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One of the crucial steps in the second generation high temperature superconducting wire program was development of the buffer-layer architecture. The architecture designed at the Superconductivity Technology Center at Los Alamos National Laboratory consists of several oxide layers wherein each layer plays a specific role, namely: nucleation layer, diffusion barrier, biaxially textured template, and intermediate layer providing a suitable lattice match to the superconducting Y1Ba2Cu3O7 (YBCO) compound. This report demonstrates how a wide range of ion beam analysis techniques (SIMS, RBS, channeling, PIXE, PIGE, NRA and ERD) was employed for analysis of each buffer layer and the YBCO film. These results assisted in understanding of a variety of physical processes occurring during the buffer layer fabrication and helped to optimize the buffer-layer architecture as a whole.

Numerous experimental results have suggested that the J c of YBa 2 Cu 3 O 7 (YBCO) films is significantly higher near the film–substrate interface than in the remainder of the film. We previously proposed that this effect is due to interfacial pinning enhancement caused by stress and the resulting misfit dislocations at the heteroepitaxial interface. To test this hypothesis we have used a non-superconducting PrBa 2 Cu 3 O 7− δ (PrBCO) buffer layer to minimize the lattice mismatch with YBCO. We find that the PrBCO layers lower J c of the 0.4 μm YBCO films in a predictable way, and that, if sufficiently thick (∼0.5 μm), they eliminate interfacial enhancement altogether. Our interpretation of this result is that the defects responsible for interfacial enhancement of flux pinning originate at the bottom of the non-superconducting PrBCO layer, which screens the pinning centers from vortices in YBCO. This result demonstrates that the pinning enhancement arises from stress at the film–substrate interface.

Retaining a dissipation-free state while carrying large electrical currents is a challenge that needs to be solved to enable commercial applications of high-temperature superconductivity. Here, we show that the controlled combination of two effective pinning centres (randomly distributed nanoparticles and self-assembled columnar defects) is possible and effective. By simply changing the temperature or growth rate during pulsed-laser deposition of BaZrO(3)-doped YBa(2)Cu(3)O(7) films, we can vary the ratio of these defects, tuning the field and angular critical-current (Ic) performance to maximize Ic. We show that the defects' microstructure is governed by the growth kinetics and that the best results are obtained with a mixture of splayed columnar defects and random nanoparticles. The very high Ic arises from a complex vortex pinning landscape where columnar defects provide large pinning energy, while splay and nanoparticles inhibit flux creep. This knowledge is used to produce thick films with remarkable Ic(H) and nearly isotropic angle dependence.

Twenty years ago in a series of amazing discoveries it was found that a large family of ceramic cuprate materials exhibited superconductivity at temperatures above, and in some cases well above, that of liquid nitrogen. Imaginations were energized by the thought of applications for zero-resistance conductors cooled with an inexpensive and readily available cryogen. Early optimism, however, was soon tempered by the hard realities of these new materials: brittle ceramics are not easily formed into long flexible conductors; high current levels require near-perfect crystallinity; and — the downside of high transition temperature — performance drops rapidly in a magnetic field. Despite these formidable obstacles, thousands of kilometres of high-temperature superconducting wire have now been manufactured for demonstrations of transmission cables, motors and other electrical power components. The question is whether the advantages of superconducting wire, such as efficiency and compactness, can outweigh the disadvantage: cost. The remaining task for materials scientists is to return to the fundamentals and squeeze as much performance as possible from these wonderful and difficult materials.

Biaxially textured SmxZr1-xOy (SZO) thin films have been grown directly on an ion beam assisted deposited (IBAD) MgO template, without using an intermediate homoepitaxial MgO layer. SZO buffer layers were deposited using reactive magnetron sputtering of a Sm (50 at.%)-Zr (50 at.%) alloy target. The SZO texture is similar to that of the MgO template. Epitaxial YBCO films, ~1mum-thick, grown by pulsed laser deposition on SZO buffered coated conductors have high critical current densities. The in-field measurements indicate that superconducting samples with SZO as buffer are as good as STO/homoepitaxial MgO buffered samples. These results demonstrate that SZO is an appropriate buffer for the fabrication of low cost YBCO/IBAD MgO coated conductors with excellent transport properties.

Microstructural evolution with the change in thickness of superconducting YBa2Cu3O7-X films on single-crystal SrTiO3 substrates deposited by pulsed laser deposition was evaluated using different structural characterization tools. A noticeable degradation of crystallinity with the increased film thickness was detected. Nevertheless, a comprehensive relationship between the microstructure and the zero-field current-density can not be established solely based on the degradation of crystallinity.

