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Applied Superconductivity, IEEE Transactions on

Issue 2 • Date June 1999

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Displaying Results 1 - 25 of 335
  • The 1998 Applied Superconductivity Conference

    Page(s): 0_1 - 0_26
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    Freely Available from IEEE
  • Microstructures and flux pinning properties in Nb/sub 3/Al tapes by ohmic-heating method

    Page(s): 1429 - 1432
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    Two kinds of Nb/sub 3/Al superconducting tapes with monocores in Nb sheaths have been fabricated from either Nb/Nb/sub 2/Al(sigma-phase) powders or Nb/Al powders. Tape samples 3 mm wide, 0.3 mm thick, and 40-50 mm long are ohmically-heated at maximum temperatures which range from 1650 to 2000/spl deg/C in vacuum, to obtain the stoichiometric composition of the A15 phase. Critical currents up to 23 T were measured by a four probe method. Microstructures were studied using an X-ray diffractometer, TEM, and EDX. The Nb/sigma powder sample showed a maximum T/sub c/ at an ohmically-heated temperature 200/spl deg/C lower than the Nb/Al powder sample. Production of A15 is influenced by the differences in diffusion length related to different starting materials. Nb/sub 3/Al grain sizes were 1-2 /spl mu/m in both the Nb/Al sample and the Nb/sigma sample. Also, /spl sigma/-phase was observed only in Nb/Al sample. The pinning force densities in the Nb/Al sample and the Nb/sigma sample showed a large peak at high magnetic field (above 20 T), and a peak at low magnetic field, respectively. From the relation between microstructure and flux pinning properties, it is supposed that the /spl sigma/-phase acts as an effective pinning center at high magnetic fields in Nb/sub 3/Al. View full abstract»

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  • Short-sample quenching of Nb/sub 3/Al precursor strand in support of reel-to-reel process development

    Page(s): 1433 - 1436
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    Niobium-aluminum precursor strands were fabricated using the conventional jelly roll method with two Nb:Al volume ratios, 3:1, and 5:1. These mono-elements were restacked in 7-, 19- and 36-core arrangements and drawn down to wires approximately 0.8 mm and 0.4 mm in diameter. Short lengths of wire were resistively heated under high vacuum to temperatures as high as 2200/spl deg/C for various times, and either allowed to cool by radiation plus lead conduction or quenched into liquid gallium. Vacuum cooling led to a disordered A15 phase, which was then ordered by annealing at 800/spl deg/C; gallium quenching tended to produce the bcc phase, which could be transformed into A15 also by annealing for various times at 800/spl deg/C. The superconducting properties of the final wires were examined by vibrating-sample magnetometry (/spl chi//sub dc/ and T/sub c/) as well as transport J/sub c/ measurement. Best results so far are for a 5:1 Nb:AI volume ratio sample Ga quenched from 2000/spl deg/C with a secondary reaction of 800/spl deg/C/3 h, giving J/sub c/=4.5/spl times/10/sup 8/ A/m/sup 2/ at 12 T, with a T/sub c/=18-18.5 K. View full abstract»

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  • Properties of fiber-reinforced niobium-tin superconductor fabricated by bronze process

    Page(s): 1437 - 1440
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    We are developing a fiber reinforced type of superconductor for large scale, high-field magnets. Formerly we used the sputtering process to develop a niobium-tin conductor reinforced with a tungsten fiber and showed that this type of conductor has excellent stress tolerance. For practical applications however, a conventional fabrication process like bronze process is desirable. Hence we have tried to fabricate a fiber-reinforced type niobium-tin conductor utilizing tantalum fiber as the reinforcing member, In this conductor, each niobium-tin filament has a tantalum core of about 20-/spl mu/m diameter, We adopted tantalum as the core material since it has both good ductility and mechanical strength comparable to stainless steel, This conductor showed a reasonable critical field of about 22 T and good mechanical strength compared to a niobium-tin conductor fabricated by the conventional bronze process. View full abstract»

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  • Improvements of (NbTi)/sub 3/Sn bronze processed superconductor performance

