Arendt, P.

Balachandran, U.

Carota, G.

Chudzik, M.

DePaula, R.

Funk, M.

Groves, J. R.

Haldar, P.

Newnam, B.

Selvamanickam, V.

Vo, N.

UNT Digital Library

,High-Current Y-Ba-Cu-O-Coated Conductor Using Metal Organic Chemical-Vapor Deposition and Ion-Beam-Assisted Deposition*V. Selvarnanickam, G. Carota, M. Funk, N. Vo, and P. HaldarIGC-SuperpowerSchenectady, NY 12304U. Balachandran and M. ChudzikEnergy Technology DivisionArgonne National LaboratoryArgonne, IL 60439P. Arendt, J. R. Groves, R. DePaula, and B. NewnamLos Alamos National LaboratoryLOS AkIIIIOS, NM 87545September 2000The submitted manuscript has been created by the University of Chicago asGperator of Argonne National Laboratory (“Argonne”) under Contract No.W-31- 109-ENG-38 with the U.S. Department of Energy. The U.S.Government retains for itself, and others acting on its bebaff, a paid-up,nonexclusive, irrevocable worldwide Iieense in said article to reproduce+prepare derivative works, distribute copies to the public, and performyrblicly and display publicly, by or on behrdfof the Gnvernrnent.\Paper to be presented at the Applied Superconductivity Conference ASC 2000, Virginia Beach,VA, September 17-22, 2000; to be published in IEEE Trans. Appl. Supercond.*This work was partly supported by the Air Force Office of Scientific Research and partly bythe U.S. Department of Energy (DOE), Energy Efficiency and Renewable Energy, as part of aDOE program to develop electric power technology, under Contract W-31 -109-Eng-38.—_..-, ~.=.,-. ,----- -.. .—-, -1DISCLAIMERThis report was-prepared as an account of work sponsoredby an agency of the United States Government. Neitherthe United States Government nor any agency thereof, norany of their employees, make any warranty, express orimplied, or assumes any legal liability or responsibility forthe accuracy, completeness, or usefulness of anyinformation, apparatus, product, or process disclosed, orrepresents that its use would not infringe privately ownedrights. Reference herein to any specific commercialproduct, process, or service by trade name, trademark,manufacturer, or otherwise does not necessarily constituteor imply its endorsement, recommendation, or favoring bythe United States Government or any agency thereof. Theviews and opinions of authors expressed herein do notnecessarily state or refiect those of the United StatesGovernment or any agency thereof.., --— ,.,.. ....;.,,,:~m .--.:r---- . . . :, . . . . .. . . . . . . . . . . .. . ..-, ,. ,:<. ., ,, ,....,. , ,... n.,,,.. .. . .. . . .,, .. . . . . . . . . . . .... .. . . .,, , .,—. .,. T .-.,.— ---.DISCLAIMERPortions of this document may be illegiblein electronic image products. Images areproduced from the best available originaldocument.——= . . ... . ... . ... - ,7. .-. —. -—. .— .-—. . . . .——.High-Current Y-Ba-Cu-O-Coated ConductorMetal Organic Chemical-Vapor DepositionIon-Beam-Assisted DepositionusingandV. Selvamanickam, G. Carota, M. Funk, N. Vo, and P. Haldar rLEf&EW E::’IGC-SuperPower, Schenectady, NY 12304, USANov o t 211NU. Balachandran, and M. ChudzikArgonne National Laboratory, Argonne, IL 60439, USA @sI-lP. Arendt, J. R. Groves, R. DePaula, B. NewnamLos Alarnos National Laboratory, Los Alamos, NM 87545, USAAbshact--YB~Cu30x (YBCO) films have been deposited onbuffered metal substrates by metal organic chemical-vapordeposition (MOCVD). Nickel alloy substrates with biaxirdly-textured yttria-stabilized zirconia (YSZ) buffer layers depositedby ion-beam-assisted deposition (IBAD) were used. A liquid-static precursor delivery system was designed, constructed, andused in the MOCVD facility at Intermagnetics for the reportedwork. At 77 & under self-field conditions, we achieved a