Ron Feenstra Oak Ridge National Laboratory
David C. Larbalestier Florida State University
Boris Maiorov Los Alamos National Laboratory
Marina Putti University of Genova and CNR/INFM-LAMIA
Yi-Yuan Xie SuperPower, Inc.
CC1: New Superconductors
Tuesday AM, April 14, 2009
Room 3012 (Moscone West)
9:30 AM - **CC1.1
Applications-Derived Challenges for New Higher-Temperature Superconductors.
M. Beasley 1 Show Abstract
1 Applied Physics, Stanford University, Stanford, California, United States
For any new superconductor to be useful in electric power applications, it must have a high transition temperature and a high depairing critical current density. These are fundamental limits to the utility of the material. Elementary considerations show that to simultaneously achieve these properties as the superconductor pairing energy increases requires isotropic superconductors with a high pair density. This in turn raises the question whether reduced dimensionality or lower carrier density are requirements for higher temperature superconductivity. In this talk the origins of these limitations and their implications in the search for new useful superconductors will be presented.
10:00 AM - **CC1.2
Excitement on the New Fe-based Superconductors
Rongying Jin 1 2 Show Abstract
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , The University of Tennessee, Knoxville, Tennessee, United States
Recently, high-temperature superconductivity has been discovered in a new class of compounds that all contain Fe layers. In this talk, a summary of recent experimental work from Oak Ridge National Laboratory on the Fe-based superconductors will be presented, including 1111, 122, 111, and 11 phases. The possible superconducting mechanism will be discussed based on experimental results obtained from both surface and bulk of these superconductors. [Research sponsored by the Division of Materials Sciences and Engineering, Basic Energy Sciences, U.S. DOE.]
10:30 AM - **CC1.3
Anisotropy, Critical Current Density, Critical Fields, and Vortex Phase Diagram in Pnictide Superconductors.
Hai-Hu Wen 1 Show Abstract
1 National Lab for Superconductivity, Institute of Physics, Chinese Academy of Science, Beijing China
By measuring magnetization and resistivity, we have determined the anisotropy, critical current density, critical fields and vortex phase diagram in pnictide FeAs-1111 and Fe-122 superconductors. It is found the anisotropy determined by the ratio of Hc2(ab, T=0)/ Hc2(c, T=0) is only about 5 in F-doped NdFeAsF (Tc=50 K), that in Ba0.6K0.4Fe2As2 is only 2. The angle dependence of resistivity in the magnetic field has also been measured and we found that the data can be scaled according to the anisotropic Ginzburg-Landau model yielding the same anisotropy. By using the value of the ratio dHc2(T)/dT near Tc, the upper critical field Hc2(0) was determined and found to be about Hc2(c, T=0) ≈ 70 T, Hc2(ab, T=0) ≈ 300 T in F-doped NdFeAsF, and Hc2(c, T=0) ≈ 150 T, Hc2(ab, T=0) ≈ 300 T in Ba0.6K0.4Fe2As2. The higher upper critical field in FeAs-122 is attributed to the possible higher density of states in the hole doped samples. Fish-tail effect and high critical current density were achieved in the Ba1-xKxFe2As2 superconductors. The vortex dynamics inferred from the magnetization relaxation measurements suggest that collective pinning model works perfectly for the pnictide superconductors. Finally vortex phase diagram has been obtained revealing a quite small area of H-T for the vortex liquid state. So far we have not found any trace of vortex jump phenomenon in pnictide superconductors. All these suggest that these superconductors have very good potential applications.In collaboration with Gang Mu, Zhaosheng Wang, Huiqian Luo, Huan Yang, Xiyu Zhu, Fei Han, Ying Jia, Bing Zeng, Bing Sheng. Cong Ren, Lei ShanReferences:. Zhaosheng Wang et al., Phys. Rev. B 78, 140501(R) (2008).. Huan Yang et al., Appl. Phys. Lett. 93, 142506 (2008).. Ying Jia et al., Supercond. Sci. Technol. 21 (2008) 105018. Huiqian Luo et al., Supercond. Sci. Technol. 21 (2008) 125014.. Huan Yang et al., Phys. Rev. B 78, 092504 (2008).. Ying Jia et al., Appl. Phys. Lett. 93, 032503 (2008). Cong Ren et al., Phys. Rev. Lett., in press. Condmat/0808.0805.. Gang Mu et al., Condmat/0808.2941.
11:30 AM - **CC1.4
Superconductivity at Very High Magnetic Fields in Pnictides.
Alex Gurevich 1 Show Abstract
1 National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, United States
An overview of recent results on the upper critical field Hc2 and anisotropy of vortex properties in pnictides is given. The talk will focus on the extremely high Hc2 values, well above the BCS paramagnetic limit, anomalous temperature dependencies of Hc2(T) along different crystallographic directions, and the effect of multiband structure and paramagnetic limitations of Hc2(T). The role of anisotropic vortex fluctuations and their effect on the resistive transition and the irreversibility field in pnictides will also be discussed.
12:00 PM - CC1.5
Upper Critical Field in Cobalt-doped SrFe2As2 Epitaxial Thin Films.
Scott Baily 1 2 , Y. Kohama 2 3 , H. Hiramatsu 4 5 , B. Maiorov 1 , F. Balakirev 2 , M. Hirano 4 5 , H. Hosono 4 5 Show Abstract
1 MPA-STC, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 MPA-NHMFL, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama Japan, 4 ERATO-SORST, Japan Science and Technology Agency in Frontier Research Center, Tokyo Institute of Technology, Yokohama Japan, 5 Frontier Research Center, Tokyo Institute of Technology, Yokohama Japan
The temperature and angular dependence of upper critical field (Hc2) are reported for SrFe1.8Co0.2As2 (nominal composition) epitaxial films between Tc and 0.5 K in pulsed magnetic fields up to 50 T. For H ∥ c, Hc2 is close to a linear function of temperature; For H ⊥ c, the temperature dependence shows significant downward curvature. This results in an anisotropy that decreases nearly linearly with temperature, approaching isotropic behavior at low temperature. We fit a two band model to the data, and show that the ability to measure the complete phase diagram including angular dependence at fixed temperature allows for a determination of the anisotropy of both bands as well as their relative diffusivities. In addition, significant constraints can be put on the relationship between BCS coupling constant matrix elements. We find an unexpected relationship between the diffusivities of the two bands, with the more anisotropic band having low diffusivity for H ∥ c.
12:15 PM - CC1.6
Thin Film Growth and Anisotropy of FeAs Based Superconductors Prepared by Pulsed Laser Deposition.
B. Holzapfel 1 , E. Backen 1 , S. Haindl 1 , K. Iida 1 , T. Niemeier 1 , T. Freudenberg 1 , J. Werner 1 , G. Behr 1 , L. Schultz 1 Show Abstract
1 , IFW Dresden, Dresden Germany
We report on recent achievements towards thin film deposition of FeAs based superconductors by Pulsed Laser Deposition. Both oxide and intermetallic FeAs based phases were investigated. E.g. LaFeAsO1-xFx thin films were deposited successfully on (001)-oriented LaAlO3 and MgO substrates from stoichiometric LaFeAsO1-xFx polycrystalline targets with fluorine concentrations up to x = 0.25 by PLD. Room temperature deposition and post annealing of the films yield nearly phase pure films with a pronounced c-axis texture and a strong biaxial in-plane orientation. Transport measurements show metallic resistance and onset of superconductivity at 11 K. µ0Hc2(T) was determined by resistive measurements and yield µ0Hc2 values of 3 T at 3.6 K for µ0H || c and 6 T at 6.4 K for µ0H || ab.
12:30 PM - CC1.7
Combined Microstructural, Magneto Optical and Dissipation Studies of Local Current Flow in Polycrystalline Oxypnictides.
Fumitake Kametani 1 , Anatolii Polyanskii 1 , Dmytro Abraimov 1 , Pei Li 1 , Akiyasu Yamamoto 1 , Jianyi Jiang 1 , Eric Hellstrom 1 , Alex Gurevich 1 , David Larbalestier 1 Show Abstract
1 , Applied Superconductivity Center, Tallahassee, Florida, United States
Polycrystalline superconducting oxypnictides have shown granularity where the inter- and intra-granular current densities differ by three orders of magnitude, although the intra-granular current density is much larger than in random, polycrystalline YBCO.In order to correlate granularity and local current flow to the microstructure, we have conducted combined microstructural, magneto optical and dissipation studies. Magneto optical images show that the highest Jc values are observed within single grains. The much lower intergranular Jc is at least partially due to many extrinsic factors – cracks and a ubiquitous wetting As-Fe phase at many grain boundaries. However, some grain boundaries are structurally clean under high resolution transmission electron microscopy examination. To rule out intrinsic limitation of current flow across clean grain boundaries, dissipation studies are undergo on the thinned polycrystalline oxypnictides by means of the low temperature laser scanning microscope.
