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ABSTRACT: Fabrication of thick YBa<sub>2</sub>Cu<sub>3</sub>O<sub>y</sub> (YBCO) films with high critical current densities(J<sub>c</sub>) has remained one of the major challenges in the coated conductor development process. In this work, we report successful fabrication of several multi-layer YBCO films with thicknesses ranging from 0.1 micrometers to 1.2 micrometers. The films were deposited on a single crystal substrate by using a multi-layer TFA-MOD technique. The effect of variation in the thickness of an individual layer in a multi-layer film on the overall properties of the film was studied by processing multi-layer films with individual layers of 0.1 micrometers, 0.2 micrometers and 0.5 micrometers. The J<sub>c</sub> value for the 0.1 micrometers thick single-layer film was as high as 7 MA/cm<sup>2</sup>, and the J<sub>c</sub> for 6-layer1.2 micrometers thick film was 1 MA/cm<sup>2</sup> at 77 K and self field. XRD, SEM and TEM were used to study the dependence of J<sub>c</sub> on the orientation, texture and microstructure of the film. It was found that the texture, connections between the two successive layers, porosity, and the crack formation affect the J<sub>c</sub> of the film. In addition, we report a multi layer fabrication route with a shorter duration of the pyrolysis reaction according to the number of coats.
IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
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ABSTRACT: Several practical applications require relatively thick Y1Ba2Cu3O7 (YBCO) coated conductors (1–2 µm) to carry a high critical current (Ic). However, as the thickness of the YBCO film increases, its critical current density (Jc) decreases. In this work, we report the successful fabrication of thick YBCO films using a multiple coatings technique while maintaining a high Jc. In particular, several YBCO films with different numbers of layers were fabricated on a LaAlO3 substrate by a multiple coatings process using a trifluoroacetate metal organic deposition method (TFA-MOD). No cracks or pores were observed in cross-sectional transmission electron microscope (TEM) images of these films; further, the layers were well connected with the smooth interface. The majority of the grains in the films were c-axis oriented. Full-width at half-maximum (FWHM) values for in-plane and out-of-plane alignments for a five-layer film were 2.45° and 1.2° respectively. Jc exceeding 1.6 MA cm−2 and critical current (Ic) of 160 A cm−1 have been obtained for a 1 µm thick film with five layers at 77 K.
Superconductor Science and Technology 03/2008; 21(4):045015. · 2.66 Impact Factor
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ABSTRACT: A novel nanomaterial synthesis technique has been developed to introduce 0D (particles), 1D (columnar defects) and 3D (domains) nanoscale pinning centres in MOD Y1Ba2Cu3O7 (YBCO) coated conductors. We have succeeded in introducing nanoscale Y enriched particles, nanoscale 90° rotated Y1/3Sm2/3Ba2Cu3O7 domains and nanoscale Zr enriched columnar defects into YBCO layers by different chemical doping. The pinning force density in Y2O3-doped YBCO film is found to be larger than that of pure YBCO film at all fields. Also it was found that YBCO films with Sm substituting for Y have yielded improved critical current density characteristics over a wide range of magnetic fields. Maximum pinning force densities exceeding 7 and 8 GN m−3 are obtained in 5% BZO-doped and Sm substituted YBCO films, respectively. Additionally, TEM studies revealed nanoscale Zr enriched columnar defects distributing in the matrix of the c-oriented YBCO film throughout the whole cross section. This indicates that chemical doping is a promising fabrication technique to create specific pinning landscapes in YBCO coated conductors.
Superconductor Science and Technology 08/2007; 20(9):S147. · 2.66 Impact Factor
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ABSTRACT: Sharp cube textured Ni-9%atW alloy substrates were successfully achieved using the powder metallurgy process and gave promise for coated conductor with reduced AC losses and improved mechanical properties. X-ray studies indicated that the newly developed Ni-9%atW alloy substrates have a good out-of-plane and in-plane orientation with FWHM values about 3.7deg and 7.05deg respectively. Smooth surface as well as fine grains were obtained in the newly developed textured substrate. Curie temperature is suppressed to be 30 K and magnetic hysteretic losses are zero for Ni-9%atW alloy substrates at 77 K.
