Simplification of the ion-beam-assisted deposition (IBAD) buffer architecture is one of the key issues for reduced manufacturing cost of second-generation superconducting wire production. In this work, we studied various radio frequency magnetron sputter deposition conditions for epitaxial growth of LaMnO3 (LMO) layers, with varying thicknesses, directly on IBAD-MgO without homo-epitaxial MgO layers. Performance of the simplified LMO/IBAD-MgO samples was qualified by pulsed-laser-deposited 1-μm-thick YBa2Cu3O7−δ (YBCO) coatings. Detailed property characterizations revealed that though the growth temperature has a substantial effect on the texture of LMO layers, neither LMO thickness nor different sputter gas compositions had a significant effect on the performance of YBCO films. The superconducting properties of YBCO on LMO/IBAD-MgO are found to be similar to those obtained on templates having homo-epitaxial MgO layers. The present results underscore the strong potential of LMO as a single cap layer directly on IBAD-MgO for the development of a simplified IBAD architecture.

Chemical solution processing of Gd2Zr2O7 (GZO) thin films via sol-gel and metalorganic decomposition (MOD) precursor routes have been studied on textured Ni-based tape substrates. Even though films processed by both techniques showed similar property characteristics, the MOD-derived samples developed a high degree of texture alignment at significantly lower temperatures. Both precursor chemistries resulted in exceptionally dense, pore-free, and smooth microstructures, reflected in the cross-sectional and plan-view high-resolution scanning and transmission electron microscopy studies. On the MOD GZO buffered Ni–3at.% W (Ni–W) substrates with additional CeO2/YSZ sputtered over layers, a 0.8-μm-thick YBa2Cu3O7−δ (YBCO) film, grown by an ex situ metalorganic trifluoroacetate precursor method, yielded critical current, Ic (77 K, self-field), of 100 A/cm width. Furthermore, using pulsed-laser deposited YBCO films, a zero-field superconducting critical current density, Jc (77 K), of 1 × 106 A/cm2 was demonstrated on an all-solution, simplified CeO2(MOD)/GZO(MOD)/Ni–W architecture. The present study establishes GZO buffers as a candidate material for low-cost, all-solution coated conductor fabrication.

Epitaxial lanthanum zirconate (LZO) buffer layers have been grown by sol-gel processing on Ni–W substrates. We report on the application of these oxide films as seed and barrier layers in coated conductor fabrication as potentially simpler, lower cost coated-conductor architecture. The LZO films, about 80–100-nm thick, were found to have dense, crack-free surfaces with high surface crystallinity. Using 0.2-μm YBCO deposited by pulsed laser deposition, a critical current density of 2 MA/cm2 has been demonstrated on the LZO films (YBCO/LZO/Ni–W). Using 0.8-μm YBCO deposited using metal organic decomposition, a critical current density of 1.7 MA/cm2 and a critical current of 135 A/cm have been demonstrated on the LZO barrier layer with a sputtered CeO2 cap layer (YBCO/CeO2/LZO/Ni–W). These results offer promise to replace several of the vacuum-deposited layers in the typical coated conductor architecture (YBCO/CeO2/YSZ/Y2O3/Ni/Ni-W).

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.

High critical current density (high-Jc) YBa2Cu3O7–δ (YBCO) films were obtained by pulsed laser ablation on biaxially textured Cu substrates. To achieve epitaxy of LaMnO3 (LMO) on Cu, thin epitaxial Ni overlayers were deposited on Cu tapes. The structure comprises the layer sequence of YBCO/LMO/Ni/Cu. For 200-nm-thick YBCO, self-field Jc values exceeding 1 × 106 A/cm2 at 77 K were achieved. Characterization of these short prototype conductors revealed good structural and morphological properties. Magnetic analysis suggested that hysteretic loss due to the ferromagnetic Ni overlayer is minimal.

Single, epitaxial buffer layers of insulating LaMnO3 (LMO) or conductive La0.7Sr0.3MnO3 (LSMO) have been grown by sputter deposition on biaxially textured Ni and Ni–alloy substrates. We report baseline investigations of their compatibility with the Yba2Cu3O7−δ (YBCO) coatings and demonstrate biaxially textured YBCO films grown by pulsed-laser deposition on these single-buffered tapes. Superconducting property characterizations revealed better properties for YBCO films on LMO-buffered tapes relative to those grown on LSMO layers. Self-field critical current densities (Jc) exceeding 1 × 106 A/cm2 at 77 K have been obtained for the YBCO (200 nm) films on LMO-buffer layers. These results offer prospects for the use of single, LMO-buffered metal tapes in the development of practical YBCO-coated conductors.

