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SESSION R1: BIAXIALLY TEXTURED YBCO CONDUCTORS
Chairs: D. M. Kroeger and Martin P. Maley
Tuesday Morning, April 1, 1997
Salon 15

8:30 AM *R1.1
DEVELOPMENT OF HIGH J

Y-123 TAPES WITH TEXTURED BUFFER LAYERS BY IBAD METHOD, Yasuhiro Iijima, Fujikura, Ltd., Materials Research Lab, Tokyo, JAPAN; Mariko Hosaka, Nobuo Tanabe, Nobuyuki Sadakata, Takashi Saitoh, Osamu Kohno, Kaoru Takeda, Fujikura, Ltd., Tokyo, JAPAN.

Ion-Beam-Assisted Deposition (IBAD) is a method to introduce biaxially aligned structure on practical polycrystalline substrates, which is one of the effective ways to eliminate intergranular weak links of Y-123 tape shaped conductors. This paper presents our experimental results on development of IBAD process, transporting properties of bitextured Y-123 films, and long tape samples by continuous deposition. The angular dependence on the incident ion beam and this thickness dependence of the crystalline alignment of YSZ films agreed with a selective resputtering model based on ion-channeling. On the contrary, larger ion radius and lower ion energy were preferred in low temperature growth, which indicates homoepitaxial crystallization would be so sensitive to ion bombarding conditions. The properties of strongly coupled current paths in bitextured Y-123 films were evaluated by Jc measurements in applied field of B//I. The higher J

samples near 1 MA/cm

(77 K, TO) had more straight current paths not disturbed by weak links. 1 m-order tape shaped YBCO conductors with J

of 2.0 x 10

A/cm

were fabricated by continuous depositions. The efforts to enhance overall Jc values (thicker Y-123 films and thinner substrate tapes) would also be presented.
This work has been carried out as a part of R&D on superconducting technology for electric power apparatuses under the New Sunshine Project of AISI, MITI, being consigned by NEDO.

9:00 AM *R1.2
STATUS OF THE RABiTS APPROACH TO FABRICATE BIAXIALLY ALIGNED, HIGH-J

SUPERCONDUCTORS, Amit Goyal, Oak Ridge National Laboratory, Metals & Ceramics Div, Oak Ridge, TN; David P. Norton, Oak Ridge National Laboratory, Oak Ridge, TN; David K. Christen, D. M. Kroeger, E. D. Specht, Oak Ridge National Laboratory, Solid State Div, Oak Ridge, TN; Mariappan Paranthaman, Oak Ridge National Laboratory, Dept of Chemical & Analytical Science, Oak Ridge, TN; John D. Budai, Qing He, F. A. List, Oak Ridge National Laboratory, Solid State Div, Oak Ridge, TN; Dominic F. Lee, Oak Ridge National Laboratory, Metals & Ceramics Div, Oak Ridge, TN; B. Saffian, Oak Ridge National Laboratory, Solid State Div, Oak Ridge, TN; J. Matthis, E. Hatfield, C. E. Clabunde, Oak Ridge National Laboratory, Oak Ridge, TN; Shara S. Shoup, Oak Ridge National Laboratory, Chemistry & Analytical Sciences Div, Oak Ridge, TN; P. M. Martin, Oak Ridge National Laboratory, Oak Ridge, TN.

Fabrication of epitaxial, high J

, biaxially aligned YBCO thick films on Rolling-assisted-biaxially-textured-substrates (RABiTS) will be reviewed. The RABiTS technique utilizes standard thermomechanical processing to obtain long lengths of flexible, biaxially oriented substrates with smooth surfaces (rms

50 nm). The strong biaxial texture of the metal (in-plane 6-7

FWHM) is conferred to the superconductor by deposition of intermediate metal and/or oxide layers which serve both as a chemical as well as a structural buffer. Conductors prepared using this process have critical current densities at zero applied field approaching 10

A/cm

at 77 K. The field dependence of J

for H//c is comparable to those of epitaxial films on single crystal substrates. The transport properties of these conductors is significantly superior to the best Bi-2223/Ag multifilamentary tapes and Ti-1223 single crystal films. Moreover, the J

(8 T) at 40 K is comparable to the best Nb

Sn at 4.2 K, 8 T. Progress made in addressing key issues in further development of this process for practical applications including 1) deposition on thinner metals and thinner buffer layers to enhance J

, 2) fabrication of alternative textured substrates with reduced magnetism followed by deposition of epitaxial buffer layers, and 3) deposition of buffer layers and YBCO by faster deposition methods including sol-gel, e beam, sputtering and MOCVD, will be presented.
* Managed by Lockheed Martin Energy Research Corp. under contract DE AC05-96OR22464 with the U.S. Department of Energy.

9:30 AM *R1.3
PROGRESS ON BIAXIALLY ALIGNED SUBSTRATES FOR YBCO COATED CONDUCTORS, Paul N. Arendt, Stephen R. Foltyn, Los Alamos National Laboratory, Superconductivity Tech Ctr, Los Alamos, NM; Paul C. Dowden, J. Randy Groves, Los Alamos National Laboratory, Materials Science & Technology Div, Los Alamos, NM.

