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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.

A nonvacuum reel-to-reel dip-coating system has been used to continuously fabricate epitaxial Gd 2 O 3 buffer layers on mechanically strengthened, biaxially textured Ni-(3 at.% W-1.7 at.% Fe), defined as Ni-alloy, metal tapes. Because of its significance as a seed layer, optimum processing conditions (postannealing speed and temperature) of Gd 2 O 3 buffer layers have been studied. Highly textured films were obtained under reducing (96% Ar + 4% H 2 ) atmosphere at temperatures between 1100° and 1150°C; postannealing speed did not significantly affect the crystalline quality of the Gd 2 O 3 . Scanning electron microscopy revealed a continuous, dense, and crack-free surface morphology for these dip-coated buffers. The Gd 2 O 3 layer thickness led to pronounced differences in the growth characteristics of the subsequent YSZ and CeO 2 layers deposited by rf-magnetron sputtering. Epitaxial YBCO films grown by pulsed laser deposition on the short prototype CeO 2 /YSZ/Gd 2 O 3 /Ni-(3 at.% W-1.7 at.% Fe) conductors yielded self-field critical current densities (J c ) as high as 1.2 x 10 6 A/cm 2 at 77 K. Pure Ni tapes were used to assess the viability of dip-coated buffers for long length coated conductor fabrication. The YBCO films, grown on 80 cm long and 1 cm wide CeO 2 /YSZ/Gd 2 O 3 buffered Ni tapes by the industrially scalable ex situ BaF 2 precursor process, exhibited end-to-end self-field J c values of 6.25 x 10 5 A/cm 2 at 77 K. These results demonstrate the reproducible epitaxy of solution-derived seed layers on pure Ni and Ni-alloy tapes as well as underscore the viability of solution approaches for the production of long length YBCO-based coated conductors.

Focused monochromatic synchrotron undulator radiation was used to measure stresses in growing α-Al2O3 on FeCrAl-based and NiAl alloys during the first few hours of high-temperature air exposures at 1000–1200°C. Selected specimens were then sectioned and examined by transmission electron microscopy to characterize the microstructure of the oxides grown during the in situ stress measurement experiments. In several cases at 1100 and 1200°C, rapid decreases in an initial tensile stress were noted within the first hour of exposure. It was found that differences in high-temperature stress development in the alumina were at least partially reflected in the observed scale microstructures. Relaxation processes limited the magnitude of growth stresses at the higher temperatures such that after a few hours, stresses were typically quite low.

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.

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

We experimentally demonstrate a novel approach to substantially modify orbital occupations and symmetries in electronically correlated oxides. In contrast to methods using strain or confinement, this orbital tuning is achieved by exploiting charge transfer and inversion symmetry breaking using atomically layered heterostructures. We illustrate the technique in the LaTiO_{3}-LaNiO_{3}-LaAlO_{3} system; a combination of x-ray absorption spectroscopy and ab initio theory reveals electron transfer and concomitant polar fields, resulting in a ∼50% change in the occupation of Ni d orbitals. This change is sufficiently large to remove the orbital degeneracy of bulk LaNiO_{3} and creates an electronic configuration approaching a single-band Fermi surface. Furthermore, we theoretically show that such three-component heterostructuring is robust and tunable by choice of insulator in the heterostructure, providing a general method for engineering orbital configurations and designing novel electronic systems.

The phonon dispersions and scattering rates of the thermoelectric material ${\mathrm{Ag}}_{1\ensuremath{-}x}{\mathrm{Sb}}_{1+x}{\mathrm{Te}}_{2+x}\phantom{\rule{0.28em}{0ex}}(x=0,0.1,0.2)$ were measured with inelastic neutron scattering, as function of both temperature $T$ and off stoichiometry $x$. In addition, detailed measurements of diffuse scattering were performed with both neutron and synchrotron x-ray diffraction. The results show that phonon scattering rates are large and weakly dependent on $T$ or $x$, and the lattice thermal conductivity calculated from these scattering rates and group velocities is in good agreement with bulk transport measurements. We also find that the scattering rates and their temperature dependence cannot be accounted for with common models of phonon scattering by anharmonicity or point defects. The diffuse scattering measurements show a pervasive, complex signal, with several distinct components. In particular, broad superstructure reflections indicate a short-range ordering of the Ag and Sb cations on their sublattice. Single-crystal Bragg peak intensities also reveal large static atomic displacements, compatible with results from Rietveld refinement of neutron powder diffraction data. Our results indicate that a complex nanostructure, arising from multiple variants of nanoscale anisotropic superstructures of cations, and large atomic displacements, is likely responsible for the strong phonon scattering.

