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Diffuse elastic neutron scattering measurements have confirmed that AgSbTe2 has a hierarchical structure, with defects on length scales from nanometers to microns. While scattering from this mesoscale structure is consistent with previously proposed structures in which Ag and Sb order on a NaCl lattice, more diffuse scattering from nanoscale structures suggests a structural rearrangement in which hexagonal layers form a combination of (ABC), (ABA), and (AAB) polytypes. Consequently, the AgCrSe2 structure is the best-fitting model for the local atomic arrangements.

The pyrochlore Lanthanum Zirconium Oxide, La2Zr2O7 (LZO), has been developed as a potential replacement barrier layer in the standard RABiTS three-layer architecture of physical vapor deposited CeO2 cap/YSZ barrier/Y2O3 seed on Ni–5%W metal tape. The main focus of this research is to ascertain whether: (i) we can further improve the barrier properties of LZO; (ii) we can modify the LZO cation ratio and still achieve a high level of performance; and (iii) it is possible to reduce the number of buffer layers. We report a systematic investigation of the LZO film growth with varying compositions of La:Zr ratio in the La2O3–ZrO2 system. Using a metal–organic deposition (MOD) process, we have grown smooth, crack-free, epitaxial thin films of LaxZr1−xOy (x = 0.2–0.6) on standard Y2O3 buffered Ni–5W substrates in short lengths. Detailed XRD studies indicate that a single epitaxial LZO phase with only (0 0 1) texture can be achieved in a broad compositional range of x = 0.2–0.6 in LaxZr1−xOy. Both CeO2 cap layers and MOD–YBCO films were grown epitaxially on these modified LZO barriers. High critical currents per unit width, Ic of 274–292 A/cm at 77 K and self-field were achieved for MOD–YBCO films grown on LaxZr1−xOy (x = 0.4–0.6) films. These results indicate that LZO films can be grown with a broad compositional range and still support high performance YBCO coated conductors. In addition, epitaxial MOD LaxZr1−xOy (x = 0.25) films were grown directly on biaxially textured Ni–3W substrates. About 3 μm thick YBCO films grown on a single MOD–LZO buffered Ni–3W substrates using pulsed laser deposition show a critical current density, Jc, of 0.55 MA/cm2 (Ic of 169 A/cm) at 77 K and 0.01 T. This work holds promise for a route for producing simplified buffer architecture for RABiTS based YBCO coated conductors.

Difficult nucleation of β-Sn during solidification of tin and tin-based lead-free solder alloys can result in high degrees of undercooling of the liquid prior to solidification. The undercooling can produce solder joints with large grains, anisotropic behavior, and undesirable mechanical properties. This paper describes our examination of the amount of undercooling of tin on both graphite (non-wetting) and copper (wetting) surfaces using in situ x-ray diffraction. The microstructure was further characterized by optical microscopy, scanning electron microscopy, and electron backscattering diffraction imaging microscopy. Undercoolings as high as 61°C were observed for Sn solidified on graphite, while lower undercoolings, up to 30°C, were observed for Sn solidified on copper. The microstructure of the high purity Sn sample solidified on graphite showed very few grains in the cross-section, while the commercially pure Sn sample solidified with only one grain and was twinned. Tin solidified on copper contained significant amounts of copper in the tin, intermetallic phase formation at the interface, and a eutectic microstructure.

The dependence of the critical current density (Jc) on the orientation of an applied magnetic field was studied for a prototype (Gd,Y)Ba2Cu3O7−x (GdYBCO) coated conductor fabricated by MOCVD on an IBAD-MgO template. Additional rare-earth cations (Y and Gd) and Zr were incorporated into the superconducting film to form (Y,Gd)2O3 and BaZrO3 nanoparticles extended nearly parallel to the a–b planes and to the c-axis, respectively, to enhance the flux pinning. In-field measurement of Jc was carried out with electrical current flowing either along or perpendicular to the longitudinal axis of the tape, while a maximum Lorentz force configuration was always maintained. Details in the angular dependence of Jc were related to the unique structure of the film, specifically the tilt in the GdYBCO lattice and the tilts in the extended (Y,Gd)2O3 and BaZrO3 nanoparticles. XRD and TEM were used to study the structure of the coated conductor. The effect of the misalignment between the external field H and the internal field B on the angular dependence of Jc is discussed.

