Fabrication Of Conductors Research Articles

Effect of the annealing process on the microstructure of La 2Zr 2O 7 thin layers epitaxially grown on LaAlO 3 by metalorganic decomposition

La 2Zr 2O 7 (LZO) films have been grown by metalorganic decomposition (MOD) to be used as buffer layers for coated conductors. A characteristic feature of LZO thin films deposited by MOD is the formation of nanovoids in an almost single crystal structure of LZO pyrochlore phase. Annealing parameters (heating ramp, temperature, pressure, etc.) were varied to establish their influence on the microstructure of the LZO layers. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used for sample characterization. The epitaxial pyrochlore phase was obtained for annealing temperatures higher than 850 °C whatever the other annealing conditions. However, the film microstructure, in particular, nanovoids shape and size, is strongly dependent on heating ramp and pressure during annealing. When using low heating ramp, percolation of voids creates diffusion channels for oxygen which are detrimental for the substrate protection during coated conductor fabrication. From this point of view high heating rates are more adapted to the growth of LZO layers.

Interface analysis of HfO2 films on (1 0 0)Si using x-ray photoelectron spectroscopy

Thin layers of HfO2 grown on the (1 0 0)Si crystal surface using atomic layer deposition or metallo-organic chemical vapour deposition were analysed using x-ray photoelectron spectroscopy (XPS) of Hf 4f, Si 2p and O 1s electron states. The chemical indepth profiling was conducted by combining XPS with Ar+ ion sputtering. In addition to establishing the deposition-sensitive oxide structure, Ar+ ion sputtering was found to lead to the formation of a metallic Hf layer on the surface of the sample. The latter observation suggests HfO2 as a feasible candidate for not only insulating applications but, thanks to the high mass and electron density of the cation, also as a material suitable for the fabrication of nanometre-sized conductors by direct oxide decomposition.

A fast sonochemical approach for the synthesis of solution processable ZnO rods

A solution based sonochemical synthesis method for ZnO rods is presented with a resulting growth rate in excess of 15 times faster than previously reported. Such material is solution processable and could be exploited in the fabrication of transparent conductors and/or large area electronics via inkjet printing methods or solution based self-assembly techniques. To understand the crystal structure and defects chemistry, the as-synthesized wurtzite crystal structures were compared and contrasted with rods grown by the more traditional and well characterized hydrothermal growth method. Fluorescence spectra were recorded and the emission characteristics correlated with the structural and conductive properties of the ZnO rods. In particular, the sonochemical crystals appear to have a higher degree of order with fewer defects. This study represents a first step toward the tailoring of the electronic properties of ZnO rods. In particular, we will concentrate on the influence that native defects have on electrical conduction and on photoluminescence. Furthermore, we show how the intensity of the ultrasonic power exploited in this synthesis has a direct influence on the crystal quality as revealed by a comparative study. An optimum value between 30% and 35% of the maximum amplitude of a 20 kHz ultrasonic probe was found to give the best conditions for the growth of crystals with fewer defects density, while at ca. 25% of the maximum amplitude we observed the higher intensities for the fluorescence spectra both in the ultraviolet and in the visible range.

Manufacturing of the ITER TF Full Size Prototype Conductor

The experience gained in the past for the ITER toroidal field model coil conductor and the results obtained so far have led to the definition of an upgraded full size prototype conductor, based on advanced Nb3Sn strand, and entirely manufactured in the European Union (EU). Samples for the characterization in the Sultan facility have been prepared by Luvata (Italy) following the conductor layout defined by ITER. ENEA was responsible for conductor fabrication. Since the conductor layout was new, a full size copper dummy conductor has been preventively produced for the setting of the cabling and jacketing tools. Then, a total of four full size superconducting cables have been prepared by using Nb3Sn advanced strands produced by Oxford Instruments (OST) and European advanced superconductors (EAS), by internal tin and bronze technology, respectively. The details of manufacturing procedures will be described in this paper.

Research on CeO 2 cap layer for YBCO-coated conductor

Two groups of coated conductor samples with different thicknesses of CeO2 cap layers deposited by pulsed laser deposition (PLD) under the same conditions have been studied. Of them, one group is of CeO2 films, which are deposited on stainless steel (SS) tapes coated by IBAD-YSZ (IBAD-YSZ/SS), and the other group is of CeO2/YSZ/Y2O3 multilayers, which are deposited on NiW substrates by PLD for the fabrication of YBCO-coated conductor through the RABiTS approach. YBCO film is then deposited on the tops of both types of buffer layers by PLD. The effects of the thickness of the CeO2 film on the texture of the CeO2 film and the critical current density (Jc) of the YBCO film are analysed. For the case of CeO2 film on IBAD-YSZ/SS, there appears a self-epitaxy effect with increasing thickness of the CeO2 film. For CeO2/YSZ/Y2O3/NiW, in which the buffer layers are deposited by PLD, there occurs no self-epitaxy effect, and the optimal thickness of CeO2 is about 50 nm. The surface morphologies of the two groups of samples are examined by SEM.