The hybrid liquid phase epitaxy (HLPE) approach has the potential to be a high rate-low cost process. This deposition process is used to grow epitaxial YBa2Cu3O7 (YBCO) films in the presence of a thin (100 to 500 nm) liquid BaO-CuO flux layer. Despite the presence of the molten flux, YBCO growth is found to be feasible on technical substrates because of the limited dissolution of the buffer layer in the thin flux layer. The high atom mobility at the growing interface under the liquid flux enables high growth rates (demonstrated to be greater than 10 nmldrs-1 in a wide temperature regime and predicted to be up to ~5 nmldrs-1). We report results on HLPE YBCO films grown on (100) strontium titanate and textured technical substrates such as rolling-assisted biaxially textured substrates (RABiTS) and ion-beam-assisted-deposited (IBAD) MgO. High values of the critical temperature above 90 K and critical current ~400 A per cm width for 3 mum thick films on single crystal substrates and promising high values on technical substrates are obtained. Furthermore, there is potential for making thicker films of the same quality since film density is maintained with thickness. Angular-dependent transport critical current as a function of applied field for these films, as well as microstructural measurements by transmission electron microscopy are also reported. The angular and field dependence of critical current density are similar to standard PLD (pulsed laser deposition) films. Although the films are of high epitaxial quality they contain yttria precipitates which are possible sources of flux pinning centers.

Polymer assisted deposition is a versatile technique to grow simple and complex metal-oxide thin films. In this paper we report the structural and electrical properties of ferroic materials, namely La0.67M0.33MnO3 (M=Sr and Ca) and Ba1 −xSrxTiO3 (x=0.3, 0.5, and 0.7) prepared using this process. The films were prepared on single crystalline LaAlO3 substrates. The films were highly c-axis oriented and epitaxial in nature. The ferromagnetic La0.67Sr0.33MnO3 and La0.67Ca0.33MnO3 films show intrinsic transport properties with maximum magnetoresistance values (at applied field of 5 T) of −50% and −88%, respectively. The highest dielectric constant (∼1010) and tunability (∼69%) of Ba1 −xSrxTiO3 film occurs at x=0.3 for films, which is at the phase boundary of tetragonal and cubic. Published by Elsevier B.V.

When a current is applied perpendicular to the vortex lattice (VL), Lorentz force may cause the VL to drift and flux-flow dissipation is observed. When the current is parallel to the applied magnetic field in a force-free (FF) configuration, a dissipation is also observed but at higher values of applied current. It has been suggested that pinning as well as free surfaces play an important role in the stabilization of the VL in the FF configuration. In thin YBa2Cu3O7 films, FF configurations can be obtained when Hparab with the current flowing parallel to the ab-planes. In this work we study the influence of thickness, growth method and pinning centers on the dissipation mechanism at variable Lorentz force and FF configurations. Comparisons of experiments done at maximum and variable Lorentz force show that there are two pinning regimes when the field is rotated in these configurations; one consistent with only a decrease in the applied force, indicated by the overlap of the power law exponent of the current-voltage curves as the field is rotated toward the ab-planes, and another very close to the ab-planes, where the dissipation characteristics change.

This study shows that biaxially textured SmxZr1−xOy(SZO) with a wide range of compositions (0.06

Misfit dislocations at YBa 2 Cu 3 O 7− δ (YBCO)/SrTiO 3 (STO) interfaces were studied to understand effects which could be responsible for the high interfacial J c in YBCO thin films. In YBCO films with thickness ranging from 5 to 100 nm, the interfacial structures (e.g. misfit dislocations) of YBCO/STO were investigated using moire fringe contrast in plan-view transmission electron microscopy (TEM). The observed moire pattern has a spacing of 17 nm which corresponds to the lattice mismatch between the YBCO a lattice spacing and the cubic STO lattice constant. As the YBCO thickness reaches 100 nm, twin structures dominate the image contrast. Our observations indicate that the moire pattern originates from the lattice mismatch between the substrate and the orthorhombic phase of YBCO.

We have studied the influence of naturally grown SrTiO3 particles at the buffer layer surface on the in-field critical current density (Jc) dependence of coated conductors. The presence of the SrTiO3 particles induces the growth of extra-correlated pinning along the c-axis direction in the YBa2Cu3O7 films that thread samples as thick as 5 µm. These correlated pinning centres produce a bigger c-axis peak and effectively reduce the Jc magnetic field (H) decay characterized by a smaller exponent α of the power law decay. This method opens up a new approach for how to increase Jc under an applied magnetic field without the need for an extra process. This study brings new meaning to the so-called optimal deposition conditions, since it will depend on the field and temperature region of the application.

Pinning in YBa2Cu3O7?x (YBCO) films is compared with mixed rare-earth (RE) films. The field dependence of critical current density and pinning force plots at 75.5?K are analysed. The work provides a guideline as to how to optimize pinning by inclusion of both random and correlated defects. In summary, Y mixed with larger RE ions appears to be optimum for effective pinning across a wide field regime as well as permitting growth at temperatures low enough for technological use.

Highly c-axis-oriented zinc oxide (ZnO) films with nano-size grains were successfully prepared on sapphire (0001) substrates by polymer-assisted deposition, where the crystallization of the ZnO was realized by a rapid thermal process (RTP). Post-processing conditions played critical roles in the structure, surface morphology, and the photoluminescence (PL) spectra of the films. The post-thermal treatment by RTP enhances the green PL of the ZnO films. Oxygen vacancies induced by the RTP may be related to the green PL from undoped ZnO.