Tuesday PM, April 14, 2009
Room 3012 (Moscone West)
2:30 PM - CC2.1
Possible High-Tc Superconductivity in Nanostructured NaxWO3-y: Sol-Gel Route.
Ali Aliev 1 Show Abstract
1 NanoTech Institute, University of Texas at Dallas, Richardson, Texas, United States
Tungsten trioxide, WO3-y infiltrated into various nanoporous matrix structures such as carbon inverse opal, carbon nanotubes paper, or platinum sponge and then intercalated with alkaline ions (Li+, Na+) exhibits a pronounced diamagnetic onset in ZFC magnetization in a wide range of temperatures, 125-132 K. Resistivity measurements show non zero jump and intensive fluctuations of electrical resistance below observed transition points. The observed magnetic and electrical anomalies in nanostructured tungsten bronzes (LixWO3-y, NaxWO3-y) suggest the possibility of localized non-percolated superconductivity . In this work we used a sol-gel technique for preparation tungsten bronzes inside of porous nanostructured host matrices. Sol-gel route allows to vary the structural parameters and concentration of composition over a wide range. To increase the volume fraction of superconducting phase first we infiltrated WO3 into nanoporous material with high surface area and then electrochemically intercalated the resultant structure with alkali ions (Li+, Na+, K+). To make the intercalation process controllable over wide current&potential range we gave preference to highly conductive and chemically stable matrix materials such as carbon and platinum. As porous host matrices carbon inverse opal, platinum sponge, and CVD grown multiwalled carbon nanotube paper have been tested. Most pronounced and reproducible onset in magnetization and resistance measurements were found for NaxWO3-y in carbon inverse opal host matrix at Tc=125 K. Obtained tungsten bronzes have dark blue color with metallic conductivity. The optical absorption of W5+ in WO3 shows the signature of small polaron formation at low temperatures. At low doping levels, the sodium tungsten bronzes are nonmetallic with electrons localized at W5+ and W6+ ions and show polaronic states. The polaronic state in WO3 is caused by strong interaction between the optical longitudinal phonons and electrons. Slightly reduced samples with doped Na+ demonstrate bipolarons which can be split into pairs of polarons under light excitation. Probably, the strong intercalation of WO3 with alkaline ions brings the compound to compositionally-induced nonmetal-to-metal transition with bipolaron current carriers. The direct evidence of polaron formation from temperature dependence of photoemission spectra and formation of bipolarons in weakly reduced WO3-y, with 3-y typically in the order of 2.95 suggest bipolaron mechanism of a Bose-Einstein condensation of trapped electron pairs in doped WO3-y. The magnetization behavior, temperature dependencies of resistance and EPR spectra of tungsten and molybdenum bronzes intercalated with alkali ions in wide range of concentrations will be presented.__________________________________________________________. A.E. Aliev. Superconductivity Science & Technology 21 (2008) 115022.
2:45 PM - **CC2.2
Current State of MgB2 Superconducting Wire Development and their Prospects for Magnet Applications.
Giovanni Grasso 1 , Silvia Brisigotti 1 , Simona Berta 1 , Andrea Tumino 1 , Eduard Demencik 1 , Davide Pietranera 1 , Lauri Rostila 1 , Roberto Penco 1 Show Abstract
1 , Columbus Superconductors SpA, Genova Italy
In spite of its recent discovery, industrialization efforts focused on the production of MgB2 superconducting wires led to encouraging results in a relatively short timescale compared to that of other superconducting materials. Compared to presently industrially available superconductors, MgB2 represents a valid alternative to NbTi, because of the concrete possibility to use it in cryogenic-free conditions, making both magnet cooling and stability much simpler issues to be addressed. Kilometer-long MgB2 wires have been already demonstrated with various wire configurations in the past few years, showing constantly improved electrical and mechanical properties. An overview of the actual wire properties and a forecast for the future progress will be given. Finally, the different applications based on MgB2 wires recently realized using our wires will be also presented, going from MRI magnets, to cryogenic-free magnets for a variety of industrial and research-focused applications.
3:15 PM - CC2.3
Transport, Flux Pinning, and Connectivity in MgB.
Mike Sumption 1 , Mike Susner 1 , E. Collings 1 Show Abstract
1 Materials Science, The Ohio State University, Columbus, Ohio, United States
In this work, the transport and pinning properties of in-situ route MgB2 strands are presented and discussed. The influence of SiC, excess Mg, and various nanoscale “artificial pinning center” introductions are intercompared. Grain boundary pinning dominates for both binary and SiC doped strands, while strands with sufficiently fine nanoscale particle additions show a shift to point pinning. In this latter study, artificial pinning centers were introduced into MgB2 bulk and wire specimens in the form of nano particulates of SiC, Si, Ta, TiC, and Si3N4. The powders were milled along with the dispersion media; the solvent was subsequently evaporated. The nano ceramics were purchased from a commercial source at an average particle size of ~30 nm and were further attrited via long term planetary milling with B to reduce the particle and agglomeration size. Power sizes and morphologies were subsequently studied by TEM to determine nanoparticulate sizes. The dopants were then introduced into monofilamentary wires in which a Nb-lined monel sheath construction was used. Transport Jc measurements were performed on these samples under a variety of magnetic fields and temperatures. The results were then compared to expectations for ideal particle spacings and optimal pinning. Pinning was seen to shift from grain boundary dominated at lower temperatures to point pinning at higher temperatures. The clearest shifts were seen for TiC and unreacted ZrB2 additions. The influence of B powder type is also discussed, comparing “95 B”, “99 B”, and a new plasma RF based B. TEM studies show the relative morphological differences, while particle size analysis, XRD, and XRF are used to characterize the powders. The properties of the B powders are seen to correlate with the transport properties of the resulting strands. Beyond this, we have modeled a number of representative strands with an enhanced resistivity analysis. The resistivity contributions of the sheath, the chemical barrier (Nb), and the MgB2 core material are separated, and compared to a temperature dependent resistivity model. The extracted values are then compared to Bc2 values and are also used to extract % connectivity for the strands. Heat capacity measurements are used to extract a Bc2 distribution, and a simple model for the connectivity and the Fp curve (which deviates from the expected Kramer function) is discussed. Finally, the relative importance of flux pinning, Bc2 improvements, and connectivity are discussed in terms of their contribution to increasing critical current density.
3:30 PM - **CC2.4
Electromechanical Properties of MgB2 Superconductor Wires.
Najib Cheggour 1 , Loren Goodrich 1 , Jack Ekin 1 , Jolene Splett 1 Show Abstract
1 , NIST, Boulder, Colorado, United States
Magnesium-boride (MgB2) superconductor wires are being developed for use in applications such as magnetic resonance imaging (MRI). Measurements are reported of the critical-current Ic of several undoped and SiC-doped MgB2 conductors as a function of axial strain ε and magnetic field B. Unlike most A15 compounds, such as Nb3Sn, for which Ic has a parabolic dependence on axial strain, MgB2 exhibits a linear relation between Ic and strain within the reversible strain regime. A review of the electromechanical properties of MgB2 wires will be made, which will include the effects of the filament size and the sheath material on the irreversible strain limit, and the impact of doping on the pinning force and electromechanical properties. Parameterization and scaling of the pinning force Fp = Ic x B with strain, temperature and magnetic field will be examined. The effective upper critical field Bc2*, where Fp extrapolates to zero, will also be explored and its dependence on strain and temperature formulated. Comparisons between MgB2 and Nb3Sn will be made.