Development of large current superconductors using high performance Nb3Sn strand for ITER

In the ITER model coil tests, degradations of the critical current were observed in Nb3Sn cable-in-conduit conductors when a large transverse electromagnetic force was applied to them. Both mass production technique of strand having high critical current enough to recover the degradation and also trial fabrication of the ITER-TF cable and conduit section were successfully performed. These results demonstrate feasibility of fabrication of the TF conductor using the high performance Nb3Sn strands. In addition, critical current degradation by spatially periodic transverse load was both experimentally and numerically studied. The simulation results show that the transverse resistance among the filaments is significantly small compared to that calculated from bronze resistivity. It is explained by the effect of superconducting current across the filament cross-section. This current however disappears when a large bending strain is applied to the strand, resulting in deterioration of the transverse resistance. It suggests that small degradation of the TF model coil (TFMC) conductor is not attributed to sufficiently low resistance among filaments as is expected in the optimized design of the ITER conductor but high resistance of the TFMC strand critical current against the transverse load. On the other hand, the developed strand has almost the same resistance against the transverse load as the TFMC strand. Therefore, the small degradation of the TF conductor, i.e., stable operation of the TF conductor is preliminarily anticipated.

In Situ Oxidation of Superconducting YBCO Films by a Supersonic ${\rm O}_{2}$ Beam

We report on the successful implementation of a supersonic molecular oxygen (O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) beam for the in situ oxidation of superconducting YBCO films. The beam is produced by a specially designed array of conical nozzles that were laser machined in a platinum foil. The array was mounted in proximity of the deposition area of a thermal co-evaporation system for YBCO film deposition. After a brief description of the basic concepts underlying the physics of supersonic beams, we describe the design of the nozzle implemented in our system. Then, we illustrate and discuss the preliminary results obtained by varying a number of key parameters of the supersonic beam. Most important parameters turn out to be the input O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> pressure and the nozzle-film distance. We show that excellent electrical properties with zero-resistance superconducting critical temperatures, T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , in excess of 90 K are reproducibly obtained over the entire 20 cm X 20 cm deposition area. These results were obtained using various types of substrates relevant to coated conductor fabrication, including Zr-doped CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> buffered cube-textured Ni-W and MgO buffered hastelloy substrates.

Application of Prebending Effect to Triplet Cables Using Bronze-Route ${\rm Nb}_{3}{\rm Sn}$ Strands

An application of the prebending effect to a cabling process using Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strands was demonstrated. The prebending effect is the enhancement effect of superconducting properties due to the repeated prebending treatment for practical bronze-route Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires. CuNb/Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and Cu/Nb3Sn strands were applied prebending treatment using 10 fixed pulleys with 0.8% prebending strain. Four kinds of triplets, i.e., prebent CuNb/Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn, no-prebent CuNb/Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn, prebent Cu/Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and no-prebent Cu/Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn triplets were fabricated. Critical currents were measured for the four kinds of triplets in magnetic fields up to 11 T at 4.2 K. The obvious critical current enhancement due to the prebending effect was maintained for the prebent CuNb/Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn triplet. The results imply that the prebending treatment for high-strength Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strands is applicable to the cable conductor fabrication.

Effect of mechanical stresses on the magnetic properties of anisotropic electrical steel

It has been shown that mechanical stresses arising in anisotropic electrical-sheet steel during both sheet making (residual stresses) and fabrication of magnetic conductors from the sheet parts (applied stresses) have a strong effect on its magnetic properties. It is shown that the principal cause of this effect is the high stress sensitivity of the magnetic texture of the metal. The main varieties of the applied stresses which are mostly responsible for the deterioration of the magnetic characteristics of the steel have been examined. Basically, these are the stretching of the band during straightening annealing and the effect of bending of the specimens while cutting them with guillotine shears during the preparation of the specimens for tests. The technique of the determination of residual stresses by measuring the flexure of the specimen after the insulating coating is removed from its one side is discussed.

Reactivity of sheath materials with Mg/B inMgB2 conductor fabrication

A systematic study on the reactivity of commonly used sheath materials (Ag, Cu, Fe,SS, Ta and Ni) with Mg/B during in situ powder-in-sealed-tube processing ofMgB2 superconductor was carried out at different temperatures. Characterizationof the samples using XRD, SEM and EDS showed that the heat treatmenttemperature and type of metal sheath have profound influences on the reactivity.The quantitative data reported here are highly useful for choosing the rightsheath material and processing temperature for the fabrication of high qualityMgB2 based conductors.