criticalcurrent (Q of 97.5 A in YBCO film grown by MOCVD on anIBAD substrate. This ICcorresponds to a critical current densityof 1.3 MA/cm2 and 130 A/cm width of tape.Index Z’erms--MOCVD,IBAD, current density, biaxial-textureINTRODUCTION[GC-Superpower has been developing a metal organicthem ical-vapor-depos ition (MOCVD) process for thefabrication of high-current YB XCUJOX(YBCO) conductorswith substrates prepared by ion-beam-assisted deposition(IBAD). MOCVD has several special features such asnonline-of-sight coating, separation of precursors from thedeposition chamber, high deposition rates, and no targetfabrication expense, all of which can be important forproduction of long lengths of YBCO conductor for electricpower applications. The possibility of using YBCO toproduce high-current tapes was first demonstrated with IBADsubstrates [1], and only IBAD substrates have been used toproduce a 100-A YBCO tape in meter-long lengths [2].Earlier, we reported that we had achieved both high (SO-A)critical currents (IC)and high (>1 MA/cm2 at 77 K) criticalcurrent densities (Jo) in YBCO films fabricated by MOCVDon IBAD substrates [3]. The performance of the MOCVD-prepared YBCO films in high magnetic fields was shown tobe comparable to that of pulsed-laser-deposition (PLD)-The research at [ntermagnetics was supported in part by contracts with theU,S, Air Force Office of Scientific Research and Argonne NationalLaboratory, Work at Argonne and Los Alamos National Laboratory wassupported by the U.S. Department of Energy, Office of Energy Efficiencyand Renew8ble Energy.(PLD)-prepared YBCO films. Here, we report the use of aliquid precursor delivery system, a doubling of the ~ toalmost 100 A, and microstructure analysis of MOCVD-prepared YBCO films.EXPERIMENTALThe metal substrates used for MOCVD of YBCO consistedof biaxially-textured buffer layers of yttria-stabilized-zirconia(YSZ) deposited by I13AD at Argonne and Los AlamosNational Laboratories (ANL and LANL), respectively.Polished Hastelloy-C and Inconel 625 metal substrates, =100pm thick were used. The YSZ buffer layers were typically0.5-1 pm thick. In the process used at ANL, an 8-cmKaufmann-type DC ion source was used to produce a 300-eVassisting ion beam of Ar/107002 that was directed onto thesubstrate surface at an angle of 35°. Electron-beamevaporation was used for YSZ deposition. The atomicdeposition rate was 1.6 &s and the ion flux was 200 pA./cm2,yielding an ion-to-atom flux ratio of 2.8. Details of the IBADprocess used at LANL have been published in Ref. 4.Briefly, Inconel 625 substrates were polished to a surfaceroughness of 3 Al nm. The assisting ion was produced by alinear DC Kaufmann-type source, with beam dimensions of2.5 x 23 cm. The atomic deposition rate was 0.5 &s, theassist ion energy was 200 eV, and the ion flux was 190pA/cm2. The YSZ-buffered metal substrates were cut intol-cm-long, 4-8-mm-wide segments for YBCO deposition byMOCVD. Single-crystal YSZ substrates and SrTIO~substrates were also used for deposition, for comparisonMOCVD of YBCO was conducted at Intermagnetics in acustom-built facility that has been described previously [3,5].Tetramethyl heptanedionate (thd) precursors were used for Y,B% and Cu. YBCO films, 1 pm thick, were deposited withina temperature regime of 700-800°C under a reactor pressureof 1-5 torr and an oxygen partial pressure of 0.3-0.8 torr.After deposition, YBCO fiIms were coated with silver pads,annealed at =400°C in oxygen..-L-..—--y~,, ,.-r, ~<- ., ,:;,”,: ,, : . r ,.:~,~~; ,’, —--—- . .‘...;< ~+ ,: ,“.,.,,.- . . . . . -.