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The controlled growth of self-assembled second-phase nanostructures has been shown to be an essential tool for enhancing properties of several composite oxide thin film systems. Here, the role of Y2O3 nanoparticles on the growth of BaZrO3 (BZO) nanorods is investigated in order to understand the mechanisms governing their self-assembly in YBa2Cu3O7- x (YBCO) thin films and to more fully control the resulting defect landscape. By examining the microstructure and current-carrying capacity of BZO-doped YBCO films, it is shown that the nanorod growth dynamics are significantly enhanced when compared to films double-doped with BZO and Y2O3 nanoparticles. The average nanorod length and associated critical current densities are found to increase at a significantly higher rate in the absence of Y2O3 nanoparticles when the growth temperature is increased. Using microstructural data from transmission electron microscopy studies and the response in critical current density, the interactive effects of multiple dopants that must be considered to fully control the defect landscape in oxide thin films are shown. [ABSTRACT FROM AUTHOR]

In this article, we report the unique microstructural characteristics of YBa2Cu3O7-x (YBCO)/BaSnO3 (BSO) nanocomposite thin films on LaAlO3 (LAO) substrates. The BSO secondary phase grows as self-assembled vertically aligned nanopillars uniformly distributed in the superconducting YBCO matrix. Detailed microstructure and strain studies including x-ray diffraction, cross-section and plan-view transmission electron microscopy, and geometric phase analysis reveal that, as the BSO doping concentration varied from 2 mol% to 20 mol%, the nanopillar density increased from 0.26 × 1011/cm2 to 1.44 × 1011/cm2 while the diameter of the nanopillars remains relatively constant (7–8 nm in diameter). The strain state of the YBCO matrix is affected by both lateral and vertical lattice strains; while, the BSO lattice is strongly tuned by YBCO rather than the substrate. A high-density array of dislocations in the order of 1013/cm2 was observed along the vertical heterogeneous interfaces throughout the YBCO film thickness for all doping concentrations. [ABSTRACT FROM PUBLISHER]

When grown on miscut SrTiO3 substrates, significant microstructural changes are observed in BaZrO3-doped YBa2Cu3O7-x thin films when compared to those on non-vicinal substrates. Scanning Electron Microscopy indicates a surface morphology strongly influenced by the vicinal angle, and an accumulation of BaZrO3 particles is observed near the step edges. Cross-sectional Transmission Electron Microscopy reveals that while the columnar formations of BaZrO3 rods typically seen on non-vicinal substrates are present, a significant increase in planar defects in a 100 vicinal film are observed. The effects observed with increasing miscut angle indicate that the modulated surface provided by the vicinal substrate influences the crystalline quality of the YBCO matrix and BZO columnar formation through the thickness of the film. [ABSTRACT FROM AUTHOR]

A special YBa2Cu3O7-x (YBCO) target with a thin sector of second phase material, in this case either Y2BaCuO5 (Y211) or BaSnO3 (BSO), was used to deposit YBCO films with non-layered nanoparticles on single crystal LaAlO3 and biaxially textured Ni-S at.% W substrates buffered with CeO2 and YSZ layers(coated conductors). Although identical processing conditions were used, TEM images indicated that random Y211 nanoparticles in the case of YBCO+Y211, and evenly spaced BSO nanocolumns iii the case of YBCO+BSO, form in the YBCO films. While YBCO plane buckling was observed at many places in the case of YBCO+Y211, a high density of stacking faults and dislocations were observed in the case of YBCO+BSO near the BSO columns. In transport critical current density (Jo) angular dependence measurements, the absence of nanocolumns in YBCO+Y211 films resulted in the absence of a peak at 0°, J(H//e), in Jc vs. θ plots, as compared to a clear peak at 0° observed in YBCO+BSO films with the nanocolumns. The in-field J measurements indicated small low-field Jc enhancements at 77 K in YBCO+Y211 films but more than an order of magnitude improvement in high-field Jc in YBCO+BSO films due to the differences in the microstructures. [ABSTRACT FROM AUTHOR]