Chemically deposited La2Zr2O7 buffer layers for YBCO-coated conductors: film growth and microstructure

An adequate buffer layer architecture is of great importance forYBa2Cu3O7−δ (YBCO)-coated conductor fabrication. We present a transmission electron microscopy (TEM) analysisof La2Zr2O7 (LZO) buffer layers on biaxially textured Ni–5 at.%W substrates for YBCO-coated conductorsprepared by chemical solution deposition (CSD). The LZO thin films were heat-treated at 900 and1050 °C respectively. Electron diffraction patterns, and bright and dark-field images were usedto determine the microstructure, texture and the nanoporosity of the films. Byx-ray diffraction the films were found to be [100] oriented and strongly biaxiallytextured. Although x-ray diffraction suggests an epitaxial growth of LZO on Ni itwas shown by TEM that this was not the case. The grain size of the films isbetween 100 and 300 nm and therefore much smaller than the Ni grain size of40 µm. Appropriate acquisition conditions for scanning electron microscopy (SEM) and TEMimaging are given to identify the nanogranularity of the films. For the film annealed at1050 °C high-resolution SEM images clearly show a polycrystalline LZO microstructure and the grain sizecan readily be determined. Electron diffraction rings are more pronounced than for the film annealedat 900 °C, indicating a higher level of polycrystallinity in the film. SEM images of the film annealed at900 °C yield no evidence of a polycrystalline microstructure; only single misoriented LZO grainsseparated by 500 nm are observed. Nanovoids 10–40 nm in size were found in the LZO bufferlayers with a high density. The voids had approximately cuboid shape, indicating ananisotropy of the surface energy in LZO. The surface planes of the voids were identified as{111} lattice planes. Despite the nanoporosity, which is a typical feature of CSD-grownbuffer layers, the LZO buffer layers act as efficient Ni diffusion barriers. Energydispersive x-ray microanalysis (EDX) in the transmission electron microscope yieldedthe composition of the films. In the LZO films no Ni-rich secondary phases weredetected and significant C contamination occurred during spectrum acquisition.

All MOD buffer/YBCO approach to coated conductors

RABiTS based metal-organic deposition (MOD) buffer/YBa2Cu3O7−δ (YBCO) approach has been considered as one of the potential, low-cost approaches to fabricate high performance second generation coated conductors. The most commonly used RABiTS architectures consisting of a starting template of biaxially textured Ni–W (5 at.%) substrate with a seed layer of Y2O3, a barrier layer of YSZ, and a CeO2 cap. In this three layer architecture, all the buffers are deposited using physical vapor deposition (PVD) techniques. Using these PVD deposited templates, 0.8-μm thick MOD-YBCO films with an Ic (critical current) of 250A/cm have been achieved routinely in short lengths. We have developed a low-cost, non-vacuum, MOD process to grow epitaxial buffer layers on textured Ni–5W substrates. The main challenge in this effort is to match the performance of MOD templates to that of PVD templates. We have recently shown that the properties of MOD-La2Zr2O7 (LZO) layers can be improved by inserting a thin Y2O3 seed layer. Using MOD-CeO2 cap layers, we have demonstrated the growth of high performance MOD-YBCO films with an Ic of 200A/cm-width on MOD-La2Zr2O7/Y2O3/Ni–5W substrates. This approach could potentially decrease the overall cost of the coated conductor fabrication.

Towards the practical PLD-IBAD coated conductor fabrication – Long wire, high production rate and Jc enhancement in a magnetic field

SRL-Nagoya Coated Conductor Center (NCCC) have succeeded in fabricating stably long coated conductor using ion-beam assisted deposition (IBAD) and pulsed laser deposition (PLD) methods. Reel-to-reel PLD equipment with a multi-plume and multi-turn deposition system (MPMT PLD) resulted in a long coated conductor with a high critical current, Ic, of 245A and length of 212.6m. Ic×L (length) reached the record of 52,087Am. At the same time, the effort to enhance Ic and Jc in a magnetic filed are also carried out using artificial pinning center and RE element: YSZ mixed Y123 target brought about a high Jc especially in the magnetic field parallel to the c-axis. This was attributed to a columnar structure of the “bamboo structure” (BaZrO3/Y123 layer-stacked structure) in Y123+YSZ sample. Gd123 was also found to be effective for enhancing pinning properties, which was considered to be due to the native stacking faults in the 123 structure. The combination of Gd element and YSZ introduction were also studied and clearly demonstrated the improvement of the anisotropy of Jc for a magnetic field angle.

