Epitaxial thin films of Yba2Cu3O7 (YBCO) have been deposited and patterned on (100) SrTiO3 and (110) NdGaO3 substrates. Wet etchants used in conventional photolithography react too quickly with YBCO thin films, resulting in undercutting of patterned structures. We have implemented a technique to pattern thin lines from films without wet or dry etching. Chromium is evaporated onto the substrates and subsequently patterned. YBCO is then deposited by pulsed laser deposition, which results in an epitaxial YBCO film on patterned areas and randomly oriented YBCO deposited on chromium. An annealing step is required for the chromium to diffuse through the undesired YBCO in order to render those sections insulating. YBCO lines patterned with this technique exhibit resistivity and critical temperatures similar to those of the unpatterned films. As we decrease the width of the YBCO lines, the effect of the edges, where there is chromium-reacted material, on transport becomes more pronounced. The resolution of the patterning technique and the profile of superconducting versus non-superconducting materials at the edges is presented.

We report the feasibility of room temperature scanning laser microscopy (RTSLM) for the study of high temperature superconducing films. RTSLM images from SmBa2Cu3O7 and how that the ac–voltage response exists only in the section of the bridge where the transport current produces a voltage drop. A photolithographically defined 60 μm × 60 μm void in a 300 μm–wide bridge was clearly visible in a RTSLM image giving the spatial resolution smaller than 60 μm. In addition, the void disturbs the transport current distribution beyond itself generating an elongated shape void of 64 μm × 85 μm with the longer side along the direction of current flow in the RTSLM image. Our results indicate that the RTSLM is a useful tool to investigate the transport current distribution in high temperature superconductors.

The current protocol for processing (Bi,Pb)2Sr2Ca2Cu3O10-x (Bi-2223) multifilamentary tapes involves the in situ formation of the primary phase from a suitable mixture of precursor phases. As such, the developments during the first few minutes of heat treatment determine to a large extent the efficiency of primary phase development, competing secondary phase development, texture evolution, and grain-to-grain connectivity. This work documents the development of the liquid phase, secondary phases, defects which may affect alignment and reaction kinetics, and the precipitation of Bi-2223 from the liquid phase.

Bi-2212 precursor films were deposited on both sides of polycrystalline Ag tapes by electrodeposition. After a melt-solidification process in flowing oxygen atmosphere, c-axis textured Bi-2212 films with Jc( 0T, 4.2K) up to 820,000 A/ cm2 were obtained. A post annealing in flowing nitrogen at 475°C for 25 minutes increased Tc from 72 K to 92 K, and Jc(H=0T) > 17, 000A/ cm2 was observed at 60 K. No scaling behavior of the pinning force was observed, indicating more than one pinning mechanism in thus obtained Bi-2212/Ag tapes.

Disk-shaped samples of REBa2Cu3Oy ( RE123, RE = Y, Ho ) with 40%-by-molar RE2BaCuO5 (RE211, same RE of RE123 ) were melt-solidified without seeding under various magnetic fields (μ0Ha = 0 ˜ 8 T) and at various cooling rates ( Cr = 5.0, 10.0°C/h) in ambient atmosphere. Crystal alignment was evaluated by the X-ray diffraction, magnetization measurement using a SQUID magnetometer and observation of microstructure using a scanning electron microscope and a polarizing microscope. The melt grown RE123 crystals were c-axis-aligned under magnetic fields parallel to the applied field, (Ha), while the effect of alignment were systematically changed by the conditions of cooling rate and RE elements and the magnitude of Ha. The best c-axis-aligned sample showed that the value of anisotropy ( where the ratio of ΔMH//Ha /ΔMH⊥Ha) was approximately 20 at 85K and at μ0H = 0.3 T for the condition of RE = Y, Cr = 5.0°C/h, μ0Ha = 8 T.

The influence of lateral critical current density (Jc) distributions on AC transport losses in self-fields at 77 K have been investigated on the Ag-sheathed (Bi, Pb)-2223 multifilamentary tapes with different filament arrangements. The trapped magnetic field distributions in a remanent state on the tape surface measured by a scanning Hall sensor depend on the filament arrangements and gradually deviate from the calculation results of magnetic profile without any Jc variations in their cross sections. The transport loss values are strongly influenced from the filament arrangements in each tape, although the main contribution to the losses comes by the hysteresis loss in the superconductor. These results are explained by the calculation results of the shape of field-free core and flux-penetration-regions, varying with filament arrangements and local Jc distributions along a width direction.

The interplay of melting equilibria and reaction kinetics is important during formation of the Ba2YCu3O6+x (Y-213) phase from starting materials in the quaternary reciprocal system Ba,Y,Cu//O,F. For experimental investigation of the process we used a combination of differential thermal analysis (DTA) for study of melting equilibria, and in-situ high-temperature x-ray diffraction (HTXRD) for study of the phase formation and reaction kinetics. DTA investigation of compositions spaced along compositional vectors extending from the oxide end to the fluoride end of the reciprocal system have given evidence of low melting liquids (∼600 °C) near the fluorine-rich end. Work is continuing to determine whether similar thermal events observed in the interior of the system also indicate low temperature liquids, and on the extent to which low-melting liquids could be involved in Y-213 phase formation. HTXRD investigations have been initiated on the conversion of 0.3 μm and 1.0 μm thick BaF2-Y-Cu precursor films to Y-213 in the presence of water vapor. Preliminary results indicated that the thickness of film has a strong influence on the texture of the Y-213 film: a 0.3 μm film showed mainly (001) texture, whereas a 1.0 μm film showed a greater volume fraction of (h00) texture. While the HTXRD method cannot directly reveal the presence of liquid, we are working to combine DTA and HTXRD data for a unified picture of Y-213 phase formation during the “BaF2 ex-situ” process for coated-conductor fabrication.