IEEE Transactions on Appiled Superconductivity 07/2007; · 1.04 Impact Factor
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ABSTRACT: Many efforts have been made to improve the current carrying capability of Y<sub>1</sub>Ba<sub>2</sub>Cu<sub>3</sub>O<sub>7</sub> (YBCO) films by introducing pinning centers using a variety of techniques. In this study, we have succeeded in producing Y<sub>2</sub>O<sub>3</sub>, BaZrO<sub>3</sub> and Sm doped YBCO films for the development of coated conductors by a metal-organic deposition method using trifluoroacetates (TFA-MOD). Jc exceeding 5 MA /cm<sup>2</sup> at 77 K and self field was obtained in Y<sub>2</sub>O<sub>3</sub> doped YBCO film. Also it was found that YBCO films with Sm substituting for Y have shown an improved critical current density characteristic over a wide range of magnetic fields. A Jc of 0.25 MA/cm<sup>2</sup> at 3 T and 77 K was obtained which is more than 10% of the zero-field Jc. Similar results were obtained in BaZrO<sub>3</sub> doped YBCO films. Additionally, TEM analysis was performed to study the microstructures and the pinning mechanisms. The results indicate that significant enhancement of self-field and in-field Jc of Y<sub>2</sub>O<sub>3</sub>, BaZrO<sub>3</sub> and Sm doped YBCO films may be due to introducing nano-scaled Y<sub>2</sub>O<sub>3</sub> particles, nano-scaled 90deg rotated Y<sub>1/3</sub>Sm<sub>2/3</sub>Ba<sub>2</sub>Cu<sub>3</sub>O<sub>7</sub> domains and BaZrO<sub>3</sub> nanodots by different chemical doping, respectively. This indicates that chemical doping is a promising approach for enhancement of current carrying capability of YBCO coated conductors.
IEEE Transactions on Appiled Superconductivity 07/2007; · 1.04 Impact Factor
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ABSTRACT: The low mass density of magnesium diboride (MgB<sub>2</sub>) and its high critical temperature make it the ideal candidate for lightweight liquid hydrogen cooled superconducting magnets that are pivotal for space applications, where the cost per kilo to orbit is still such an expensive barrier. The feasibility of MgB<sub>2</sub> magnets strongly depends on the effect of applied stresses during manufacturing and operational procedures. In this work we introduce our research on mechanical properties of PIT processed wires for magnet applications and for the first time we present results on Ti-sheathed MgB<sub>2</sub> wires. Recently we improved our testing capability with new equipment and tested two coils: the first one was a coil with Fe-sheathed wire and the second one, in order to promote the use of this compound for space activities, uses wires with titanium as a sheath material. These wires show similar results to those sheathed with Fe, at 4 K the critical current density J<sub>c</sub> is well above 7times10 <sup>5</sup> A/cm<sup>2</sup>. The Ti-sheathed coil is still under testing
IEEE Transactions on Appiled Superconductivity 07/2006; · 1.04 Impact Factor
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ABSTRACT: The work reported in this paper aims at a better understanding of doping effects on high temperature superconducting YBa2Cu3O7−δ (YBCO or M-doped YBCO), in the form of large grains, fabricated by the top seeded melt-growth process. The study focused on the performance of YBCO large grains doped with Co, Ga, Ni and Zn substituting for the Cu site. The rate of Tc suppression with dopant concentration varies significantly among different dopants. Zn doping shows the highest depression rate, followed by Ni, Ga and Co doping. This we attribute to the fact that Zn and Ni substitute at Cu (2) sites on CuO2 planes in the lattice, whereas Co and Ga occupy Cu (1) sites along CuO chains and they have different magnetic moments. Trapped field, levitation force and Jc are enhanced due to pinning caused by local suppressed superconducting regions, and the enhancement effects are the highest in the case of Zn doping.