    Page(s): 1441 - 1443
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    Research results are given for stabilized (NbTi)/sub 3/Sn strand with titanium artificial doped filaments. This work has been performed with the aim to improve the critical current density of the bronze processed strands designed for ITER. Strands with diameters in range 0.4 mm to 1.7 mm with composite filaments containing one or four cores made of Nb-Ti alloy as sources of doping element have been investigated. Critical current densities for some strands were investigated in the range of magnetic fields 8-22 T. It was shown that the strand containing 12684 filaments with 4 cores of Nb-Ti alloy in each filament had the best superconducting properties. J/sub c/ (non Cu) of this type of the strand with diameter of 0.81 mm was equal to 750 A/mm/sup 2/ at 12 T and had hysteresis losses /spl sim/100 mJ/cm/sup 3/ (/spl plusmn/3 T). This value was 1.3 times larger than the J/sub c/ value of the strand, which contained 1 core of Nb-Ti alloy. The maximum J/sub c/ (non Cu) attained for the strand 0.5 mm in dia with 12684 filaments was equal to 900 A/mm/sup 2/ at 12 T. Hysteresis losses for this strand were also less than 100 mJ/cm/sup 3/ (/spl plusmn/3T). It was shown that the developed strand with four cores of Nb-Ti alloy met both ITER Specifications HP-I and HP-II simultaneously. Also it is a perspective material for high field applications. View full abstract»

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  • Recent development of niobium-tin superconducting wire at OST

    Page(s): 1444 - 1446
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    Oxford Superconducting Technology (OST) produces Nb/sub 3/Sn superconductive composites via several different fabrication methods. We report here some aspect of improvements made in these products. Enhancement in very high field properties have been introduced for bronze processed composite using Nb filaments with Ta addition and bronze matrix with Ti addition. In modified jelly roll (MJR) composite non-copper critical current density has been improved to over 3000 A/mm/sup 2/ at 10T by modifying design. This performance is reproduced routinely in production. View full abstract»

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  • The effect of hot isostatic pressing on the strain tolerance of the critical current density found in modified jelly roll Nb/sub 3/Sn wires

    Page(s): 1447 - 1450
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    The critical current density of Hot Isostatic Pressed (HIP'ed) and unHIP'ed Nb/sub 3/Sn Modified Jelly Roll wires has been measured as a function of magnetic field and of strain at 4.2 K. The reversibility of critical current density was investigated for both wires. The critical current and upper critical field were decreased for the HIP'ed sample. The reduced upper critical field of the HIP'ed wire was found to be less sensitive to strain than the unHIP'ed wire. The index (m) of the flux pinning scaling law is found to have increased from 0.86 to 2.14 as a result of the HIP processing. View full abstract»

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  • Progress in the development of Nb/sub 3/Sn conductors based on the "Powder in tube" method with finer filaments

    Page(s): 1451 - 1454
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    Inspired by the successful operation of the 11 T Nb/sub 3/Sn experimental dipole magnet MSUT, a new large bore 10 T@4.5 K Nb/sub 3/Sn model dipole magnet is under development in The Netherlands. For application in this system, Shape Metal Innovation (SMI) has developed a new "Powder in Tube" type of Nb/sub 3/Sn conductor with an increased number of filaments. At a strand diameter of 0.9 mm, the diameter of the filaments after reaction for only 33 hours at 675/spl deg/C has been reduced to about 20 microns. The non-copper critical current density has been measured to be as high as 1890 A/mm/sup 2/ at 10 T@4.25 K. View full abstract»

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  • Low field flux jumping in high performance multifilamentary Nb/sub 3/Al and Nb/sub 3/Sn composite strands