A thin layer of SrTiO3 has been successfully used as a buffer layer to grow high quality superconducting YBa2Cu3O7−δ (YBCO) thick films on polycrystalline metal substrates with a biaxially oriented MgO template produced by ion-beam-assisted deposition (IBAD). Using this architecture, 1.5 μm-thick-YBCO films with an in-plane mosaic spread in the range of 2–3° in full width at half maximum, and a critical current density over 2 MA/cm2 in self-field at 75 K have been achieved routinely. More interestingly, we found the thickness of SrTiO3 buffer layers strongly affects the properties of YBCO films. The critical current density of YBCO films increases dramatically when the thickness of SrTiO3 buffer layer reaches an optimum range of 40–120 nm. Microstructure studies, including transmission electron microscopy (TEM), X-ray diffraction (XRD) and scanning electron microscopy (SEM), and ion-milling experiments suggest that the YBCO texture evolution, STO outgrowths and STO surface dents are strongly related to STO thickness. They are the key factors for YBCO self-field Jc variation.

We conducted a comparative study of microstructural properties for YBa2Cu3O7 (YBCO) films on single-crystal MgO and polycrystalline Ni-based metal substrates with ion-beam-assisted deposited (IBAD) MgO as a template. The film grown on the metal substrate shows more crystalline imperfections with density of screw dislocations four times higher than that of the film on single-crystal MgO, as revealed by high-resolution x-ray diffraction (HRXRD). These high-density screw dislocation cores connect well and form bigger clustered grains as detected by scanning tunneling microscopy. Transmission electron microscopy studies confirm that the structural quality of YBCO on the Ni-based alloy is comparable to that on single-crystal MgO. All these factors contribute to our routine fabrication of high-quality YBCO films on metal substrates with critical current densities in self-field as high as those for the films grown on single-crystal MgO substrates. Superconducting properties in fields are also discussed.

The angular-dependent critical current density J/sub c/ in YBa/sub 2/Cu/sub 3/O/sub 7/ films grown by pulsed laser deposition exhibit a sharp peak for magnetic field orientations near the ab plane, which arises from the combined effects of intrinsic pinning and extended defects parallel to the planes. An analysis of the temperature and field dependence of the height and width of this peak allows us to distinguish both contributions. We find that, in a film on single crystal substrate, the peak at low fields is due primarily to the extended defects, but at high fields it is dominated by intrinsic pinning. We compare these results with those of coated conductors with a larger density of ab-oriented correlated defects. We show a novel effect consisting in an inverse correlation between J/sub c/ and the power law exponent (N) of the I-V curves that only occurs in the intrinsic-pinning dominated regime, and we present an interpretation of its origin.

We carried out systematic investigation on the processes and characteristics of REBa/sub 2/Cu/sub 3/O/sub 7/ or RE123 (RE=Nd, Sm, Eu, Dy, Ho, Er, and Yb) films on single crystal SrTiO/sub 3/ for coated conductors. The higher transition temperature, the higher growth rate, and the much better surface morphology for the large RE's such as Nd123, Sm123, and Eu123 make them attractive for thick films. The larger processing window for some other RE123 materials such as Dy123 and Yb123, on the other hand, makes them striking for scale-up and fabrication of long-length conductors. In the case of mixed RE's, enhanced pinning from ion size variance is also observed. We present our comparative study of the field- and angle-dependent critical current densities between these RE123 and Y123 films.

Copper-doped SrTiO/sub 3/ (STO) powders were processed by conventional bulk preparation techniques to establish solubility limits of Cu in STO. The maximum solubility of Cu in STO was identified to be /spl sim/1%. Epitaxial Cu-doped SrTiO/sub 3/ (STO) buffer layers were then prepared by pulsed laser deposition (PLD) and chemical solution deposition (CSD) on ion-beam-assisted deposition (IBAD) magnesium oxide (MgO) flexible metallic textured tapes. Transmission electron microscopy (TEM) analysis of the /spl sim/100 nm thick buffer layer deposited by PLD showed a smooth Cu-doped STO/MgO interface. Films deposited by CSD had an average film thickness of 30 nm and exhibited growth by heterogeneous nucleation with no secondary reaction phases. YBa/sub 2/Cu/sub 3/O/sub 7-/spl part// (YBCO) films were deposited onto the Cu-doped STO buffer layers by PLD.

Epitaxial BiFeO3 thin films have been grown on the (0 0 1) SrTiO3 and LaAlO3 substrates by liquid phase epitaxy (LPE) and sol–gel methods. The films had an in-plane texture of 2° and out-plane texture of 0.6° and showed a 4-fold symmetry about the c -axis, indicating a distortion of the bulk rhombohedral cell to a tetragonal or cubic structure. The LPE films were both ferroelectric and ferromagnetic. The sol–gel films showed a small linear increase of the magnetisation with the applied magnetic field, indicating they possibly had the same antiferromagnetic behaviour as the bulk crystal. The LPE films exhibited a large leakage current, which probably originated from a relatively high level of Fe2+ in the films induced by the high growth temperature. Fe2+ might also account for the origin of the ferromagnetism in LPE films.