4:30 PM - **CC2.5
Recent Understanding of the Role of Filament Connectivity on Jc in Bi-2212 Round Wire
Eric Hellstrom 1 , Natanette Craig 1 , Van Griffin 1 , Jianyi Jiang 1 , Fumitake Kametani 1 , David Larbalestier 1 , Michael LoSchiavo 1 , XiaoTao Liu 1 , David Myers 1 , Justin Schwartz 1 , TengMing Shen 1 , Ulf Trociewitz 1 , Akiyasu Yamamoto 1 , Seung Hong 2 , Yibing Huang 2 , Hanping Miao 2 , Maarten Meinesz 2 Show Abstract
1 Applied Superconductivity Center, NHMFL, Florida State University, Tallahassee, Florida, United States, 2 , Oxford Superconducting Technology, Carteret, New Jersey, United States
The microstructure of fully-processed round Bi-2212 wire shows the filaments are interconnected with 2212 bridges. In the past, we believed these filaments were detrimental to Jc. A new study using through-process quench studies and serial sectioning indicates this bridging is critical to achieve high Jc. Of particular significance is our observation that filaments in multi-filamentary Bi-2212 round wire can bond to adjoining filaments during the heat treatment. This is important because 2212 precursor powder that melts in the filament forms liquid and large grains of nonsuperconducting phases plus large pores, which is an agglomeration of gas that was between the precursor grains in the ~65-75% dense green wire. As the 2212 grains form on cooling, they run into the large nonsuperconducting grains and pores in this individual filament where it is difficult for them to grow. These regions have low Jc. In real 2212 wires where the filaments are close together, we found filaments bonded together during the heat treatment. We believe this occurs due to Ag dissolving into the liquid at Ag GBs and precipitating away from the Ag GB, allowing the filament to “move” along the Ag GB. When two filaments that are moving towards one another along the same GB meet, they bond, which means they touch one another. This bonded region acts like it is a larger filament as 2212 forms, allowing larger, longer 2212 grains to grow between the bonded filaments. Our observations show that the filament bonding occurs randomly along the length of the filaments, creating a 3-D interconnection between the filaments. The 2212 grains that grow between the bonded filaments create alternate paths between filaments that allow the supercurrent to bypass the large nonsuperconducting phases and pores. The consequences of filament bonding on the electromagnetic properties, in particular connectivity and Jc, of 2212 round wires will be presented.
5:00 PM - **CC2.6
High Critical Currents and Enhanced Pinning in MOCVD-derived Superconducting Films
Venkat Selvamanickam 1 , Yimin Chen 2 , Maxim Martchevskii 2 , Goran Majkic 1 Show Abstract
1 , University of Houston, Houston, Texas, United States, 2 , SuperPower, Schenectady, New York, United States
Metal Organic Chemical Vapor Deposition (MOCVD) has been proven to be an excellent technique to fabricate second-generation (2G) HTS conductors. Kilometer lengths of 2G HTS wires with a critical current performance exceeding 200 A/cm has been demonstrated recently using MOCVD. Further, critical currents exceeding 300 A/cm have been achieved in lengths over 600 m. Increase in critical current performance is an important requirement to achieve a price-performance metric of $ 50/kA-m in 2G wires without significant volume. Several approaches are being pursued to enhance critical currents of MOCVD-derived films including refining the microstructure to minimize the thickness dependence of critical current density. Process improvements are being conducted to eliminate microstructural detractors to current flow in films thicker than 1 micrometer. Zr doping to the precursor chemistry has resulted in enhanced critical current in MOCVD-derived films at high magnetic fields, over a wide angular range. A systematic study of Zr and other dopants is being conducted to elucidate their influence on pinning enhancement in REBa2Cu3Ox. Techniques to modify the asymmetry in the angular dependence of critical current in a magnetic field are also being investigated. The presentation will summarize the latest developments in critical current and pinning behavior of high performance MOCVD-derived superconducting films.
5:30 PM - **CC2.7
Second Generation HTS wire manufacturing at American Superconductor Corporation
Srivatsan Sathyamurthy 1 , Xiaoping Li 1 , Cees Thieme 1 , Mark Teplitsky 1 , Jim Inch 1 , Dave Tucker 1 , Elliott Thompson 1 , David Buczek 1 , Jeff Schreiber 1 , Steve Fleshler 1 , Ken DeMoranville 1 , Martin Rupich 1 Show Abstract
1 , American Superconductor, Devens, MA, Massachusetts, United States
Manufacturing of Second Generation (2G) High Temperature Superconductor (HTS) wires based on RABiTSTM/MOD process is currently underway at American Superconductor (AMSC). AMSC’s approach uses a full-scale manufacturing line designed around a low-cost, wide-strip technology in which a 4 to 10 cm wide strip is fully processed, then slit into multiple narrower tapes which are then laminated to metallic stabilizers, producing a 3-ply wire called 344 superconductors. The low-cost lamination process provides the flexibility to tailor the electrical, thermal, and mechanical properties of the 344 superconductors to the specific needs of the customer or for a specific application. Current production of 344 superconductors, using a 0.8 micron thick HTS coating, results in a wire with a critical current in the range of 70 to 90 A (175 – 225 A/cm-w) at 77K, self-field. Although this performance is sufficient for initial demonstrations, higher critical currents are required for actual commercial applications. Thus efforts are underway to increase the minimum critical current of the 344 superconductors to above 125A, equivalent to AMSC’s First Generation (1G) HTS wire. In this paper, we will discuss the research and development efforts to increase the thickness of the MOD-based YBCO layers to above 1 micron and our progress in transferring the thick-film, high Ic technology into the manufacturing process. We will also review the current status of AMSC’s 2G wire manufacturing capability and performance.
Ron Feenstra Oak Ridge National Laboratory
David C. Larbalestier Florida State University
Boris Maiorov Los Alamos National Laboratory
Marina Putti University of Genova and CNR/INFM-LAMIA
Yi-Yuan Xie SuperPower, Inc.
CC4: Flux Pinning II
Wednesday PM, April 15, 2009
Room 3012 (Moscone West)
2:30 PM - **CC4.1
Pinning Strategies in YBCO Coated Conductors.
Judith MacManus-Driscoll 1 , Sophie Harrington 1 , Stuart Wimbush 1 , Stuart Wimbush 1 , John Durrell 1 , H. Wang 2 , J. Lee 2 , Lata Sahonta 1 , Boris Maiorov 3 , Giorgio Ercolano 2 , Ahmed Kursumovic 3 Show Abstract
1 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom, 2 Department of Electrical and Computer Engineering , Texas A&M University, College Station, Texas, United States, 3 MPA-STC, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
This talk will address a range of issues related to pinning strategies in HTS. Both core pinning and magnetic pinning will be covered, as well as the possibility of including both these mechanisms together. The different aspects of the nanomaterials engineering to be considered include the control of chemical compatibility, and the size, geometry, orientation, distribution and population density of the second phases. Also, the suitability of the different methods for in-situ versus ex-situ processing will be considered. New data using pinning additives with very high performance will be used to illustrate the points to be covered.
3:00 PM - CC4.2
Tuning Flux-pinning and Critical Current Density for YBa2Cu3O7-δ Coated Conductors via BaZrO3 Compositional Control.
Sung Hun Wee 1 2 , Amit Goyal 1 , Yuri Zuev 1 , Claudia Cantoni 1 , Sy Cook 1 Show Abstract
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States
Influence of BZO concentration on the flux-pinning and critical current density (Jc) for YBa2Cu3O7-δ (YBCO) films has been systematically investigated. All samples were epitaxially grown on LaMnO3-buffered, ion-beam-assisted deposition (IBAD) MgO metallic templates via pulsed laser deposition. The thickness of the films was 0.8 μm. The samples with BZO concentration in the range of 0.05 - 2 vol % exhibited a higher self-field Jc of 3.0-4.1 MA/m2 at 77 K compared to pure YBCO film with the Jc of 2.8 MA/cm2. In the presence of applied magnetic fields, it is found that the flux-pinning in different field regimes is optimized at different BZO incorporation levels. At 77 K, 1 vol% BZO addition resulted in the highest Jc at the low field regime from 0 to ~1.6 T. In the higher applied magnetic fields, 2 - 4 vol % BZO doped YBCO films exhibited the highest Jc at fields up to and over ~7.3 T, respectively. Similar compositional optimization of flux-pinning at different field regimes is also observed at 65 K. YBCO films with 1 - 2 vol % BZO additions exhibited maximum pinning forces (Fpmax) of 9.3-9.5 GN/m3 at 77 K which is a factor of 2 higher than that for a pure YBCO film deposited on the same substrate. At 65 K, Fpmax of 62-74 GN/m3 were also achieved from 1 - 4 vol % BZO doped YBCO films. Detailed structural and superconducting properties for YBCO films as a function of BZO concentration will be presented. Research was sponsored by the US Department of Energy, Office of Electricity Delivery and Energy Reliability - Superconductivity Program, under contract DE-AC05-00OR22725 with UT-Battelle, LLC managing contractor for Oak Ridge National Laboratory.
3:15 PM - CC4.3
Controlled Nanorod Alignment in YBa2Cu3O7-x Thin Films by Microstructural Tuning.
