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Applied Superconductivity, IEEE Transactions on

Issue 2  Part 2 • Date June 1995

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Displaying Results 1 - 25 of 219
  • Advances in the development of silver sheathed (Bi,Pb)2223 composite conductors

    Page(s): 1145 - 1149
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    Significant advances have been made in the critical current density of the technologically interesting (Bi,Pb)2223 composite conductors. Engineering current density, J/sub e/, of 9100 A/cm/sup 2/, corresponding to a filament current density, J/sub c/, of 32600 A/cm/sup 2/ (77 K, self-field) has been achieved by increasing the fraction of oxide in the conductor and improving the thermomechanical processing of the conductor. The filament microstructure may be further optimized by decreasing the volume fraction of secondary phases and porosity. The strain tolerance of the higher oxide fraction conductors remains adequate for applications by increasing the number of filaments in the conductors. Composite tapes with twisted filaments have been produced that have promising electrical properties in applied magnetic fields.<> View full abstract»

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  • Critical current densities at 77 K and 4.2 K of Bi(2223) tapes prepared by cold and hot deformation

    Page(s): 1150 - 1153
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    Monofilamentary Bi(2223) tapes have been prepared by the Powder-In-Tube technique using various alternatives for the final thermomechanical processing. In particular, both cold and hot deformation processes were investigated and their critical current densities at 77 K and 4.2 K were measured. For long cold rolled Bi(2223) tapes, transport j/sub c/ values up to 30000 A/cm/sup 2/ were obtained at 77 K and 0T. The value of j/sub c/ was found to increase from 17000 A/cm/sup 2/ at the oxide center to 46000 A/cm/sup 2/ at the borders of the oxide layer. At 4.2 K and 28 T, j/sub c/ values of 45000 and 30000 A/cm/sup 2/ were measured for B parallel and perpendicular to the tape surface, respectively. The j/sub c/ (B) hysteresis was found to disappear at higher fields. The present state of hot deformed Bi(2223) tapes is presented. For rolling temperatures up to 850/spl deg/C, a maximum of j/sub c/ (77 K, 0T)=18000 A/cm/sup 2/ was observed at 800/spl deg/C, j/sub c/ being considerably lower for higher rolling temperatures. The results obtained so far show generally lower j/sub c/ values than for cold rolled tapes. This is essentially due to microcracks and to sausaging effects, which are more pronounced than for cold rolled tapes. For static hot deformation at 800/spl deg/C of short, pressed Bi(2223) tapes an enhancement of j/sub c/ (77 K, 0T) by 20% up to >40000 A/cm/sup 2/ was observed. In addition, the decrease of j/sub c/ for B perpendicular to the tape surface is less pronounced compared to cold deformed tapes.<> View full abstract»

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  • Progress towards a long length metallic precursor process for multifilament Bi-2223 composite superconductors

    Page(s): 1154 - 1157
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    A process based on metal precursors has been developed for fabricating 361-filament Bi-2223 oxide superconductor-silver composite tapes with oxide and whole wire critical current densities of 20.8 kA/cm/sup 2/ and 3.74 kA/cm/sup 2/ at 77 K over 85 m (1 /spl mu/V/cm criterion). Fabrication of approximately 50 m lengths for a cumulative 1 km yielded average oxide critical current densities of 15.2 kA/cm/sup 2/ and 11.9 kA/cm/sup 2/ using 1 /spl mu/V/cm and 10/sup -11/ /spl Omega/ cm criteria. Within tape I/sub c/ variability was less than 5% except for I/sub c/ drop-offs near the tape ends. The oxide superconductor exhibited a high degree of the required texture. A 1.12 T (at 4.2 K) instrumented magnet with a 2.5 cm bore was fabricated by a react- and-wind approach from the tapes and delivered to Oak Ridge National Laboratory for quench studies.<> View full abstract»

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  • Improved J/sub c/ property of Bi2223 tapes made using AgCu alloy-sheath doped with Ti, Zr, Hf or Au