Superconductor Science and Technology 05/2006; 19(7):S556. · 2.66 Impact Factor
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ABSTRACT: In this study, nanosized Y2BaCuO5 (Y211) particles were synthesized by using the microemulsion method. The water-in-oil (w/o) microemulsion system constituted of n-octane, cetyltrimethylammonium bromide (CTAB), butanol and water. The effects of the reaction time and heat treatment on the Y211 particle size were studied. SEM and TEM investigations indicate that the average particle size of the synthesized Y211 was less than 110 nm. Melt-textured superconducting yttrium barium copper oxides (YBCOs) were fabricated by using the synthesized nanosized Y211 powder with and without Pt doping. Trapped field and critical current density (JC) were enhanced in the melt-textured YBCO as a result of using the nanosized Y211 as the starting precursor.
Superconductor Science and Technology 04/2006; 19(6):589. · 2.66 Impact Factor
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ABSTRACT: The peculiar features of magnesium diboride make it suitable for many potential applications. In the last four years of investigation of MgB2, the scientific community's research was mainly motivated by features such as low cost, compatibility with straightforward processing methods, relatively high critical temperature, and absence of weak links between grains. Other applications suggest the accentuation of other MgB2 properties. In particular its very low mass density makes it attractive for space activities, where the cost per kilogram for orbiting is still a huge obstacle, e.g. the cost of transport to low Earth orbit can reach 15 k$ kg−1. In order to promote the use of this compound for space activities, we tested titanium as a sheath material. Titanium is non-magnetic and its alloys are almost half the weight of steel but with yield stresses up to three times higher. We fabricated Ti-sheathed MgB2 through the powder-in-tube process. These wires show similar results to those sheathed with Fe. At 4 K the critical current density Jc is well above 7 × 105 A cm−2. The interface between the superconducting intermetallic compound and the lightweight sheath does not show any evidence of reaction and diffusion up to 900 °C. An analysis was carried out using x-ray diffraction, scanning electron microscopy with an energy dispersive spectrometer, and electron microprobe analysis.
Superconductor Science and Technology 12/2005; 19(1):129. · 2.66 Impact Factor
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ABSTRACT: The current-carrying capability of superconducting wires is degraded by stress. Therefore electromechanical properties are one of the key feedback parameters needed for progress in conductor applications. In this work, uniaxial tensile stresses and bending stresses were applied to Fe /MgB2 wires at room temperature, followed by measurement of critical current using a transport method at 4.2 K. Basic mechanical properties were calculated from the measured stress–strain characteristics. The irreversible tensile strain at which the critical current density of MgB2 wire starts to degrade was found to be 0.5%. In addition, the degradation of Ic with decreasing bending diameters was found to be very rapid for wires that were deformed after the heat treatment that forms the MgB2 compound, while not much degradation of Ic was found for wires that were bent before being annealed. SEM observations confirmed that cracks could be healed by post-annealing.
Superconductor Science and Technology 11/2005; 18(12):S369. · 2.66 Impact Factor
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ABSTRACT: Superconducting coils with different dimensions were manufactured via a wind-reaction process by using Fe-sheathed MgB<sub>2</sub> wires, which were fabricated using the powder-in-tube method and ultra-fine starting precursors. Very good grain connectivity as well as high core density was obtained in Fe-sheathed wires and tapes. At 20 K and self-field, the critical current of the coil with ID 12 mm and 12 turns is 360 A, which is equivalent to the J<sub>c</sub> of 1.8×10<sup>5</sup> A/cm<sup>2</sup>. At 6 Tesla external magnetic field and 4.2 K, the coil with ID 14 cm and 10 turns possesses the J<sub>c</sub> of 1×10<sup>4</sup> A/cm<sup>2</sup>. In-field current carrying capability of MgB<sub>2</sub> wires and tapes were further enhanced by Ti additive. These results demonstrate the potential of MgB<sub>2</sub> superconducting wires and tapes for large-scale applications.