Sol-gel processing of La2Zr2O7 (LZO) buffer layers on biaxially textured Ni–1.7% Fe–3% W alloy substrates using a continuous reel-to-reel dip-coating unit has been studied. The epitaxial LZO films obtained have a strong cube texture and uniform microstructure. The effects of increasing the annealing speed on the texture, microstructure, and carbon content retained in the film were studied. On top of the LZO films, epitaxial layers of yttria-stabilized zirconia and Ceria (CeO2) were deposited using rf sputtering, and YBa2Cu3Ox (YBCO) films were then deposited using pulsed laser deposition. Critical current densities (Jc) of 1.9 MA/cm2 at 77 K and self-field and 0.34 MA/cm2at 77 K and 0.5 T have been obtained on these films. These values are comparable to those obtained on YBCO films deposited on all-vacuum deposited buffer layers and the highest ever obtained using solution seed layers.

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.

In an effort to develop alternative single buffer layer technology for YBa2Cu3O7-δ (YBCO) coated conductors, we have investigated LaMnO3 (LMO) as a potential buffer layer. High-quality LMO films were grown directly on biaxially textured Ni and Ni-W (3%) substrates using rf magnetron sputtering. YBCO films were then grown on LMO buffers using pulsed laser deposition. Detailed X-ray studies have shown that both YBCO and LMO layers were grown with a single epitaxial orientation. Rutherford backscattering spectroscopy (RBS) analyses have indicated the ratio of La to Mn ratio is 1:1. SEM micrographs indicated that 3000-Å-thick LMO films on biaxially textured Ni (100) substrates were dense, continuous and crack-free. A high Jc of over 1 MA/cm2 at 77 K and self-field was obtained on YBCO films grown on LMO-buffered Ni or Ni-W substrates. We have identified LaMnO3 as a good diffusion barrier layer for Ni and it also provides a good template for growing high current density YBCO films.

We have investigated the diffusion mechanism of Hg and Tl cations in cation-exchange process that has been used successfully for fabrication of Hg-based high-Tc superconducting films. Scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) was employed to map the distribution of Tl and Hg cations in films quenched at different stages of the cation exchange process. SEM/EDS mappings showed that the nonuniform distribution of Hg is visible in micrometer size on the surface of samples quenched after short-time (∼10min) Hg-annealing, but this nonuniformity disappears for longer-time (∼45 min) Hg-annealing samples. This change could be ascribed to different stages in Hg diffusion -- the former is the early stage when Hg is concentrated in the channels and the latter Hg-cations have already diffuse to grains. Our experimental results hence suggest that Hg-cations channel through defects in the films then diffuse into grains along a-b planes and vise versa for Tl-cations. The diffusion mechanism of anions (oxygen) in post annealing has also been discussed. Fluorine-doped Hg-1212 films were post annealed in flowing oxygen at 300 °C for several hours. Magnetic measurement has shown these samples are comprised pure overdoped Hg-1212 phase with smooth and sharp transition below 120 K, but resistivity vs. temperature measurement shows a kink at ∼123 K. This implies that the optimally doped Hg-1212 phase with higher Tc might be surrounded by overdoped Hg-1212 phase and their contribution to magnetization is minimized, thus the possible diffusion mechanism for anions is also through grain boundaries at a much larger time scale compared to the cations.

Sol-gel processing of La2Zr2O7 (LZO) buffer layers on biaxially textured Ni-3 at.% W alloy substrates using a continuous reel-to-reel dip-coating unit has been studied. The epitaxial LZO films obtained have a strong cube texture and uniform microstructure. The effect of increasing the annealing speed on the texture, microstructure and the carbon content retained in the film were studied. On top of the LZO films, epitaxial layers of Yttria Stabilized Zirconia (YSZ) and Ceria (CeO2) were deposited using rf sputtering, and YBa2Cu3Ox (YBCO) films were then deposited using Pulsed Laser Deposition (PLD). A critical current density (Jc) of 1.9 MA/cm2 at 77K and self-field and 0.34 MA/cm2 at 77K and 0.5T have been obtained on these films. These values are comparable to those obtained on YBCO films deposited on all-vacuum deposited buffer layers, and are the highest ever obtained using solution seed layers. The use of all-solution buffers for coated conductor processing has also been explored. A critical current density of 1.1 MA/cm2 at 77 K and self-field was obtained on YBCO films grown be PLD on LZO buffered nickel substrates.