We present a study of the sharp peak that develops near the ab -plane orientation in the angular dependent critical current of YBa 2 Cu 3 O 7 (YBCO) films. This peak arises from correlated pinning associated to intrinsic pinning by the layered structure of the YBCO, and from extended planar defects. We measure films produced by pulsed laser deposition (PLD) and metal organic deposition (MOD) on ion beam assisted deposition––MgO, and by PLD on single crystalline substrates. We show that the width and height of the peak increases with the out-of-plane mosaic spread of the films. We discuss the implications of the different structures (columnar and laminar respectively) of the PLD and MOD films.

This report describes recent developments of second-generation Y1Ba2Cu3O7−δ (YBCO) coated conductors deposited on biaxially textured MgO templates. The materials system architecture implemented to achieve high critical currents in YBCO films is described. The average full-width at half maximum (FWHM) in-plane texture obtained for MgO films processed on meter-length tapes is 7°, while that for the YBCO films is 3°. The best YBCO in-plane values approach 2° and the out-of-plane values approach 1°. Critical currents (1 cm wide tapes, 75 K, self field) have attained 423 A for 7 cm length and 233 A for 50 cm length tapes.

Metal oxides are emerging as important materials for their versatile properties such as high-temperature superconductivity, ferroelectricity, ferromagnetism, piezoelectricity and semiconductivity. Metal-oxide films are conventionally grown by physical and chemical vapour deposition. However, the high cost of necessary equipment and restriction of coatings on a relatively small area have limited their potential applications. Chemical-solution depositions such as sol-gel are more cost-effective, but many metal oxides cannot be deposited and the control of stoichiometry is not always possible owing to differences in chemical reactivity among the metals. Here we report a novel process to grow metal-oxide films in large areas at low cost using polymer-assisted deposition (PAD), where the polymer controls the viscosity and binds metal ions, resulting in a homogeneous distribution of metal precursors in the solution and the formation of uniform metal-organic films. The latter feature makes it possible to grow simple and complex crack-free epitaxial metal-oxides.

A thin layer of SrTiO3 (STO) has successfully been used as a buffer layer to grow high-quality superconducting YBa2Cu3O7-δ(YBCO) thick films on polycrystalline metal substrates with a biaxially oriented MgO template produced by ion-beam-assisted deposition. Using this architecture, 1.5-μm-thick YBCO films with an in-plane mosaic spread in the range of 2.5° to 3.5° in full width at half-maximum and critical current density over 2 × 10 6A/cm2 in self-field at 75 K have routinely been achieved. It is interesting to note that the pulsed laser deposition growth conditions of SrTiO3 buffer layers, such as growth temperature and oxygen pressure, have strong effects on the superconducting properties of YBCO. Detailed studies using transmission electron microscopy, scanning electron microscopy, and atomic force microscopy were used to explore the microstructures of STO deposited at different conditions and to understand further their effects on the growth and properties of YBCO films.

It is shown that local mechanical bending of YBa2Cu3O7−b Ag-coated superconducting films deposited on flexible metal substrates in the temperature interval 77–300 K may increase the critical density Jc of the transport current to values as high as 106 A/cm2 or even higher at 77 K. Also, bending decreases the voltage criterion. This means a rise in the intergranular conductivity and, accordingly, a reduction of Joule losses.

The diffusion behavior of elements constituting Hastelloy C-276 (C, Si, Mn, Co, W, Fe, Cr, Mo, and Ni) in alumina films was investigated using secondary ion mass spectroscopy. The films were deposited by ion-beam-assisted deposition and annealed in vacuum over a temperature range of 500–1000 °C. Characterization of film microstructure was performed using transmission electron microscopy and selected area diffraction analyses. The films were predominantly amorphous with alumina nanocrystallites nonuniformly dispersed throughout the volume both before and after annealing. A relatively wide interface region between the Hastelloy substrate and alumina film was formed in the as-deposited sample due to ion beam mixing. No diffusion of any of the substrate elements was observed after annealing, except for Mn, Cr, and Ni. The impurity depth distributions consisted of two components, which differed by several orders of magnitude with respect to diffusion coefficient and solubility. Activation energies and temperature dependencies of the diffusion coefficients were determined, and a diffusion mechanism was discussed.

The ac losses in three disk-shaped YBa2Cu3O7 (YBCO) films, which were deposited on SrTiO3 by the pulsed-laser-deposition technique and had thicknesses, d, of 0.2, 1.0, and 3.0 μm, were measured in perpendicular applied ac magnetic fields to ∼0.14 T at 10 Hz in liquid nitrogen. The losses at low fields were found to be a strong function of the film thickness. The measured losses were compared with the theoretically calculated losses. The ac losses calculated using a field-independent critical-current density, the Bean model [J. R. Clem and A. Sanchez, Phys. Rev. B 50, 9355 (1994)], agreed very well with the 0.2-μm-thick film, while the calculated losses agreed well with the measured ones when a field-dependent critical-current density, the Kim model [D. V. Shantsev, Y. M. Galperin, and T. H. Johansen, Phys. Rev. B 61, 9699 (2000)], was used for the films of thickness 1.0 and 3.0 μm. However, a surprising discrepancy was found in the values of Bc and B0 for thinner YBCO films depending on whether they were ...

