ORAL SESSION 2D3: Conductors and Coated Conductors

Tuesday, Feb. 22, 3:30 p.m. – 6:00 p.m., Room 301F (GRB)

Chairs: D. Peterson (Los Alamos Nat'l. Lab), P. McIntyre (Texas A&M U)

2D3.1 Development of Meter-Long YBCO Coated Conductors Produced by Ion Beam Assisted Deposition and Pulsed Laser Deposition

S.R. Foltyn, P.N. Arendt, Q.X. Jia, P.C. Dowden, R.F. DePaula, J.R. Groves, and J.Y. Coulter, Superconductivity Technology Center, Los Alamos National Laboratory, Los Alamos, NM 87545

Presenting Author: S.R. Foltyn

The approach being taken At Los Alamos to fabricate coated conductors involves ion beam assisted deposition (IBAD) of a biaxially aligned layer of cubic zirconia (YSZ) on a thin polycrystalline nickel alloy strip, and subsequent epitaxial growth of YBCO by pulsed laser deposition. With this process, we have reproducibly obtained critical current (I_c) levels of over 100 A (75 K, self field) for meter-long by centimeter-wide tapes, and on shorter lengths have achieved engineering current densities exceeding 40,000 A/cm².

Having demonstrated commercially attractive I_cs in statistically significant lengths, we have turned our attention to the issues of reducing cost and further improving performance, issues that will ultimately determine the economic viability of second-generation wire.

The use of MgO offers the potential for dramatic cost reduction of the IBAD step because it develops the required texture at least 100 times faster than YSZ. In the performance area, we have begun work on a long standing problem with YBCO, which is that the 5 MA/cm² current densities that are routinely observed in thin films cannot be sustained in films much thicker than 0.5 m m. Recent results in both areas will be presented.

2D3.2 Progress in the Fabrication of High-J_c YBCO Coated Conductors on Rolling Assisted Biaxially Textured Substrates (RABiTS)*

D.K. Christen, A. Goyal, F.A. List, D.F. Lee, M. Paranthaman, D.B. Beach, R. Feenstra, D.M. Kroeger, E.D. Specht, D.P. Norton, X. Cui, D. Verebelyi, C. Park, T. Chirayil, and P.M. Martin, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6116, USA.

Presenting Author: D.K. Christen

Significant progress has been made in the fabrication of non-magnetic, biaxially textured metal templates, in the deposition of epitaxial oxide buffer layers, and in the fabrication of lengths. Non-magnetic Ni-Cr alloy tapes have been fabricated by rolling and annealing which have a single cube orientation texture (~100%) and in-plane and out-of-plane grain orientation distributions which are as sharp as those obtained in pure nickel. Effective buffer layers have been deposited epitaxially on these alloy substrates and critical current densities greater than 1MA/cm² have been obtained in YBCO films deposited on them by pulsed laser ablation and the BaF₂ precursor process. Tensile tests indicate that the Ni-Cr alloy templates are significantly stronger than Ni. Fully buffered lengths of RABiTS on Ni templates can now be prepared by reel-to-reel vapor deposition processes. Efforts to prepare lengths of conductor have been focused on development of a reel-to-reel system for conversion of BaF₂ precursor deposits on RABiTS. Progress has been made toward the development of non-vacuum processes for deposition of buffer layers. Dense, crack-free, epitaxial deposits of several rare earth oxides have been obtained on textured Ni substrates by sol-gel process. High J_c superconductor deposits have been obtained on these buffers by completing the buffer structure using vapor deposition. Progress toward completion of the buffer structure by non-vacuum processes will be reported.

*Research sponsored by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Office of Utility Technologies - Superconductivity Program, and the Office of Energy Research, Basic Energy Sciences, under contract DE-AC05-96OR22464 with Lockheed Martin Energy Research Corp.