We have developed a simplified buffer layer architecture for the rolling-assisted biaxially textured substrates (RABiTS) template approach. The overall purpose of this research is to enable potentially a low-cost, high throughput and high yield manufacturing processes for buffer fabrication and to gain fundamental understanding of the growth of buffer layers for RABiTS templates. This understanding is critical to the development of a reliable, robust, and long-length manufacturing process for second generation wires. In this study, efforts are being made to either reduce the number of vacuum deposited layers or to replace one or more of these vacuum deposited layers with a solution based layer. We have chosen Gd2O3 - ZrO2 system as a potential barrier layer for this study. We have deposited epitaxial Gadolinia Stabilized Zirconia (GSZ) (Zr1-xGdxOy; x = 0-1) films on 30-nm thick e-beam evaporated Y2O3 seeded Ni-W (3 at. %) (Ni-3W) substrates using a metal-organic decomposition (MOD) process. Detailed X-ray studies indicated that all of the MOD-GSZ layers were cube textured and both in-plane and out-of-plane lattice parameters increases linearly with increasing the Gd content. We have also developed process conditions for reactively sputter deposited epitaxial Gd2Zr2O7 (Gadolinium Zirconium Oxide (GZO); Zr1-xGdxOy (x = 0.5)) films on the e-beam evaporated Y2O3/Ni - 3W substrates. YBCO films with a critical current density Jc of 2.14 times 106 A / cm2 and 1.4 times 106 A / cm2 at 77 K and self-field were grown on the newly developed architectures of Gd2Zr2O7/Y2O3/Ni - 3W and Zr1-xGdxOy (x = 0.2)/Y2O3/Ni - 3W substrates, respectively using a pulsed laser deposition (PLD) process. This work promises a route for producing cost-effective simplified buffer architectures for the RABiTS-based YBCO coated conductors.

Two different types of defect structures have been identified to be responsible for the enhanced pinning in metal organic deposited YBCO films. Rare earth additions result in the formation of nanodots in the YBCO matrix, which form uncorrelated pinning centers, increasing pinning in all magnetic field orientations. 124-type intergrowths, which form as laminar structures parallel to the ab-plane, are responsible for the large current enhancement when the magnetic field is oriented in the ab-plane. TEM studies showed that the intergrowths emanate from cuprous containing secondary phase particles, whose density is partially controlled by the rare earth doping level. Critical process parameters have been identified to control this phase formation, and therefore, control the f 24 intergrowth formation. This work has shown that through process control and proper conductor design, either by adjusting the composition or by multiple coatings of different functional layers, the desired angular dependence can be achieved.

The development of biaxially textured, second-generation, high-temperature superconducting (HTS) wires is expected to enable most large-scale applications of HTS materials, in particular electric-power applications. For many potential applications, high critical currents in applied magnetic fields are required. It is well known that columnar defects generated by irradiating high-temperature superconducting materials with heavy ions significantly enhance the in-field critical current density. Hence, for over a decade scientists world-wide have sought means to produce such columnar defects in HTS materials without the expense and complexity of ionizing radiation. Using a simple and practically scalable technique, we have succeeded in producing long, nearly continuous vortex pins along the c-axis in YBa2Cu3O7?? (YBCO), in the form of self-assembled stacks of BaZrO3 (BZO) nanodots and nanorods. The nanodots and nanorods have a diameter of ~2?3?nm and an areal density ('matching field') of 8?10?T for 2?vol.% incorporation of BaZrO3. In addition, four misfit dislocations around each nanodot or nanorod are aligned and act as extended columnar defects. YBCO films with such defects exhibit significantly enhanced pinning with less sensitivity to magnetic fields H. In particular, at intermediate field values, the current density, Jc, varies as Jc~H??, with ?~0.3 rather than the usual values 0.5?0.65. Similar results were also obtained for CaZrO3 (CZO) and YSZ incorporation in the form of nanodots and nanorods within YBCO, indicating the broad applicability of the developed process. The process could also be used to incorporate self-assembled nanodots and nanorods within matrices of other materials for different applications, such as magnetic materials.

Implementation of improved processing for BaF/sub 2/ ex situ YBCO coatings from e-beam evaporated precursors enables faster conversion with rates up to 12 /spl Aring//s and critical currents I/sub c/ at 77 K greater than 350 A/cm-width on a RABiTS template. Details of the faster processing are described and compared to an earlier slower process. A linear relation between I/sub c/ and YBCO layer thickness provides evidence of new opportunities to further improve I/sub c/.

A novel buffer layer architecture consisting of LaMnO3/MgO/TiN is proposed as a suitable structural and chemical template for the epitaxial growth of high-Tc superconductors on Cu metal surfaces. For the first time, high Jc values are reported for YBCO films grown by laser ablation on (001) Cu single crystals, textured Cu surfaces and textured Cu?48%?Ni?1%?Al alloys, without intervening metal coatings. The Jc for single-crystal-like substrates is as high as 3.5?MA?cm?2 and values of 2?MA?cm?2 were obtained on the Cu?alloy tape substrates.

In situ X-ray diffraction has been used to study the conversion of ∼3000 A thick, evaporated barium fluoride precursor films to YBCO on buffered metal substrates for a range of conversion time, ramp rate, water vapor pressure, oxygen pressure, and temperature. All films were taken from the same continuously processed tape. Critical current densities as high as 1.34 MA/cm 2 have been obtained for a precursor reaction rate of 2.0 A/s. Higher reaction rates (up to 17 A/s) lead to lower critical current densities and incompletely developed YBCO. The reaction rate increases with increasing P H 2 O , increasing T , and decreasing P O 2 . The reaction rate increases linearly with increasing P H 2 O for the range of pressures used here (0.0125–5.0 mTorr). The formation of non-epitaxial YBCO is generally associated with lower T and higher reaction rate, whereas the formation of barium cerate, which results from a reaction of the precursor and the CeO 2 -capped substrate, is generally associated with higher T and lower reaction rate. General trends in the formation of crystalline phases during conversion may serve as a baseline for development of higher rate conversion processing for thicker, higher performance YBCO.