We have used ion-assisted ion-beam deposition techniques to prepare biaxially aligned template films on nickel alloy substrates. These template films are then overcoated with intermediate buffer layer films using either pulsed laser deposition or magnetron sputter deposition techniques. The final YBCO film is then applied using pulsed laser deposition. There is a complex interaction of deposition parameters which affect the growing ion-assisted films. We will discuss optimization of several of these parameters, e.g., sputter gas species, sputter beam energy, incident vapor to substrate angle, assist ion-beam to substrate angle, etc. We will also discuss current efforts and progress toward reducing the deposition time needed to obtain good quality template films.

10:30 AM *R1.4
HIGH-CURRENT-DENSITY PLD-YBaCuO FILMS ON PLANAR AND CURVED SUBSTRATES: PROCESSING AND PERSPECTIVES, H. C. Freyhardt, J. Dzick, K. Heinemann, J. Hoffmann, A. Isaev, Univ of Goettingen, Inst fur Metallphysik, Goettingen, GERMANY; J. Wiesmann, Univ Goettingen, Inst fur Metallphysik, Geottingen, GERMANY; F. Garcia-Moreno, S. Sievers, A. Usoskin, Univ of Goettingen, Zentrum fur Funktionswerkstoffe, Goettingen, GERMANY.

YBaCuO tapes are considered to represent HTS conductors of the second generation. To achieve high critical current densities, YBaCuO has to be deposited on well biaxially aligned substrate surfaces. In this contribution, we report on recent results of the IBAD processing of bi-YSZ buffer layers on planar and cylindrical technical substrates. The bi-YSZ is highly textured with optimum FWHM

, for thick planar buffer films. A sophisticated pulsed-laser-deposition (PLD) technique allows the preparation of YBaCuO films with maximum current densities, J

, up to 2 MA/cm

(77 K, self field) and with well reproducible J

values, which are about a factor of 2 smaller. Technically relevant properties and the perspectives of these conductors, in particular for applications in power engineering, will be discussed.
Work supported by the German BMBF under grant numbers 13N6009 and 13N6482, by Siemens AG and by Alcatel/Kabelmetal.

11:00 AM *R1.5
IN-PLANE ALIGNED YBCO THIN FILM TAPE FABRICATED BY ALL PULSED LASER DEPOSITION, Katsuya Hasegawa, N. Yoshida, K. Fujino, H. Mukai, Sumitomo Electric Industries Ltd, Osaka Research Labs, Osaka, JAPAN; Kazuhiko Hayashi, Ken-ichi Sato, Sumitomo Electric Industries Ltd, Osaka Research Lab, Osaka, Japan; Shoichi Honjo, Tokyo Electric Power Co Inc, Power Engineering R&D, Yokohama Kanagawa, JAPAN; Y. Sato, Tokyo Electric Power Co Inc, Power Eng R&D Center, Yokohama, JAPAN; T. Ohkuma, Tokyo Electric Power Co Inc, Power Engr R&R Center, Yokohama, JAPAN; H. Ishii, Y. Iwata, Tokyo Electric Power Co Inc, Power Engr R&D Center, Yokohama, JAPAN; T. Hara, Tokyo Electric Power Co Inc, Power Engr R&R Center, Yokohama, JAPAN.

Much effort has recently been undertaken on the fabrication of YBCO thin film tapes with high J

values for power application. It is necessary to develop a method to form in-plane alignment of YBCO with high deposition rate. We have tried to do this using pulsed laser deposition (PLD) which has an advantage of high deposition rate. We investigated deposition conditions of YSZ buffer layer on flexible Ni based alloy substrates using PLD. We have discovered that in-plane alignment of YSZ is possible by inclining the substrate to the plasma plume. Highly in-plane aligned YSZ films were realized with high deposition rate of 0.5

m/min. The YBCO films deposited on the YSZ were also highly in-plane aligned. Long and high Jc YBCO tapes were successfully fabricated. The J

value of 1.5 x 10

A/cm

(77.3 K, OT) was obtained over the whole length of 1 meter. The best J

value of 4.3 x 10

A/cm

(77.3 K, OT) was achieved for a short sample, and FWHM of YBCO(103) poles was 12.8

. An overall critical current density including substrate was improved up to 4000 A/cm

at 100 mm length. A magnetic shielding type fault current limiter using YBCO tape showed good current-limiting properties.

11:30 AM *R1.6
NEW SCHEME FOR CONTINUOUS DEPOSITION OF YBCO FILMS ON A 20CMx20CM SQUARE WITHOUT SAMPLE ROTATION, Helmut Kinder, Susanne Rieder-Zecha, Bernd Utz, Technische Univ Muenchen, Dept of Physics, Garching, GERMANY.

For the fabrication of YBCO coated conductors the production rate will be all important. It scales with the growth rate and the deposition area. The former is intrinsically limited to some tens of nm/min, so latter must be increased as much as possible. A square area can be profitably used for tape production by placing many tapes in parallel, or by arranging a single tape in loops. Other examples where square deposition areas are required are resistive fault current limiters on large technical substrates. In last years we were developing a deposition scheme for YBCO thin films on very large areas by thermal reactive co-evaporation. To allow for ballistic propagation of the metal atoms in a fairly good vacuum, and yet to achieve homogeneous oxidation conditions, we used a heater with a rotating sample holder moving the substrates in and out of an oxygen pocket during deposition. This rotary setup is not suitable for tapes or for large rectangular substrates. Therefore we have developed a new scheme where the substrate has a fixed position, and the oxygen pocket is set in linear motion. To achieve a continuous production process, we have also developed an in-situ refill mechanism for the thermal boats using vibrator conveyors, and a new method of rate control using compensated atomic absorption spectroscopy (AAS). First results will be reported.

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