No Title

SESSION R2: PROCESSING ISSUES FOR COATED CONDUCTORS
Chairs: Paul N. Arendt and Amit Goyal
Tuesday Afternoon, April 1, 1997
Salon 15

1:30 PM *R2.1
FABRICATION OF LONG Tl-1223 SUPERCONDUCTING TAPES ON BIAXIALLY TEXTURED SILVER SUBSTRATES, Toyotaka Yuasa, Hitachi Ltd, Ibaraki, JAPAN; Naomi Inoue-Sugiyama, Hiroyuki Akata, Kazutoshi Higashiyama, Hitachi Ltd, Hitachi Research Lab, Ibaraki, JAPAN; Kei Kimura, Super-GM, Dept of Engineering Research, Osaka, JAPAN.

In fabricating a Tl-1223 superconductor, crystal alignment is needed to obtain a high transport Jc. For this purpose, we developed biaxially textured silver substrates using a hot-rolling technique. Over 80

of grains of silver substrates were aligned in a

<001> direction. The FWHM in the x-ray

scan at

= 54.7 was about 8 degrees. These substrates do not require to use of a buffer layer; thus, we were able to fabricate a Tl-1223 superconductor directly. We deposited precursor oxide (Ba/Sr-Ca-Cu-O) films on the substrate ( length: 15 mm) using the spray pyrolysis method. Then, the precursor films were fired in the controlled thallium oxide vapor atmosphere. Although a certain degree of the Tl-1223 grains were aligned biaxially, we observed 3 different orientational angles of 0, 26 and 45

in the film. These orientational angles agree well with theoretical values of Near Coincidence Site Lattices (NCSL). With biaxial crystal orientation, the Tl 1223 superconducting film showed Jcs of 100,000 A/cm

at 77 K, OT and 12,000 A/cm

at 77K, 1T. ln the fabrication of long tape, we developed a continuous fabrication process of Tl-1223 superconducting tape. First, we deposited the precursor film on the silver tape (40

) using the continuous spray pyrolysis method. The 2

thick precursor film was fabricated on a 10 m length of silver tape traveling at the rate of 1.0 m/h. The precursor film had the stoichiometric composition of a Tl-1223 superconductor. Second, the tapes were continuously heat treated by passing them through a furnace in a controlled flow of Tl-oxide vapor to convert the precursor to a Tl-1223 superconductor. This work was 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.

2:00 PM *R2.2
RAPID THICK FILM YBCO GROWTH FOR WIRES AND TAPES BY PHOTO-ASSISTED MOCVD, A. Ignatiev, Q. Zhong, P. C. Chou, X. Zhang, Y. M. Chen, Univ of Houston, Texas Ctr for Superconductivity, Houston, TX.

The development of YBCO-based wires and tapes requires a technology for the formation of high quality superconducting YBCO thick films on top of metallic substrates. Metal organic chemical vapor deposition (MOCVD) has been shown in the past as a technique for the growth of YBCO; however, moderate film quality and slow growth rates have been detractors for the technology. A modification of the MOCVD technique, however, has been developed that overcomes these drawbacks: photo-assisted MOCVD. YBCO films have been grown in both horizontal and vertical quartz reactors where the only source of energy for the reaction has been photo irradiation from a bank of tungsten halogen lamps. YBCO films grown with this technology have shown T

91 K, and J

> 1 x 10

A/cm

. In addition, and just as critical, growth rates greater than 1

m/min have been realized with photo-assisted MOCVD. These growth rates support rapid thick film growth of YBCO, and films of up to 8

m have been grown with, however, a measured decrease of J

with increasing thickness. This effect has been shown to be due to a lack of pinning centers in the thick films and has been rectified through the injection of point defects into the thick films by 1 MeV proton bombardment. An approach is underway to degrade the crystalline quality of the thick YBCO films during growth in an attempt to generate additional pinning centers. The high growth rates exhibited by photo-assisted MOCVD, however, fully support the commercial needs of the technology for high yield YBCO wire and tape fabrication. The application of the photo-assisted MOCVD technique to YBCO growth on metallic substrates has been initiated, and has shown preliminary positive results for the fabrication of YBCO on patterned silver and nickel substrates.

2:30 PM R2.3
A MOCVD APPROACH TO BIAXIALLY-TEXTURED THICK FILM Y-Ba-Cu-O SUPERCONDUCTOR FABRICATION ON METALLIC SUBSTRATES, Venkat Selvamanickam, Michael Walker, Pradeep Haldar, Intermagnetics General Corp, Latham, NY; Ana Ivanova, SUNY-Albany, Albany, NY; Alain E. Kaloyeros, SUNY-Albany, Dept of Physics, Albany, NY; David B. Fenner, Fenner Engineering Assocs, Simsbury, CT; Michael T. Lanagan, Argonne National Laboratory, Ceramic Section, Argonne, IL; Gregory Kozlowski, Wright State Univ, Dept of Physics, Dayton, OH; Charles E. Oberly, Air Force Wright Laboratory, WL/POOX, Dayton, OH; Siu-Wai Chan, Columbia Univ, Dept of Materials Science, New York, NY.