    Page(s): 1158 - 1161
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    Bi2223 superconducting tapes have been prepared by the powder-in-tube technique using Ag-10at%Cu-xat%M (x=0-1.0, M=Ti, Zr, Hf or Au) alloy sheaths. The alloy-sheathed tape samples, prepared by repeating 2 or 3 times of sintering and cold pressing, showed high J/sub c/ values. The higher critical current densities, J/sub c/'s, 5-6/spl times/10/sup 4/A/cm/sup 2/, at 4.2 K, 14 T were obtained for the Ag-10at%Cu-(0.03-0.1at%Ti, 0.1at%Zr, 0.1at%Hf and 0.3at%Au) tape samples. Microstructural examinations of these samples revealed a modified Bi2223 grain structure at the sheath/core interface and also a denser and more aligned microstructure. X-ray diffraction analysis, vibrating sample magnetometer measurement and ac susceptibility studies seem to suggest an enhancement of the Bi2223 phase formation with high T/sub c/ and improved texture, resulting in higher J/sub c/.<> View full abstract»

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  • The influence of filament size and atmosphere on the microstructure and J/sub c/ of round multifilament Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ wires

    Page(s): 1162 - 1166
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    Round multifilament Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ wires having 37 and 259 filaments fabricated by the oxide-powder-in-tube method were given a step solidification partial melt heat treatment in air and oxygen atmospheres. Significant improvement in the critical current density (J/sub c/), as high as 1.65/spl times/10/sup 5/ A/cm/sup 2/ at 4.2 K zero field, was obtained for samples treated in pure oxygen versus air anneals. Moreover, as the filament size decreased the J/sub c/ increased. We discuss the development of 2212 microstructure and its dependence on filament size and heat treatment atmosphere in round multifilament 2212 wires.<> View full abstract»

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  • Effect of composition and oxygen content on the microwave properties of evaporated Y-Ba-Cu-O thin films

    Page(s): 1167 - 1172
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    Thin films of YBa/sub 2/Cu/sub 3/O/sub 7-x/ have been grown by electron beam evaporation of the metals in the presence of atomic oxygen, with small systematic variations in cation composition. Films grown close to the stoichiometric composition or with excess yttrium are smooth while those with excess barium are substantially rougher. The effect of these differences in cation composition on both microwave and dc properties is dominated by the associated large changes in film morphology. This determines the oxygenation state, and hence the electrical properties, of the superconductor both in the as-grown state and after annealing in a furnace or with atomic oxygen. For all films a strong correlation is found between penetration depth, resistivity and c-lattice parameter which all decrease with increasing oxygen content. In our standard growth regime and at higher oxygen contents the films are overdoped and T/sub c/ falls with increasing oxygen content.<> View full abstract»

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  • Effect of oxygen over-doping on T/sub c/ and R/sub s/ of YBCO films

    Page(s): 1173 - 1176
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    Data on bulk YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) have shown that optimum critical temperatures are obtained in material that has less than the maximum (stoichiometric) oxygen content, x=0. We have prepared films of YBCO that were over doped with oxygen and have measured their properties. In some of these films, T/sub c/'s were degraded to as low as 85 K and R/sub s/'s to >10 m/spl Omega/ (at 77 K and 10 GHz). Re-annealing at 450/spl deg/C at experimentally optimized oxygen pressures raised T/sub c/'s significantly in all cases but had only a marginal effect on R/sub s/ values. Large improvements in R/sub s/ were obtained in the films which initially had very high surface resistances only by annealing them at higher temperatures. Growth and annealing conditions are described by which YBCO films with T/sub c/'s of >90 K and R/sub s/'s of /spl les/0.5 m/spl Omega/ (at 77 K and 10 GHz) were prepared.<> View full abstract»

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  • Laser patterning of YBa/sub 2/Cu/sub 3/O/sub x/ thin films protected by in-situ grown SrTiO/sub 3/ cap layer