Power applications of high-temperature superconducting (HTS) coated conductors will require stabilization against thermal runaway. We have developed conductive buffer layers to electrically couple the HTS layer to the underlying metal substrate. The structure comprises the layer sequence of SrRuO3 (SRO) on LaNiO3 (LNO) on biaxially textured Ni substrates. We report baseline investigations of compatibility of SRO/LNO multilayer structure with processing of Yba2Cu3O7−δ (YBCO) and demonstrate biaxially textured YBCO films on conductively buffered Ni tapes. These YBCO coatings exhibit self-field Jc values as high as 1.3 × 106 A/cm2 at 77 K, and the entire structure (HTS + conductive buffers + metal substrate) shows good electrical connectivity. These results demonstrate that SRO/LNO buffer layers may provide a basis for stabilized coated conductors.

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.

Chemical solution epitaxy was used to deposit an epitaxial film of Gd2O3 on roll-textured nickel. A 2-methoxyethanol solution of gadolinium methoxyethoxide was used for spin-coating and dip-coating. Films were crystallized using a heat treatment at 1160 °C for 1 h in 4% H2/96% Ar. Single-layer films were approximately 600 Å in thickness, and thicker films could be produced using multiple coatings. θ/2θ x-ray diffractograms revealed only (0041) reflections, indicating a high degree of out-of-plane texture. A pole-figure about the Gd2O3 (222) reflection indicated a single in-plane epitaxy. Scanning electron microscopy showed that the films were smooth, continuous, and free of pin holes. Atomic force microscopy revealed an average surface roughness of 53 Å. Electron diffraction indicated that the misalignment of the majority of the grains in the plane was less than 10°. High-current (0.4 MA/cm2) Yba2Cu3O7–δ films were grown on roll-textured nickel substrates using Gd2O3 as the base layer in a three-layer buffer structure.

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.

Electron backscatter Kikuchi diffraction was used to study texture development and grain boundary networks in rolling-assisted-biaxially-textured-substrates, and the transfer of such a biaxial texture and preferential grain boundary network to epitaxial YBCO films grown on such substrates. It was found that the rolling texture in the Ni substrate is highly complicated, with most of the grains having orientations at and between the “B” and “S” orientations. No cube nuclei could be discerned in the etched, as-rolled sample. On recrystallization, a sharp {001}〈100〉, cube texture was imparted to the Ni substrate. It was found that the substrate was percolatively connected within 3°. Examination of epitaxial oxide layers on Ni showed that excellent epitaxy was obtained. At times, undesirable orientations nucleated during growth of the oxide layer, however, these were engulfed by the growing film (with correct orientation). Orientation image micrographs of an epitaxial YBCO film on a RABiT substrate with a J c of 1.6 MA/cm 2 at 77 K showed that most of the film was percolatively connected within 2°. A comparison of the spatially correlated and uncorrelated grain boundary misorientation distributions showed that local grain-to-grain correlations were present between the grains. Comparison of the data obtained for the YBCO film with those obtained for the underlying Ni substrate showed that both the macroscopic texture and the grain boundary networks were very similar in the two cases, implying excellent epitaxy of the multilayers.

In order for many large-scale bulk applications of high-temperature superconducting materials to be realized, the cost/performance of the superconductors needs to be optimized. From a performance standpoint, a long, flexible, single-crystal-like wire is required; from a cost-and-fabrication standpoint, an industrially scalable, low-cost process is required. Both of these critical requirements are met by rolling-assisted biaxially textured substrates, a conductor-fabrication technique that employs simple, scalable, thermomechanical processing techniques to obtain a near-single-crystal-like, flexible metal substrate in arbitrary lengths on which epitaxial oxide buffer layers and superconductors are then deposited.

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.