Second-generation coated conductor composite HTS wires have been fabricated using a continuous reel-to-reel process with deformation-textured Ni–W substrates and a metal-organic deposition process for YBa2Cu3O7−x. Earlier results on 1 m long and 1 cm wide wires with 77 K critical current performance greater than 100 A cm−1 width have now been extended to 7.5 m in length and even higher performance, with one wire at 132 and another at 127 A cm−1 width. Performance as a function of wire length is remarkably uniform, with only 2–4% standard deviation when measured on a 50 cm length scale. The length-scale dependence of the deviation is compared with a statistical calculation.

Fabrication of a biaxially textured, strengthened Ni substrate with small alloying additions of W and Fe is reported. The substrates have significantly improved mechanical properties compared to 99.99% Ni and surface characteristics which are similar to that of 99.99% Ni substrates. High quality oxide buffer layers can be deposited on these substrates without the need for any additional surface modification steps. Grain boundary misorientation distributions obtained from the substrate show a predominant fraction of low-angle grain boundaries. A high critical current density, J c , of 1.9 MA/cm 2 at 77 K, self-field is demonstrated on this substrate using a multilayer configuration of YBCO/CeO 2 /YSZ/Y 2 O 3 / Ni–3at.%W–1.7at.%Fe. This translates to a I c /width of 59 A/cm at 77 K and self-field. J c at 0.5 T is reduced by only 21% indicating strongly-linked grain boundaries in the YBCO film on this substrate.

A reel-to-reel tape handler mounted on a four-circle diffractometer is used to provide a characterization by X-ray diffraction of the entire 1 m length of a YBa2Cu3O7/CeO2/YxZr1−xO2/CeO2/Pd/Ni (YBCO/CeO2/YSZ/CeO2/Pd/Ni) tape. Cube-textured Ni was formed by rolling and annealing; epitaxial CeO2/YSZ/CeO2/Pd buffer layers were deposited by reactive sputtering; YBCO was converted ex situ from Y, BaF2, and Cu codeposited by e-beam evaporation. Rocking curve FWHM (mean±standard deviation) for 95 segments of 1 cm length are: YBCO (0 0 5)=6.2±0.5° , YSZ (0 0 2)=10.4±0.4° , and Ni (0 0 2)=7.6±0.3° . φ scan FWHM are: YBCO (1 1 3)=9.6±0.4° , YSZ (1 1 1)=13.0±0.4° , and Ni (1 1 1)=10.6±0.4° . Greater than 95% of the tape at each point is cube textured from Ni to YBCO. The critical current density Jc is 0.36±0.04 MA/cm2 at 77 K and is inversely correlated with the rocking curve FWHM. Calculations suggest that Jc might be increased by a factor of 2.1 by producing a sharper texture and that the uniformity of the texture will support scaling to kilometer lengths.

Low-cost, non-vacuum bulk solution technique has been developed to deposit epitaxial Gd 2 O 3 and La 2 Zr 2 O 7 (LZO) buffer layers directly onto both textured Ni and mechanically strengthened biaxially textured Ni–W(3 at.%)–Fe(1.7 at.%) (hereafter referred to as Ni–W) substrates. A reel-to-reel continuous dip-coating unit was used to produce meter lengths of highly textured, crack-free Gd 2 O 3 and LZO buffers on Ni and Ni–W tapes. Auger electron spectroscopy analysis of the textured Ni–W substrates indicated the presence of sulfur segregation to the surface, which possibly facilitated the growth of solution seed layers directly on Ni–W substrates. On dip-coated seed layers, a reel-to-reel sputtering unit was used to deposit epitaxially 200 nm thick YSZ layers followed by 10 nm thick CeO 2 to complete the RABiTS architecture. Pulsed laser deposition was used to grow YBa 2 Cu 3 O 7− δ (YBCO) films on these tapes in short lengths. YBCO films with J c values of 1.2×10 6 and 1.9×10 6 A/cm 2 at 77 K were obtained on Gd 2 O 3 and LZO buffered Ni–W substrates, respectively. YBCO films grown by ex situ BaF 2 precursor process on 80 cm long, 1 cm wide CeO 2 /YSZ/Gd 2 O 3 /Ni tapes exhibited end-to-end J c of 6.25×10 5 A/cm 2 at 77 K and self-field. This demonstrates that the solution layers provide a very good crystallographic template for the growth of high current density YBCO films, with performance approaching that of vacuum-deposited seed layers.

Progress made in the fabrication of rolling assisted biaxially textured substrates (RABiTS) and epitaxial deposition or formation of HTS on such substrates is reported. Significant progress has been made in understanding the role of meso-scale defects such as grain boundaries on long-range current flow of HTS conductors made using the RABiTS approach. Both experimental and theoretical calculations suggest that in well-textured samples these commonly present defects do not provide an intrinsic barrier to current flow in long-length conductors. Significant progress has also been made in the reel-to-reel deposition of oxide buffer layers and in the fabrication of long-length superconductors using the ex situ BaF 2 technique. Finally, non-magnetic, mechanically strengthened, biaxially textured metal templates have been fabricated with high quality oxide buffer layers. Epitaxial formation of YBCO on such substrates yields critical current densities over 1 MA/cm 2 at 77 K, 0 T.