    Page(s): 1177 - 1180
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    We report our studies on laser processing techniques suitable for patterning of YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) thin films, as well as YBCO/SrTiO/sub 3/ bilayers, consisting of in-situ grown YBCO films with 100-nm-thick single-crystalline SrTiO/sub 3/ cap layers. The patterning is achieved through both laser inhibition, in which an intense, focused laser beam locally melts YBCO transferring it into an insulating glass-like material, and laser writing, based on a laser-controlled diffusion of oxygen in or out of the YBCO film. We have found that oxygen easily migrates through the SrTiO/sub 3/ layer, allowing to reversibly convert the underlying YBCO film between the superconducting and semiconducting (virtually insulating at low temperatures) phases. Using laser inhibition and writing, we were able to form in a single YBCO/SrTiO/sub 3/ sample well-defined regions of various electrical properties, showing that laser processing can be successfully used in patterning and/or electrical trimming of multilayered YBCO circuits. Aging studies, performed on an almost 2-years-old laser-written YBCO film, showed a very good, both structural and electrical stability of our laser-processed structures.<> View full abstract»

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  • Ion implantation in high temperature superconducting films

    Page(s): 1181 - 1184
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    Reactive ion implantation (RII) has been used to inhibit superconductivity in oxide superconductor materials. By introducing ions which are chemically reactive with oxygen into a high temperature superconductor (HTS) oxide film, the conductivity of the material may be inhibited by the interaction of the implanted ions with the oxygen in the oxide. Both Si and B ions, with doses ranging from 1/spl times/10/sup 15/-1/spl times/10/sup 17//cm/sup 2/, were implanted into epitaxial YBCO films with injection energies ranging from 20-180 keV, depending on the film thickness. The implanted ions do not alter the overall crystal structure of the HTS film, but do inhibit the electrical conductivity and diamagnetism. Multiple ion implantations have also been employed to achieve uniform ion distributions.<> View full abstract»

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  • High energy physics conductor scale-up progress of the Supercon artificial pinning center process

    Page(s): 1185 - 1188
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    The Supercon APC process is briefly reviewed. Process parameters requiring optimization for commercial production are discussed. Issues involved in successful monofilament and multifilament billet size scale-up the APC process for HEP composites, nominally 6 /spl mu/m filaments and composite diameters <1 mm, are presented. The Supercon APC composite piece length and mechanical properties are excellent. The present best composite J/sub c/ results are presented.<> View full abstract»

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  • First commercial application of NbTi superconductor employing artificial pinning centers

    Page(s): 1189 - 1192
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    Supercon has applied its artificial pinning center (APC) technology to develop a multifilamentary NbTi superconductor for MRI application. This technology is particularly well suited to large filament, low field use. The conductor microstructure and performance (e.g., critical current) are presented. The influence of conductor geometry (e.g., filament placement, spacing to diameter ratio) on filament quality is discussed. The conductor has been incorporated into Magnetic Resonance Imaging (MRI) magnets by GE Medical Systems, and the magnets performance is discussed.<> View full abstract»

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  • Some more experimental results on fine filamentary NbTi wires with Cu matrices alloyed with Mn, and Mn-Si

    Page(s): 1193 - 1196
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    In order to produce fine (1-10 /spl mu/m) NbTi multifilamentary superconducting strands, i.e. conductors used in AC applications, Cu alloys containing Mn and MnSi are used as interfilamentary matrix materials. Hardness of these alloys as a function of strain, filamentary spacing at which proximity coupling occurs, critical current density and filament-matrix interface reaction, have been studied. The information obtained will be useful in the determination of the design of fine NbTi multifilamentary superconducting wires and the thermomechanical processes to be used in their manufacture.<> View full abstract»

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  • Microstructural and compositional gradients in the filament-matrix region of Nb-Ti wire composites