${\mathrm{KTaO}}_{3}/{\mathrm{KNbO}}_{3}$ strained-layer superlattices of variable periodicity were grown by pulsed laser deposition on ${\mathrm{KTaO}}_{3}$ substrates. The ${\mathrm{KNbO}}_{3}$ layers were found to be strained in plane to match the substrate lattice parameter. Therefore, the applied strain is independent of the layer thickness. High-temperature x-ray diffraction was used to measure the ferroelectric-paraelectric phase transition temperature ${T}_{c}$. For superlattice periodicity $\ensuremath{\Lambda}\ensuremath{\le}5.1\mathrm{nm}$, ${T}_{c}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}475\mathrm{K}$, independent of $\ensuremath{\Lambda}$. For $\ensuremath{\Lambda}g5.1\mathrm{nm}$, ${T}_{c}$ increases to 825 K at $\ensuremath{\Lambda}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}33.8\mathrm{nm}$.

Progress in the fabrication of epitaxial, high-Jc, biaxially aligned YBCO thick films on Rolling-assisted biaxially textured substrates (RABiTs) is reported. RABiT substrates comprise a biaxially textured metal substrate with epitaxial oxide buffer layers suitable for growth of superconductors. Oxide buffer layers have been deposited using three techniques: laser ablation, electron-beam evaporation, and sputtering. Epitaxial YBCO films grown using laser ablation on such substrates have critical current densities approaching 3 × 106 A/cm2 at 77 K in zero field and have field dependences similar to epitaxial films on single crystal ceramic substrates. Critical current densities in excess of 0.2 MA/cm2 have been obtained on stronger, nonmagnetic substrates. In addition, samples with Je of 12.5 kA/cm2 at 77 K have been fabricated. The highest strain tolerence obtained so far is 0.7% in compression and 0.25% in tension. Deposited conductors made using this technique offer a potential route for the fabrication of long lengths of high-Jc wire capable of carrying high currents in high magnetic fields and at elevated temperatures.

When some of the iron in the B2 iron aluminide Fe-45 at.% Al is replaced by nickel, several important changes occur. Nickel dramatically slows down the removal of quenched-in thermal vacancies during annealing. Also, nickel additions render the hardening due to thermal vacancies less effective than that in binary iron aluminides. Both of these effects may be linked to the formation of nickel-vacancy complexes. Nickel additions also cause substantial solid solution strengthening, and possible reasons for this result are discussed. Our findings are supported by vacancy concentration determinations, by yield strength measurements, and by transmission electron microscope observations.

Epitaxial BaZrO 3 (barium zirconium oxide) films were grown on single crystal substrates. A BaZrO 3 precursor solution was prepared by sol-gel synthesis using an all-alkoxide route. The barium precursors were prepared by reacting barium metal with 2-methoxyethanol, and zirconium precursors were prepared by exchanging ligands between zirconium n-propoxide and 2-methoxyethanol. The resulting BaZrO 3 precursor solution was partially hydrolyzed and spin-coated on sapphire (100), SrTiO 3 (strontium titanium oxide) (100), and LaAlO 3 (lanthanum aluminum oxide) (100) substrates. The films were post-annealed in oxygen at 800 °C for 2 min in a rapid thermal annealer. The coating and the annealing procedures were repeated three times to obtain the desired thickness, 300 nm. X-ray diffraction studies showed the presence of a single (100) cube texture for BaZrO 3 films on SrTiO 3 and LaAlO 3 substrates. The BaZrO 3 films grown on sapphire had a random texture. The BaZrO 3 films grown on SrTiO 3 substrates had a sharp texture compared to that on LaAlO 3 substrates. This may be due to the relatively smaller lattice mismatch between SrTiO 3 and BaZrO 3 .

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

Grain orientation and grain boundary misorientation distributions in high critical current density, high-temperature superconductors were determined using electron backscatter Kikuchi diffraction. It is found that depending on the type of superconductor and the processing method used to fabricate it, there exist different scales of biaxial texture from no biaxial texture, local biaxial texture, to complete biaxial texture. Experimentally obtained grain boundary misorientation distributions (GBMDs) were found to be skewed significantly to low angles in comparison to what is expected on the basis of macroscopic texture alone, suggesting that minimization of energy may be a driving force during the processing of high critical current density materials. In addition, a higher than expected fraction of coincident-site lattice boundaries is observed. Examination of maps of grain boundary misorientations in spatially correlated grains, i.e. the grain boundary mesotexture, suggests the presence of percolative paths of high critical current density. A combination of orientation measurements, theoretical modeling of GBMDs and modeling of percolative current flow through an assemblage of grain boundaries is performed to gain an insight into the important microstructural features dictating the transport properties of high-temperature superconductors. It is found that maximization of low energy, in particular, low-angle boundaries, is essential for higher critical currents. The combination of experimental and analytical techniques employed are applicable to other materials where physical properties are dominated by intergranular characteristics.