Ca diffusion was studied in c -axis and a -axis oriented YBCO films by Secondary Ion Mass Spectroscopy (SIMS). The films were grown by pulsed laser deposition (PLD). Ca(NO 3 ) 2 solutions were deposited on the film surface and annealed over a large temperature range (300–870 °C) in air. The rate of Ca diffusion was measured to be the same in the c -axis and a -axis oriented films. The activation energy for Ca diffusion in YBCO was measured to be 67±10 kJ/mol. Fast diffusion along the grain boundaries was observed at temperatures below 700 °C with an activation energy of 46±12 kJ/mol. At 300 °C, the grain boundary diffusion coefficient is around 1.7×10 −14 cm 2 s −1 , which is 100 times larger than the corresponding bulk diffusion coefficient.

A single LaMnO3 buffer layer was developed for the growth of superconducting thick YBa2Cu3O7−δ (YBCO) films on polycrystalline Ni-alloy substrates where a biaxially textured MgO layer, produced by ion-beam assisted deposition (IBAD), was used as a template. Using pulsed laser deposition, a 1.65-μm-thick YBCO film with a critical current density of 1.4 × 106 A/cm2 in self field at 75 K was achieved on sputtered LaMnO3-buffered IBAD MgO substrates. This corresponds to a critical current (Ic) of 231 A/cm-width. This result demonstrates the possibility of using both LaMnO3 buffer and IBAD MgO template for producing high current density YBCO-coated conductors.

Epitaxial YBCO films with a thickness of 0.9 μm have been deposited by ex situ conversion of a trifluoroacetate-based metal organic decomposition precursor on both RABiTS TM (NiW) and MgO-IBAD Hastelloy substrates. These are potential processes for fabricating second generation coated conductor wires. I c values, at 77 K and self-field, as high as 202 and 194 A/cm-width have been achieved on the RABiTS TM and MgO-IBAD samples, respectively.

We present our results to improve ion beam assisted deposition (IBAD) of magnesia (MgO) templates for subsequent YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) deposition. The substrate surface roughness has a significant effect on the initial nucleation texture of IBAD MgO films. We have found that reduction in our substrate surface roughness to /spl sim/ 3.5 nm has resulted in better in-plane texture for IBAD MgO films than those deposited on rougher metal substrates. We have further improved the IBAD MgO deposition parameters by using an in situ reflected high-energy electron diffraction (RHEED) analysis tool that allows for monitoring of IBAD MgO growth. We have found a direct correlation between the RHEED generated intensity versus time curve and in-plane texture. Utilizing X-ray diffraction analysis, we have been able to determine the optimum deposition parameters to routinely grow films in batch mode that have a phi scan /spl Delta//spl phi/ from 6 - 7/spl deg/. Coupling the improvements in substrate preparation with optimization of IBAD MgO deposition has allowed for both batch and continuous deposition (termed c-IBAD MgO) on metallic substrates that result in superior superconducting properties. We have demonstrated that deposited meter lengths have had phi scan FWHM values from 8 - 9/spl deg/ with /spl plusmn/ 10% uniformity. Additionally, we have been able to widen the processing zone in our system and coat two, one-meter lengths simultaneously while preserving good texture quality (/spl Delta//spl phi//sub ave/ /spl sim/ 8/spl deg/) and uniformity (60 - 80% of tape length within /spl plusmn/ 5% of /spl Delta//spl phi//sub ave/) for both tapes.

We demonstrate the applicability of continuous electropolishing for the preparation of metal tapes for ion-beam assisted deposition of MgO for the fabrication of in-plane textured template layers. These templates are used for the fabrication of second generation high temperature superconducting wires utilizing YBa2Cu3O7−δ coatings on metallic substrates. Surface roughness values below 1 nm and local slopes of less than 1° could be achieved with the electropolishing process. Mean surface roughness values are lower with the use of electropolishing and slopes of surface roughness inclines are significantly reduced compared to the best results of mechanical polishing (3.5 nm and 5°, respectively). The cost-effective process of electropolishing shows great promise for the fabrication of second generation high temperature superconducting wire.