    Page(s): 1197 - 1200
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    Transverse cross-sections of Nb-Ti wire composites after final /spl alpha/-Ti precipitation heat treatment (10-480hr/420/spl deg/C) were examined and analyzed in the filament-matrix region with scanning electron microscope-backscatter electron imaging (SEM-BEI) and electron micro probe analysis (EMPA). SEM-BEI micrographs were image analyzed to quantify the average effective /spl alpha/-Ti precipitate diameter, d*, and volume fraction of /spl alpha/-Ti as a function of distance into the filament. Cu concentration profiles were found in the same regions by EMPA. The compositional results show trace amounts of Cu (>0.1 at%) interdiffused up to 50 /spl mu/m into the Nb-Ti filaments. The interdiffused Cu at the interface increased /spl alpha/-Ti nucleation and thus increased /spl alpha/-Ti volume fractions by 50% relative to the nominally pure Nb-Ti at the center of the filament for short heat treatment times (30 hours of total heat treatment time).<> View full abstract»

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  • Critical current density and n-value of NbTi wires at low field

    Page(s): 1201 - 1204
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    The manufacturing process of NbTi wires for lower field applications is optimized concerning both the number of heat treatments and the final true strain, the strain of a wire from the wire diameter at the last heat treatment to the final diameter. The sample wires were made from Nb 54wt%Ti alloy and were manufactured to vary the number of heat treatments (0, 1, 2, and 3) and the final true strain (0 to 3). One of these samples, which had one heat treatment and drew with the final true strain of 0.33, achieved J/sub c/ of 3360 A/mm/sup 2/ and n-value of 111 at 3 T. This J/sub c/ is as good as a J/sub c/ of the wires made from conventional materials and this n-value is 3 times as large as the n-value of wires mentioned above. Furthermore, the n-value at 3 T and the minimum value of the cross-sectional area of each filament show a correlation coefficient of 0.73.<> View full abstract»

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  • Critical current limiting factors of hot isostatically pressed (HIPed) PbMo/sub 6/S/sub 8/ wires

    Page(s): 1205 - 1208
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    PbMo/sub 6/S/sub 8/ wires with a molybdenum barrier and a stainless steel matrix were hot isostatically pressed (HIP) at 990/spl deg/C and 1225/spl deg/C for 4 hours at 110 MPa. The critical current density, its distribution, as well as the ac-susceptibility were investigated. The higher the applied HIP temperature, the better the critical current density becomes. A comparison of inductive T/sub c/ transitions suggests that HIPing is able to considerably reduce the width of the transition. In addition, at 1225/spl deg/C, the T/sub c/ onset is shifted from 12.4 K to 14.2 K. The high field behavior of J/sub c/ strongly depends on the effective upper critical field which is essentially determined by grain boundaries. In a degraded wire sample, a qualitative correlation between effective upper critical field and the width of the inductive transition was found. This knowledge should allow to overcome the apparent limitation of J/sub c/ at high fields (2/spl times/10/sup 8/ Am/sup -2/ and 3/spl times/10/sup 8/ Am/sup -2/ at 20 T, 4.2 K and 1.8 K, respectively).<> View full abstract»

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  • Hot isostatic pressing of Chevrel phase bulk and hydrostatically extruded wire samples

    Page(s): 1209 - 1213
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    In order to lower final sintering temperatures for Chevrel phase (CP) wires, we have investigated low-temperature hot isostatic pressing (HIP'ing) of both bulk and wire samples. We have fabricated (Pb,Sn)-based Chevrel phase (CP) monofilament and 61 filament wires by hydrostatic extrusion of (Cu or Cu-Ni)/(Nb or V)/CP composites, followed by cold drawing. We have investigated the CP/barrier reaction during heat treatment, finding V is unsuitable, but Nb is suitable at these lower temperatures for prereacted Pb/sub 1-x/Sn/sub x/Mo/sub 6/S/sub 8/ cores. We prepared powders of the binary Chevrel phase Mo/sub 6/S/sub 8/ by acid leaching of Li/sub x/Mo/sub 6/S/sub 8/ and Ni/sub x/Mo/sub 6/S/sub 8/. We prepared bulk samples of PbMo/sub 6/S/sub 8/ and Pb/sub 1-x/Sn/sub x/Mo/sub 6/S/sub 8/ by HIP'ing mixtures of "Pb+Mo/sub 6/S/sub 8/" powders (in situ route) or by prereacting Pb, Sn and Mo/sub 6/S/sub 8/ powders before HIP'ing (prereacted route). The in situ powders were HIP'ed under different time-temperature-pressure conditions up to 12 h/600/spl deg/C/200 MPa, producing partially consolidated PbMo/sub 6/S/sub 8/ samples. Further HIP'ing of all samples at temperatures of 700, 800 and 1000/spl deg/C, 200 MPa pressure and times of 8 and 80 hours produced additional consolidation, up to 95% of full density. As the aggressiveness (temperature and time under pressure) of the HIP process increased, the density, hardness, critical temperature, and magnetization critical current density increased.<> View full abstract»