Inclined substrate deposition (ISD) offers the potential for rapid production of high-quality biaxially textured buffer layers suitable for YBCO-coated conductors. We have grown biaxially textured MgO films by ISD at deposition rates of 20–100 Å/sec. Columnar grain structures with a roof-tile-shaped surface were observed in the ISD-MgO films. X-ray pole figure analysis revealed that the (002) planes of the ISD-MgO films are titled at an angle from the substrate normal. A small phi-scan full-width at half maximum (FWHM) of ≈9° was observed on MgO films deposited at an inclination angle of 55°. YBCO films were also grown on ISD-MgO-buffered Hastelloy C276 substrates by pulsed laser deposition. We obtained a critical current density of ≈2 × 105 A/cm2 at 77 K in self-field on 0.5-μm-thick, 0.5-cm-wide, 1-cm-long samples. This work has demonstrated that biaxially textured ISD MgO buffer layers deposited on metal substrates are promising candidates for fabrication of high-quality YBCO-coated conductors.

The fabrication of bulk, stoichiometric MgB2wires is a challenge because of the difficulties associated with the volatility and reactivity of magnesium and the brittleness of MgB2. Metal-clad processing of MgB2is a convenient, practical method of overcoming these problems. With such a fabrication approach, iron-clad MgB2superconductor wires exhibiting desirable characteristics with the transport Jcof ∼105 A/cm2at 4.2K have been obtained. In this paper, understanding of the composite wire structures, effect of processing parameters, grain boundary characteristics, and critical current bahavior of the MgB2wires will be described.

We have used a low temperature magnetic imaging system to determine current pathways in 5 cm long “good” and “bad” regions of a 1-cm-wide YBa2Cu3O7-δ coated conductor. The good and bad regions were identified with 4 point probe measurements taken at 1 cm intervals along the tape length. The current density map from the good region showed the expected edge peaked structure, similar to that seen in previous work on high quality test samples grown on single crystal substrates. The structure was also consistent with theoretical understanding of thin film superconductors where demagnetizing effects are strong. The maps from the bad region showed that the current was primarily confined to the right half of the sample. The left half carried only a small current that reached saturation quickly. Effectively halving the sample width quantitatively explains the critical current measured in that section. Spatially resolved x-ray analysis with 1 mm resolution was used to further characterize the bad section and suggested an abnormally large amount of a-axis YBCO present. This may be the result of non-uniform heating leading to a low deposition temperature in that area.

Three types of metastable modulations in Ru-based superconductor RuSr2Gd1.4Ce0.6Cu2O10-δ are observed by electron diffraction at room temperature and reported in this paper. The modulations are sensitive to the irradiation of the electron beam and the sample storage time. Having the tetragonal symmetry (I4/mmm) with a=0.384nm, c=2.864nm, the structure of RuSr2Gd1.4Ce0.6Cu2O10-δ?resembles that of YBa2Cu3O7-δ by inserting a fluorite type Gd1.4Ce0.6O2 layer instead of the Y layer and Ru ions residing in the Cu(1) site. In this compound, superconductivity is confined to the CuO2 layer while magnetism stems from the RuO2 layer. The metastable modulations display the interaction between the two layers from the structural point of view. The results suggest that although, superconductivity and magnetism are decoupled from each other in the unconventional superconductor, the effect may be limited by metastable lattice modulation.

A low-cost, non-vacuum reel-to reel dip-coating system has been used to continuously fabricate epitaxial Gd2O3 buffer layers on mechanically strengthened, biaxially textured Ni- (3at.%W-1.7at%Fe), defined as Ni-alloy, metal tapes. X-ray diffraction analysis of the seed Gd2O3 layers indicated that well textured films can be obtained at processing temperatures (Tp) between 1100 and 1175°C. Processing speed did not significantly affect the crystalline quality of the Gd2O3. Scanning electron microscopy revealed a continuous, dense and crack-free surface morphology for these dip-coated buffers. The Gd2O3 layer thickness led to remarkable differences in the growth characteristics of the subsequent YSZ and CeO2 layers deposited by rfmagnetron sputtering. Epitaxial YBCO films grown by pulsed laser deposition on the short prototype CeO2/YSZ/Gd2O3/Ni-(3at%W-1.7at%Fe) conductors yielded self-field critical current densities (Jc) as high as 1.2×106 A/cm2 at 77 K. Pure Ni tapes were used to asses the viability of dip-coated buffers for long length coated conductor fabrication. The YBCO films, grown on 80 cm long and 1 cm wide CeO2/YSZ/Gd2O3 buffered Ni tapes by the industrially scalable ex-situ BaF2 precursor process, exhibited end-to-end self-field Jc of 6.25×105 A/cm2 at 77 K.

Currently, due to simultaneous large area coating thermal evaporation (TE) allows the highest YBa2Cu3O7 (YBCO) volume deposition rates among various coating techniques. The simultaneous large area deposition translates into long length when the deposition area is closely filled up with metal tape. On short RABiTS samples thermal evaporation has already established critical current densities in excess of 1 MA/cm2 at 77K. Recently, the deposition technique has been scaled up using a multi-turn tape winder for a simultaneously coatable length of 4 meters of 1 cm wide tape. The reel to reel tape deposition system is designed for long term operation based on a vapor composition control by atomic absorption spectroscopy and in situ refillable evaporation sources. In the initial setup phase the system has been able to reproduce the above results on small samples. The first results on continuously moving tape substrate coating up to a length of several meters will be reported.