    Page(s): 1455 - 1458
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    The problem of flux jumping in NbTi superconducting strands was solved 30 years ago by the introduction of suitably fine multifilamentary subdivision accompanied by twisting. But with recent advances in A15 superconductors we are entering a regime in which J/sub c/ may be increasing at a rate faster than effective filament diameter, d/sub eff/, can be reduced. This is particularly true for Nb-clad melt-processed Nb/sub 3/Al strands which at fields below H/sub c2,Nb/ have subelements which are superconductively coupled via the Nb matrix. Control of d/sub eff/, while still requiring attention, is less of a problem for the new very high J/sub c/ Nb/sub 3/Sn strands whose sub-elements, although fully bridged, are still able to be reduced in size. The results of some low field magnetization experiments are presented and interpreted in terms of a simple model. View full abstract»

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  • Film orientation of RE123 prepared by chemical solution deposition

    Page(s): 1459 - 1462
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    We investigated processing temperature dependencies of the preferred orientation axis of REBa/sub 2/Cu/sub 3/O/sub 7-y/ (RE123; RE=Yb, Er, Y, Gd, Sm, Nd, Pr and La) films prepared on various substrates by chemical solution deposition (CSD) using metal naphthenates. In the case of RE=Er, Y, Gd and Sm prepared on SrTiO/sub 3/, a/b-axis oriented films were obtained in a region of low temperatures, whereas there is no such temperature region for RE=Yb, Nd, Pr and La films. On the other hand, RE123 films prepared on LaAlO/sub 3/ gives a/b-axis orientation in a region of low temperatures except for Yb123 film. The (102) pole figures of these films give four high density points with four-fold symmetry, indicating that their axes are in-plane aligned. In order to confirm relationship between a/b-axis oriented growth and ionic radius of RE elements (R/sub i,RE/), we prepared rare-earth mixed Yb/sub 1-x/Er/sub x/Ba/sub 2/Cu/sub 3/O/sub 7-y/ and Sm/sub 1-x/Nd/sub x/Ba/sub 2/Cu/sub 3/O/sub 7-y/ films. Orientation of these films changed critically at certain average R/sub i,RE/'s. View full abstract»

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  • Bulk texture and transport properties of magnetic field/liquid assisted textured YBa/sub 2/Cu/sub 3/O/sub 7-x/ tape-cast films

    Page(s): 1463 - 1466
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    Textured YBa/sub 2/Cu/sub 3/O/sub 7-x/ films (thickness=250 /spl mu/m) were fabricated by tape casting in an applied magnetic field (H=6 T). Platinum (1 wt.%) was incorporated to induce liquid phase-assisted densification in films fired on silver (Ag) foil to 935-942/spl deg/C under reduced pO/sub 2/(g) conditions. The transport critical current densities (J/sub ct/) of such films exhibited nearly field insensitive behavior between H=0-3 T (H/spl par/c-axis) at 77 K, with J/sub ct/>1000 A/cm/sup 2/ at H=0 T. View full abstract»

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  • High rate deposition of 5 /spl mu/m thick YBa/sub 2/Cu/sub 3/O/sub 7/ films using the BaF/sub 2/ ex-situ post annealing process

    Page(s): 1467 - 1470
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    We have investigated the crystallization of thick YBCO films under various annealing conditions. The films were deposited by high-rate co-evaporation of Y, Cu and BaF/sub 2/ onto room-temperature SrTiO/sub 3/ substrates at rates exceeding 10 nm/s. TEM microscopy was performed to establish the microscopic structure of partially processed films and help elucidate the growth mechanism. In-situ resistivity measurements were used to monitor the crystallization of the YBCO films during the annealing process. Resistivity measurements and TEM microscopy of samples at different stages of the film growth are compared. Our results indicate that, in addition to oxygen partial pressure, water vapor pressure is an important parameter which defines the dynamics of film growth and crystallization. 5 /spl mu/m thick films with J/sub c/>2/spl times/10/sup 5/ A/cm/sup 2/ (1 T H/spl par/c) have been fabricated. View full abstract»

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  • Fabrication of YBCO thick films on cube textured Ni substrate with NiO intermediate layer

