Continuous coaters capable of producing 1.1 m long x 1 cm wide tapes of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (YBCO) on biaxially oriented yttria-stabilized zirconia (YSZ) on flexible Ni-alloy substrates have been developed at this laboratory. Using a 1 {micro}V/cm criterion, the authors have achieved transport critical current (I{sub c}) values of 29 A (75 K, self field) between voltage taps spaced 1 m apart. The corresponding critical current density (J{sub c}) value for this tape is 290 kA/cm{sup 2}. For shorter tapes, (12 cm voltage tap separation) they have attained J{sub c} values of 0.67 MA/cm{sup 2}. Individual 1 x 1 cm sections within these shorter tapes have attained J{sub c} values of 1 MA/cm{sup 2}

Arendt, P. N.

Coulter, J. Y.

DePaula, R.

Dowden, P. C.

Foltyn, S. R.

Groves, J. R.

UNT Digital Library

Q LA-UR- Title: Au fhor(s): Submitted to: Los Alamos N A T I O N A L  L A B O R A T O R Y  PROCESSING OF YBCOABAD YSZ COATED CONDUCTORS ON FLEXIBLE SUBSTRATES P. N. ARENDT, MST-7 S. R. FOLTYN, MST-STC P. C. DOWDEN, MST-STC J. R. GROVES, MST-STC R. DEPAULA, MST-7 J. Y. COULTER, MST-STC 1998 SUPERCONDUCTIVITY CONFERENCE, OKINAWA, JAPAN L O ~  Alamos National Laboratory, an affirmative actiodqual opportunity employer. is operated by the University of California for the U.S. Department of Energy under contract W-7405-ENG-36. By acceptance of this article, the publisher recognizes that the US. Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or to allow others to do so, for US. Government purposes. The Los Alamos National Laboratory requests that the publisher identify this article as work performed under the auspices of the U.S. Department of Energy Form No. 836 R5 ST 2629 lOB1 . '  DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government Neither the United States Government nor any agency thmof, nor any of their employees, makes any warranty, express or implied. or assumes any legal liability or responsibility for the accuracy, completeness, or use- fulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any spe- cific commercial product, proms, or service by trade name, trademark, manufac- turer, or otherwise does not necessarily constitute or imply its endorsement, recorn- mendation. or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. PROCESSING OF YBCO/IBAD YSZ COATED CONDUCTORS ON FLEXIBLE SUBSTRATES P.N. Arendt, S. R. Foltyn, P. C.  Dowden, J. R. Groves, R. DePaula, J. Y. Coulter Superconductivity Technology Center Materials Science and Technology Division Los Alamos National Laboratory Los Alamos NM 87545 ABSTRACT Continuous coaters capable of producing 1.1 m long x 1 cm wide tapes of YBa,Cu,0,-8 (YBCO) on biaxially oriented yttria-stabilized zirconia (YSZ) on flexible Ni- alloy substrates have been developed at our laboratory. Using a l pV/cm criterion, we have achieved transport critical current (I,) values of 29 A (75 K, self field) between voltage taps spaced 1 m apart. The corresponding critical current density (J,) value for this tape is 290 kA/cm2. For shorter tapes, (12 cm voltage tap separation) we have attained J, values of 0.67 MA/cm2. Individual 1 x 1 cm sections within these shorter tapes have attained J, values of 1 MA/cm2. INTRODUCTION Coated tapes of superconducting YBCO are considered to be the second generation of high-temperature superconducting wire. Several laboratories have reported efforts to produce wires in lengths of up to 1 m of this material. These laboratories use either of two techniques to deposit template films of biaxially oriented YSZ on polycrystalline metal substrates. These techniques are ion-beam assisted deposition (IBAD) [ 11 [2] or inclined substrate deposition [3]. These template films are then over coated with films of YBCO. These latter films are heteroepitaxially deposited using pulsed laser deposition (PLD) techniques. Other laboratories are employing modified bias sputtering to obtain biaxially oriented YSZ films [4] or thermomechanical processing of Ni to obtain an oriented