2D3.3 Coated Conductor Development by Photo-Assisted MOCVD Growth of YBCO Thick Films and Buffer Layers

A. Ignatiev, P.C. Chou, Yimin Chen, Xin Zhang, and Z. Tang, Texas Center for Superconductivity and Space Vacuum Epitaxy Center, University of Houston, Houston, TX 77204-5507

Presenting Author: A. Ignatiev

Tremendous interest is currently focused on the fabrication of superconducting YBa₂Cu₃O_7-x (YBCO) for application to high current superconducting wires and tapes due to YBCO’s high demonstrated critical current density, and maintained high current density under applied magnetic fields. However, for wire fabrication, the powder-in-tube technique applied successfully to the Bi and Tl-based superconductors is not successful for YBCO materials. As a result, YBCO-based superconducting wires are being fabricated from YBCO films deposited on flexible metal substrates with appropriate buffer layers. We have applied photo-assisted MOCVD (PhAMOCVD) to the fabrication of both the buffer layers and the YBCO on atomically-textured nickel substrates. The major benefits of PhAMOCVD are its very high growth rate (~1 micron/min) and excellent atomic ordering. The CeO₂/YSZ buffer layer system was chosen for PhAMOCVD processing, with excellent results for CeO₂ test depositions on LaAlO₃ (f -scan FWHM of ~1) followed by equally good YSZ depositions on the CeO₂ (f -scan FWHM of <2). Growth of CeO₂ on roll textured Ni foils resulted in f -scan FWHM of ~10 – similar to that of the starting Ni. YSZ growth on the CeO₂ by PhAMOCVD resulted in good films Ni substrate with f -scan FWHM ~8 – somewhat better than that of the substrate. YBCO growth on the buffer layer system on nickel has showed promising results with T_c~88-90K and J_c ~ 6 x 10⁵ A/cm² for short pieces of nickel substrate.

2D3.4 YBCO Coated Conductor Development at IGC

V. Selvamanickam 1, G. Galinski 1, C. Trautwein 1, G. Carota 1, J. DeFrank 1, P. Haldar 1, U. Balachandran 2, M. Chudzik 2, Y. Coulter 3, P. Arendt 3, B. Newnam 3, and D.E. Peterson 3. 1 Intermagnetics General Corporation, Latham, NY. 2 Argonne National Lab, Argonne, IL. 3 Los Alamos National Lab, Los Alamos, NM.

Presenting Author: V. Selvamanickam

Intermagnetics has been developing coated YBCO Superconductor using a Metal Organic Chemical Vapor Deposition (MOCVD) process as a high performance, low cost alternative HTS conductor for electric power applications. Biaxially-textured oxide buffer layers for the superconductor were prepared at Argonne and Los Alamos National Labs by Ion Beam Assisted Deposition (IBAD). MOCVD reactor design, precursor delivery scheme and process conditions were optimized to deposit epitaxial YBCO films with critical current densities (J_c) greater than 1 MA/cm² and critical currents (I_c) greater than 50 A at 77 K. These films have been found to exhibit a strong performance in the presence of a magnetic field too. At 75 K, critical current densities of 570,000 A/cm² (I_c = 20 A) and 215,000 A/cm² (Ic = 7.5 A) have been achieved at 1 T with the magnetic field perpendicular (B ^ c) and parallel (B₂ ½ ½ c) to c-axis respectively. At 64 K, the J_c values are 1.2 MA/cm² (Ic = 43 A) and 770,000 A/cm² (I_c = 27 A) at 2 T and 5 T respectively in the B ^ c orientation and 520,000 A/cm² (I_c = 18.2 A) and 300,000 A/cm² (I_c = 10.6 A) at 2 and 5 T respectively in the B ½ ½ c orientation. The results demonstrate that MOCVD is a viable alternative to Physical Vapor Deposition techniques for YBCO conductor fabrication.

The work at Intermagnetics was supported by Air Force Office of Scientific Research, Department of Energy, and the New York State Energy Research and Development Authority.