IEEE Transactions on Appiled Superconductivity 07/2005; · 1.04 Impact Factor
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ABSTRACT: For large-scale electric power applications of MgB<sub>2</sub> wire, especially at AC environments, development of nonmagnetic sheath material is essential. In this study, Cu-sheathed MgB<sub>2</sub> wire was fabricated using the powder-in-tube method and ultra-fine Mg and B precursor prepared by high-energy ball milling. Lowering the annealing temperature and shortening the annealing time effectively limit the reaction between Mg and Cu. Critical current density of the wire annealed at 700°C for 5 minutes is 4.3×10<sup>4</sup> A/cm<sup>2</sup> at 20 K and self-field. Adding excess Mg in precursor further enhances critical current to 250 A at 20 K and self-field. These results demonstrate the potential of Cu-sheathed MgB<sub>2</sub> wires for large-scale applications.
IEEE Transactions on Appiled Superconductivity 07/2005; · 1.04 Impact Factor
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ABSTRACT: Much effort has recently been made to develop chemical methods for the manufacturing of coated conductors because of their scalability, low cost and high deposition rate. In this research, epitaxial buffer layers of Gd<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub> (GZO) have been grown on Ni substrates using a newly developed metal organic decomposition (MOD) approach. The solution prepared from metal-organic precursors was deposited on Ni substrates using the dip coating technique and then was annealed at a high temperature. Texture analysis shows full-width-at-half-maximum (FWHM) values for out-of-plane and in-plane alignments as 6.5° and 8.1°, respectively. Pole figure studies indicate a single cube-on-cube texture while SEM micrographs reveal a dense, continuous, and crack-free buffer layer. MOCVD was used to grow 1 μm YBCO film on this GZO buffered Ni substrate. A critical current, J<sub>c</sub>, of about 1.3 MA/cm<sup>2</sup> at 77 K and self-field was obtained on YBCO (MOCVD)/GZO(MOD)/Ni. These results give promise to using a single buffer layer for scalable coated conductors.
IEEE Transactions on Appiled Superconductivity 07/2005; · 1.04 Impact Factor
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ABSTRACT: Melt-textured YBCO superconductors are capable of carrying higher current densities than comparable copper conductors, and can therefore be used in electromechanical devices requiring high power densities. The advantage of textured YBCO superconductors is most pronounced in large systems such as electromagnetic launchers for aircraft carriers. In general, an electromagnetic launcher consists of a series of stationary pulsed electromagnets (the primary), which attract and/or repel a carriage carrying one or more magnets (the secondary). Several possibilities exist for the incorporation of HTSs into EM launchers, with the most direct being upgrading the magnets in the secondary to melt-textured YBCO. A system was developed to study propulsive force in a coaxial-type launcher. Results from this study are presented and their implications for launcher development discussed. A second type of launcher was also studied, with a power supply integrated into the launcher primary, so that the primary serves as a superconducting magnetic energy storage system. A method of optimizing energy conversion in a system of this type has been found. The time dependence of the magnetic field in this type of launcher is presented.
Superconductor Science and Technology 12/2004; 18(2):S6. · 2.66 Impact Factor
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ABSTRACT: A sharp cube textured Ni overlayer on Cu substrates has been developed for the manufacturing of long-length RABiTS-based coated conductor tapes. Using a low-cost, non-vacuum and easily scalable technique of electroplating, smooth, crack-free and continuous Ni overlayers were deposited on cube textured Cu substrates without any intermediate layers. In addition, sharp cube textured Sm-doped CeO2 buffer layers have been grown on the Ni-plated Cu substrates using pulsed laser deposition and found to exhibit in-plane and out-of-plane FWHM values of 6.50° and 5.25°, respectively. This electroplating process promises an efficient route for manufacturing Cu-based HTS coated conductors.