Metal Organic Chemical Vapor Deposition (MOCVD) has been successfully used to fabricate biaxially textured Y-Ba-Cu-O superconductors on metallic substrates. A high degree of biaxial texture was achieved in long lengths of metallic substrates by a metal working process. Metal and ceramic buffer layers were deposited on the textured substrates by a variety of techniques such as laser ablation, sputtering, e-beam evaporation, and Metal Organic Deposition (MOD). Biaxially-textured, stoichiometric, and dense YBCO films have boon deposited by MOCVD on the buffered metallic substrates. The growth process of buffer layers and the superconducting layer on the textured substrates has been examined by cross-sectional Transmission Electron Microscopy. Superconducting properties of YBCO thick films deposited under identical conditions on biaxially textured metal substrates and single crystal ceramic substrates have been compared. The in-plane texturing of metal substrates and YBCO films have been examined by Electron Back Scattered Diffraction. A continuous MOCVD reactor has been developed for long length deposition of biaxially-textured superconducting tapes on buffered metallic substrates. Our results show that MOCVD is a viable deposition approach for biaxially textured, superconducting thick film conductors.
This work has been partly supported by the Department of Energy and the Air Force Office of Scientific Research.

3:15 PM *R2.4
USE OF A MODIFIED BIAS SPUTTERING TECHNIQUE TO FABRICATE IN-PLANE TEXTURED BUFFER LAYERS FOR YBCO FILM GROWTH, Masao Fukutomi, Nat Research Inst for Metals, Ibaraki, JAPAN; Masakazu Saitoh, Mitsuba Corp, Gumma, JAPAN; Kazunori Komori, Kazumasa Togano, Nat Research Inst for Metals, Ibaraki, JAPAN.

We have proposed a new bias sputtering technique to grow in-plane textured yttria-stabilized zirconia (YSZ) buffer layers on polycrystalline metallic and alumina substrates for deposition of YBa

(YBCO) films. The principle of developing an in plane texturing by this technique is basically the same as that of ion beam assisted deposition (IBAD); an in-plane texturing occurs by off-normal ion beam bombardment because of the higher sputtering yields of all orientations other than the channeling direction. In our process, however, a flux of energetic particles impinging on the growing film is generated using specially devised dc and/or rf biased electrodes installed in a magnetron sputtering system instead of a separate ion-source in IBAD. So far, a x-ray phi-scan width of 17

(FWHM) was attained for about 0.5

m thick YSZ films on Hastelloy tapes. Epitaxial YBCO films grown on these buffer layers using pulsed laser deposition showed the Jcs exceeding 10

A/cm

(77 K, OT). In this paper, we will also present variations of the bias sputtering technique to obtain the textured films on both sides of the tape substrates and on large area substrates. Although the proposed process offers a very convenient method to grow textured films, growth rates of the films must be increased ( currently

0.1 nm/s) for large scale application of YBCO films.

3:45 PM *R2.5
THE MECHANISM FOR TEXTURE DEVELOPMENT IN FILMS PREPARED BY ION BEAM ASSISTED DEPOSITION, Michael J. Cima, MIT, Dept of MS&E, Cambridge, MA; Kevin G Ressler, Neville Sonnenberg, MIT, Ceramics Processing Res Lab, Cambridge, MA.

The mechanism of biaxial alignment is examined for yttria-stabilized zirconia (YSZ) films deposited by ion beam assisted deposition (IBAD). (200) biaxial aligned films have been deposited at both high and low temperatures and using e-beam and ion beam as the deposition sources. Model experiments on different orientations or single crystal YSZ were undertaken to elucidate mechanism. Two temperature dependent IBAD growth modes are observed. Biaxial alignment does not occur due to ion channeling or due to different crystallographic orientations etching at different rates. IBAD biaxial alignment occurs so the damage tolerant planes face the assisting ion beam. The growth direction of misaligned grains changes in discrete units corresponding to the introduction of low angle grain boundaries and special boundaries in the crystal. Low angle grain boundaries are introduced to grains with larger amounts of ion induced damage. Thus, a growth direction change occurs with highest frequency for misaligned grains and with lowest frequency for grains with damage tolerant planes exposed to the ion beam.

