The microstructural changes associated with the reduced dependence of critical current density (Jc) versus thickness of thick, epitaxial YBa2Cu3O7–δ (YBCO) films on rolling-assisted biaxially textured substrates (RABiTS) were investigated. Pulsed laser deposited YBCO films varying in thickness from 1.0 to 6.4 ?m on RABiTS with an architecture of Ni–3 at.% W/Y2O3/yttrium-stabilized-zirconia/CeO2/YBCO were prepared for cross-sectional transmission electron microscopy studies. Dramatic improvements in physical properties and microstructural quality were observed resulting from the use of Ni–3 at.% W substrates, which provided a sharper texture over earlier Ni substrates, and replacement of CeO2 with Y2O3 as the seed layer within the buffers. The YBCO films showed exceptional orientation up to 6.4 μm thickness, with no misoriented grains or dead layers observed and only limited reaction between the YBCO and CeO2 cap layer. The high quality of the films was also attributed in part to the formation of a tungsten oxide layer forming at the top of the Ni–3% W substrate, limiting the growth of deleterious NiO into the conductor.

The change in microstructure associated with the decrease in critical current density (Jc) of Yba2Cu3O7−δ (YBCO) films with increasing thickness was examined. Samples of pulse laser deposited YBCO films varying in thickness from 0.19 to 3.0 μm on rolling-assisted biaxially textured substrates with an architecture of CeO2/YSZ/CeO2/Ni were prepared by tripod polishing for cross-sectional electron microscopy. More randomly oriented grains in the upper portion of the YBCO film surface were observed with increasing film thickness, resulting in less cube texture. In addition, increases in mismatch across the boundaries of the c-axis grains with increasing time during deposition, along with the development of BaCeO3 and Y2BaCuO5 phases at the YBCO/CeO2 interface, contributed to the degradation of film properties. Surface outgrowths of the YBCO film were examined as well as the defect structures and second-phase formations within the films.

Superconducting Yba2Cu3O7−δ (YBCO) films with critical transition temperature Tc(0) of 90 K were fabricated via a fluorine-free, metal trimethylacetate based sol-gel route. Precursor films were spin-coated onto single-crystal (001) LaAlO3 (LAO) and (001) SrTiO3 (STO) substrates. Optimization of the burnout process resulted in films with excellent out-of-plane and in-plane texture. Transport critical current densities, Jc, of 1.6 and 1.1 MA/cm2 were obtained at 77 K in self-field on films grown on LAO and STO substrates, respectively. This is the first demonstration of high-Jc YBCO film fabrication using a fluorine-free, ex-situ process.

We investigated the influence of a chemisorbed S template with c(2 × 2) structure on the epitaxial growth of different oxide buffer layers on {100}〈100〉 Ni. The sulfur superstructure spontaneously forms on the Ni surface during the texturing anneal as a consequence of segregation. However, depending on the initial S bulk concentration and/or specific annealing conditions, the S layer can cover less than the entire substrate's surface. We show that an incomplete c(2 × 2) coverage causes degradation of the seed buffer layer texture as compared to the substrate texture. A simple step consisting of an H2S predeposition anneal can be used to control the superstructure coverage and optimize the seed layer texture.

We investigated the dependence of critical current density (Jc) on thickness of Yba2Cu3O7−δ (YBCO) films grown by pulsed laser deposition on (100) SrTiO3 (STO) and on rolling-assisted biaxially textured substrates (RABiTS). The thickness of YBCO films varied from 0.19 to 3 μm. The highest Jcs of 5.3 and 2.6 MA/cm2 at 77 K, self-field were obtained for 0.19-μm YBCO films on STO and RABiTS, respectively. Jc was found to decrease exponentially with YBCO thickness on both substrates. However, the results suggest different mechanisms are responsible for the Jc reduction in the two cases. On STO, growth of a-axis grains within c-axis films and broadening of the in-plane texture were observed in thick films. On RABiTS, degradation in cube texture as well as development of a porous surface morphology were found to correlate with film thickness.

Sol-gel processing of La2Zr2O7 (LZO) buffer layers on biaxially textured Ni–1.7% Fe–3% W alloy substrates using a continuous reel-to-reel dip-coating unit has been studied. The epitaxial LZO films obtained have a strong cube texture and uniform microstructure. The effects of increasing the annealing speed on the texture, microstructure, and carbon content retained in the film were studied. On top of the LZO films, epitaxial layers of yttria-stabilized zirconia and Ceria (CeO2) were deposited using rf sputtering, and YBa2Cu3Ox (YBCO) films were then deposited using pulsed laser deposition. Critical current densities (Jc) of 1.9 MA/cm2 at 77 K and self-field and 0.34 MA/cm2at 77 K and 0.5 T have been obtained on these films. These values are comparable to those obtained on YBCO films deposited on all-vacuum deposited buffer layers and the highest ever obtained using solution seed layers.

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.