2D3.5 Tape Processing of HBCCO, BSCCO, and YBCO Thick Films on Metallic Substrates with High J_c by the Spray/Press Technique

R.L. Meng, D. Pham, Y.Q. Wang, J. Cmaidalka, J. Hildebrand, B.R. Hickey, Y.Y. Sun, Y.Y. Xue, and C.W. Chu, Department of Physics and Texas Center for Superconductivity, University of Houston, Houston, TX 77204-5932

Presenting Author: R.L. Meng

Our simple spray/press technique has been developed for the fabrication of thick film tapes of HBCCO, BSCCO, and YBCO on metallic substrates with high J_c. The technique has successfully incorporated crucial processing factors to achieve composition uniformity, phase purity, preferred microstructure, grain alignment, and high density for high temperature superconducting tapes of high performance. We have obtained a J_c of 1.1x10⁵ A/cm² in YBa₂Cu₃O_6+d thick films on Ag/Pd substrates at 77K and self-field; 7x10⁴ A/cm² in HgBa₂Ca₂Cu₂O_8+d thick films on Ni substrates with a buffer layer at 77K and self-field; and 5x10⁵ A/cm² and 3x10⁵ A/cm² in Bi₂Sr₂CaCu₂O_x thick films on Ni substrates with a buffer layer at 4.2K in self-field and 8T, respectively. Effects of deposition, precursor, chemical routes, calcination conditions, thermal treatment, processing atmosphere, and mechanical deformation on the phase formation, grain growth, grain alignment, morphology, microstructure, connectivity, film uniformity, density, and J_c of the YBCO, HBCCO, and BSCCO thick films on metallic substrates will be presented and discussed.

2D3.6 Viable YBCO Coated Conductor Technology

S. Annavarapu 1, L. Fritzemeier 1, Q. Li 1, A. Malozemoff 1, V. Prunier 2, M. Rupich 1, C. Thieme 1, and W. Zhang 1. 1 Research & Development, American Superconductor, Two Technology Drive, Westborough 01581, USA. 2 On assignment from Electricite de France, Research and Development - CIMA, Les Renardieres, France.

Presenting Author: M. Rupich

A major driving force in the commercialization of the HTS technology is the performance/cost ratio. In spite of its superior performance, YBCO coated conductor technology must avoid uneconomical processes to be competitive with the well-developed BSCCO-OPIT HTS wire technology. To this end, American Superconductor has developed a solution-based Y₂O₃/BaF₂/CuO deposition technique achieving J_c levels greater than 0.5MA/cm² on buffered textured Ni substrates. The challenges of increasing the J_c and extending the technique to long lengths of textured metal substrate are being addressed and will be reported. It is also desirable from a cost-perspective to replace vacuum techniques for the buffers by solution techniques. Encouraging results have been obtained on textured metal substrates, and the results of ongoing efforts to integrate these techniques into the conductor fabrication will be reported.

2D3.7 LPE process application to RE123 coated conductor

Yuichi Nakamura, Natsuro Hobara, Kazuomi Kakimoto, Teruo Izumi, and Yuh Shiohara, Superconductivity Research Laboratory, 1-10-13 Shinonome, Koto-ku, Tokyo, 135-0062 Japan

Presenting Author: Y. Nakamura

RE123 superconductive oxides are expected to be utilized for electric conductors due to its high performance of superconductivity at 77 K. For practical applications of long RE123 coated conductors, it is important to attain high engineering critical current and high production rate. The liquid phase epitaxy (LPE) process has an advantage to fabricate thick superconducting layer at high

growth rate with high superconducting properties in comparison with commonly used vapor deposition processes. Since a Ba-Cu-O solution used in the LPE process has a high reactivity with metal substrates, such reaction must be prevented to grow the superconducting RE123 layer on metal substrates by LPE. We selected MgO as a buffer layer on the Hastelloy substrate. In addition, it was found that the LPE growth of Y123 from MgO saturated solution was necessary to prevent dissolution of the MgO buffer layer although the grown Y123 phase contained some amounts of MgO. Using this MgO substituted Y123 layer as a secondary buffer layer, the Y123 layer with the T_c value of 91K was successfully grown from the solution without MgO on the MgO single crystal. After these preliminary works, we succeeded in growing Y123 on the Hastelloy substrate by the LPE process using these double buffer layers.

This work is supported by the New Energy and Industrial Technology Development Organization (NEDO) as Collaborative Research and Development of Fundamental Technologies for Superconductivity Applications.