Solution-based techniques have been examined as potential low-cost processes for manufacturing YBCO coated conductors. YBCO films prepared from metal trifluoroacetate precursors have achieved performance levels equaling or exceeding that of vapor deposited films with the same thickness on CeO/sub 2//YSZ(sc) substrates. J/sub c/'s of 4.5 MA/cm/sup 2/ and 2 MA/cm/sup 2/ have been achieved in 0.4 /spl mu/m thick YBCO films on CeO/sub 2//YSZ(sc) and CeO/sub 2//YSZ/CeO/sub 2//Ni substrates, respectively. Textured Gd/sub 2/O/sub 3/ buffer layers have been deposited on deformation textured Ni substrates in a reel-to-reel process. The performance of YBCO films deposited on substrates containing the Gd/sub 2/O/sub 3/ seed layers is comparable in performance to YBCO films grown on all vacuum deposited buffer layers.

A reel-to-reel electron beam evaporation system has been developed to continuously deposit Y–BaF2–Cu precursor for ex situ YBa2Cu3O7−x (YBCO) processed films. The quality of a YBCO film on biaxially textured, oxide buffered, Ni tape strongly depends on the condition of the precursor deposit. For continuous precursor deposition, a uniform cation stoichiometry (i.e., Y:Ba:Cu=1:2:3) over the entire length of precursor film is essential. Rutherford backscattering spectrometry studies indicated that the partial pressure of water vapor during the deposition has a significant effect on cation deposition rates and the oxygen content in the precursor film. The oxygen content of the precursor is increased and the precursor stability upon exposure to air is improved by introduction of water vapor during precursor deposition. High quality precursor films with a thickness of 300 nm have been deposited on lengths of rolling-assisted, biaxially textured substrates in the reel-to-reel electron beam evaporation system. In this paper, long length precursor deposition processing will be discussed. Properties of some post-annealed YBCO films will also be presented.

We report the development of an all-sputter-deposited buffer multilayer architecture for the growth of high critical current density ( J c ) YBa 2 Cu 3 O 7− δ (YBCO) films on metallic tapes. The structure comprises the layer sequence of CeO 2 /YSZ/LNO (YSZ: yttria stabilized zirconia, LNO: LaNiO 3 ) on biaxially textured Ni substrates. X-ray diffraction analysis of the base LaNiO 3 (LNO) layers indicated that well textured films can be obtained at deposition temperatures ( T dep ) between 450°C and 500°C, while higher T dep yielded polycrystalline films. The degree of LNO crystallinity was also influenced by the oxygen partial pressure during the growth. Scanning electron microscopy observations revealed a smooth, dense and crack-free surface morphology, independent of film thickness in the range of 50–300 nm. Subsequent YSZ and CeO 2 films were deposited to complete the buffer-layer structure. Epitaxial YBCO films grown by pulsed laser ablation on the CeO 2 /YSZ/LNO/Ni multilayer structure have self-field J c values as high as 1.3×10 6 A/cm 2 at 77 K. Effects of the LNO base-layer thickness on the quality of buffers and on the superconducting properties of YBCO films showed no remarkable differences. The present results demonstrate a viable approach for the production of long length YBCO superconducting wires.

Methoxyethoxide complexes in 2-methoxyethanol were used to produce epitaxial thin films of SrBi2Nb2O9, SrBi2Ta2O9, BaBi2Nb2O9, and BaBi2Ta2O9 on [100] oriented single-crystals of SrTiO3 and LaAlO3. Films were prepared by spin coating substrates with alkoxide solutions and firing in air at 850 °C for 20 minutes. With the exception of BaBi2Ta2O9 on LaAlO3, all of the films were the desired c-axis oriented Aurivillius phase. Out-of-plane orientation was confirmed by θ-2θ scans which showed only [002/] reflections, and in-plane orientation was determined by phi-scans about the [105] plane. Lattice constants and full-width at half-maximum (fwhm) values for both in-plane and out-of-plane reflections are reported.

Epitaxial, uniformly strained superlattices of ferroelectric KNbO3 and paraelectric KTaO3 are studied with respect to their structural and dielectric properties. For dielectric measurements, perfectly lattice-matched conducting KNbO3Sr(Ru0.5Sn0.5)O3 electrodes are used, and a broad, frequency-dependent maximum is observed in the capacitance-vs-temperature curves. Niobium K-edge glancing-angle EXAFS provides information regarding the crystal structure of KNbO3 films as thin as two unit cells in superlattices with equal KTaO3 and KNbO3 layer thicknesses, showing a clear difference between these thinnest-layer superlattices and films of the KNbO3K(Ta0.5Nb0.5O3 solid-solution. X-ray diffraction measurements, on the other hand, indicate that these samples exhibit the same transition temperature KNbO3Tc, indicating the importance of long-range electrostatic interactions. Analysis of the transition temperature for various structures leads to a clear identification of the effect of size and strain on KNbO3Tc.