A LaAlO3 precursor solution was prepared via an all alkoxide sol-gel route. The solution of lanthanum methoxyethoxide and aluminum methoxyethoxide in 2-methoxyethanol was prepared via ligand exchange starting from lanthanum isopropoxide and aluminum sec-butoxide and was used to make both LaAlO3 powders and films. Complete hydrolysis of the solution formed a gel that yielded well-crystallized LaAlO3 powders when fired in air at 800 °C. A partially hydrolyzed solution was spun-cast on SrTiO3 (100) single crystal substrates. Epitaxial films of LaAlO3 were subsequently formed during pyrolysis in O2 at 800 °C in a rapid thermal annealing furnace for a total of 8 min. The films were strongly c-axis oriented, verified by x-ray rocking curve results from the (003) plane with full-width at half-maximum (FWHM) = 0.87°, and had good in-plane texture shown by a φ scan of the (202) plane with FWHM = 1.07°.

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

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.

Iron aluminide intermetallics, which exhibit excellent oxidation and sulfidation resistance, were found to be suitable as the matrix phase in metal matrix composites, or the binder in hard metals (or cermets). In particular, ceramics such as TiB2, ZrB2, TiC and WC could all be liquid-phase sintered with an Fe-40 at% Al iron aluminide. The processing and properties of such iron aluminide composites were assessed. Density, hardness, bend strength, and fracture toughness data are presented. Nearly complete densification was achieved for ceramic volume fractions up to 60%. For iron aluminide-tungsten carbide composites containing 60 vol% WC, room temperature three-point bend strengths and fracture toughnesses reached 1460 MPa and 20 MPa m 1 2 , respectively. Consistent with the high fracture toughness values, the fracture surfaces showed evidence for ductile deformation of the iron aluminide binder.

As part of an effort to develop a new, non-vacuum-processed substrate for high current superconducting films, thin films of LaAlO{sub 3} and NdAlO{sub 3} were deposited on biaxially textured (100) nickel substrates using a solution deposition technique. On heating to 1150 C in Ar-4% H{sub 2} for 1 h, epitaxial films were obtained. Out-of-plane alignment was confirmed by obtaining rocking curves of the (002) plane of the LaAlO{sub 3} (full width at half-maximum (fwhm) = 7.2{degree}) and the NdAlO{sub 3} (fwhm = 5.8{degree}) films. In-plane alignment was demonstrated by obtaining phi scans of the (110) plane of the LaAlO{sub 3} (fwhm = 13.4{degree}) and the NdAlO{sub 3} (fwhm = 8.8{degree}) films. Grain alignment in the films is approximately equivalent to the alignment of the Ni substrate. Analysis of pole figures indicated that in both films there are two-in-plane orientations present, the major being (001)[100] and the minor (001)[110].

Relaxor ferroelectrics exemplify a class of functional materials where interplay between disorder and phase instability results in inhomogeneous nanoregions. Although known for about 30 years, there is no definitive explanation for polar nanoregions (PNRs). Here we show that ferroelectric phonon localization drives PNRs in relaxor ferroelectric PMN-30%PT using neutron scattering. At the frequency of a preexisting resonance mode, nanoregions of standing ferroelectric phonons develop with a coherence length equal to one wavelength and the PNR size. Anderson localization of ferroelectric phonons by resonance modes explains our observations and, with nonlinear slowing, the PNRs and relaxor properties. Phonon localization at additional resonances near the zone edges explains competing antiferroelectric distortions known to occur at the zone edges. Our results indicate the size and shape of PNRs that are not dictated by complex structural details, as commonly assumed, but by phonon resonance wave vectors. This discovery could guide the design of next generation relaxor ferroelectrics.

There is a long-standing debate over the length scales needed to understand the behavior of materials and the role of surfaces, defects, and inhomogeneities. Indeed the properties of most materials are ultimately determined by defects —including grain boundaries and surfaces-that are either introduced during processing or in-service, and defect density and distribution must be considered for high-fidelity integrated computational modeling and engineering. Scientists at ORNL together with partners at Argonne have developed a powerful 3D X-ray Crystal Microscope that can nondestructively characterize the local 3D crystal structure of polycrystalline materials with submicron resolution and with sensitivity to the local crystal structure, orientation, elastic strain tensor and the local Nye tensor. This emerging tool provides unprecedented tests of materials models under different processing/environmental conditions and provides new insights into the impact of unpaired dislocations, elastic strain and surfaces and interfaces. The promise of the 3D Microscope and the emergence of similar instruments at synchrotrons around the world will be discussed with respect to ICME.