Fabrication of Conductors and Inductors by Nano-Particle Deposition through Direct Write Technology

Direct Write Technologies are being utilized in antennas, engineered structures, sensors, and tissue engineering. One form of the Direct Write Technologies is Maskless Mesoscale Material Deposition (M3D) for Optomec, Inc. M3D is a process that uses aerosol formation, transport and deposition. Inks for the M3D utilize nano-particles in suspension for deposition. Several different conductive inks were deposited with M3D and characterized for electrical resistivity and microstructure. Soft magnetic material was formulated as an ink suspension, deposited and characterized. This paper will report on the results obtained after sintering conductive nano-particle inks and soft magnetic material. Sintering was performed with a 2W frequency doubled Nd:YAG CW laser, a conventional muffle furnace and a novel photonic curing method. Depositions of various conductive inks were examined for physical dimensions (width and thickness) and microstructure. A study of the sintering characteristics if these ink was also included. This paper will also report on the results obtained from depositing a soft magnetic material. Permeability results were calculated from magnetic structures created with the deposition. These results are compared to conventional methods of soft magnetic material formation and construction. Physical properties of the deposited inks are also measured and reported.

Fabrication and Properties of High Temperature Protonic Conductors

not Available.

Evolution Of Detector Magnets From CELLO to ATLAS and CMS and Toward Future Developments

The evolution of physics with colliding beams has required ever increasing volumes of magnet field around the interaction points for effective particle detection. This has been the main driver for the development of detector magnet system over the past 25 years. This paper traces the evolution of detector magnet technology through the engineering solutions developed to meet the increased scale and field strength. The paper will address major aspects of detector magnet engineering from design and analysis to conductor and magnet fabrication technology. Advances in conductor design for stability, fabrication and protection will be described. The paper will evaluate the techniques developed to achieve high transparency, efficient cooling (direct vs. indirect) and magnetic force transfer. The current state of the art at both large (CMS and ATLAS) scale and small scale (BESS) will be reviewed. Future requirements for detector magnets will be reviewed

Long length coated conductor fabrication by inclined substrate deposition and evaporation

The commercial development of coated conductors is rapidly progressing. As a result we present an economic route to produce second generation HTS tape from the initial substrate preparation to the final metal coating. The most important and technically challenging steps are the deposition of an oriented buffer layer and the superconductor film in a reel-to-reel configuration. New evaporation techniques have been developed to enable reliable, high rate tape coating. Highly oriented MgO - buffer layers are realized by inclined substrate deposition (ISD) and DyBCO is deposited by simple e-gun evaporation yielding critical currents beyond 200 A/cm. Coated conductors have been fabricated up to 40 m length and are currently tested in a variety of applications.

Reel to Reel Coated Conductor Fabrication by Evaporation

The commercial development of coated conductors is rapidly progressing. As a result we present an economic route to produce second generation HTS tape from the initial substrate preparation to the final metal coating. The most important and technically challenging steps are the deposition of an oriented buffer layer and the superconductor film in a reel-to-reel configuration. New evaporation techniques have been developed to enable reliable, high rate tape coating. Highly oriented MgO - buffer layers are realized by inclined substrate deposition (ISD) and DyBCO is deposited by simple e-gun evaporation yielding critical currents beyond 200 A/cm. Coated conductors have been fabricated up to 40 m length and are currently tested in a variety of applications

Fabrication and characterization of solid state proton conductor (NH 4) 2SiP 4O 13–NH 4PO 3 for fuel cells operated at 150–250 °C

NH 4PO 3–(NH 4) 2SiP 4O 13 composite, a potential electrolyte for intermediate temperature fuel cells that operated around 250 °C, was synthesized with a solid-state reaction method. Electromotive forces (emfs) as measured with hydrogen concentration cells showed that the composite was a pure proton conductor at hydrogen partial pressure from 10 2 to 10 5 Pa. Its proton transference numbers were determined to be 1.0 at 150 °C, 0.99 at 200 °C, and 0.99 at 250 °C. Fuel cells that used NH 4PO 3–(NH 4) 2SiP 4O 13 as electrolytes were also fabricated. Maximum power density was 6.6 mW/cm 2 at 250 °C when dry hydrogen and dry oxygen were used as the fuel and oxidant, respectively. Improved cell performance is expected by increasing cathode activity, increasing the electrolyte density, and decreasing the electrolyte thickness.

Synthesis and Characterization of Nanowire-Based Anisotropic Conductors

We investigated the potential of commercially available porous templates to be used for the fabrication of functional anisotropic conductors. A galvanostatic deposition technique was used to fabricate arrays consisting of 200 nm diameter nanowires inside the pores of polycarbonate membranes. A tape lift-off procedure allowed the complete removal of any residual metal from both sides of the polymer membrane to form an anisotropic conductive film. The 10 microm thick film has roughly 3 x 10(8) nanowires per cm2, and it showed near zero electrical resistance perpendicular to the surface while appearing completely open to circuits between any points on the surface. The preparation of the film, characterization using SEM, AFM, and resistance measurements are presented. The 1D conductivity of these membranes may have many potential applications for microelectronic interconnects for packaging technologies.