optimized temperatures of 200 °C. The most sharply textured films were obtained for Gd 2 Zr 2 O 7 and Eu 2 Zr 2 O 7 . The time constant of texture evolution was about half compared to yttria-stabilized-zirconia. The texture sharpness degrades with the ion radius of rare-earth elements being apart from the ones for Gd, Eu.

Liquid phase epitaxy of YBa2Cu3Ox on MgO substrates with seed films

Abstract YBa2Cu3Ox (Y123) films can not be grown on MgO substrates by liquid phase epitaxy (LPE) directly, but they have been grown successfully on the substrates with Y123 thin films (seed films) deposited from a vapor phase. We employed a partial vertical dipping to investigate the initial growth mechanism of the Y123 films on (100)MgO substrates with the seed films. At the initial stage of LPE, the seed films partially dissolved in the BaOCuO solution, and island crystallites epitaxially formed on the MgO substrates. The results indicate that the grains in the seed films which exceed the critical grain size serve as nuclei, and the smaller grains dissolve. The island crystallites extended laterally and coalesced with one another. Subsequently, spiral growth proceeded, and finally the films grew to be single-crystalline.

High-speed deposition of high-quality RE123 films by a PLD system with hot-wall heating

We have studied the use of a hot-wall heating system for producing GdBa2Cu3O7?X (Gd123) films with large critical current (Ic), stably, at high speed, by a pulsed laser deposition (PLD) method. We achieved a material yield from the PLD system with hot-wall heating of about 50% through optimization of the evaporation conditions. With the PLD system, we were able to fabricate a Gd123 film about 20?cm long with a high Ic of 997?A (77?K, self-field) at about 6??m thickness. The maximum Ic that we achieved for a Gd123 film about 2?cm long was 1040?A (77?K, self-field) at about 6? ?m thickness. Furthermore, we were able to form a Gd123 film about 1? ?m thick and 20?cm long with an Ic of 352?A (77?K, self-field) at a high speed of 60? m?h?1 using high laser power. For the production of long conductors coated with RE123 (REBa2Cu3O7?X, where RE stands for rare earth) using hot-wall heating, it was found that RE123 coated conductors over 100?m long with Ic of over 200?A had uniform Ic distributions with ? 2% variations in the direction of the length.

Estimation of E–J characteristics in a YBCO coated conductor at low temperature and very high magnetic field

Abstract E – J characteristics in a YBCO coated conductor at low temperature and very high magnetic field up to 27 T have been estimated using experimental E – J characteristics below 12 T along with a scaling analysis based on the percolation model. 1 mm thick YBCO films was deposited on a biaxially aligned Y 2 O 3 /YSZ/Hastelloy substrate fabricated by the IBAD technique. The critical current I c for the 1 cm wide tape was 85 A at 77 K in self-field. We measured E – J characteristics in perpendicular field up to 12 T using 100 μm wide and 1 mm long bridge patterned in the tape. Statistic J c distribution and pinning properties were analyzed from the E – J characteristics. Using the pinning parameters determined by the scaling analysis, we can calculate the critical current properties as a function of temperature and magnetic field. E – J characteristics at low temperature and very high magnetic field up to 27 T were estimated analytically and compared with the experimental data. Estimated value of J c and n -value, and their error analysis were also discussed.

Percolative transition and scaling of transport E-J characteristics in YBCO coated IBAD tape

We have investigated extended electric field-vs.-current density E-J characteristics in YBCO coated IBAD tapes. The results of a Monte-Carlo study on the depinning in a random pin medium were compared with measurements. Using a low temperature scanning laser microscope, we examined the percolative behavior of the local resistive transition in the YBCO tape. It was also shown that the depinning probability, which is proportional to the dynamic resistance of the E-J curves, is scaled as a function of reduced current density with the aid of a power index. Consequently, the E-J characteristics in the tapes can be described by the combination of the two kinds of scaling laws: one is the scaling law of the depinning probability predicted in a random network and the other is the scaling law for the flux pinning force. These properties agree well with the percolation model of depinned clusters.