metal template substrate [5] for subsequent YBCO depositions. These latter techniques have promise for producing long lengths of template material; however, no YBCO I, values have been reported for conductor lengths greater than a few cm. EXPERIMENTS Substrates The substrates used in these studies are 50 to 100 pm thick nickel-based alloys. These are chosen for their corrosion resistance at elevated temperatures and include Inconel 625 and Hastelloy C-276. The substrates are not polished if their as rolled surface finishes have RMS surface roughness values of 300 A, or less, as measured by a 100 pm long surface profilometry scan in the rolling direction. The substrates are cleaned with soap and water followed by a deionized water rinse and a solvent rinse. This is followed by a light vacuum bake at < Torr and 650 "C for one hour. The substrates are then mounted in the YSZ IBAD system for the template coating. YSZ film deposition The YSZ IBAD film deposition system is configured for either of two types of film depositions. It is capable of depositing onto fixed tapes mounted in the deposition zone or onto tapes moving in continuous loops through the deposition zone. In the fixed tape mode, up to four 1 cm wide by 23 cm long substrates may be coated simultaneously. In the continuous mode, lengths of tape 1.13 m long are spliced together into loops and mounted on a tape drive. Two 1 cm wide tapes are coated simultaneously during a deposition run. Shielding is added to the tape drive system so that vapor is not coated onto portions of the tape, which are not in the ion-assist zone. The tapes are passed through the deposition zone at a frequency of 0.6 Hz. Thus, in a run of several hours, the tapes pass through the deposition zone many times resulting in a relatively uniform in-plane texture along the length of the 1.13 m tapes. The long axes of the substrates are mounted parallel to the long axis of a 23 cm long ion-assist gun. A Faraday cup ion probe translates along the long axis of the substrates in order to map the ion current density as a function of position. A quartz crystal oscillator is used to monitor the vapor deposition rate. The assist-ion beam voltage is 200 eV and the sputter ion beam voltage is 550 eV. The currents in each of these beams are set such that the ion current to film deposition rate ratio is relatively constant during a deposition run. The ratio that is used during deposition is approximately 300 pA/cm2/(0.4 ksec). The total YSZ film thickness is - 1 pm. Pulsed laser deposition system After the YSZ template films are coated onto the substrates, the tapes are mounted in a pulsed laser deposition (PLD) loop coating system described elsewhere [6] .  Briefly, the tapes are driven over a heater, which results in a substrate temperature of approximately 790 "C. During deposition, the background gas pressure is 0.2 Torr oxygen. The YBCO deposition rate is 70 A /sec. After deposition, the films are given a separate anneal in 1 atm oxygen at 450 "C to convert the YBCO to the orthorhombic phase. The tapes are then transferred to a loop drive magnetron sputter deposition system and over coated with a 2 pm thick silver film, which serves as a protective and stabilization layer. To decrease their contact resistance, the silver films are then annealed at 550 "C in 1 atm. oxygen for thirty minutes. Critical current measurement The I, measurements are done with DC transport 4-point I-V probe techniques using a 1 p.V/cm criterion. Current leads are placed at each end of the tapes and have a total surface area of approximately lcm2. Detailed I, measurements are done at each cm position along the length of the tapes using spring loaded voltage contacts. Integrated I, measurement for the tapes are done using contacts, which are separated by 1 m for the longer tapes or by 12 cm for the shorter tapes. RESULTS 1.2 a- ' E 0.8 2 0.6 2 - 0.4 0.2 0 0 Detailed individual 1 x 1 cm segment I, and J, values (75 K, self field) for a short tape with YBCO film thickness of 0.9 pm are