F. Javier Baca 1 2 , Paul Barnes 1 , Rose Emergo 2 , Timothy Haugan 1 , Chakrapani Varanasi 3 , Jack Burke 3 , Joshua Reichart 1 , Judy Wu 2 Show Abstract
1 , U.S. Air Force Research Laboratory, Wright Patterson Air Force Base, Ohio, United States, 2 Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas, United States, 3 , University of Dayton Research Institute, Dayton, Ohio, United States
Control over microstructural defects in YBa2Cu3O7-x thin films has been well established as essential for improving vortex pinning. While materials such as BaZrO3 (BZO) and BaSnO3 (BSO) effectively provide this type of defect by forming columns within the YBCO matrix on the nanometer scale, their alignment is generally constrained along the direction of the c-axis. Our experiments show that the surface modulation of a vicinal SrTiO3 substrate provides a mechanism to strongly influence the YBCO microstructure as well as the direction of nanorod alignment. We study these microstructural effects by Transmission Electron Microscopy, and show the resulting increase in critical current density. Notably, we have observed that miscut angles of 20° produce nanorod alignment parallel to YBCO a-b planes, and thereby directly enhance the angularly anisotropic critical current density in the H || a-b direction. While the formation and alignment of the nanocolumns is associated with the alignment of microstructural defects such as dislocations, it is also known that vicinal substrates introduce defect structures of their own into the YBCO matrix. Therefore, we study the effect of the vicinal angle on the defect structures as a means to tune the alignment of the BZO and BSO nanorods.
3:30 PM - CC4.4
The Effect of the Second-phase Lattice Parameter on the Self-assembly of Nano-rods using Additions to REBCO.
Matt Feldmann 1 , Terry Holesinger 1 , Boris Maiorov 1 , Leonardo Civale 1 Show Abstract
1 , LANL, Los Alamos, New Mexico, United States
The development of a viable HTS Coated Conductor wire technology requires microstructural control across multiple length scales for improved pinning. On the nanoscale, pinning enhanced microstructural control may be obtained by the addition of suitable second-phase metal oxides in the REBCO matrix, which may self-assemble into ordered nano-particles or nano-rods. In this work, we performed a systematic study of the effect of this second-phase lattice parameter on the self-assembly of nano-rods using additions to REBCO. Cross-sectional TEM is used to determine the size (length) and degree of ordering of the nano-rods. The efficiency of the nano-rods as pinning centers is determined through Jc(H) and the orientation dependence of Jc in an applied magnetic field.
3:45 PM - CC4.5
Correlation Between Interfacial Defects and Pinning Properties in Nanostructured YBa2Cu3O7-δ Thin Films.
Haiyan Wang 1 , Chen-Fong Tsai 1 , Jie Wang 1 Show Abstract
1 Electrical and Computer Engineering, Texas A & M University, College Station, Texas, United States
In this work, we conducted a detailed microstructural study on several selected nanostructured YBa2Cu3O7-δ (YBCO) thin films processed using sectioned targets. All samples were deposited by a pulsed laser deposition technique. The doping materials include CeO2, BaZrO3, and Y2O3. The interfacial defects, including misfit dislocations, secondary phases and stacking faults in different systems were studied and compared using cross-section transmission electron microscopy (TEM) and high resolution TEM. We also conducted detailed superconducting property measurements to correlate these interfacial defects for different systems with their flux-pinning properties. We observed that, YBCO/CeO2 nanolayer thin film present the highest misfit dislocation density at the interfaces and therefore results in the best flux pinning performance among all three cases in the low field regime. The general trend is that the higher the misfit dislocation density, the better the in-field performance, especially in the low field regime. This study suggests that the misfit dislocations are effective pinning centers in the low field regime (H<1T) and at low measurement temperatures. The nanoparticles pin effectively in the high field regime (H>1T).
4:00 PM - CC4.6
Effects of second phase compositions and processing parameters on the formation of nanocolumns in YBa2Cu3O7-x.
Chakrapani Varanasi 1 3 , J. Burke 1 3 , J. Reichart 3 , H. Wang 2 , P. Barnes 3 Show Abstract
1 , University of Dayton Research Instititute, Dayton, Ohio, United States, 3 AFRL/RZPG (UDRI), Air Force Research Laboratory, Wright Patterson AFB, Ohio, United States, 2 , Texas A&M, College Station, Texas, United States
Recent results of a systematic study of the effects of second phase compositions and processing parameters on the formation of nanocolumns and corresponding influences on the flux pinning properties of YBa2Cu3O7-x (YBCO) coatings will be presented. Differentcompositions of second phase materials such as BaGeO3, BaSiO3 Y2BaCuO5, etc. in addition to BaSnO3 (BSO), were studied to investigate the nanocolumns formation in YBCO films. It is shown that not all second phase materials form nanocolumns nor enhance Jc in YBCO similar toBaSnO3 even though the films were processed under identical conditions. Differences in the lattice strain and lattice substitutions can affect the nanoparticle/ nanocolumns sizes and critical current density (Jc) & Tc of the films. In the case of YBCO+BaSnO3, processing parameters such as laser repetition rate (frequency), growth temperature etc. were varied and the films were analyzed by Transmission Electron Microscopy (TEM). The TEM images of samples grown at 780°C show high number density (2.5x10E11 /cm2) of BSO nanocolumns but the films grown at 810°C show discrete nanoparticles indicating that the growth temperature is very important to form nanocolumns. An increase in the frequency from 4- 20 HZ has a minor effect on the BSOnanocolumns diameter and number density. The Jc variation of YBCO films with different compositions of nanocolumns/nanoparticles will be presented and the results will be discussed in the light of these microstructures.
4:45 PM - CC4.8
Electrochemical Synthesis of Highly Crystalline MgB2 Nanowires.
Akihisa Miyazoe 1 , H. Abe 2 , K. Kurashima 2 , T. Aoyagi 2 , T. Kimura 2 , Y. Sugimoto 2 , K. Nakajima 2 , T. Ando 3 , N. Hirota 2 , H. Ohsaki 1 , H. Wada 4 Show Abstract
1 Advanced Energy, The University of Tokyo, Kashiwa Japan, 2 , National Institute for Materials Science, Tsukuba Japan, 3 Chemical System Engineering, The University of Tokyo, Tokyo Japan, 4 Advanced Materials Science, The University of Tokyo, Kashiwa Japan
Superconducting nanowires are of increasing importance as the material for photonic devices including superconducting single photon detectors (SSPD) and/or superconducting transition edge sensors (TES). MgB2 (magnesium diboride) has the highest superconducting critical temperature (Tc = 39 K) among the known intermetallic superconductors. MgB2 nanowires are of interest in terms of photonic devices operating at high temperatures. We have electrochemically synthesized highly crystalline MgB2 nanowires incorporated in thin films of MgO (magnesium oxide). The MgB2 nanowires form a superconducting network inside the MgO films, which shows sharp, two-step superconducting transitions at 37 and 35 K. The MgB2 nanowires have a high potential as the material for SSPD and/or TES due to the steep change in resistance at 35 K.MgB2 nanowires were electrochemically synthesized on iron substrates in electrolytes consisting of MgCl2, NaCl, KCl and MgB2O4. The electrochemical process was elucidated by electrochemical measurements, such as cyclic voltammetry (CV) and chrono amperometry (CA). X-ray diffraction (XRD) measurements were performed on the specimens synthesized at different potentials. Magnetization measurements were also performed using a superconducting quantum interference device (SQUID) to ascertain that the specimens contain MgB2. Cross-sectional observations of the specimens were conducted using a scanning electron microscope (SEM), an electron probe micro analyzer (EPMA) and a transmission electron microscope (TEM). Tc(s) of the specimens were evaluated by measuring the transport resistance. Volume fractions of MgB2 and MgO phases were estimated at 30 and 70%, respectively, from XRD. EPMA and TEM observation showed that the MgB2 phase has the form of highly crystalline nanowires with a width of several nanometers to hundreds of nanometers, which were embedded in the MgO phase. The MgB2 nanowires grew aligning the c plane perpendicular to the substrates. Tc(s) of the films were determined to be 37 and 35 K at self field on the basis of transport measurements. The steep change in resistance at 35 K showed that the MgB2 nanowires have a high potential as the material for photonic devices. This research was supported by Nanotechnology Network Program of MEXT.
5:00 PM - CC4.9
Superconducting Properties of W-Based Focused-Ion-Beam-Induced Nanodeposits.