Electrically conductive LaNiO 3 buffer layers have been grown on textured nickel tapes by sputter deposition in a reducing atmosphere. These conductive buffered Ni tapes can be employed as long flexible substrates for biaxially aligned high-temperature superconductors, and can electrically stabilize the superconductor during transient loss of superconductivity. Deposition temperatures of about 400°C result in epitaxial growth of LaNiO 3 films, while higher deposition temperatures may cause the formation of La 2 NiO 4 films. X-ray θ –2 θ , θ , and φ scans reveal that the LaNiO 3 films have good out-of-plane and in-plane orientations of 5° and 9–10°, respectively. Subsequent oxygen anneals at 750°C and 850°C change neither the biaxial orientations of the film nor cause any cracks or other surface defects. The resistivity of the LaNiO 3 films can be further reduced by increasing the annealing temperature and oxygen pressure during post-annealing. Highly textured YBa 2 Cu 3 O 7 (YBCO) films were grown on the LaNiO 3 -buffered Ni by pulsed laser deposition (PLD).

In an effort to develop alternative single buffer layer architectures for YBCO (YBa2Cu3O7-y) coated conductors, we have studied RE2O3 (RE = Y, and rare earths) as candidate materials. High-quality Y2O3, Gd2O3 and Yb2O3 buffer layers were grown epitaxially on biaxially textured Ni (100) substrates using reactive electron beam evaporation. Using thermodynamic considerations for the formation of metal oxides, we employed both reducing atmospheres and water vapour to oxidize the film in situ to form stoichiometric RE2O3. We have also prevented NiO formation at the substrate-film interface during this process. Detailed x-ray studies have shown that the Y2O3, Gd2O3 and Yb2O3 films were grown with a single epitaxial orientation. The lattice mismatch between YBCO and Gd2O3 was small as compared with that of YBCO with other rare earth oxides. SEM micrographs indicated that ~0.5 ?m thick Y2O3 films on rolled-Ni substrates were dense, continuous and crack free. A high Jc of 1.8 ? 106 A cm-2 at 77 K and self-field was obtained on YBCO films grown on alternative buffer layers with a layer sequence of YBCO/Yb2O3 (sputtered)/Y2O3 (e-beam)/Ni.

The biaxial textures created in metals by rolling and annealing make them useful substrates for the growth of long lengths of biaxially textured material. The growth of overlayers such as high-temperature superconductors requires flat substrates with a single, sharp texture. A sharp cube texture is produced in high-purity Ni by rolling and annealing. We report the effect of rolling reduction and annealing conditions on the sharpness of the cube texture, the incidence of other orientations, the grain size and the surface topography. A combination of high reduction and high-temperature annealing in a reducing atmosphere leads to >99% cube texture, with a mosaic of about the rolling direction, about the transverse direction, and about the normal direction.

Epitaxial buffer layers of CeO 2 and yttria-stabilized ZrO 2 (YSZ) have been deposited on biaxially textured nickel using conventional electron beam evaporation and r-f sputtering. Epitaxial films of YBa 2 Cu 3 O 7− δ (YBCO) have been then grown on these buffered substrates using pulsed laser deposition (PLD). Despite intermittent exposure of the buffered substrates to 1 atm air, the resulting YBCO conductors exhibited transport critical current densities ( J c ) of 0.8 MA/cm 2 at 77.3 K and H =0 T. The dependence of J c of these conductors on temperature and magnetic field is similar to that of conductors prepared solely by in situ PLD. These results suggest that it may be possible to use more flexible and easily scalable fabrication methods for preparing long YBCO conductors.

This paper describes the development of two buffer layer architectures on rolled-Ni substrates using an electron beam evaporation technique. The first buffer layer architecture consists of an epitaxial laminate of CeO 2 /Pd/Ni. The second alternative buffer layer consistes of an epitaxial laminate of YSZ/CeO 2 /Ni. The cube (100) texture in the Ni was produced by cold-rolling followed by recrystallization. The CeO 2 films were grown epitaxially on both Pd-buffered and textured-Ni substrates. The YSZ films were grown epitaxially on CeO 2 -buffered Ni substrates. The crystallographic orientation of the Pd, CeO 2 , and YSZ films were all (100). We also studied the effect of CeO 2 layer thickness and crack formation on textured-Ni substrates. The layer thickness was found to be critical. For some thickness, cracks formed in the CeO 2 layer. The presence of YSZ layers on the CeO 2 layers seem alleviate the cracks that are formed underneath. Our SEM studies showed that both CeO 2 (3–10 nm thick underlayer) and YSZ layers were smooth and continuous.

Techniques are reported for sputter deposition of biaxially oriented buffer-layers on textured Ni tapes. These buffered tapes can be employed as long, flexible, or large area substrates for biaxially-aligned high-temperature superconductors (HTS) with high critical current density Jc. Using deposition techniques at temperatures as low as 25°C, epitaxial Pd or Pt films were first deposited as a base layer on the textured Ni tapes, followed by deposition of biaxially oriented Ag or CeO2 buffer layers. Using Ar/4%H2 sputter gas, biaxially oriented CeO2 films were also grown directly on the textured Ni tapes, followed by the epitaxial growth of YSZ films. All the films show both strong in-plane and out-of-plane orientations. The effects of Ni surface smoothness on buffer-layer texture were also investigated.