Superconductor Science and Technology 11/2004; 18(1):107. · 2.66 Impact Factor
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ABSTRACT: Ni based alloys have received considerable attention as the substrates for HTS coated conductors due to improved mechanical properties and reduced magnetization. Powder metallurgy is one of the promising processes for the fabrication of long alloy textured substrates. In this paper, Ni–3 at.% W alloy substrates were prepared by using high purity metal powders as starting materials. The Ni and 3 at.% W powder mixture was high energy ball milled for different periods, isostatically pressed, sintered, rolled and texture annealed. The high energy ball milling process made the powders mix uniformly and the grain sizes decrease significantly, which led to higher boundary energy and residual strain energy. The longer ball milling period resulted in a finer grain size and sharper texture in the substrate, which were confirmed by EBSD and SEM analysis. SEM and AFM observations indicate the surface of textured Ni–3 at.% W substrates is smooth and the roughness value (Rrms) is about 1.126 nm, which is suitable for deposition of buffer layers.
Superconductor Science and Technology 06/2004; 17(7):947. · 2.66 Impact Factor
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ABSTRACT: A fabrication process of iron-clad MgB2 superconducting tapes was developed by using a nano-sized precursor and highly deformed iron sheath. Quenching experiments demonstrate that the precursor fully reacts and forms MgB2 under a high pressure of 600 MPa provided by the deformed iron sheath. Very good grain connections as well as a high core density of 2.55 g cm−3 were therefore obtained. High 20 K Jc of 3.1 × 105, 1.6 × 105 and 4.9 × 104 A cm−2 at self-field, 1 and 2 T, respectively, were acquired. The results suggest that using a nano-sized precursor approach to fabricate MgB2 superconducting tape is a very promising process.
Superconductor Science and Technology 05/2004; 17(7):L27. · 2.66 Impact Factor
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ABSTRACT: Helical windings of Fe-sheathed MgB2 wires with different dimensions were fabricated by a wind-and-react process. Wires with a cross-sectional area of 1 mm2 and 20% superconductor core were made using the powder-in-tube (PIT) method and ultra-fine starting precursors. Very good grain connectivity as well as high core density was obtained by using this method. At 20 K and self-field, the critical current of a coil with an ID of 12 mm and 12 turns was 360 A, which is equivalent to a Jc of 1.8 × 105 A cm−2. At a 6 T external magnetic field and 4.2 K, a coil with an ID of 140 mm and 10 turns possessed a Jc of 1 × 104 A cm−2. These results are a step towards the application of MgB2 wires in the temperature range of 20–30 K and high magnetic fields.
Superconductor Science and Technology 03/2004; 17(4):717. · 2.66 Impact Factor
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ABSTRACT: The infiltration driving force and the growth mechanism of the liquid infiltration and seeded growth process on YBa2Cu3O7−x were studied. The main driving force for the liquid infiltration is either the capillary force or the chemical potential, while gravity does not play a significant role and may be neglected. The particle size and distribution of the Y-211 inclusions of the final Y-123 specimen prepared by the liquid infiltration and seeded growth process are solely determined by the particle size and distribution of the Y-211 preform. The critical current density at 77 K was determined to be 80 000 A cm−2 under self-field and 35 000 A cm−2 under 1.5 T. The superconducting properties are highly enhanced using this method compared to the conventional melt texture growth process.
Superconductor Science and Technology 12/2003; 17(2):269. · 2.66 Impact Factor
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ABSTRACT: Ni and Ni-based alloys have received considerable attention as the substrates for HTS coated conductors. A critical step in the successful fabrication of coated conductor composites on metal substrates is to produce cube texture by mechanical deformation using the rolling assisted biaxial textured substrate (RABiTS) approach. In this paper, we investigated the effects of mechanical deformation and heat treatment on the growth of texture in nickel and nickel–tungsten alloys with the objective of understanding mechanisms of mechanical texturing in coated conductor substrates. The results show that the sharpest cube texture is obtained by cold rolling nickel and nickel tungsten alloys in passes of less than 5% deformation followed by annealing at high temperature.
Superconductor Science and Technology 08/2003; 16(9):1077. · 2.66 Impact Factor