illustrated in Fig. 1. The overall J, variation for the individual 1 2 3 4  5 6  7 8 9 1 0 1 1 1 2  segments is +25%. The integrated I, and J, values for the 12 cm tape length Position on tape (cm) Figure 1. Individual segment J, values for a 12 cm long 60 A are 60 A and 0.67 tape. YBCO thickness = 0.9 pm MA/cm2, respectively. M a n y  i n d i v i d u a l  segments have Jc values at or above 0.75 MA/cm2, with one of the segments attaining a peak value of 1 MA/cm2. The YBCO in-plane texture for this film, as determined by phi scan of the (1 1 1) peak, was 12" FWHM. These results show improvement over those we reported for these proceedings last year [6] .  At that time, our best 12 cm tape had YBCO film thickness of 1.7 pm with an integrated I, of 70 A, an integrated J, of 410 kNcm2, and an overall individual segment J, variation of 40 %. A study of YBCO Jc vs. its in-plane texture done by our laboratory several years ago [7] for 1 cm wide by 4 cm long strips of YBCO on both a single crystal YSZ substrate as well as B A D  YSZ on Ni-alloy substrates is illustrated in Fig. 2. For this study, the total length of the films measured within the current pads and voltage taps is approximately 1 cm. Also 3.0 2.5 &j- 2.0 E 2 1.5 I v -" 1.0 0.5 0.0 I 1 I \  1 cm wide segments on I 0 5 10 15 20 25 30 35 40 45 YBCO FWHM (degrees phi) Figure 2. YBCO J, vs. in-plane texture for 1 cm wide by 1 cm long tapes and tape segments. YBCO thickness' = 0.9 to 1.0 pm included in this plot are the J, values for the individual 1 cm x 1 cm segments of the 60 A tape reported above. These most recent r e s u l t s  show an improvement of 2.5 to 5 times in the YBCO J, values as a function of the in-plane texture. These are attributed to improved Y B C O  d e p o s i t i o n  parameters and improved handling procedures within our laboratory for the tape processing. For longer tapes, our best result, to date, is 70 0.7 li an I, of 29 A (75.4 K, self field) over a full meter. The YBCO film thickness for this tape is 1.0 pm. Thus, the corresponding 3 integrated J, value for this tape is 290 kA/cm2. Fig. 3 2 is an illustration of the 1.3 Z C segment-by-segment I, variation for this tape. In 1.2 2 - E this case, the highest I, (I) u .- t.1 .= b J.0 1 10 19 28 37 46 55 64 73 82 91 100 Position on tape (cm) Figure 3. Segment-by-segment I, and J, values for 1 m tape with a 1 pm YBCO coating on an B A D  YSZ layer. The 50 pm thick substrate was coated in its as-rolled condition. value is 67 amps, or approximately twice the end-to-end value. These results indicate that continued efforts to ameliorate the individual segment variations should result in tapes with improved integrated I, values. Finally, it is noted that this 29 A tape was used as an exhibit at a recent conference [8] and was passed among the attendees to provide a “feel” for handling of second generation tape. Upon its return to our laboratory, the tape was again measured over 1 m and the 29 A result was confirmed. CONCLUSIONS We have fabricated robust, high I, and high J, YBCO coatings on flexible substrates using continuous coating processes. Future work will be directed at improving the IC uniformity and improving the integrated end-to-end I, values of our 1 m tapes. REFERENCES [I] Y. Iijima, et al., Appl. Phys. Lett. 71 (1997). [2] P. N. Arendt, et al., Appl. Superconductivity 4 429 (1998). [3] K. Hasegawa, et al., Advances in Superconductivity ZX. 745 Springer, Tokyo (1997). [4] M. Fukutomi, et al., Appl. Superconductivity 4 447 (1998). [5] A. Goyal, et al., Appl. Phys. Lett. 69 1795 (1996). [6] S. R. Foltyn, et al., Proceedings 1997 International Workshop on Superconductivity, 68 (1997). [7]  X. D. Wu, et al., Appl. Phys. Lett. 67 2397 (1995). [SI DOE Wire Workshop, Tampa Bay FL, January 29-30 (1998) 

Processing of YBCO/IBAD YSZ coated conductors on flexible substrates

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Processing of YBCO/IBAD YSZ coated conductors on flexible substrates

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