X-ray diffraction rocking curves are used to measure the c axis alignment of TlBa 2 Ca 2 Cu 3 O x films grown on polycrystalline substrates with thickness varying from 3 to 10.5 μm. Films thicker than 3 μm are found to contain two layers: a well aligned (3.5° FWHM) bottom layer, and a poorly aligned (greater than 12° FWHM) top layer. Azimuthal scans show that the component with good long-range out-of-plane alignment retains its characteristic colony microstructure of local in-plane alignment as film thickness increases. The length dependence of the critical current density may be accounted for by assuming that all the supercurrent is carried by the well-aligned component.

The temperature ( T ) and O 2 partial pressure ( p [O 2 ]) dependence of the oxygen content ( y ) in Pr 1+ z Ba 2− z Cu 3 O y (Pr123) were determined over the entire range of z and the data were represented by chemical thermodynamic models. Comparison of the results with those published previously for Y123, La123 and Nd123, indicated that the La123 system was the most atypical. Thermodynamic arguments suggest the presence of Pr +4 as y approaches its maximum value. The T - z - p [O 2 ] dependence of high-temperature decomposition was also determined. Resistivity, dc magnetization, and susceptibility measurements as low as 5 K revealed only paramagnetic and semiconducting behavior.

The temperature ( T ) and O 2 partial pressure ( p [O 2 ]) dependence of oxygen content ( y ) in Nd 1+ z Ba 2− z Cu 3 O y were determined over the entire range of z . These data were represented by chemical thermodynamic models. The T - z - p [O 2 ] dependence of high-temperature decomposition was also determined, as were the effects of various T - t - p [O 2 ] treatments on the superconducting transition temperature ( T c ). These results were compared with those from the Y and La homologs.

The microstructure of high-Jc Bi-2223 powder-in-tube tapes was studied using x-ray and electron diffraction. Although the c-axis is nominally aligned perpendicular to the tape surface (FWHM∼20‡), x-ray phi scans and pole figures show no evidence of any in-plane texture, either macroscopically or locally. Electron backscatter diffraction patterns acquired in a scanning electron miscroscope (SEM) were used to measure individual grain orientations. Grain boundary misorientation between adjacent grains was described by rotation angles and axes (i.e. the disorientation) and compared with theoretical values of ideal coincidence site lattices (CSLs). Data collected from over 113 spatially correlated grains resulting in 227 grain boundaries, show that over 40% of the boundaries are small angle. In addition, 8% of the boundaries were found to be within the Brandon criterion for CSLs (larger than ⌆1 and less than ⌆50). Grain boundary “texture maps” derived from the SEM image and orientation data reveal the presence of percolative paths between low energy boundaries.

The effects of composition, temperature ( T ) and O 2 partial pressure ( p [O 2 ]) on solid-liquid equilibria were determined experimentally for most of the phase fields in the BaOCuCuO system. These relationships are illustrated in both a p [O 2 ]−10 4 / T diagram and in ternary phase diagrams. Thermodynamic values reported for BaCuO 2 and BaCu 2 O 2 by Voronin and Degterov [1–3] were verified via equilibria involving oxides, BaCO 3 , O 2 , and CO 2 . The T − p [O 2 ]− y interdependence was determined for Ba 2 CuO 3+ y .

Using magnetic methods, we have studied the effects of Pb substitution on the irreversibility line and other features of c -axis aligned Tl based cuprate superconductors with the “1223” structure. Specifically, the properties of (Tl 0.5 Pb 0.5 )Sr 2 Ca 2 Cu 3 O 9 are compared with those of grain-aligned TlBa 2 Ca 2 Cu 3 O 9 and Tl(BaSr) 2 Ca 2 Cu 3 O 9 materials. The irreversibility line H irr ( T ) is notably higher for the Pb substituted material ( 1.7 T at 77 K with Hc ) and markedly anisotropic for all of the samples. Also, results for the persistent current density are reported. Flux-creep studies of the current-decay rate show that the current is the most stable in the aligned (Tl 0.5 Pb 0.5 )Sr 2 Ca 2 Cu 3 O 9 , and that the decay rate of all three materials increases monotonically as the temperature increases.

Fabrication of Tl-1223 conductors in two geometries is reported. Powder-in-tube (PIT) tapes were fabricated using aerosol generated precursor powders mixed with Tl/sub 2/O/sub 3/. Effect of processing variables such as temperature, time and uniaxial pressure were studied. Under optimum processing conditions the tapes have sharp transitions (widths /spl sim/1 K) and zero-field J/sub c//spl sim/0.9/spl times/10/sup 4/ A/cm/sup 2/ at 77 K, However the tapes lack any detectable grain orientation texture and are severely weak-linked. On the other hand, thick films (3-30 /spl mu/m) of Tl-1223 on Ag made using a variety of precursor deposition techniques followed by thallination in a two-zone flow reactor, show significantly reduced weak-link behavior and high zero-field J/sub c/'s (>10/sup 4/ A/cm/sup 2/). It is found that these films are c-axis aligned (rocking curve FWHM/spl sim/3-11/spl deg/) and also possess varying degrees of local in-plane texture. Microstructural development in these thick films is found to be similar to that observed previously for films on polycrystalline YSZ. Such thick films present a working model of a practical Tl-1223 conductor. >