We have investigated epitaxial superconducting SmBa2Cu3O7 (Sm123) films grown by pulsed-laser deposition on single-crystal SrTiO3 substrates. The deposition temperature plays an important role in determining the superconducting properties of Sm123 films. The superconducting transition temperature increases with the deposition temperature whereas the transition width decreases at deposition temperatures in the range of 700–875 °C. A Sm123 film deposited at 850 °C exhibits a transition temperature above 93 K with a transition width less than 0.5 K. Even though Sm123 films exhibit a higher transition temperature than Yba2Cu3O7 (Y123), the Sm123 shows lower critical current density at liquid-nitrogen temperature. The nominal critical current density of Sm123 film is less than 1 MA/cm2 at 75.4 K. Nevertheless, the Sm123 films have less anisotropy and stronger pinning characteristics compared to Y123. They are also much smoother with fewer particulates, as revealed by scanning electron microscopy.

Ca-gels were applied to highly dense YBCO pellets and PLD thin films followed by high temperature post-annealing. Parameters of Ca diffusion in YBCO (diffusion coefficients, activation energy, etc.) as a function of temperature and oxygen partial pressure were determined by depth profiling SIMS. Fast Ca diffusion along the grain boundaries was observed by FIB and SIMS. The effect of Ca doping on Tc and Jc was studied by VSM. Ca distribution in the samples, induced by preferential diffusion along the grain boundaries, did not appear to change superconducting properties within the grains but showed increased Jc across the grain boundaries.

Nickel-based superalloys have been coated with magnesium oxide (MgO) using ion-beam-assisted deposition (IBAD). This technique produced a well-oriented bi-axially textured MgO template layer with a Ф scan full width half maximum of 6.4°. The layer architecture for these samples was as follows: polished hastelloy C276/amorphous Si3N4/IBAD MgO/ pulsed laser deposited (PLD) Y2O3–ZrO2/PLD CeO2/PLD YBa2Cu3O7?δ. The subsequent heteroepitaxial PLD of 1.5-mm-thick YBCO showed a nominal critical current density of over 1 MA/cm2 (75 K, self-field) along a microbridge and had an in-plane mosaic spread of 4.8° and an out-of-plane spread of 1.3°. These results compare well with our earlier work using IBAD yttria-stabilized zirconia (YSZ) as a template layer and indicate that IBAD MgO is a suitable substitute. Furthermore, these results suggest that IBAD MgO could be adapted to and increase the feasibility of a continuous process to fabricate longer lengths of coated conductors at speeds 100 times faster than that previously realized with IBAD YSZ.

The microstructure and grain boundary structure in YBa2Cu3O7−δ (YBCO) thick film coated conductors are characterized by transmission electron microscopy. The films contain low-angle [0 0 1] tilt grain boundaries with periodic arrays of edge dislocations parallel to the c-axis. A majority of the grain boundary planes are of either the (1 0 0) or the (1 1 0) type. Grain boundary dislocations (GBDs) with a [1 0 0] Burgers vector were observed in tilt boundaries with (1 0 0) boundary planes. However, partial dislocations, separated by stacking faults, were found at boundaries with near (1 1 0) grain boundary planes. Extensive g · b and g · R analyses confirmed the partials to be of 1/2[1 1 0] type. These results suggest that the characteristics of dislocation structures, which have been proposed in various grain boundary-based flux-pinning models, depend not only on the misorientation angle θ, but also on the types of grain boundary plane. The effect of dissociated GBDs on the transport properties of low angle grain boundaries in YBCO coated conductors is discussed.

We have examined the effect of film thickness on in-plane texture for ion-beam assisted deposition (IBAD) of MgO films. Plan-view dark-field transmission electron microscopy (TEM) has revealed that texture develops rapidly, reaching its best value at a critical thickness of/spl sim/10 nm. These results have been confirmed by quantifying the in-plane texture of these samples at each thickness with X-ray diffraction /spl phi/-scans. We have also examined the effects of variable deposition rate on texture formation. X-ray diffraction shows that the optimum in-plane texture is achieved at the critical thickness with a rate of 0.2 nm/s. However, TEM imaging has shown that the distribution of well-aligned grains decreases with an increase in rate. As such, deposition at 0.1 nm/s was found to be sufficient for achieving good in-plane distribution values and good surface coverage for subsequent depositions. By combining the results of both of these experiments, we were then able to optimize our deposition process and apply them to the growth of IBAD MgO on metal substrates.

CuNiAl and NiCr alloys were made and processed to non-magnetic, bi-axially textured substrates. Epitaxial YSZ and YBCO were deposited by pulsed laser deposition on the CuNiAl. Samples were cross sectioned and investigated with TEM. It appears that Al forms a thin oxide layer at the CuNiAl surface that acts as a template for the subsequent YSZ layer. The 1.2 /spl mu/m YBCO layer had a current density of 0.16 MA/cm/sup 2/ at 75 K and self field. On the NiCr substrates an Y/sub 2/O/sub 3/ seed layer was deposited with E-beam evaporation, followed by RF sputter deposition of YSZ and a CeO/sub 2/ cap layer. These substrates were coated with a 0.4 /spl mu/m YBCO layer using a trifluoroacetate solution, a very cost effective metal-organic deposition process. These samples carried critical currents exceeding 0.7 MA/cm/sup 2/ at 77 K, self field.