Amalio Fernandez-Pacheco 1 2 , Javier Sese 1 , Rosa Cordoba 1 , Jose De Teresa 2 , Ricardo Ibarra 1 2 , Isabel Guillamon 3 , Hermann Suderow 3 , Sebastian Vieira 3 Show Abstract
1 INA, University of Zaragoza, Zaragoza Spain, 2 ICMA, CSIC-University of Zaragoza, Zaragoza Spain, 3 , Universidad Autonoma de Madrid, Madrid Spain
W-based nanodeposits created by focused-ion-beam-induced deposition (FIBID) were recently found to be superconducting with TC~ 5 K . This high TC was explained by the amorphous nature of the nanodeposit. We have grown W-based nanodeposits by FIBID using the precursor gas W(CO)6 in a Nova 200 Nanolab from FEI. The nanodeposist composition has been investigated by EDX and XPS techniques, giving as a result that the W content is about 40% and homogeneous across the whole thickness. Our TEM study indicates that the nanodeposit shows amorphous nature. As previously found, the nanodeposits become superconducting below TC~ 5 K, this value being only slightly dependent on the ion beam voltage used in the range 5-30 kV. Transport measurements under magnetic field and as a function of the current in the temperature range 300 mK- 300 K have been performed with a PPMS, giving information on the critical fields and critical currents below TC. STM measurements indicate that the compound follows the BCS theory, the superconducting properties being very homogeneous down to atomic scale. Outstanding clear hexagonal vortex lattice is observed with STM by application of magnetic field , the grain boundaries being the only vortex pinning sites. Spectroscopic studies of the density of states across single vortex have been performed. The magnetotransport results of very narrow nanowires (around 100 nm) suggest features related to their finite size. Artificial pinning of the vortex and its impact on the STM and magnetotransport properties is in progress. The stable and predictable properties of this BCS-reference compound in combination with the flexible nanopatterning properties of focused-ion-beam open an exciting route to investigate basic aspects of superconducting materials.References E.S. Sadki, S. Ooi, K. Hirata, Appl. Phys. Lett. 85, 6206 (2004) I. Guillamón, H. Suderow, S. Vieira, A. Fernández-Pacheco, J. Sesé, R. Córdoba, J.M. De Teresa, M.R. Ibarra, New Journal of Physics 10, 093005 (2008)
5:15 PM - CC4.10
Anisotropic Superconductivity in MoGe-Permalloy Heterostructures.
Andrey Belkin 1 2 , R. Divan 3 , Thomas Proslier 1 , M. Iavarone 1 , Valentyn Novosad 1 , Goran Karapetrov 1 Show Abstract
1 Material Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 BCPS, Illnnois Institute of Technology, Chicago, Illinois, United States, 3 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
We investigate magneto-transport properties of magnetically coupled superconductor-ferromagnet heterostructures. We show that the superconducting order parameter of such system can be localized in narrow mesoscopic channels by virtue of the stray magnetic field emanating from domains of the ferromagnet. In case of magnetic stripe domain structures, this effect gives possibility to create superconducting nanowires without the need to employ nanoscale lithography technique.Permalloy is a ferromagnet which forms well-ordered stripe magnetic domains at thicknesses higher than certain critical value. The orientation of these stripes adjusts parallel to the external in-plane magnetic field. Each stripe has out-of-plane magnetization that periodically changes sign inducing an in-plane anisotropy in the superconducting order parameter of the adjacent MoGe film. We show from the superconducting phase diagram that near the S-N boundary the order parameter is localized in narrow mesoscopic channels just above the magnetic domain walls. By changing the orientation of magnetic stripe domains it is possible to re-configure the direction of the superconducting channels and enable one to control the in-plane transport anisotropy of the superconductor.We also explore the vortex dynamics in superconducting thin film. MoGe is an amorphous superconductor with very small coherence length (~5nm) and negligible pinning. We show that vortex dynamics in the configuration with stripe domains parallel to the transport current significantly differs from the one in the configuration with domains perpendicular to the current.This work as well as the use of the Center for Nanoscale Materials at Argonne National Laboratory and the Electron Microscopy Center were supported by UChicago Argonne, LLC, Operator of Argonne National Laboratory ("Argonne"). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357.
5:30 PM - CC4.11
Magnetic Pinning Centers.
Alejandro Silhanek 1 , Werner Gillijns 1 , Joris Van de Vondel 1 , Vitali Metlushko 2 , Bojan Ilic 3 , Victor Moshchalkov 1 Show Abstract
1 , INPAC, K.U.Leuven, Leuven Belgium, 2 Department of Electrical and Computer Engineering, University of Illinois, Chicago, Illinois, United States, 3 Cornell Nanofabrication Facility, Cornell University, Ithaca, New York, United States
Finding a way to enhance the maximum dissipationless electrical current carried by a superconductor has been a long standing objective which brings direct technological benefits. This limiting current is essentially determined by the ability to anchor the quantum flux lines in the superconductor. The vast majority of the investigations so far have been devoted to pinning centers where the superconducting order parameter is locally suppressed, thus generating a minimum in the self energy of a vortex line (so called, core pinning). Recently considerable attention has been devoted to an alternative way of enhancing the critical current in superconductors by lowering the magnetic energy of the system by means of local modulations of the field . This effect can be achieved by introducing magnetic particles in a superconducting matrix  or through deposition onto the surface of the sample . In most of the experimental investigations performed so far, no precautions were taken to electrically isolate the magnetic particles from the superconducting material which presumably results in a substantial core pinning due to proximity effects or local suppression of the critical temperature.In this talk I will present a detailed investigation of the flux pinning and dynamic properties of vortices in low critical temperature superconductors deposited on top of different arrays of permanent magnets of submicrometer size. A combination of electrotransport, magnetization, Bitter decoration and scanning hall probe microscopy techniques allows us to clearly separate the purely magnetic contribution from other unwanted effects. We demonstrate that for high values of the magnetic moment, the efficiency of these sorts of pinning sites is threatened by the spontaneous creation of vortex-antivortex pairs. The existence of these bound pairs gives rise to a flux-flow regime even at zero external fields. The exact number of vortex – antivortex pairs can be determined either by rectification effects or by the synchronous motion of the vortex lattice at high frequencies, known as mode locking. The generalization of these results to high-Tc superconductors sets a natural limit for the potential application of magnetic pinning centers and shed light on the basic pinning mechanisms.  L.N. Bulaevskii, E.M. Chudnovsky, M.P. Maley, Appl. Phys. Lett. 76, 2594 (2000). T.H. Alden, J.D. Livingston. Journ. Appl. Phys., 8,6 (1966). D.J. Morgan, J.B. Ketterson. Phys. Rev. Lett., 80, 3614 (1998).
5:45 PM - CC4.12
Flux Pinning Enhancement and Vortex Lattice Matching Effects in Amorphous Superconducting Thin Films.
Jose Vicent 1 , David Perez de Lara 1 , Elvira Gonzalez 1 , Alejandro Alija 2 , Jose Martin 2 , Maria Velez 2 Show Abstract
1 Fisica Materiales, Univ. Complutense, Madrid, Madrid, Spain, 2 Fisica, Universidad Oviedo, Oviedo Spain
Electron beam lithography (EBL), sputtering and etching techniques have been used to grow a-MoSi3 superconducting films on top of array of nanomagnets. The superconducting films show critical temperature in the range 7.3 – 7.5 K. In comparison with Nb films fabricated on the same type of magnetic arrays, the a-MoSi3 films show an enhancement of the matching effects between the vortex lattice and the unit cell of the mesoscopic array of nanomagnets with larger coherent motion of the vortices than in Nb film at the same matching conditions. Vortex dynamics channeling effects and the interplay between the periodic vortex-magnetic dot interaction and the random vortex-intrinsic defects interaction will be discussed.
CC5: Poster Session
Wednesday PM, April 15, 2009
Salon Level (Marriott)
9:00 PM - CC5.1
Effect of Alkali Metal Ion Doping in the Iron-based FeSe Superconductor.
Cha-Ming Yang 1 , Po-Wei Chen 1 , In-Gann Chen 1 , Maw-Kuen Wu 2 Show Abstract
1 Department of Materials Science and Engineering, National Cheng Kung University, Tainan Taiwan, 2 Institute of Physics, Academia Sinica, Taipei Taiwan
Recently, ironed based superconductors, e.g. La[O1-xFx]FeAs with Tc=26K by Hosono et. al. and SmFeAsO0.85 with Tc =56K by Zhao et. al., have attracted extensive attention. However, the poisonous arsenic compounds represent special concerns for both scientific studies and engineering applications. On the other hand, the simple binary FeSe compound with Tc=8K by Wu et. al. exhibits interesting superconducting properties with less toxic and easier to synthesize. Furthermore, Wu et. al. also shown that Tc increased to ~15K by partially substituting Se with Te(50at.%) with a lattice distortion at room temperature, which induced a phase transformation from symmetric tetragonal to as-symmetric triclinic structure at low temperature. It is expected that by doping alkali metal ion will introduce lattice distortion and increase hole density for charge balance. Therefore, we explore the effect of alkaili metal ion doping, i.e. Li1-xFexSe and Na1-xFexSe compounds, on the crystal structure and superconducting properties. The phase and lattice distortion were characterized by XRD, with the lattice parameter decreases in Li1-xFexSe, and remains un-changed in Na1-xFexSe. The SEM, EPMA, and TEM were used to characterize the microstructure and the content of alkali metal distributions. The superconductivity measured by SQUID show that Tc~7K for both Li1-xFexSe and Na1-xFexSe compounds. The effect of doping amount on the magnetization vs. temperature characteristics will be discussed in detail. . This research is supported by NSC 96-2112-M-006 -012 -MY3.
