J.-C. Grivel

Fabrication of the Textured Ni-9.3at.%W Alloy Substrate for Coated Conductors

It is difficult to obtain a sharp cube texture in the Ni-9.3at.% W substrate used for coated conductors due to its low stacking fault energy. In this paper, the traditional cold rolling procedure was optimized by introducing an intermediate recovery annealing. The deformation texture has been improved after three recovery annealing cycles at 500°C for 2 h during the cold rolling process. After optimized recrystallization annealing, a Ni-9.3at.% substrate with a cube texture content of 87.7% (<;10°) has been obtained. The effect of the intermediate annealing on cube texture formation is attributed to the improved deformation texture and to the enhanced pre-existing cube oriented structure in the deformed matrix.

Development of One Meter Long Double-Sided

High performance long-length coated conductors fabricated using various techniques have attracted a lot of interest recently. In this work, a reel-to-reel design for depositing double-sided coatings on long-length flexible metallic tapes via a chemical solution method is proposed and realized. The major achievement of the design is to combine the dip coating and drying processes in order to overcome the technical difficulties of dealing with the wet films on both sides of the tape. We report the successful application of the design to fabricate a one-meter-long double side coated CeO₂/Ni-5at%W template. The CeO₂ films on both sides exhibit a dense, crack-free morphology, and a high fraction of cube texture on the surface. Homogeneity studies on global texture over the length also reveal that the average full width at half maximum values of the in-plane and out-of-plane orientation on the CeO₂ layer are 7.2 ^° and 5.8^° with standard deviation of 0.26^° and 0.34^°, respectively, being indicative of the high quality epitaxial growth of the films prepared in the continuous manner. An all chemical solution derived YBCO^Low-TFA/Ce_0.9La_0.1O₂ /Gd₂Zr₂O₇/CeO₂ structure is obtained on a short sample, demonstrating the possibility of producing long-length texture templates for coated conductors by this low cost deposition route.

\hbox{CeO}_{2}

We have developed a fluorine-free metal-organic decomposition method using acrylic acid as the solvent for the synthesis of GdBCO superconducting thin films. Commonly used propionic acid was also used to make a comparison with acrylic acid. Acrylic acid was found to be polymerized during drying, resulting in high thermal stability of the precursor solution. Due to the elevated decomposition temperature of the organic compounds in the acrylic-acid-based precursor, the formation of intermediate phases such as CuO was found delayed; therefore, the grain growth and phase segregation were suppressed. The superior quality of pyrolyzed films induced by the use of polymerizable acrylic acid is reflected in the Jc of the GdBCO films, which achieved 1.2MA/ cm2.

Buffered Ni-5at.%W Templates by Reel-to-Reel Chemical Solution Deposition Route

Dy1−x(Gd or Yb)xBa2Cu3O7−δ samples were prepared using chemical solution deposition (CSD), based on trifluoroacetate metal-organic decomposition (MOD) methods. Xray diffraction results demonstrated the formation of the RE123 superconducting phase with a strong in-plane and out-of-plane texture. c-lattice constants were observed to decrease for all samples doped with Gd or Yb. Measurements of the onset critical transition temperature (T c ) were found to decrease with increasing Yb content, while only minor changes were observed for samples with Gd. Critical current density (Jc) analysis demonstrated that doping with Yb significantly increased the self-field Jc value from 3.8 MA/cm to 6.0 MA/cm for the pure and 10 % Yb doped sample, respectively. In contrast, samples doped with Gd were characterized by the lowest self-field Jc values. Investigation of pinning force mechanisms revealed that the samples in this study were dominated by normal surface pinning.Dy_1-x(Gd or Yb)_xBa₂Cu₃O_7-δ samples were prepared using chemical solution deposition, based on trifluoroacetate metal-organic decomposition methods. X-ray diffraction results demonstrated the formation of the RE123 superconducting phase with strong in-plane and out-of-plane texture. For all samples doped with Gd or Yb, c-lattice constants were observed to decrease. Measurements of the onset critical transition temperature (T_c^onset ) were found to decrease with increasing Yb content, whereas only minor changes were observed for samples with Gd. Critical current density (J_c) analysis demonstrated that doping with Yb significantly increased the self-field J_c value from 3.8 MA/cm² to 6.0 MA/cm² for the pure sample and the 10% Yb-doped sample, respectively. In contrast, samples doped with Gd were characterized by the lowest self-field J_c values. Investigation of pinning force mechanisms revealed that the samples in this study were dominated by normal surface pinning.

Manufacture of

Ni-5 at.%W (Ni5W) tapes with a strong cube texture were fabricated using the RABiTS technique and by starting from cylindrical shaped ingots. In contrast to a conventional cuboid-shaped ingot, a cylinder shaped ingot has no anisotropy along the axial direction and the resulting tape will therefore, during heavy cold rolling, be characterized by a lower concentration of stress along the edges of the ingot. It can reduce fabrication costs and increase process efficiency. The fraction of cube texture on the surface of the finally recrystallized tapes was investigated using the EBSD technique. It was observed that the fraction of cube texture within 10° from the ideal {001}〈100〉 orientation was ~98% and the fraction of LAGBs was ~90%. The as-obtained tapes have a strong cube texture also very close to the edge of the tape and they would therefore increase the fraction of applicable material while simplifying the heavy rolling process. Accordingly, it suggests that this fabrication method is a good choice to most small scale research laboratories for achieving long length Ni5W tapes for coated conductors with an easy way and a higher fraction of applicable material.