    Page(s): 1471 - 1474
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    High quality, sharp cube textured Ni substrates have been fabricated by a cold rolling and a recrystallization annealing process. X ray results show that there are some problems to be noted in the prevalent quality evaluation for a cube textured Ni substrate. In-plane-aligned, c axis-oriented YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) thick films were grown on the textured Ni substrate with self-oxidized NiO intermediate layer by an ink-printed and floating zone heating method. The values of the resistively measured T/sub c/ (onset) were 86 K. This is a very useful and promising method for producing the long YBCO tapes with high J/sub c/, although J/sub c/ is lower at present. View full abstract»

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  • Filamentary YBCO conductors for AC applications

    Page(s): 1475 - 1478
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    High current density YBCO conductors as they are presently conceived for use at liquid nitrogen temperatures are in the form of tapes, usually the order of a centimeter in width and suitable only for dc use. Possibilities for developing similar YBCO conductors for ac applications are discussed, and the ac loss expected from such conductors is computed. The conversion from a dc to an ac conductor requires breaking up a wide-tape dc conductor into narrow strip-like filaments which spiral about the conductor axis. Various ways of producing this pattern are proposed. View full abstract»

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  • Microstructure and texture evolution in oxide films prepared by ion-beam assisted laser deposition

    Page(s): 1479 - 1482
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    Using Ion-Beam Assisted Laser Deposition (IBALD), biaxially oriented films of Yttria stabilized Zirconia were deposited on polycrystalline and amorphous substrates. The film texture in dependence of deposition parameters was examined with X-ray texture analysis. As deposited films were analyzed by transmission electron microscopy and atomic force microscopy. All films showed a columnar film growth structure. The diameter of the columns increased with film thickness and could be related to the film in-plane orientation. The nucleation process was found to be polycrystalline and independent of the ion-beam assistance. At an early growth stage, a growth structure of [001] oriented columns emerges from the randomly oriented crystallites. The film in-plane texture forms in a competition of [001] oriented columns, where columns oriented with their [111] axis parallel to the impinging ion-beam dominate the film texture. The out-of plane growth orientation was found to depend on substrate temperature and laser energy density, while the ion-beam affects mainly the in-plane orientation. View full abstract»

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  • Melt growth and superconducting properties of textured Ag-YBa/sub 2/Cu/sub 3/O/sub 7/ conductors

    Page(s): 1483 - 1486
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    Textured Ag foils 200 /spl mu/m thick have been obtained after cold rolling and recrystallization at 800/spl deg/C with a reduction ratio of up to 95%. Subsequently, a thick layer of YBa/sub 2/Cu/sub 3/O/sub 7/ (20 /spl mu/m) has been deposited by screen printing, A directional solidification process under a temperature gradient with displacement velocity between 1 mm/h and 10 mm/h has been performed to induce a biaxial texture to the superconducting layer. This last treatment has been performed at low P(O/sub 2/) atmosphere and at maximum temperatures below 945/spl deg/C. The texture of the layers has been studied by X-ray diffraction, rocking curves and pole figures, whilst the critical currents have been measured inductively by SQUID magnetometry. The relationship between the in-plane crystalline orientation and the observed critical currents has been discussed. View full abstract»

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  • Magnetic field anisotropy of high critical current YBCO coated conductors

    Page(s): 1487 - 1489
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    High critical current (>100 A) YBCO thick films, or coated conductors, are being developed for superconductor applications. The critical current I/sub c/ of these materials exhibits a magnetic field dependence that depends on the angle of the applied field. Measurement of this anisotropy is critical to the development of high temperature superconductor applications. We have developed the capability to characterize the magnetic field anisotropy of large, high critical current YBCO superconductors as a function of angle. We have measured the magnetic field anisotropy of the critical current in the H/spl perp/I orientation of three samples in fields from 0 to 7 T and at temperatures from 75 K to 64 K. The results of these measurements characterize the field dependence of these materials and reveal performance issues of importance to applications. In contrast to previous measurements on thin films, which show that I/sub c/ for the H/spl par/c orientation has the strongest field dependence, we demonstrate that the intermediate angle of /spl sim/45/spl deg/ to the normal to the tape plane shows the greatest field dependence for these coated conductors on technical substrates. The field performance, anisotropy, and temperature dependence are discussed in relation to sample quality. View full abstract»