X-ray microdiffraction has been used to map the orientational distribution of grains in a 4 × 5mm 2 polycrystalline film of Tl 1− y Ba 2 Cu 2 Cu 3 O x (Tl-1223) grown on yttira-stabilized zirconia (YSZ). The film consists of “colonies”, each containing ∼ 10 4 grains with their a -axes aligned; the c -axes of all grains are aligned normal to the film, but there is no overall a -axis alignment. While the grain boundaries within a colony are small angle, colonies are separated by large-angle tilt boundaries. The typical colony size is 0.4 mm. Measured critical currents are compared with simulations based on observed distributions of grain alignment; we find that variations in grain alignment account for the observed variations in the critical current density. Simulations over longer distances indicate that a colony structure can substantially increase the critical current, especially in magnetic fields.

Microstructural origins for reduced weak-link behavior in high-Jc melt-processed YBCO, spray pyrolyzed thick films of Tl-1223, metallic precursor Y-124 polycrystalline powder-in-tube (PIT) wires and PIT Bi-2212/2223 are discussed. Since the materials studied are the highest Jc, polycrystalline, high-Tc superconductors fabricated worldwide, the results provide important guidelines for further improvements in superconducting properties, thereby enabling practical applications of these materials. It is found that strongly linked current flow within domains of melt-processed 123 occurs effectively through a single crystal path. In c-axis oriented, polycrystalline Tl-1223 thick films, local in-plane texture has been found to play a crucial role in the reduced weak-link behavior. Formation of “colonies” of grains with a common c-axis and modest in-plane misorientation was observed. Furthermore, a colony boundary in general has a varying misorientation along the boundary. Large regions comprised primarily of low angle boundaries were observed. Percolative transport through a network of such small angle boundaries appears to provide the nonweak-linked current path. Although powder-in-tube BSCCO 2212 and 2223 also appear to have a “colony” microstructure, there are some important differences. Colonies in BSCCO consist of stacks of grains with similar c-axis orientation in contrast to colonies in Tl-1223 films where few grains are stacked on top of one another. Furthermore, most grains within a colony in BSCCO have the same lateral dimensions as that of the colony, resulting largely largely in “twist” boundaries. Further microstructural characterization of high-Jc PIT 2212 and 2223 is currently underway. In the case of Y-124 wires, weak macroscopic in-plane texture is found. Additional measurements are underway to determine if a sharper, local in-plane texture also exists. It is found that in three of the four types of superconductors studied, reduced weak-link behavior can be ascribed to some degree of biaxial alignment between grains, either on a “local” or a “global” scale.

The effects of composition, processing time ( t ), temperature ( T ) and O 2 partial pressure ( p O 2 ) on the superconducting transition temperature, T c , were investigated for La 1+ z Ba 2- z Cu 3 O y . Tallon and Flower's prediction of T c ≈ 100 K [Physica C 204 (1993) 237] at z = 0 could not be attained. Instead, the T c maximum of 93–94K is similar to that of the yttria analog. As z was increased, the T c values increased gradually by a few kelvin until z = 0.2, which is at the orthorhombic to tetragonal transition, and then decreased more abruptly, with no superconductivity for z ≥0.5. Crucial steps in the process at all z values include the highest temperature anneal (1065°C) in 0.1 MPa O 2 , reduction of the oxygen content at 950°C and cooling to 300–400°C, both at 100–1000 Pa O 2 , and reoxygenation at 0.1 MPa O 2 during slow cooling (5–20°C/min) to T c decreased fairly monotonically with decreasing y at z = 0.08, and a La excess of 0.2 and Cu nonstoichiometry on both sides of Cu/(La+Ba) = 1 generally depressed T c .

Tl 1− y Ba 2 Ca 2 Cu 3 O x , y c -axes normal to the film; a - and b -axes are randomly oriented on a macroscopic scale. We describe X-ray pole-figure measurements from 0.1 mm regions of Tl-1223 films. For samples with the highest critical currents, the a -axes of the grains are locally aligned over distances up to 1 mm. Regions of higher critical current are associated with regions of high a -axis alignment.

The textures, surface morphologies, structural perfection, and properties of diamond films grown by activated chemical vapor deposition (CVD) vary greatly with the growth conditions. The evolution of two commonly observed polycrystalline morphologies, which give rise to 〈110〉 textures, will be described as well as the development of four films grown to produce 〈100〉, 〈111〉 and “near 〈100〉” textures with various combinations of growth facets. These films were grown to test models of texture development. Films free of twins, microtwins, and stacking faults are deposited when only {100} facets are permitted to grow. In polycrystalline materials, special conditions must be met to avoid the formation of planar defects at the peripheries of individual crystallites. The planar defects grow from {111} or mixed microfaceted surfaces. Twinning plays an important role in the growth of {111} faceted surfaces. The films have been characterized with Raman spectroscopy, X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and optical methods.