\hbox{GdBa}_{2}\hbox{Cu}_{3}\hbox{O}_{7 - x}

Ni-12at.%V alloy is a promising candidate for non-magnetic cube textured metallic substrates used for high temperature coated conductors. In this work, a textured Ni-12at.%V substrate has been fabricated by powder metallurgy route. After cold rolling and recrystallization annealing, a cube texture content as high as 99% (<;10°) was obtained, and the low angle grain boundary fraction is 89%. In addition, the FWHM values of phi-scan and rocking curve are 7.77° and 7.37°, respectively. According to micro-hardness measurement, the HV value of Ni-12at.%V tape is three times higher than that of pure Ni and to a certain extent higher than that of Ni-5at.%W. Furthermore, the Curie temperature of the Ni-12at.%V substrate is decreased to less than 77 K due to the addition of vanadium element in Ni.

Superconducting Thin Films Using High-Thermal-Stability Precursors Playing the Role of Intermediate-Phase Grain-Growth Inhibitors

In the chemical solution deposition process of YBCO superconducting films, fluorine is widely regarded to be of significant importance in avoiding the formation of BaCO3, which hinders the growth of high-quality YBCO films. On the other hand, great efforts have been made to decrease the fluorine content in the precursor solution due to the environmental contaminations of the fluorinated gaseous by-products. In this study, we demonstrate that an F/Ba atomic ratio of 2 in the precursor solution is sufficient according to the results of energy dispersive spectrometry and attenuated Fourier transform infrared studies. The intermediate phase evolution prior to the end of the sintering stage is also investigated by X-ray diffractometry and scanning electron microscopy. Liquid-like structures are observed, which are proposed to be responsible for the film densification in the early stage of YBCO formation. The formation of YBCO is accompanied by the consumption of oxygen-doped BaF2 (BOF), which is found to be highly textured. Moreover, in the early stage of YBCO formation, the crystallinity and texture of BOF enhance despite its consumption. After a full heat treatment, YBCO films with Jc of 5 MA/cm2 (77 K, 0 T) could be routinely obtained on lanthanum aluminate single-crystal substrates.

Superconducting Dy1-x(Gd,Yb)xBa2Cu3O7-δ thin films made by Chemical Solution Deposition

A recently developed two-level undercut-profile substrate (2LUPS), containing two levels of plateaus connected by a curved wall with an undercut profile, enables self-forming filaments in a coated conductor during physical line-of-sight deposition of buffer and superconducting layers. In the present study, the 2LUPS concept is applied to a commercial cube-textured Ni-5at.%W tape, and the surface of the 2LUPS coated with two Gd2Zr2O7 buffer layers using chemical solution deposition is examined. Except for narrow regions near the edge of upper plateaus, the plateaus are found to be covered by strongly textured Gd2Zr2O7 buffer layers after dip coating and sintering.

Study on Fabrication of Ni-5 at.%W Tapes for Coated Conductors from Cylinder Ingots

In this work, four fluorine-free solutions based on various carboxylates (propionates, butyrates, valerates, and hexanoates, respectively) were prepared and used for deposition of YBCO films on LaAlO3 single-crystal substrates, in order to further understand the role of precursors on properties of the final films. After the same pyrolysis and sintering processes, the films from propionates and butyrates show pure YBCO phase and were epitaxially grown, as determined by X-ray diffractometer analysis. There are clear differences in morphologies of these four films, i.e., the films from propionates and butyrates exhibit platelike grains without distinct grain boundaries, while almost randomly orientated grains were observed on the surface of the other two films. As a result, we noticed significant discrepancies on their superconducting performance. The films from propionates and butyrates give Jc values (at 77 K, self-field) of 2.1 MA/cm2 and 1.3 MA/cm2, respectively, while no superconducting transition above 70 K was observed in the other two films. A relatively larger amount of carbonaceous residue left as a by-product after decomposition of carboxylates with longer ligands, particularly under fast pyrolysis and sintering processes, could be one of the explanations of the poor superconductivity in the films from the valerateand hexanoate-based precursors.

Fabrication of a Textured Non-Magnetic Ni-12at.%V Alloy Substrate for Coated Conductors

An optimized buffer layer architecture prepared by a metal organic deposition method on biaxially textured metallic substrate is proposed and developed successfully. The major achievement of this work is to choose a Ce_0.9La_0.1O₂ layer as cap layer that possesses an excellent lattice match with the superconductor layer, and to employ 200 nm thick Gd₂Zr₂O₇ film as barrier layer. The effect of thermal cycling on the texture and morphology of the crystallized films and NiW substrate is discussed in detail. The texture quality and the epitaxial relationship between the buffer layer stack and the metallic substrate were studied by synchrotron x-ray diffraction. Well textured, smooth and crack-free Ce_0.9La_0.1O₂/Gd₂Zr₂O₇ buffer layer stacks are obtained, demonstrating the possibility of producing a high quality buffer layer stack by a low cost chemical solution deposition route.