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  • Microstructures and properties of laser-ablated epitaxial Y-Ba-Cu-O thin films for electronic device applications

    Page(s): 1214 - 1217
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    A study of the microstructures and properties of a series of laser-ablated films of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// on [001] MgO with thicknesses of between 800 and 1900 nm is presented. Transmission electron microscopy has been used to reveal the orientation and defect microstructures of the films and it is shown that both the orientation and threading dislocation content change with deposit thickness. Measurements of surface resistance show no clear correlation with thickness whereas critical current density appears to decrease with increasing thickness. Possible relationships between the microstructures and properties are discussed.<> View full abstract»

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  • Thin film composites of Au and YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//

    Page(s): 1218 - 1221
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    We are using a novel bilayer deposition process to grow composite films of Au with YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//. The composites have well-separated regions of Au and YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//, and we see no evidence for structural or chemical degradation of the grains and grain boundaries. For composite films on MgO substrates, the transport properties indicate the presence of weakened superconductivity in the films. Composites on SrTiO/sub 3/ and LaAlO/sub 3/ do not show this as strongly. The MgO composites behave like arrays of Josephson junctions and show promise as materials for flux flow devices.<> View full abstract»

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  • YBa/sub 2/Cu/sub 3/O/sub 7-x/ 45/spl deg/ [001] tilt grain boundaries induced by controlled low-energy sputtering of MgO substrates: transport properties and atomic-scale structure

    Page(s): 1225 - 1228
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    Grain boundaries can act as weak links in the high T/sub c/ materials. If properly controlled, these grain boundaries can be used in various device applications. We have been able to reproducibly form 45/spl deg/ [001] tilt grain boundary junctions in YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films. The films were grown-on MgO substrates using a pre-growth substrate treatment. A low energy broad beam argon ion source was used to irradiate a select region of (100) MgO substrates. The film on the milled portion of the substrate grows predominantly with a grain orientation rotated 45 degrees about the c-axis with respect to the grain on the unmilled portion. Backscattered electron Kikuchi patterns have been used to confirm that the rotation occurs across the entire milled portion of the substrate. Transport properties of these films are discussed and related to high resolution electron microstructural and microchemical analyses of the grain boundaries. This technique has potential use in device applications as a method for controlled grain boundary engineering.<> View full abstract»

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  • Homoepitaxial growth of YBCO thin films an YBCO single crystals

    Page(s): 1229 - 1232
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    YBCO films were grown on [001] YBCO single crystal substrates using the off-axis RF magnetron sputtering method. The interface between the substrate and the film was observed using TEM. The crystal orientation of the film was found to be dependent on the growth temperature. C-axis oriented films with smooth interfaces and holes on their surfaces were obtained at 760/spl deg/C. A-axis oriented films grown at 580/spl deg/C had smooth surfaces, but the interface was rather poor. Lattice mismatches occurred at the interface due to deoxidization and oxidization of the substrate during the film growth-process.<> View full abstract»

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  • Effects of surface treatment of single-crystal MgO substrates on the growth and properties of YBa/sub 2/Cu3O/sub 7-y/ films