-,,The out-of-planeand in-plane textures of the YSZ bufferlayers were examined by X-ray diffraction and pole figuremeasurements.The surface morphology of the YBCO filmswas studied by scanning electron microscopy (SEM),followed by compositional analysis by energy dispersiveX-ray spectroscopy (EDS). The thickness of the films wasmeasured by surface profilometry.The current density of thefilms was tested in liquid N in zero applied magnetic field.The samples were not patterned and JCwas measured acrossthe entire width of the samplrx continuous DC currents up to100 A were used in the measurements.LIQUID PRECURSOR DELIVERYThe schematic diagram in Fig. 1 shows the configuration ofthe MOCVD system at Intermagnetics. Precursor delivery isa three-step process. In the first step, a liquid precursor ispumped at a constant flow rate by a liquid-delivery pump. Inthe second step, the liquid precursor is flash-vaporized in avaporizer maintained at a constant temperature. Thevaporized precursor then flows in a carrier gas, such as Ar,through heated lines and is injecied onto a hot substratethrough a shower head. All components of the precursordelivery system have been designed and developed atIntermagneticsoThere are several advantages to liquid-precursor deiive~when compared with solid-precursor delivery. The keyadvantages are listed in Table I.The composition of YBCO films prepared by the ,liquid-precursor delivery system during 12 deposition runs showedthat the film composition was reproducible within ~5% of thetarget composition.CRITICAL CURRENT MEASUREMENTSIt was reported previously that 1. values of 50 A wereachieved in YBCO films grown by MOCVD on lBADsubstrates at 77 K under self-field conditions [3]. Highvalues of Ic were also maintained in the presence of amagnetic field. At 75 K, with the magnetic fieldperpendicular to the c-axis (B L c), JCvalues of 570,000 and240,000 A/cm2 were achieved in fields of 1 and 5 T,respectively. With the field parallel to the c-axis (B IIc), JCFig. 1, Schematic dingram of the MOCVD system used at [ntermagnetics.TABLE ICOMPARISON OF SOLID- AND LIQUID-PRECURSORDELIVERY SYSTEMSClsaracter- SolidPrecursor LiquidprecursoristicTechnique Precursorsare Precursoris flashindividuallysublimed vaporized at a singleseparately tlom 3 locationovensTemperature Diflictdt (film Single-point ofControl composition is control. Easiersensitive to evenI“C change)Precrmor Bad for long More stable inStability deposition periods solution formPrecursor Changes as precursor Constant volume ofVapor is depleted precursor isPressure vaporized. Vaporpressure is constantDeposition Difficult to increase Easily incremed byRate bczause of turbulence increasing precursorof crcm”ergas at high flow rate.ratesvalues of 215,000 and 100,000 A/cm* were achieved in fieldsof 1 and 2.5 T, respectively. At 64 ~ the JCvalues were 1.2MA/cm* and 770,000 Alcm2 at 2 and 5 T, respectively, in theB 1 c orientation. In the B IIc orientation, the J. values were680,000, 520,000, and 300,000 A/cm2 at 1, 2, and 5 T,respectively. Since that report was published, the ~ ofYBCO films made by MOCVD on IBAD YSZ substrates hasbeen doubled to almost 100 A, as shown in the current-voltage (I-V) curve in Fig. 2. The IC of 97.5 A exhibited inFig. 2 corresponds to a JCvalue of 1.3 MA/cm* and translatesto 130 LUcm width of film. These values compare very wellwith those achieved in YBCO tllms deposited on buffered-metrd substrates by pulsed-laser deposition.1.41.210.80.60.40.20I 1’1:-1.t10 20 40 60 80 100Current (AFig. 2. I-V curve obtained from YBCO film deposited by MOCVD onIBAD substrate. The ~ is 97.5 A, which corresponds to 130 A/cm width oftape.T------.,,:,- ,+,, . .. . >,-. .,.. ,.. ,... * .4- . . ..- —- , ,: , -7, ., -’. .