The superconducting properties of YBa2Cu3O7-δ (YBCO or 123) thin films doped with BaZrO3 (BZO) nanopartides by multilayer and single-target methods were studied and compared. Thin films of 123 + BZO were processed by pulsed laser deposition on LaA1O3 and SrTiO3 single crystal substrates. Multilayer (BZO0.6 nm-1.4/12315nm)19 structures were grown by alternating deposition from 123 and BZO targets, and BZO additions of 0–2 Vol% were deposited using (1231-xBZOx) single-targets. The multilayer and single-target methods of BZO addition caused significant differences of superconducting transition temperatures (Tc) measured by AC susceptibility, and critical current densities (Jc) measured by both magnetic and transport methods as a function of temperature (T), applied magnetic field (H) and angle of H field incidence (θ). Single-target films had almost linear decrease of Tc and self-field Jc with BZO vol% addition, and compared to multilayer films had lower Jc (77 K, H < 4 T) however had improved high-field properties for Jc (77 K, H > 4 T). Multilayer films had almost no decrease of Tc and self-field Jc for high BZO additions up to 10 Vol% and very strong peak of Jc(H//ab in — plane) and constant and high Jc(H,0 < θ < 80°). Single-target BZO-2 Vol% films had slightly enhanced Jc (H//c — axis), consistent with results by other authors. [ABSTRACT FROM AUTHOR]

With progress of the YBCO-coated conductor to longer lengths, application of the conductor is nearing. An overview of a couple of current U.S. Air Force application programs is presented. A discussion is then made of where research and development of the YBCO-coated conductor should progress and examples in the U.S. Air Force program. These areas include magnetic flux pinning in YBCO thin films, reduction of the ac losses experienced in the YBCO conductor, and stability and quench issues when implementing the YBCO-coated conductor. [ABSTRACT FROM AUTHOR]

Nanoparticle dispersions of various phases were added to YBa2Cu3O7-x (YBCO or 123) thin films by multilayer pulsed laser deposition, to determine their effect on flux pinning. The different pinning materials examined include Y2BaCuO2 (Y211 or green-phase), La2BaCuO2 (La211 or brown-phase), Y2O3, CeO2, and MgO, with lattice constant mismatches varying from 0.5% to 12% with respect to YBCO. Y211 and Y2O3 provided significant pinning increases at temperatures of 65 K and 77 K, however other phases provided enhancements only at 65 K (for CeO2 and La211) for limited range of applied field strengths. An interesting correlation between Tc transition widths and pinning strengths was observed. The additions produced markedly different nanoparticle and film microstructures, as well as superconducting properties. [ABSTRACT FROM AUTHOR]

A comparison study is given of a typical superconducting YBa2Cu3O7-d (Y123) film and a Y123 film containing a nonsuperconducting Y2BaCuO5 (Y211) phase nanoparticulate dispersion. The inclusion of the second phase nanoparticulates was for the express purpose of increasing superconducting film's magnetic pinning strength with the resultant improved in-field critical current density. LaAlO3 substrates were used and the Y123 and Y211 nanoparticulates were grown by pulsed laser deposition (PLD). The Y211 nanoparticulate dispersion in the Y123 resulted from multiple consecutive depositions by PLD of the respective targets. The Y123 phase maintained excellent epitaxy with high in-plane orientation with and without the Y211 inclusions. With the Y211 additions, the critical current densities of the films increased significantly in applied magnetic fields as compared to the high quality Y123 film with no Y211 additions. [ABSTRACT FROM AUTHOR]

To evaluate possible flux pinning enhancement in YBa2Cu3O7-x (Y123) films due to partial rare-earth ion substitutions, Ce and Tb doping are studied. Bulk ceramic targets of varying compositions (Y1-xRExBa2Cu3O7-x) were made with several doping levels (x = 0.00 1 to 0.1, RE = Ce or Tb) by using regular solid-state reaction and sintering procedures. These targets were used to deposit Ce and Tb doped YBCO films onto SrTiO3 single crystal substrates by pulsed laser ablation. Doped YBCO films were characterized for Tc, magnetic field dependence of Jc (at 77 K), microstructure, and other properties. The results are compared to undoped YBCO films processed in similar manner. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy (XPS) depth profiling was used to investigate the compositional and chemical profile of a typical YBCO coated conductor architecture. Results of the process revealed that the Y(3d) photoelectronic peak shape in these films is very different from bulk YBCO. To investigate this, several samples of Y[sub 1]Ba[sub 2]Cu[sub 3]O[sub 7-x] thin films were intentionally created of varying quality. The films were deposited on LaAlO[sub 3] by pulsed laser deposition with J[sub c] values ranging from poorly conducting up to several MA/cm². Initial results indicated a potential correlation between the Y(3d) XPS peak shape (full-width-half-maximum) of the YBCO and the film quality. A potential correlation may also exist with the Cu(2p)/Ba(3d) ratio indicating an interrelationship to the FWHM of the Y(3d) peak. Film quality was determined by current transport, resistive T[sub c], and AC magnetic susceptibility measurements. [ABSTRACT FROM AUTHOR]