4:15 PM R2.6
YBCO SUPERCONDUCTOR TEXTURE CONTROL USING ION-ASSISTED PULSED-LASER DEPOSITION OF INTERMEDIATE LAYERS, Ronald P. Reade, Paul Berdahl, Richard E. Russo, Lawrence Berkeley National Laboratory, Berkeley, CA.

The development of biaxially-textured YSZ intermediate layers for YBCO superconductor growth on difficult substrates (randomly-textured polycrystalline or amorphous materials) was introduced by Iijima et al. using ion-assisted sputtering and Reade et al. using ion-assisted pulsed-laser deposition more than five years ago. Since that time, significant improvements in the texturing have been demonstrated to provide YBCO films on flexible metal tapes with critical current densities greater than 1 MA/cm2. However, it is clear that the fundamental mechanisms of ion-assisted texturing are still not established. A better understanding is needed for purposes of process control and for improving critical parameters such as deposition rates, minimum intermediate layer thickness, etc. We will present recent studies of process parameters related to ion beam divergence and thus texture control, texturing as a function of layer thickness, and methods to induce greater texture control in thinner layers. Recent results for YBCO deposition on flexible metal substrates and YBCO multilayer structures for hybrid electronic devices will be discussed. We will summarize the advantages, particularly for multilayer and hybrid devices, and disadvantages of ion-assisted processing versus other methods for texturing.

4:30 PM R2.7
YBCO GROWTH ON TEXTURED BUFFER LAYERS PREPARED BY ION-BEAM-ASSISTED DEPOSITION, Connie Pin-Chin Wang, Stanford Univ, Stanford, CA; Khiem Do, Stanford Univ, Ginzton Lab, Stanford, CA; Malcolm R. Beasley, Theodore H. Geballe, Robert H. Hammond, Stanford Univ, Dept of Applied Physics, Stanford, CA.

Ion beam assisted deposition (IBAD) has been demonstrated to be potentially a good scale-up scheme for large area YBa

applications. An in-plane textured buffer layer (MgO, YSZ, etc.) can be deposited on an amorphous (Si

, SiO

, etc.) or a polycrystalline metallic substrate. Consequently, YBCO growth can be in plane textured with high J

. However, the contribution of ion beam to the microstructure evolution still remains to be understand. We have deposited biaxially textured MgO on Si

and Ni substrates. We used

RHEED to characterize the IBAD process in real time, and

planar view and cross-section TEM, AFM and XRD to examine the substrate/buffer, buffer/ YBCO interface as a function of growth parameters, such as substrate type, substrate temperature, pressure, ion/atom flux ratio, film thickness, and ion incidence angle. In this paper, we will present the recent result and analysis of the ion induced-texture experiment. We will also discuss the potential candidates for the second buffer layer (NiO, CeO

, metal or metal oxide) and the substrate, and report the quality of YBCO films attained using some of these buffer layers.

4:45 PM R2.8
LARGE-AREA DEPOSITION OF YBCO FILMS AND TEXTURED BUFFER LAYERS ON CERAMIC SUBSTRATES, Wolfgang Schmidt, H. -W. Neumuller, H. -K. Kramer, Siemens AG, Dept ZT EN4, Erlangen, GERMANY; Helmut Kinder, Technische Univ Muenchen, Dept of Physics, Garching, GERMANY; M. Bauer, R. Semerad, Technische Univ Muenchen, Garching, GERMANY; H. C. Freyhardt, K. Heinemann, Univ of Goettingen, Inst fur Metallphysik, Goettingen, GERMANY; J. Wiesmann, Univ Goettingen, Inst fur Metallphysik, Geottingen, GERMANY.

Thick films of YBCO have been prepared by thermal co-evaporation on polycrystalline zirconia for the development of a resistive fault current limiter. To achieve critical current densities above 10

, buffer layers of biaxially textured cubic zirconia were prepared by IBAD using a dual-beam ion-gun sputtering system. Within a joint project

a 100 kVA function model of a resistive limiter is planned, which requires a YBCO film thickness of about 2

m and a film area of about 400 cm

. To achieve this requirement, an upscaling of the deposition processes to areas of 20x20 cm

is performed. Due to the beam size of the ion-guns in the IBAD system, the homogeneous area is presently limited to sample sizes of 10x10 cm

within which half-widths of the in-plane orientation of about 14

are routinely achieved in YSZ films with thicknesses of 0.9

m. The YBCO films deposited on those buffer layers with thermal co-evaporation have thicknesses of 0.7

m and 1.4

m, respectively, and critical current densities in the range of 0.5 . . . 1x10

. Meander shaped strip lines were etched from the 10x10 cm

samples with a width of 1 cm carrying critical currents of up to 90

over a length of about 40 cm.

Work performed within the Siemens joint project ''HTS for Power Engineering,'' cofunded by the German BMBF.

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