Showing papers by "Dominic F. Lee published in 2000"

Low angle grain boundary transport in YBa2Cu3O7−δ coated conductors

Abstract: Second generation, high-temperature superconducting wires are based on buffered, metallic tape substrates of near single crystal texture. Strong alignment of adjacent grains was found to be necessary from previous work that suggested large angle, YBa2Cu3O7−δ [001]-tilt boundaries reduce Jc exponentially with increasing misorientation angle (θ). We pursue the low-θ regime by evaluating single grain boundaries (GB) and biaxially aligned polycrystalline films utilizing both the rolling-assisted biaxially textured substrates and ion-beam assisted deposition coated conductor architectures. Analysis concludes that an exponential dependence on Jc is applicable for θ≳4°, where the spacing between the periodic disordered regions along the GB become smaller than a coherence length.

Low-cost YBCO coated conductor technology

Abstract: Deformation-textured, non-silver substrates, and solution-based deposition of buffer and superconductor layers offer routes to a low-cost YBCO coated-conductor technology for high-temperature superconducting wire Several significant steps towards such a technology are reported here: a solution-based Gd2O3 seed buffer layer was deposited by a web-coating technique over a metre-length tape of deformation-textured nickel with excellent texture and uniformity Also, short full-stack samples with YBCO performance up to 08 MA cm-2 at 77 K were prepared at Oak Ridge National Laboratory (ORNL) and American Superconductor (ASC) using a CeO2/YSZ/CeO2 buffer sequence on textured nickel and a trifluoroacetate (TFA) precursor YBCO process; in this case the buffers are deposited by e-beam and magnetron sputtering

Epitaxial growth of La2Zr2O7 thin films on rolled Ni-substrates by sol-gel process for high Tc superconducting tapes

Abstract: A solution process was used to grow epitaxial La 2 Zr 2 O 7 (LZO) buffer layers on roll-textured Ni (100) substrates to produce YBa 2 Cu 3 O 7− δ (YBCO)-coated conductors. The LZO precursor solution was prepared by an all alkoxide sol–gel route using mixed metal methoxyethoxides in 2-methoxyethanol. The partially hydrolyzed solution was either spin-coated or dip-coated onto the textured Ni substrates. The amorphous thin film was then heat treated at 1150°C under (96%)Ar/(4%)H 2 atmosphere for 1 h. X-ray diffraction (XRD) of the buffer layer indicated a strong c -axis orientation on the Ni (100) substrate. The LZO (222) pole figure revealed a single cube-on-cube texture. SEM images of the LZO buffer layer showed a dense microstructure without cracks. The YBCO deposited on the sol–gel LZO-buffered Ni substrates with sputtered YSZ and CeO 2 top layers had a critical current density of 480,000 A/cm 2 at 77 K and self-field.

YBa2Cu3O7-y−coated conductors with high engineering current density

Abstract: Short segments of YBa2Cu3O7-y (YBCO) coated conductors were fabricated on rolling-assisted biaxially textured substrates (RABiTS) with a layer sequence of CeO2/YSZ/Ni using an ex situ BaF2 precursor process. Pulsed laser deposition (PLD) was used to deposit both YSZ and CeO2 layers. The YBCO films were grown using e-beam coevaporated Y–BaF2–Cu precursors followed by postannealing. An overall engineering current density, JE, of 28,000 A/cm2 and critical current, Ic, of 147 A/cm width at 77 K were achieved for a 1.6-μm-thick YBCO film. This result demonstrates the possibility of using both the ex situ BaF2 precursor approach and the RABiTS process for producing long lengths of high-JE coated conductors.

Method of depositing a protective layer over a biaxially textured alloy substrate and composition therefrom

Abstract: A laminate article consists of a substrate and a biaxially textured protective layer over the substrate. The substrate can be biaxially textured and also have reduced magnetism over the magnetism of Ni. The substrate can be selected from the group consisting of nickel, copper, iron, aluminum, silver and alloys containing any of the foregoing. The protective layer can be selected from the group consisting of gold, silver, platinum, palladium, and nickel and alloys containing any of the foregoing. The protective layer is also non-oxidizable under conditions employed to deposit a desired, subsequent oxide buffer layer. Layers of YBCO, CeO 2 , YSZ, LaAlO 3 , SrTiO 3 , Y 2 O 3 , RE 2 O 3 , SrRuO 3 , LaNiO 3 and La 2 ZrO 3 can be deposited over the protective layer. A method of forming the laminate article is also disclosed.