-..7 ~Y.J,k.,-. ““,--~ ‘ x~, ‘.. ,.,-, ,*CMICROSTRUCTURE ANALYSISThe surface morphology of the films was examined by SEM.We found that the surface morphology of the films becamerougher with increasing thickness in the range from 0.1 toI pm. A puzzling finding was that the rougher films almostalways yielded a higher J. than the smoother films. Figs. 3and 4, respectively, show a relatively smooth film and a veryrough film, both 1 pm thick. Contrary to expectations, thesmooth film sustained an ICof only I A, whereas the roughfilm exhibited an ICof almost 100A.The cause of surface roughness in films of the samethickness, as seen in Figs. 3 and 4, could be that the roughfilms are usually off-stoichometric. The off-stoichiometriccompositions were deliberately chosen to achieve higher JC.The information obtained from the analysis of thesurface morphology of the films does not provide completedetails of the microstructure and its influence on the criticalcurrent, Therefore, steps have been taken to examine thecross-sectional microstructure of MOCVD-prepared YBCOFig, 3, Microstructure. of a 1 pm YBCO film deposited by MOCVD on aIBAD substrate, [n spite of the relatively smooth film surface, the filmsustained mr Ic of only 1.3A.Fig, 4. Microstructure of is I ~m YBCO film deposited by MOCVD on aIBAD subslra[c, In spite of the rough film surface, the film sustained a Ic of97S A (data shown in Fig. 2).films. Samples were fractured and their cross sectionsexamined by SEM. Fig. 5 shows the microstructure of aYBCO film on an SrTiOs substratq the film is dense and hasa columnar structure. EDS spectra were obtained fromvarious sections of the sample, and the YBCO and SrTi03substrate regions were confirmed.More detailed analyses will be performed and willinclude YBCO on metal substrates to increase ourunderstanding of the relationship between microstructure andJc.CONCLUSIONSYBCO films have been deposited by MOCVD onbiaxially-textured YSZ buffer deposited by IBAD. A liquid-precursor delivery system was designed and constructed foruse in the MOCVD facility. Through improvement to theMOCVD equipment and optimization of process conditions,~ as high as 97.5 A (corresponding to a J, of 1.3 MAlcm2)was achieved at 77 K under self-field conditions. This JCvalue corresponds to 130 A/cm-width of tape. Microstructureanalysis of the tapes revealed a very rough surfacemorphology in the high-JCfilms.[1][2][3][4][5]REFERENCESY. Iijima, N. Tanabe, and O. Kohno, Adv. in Supercond. W. ed.Hayakawa and Koshizuka Springer Verlag, Tokyo, pp. 679-682(1992).S. R. Foltyn, P. N. ArendL P. C. Dowden, R F. DePaul% J. R. Groves,J. Y. Coulter, Q. Xi% M, P. Maley, and D. E. Peterson, IEEE Trans.Appl. Superconductivity vol. 9, 1519 (1999). also 1999 WireDevelopment Workshop Proceedings (U.S. Dept. of Energy), CocoaBeach, FL, January 12-13, 1999, pp. 215-228.V. Selvamanickam G. GaIinski, G. Carota, J. DeFrank, C. Trautwein,P. Haldar, U. Balachandrrur, and M. Chudzik, J. Y. Cordter, P. N.Arendt. J. R. Groves. R F. DePaula. B. E. Newnam, and D. E. PetersonPhysicuC vol. 333 pp. 155-162 (2000).P. N. Arendt. S. R. Foltyn, J. R Groves, R F. DePard~ P. C. Dowden,J. M. Roper, and J. Y. Coulter, AuDI. Superconductivity vol. 4, 429.(1996). -. .V. Selvamanickam, G. Galinski, J. DeFrank, C. Trautwein, P. HaIdar,. .. ---- - . .U. Balachandran, and M. ChuazlK, lhh~ I runs. Appl.Superconductivityvol. 9,1523 (1999).Fig. 5 Fracture surface ofa YBCO film on an SrTiOj substrate. A columnargrain growth is evident, and the film appears to be dense.

High-current Y-Ba-Cu-O-coated conductor using metal organic chemical-vapor deposition and ion-beam-assisted deposition.

High-current Y-Ba-Cu-O-coated conductor using metal organic chemical-vapor deposition and ion-beam-assisted deposition.

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