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  • Processing dependence of biaxial texture in yttria-stabilized zirconia by ion-beam-assisted deposition

    Page(s): 1490 - 1493
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    Biaxially textured yttria (8 mol%)-stabilized zirconia (YSZ) thin films were deposited on randomly oriented Hastelloy C and Stainless Steel 304 at room temperature as a buffer layer for subsequent deposition of oriented YBa/sub 2/Cu/sub 3/O/sub x/ films. The 0.16-1.3 /spl mu/m thick YSZ films were deposited by e-beam evaporation at rates of 1.2-3.2 /spl Aring//sec. Biaxially textured films were produced with an Ar/O/sub 2/ ion beam directed at the substrate during film growth. X-ray diffraction was used to study in-plane and out-of-plane orientation as a function of ion bombardment angle, film thickness, ion-to-atom flux ratio, and substrate material. In-plane and out-of-plane average-misorientation angles on these YSZ films that were deposited by ion-beam-assisted deposition were as low as 17 and 5.4/spl deg/, respectively, on as-received substrates. View full abstract»

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  • Axial strain dependence at 77 K of the critical current of thick YBaCuO films on Ni-alloy substrates with IBAD buffer layers

    Page(s): 1494 - 1497
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    The strain sensitivity of YBCO coated conductors has been investigated by measuring the critical current density J/sub c/ in self field at 77K, as a function of applied tensile strain. The YBCO coated conductor used an Inconel substrate. One side was coated with a biaxially textured YSZ buffer layer, using ion-beam-assisted-deposition (IBAD), and was subsequently coated with a 2.5 micron thick YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// layer by pulsed laser deposition (PLD). The superconductor was then coated with a silver cap layer. For the I/sub c/-strain measurements 78 mm long sections were cut from a 115 cm long length. This was previously produced to demonstrate the feasibility of long YBCO coated conductors using the IBAD process. At 77K up to 0.5% strain does not change J/sub c/ by more than 3% This strain dependence is better than the tensile stress dependence of J/sub c/ when samples are bent at room temperature. View full abstract»

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  • The microstructure of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// films and yttria stabilised zirconia buffer layers deposited on inclined Hastelloy substrates

    Page(s): 1498 - 1501
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    YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// films have been grown on polycrystalline metallic substrates using intermediate yttria stabilised zirconia (YSZ) buffer layers. The buffer layers were grown by pulsed laser deposition using the inclined substrate deposition technique, whereby the substrate is tilted so that the ablated species arrive under an oblique incidence angle. One of the consequences of the inclined geometry is the alignment of the buffer layer crystal grains within the plane of the film which enables the subsequent deposition of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// films With J/sub c/s of up to 10/sup 5/ A/cm/sup 2/. We present results showing that the optimum substrate inclination angle for the YSZ buffer layer deposition is around 55/spl deg/, and that the in-plane alignment improves linearly with film thickness. We also show transmission electron micrographs which demonstrate that grain sizes get larger and appear to be better aligned towards the buffer layer surface. We use these results to propose a mechanism by which texture occurs during inclined substrate deposition. The mechanism is based on three requirements inferred from our microstructural data: columnar growth, tilting of grains towards the incoming ablated species, and a preferred growth orientation normal to the substrate surface. View full abstract»

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  • YBCO films on metal substrates with biaxially aligned MgO buffer layers

    Page(s): 1502 - 1505
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    We successfully deposited high quality YBCO films on metal tapes with biaxially aligned MgO buffer layers. e-gun evaporation on inclined substrates with a very high deposition rate of up to 250 nm/min was used for the deposition of the buffer layers. The MgO layers are biaxially textured with an in-plane full width at half maximum of 80. The MgO [001]-axis is not parallel to the substrate normal but tilted significantly towards the deposition direction. YBCO films were deposited on ISD buffer layers by reactive thermal co-evaporation. The critical current density of the films was found to be anisotropic due to the tilt of the [001]-axis. Critical current densities up to 7.9/spl times/10/sup 5/ A/cm/sup 2/ at 77 K were achieved. View full abstract»