Short segments of YBa2Cu3O7-y (YBCO) coated conductors were fabricated on rolling-assisted biaxially textured substrates (RABiTS) with a layer sequence of CeO2/YSZ/Ni using an ex situ BaF2 precursor process. Pulsed laser deposition (PLD) was used to deposit both YSZ and CeO2 layers. The YBCO films were grown using e-beam coevaporated Y–BaF2–Cu precursors followed by postannealing. An overall engineering current density, JE, of 28,000 A/cm2 and critical current, Ic, of 147 A/cm width at 77 K were achieved for a 1.6-μm-thick YBCO film. This result demonstrates the possibility of using both the ex situ BaF2 precursor approach and the RABiTS process for producing long lengths of high-JE coated conductors.

In order to develop an alternative buffer layer architecture using the sol-gel process to produce YBCO (YBa2Cu3O7-δ) coated conductors, Yb2O3 has been chosen as the candidate material. Buffer layers of Yb2O3 were epitaxially grown on biaxially textured-Ni (100) substrates by the sol gel process for the first time. The Yb2O3 precursor solution was prepared from an alkoxide sol-gel route in 2-methoxyethanol and was deposited on textured-Ni (100) substrates by either spin coating or dip coating methods. The amorphous film was then processed at 1160°C under flowing (96%)Ar/H2(4%) gas mixture for one hour. The Yb2O3 film exhibited a strong c-axis orientation on the Ni (100) substrates. The phi and omega scans indicated good in plane and out of plane orientations. The X-ray (222) pole figure showed a cube-on-cube epitaxy. High current YBCO films were grown on the Yb2O3 sol-gel buffered-Ni substrates.

Epitaxial YBa2Cu3O7-δ (YBCO) films were fabricated using laser ablation of YBCO onto rolling-assisted-biaxially-textured-substrates (RABiTS) at a temperature of 650°C. The configuration of the sample was YBCO/YSZ/CeO/Ni. The CeO2 and YSZ buffer layers were deposited using electron-beam evaporation and sputtering, respectively. Both of these techniques are considered to be industrially scalable. SEM images of the YBCO reveal a range of structures ranging from jumbled a-axis to dense c-axis morphologies depending upon the deposition conditions. X-ray θ-2θ scans show a similar c-axis dependence on the deposition conditions.

Much of the conductor development effort in the last decade has focused on optimizing the processing of (Bi, Pb)2Sr2Ca2Cu3Ox oxide-powder-in-tube conductors and (Bi, Pb)2Sr2CaCu2O8 (Bi-2212) and TlBa2Ca2Cu3Ox thick film conductors. It is demonstrated that in each of these conductors, critical current densities are dictated by the grain boundary misorientation distributions (GBMD's). Percolative networks of low-angle boundaries with fractions consistent with the active cross-sectional area of the conductor exist in each of these conductors. Further enhancements in the properties require increased numbers of small-angle grain boundaries. Given the processing methods used to fabricate these materials, no clear route employing a simple modification of the established processing method is apparent. To address this need, conductors with controlled or predetermined GBMD's are necessary. Development of biaxial texture appears to be the only possible way to increase the number of small-angle boundaries in a practical and controllable manner. We summarize in this paper recent results obtained on epitaxial superconducting films on rolling-assisted-biaxially-textured-substrates (RABiTS). This technique uses well established, industrially scalable, thermomechanical processes to impart a strong biaxial texture to a base metal. This is followed by vapor deposition of epitaxial buffer layers (metal and/or ceramic) to yield structurally and chemically compatible surfaces. Epitaxial YBa2Cu3O7–δ films grown using laser ablation on such substrates have critical current densities exceeding 106 A/cm2 at 77 K in zero field and have a field dependence similar to epitaxial films on single crystal ceramic substrates. Deposited conductors made using this technique offer a potential route for the fabrication of the next generation high temperature superconducting (HTS) wire capable of carrying high currents in high magnetic fields and at elevated temperatures.

A new technique, referred to as rolling-assisted-biaxially-textured-substrates (RABiTS) has recently been proposed by Goyal et al., to fabricate long-range, biaxially textured substrates with suitable metal/ceramic surfaces for epitaxial growth of electronic devices [1]. Using standard thermomechanical processing, long lengths of flexible, biaxially oriented substrates with smooth surfaces (rms∼50nm) are obtained [1]. Epitaxial metal and/or oxide layers which can serve both as a chemical as well as a structural buffer are deposited on the biaxially textured metal. The metal with a suitable set of epitaxial, multi-layers comprises the substrate which is expected to have many potential applications, including superconductivity, photovoltaics and ferroelectrics [1].

When high temperature superconductors are deposited on a set of epitaxial multilayers on biaxially textured RABiT substrates, extremely high critical current densities, approaching 106 A/cm2 at 77K have been obtained [2].