The microstructures of continuously processed YBa/sub 2/Cu/sub 3/O/sub y/ (YBCO) coated conductors processed with three different architectures are presented. YBCO films were deposited directly on ion-beam-assisted deposition (IBAD) yttria-stabilized zirconia (YSZ) or on intervening layers of Y/sub 2/O/sub 3/ or CeO/sub 2/. Different interfacial reactions were observed in each case. The volume changes that occur with the interfacial reactions were calculated based on the identified reaction products. The calculated volume changes correlate with the observed microstructures and appear to be an important factor in determining an optimal buffer layer system. The interfacial reactions do not preclude the attainment of high I/sub c/ and J/sub c/ values in these coated conductors.

It is well known that the properties of grain boundaries in YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// films differ drastically from bulk material. It has been shown both experimentally and theoretically that the grain boundaries in YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// superconductors are depleted of carriers as compared to the bulk. This depletion leads to weak intergrain links and limits critical currents in the superconductor. Recently, the promise for improved grain boundaries has been shown in Ca-doped YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films and in Ca doped YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// biaxial grain boundaries. In this study, the effect of Ca-doping of grain boundaries in YBa/sub 2/Cn/sub 3/O/sub 7-/spl delta// films and bulk have been investigated in an attempt to increase the hole concentration at the grain boundaries and to improve J/sub c/. Ca-gels were applied to sintered YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// pellets and thin films. High temperature post-anneals were used to diffuse Ca preferentially into the grain boundaries. The distribution of Ca in the samples was studied by secondary ion mass spectrometry (SIMS). The effect of Ca-doping on T/sub C/ and J/sub C/ was studied by VSM. In epitaxial thin films increased J/sub C/ were found at 40 K, but not at 77 K.

Measurements of the effects of static and cyclic (fatigue) transverse stress on the critical current of Ya-Ba-Cu-O coated tapes made by ion-beam-assisted deposition (IBAD) are reported at 76 K in self magnetic field. Ya-Ba-Cu-O films (/spl sim/1 /spl mu/m thick) on Inconel substrates (100 /spl mu/m thick) with IBAD buffer layers had critical-current densities J/sub c/ exceeding 1 MA/cm/sup 2/ and n values of about 50 (where n is an index of the sharpness of the superconductor-to-normal transition). Under static loads of 100 MPa, the degradation in J/sub c/ was less than 5% (7% at 120 MPa). When subjected to cyclic loading, there was less than 2% additional degradation in J/sub c/ after 2000 fatigue cycles. Microscopic examination of the samples indicates that this limited J/sub c/ degradation may have arisen from longitudinal cracks forming near the edges of the sample after being subjected to these high transverse pressures. This fracture mode would indicate that longitudinal side support from high-yield substrates or epoxy impregnation of magnet structures may provide additional tolerance against degradation in J/sub c/ from transverse stress.

Monolithic integration of high quality YBCO films on polycrystalline yttrium-iron-garnet (YIG) substrates represents an advance of great technical significance for magnetically tunable microwave components. We have solved the problems of crystallographic incompatibility between the two materials and the lack of an epitaxial template for the growth of well-oriented YBCO films. Using a buffer layer of biaxially oriented yttria-stabilized zirconia (YSZ), deposited by an ion-beam-assisted-deposition (IBAD) technique, we routinely produced device quality YBCO films on polycrystalline YIG substrates. The YBCO films were c-axis oriented with an in-plane mosaic spread of less than 7/spl deg/ FWHM. The films had transition temperatures above 88 K, transition widths less than 0.3 K, and critical current densities above 10/sup 6/ A/cm/sup 2/ in self-field at 75 K. The surface resistance of the films was /spl sim/0.86 m/spl Omega/ at 10 GHz and 76 K.

The study reports the discovery of a new structure and spacing versus angle relation for a prevalent type of small-angle grain boundary in YBa 2 Cu 3 O 7-δ δ (YBCO)-coated conductor films. Small-angle [001] tilt grain boundaries with (110) planes exhibit partial grain boundary dislocations (GBDs) separated by stacking faults. The dissociated grain boundary structures have twice the number of GBDs and shorter interdislocation core channel widths than Frank's geometrical rule predicts. This will require a significant alteration of models of supercurrent flow through arrays of small-angle grain boundaries in YBCO coated conductors. A thorough analysis of the stacking fault energy has been conducted based on the basis of anisotropic elasticity.

Conventional crystallographic analysis of cubic stabilised zirconias (CSZ) over a wide range of stabilisers and stoichiometries has shown O atom displacements along lattice vectors and cation disorder with irreproducible characteristics. However, because diffraction is only sensitive to the average long-range order and biased towards periodic and symmetric distortions, it is essential to supplement it with probes of short-range order that may reveal additional, element-specific details about local ordering. We have performed X-ray Absorption Fine Structure (XAFS) spectroscopy measurements on a series of Er-Y-(U-Ce)-Zr oxides to determine the local environment around each of the cations. Results from these experiments demonstrate that not only are there significant element- and composition-dependent distortions away from the crystallographic structure but also interactions between specific pairs of the metal ions indicative of cooperative behaviour. This suggests that some of the metal ions are not randomly, isomorphically substituted into the lattice but instead have tendencies to form nanometer-scale clusters and networks. In this respect, substantial differences are seen in the influence of Ce and U on the Y-centered distortions, consistent with different roles for these two elements in inert matrix fuel (IMF) matrices. This type of nanometer-scale heterogeneity is typically coupled to the phase stability and other properties of other materials and may therefore be important to these zirconias in their IMF application.