    Page(s): 1233 - 1236
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    The preferred orientation and the inplane alignment of YBa/sub 2/Cu/sub 3/O/sub 7-y/ (YBCO) thin films deposited on MgO [100] substrates by on-axis DC magnetron sputtering have been investigated. The deposition temperature highly influences the preferred orientation of films. Films were oriented with the a-axis perpendicular to the substrates for low temperature depositions and with the c-axis for high temperature depositions. In the c-axis oriented films, there exist YBCO grains with the a(or b)-axis parallel to MgO [100] and 4-5/spl deg/ -rotated ones. 45/spl deg/ -rotated grains exclusively grow under the conditions of higher temperatures and on the substrates treated by acid-etching. The volume ratio between both types of YBCO grains is strongly connected with critical current density, even in the c-axis oriented films.<> View full abstract»

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  • Growth optimization and characterization of a-axis oriented Y-Ba-Cu-O thin films on [100] LaSrGaO/sub 4/ substrates

    Page(s): 1237 - 1240
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    We have grown high quality a-axis oriented YBa/sub 2/Cu/sub 3/O/sub 7-x//PrBa/sub 2/Cu/sub 3/O/sub 7-y/ films on [100] LaSrGaO/sub 4/ substrates. We have optimized the crystalline orientation and the superconducting properties of our films. We have performed annealing studies on a- and c-axis films in vacuum and oxygen to compare the oxygen depletion of the films and found that T/sub c/ degradation of a-axis films is comparable to that of c-axis films. To further optimize the a-axis films for trilayer junction fabrication, we significantly reduced the surface roughness of the films by a gradual lowering of oxygen pressure during the deposition.<> View full abstract»

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  • Microstructure and properties of YBa/sub 2/Cu/sub 3/O/sub 7/ thin films grown on vicinal LaAlO/sub 3/ substrates

    Page(s): 1241 - 1245
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    Thin films of YBa/sub 2/Cu/sub 3/O/sub 7/ have been grown on vicinal LaAlO/sub 3/ substrates by pulsed-laser deposition. In most cases, the substrate surface, nominally [001], has been rotated /spl sim/6/spl deg/ about an axis parallel to the <110> direction. Films grown on these surfaces were found to have substantially improved properties compared to those obtained for films deposited on [001]-oriented substrates under equivalent conditions at our facility. The surface morphology of the films exhibited an elongated granular structure which differed markedly from the more equiaxed grain structure found in films grown on [001]-oriented substrates. Furthermore, this particular elongated morphology and improvement in properties seems to occur only for films deposited at higher laser energies (/spl sim/30J/cm/sup 2/).<> View full abstract»

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  • Recent advances in long length Bi-2223 HTS multifilamentary composite wire development

    Page(s): 1246 - 1250
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    Developing applications for HTS technology are now enabled by a new generation of superconducting wires that bring together the required electrical and mechanical properties in long lengths that are durable when exposed to practical application environments. Advances in the development and scale-up of long-length Bi-2223 HTS composite wire are reviewed. Powder-in-tube processing was used to produce multifilamentary tapes in continuous lengths up to 1 kilometer. Electrical performance and uniformity results are reported for the wire in 300 meter and 1 kilometer lengths. Mechanical and environmental durability performance results are reported for multifilament wire tapes being developed for react-and-wind cable application as well as for wind-and-react coil and magnet applications. The use of these wires in practical demonstration applications is also reported.<> View full abstract»

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  • Preparation and characterization of silver sheathed BSCCO-2223 tapes

    Page(s): 1251 - 1254
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    Critical current densities of 17000 A/cm/sup 2/ were achieved in short samples of Bi-2223/Ag tapes prepared by a conventional powder in tube technique. The preparation was varied to get an optimum grain size and texture of the microstructure. Microstructural examinations and inductive measurements of the transition temperature have been performed. The critical current and current-voltage characteristics have been studied in applied magnetic field up to 8 T and at temperatures between 4.2 K and 77 K. At temperatures close to 77 K and in fields up to 1 T the critical current density is strongly field dependent and obeys a potential law. At lower temperatures a quite different behavior is observed. In addition a small pancake-coil has been built by the wind & react method and tested at 77 K.<> 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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Britton L. T. Plourde
Syracuse University
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