We report on the superconducting properties of TlBa2Ca2Cu3O9−y (Tl-1223) thick films grown on smooth and rough Ag substrates. Thallium-free precursor films of the type Ba2Ca2Cu3Ag0.37O7 were deposited on Ag substrates using a spray-pyrolysis technique followed by post-thallination in a two-zone furnace. X-ray diffraction (XRD) results showed the presence of c-axis aligned Tl-1223 films and some degree of local in-plane texture (often referred to as a colony microstructure). The microstructure of the Ag surface dictates the growth behavior of Tl-1223 films. The transport critical-current densities (Jc) for Tl-1223 films grown on smooth and rough Ag substrates were ∼ 65,000 A/cm2 and ˜ 37,000 A/cm2, respectively, at 77 K and zero field. The films grown on smooth Ag substrates were strongly linked and had good in-field properties with a Jc value of ∼104 A/cm2 at 77 K and 0.5 T.

The epitaxial growth of CeO2 on various (001) metal surfaces using pulsed-laser deposition is discussed. In particular, the growth of (001) CeO2 on (001) Pd, Ag, and Ni is described. Emphasis is given to the specific deposition conditions which successfully alleviate the formation ornative oxides at the metal/metal oxide interface. The control of the epitaxial relationships between the oriented oxides films and the underlying noble and oxidizing metal surfaces is addressed.

A detailed examination of the Y2BaCuO5 (211)/ YBa2Cu3O7−x (123) interface in several melt-processed 123 samples prepared using different methods was undertaken using analytical electron microscopy. It is found that there exists a significant increase in the a-b planar stacking fault density in 123, near the 211/123 interface. When viewed along [001], these faults appear as disks with diameter from a few to 30 nm and are bounded by dislocation loops. Most stacking faults are confined to the (001) basal plane. The size and density of defects around the 211 particles suggest that these defects could act as effective flux-pinning sites and may explain the observations of increased Jc with increasing volume fraction of 211 and a maximum in Jc when the applied field parallel to the c-axis.

We report on the epitaxial growth of superconducting molybdenum films on sapphire substrates. These films are to be etched into arrays of isolated cylinders, each 1–5μm in diameter. When placed in a magnetic field and biased at 0.95 Tc(H), the flux movement associated with their bolometric response to the energy deposited when radiation is absorbed will provide the basis of a gamma-ray detector.

The films were prepared by UHV sputter deposition at temperatures between 650° and 840°C. Besides standard XRD analysis the films were examined by TEM. An epitaxy orientation relationship with sapphire was found similar to that observed for niobium. Electrical conductivity measurements were made as a function of temperature down to Tc, the superconducting transition temperature, which ranged from below 0.35K to above 0.8K for films with a high room temperature resistance ratio (e.g. 300 in a 0.9pjn thick film). Results from a range of films will be presented and their Tc’s discussed.

Comparison of Auger electron spectra for intergranular and transgranular areas on fracture surfaces of sintered YBa2Cu3O7-x indicates the presence of a grain-boundary layer which is copper-rich and oxygen-poor compared to the bulk. This layer is believed to be an important factor limiting the critical current density in sintered material. The composition of the grain-boundary layer is strongly affected by small changes in sample composition, as might be expected for a line compound. These small deviations from the stoichiometric composition also affect the critical current density and the electrical resistivity above the transition temperature.

Microadditions of cerium retard annealing embrittlement in some but not all metallic glass compositions in the FeBSi system. Effects on embrittlement of doping with both cerium and oxygen have been determined for a series of compositions, FexB13 Si87-x. For X > 80, cerium retards annealing embrittlement and oxygen promotes it, suggesting that the beneficial effect of cerium additions results from gettering of impurities. The results indicate that for those compositions in the FeBSi system with the highest values of the saturation magnetization, Ms, microadditions of cerium can prevent annealing embrittlement until the onset of crystallization.

The addition of cerium in parts—per—million quantities has been shown to be effective in inhibiting the annealing embrittlement of melt—spun amorphous ribbons [1]. The effects of cerium doping on magnetic domain structures are reported in this paper. Domain structures have been observed using the Bitter colloid technique on the free surfaces of asquenched ribbons, as well as on both surfaces of ribbonswhich have been thinned by electropolishing. In the binary and quaternary alloys, the optimum (in terms of mechanical properties) cerium content gives ribbons which are apparently free of quenched—in stresses, since they lack the commonly observed “maze domains” which are found for both undoped and excessively doped ribbons. In contrast, the ternary alloy, which shows little decrease in annealing embrittlement versus doping, is free of maze domains in the as—quenched condition, with or without doping. The effect on the former two alloys is interpreted in terms of enhanced stress—relief during the quench.

The crystallization of rapidly solidified Zr-Ni metallic glasses has been studied by differential scanning calorimetry (DSC), x-ray diffraction (XRD), and transmission electronmicroscopy (TEM). Evidence has been found for a metastable phase which is the first crystalline phase to form upon heating in compositions of 57 to 63.2 at. % Zr. This phase seems to be more easily formed and is most stable in the region of 58 to 59 at. % Zr. Uponsubsequent heating to higher temperatures, the metastable phase transforms to the equilibrium phases ZrNi and Zr2Ni. The relationship of this new phase to phase separation at the eutectic composition of 63.5 at. % Zr is discussed in support of the conclusions drawn from low temperature specific heat studies reported previously [1,2].