Magnetization vs. applied field measurements (M-H loops) were taken on YBCO thin films with filaments patterned into them. The YBCO was deposited onto LaAlO[sub 3] substrates using PLD, and the filaments were formed by laser ablation. M-H loops were taken at 4.2 K in fields up to ±9 T using a vibrating sample magnetometer technique, the field applied perpendicular to the film width, d. The losses were seen to be greatly reduced by filament width reductions following the standard expression Q[sub h]/H[sub m] ∝ dJ[sub c]/10. The penetration field was also well described by the standard "high field" expression H[sub p] = (0.4J[sub c]t) ln(d/t + 1), where t is the film thickness. The regimes of applicability of the loss expression were investigated, in particular near H[sub m] ≈ H[sub p]. A more general form of the loss equation was obtained and compared with the high-field approximation. The result was that although Q[sub h]/H[sub m] still increased in proportion to d, the rate of increase decreased as H[sub m] approached H[sub p]. [ABSTRACT FROM AUTHOR]

Epitaxial growth of YBa2Cu3O7−x (YBCO) layers on TiN(001) surfaces was explored, both with and without CeO2 intermediate layers. The epitaxial TiN layers were grown on MgO(001) and textured Ni substrates. Thin CeO2 (∼200 nm thick) and YBCO (∼300 nm thick) layers were grown on TiN-coated MgO substrates, using pulsed laser deposition. While YBCO grown directly on TiN was of poor quality, a good epitaxial YBCO layer was obtained using a thin CeO2 cap layer on the TiN. A superconducting critical transition temperature (Tc) of 89 K was measured by AC susceptibility. The critical current density (Jc) was 6×105 A/cm2 obtained at 77 K by whole body transport current measurement in self-field using a 1 μV/cm criteria. These results suggest that transition metal nitrides, such as TiN, are potentially useful as buffer layers for YBCO thin films. Advantages of the nitride buffer layers compared to conventional oxide buffers include high electrical and thermal conductivity, better mechanical toughness, good diffusion barrier characteristics, and relative ease of deposition. [Copyright &y& Elsevier]

Magnetization results of YBa2Cu3O7-d films processed with interlayers of CeO2 inclusions are presented. Unexpected flux pinning results that are different from previous observations with nanoparticulate layered inclusions were observed. Flux pinning was found to be in some cases either slightly improved at either low fields <0.5 T or in other cases at high fields >8 T although degraded, sometimes severely, at interim magnetic fields. Most unexpectedly, the pinning performance of the various samples rapidly converges as the temperature is reduced from 77 to 65 K, causing all films to have similar Jc(H) behavior at 65 K even though dramatically different at 77 K. [ABSTRACT FROM AUTHOR]

Magnetization results of YBa2Cu3O7-d films processed with interlayers of CeO2 inclusions are presented. Unexpected flux pinning results that are different from previous observations with nanoparticulate layered inclusions were observed. Flux pinning was found to be in some cases either slightly improved at either low fields <0.5 T or in other cases at high fields >8 T although degraded, sometimes severely, at interim magnetic fields. Most unexpectedly, the pinning performance of the various samples rapidly converges as the temperature is reduced from 77 to 65 K, causing all films to have similar Jc(H) behavior at 65 K even though dramatically different at 77 K. [ABSTRACT FROM AUTHOR]

We report the systematic substitution of Nb at the Cu1 site of YBa 2Cu3Oy in thin films to form a new phase of YBa 2Cu2NbO8. These films were deposited on SrTiO3(100) crystals using pulsed laser deposition and deposited at an optimal temperature of 850 °C. Films were characterized using x-ray diffraction (XRD), atomic force microscopy, x-ray photoelectron spectroscopy (XPS), micro-Raman spectroscopy, and transmission electron microscopy. XRD of these films indicate c-axis oriented YBa2Cu2NbOy formation. XPS and micro-Raman spectroscopy analysis suggests Cu exists in the +2 state. [ABSTRACT FROM AUTHOR]

Abstract: We have studied the transport current distributions in striated YBa2Cu3O7−x (YBCO) films and coated conductors using variable temperature scanning laser microscopy (VTSLM). VTSLM images reveal the location of incomplete separation between filaments due to un-optimized sample processing parameters. When the current flows parallel to the completely separated striations, the current seems to flow within a strip without inter-mixing via the substrate. Initial resistivity measurements on metallic inter-filamentary connections (gold dots) exhibit a semiconducting behavior. VTSLM images clearly show that the current flows between filaments via the metallic inter-connect, indicating the semiconducting resistive behavior is due to the interface between YBCO and metallic layer. The results demonstrate the potential of VTSLM technique in investigating current sharing and normal metal inter-connect issues for the coated conductor development for ac applications. [Copyright &y& Elsevier]