A “second-generation” of high Tc conductors, consisting of YBCO coatings on flexible metal substrates, has recently reached a milestone with meter-long tapes capable of carrying over 100 A in a 1 cm width at liquid nitrogen temperature. Having reached this level of performance, however, we have encountered difficulties in the self-field characterization of such high current material. In particular, measurement of critical current uniformity along the tape length has in some cases resulted in damage to weaker tape segments during measurement of higher-current ones. To address this problem we have developed a novel measurement technique that uses permanent magnets to locally suppress the critical current of the tape section being measured to a level that is “safe” for the rest of the tape.

We report on measurements of the ac losses of YBa2Cu3O7−x conductors on technical substrates. The samples are taken from conductors 1 m long produced with an ion beam assisted deposition step in the manufacturing process yielding 1 cm wide conductors with critical currents approaching 100 A at 77.4 K. The losses due to combinations of ac transport currents and ac magnetic fields were measured calorimetrically and the results compared to theoretical estimates. While the results of our measurements are similar to the theoretical estimates, there are some important differences in the qualitative behavior.

Processes for producing both the yttrium-stabilized zirconia (YSZ) template film by ion beam-assisted deposition (IBAD) and the YBa 2 Cu 3 O x (YBCO) superconducting film by pulsed laser deposition (PLD) at 1-m lengths have achieved I c values of 122 A and J c values of 1 MA/cm 2 . Improvements have been made in all stages of the process. Variations of I c along the length of the 1-m samples stimulated development of a new in-field I c measurement capability. The use of MgO as an IBAD template film has made great progress and can potentially decrease the time to produce the template film by more than an order of magnitude. A combination of electrical and microstructural investigations is being made to understand and improve the properties of the YBCO-coated conductors.

The microstructural development of YBa2Cu3Oy (Y-123) coated conductors based on the ion-beam-assisted deposition (IBAD) of yttria-stabilized zirconia (YSZ) to produce a biaxially textured template is presented. The architecture of the conductors was Y-123/CeO2/IBAD YSZ/Inconel 625. A continuous and passivating Cr2O3 layer forms between the YSZ layer and the Inconel substrate. CeO2 and Y-123 are closely lattice-matched, and misfit strain is accommodated at the YSZ/CeO2 interface. Localized reactions between the Y-123 film and the CeO2 buffer layer result in the formation of BaCeO3, YCuO2, and CuO. The positive volume change that occurs from the interfacial reaction may act as a kinetic barrier that limits the extent of the reaction. Excess copper and yttrium generated by the interfacial reaction appear to diffuse along grain boundaries and intercalate into Y-123 grains as single layers of the Y-247, Y-248, or Y-224 phases. The interfacial reactions do not preclude the attainment of high critical currents (Ic) and current densities (Jc) in these films nor do they affect to any appreciable extent the nucleation and alignment of the Y-123 film.

We report the fabrication of SmBa2Cu3O7−δ (Sm123) films on YBa2Cu307−δ(Y123) buffer layers 10–20nm thick using pulsed-laser deposition. Significant improvement in the superconducting properties of Sm 123 such as Tc and Jc has been observed when Y123 buffer layers are used on various substrates (LaAlO3, SrTiO3, NdGaO3 and CeO2/(yttrium-stabilized zirconia)). The buffered Sm 123 films have a high Tc of 93.1 K and a high Jc of 1.9 × 106 Acm−2 at 75 K in zero magnetic field. Compared with Y123, the buffered Sm123 samples have com-parable microwave surface resistance values and pinning characteristics with reduced anisotropy measured by the angle-dependent Ic. The effects of the Y123 buffer layer on the superconducting properties of Sm 123 are investigated and discussed in relation to the initial film growth chemistry and the substitution of Sm on Ba sites.

Transmission electron microscopy (TEM) has been applied to the microstructural investigation of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thick films deposited on polycrystalline Ni-based metal substrates by pulsed laser deposition. The films were found to be strongly textured with c-axis oriented grains aligned perpendicular to the substrates. Despite the large average in-plane misorientation (/spl theta//spl sim/14/spl deg/), as was estimated from selected area electron diffraction and X-ray diffraction, TEM inspection reveals colonies of submicron-sized grains with low angle (/spl theta//spl les/7/spl deg/) tilt grain boundaries. The linkage of the colony structures may provide a continuous percolation pathway for the supercurrent transport in YBCO, which may provide the mechanism for the higher than expected critical current density J/sub c/. Periodic arrays of grain boundary dislocations were observed, which may serve as effective flux pinners.