9:00 PM - CC5.10
Fabrication of YBa2Cu3O7-δ Films with MgO Addition on IBAD-MgO Templates via Pulsed Laser Deposition.
Sung Hun Wee 1 2 , Amit Goyal 1 , Yuri Zuev 1 , Claudia Cantoni 1 , Sy Cook 1 , Victor Maroni 3 Show Abstract
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, 3 , Argonne National Laboratory, Argonne, Illinois, United States
Microstructual and superconducting properties for YBa2Cu3O7-δ (YBCO) films with upto 4vol% MgO additions were studied. All films were grown on ion-beam-assisted deposition (IBAD)-MgO substrates using pulsed laser deposition. Regardless of MgO content, all YBCO + MgO films have excellent in-plane and out-of-plane textures. Epitaxial, MgO nanodots/nanorods were found to be oriented along the c-axis of the YBCO. The MgO nanodots/nanorods have a cube-on-cube and a 45o rotated cube-on-cube epitaxy within the YBCO matrix. The non-superconducting, c-axis correlated, MgO columns result in enhanced flux-pinning for the field parallel to the c-axis of the film as compared to pure YBCO. However, there is a rapid Tc drop with an increase in MgO addition due to the substitution of Mg for Cu sites. Raman spectroscopy confirmed the Mg substitution on the Cu1 site. Detailed field and angular dependence of Jc as a function of MgO content will be presented. Research was sponsored by the US Department of Energy, Office of Electricity Delivery and Energy Reliability - Superconductivity Program, under contract DE-AC05-00OR22725 with UT-Battelle, LLC managing contractor for Oak Ridge National Laboratory.
9:00 PM - CC5.11
Unusual Flux Pinning Properties of YBCO with BaZrO3 Nanoparticle Layered Additions.
Timothy Haugan 1 , Francisco Baca 1 , Matthew Mullins 1 , Eric Brewster 1 , Joshua Reichart 1 , Paul Barnes 1 , Boris Maiorov 2 , Michael Sumption 3 , Haiyan Wang 4 Show Abstract
1 , The Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States, 2 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 , The Ohio State University, Columbus, Ohio, United States, 4 , Texas A&M University, College Station, Texas, United States
The addition of nanosized defects to enhance flux pinning of YBa2Cu3O7-z (YBCO) superconductors has been studied world-wide by many research groups with great success. However enhanced flux pinning properties are generally studied at 65-77 K and mostly for applied magnetic fields H//c, and flux pinning properties at < 65 K and H//ab are not considered as well. Increasing Jc(H) at lower temperatures < 30K for YBCO coated-conductors is also important, to potentially achieve the highest engineering critical current densities at any temperature of any known superconductor-wire that can be manufactured in km-lengths. In this paper we demonstrate that flux pinning enhancements at 77 K do not always correlate with enhancements at 65 K and lower temperatures. We show that a (BZO/YBCO)N film with average flux pinning at 77 K has clearly the strongest pinning properties at 30 K and H > 1 T, when compared to commonly-known and optimized strong flux pinning YBCO+nanoparticle films including (M/YBCO)N with M = Y2O3 or Y2BaCuO5, as well as (YBCO)1-x(BZO)x films with BZO incorporated as nanorods with x = 2-4 Vol%. Other unusual flux pinning properties were observed for the (BZO/YBCO)N multilayer films, including potentially world-record high Jc(77K,H//ab) and also strong decrease of Jc(77K,H//c=2T) for (BZO~0.5nm/YBCO)N for YBCO layer thickness less than 10 nm. Possible explanations of these unusual flux pinning properties will be presented.
9:00 PM - CC5.12
Microstructure of All-solution-derived BaZrO3 Interface-templated YBa2Cu3O7 – LaAlO3 Films.
Patricia Abellan 1 , Felip Sandiumenge 1 , Marta Gibert 1 , Joffre Gutierrez 1 , Anna Palau 1 , Alberto Pomar 1 , Teresa Puig 1 , Xavier Obradors 1 Show Abstract
1 , ICMAB-CSIC, Bellaterra Spain
Nanostructuration of superconducting films is receiving a tremendous interest owing to need to increase their pinning efficiency. The most popular approach to date consists of the introduction of secondary phase, non-superconducting, nano-particles into the superconducting matrix, and to a less extent the introduction of continuous or quasi-continuous non-superconducting layers. An alternative procedure consists of the growth of epitaxial films on templated substrates in order to induce growth induced defects that ideally would thread the film thickness. Our preliminary results obtained using BaZrO3 nanodots indicate an increase of Jc at high magnetic fields and temperatures thus suggesting the potential interest of such nanostructures.Self assembled nanodots with sizes comprised within 4 – 10 nm, both in height and width, exhibiting a narrow size distribution, have been obtained on (001)LAO from barium acetate and zirconium acetylacetonate precursors. The size and density of the nanodots can be tuned through the modification of the precursor solution concentration and growth conditions. YBCO was deposited on top of the nanostructured substrate surface following a TFA route. The microstructure of the films was investigated by high resolution transmission electron microscopy and electron energy loss spectroscopy.The nanodots typically decorate the substrate step ledges, and therefore their distribution is mainly governed by the underlying step configuration. A detailed analysis shows that despite the huge misfit strain of the BZO – LAO system (9.5 %), the BZO nanodots appear fully relaxed through a complex misfit dislocation structure built by dislocations with Burgers vectors b=1/2<110>. The shape of the nanodots tends be equiaxed though deviations may occur. The shape of the nanodots appears to be important in determining the neighbouring YBCO structure. In no case, however, threading dislocations were found associated to the nanodots, though the YBCO lattice may appear notably distorted ahead of the dot-matrix interface. In particular, bending of the (001) planes is more apparent as the height to basal diameter ratio increases, and may extent between 4 to 8 unit cells beyond the interface towards the film surface. As a further consequence, the presence of interfacial nanodots induces the nucleation of a/b-oriented grains, exhibiting clean and structurally abrupt 90-degrees- GBs.
9:00 PM - CC5.13
Formation of MgO Nanorods for Enhancing Critical Currents in the Superconductor Thin Film.
Kyunghoon Kim 1 , John Mathis 2 , Hans Christen 1 , Pamela Fleming 1 , David Christen 1 , Claudia Cantoni 1 Show Abstract
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Physical Science Department, Embry-Riddle Aeronautical University, Daytona Beach, Florida, United States
The critical current density under the external magnetic field is one of the important parameters for evaluating high temperature superconductor wires. Even though the superconducting wire shows sufficiently high current value with zero magnetic field, it is clearly observed that the electrical properties are degraded with increasing magnetic field. This phenomena is explained by energy dissipation by the moving magnetic vortices due to the current-induced Lorentz force. In order to overcome this problem, one needs to immobilize the vortices. Recently, it has been shown that nanocolumns of stacked, self-aligned nanodots act as strong pinning sites inside high-temperature superconducting thin films grown by either pulsed laser deposition (PLD) and MOCVD. In this research, we have used PLD to form MgO nanorods on a thin gold layer at high temperature in oxidizing ambient. The MgO nanorod structure appears to grow from isolated Au nanodots or clusters. The process conditions for growing MgO nanorods on single crystal substrates will be presented. The size, the density and the distance between the nanorods are the important factors to consider. Such structures should be very desirable for generating pinning centers for high temperature superconductor wires, where optimized nanorods would be formed on the buffer layers which are the initial layer for HTS coatings such as YBa2Cu3O7-δ
9:00 PM - CC5.14
Evaluation of Artificial Pinning Sites of Nanodot-dispersed MOD-YBCO Films on Surface-modified Templates.
Kookchae Chung 1 , Youngkuk Kim 1 , Jaimoo Yoo 1 , Xiaolin Wang 2 , Shi Xue Dou 2 Show Abstract
1 , Korea Institute of Materials Science, Changwon Korea (the Republic of), 2 , Institute for Superconducting & Electronic Materials, Wollongong, New South Wales, Australia
Nanodot-dispersed MOD-YBCO films have been fabricated on the surface-modulated templates. MOD-YBCO precursor solution was prepared and mixed with the (ZrO2, BaZrO3) nanodot-dispersed solution which was synthesized by sol-gel process. The surface-modulated templates was consisted of the (MgO, BaZrO3) nanodot-deposited substrates, where nanodots was deposited and formed by rf-sputtering and electro-spray, respectively. Since the superconducting phase cannot form on top of the nanodots, it is highly feasible to induce the strong pinning sites such as the columnar defects in superconducting materials using nanodots as a seed. The surface morphologies and cross-section profiles of the surface-modulated templates were examined. Also, the correlated artificial pinning sites in the nanodot-dispersed MOD-YBCO films are discussed with the microstructural development and the magnetic fields dependence of critical current density.“This work was supported by the Global Partnership Program from the Korea Foundation for International Cooperation of Science & Technology(KICOS) through a grant provided by the Korean Ministry of Education, Science & Technology(MEST) in 2006 (M60602000012).”