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.

In this article, experiments designed to ascertain the percolative nature of current flow in high critical-current density (Jc) polycrystalline superconductors are reviewed. A direct correlation between the grain-orientation texture with current transport in high-Jc TlB2Ca2Cu3Ox thick films and Bi2Sr2Ca2Cu3Ox powder-in-tube tapes is obtained. Magnetooptical visualization of the current flow in the same regions confirms the percolative nature of current flow. Furthermore, numerical modeling of the current flow based on the observed grain boundary character distribution and the effects of the grain boundary misorientation angle on (Jc) was found to predict the percolative nature of current flow. These studies indicate that in order to increase the (Jc) further, increased fractions of small-angle boundaries are required and, hence, provide a research direction for the next generation of high-temperature superconducting wire.

Fabrication of epitaxial, high- J c , biaxially aligned YBCO thick films on rolling-assisted biaxially-textured substrates (RABiTS) is summarized. The RABiTS technique utilizes standard thermomechanical processing to obtain long lengths of flexible, biaxially oriented substrates with smooth surfaces (rms ∽50 nm). The strong biaxial texture of the metal (in-plane 6–7° FWHM) is conferred to the superconductor by deposition of intermediate metal and/or oxide layers which serve both as a chemical as well as a structural buffer. Epitaxial YBCO films grown using laser ablation on RABiTS™ have critical current densities exceeding 10 6 A cm −2 at 77 K in zero-field and have field dependences similar to epitaxial films on single crystal ceramic substrates. The texture of the base metal has been achieved in lengths over 1 m and scaleable techniques are being pursued to deposit epitaxial multilayers. Deposited conductors made using this technique offer a potential route for the fabrication of long lengths of high- J c wire capable of carrying high currents in high magnetic fields and at elevated temperatures.

The equilibrium magnetization was studied in magnetically aligned Hg-based cuprate superconductors with a crystal structure containing one, two, and three adjacent Cu-O layers. The mixed state magnetization was measured with the magnetic field applied perpendicular to the layers, along with low field Meissner effect and normal state susceptibility studies for volume correction factors. The internally consistent analysis is used to identify systematics as the number {open_quote}{open_quote}{ital n}{close_quote}{close_quote} of Cu-O layers increases. The study reveals a linear increase in the slope of upper critical field {minus}{ital dH}{sub {ital c}2}/{ital dT} with {open_quote}{open_quote}{ital n}{close_quote}{close_quote}. Most importantly, we find a nearly constant carrier doping per Cu-O layer. This result is compared with other studies, e.g., Rietveld analysis of neutron diffractometry, and its implications are discussed. {copyright} {ital 1996 The American Physical Society.}

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.

A quantitative model is presented for the high critical current densities ({ital J}{sub {ital c}}) supported by superconducting materials with uniaxial alignment, such as {ital c}-axis textured Bi-Sr-Ca-Cu-O tapes. Current follows percolative paths across small-angle grain boundaries. Because {ital j}{sub {ital c}} is low for intragranular conduction parallel to the {ital c} axis, the 3D flow required for percolation is produced by conduction perpendicular to the {ital c} axis in tilted grains. For optimized microstructures, {ital J}{sub {ital c}} ranging from 3 to 30{percent} of the intragranular value is predicted for percolation across small-angle grain boundaries with misorientations below 10{degree} and 20{degree}, respectively. {copyright} {ital 1996 The American Physical Society.}

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.

The electron backscattering pattern technique has been applied to the microstructural investigation of Tl(1223) thick films formed by vapor-phase thallination of Ag-containing Ba–Ca–Cu–oxide precursors. For samples grown on polycrystalline YSZ, considerable biaxial alignment is found in localized, multigrain regions as wide a 100 μm or more. However, on scales above 1 mm the overall texture remains only uniaxial with the c-axes (i.e., [001]) aligned perpendicular to the plane of the substrate. On single-crystal KTaO3 an epitaxial relationship is evident which persists to the surface of a 3 μm thick film. Modest variations in the processing protocol yield films containing grains oriented with the c-axis in the plane, resulting in the degradation of transport properties. The data suggest a growth mode in which sparse nucleation occurs at the substrate followed by rapid lateral crystallization.

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. >