We analyze fundamental issues related to the thermal and electrical stability of a coated conductor during its operation. We address the role of conductive buffer layers in the stability of Ni-based coated conductors, and the effect of a metallic cap layer on the electrical properties of Ni alloy-based superconducting tapes. For the first case we report on the fabrication of a fully conductive RABiTS architecture formed of bilayers of conductive oxides SrRuO3 and LaNiO3 on textured Ni tapes. For the second case we discuss measurements of current-voltage relations on Ag/YBa2Cu3O7-d and Cu/Ag/ YBa2Cu3O7-d prototype multilayers on insulating substrates. Limitations on the overall tape structure and properties that are posed by the stability requirement are presented., Comment: 4 pages, 5 figures

Immobilization of vortices, or flux pinning, is both an enduring scientific issue and one of the most important problems in optimizing high temperature superconductors (HTSs) for commercial use. Here, we demonstrate a practical approach to the creation of a multi-modal flux pinning landscape in Y Ba2Cu3O7 (YBCO) films employing an industrially scalable metal–organic chemical vapor deposition technique. Through controlled additions of Nb, we have achieved a novel distribution of crystallographic defects that immobilize (pin) vortices in the YBCO matrix. That is, with only the addition of a single dopant element, a tri-modal, non-superconducting defect structure is induced that threads through the YBCO matrix laterally (parallel to the ab planes of YBCO), vertically (parallel to the YBCO c-axis), and isotropically in the form of random spherical defects. For optimally doped samples, the influence of these multi-modal nanocrystalline defect structures on the flux pinning properties manifests itself as a significant improvement in the critical current density (Jc) for all magnetic field orientations. The results demonstrate the possibility of achieving an ideal flux pinning landscape (from an orientation and strength viewpoint), which permits the design of HTS wires with fully-tunable properties by processes suitable for large-scale manufacturing.

Systematic effects of Zr additions on the structural and flux pinning properties of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) films deposited by metal-organic chemical vapor deposition (MOCVD) have been investigated. Detailed characterization, conducted by coordinated transport, x-ray diffraction, scanning and transmission electron microscopy analyses, and imaging Raman microscopy have revealed trends in the resulting property/performance correlations of these films with respect to varying mole percentages (mol%) of added Zr. For compositions {le} 7.5 mol%, Zr additions lead to improved in-field critical current density, as well as extra correlated pinning along the c-axis direction of the YBCO films via the formation of columnar, self-assembled stacks of BaZrO{sub 3} nanodots.

A unique, three-dimensional (3D), biaxially textured, MgO, nanofence comprised of single crystal MgO nanobelt segments or links was synthesized via epitaxial growth on (100) SrTiO(3) substrates. Individual single crystal MgO nanobelt segments comprising the nanofence have a square cross-section with dimensions in the range of 10-20 nm and with lengths in the range from 100 nm up to 1 microm. X-ray diffraction shows that the 3D MgO nanofence has an epitaxial relation with (100) SrTiO(3) substrates with a cube-on-cube, {100}100 orientation and with values of the full width at half-maximum of the (200) omega-scan and the (110) varphi-scan at 4.5 degrees and 5.5 degrees , respectively. Such a biaxially textured oxide nanofence with single crystal segments can be used as a 3D nanotemplated substrate for epitaxial growth of wide-ranging, 3D, electronic, magnetic and electromagnetic nanodevices.

Neutron powder diffraction has been used to refine the structure of the high- T c superconductor Tl 2 Ca 1 Ba 2 Cu 2 O 8 to determine the precise oxygen co-ordination and the effective valence of copper. The results are in excellent agreement with the Dupont X-ray structure, confirming the possible substitution of about 9% of the Ca-sites with Tl in our sample. The Tl-sites may be either 3% Tl-deficient or 7% Ca-substituted. The apparent valence of copper is 2.22. Oxygen in the center of the Tl square implies an average valence of less than 3 for Tl, and it is therefore not suprising that this oxygen is desordered toward the mid-point of the shortest Tl-Tl distance. High resolution electron images and diffraction reveal a quite different superstructure to the 5 x 5.4 A superstructure seen in Bi 2 Sr 1 Ca 2 Cu 2 O 8 . Very weak and diffuse superlattice spots may be due to a charge density wave in the TlO plane with period 6 x 3.8 A.

The solidification behavior of two low-melting-point metals, Sn and In, on three substrates has been examined using in situ x-ray diffraction. Undercoolings of up to 56.1°C were observed for Sn solidified on graphite, which is a nonwetting substrate, while lower undercoolings were observed for Sn on Au/Ni/Cu (17.3°C) and on Cu (10.5°C). Indium behaved quite differently, showing undercoolings of less than 4°C on all three substrates. The lattice expansion/contraction behavior of Sn, In, and intermetallic compounds (IMCs) that formed during the reaction of Sn with Au/Ni/Cu surfaces were also measured during heating and cooling. Results showed anisotropic and nonlinear expansion of both Sn and In, with a contraction, rather than expansion, of the basal planes of In during heating. The principal IMC that formed between Sn and the Au/Ni/Cu surface was characterized as Cu6Sn5, having an average expansion coefficient of 13.6 × 10−6/°C, which is less than that of Sn or Cu.