9:00 PM - CC5.15
Influence of Artificial Nanostructure Pinning on the Critical Current Density in YBa2Cu3O7-X Thin Films.
Mike Sumption 1 , Tim Haugan 2 , Paul Barnes 2 , Chakrapani Varanasi 3 , Mike Susner 1 Show Abstract
1 Materials Science, The Ohio State University, Columbus, Ohio, United States, 2 Power Generation, Air Force Research Laboratory, Dayton, Ohio, United States, 3 , University of Dayton Research Institute, Dayton, Ohio, United States
Critical currents and flux pinning have been studied in various temperature and field regimes for PLD YBCO modified by several kinds of nanometer scale pinning. 211 additions, added either as layers, or as a 3-D distributions, were compared to control samples and also samples with pinning caused by minute levels of Ce or Tb doping. Also included were samples with BZO and BSO doping. Significant increases in Jc were seen for several kinds of inclusions and dopants over the whole of the 4.2 K to 77 K temperature regime. These increases were parameterized using B*, Jsf, and α values, and the character of the pinning was investigated. Enhancement in B* over that of the control samples were evident for samples with BZO and BSO additions, this is attributed to columnar-like defects in these samples. The low field plateau critical current, Jsf, tended to be lower for samples with aggressive pinning additions. Magnetically determined critical current density (Jc) was fit to Jc =C* B^(-α) and values of α were suppressed from the control sample values of α = 0.5 to lower values for pinned samples, reaching as low as α = 0.2 for the layer pinned 211 sample at low temperatures. Critical current densities at 1 T were compared for various samples, and pinned samples performed better than control samples is this regime. Some dopants, including notably BZO and BSO tended perform well at 77 K, but also increased in Jc more rapidly than other samples as temperature was reduced.*This work was supported by the summer faculty program of the AFRL
9:00 PM - CC5.16
Probing in-depth Raman Profiling Spectroscopy of the YBa2Cu3O7-δ Films.
Branescu Maria 1 , Vailonis Arturas 2 , Ian Ward 3 , Coralie Naudin 4 , Emmanuel Leroy 5 Show Abstract
1 , Nat. Inst. Mat. Phys., Bucharest Romania, 2 , Stanford University, Palo Alto, California, United States, 3 , EAG, Sunnyvale, California, United States, 4 , Horiba Jobin-Yvon, , Villeneuve d'Ascq France, 5 , Horiba Jobin-Yvon, , Edison, New Jersey, United States
We present and discuss high spectral and spatial resolution Raman spectra taken at the room temperature, in the depth of YBa2Cu3O7-δ (YBCO) films in-situ grown by pulsed laser deposition. We utilized the profiling Raman system with the confocal microscopy capability at the detection, and the green laser’ with 488 cm-1 wavelength that provides the resonance of the most significant Raman mode of the YBCO films . To probe and argued that the profiling Raman system work well in the depth of the YBCO films, we analyze the depth dependant’ changes of the electronic scattering Raman active continuum of the YBCO films in a large domain of the energy spectrum (100 cm-1 - 4,000 cm-1), reflecting the phonon modes as well as the magnon exchange pairing. The parameters’ range of the depth profiling Raman system providing the maximum signal intensity and number of distinctive Raman spectra corresponding to different depths of the YBCO films are outlined .Raman spectra maps taken on a given area of 4 µm squares and 200 µm squares respectively reflect the predominantly c-axis oriented YBCO films. Few a-axis and mix (a-axis / c-axis) oriented grains with a total area of about 10 µm squares are observed inside the 200 µm squares investigated area. Scanning electron microscopy pictures of a thin and a thick YBCO films highlight typical surface morphology. The interrelations between the degree of epitaxy of the crystalline structure, revealed by x-ray Φ scan and the depth Raman profiling spectra have been investigated. The Raman profiling spectra of the YBCO films are proving to be very appealing technique, reflecting the ‘movie’ of the in-situ epitaxial growth process at a convenient time and environment after deposition. 1 - M. Branescu and C. Naudin, "Depth Raman spectra and laser-induced structural and oxygenation changes in thick YBa2Cu3O7-δ films", J. Optel. Adv. Mat. 3, 661 (2007). 2 - M. Branescu, C. Naudin, M. Gartner, G. Nemes, “Depth profiling Raman spectroscopy of a thin YBa2Cu3O7-δ film”, Thin Solid Films 516, 8190 (2008).
9:00 PM - CC5.17
Epitaxial Growth of Lanthanum Tantalate Thin Films with Improved Texture on Biaxially Textured Ni-W Substrates.
Vemuru Krishnamurthy 1 , M. Paranthaman 1 , O. Polat 2 3 , T. Aytug 1 Show Abstract
1 Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge , Tennessee, United States, 2 Materials Science and Technology Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee, United States, 3 Department of Physics & Astronomy, University of Tennessee, Knoxville, Tennessee, United States
The development of transition metal oxide seed layers with improved texture using the chemical solution decomposition (CSD) route is essential for achieving high critical current density YaBa2Cu3O7-δ (YBCO) films. We have investigated the epitaxial growth of pyrochlore structured La3TaO7 (LTO) films on biaxially textured Ni-3 at. % W (Ni-W) substrates using the CSD method. A precursor solution with 0.25 M concentration of cations was spin coated on Ni-W substrates. The optimal film growth and crystallization conditions were determined by spin coating films under different conditions of controlled humidity (22% – 99%) followed by annealing in a flowing Ar + 4 at. % H2 gas atmosphere at various temperatures in the range of 900 to 1100 °C for 60 minutes. We have identified the process conditions for the growth of smooth and (004) oriented epitaxial LTO thin films on Ni-W substrates using x-ray diffraction (XRD) for texture analysis and atomic force microscopy. We will discuss the effect of LTO thin film processing parameters and substrate texture on the sharpening of the texture of LTO seed layers. This research was sponsored by the U.S. Department of Energy, Office of Basic Energy Sciences (BES) - Division of Materials Sciences and Engineering (DMSE). This research was performed at the Oak Ridge National Laboratory, managed by UT-Battelle, LLC for the USDOE under contract DE-AC05-00OR22725.
9:00 PM - CC5.18
Electrodeposited- Buffer Layers for YBa2Cu3O7-δ Superconductors
Wenjun Zhao 1 , Andrew Norman 1 , Sovannary Phok 1 , Jonathan Mann 1 , Raghu Bhattacharya 1 Show Abstract
1 , National renewable energy lab, Golden, Colorado, United States
We have studied the microstructure of electrodeposited (ED) Gd2O3 (GO) and Gd2Zr2O7 (GZO) buffer layers for YBa2Cu3O7-δ (YBCO) superconductors with conventional transmission electron microscopy (TEM). The heterostructure of GO/GZO showed a better crystalline quality than the only GZO buffer layer (without a GO cap layer). Cross-sectional TEMs showed the ED-GO layer is pore free while the ED-GZO layer contains pores with a high density. A pulsed laser deposited YBCO superconductor grown on the GO/GZO heterostructure buffer layer produced a critical current density (Jc) of 3.3x10E6 A/cm2 at 77K in zero field. A new ED method has been developed to reduce the pore density in the GZO buffer layer. The superconductivity will be compared with the above data.We have also investigated ED-CeO2/GZO/Ni. The interdiffusion of CeO2 and GZO was found by energy dispersive spectrum (EDS) in a TEM. CeO2 with different thicknesses were examined and an optimal thickness was obtained. A YBCO superconductor grown by metal-organic deposition with trifluoroacetates (MOD-TFA) showed a promising electrical property.