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  • Direct deposition of c-axis textured MBCO thick film on unoriented metallic substrate for the development of long superconducting tapes

    Page(s): 1506 - 1509
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    Direct peritectic growth (DPG) is a novel process in which textured YBCO thick films are deposited directly onto an unoriented silver alloy. No buffer layer is employed between the YBCO superconducting film and the silver alloy substrate. The textured YBCO grains have been obtained through peritectic solidification over a wide range of temperature and time. No observable reaction of the substrate was found with the YBCO melt at the maximum processing temperatures near the peritectic point (from 950/spl deg/C to 1030/spl deg/C). The transport J/sub c/ has reached a respectable value of 8/spl times/10/sup 4/ A/cm/sup 2/ at 77 K and in zero magnetic field. In this paper, we show that the DPG method is capable of producing highly textured YBCO thick films, which are scalable to long lengths with low cost. View full abstract»

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  • Cracking of rare earth barium cuprate films prepared by liquid phase epitaxy

    Page(s): 1510 - 1513
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    A high growth rate of REBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (RE=rare earth elements) superconducting films is achieved with liquid phase epitaxy. The occurrence of cracks is one of the major problems for applications of these thick films. To achieve crack free films, it is necessary to understand the formation of cracks in REBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// films. Investigations were carried out on YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// and (Y,Pr)Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// films on NdGaO/sub 3/ substrates and on new SrPrGaO/sub 4/ substrates with tetragonal K/sub 2/NiF/sub 4/ structure (space group I4/mmm). A thermodynamic model for understanding the crack spacing together with mechanical properties determined in melt textured YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// bulk samples was applied. View full abstract»

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  • Bench scale evaluation of batch mode dip-coating of sol-gel LaAlO/sub 3/ buffer material

    Page(s): 1514 - 1518
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    In a joint program between the University of Tennessee Space Institute (UTSI) and Oak Ridge National Laboratory (ORNL), thin films of lanthanum aluminate (LAO) were formed on [100] strontium titanate (STO) single crystals and on biaxially textured nickel by dip-coating from sol-gel precursors and then annealing. XRD texture measurements were used to evaluate coating parameters including substrate withdrawal speed, degree of hydrolysis, and thermal processing temperature, duration, and atmosphere. LAO films on the order of 1000 thick showed 100% biaxial epitaxy on STO single crystals but only about 50% in-plane epitaxy on nickel. An increase in substrate withdrawal velocity resulted in thicker films. On STO film texture degraded with increased film thickness, but on nickel this effect was not noted, being obscured as a result of the rather poor and variable texture of the nickel substrate used. LAO on STO texture was improved by increases, within the ranges investigated, in the degree of hydrolysis, and in the thermal processing time, temperature, and oxygen concentration. No impediments to production scale-up were found. View full abstract»

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  • High-T/sub c/ coated conductors-performance of meter-long YBCO/IBAD flexible tapes

    Page(s): 1519 - 1522
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    One meter long tapes based on 50-100 /spl mu/m thick by 1 cm wide nickel alloy substrates have been coated in a continuous process with a textured yttria-stabilized zirconia layer by ion beam-assisted deposition, followed by a 1-2 /spl mu/m thick layer of YBCO by pulsed laser deposition. The best result to date is a tape with a critical current (I/sub c/) at 75 K of 96 A over an 87 cm measurement length. The overall critical current density and engineering current density are 1 MA/cm/sup 2/ and 10 kA/cm/sup 2/, respectively. Using a special probe, individual I-V curves were generated for each centimeter of tape length in order to investigate longitudinal uniformity of the transport properties: the highest and lowest I/sub c/ values fall within a range of /spl plusmn/25%. View full abstract»

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IEEE Transactions on Applied Superconductivity contains articles on the applications of superconductivity and other relevant technology.

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Editor-in-Chief
Britton L. T. Plourde
Syracuse University
bplourde@syr.edu
http://www.phy.syr.edu/~bplourde