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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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

We examined the effects of excimer laser surface processing and of laser alloying with titanium on the mechanical and tribological properties of A-7 tool steel. We found that laser processing and alloying had no discernible effect on the mechanical properties of tempered steels. However, the dry, sliding friction coefficient of both laser processed and alloyed surfaces was reduced. Substantial but transient reductions in the friction are consistent with formation of a low friction transfer film. Long-lived reductions of friction in the laser processed case are associated with an absence of the adhesive wear which is conspicuous in the untreated case.

A coating system for the deposition of in-plane oriented yttria-stabilized zirconia (YSZ) template films on 1 cm wide flexible metal substrates is presented. In static mode, the system is capable of producing high quality template films on 20 cm substrate lengths. In a continuous coating mode, the system is capable of producing good quality template films on 1.1 m substrate lengths. Superconducting YBa 2 Cu 3 O 7− δ (YBCO) films subsequently deposited onto these template films have demonstrated critical currents ( I c ) of 200 A (1.5 cm length), 70 A (12 cm length) and 4 A (1 m length).

High-temperature superconductor YBa 2 cU 3 O 7- x (YBCO) Josephson junctions were fabricated in an edge junction geometry using Y 0.7 Ca 0.3 Ba 2 O 7- x as a barrier material. The films were deposited by pulsed-laser deposition and patterned by argon ion milling. The edge morphology of the bottom electrode after ion milling was investigated by atomic force microscopy. The yield of devices in terms of supercurrent continuity is nearly 100%. Critical current densities exceeding 10 6 A/cm 2 at 75 K were obtained through crossovers of YBCO/YBCO under our processing conditions. Resistively shunted junction current-voltage characteristics and microwave-induced Shapiro steps were observed in a wide temperature range from 75 K to 84 K for the junctions.

Pulsed laser deposition (PLD) is emerging as a popular thin film deposition technique for complex materials, especially metal oxides such as high temperature superconductors. Advantages over other thin film techniques are ease of stoichiometric deposition, high deposition rates, and processing pressure independence. Furthermore, multilayer deposition can be accomplished by simply switching different targets into the laser beam. Two common problems associated with PLD are particle deposition and target modification. In this paper we summarize some of the advantages, difficulties, and future directions of PLD.

Surface and grain topography of YBa 2 Cu 3 O 7− x epitaxial thin films grown on (100) NdGaO 3 using pulsed laser deposition has been studied using atomic force and scanning tunneling microscopy under ambient conditions. X-ray diffraction and transmission electron microscopy results support the force microscopy findings. Parametric studies of the effect of substrate temperature, annealing time and deposition rate were performed on 33 nm thick films. The observed island re-orientation as a function of time-at-temperature suggest that under our epitaxial growth conditions, the nuclei ripening time can be on the order of seconds. Implications for the observed island structure on transport and microwave surface resistance properties are briefly discussed.

One- and two-inch diameter wafers of (100) LaAlO 3 , NdGaO 3 and buffered sapphire have been coated on both sides with thin films of YBa 2 Cu 3 O 7− x by the pulsed laser deposition technique. Deposition parameters have been optimized to produce uniform, 90 K films which have surface resistance values between 0.2–0.3 mΘ at 4 K and 22 GHz.

Target modifications due to laser irradiation during the pulsed laser deposition of high- T c YBa 2 Cu 3 O 7− x thin films were studied. Although phase segregation occurs on the target surface as the formation of yttrium-rich phases results in a pronounced decrease in the overall evaporation rate, the corresponding evaporant stoichiometry, as measured in the deposited film, remains unchanged. Deposition rate dependence on laser fluence and background gas pressure were also determined for evaporations from conditioned targets.

The microstructure of laser deposited, superconducting Y-Ba-Cu-O thin films grown on [001] SrTiO 3 substrates has been characterized as a function of laser pulse rate. Over a range of deposition rates from 1–50 A/s, the films consist mainly of the c -axis oriented epitaxial, YBa 2 Cu 3 O 7− x phase with a high density of polytypoidic stacking defects. High transport critical current densities, J c , are attributed to the retention of the primarily c -axis oriented microstructure along with the distribution of stacking defects that provide good flux pinning. At higher deposition rates we observe new growth directions, specifically the a,b -axis and the [103] growth directions are favored. We conclude that within the deposition rate range of 1–150 A/s, there is no significant fundamental change in microstructure except for outgrowth formation. Therefore, we are optimistic that much higher rates can be attained in the near future, although controlling the outgrowth formation may be difficult.

Superconducting films of YBa 2 Cu 3 O 7−δ have been prepared on yttrium stabilized cubic zirconia in situ by laser (308 nm) ablation. Films have been deposited at 650°C with and without the presence of a second (annealing) excimer radiation pulse (308 nm) incident on the substrate. These films are compared to high-quality films prepared at 790 ° C. In annealing experiments, time delays between the synchronized excimer lasers were varied from 0 to 1000 μs to explore the effect of the annealing radiation throughout the mass arrival time range at the substrate. Little improvement was observed in the overall quality of the deposited films at any time delay. Model calculations indicate that a possible reason for the lack of improvement originates in a temporal width mismatch of the temperature increase of the substrate surface and the mass arrival of the ablated material.

The effect of oxygen depletion on YBCO film is investigated via penetration depth measurements. The T -dependence is measured in high precision for each oxygen concentration. λ ( T / T c )/ λ (0) vs . T / T c for our films is almost identical for different oxygen content. For a fully oxygenated film, it agrees extremely well with the crystal data for T > 25K. 1/λ 2 (0) which is proportional to superfluid density is reduced by factor 10 as T c is reduced to 48K. T c vs . 1/ λ 2 (0) in our result basically reproduces μSR result on bulk by Uemura et al. except the approximately 25% smaller value in 1/λ 2 (0) of film, which can be interpreted as impurity effect in a d -wave superconductor.

We present the magnetic penetration depth λ(T) in two laser ablated YBa2Cu3O7−δ thin films, determined by the two-coil method. The slope of 1 λ 2 (T) near Tc, the only exactly measurable quantity, extrapolates to 930A at T = 0, which compares well with 830A in the high quality single crystal recently reported by Hardy , and which exhibited a linear T dependence at low T. For T