Nucleation of epitaxial yttria-stabilized zirconia on biaxially textured (001) Ni for deposited conductors

Abstract: The nucleation of (001)-oriented yttria-stabilized zirconia (YSZ) directly on the (001) Ni surface is realized via nucleation on an oxygen-terminated nickel surface using pulsed-laser deposition. Under conditions where the nickel surface is either oxygen free or substantially covered with NiO, a mixed orientation of YSZ occurs. The epitaxial YSZ layer grown on a biaxially textured Ni(001) surface was used as a single buffer layer for a high temperature superconducting coated conductor architecture, yielding superconducting YBa2Cu3O7 films with high critical current densities, Jc. This architecture eliminates the necessity for a multilayer buffer architecture, since high Jc superconducting films are achieved with no intermediate buffer layer between the (001) YSZ and the biaxially textured metal.

Epitaxial growth of gadolinium oxide on roll-textured nickel using a solution growth technique

Abstract: 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 A 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 A Electron diffraction indicated that the misalignment of the majority of the grains in the plane was less than 10° High-current (04 MA/cm2) Yba2Cu3O7–δ films were grown on roll-textured nickel substrates using Gd2O3 as the base layer in a three-layer buffer structure

Method for preparing preferentially oriented, high temperature superconductors using solution reagents

Abstract: A multi-domained bulk REBa 2 CU 3 O x with low-angle domain boundaries which resemble a quasi-single domained material and a method for producing the same comprising arranging multiple seeds, which can be small single crystals, single domained melt-textured REBa 2 CU 3 O x pieces, textured substrates comprises of grains with low misorientation angles, or thick film REBa 2 CU 3 O x deposited on such textured substrate, such seeds being tailored for various REBa 2 CU 3 O x compounds, in specific pattern and relative seed orientations on a superconductor precursor material which may be placed in contact with a porous substrate so as to reduce the amount of liquid phase in the melt. Because seeds can be arranged in virtually any pattern, high quality REBa 2 CU 3 O x elements of virtually unlimited size and complex geometry can be fabricated.

Epitaxial yttria-stabilized zirconia on biaxially-textured (001) Ni for YBCO coated conductor

Abstract: Epitaxial YSZ film was deposited directly on biaxially-textured (001) Ni tapes using pulsed-laser deposition. Nucleation of the YSZ film on Ni is achieved without the intentional removal of the native oxide from the Ni (001) surface. The epitaxial YSZ layer grown on the Ni (001) surface was used as a single buffer layer for a high temperature superconducting coated conductor architecture, yielding YBa 2 Cu 3 O 7 films with critical current density of 1 MA/cm 2 at 77 K. This architecture eliminates the necessity for a multilayer buffer architecture, as high J c superconducting films are achieved with no intermediate buffer layer between the (001) YSZ and the biaxially textured metal.

Progress towards a low-cost coated conductor technology

Abstract: Progress in the development of an economically and technically viable YBCO coated conductor technology for HTS wire using deformation-textured buffered substrates and solution-deposited superconductor layers is reported. Biaxially textured Ni substrates have been fabricated using a deformation texturing process. Epitaxial oxide buffer layers have been deposited by a combination of e-beam deposition and magnetron sputtering. Epitaxial YBCO films have been grown using a trifluoroacetate solution precursor. The resulting composite conductors have critical current densities approaching 2 MA/cm 2 at 77K in self-field. Critical current densities of 4.5 MA/cm 2 have been also obtained on CeO 2 buffered YSZ single crystal substrates, demonstrating performance parity with vacuum deposited YBCO films.

Microstructural homogeneity and electromagnetic connectivity of YBa2Cu3O7−δ grown on rolling-assisted biaxially textured coated conductor substrates

Abstract: The electromagnetic connectivity and microstructure of three YBa 2 Cu 3 O 7− δ (YBCO) films grown on biaxially textured substrates were investigated by magneto optic (MO) imaging and scanning electron microscopy (SEM). The films were deposited by pulsed laser deposition (PLD) on yttria-stabilized zirconia (YSZ) and CeO 2 -buffered, biaxially textured Ni tapes. The transport critical current density ( J c ) values of the films were 0.3, 0.6 and 0.7 MA/cm 2 (77 K, 0 T). MO imaging revealed clearly granular electromagnetic behavior in the lowest J c and one of the higher J c samples, but considerably better connectivity in the sample with a J c value of 0.6 MA/cm 2 . High resolution SEM showed a dense and rather featureless microstructure in the YBCO of the most highly electromagnetically connected sample, whereas pores and/or second phase particles cluttered the YBCO layers of the granular samples. Thus, the granular behavior in these samples appears to be caused by pores and second phase particles that locally obstruct the superconducting current in the YBCO layer. Control of these types of defects clearly is important for raising the J c value.