9:00 PM - CC5.2
Growth of SmFeAsO0.85 Superconducting Single Crystals at High Pressure
Hyun-Sook Lee 1 , Jae-Hyun Park 1 , Jae-Yeap Lee 1 , Nak-Heon Sung 2 , Ju-Young Kim 2 , Beong Ki Cho 2 , Tae-Yeong Koo 3 , Chang-Uk Jung 4 , Hu-Jong Lee 1 5 Show Abstract
1 Physics, Pohang University of Science and Technology, Pohang Korea (the Republic of), 2 Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of), 3 , Pohang Accelerator Laboratory, Pohang Korea (the Republic of), 4 Physics, Hankuk University of Foreign Studies, Yongin Korea (the Republic of), 5 , National Center for Nanomaterials Technology, Pohang Korea (the Republic of)
Superconducting single crystals of nominal composition of SmFeAsO0.85 without fluorine doping were grown at a pressure of 3.3 GPa and at a temperature of 1350-1450 °C by using the self-flux method. Plate-like single crystals of a few-150 μm in their lateral size were obtained. Single crystals showed the superconducting transition at about 53.5 K with a narrow transition width of 0.5 K in the resistive-transition. The X-ray diffractometry patterns and the Cs-corrected high-resolution scanning transmission electron microscopy images indicate that our single crystals have a well-defined tetragonal structure. The chemical compositions of the crystals were estimated by using the electron-probe X-ray microanalysis. In addition to the sharp transition width and good crystallinity of our single crystals, larger residual resistivity ratio (~5) compared to those reported in other (Sm,Nd)FeAsO1-xFx single crystals implies that our SmFeAsO0.85 single crystal is considered to be of high quality. Growing FeAs-based single crystals without involving F elements provides an easier root to find the optimum condition for the crystal formation and simpler interpretation of the electronic structure leading to the superconductivity in this family of materials.*This work was supported by Steel Science Project of POSCO, Republic of Korea
9:00 PM - CC5.3
Neutron irradiation effects in pnictide SmFeAsO1-xFx and Ba(Fe1-xCox)2As2.
Jianyi Jiang 1 , A. Yamamoto 1 , J. Weiss 1 , E. Hellstrom 1 , D. Larbalestier 1 , M. Eisterer 2 , H. Weber 2 Show Abstract
1 National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, United States, 2 Atomic Institute of the Austrian Universities, Vienna University of Technology, Vienna Austria
Bulk SmFeAsO1-xFx was irradiated in a fission reactor with fast neutron fluence up to 4×1021m-2. After irradiation the upper critical field and the critical current density Jc increases. The second maximum in the field dependence of Jc disappears and the critical current density becomes a monotonic decreasing function of the applied magnetic field. The length scale for current flow increases becoming significantly larger than the grain size indicating that intergranular current through the grain boundaries is also enhanced. This is an indication that the grain boundary problem is less severe than in YBCO and BSCCO, and that the macroscopic currents are limited by comparatively weak pinning. Effects of neutron irradiation in single crystal Ba(Fe1-xCox)2As2 will also be presented.
9:00 PM - CC5.4
Influence of Ni and Cu Contamination on the Superconducting Properties of MgB2 Filaments.
Alexandra Jung 1 , Antje Drechsler 1 , Heinrich Orschulko 1 , Bernd Ringsdorf 1 , Brigitte Runtsch 1 , Sonja Schlachter 1 , Wilfried Goldacker 1 Show Abstract
1 Institut für Technische Physik, Forschungszentrum Karlsruhe, Eggenstein-Leopoldshafen Germany
Technical MgB2 conductors require a sheath composite consisting of different materials in order to achieve good deformability, thermal and mechanical stability and/or low ac losses. Metals with high thermal and electrical conductivity like Cu ensure thermal stability at cryogenic temperatures. Fe, Monel or stainless steel guarantee the mechanical stability. In in-situ wires the heat treatment that is necessary for the formation of the MgB2 phase also enables reactions of the MgB2 filament with the sheath materials. As these reactions and the so formed impurity phases can lead to a decrease of the critical current and a hindered current transfer into the filament, Nb or Ta barriers are often introduced at the filament-to-sheath interface to prevent undesired reactions. Especially in heavily deformed multifilamentary wires, the reaction barriers can break, losing their function locally. In this contribution, we elucidate the influence of Ni- and Cu-based impurity phases on the superconducting properties of the MgB2 filaments by studying samples with a direct MgB2 / metal matrix interface. Heat treatments at different temperatures were performed in order to investigate MgB2 phase formation and diffusion processes of the poisoning elements leading to the formation of secondary phases. The impurity phases are identified and localized by means of XRD and SEM / EDX. The superconducting properties are specified by Tc measurements and by comparing the field dependence of the current carrying capability.
9:00 PM - CC5.5
Self-propagating High Temperature Synthesis (SHS) of Nanosized Boron Powders and its Application to MgB2 Superconducting Wires.
Young-Kuk Kim 1 , Jaimoo Yoo 1 , Kookchae Chung 1 , Shi Dou 2 , Xiaolin Wang 2 Show Abstract
1 , Korea Institute of Materials Science (KIMS), Changwon, Kyungnam, Korea (the Republic of), 2 , Institute for superconducting and electronic materials, Wollongong, New South Wales, Australia
Fine boron powders with amorphous structure were synthesized by Self-propagating high temperature synthesis (SHS). Compared with conventional solid state reaction method, SHS method provides a fast and cost-effective route for fine amorphous boron powders essential to high quality MgB2 wire fabrication. In SHS process, the boron oxide powders were reduced to elemental boron through oxidation of magnesium powders. In particular, nanosized amorphous boron powders (mean diameter < 100nm) were synthesized by applying diluent to reactant mixture for SHS process through reducing maximum reaction temperature or adiabatic combustion temperature (Tad). In this study, we fabricated MgB2 wires by the powder-in-tube method using magnesium and SHS-processed fine boron powders as starting materials and the effect of SHS- processed boron powder on the microstructure and flux pinning properties of in-situ processed MgB2 wires were discussed.
9:00 PM - CC5.6
Structural-microstructural Characteristics and its Correlations with the Superconducting Properties of in-situ PIT Processed MgB2 Tapes with Ethyltoluene and SiC Powder Added.
Anjana Asthana 1 , Akiyoshi Matsumoto 1 , Hitoshi Kitaguchi 1 , Yoshio Matsui 2 , Toru Hara 2 , H. Yamada 3 , N. Uchiyama 3 Show Abstract
1 Superconducting Materials Center, National Institute for Materials Science, Tsukuba, Ibaraki, Japan, 2 Advanced Electron Microscopy Group, National Institute for Materials Science, Tsukuba, Ibaraki, Japan, 3 Maglev System Development Division, Central Japan Railways Company, Tsukuba, Ooyama, Japan
We performed the structural-microstructural investigations of pure MgB2, ethyltoluene and both ethyltoluene and SiC added MgB2/Fe tapes by using the technique of transmission electron microscopy. The analysis of the microstructure shows that the grain size for the pure and ethyltoluene added MgB2 tape sample is in the range of 10-100nm, however with the addition of both ethyltoluene and SiC, the grain size decreases to about 5-80 nm. The a-axis length of the ethyltoluene added tape samples is slightly decreased, whereas for both ethyltoluene and SiC added sample, a-axis length is decreased by 0. 4% as compared to the pure MgB2 tape sample, showing the amount of carbon substitution is less in ethyltoluene added tape samples. The reason for the higher Jc values of ethyltoluene added MgB2 tape sample as compared to the pure MgB2 tapes is the presence of less amount of impurity phase, MgO. The large improvement in Jc-B properties for the ethyltoluene and SiC added MgB2 tape sample is attributed to 1) the enhancement of upper critical field, Bc2, by the substitution of carbon for boron, 2) pinning by nanosized (5-20 nm) particles of Mg2Si and other silicides 3) enhanced grain boundary pinning due to the smaller grain size and 4) presence of less amount of impurity phase, MgO as compared to the pure sample.
9:00 PM - CC5.7
Effect of CeO2 Doped on the Jc (H, T) Enhancement of Y-Ba-Cu-O Samples Fabricated by Infiltration and Growth Method.
Po-Wei Chen 1 , Shin-Yun Chen 2 , Yung-Sheng Shiao 1 , In-Gann Chen 1 , Maw-Kuen Wu 3 Show Abstract
1 Department of Materials Science and Engineering, National Cheng Kung University, Tainan Taiwan, 2 Department of Polymer Engineering, National Taiwan University of Science and Technology, Taipei Taiwan, 3 Institute of Physics, Academia Sinica, Taipei Taiwan
It is well known that CeO2 addition are effective in reducing the coarsening of Y2Ba1Cu1O5 (Y211) particles on top seeded melt textured (TSMT) Y-Ba-Cu-O (YBCO) bulk superconductors and result in the enhancement of the critical current density (Jc). In this study, large single grain YBCO superconductors with CeO2 doped have been fabricated by infiltration and growth (IG) technique. It is noticeable that IG-YBCO samples with CeO2 addition show a superior Jc (H, T) with a peak effect which is not usually observed in TSMT-YBCO samples before. In addition, the peak effect is more extend with increasing CeO2 addition. And the Jc (3T, 65K) of IG-YBCO sample with 1.5wt% CeO2 addition reach 105 A/cm2, which is two times higher than that of TSMT-YBCO samples. The SEM and EPMA results indicated that the distribution of second phase Y211 is homogeneous throughout the bulk and the particle size is around 1μm, which is similar to TSMG-YBCO with CeO2 addition without peak effect on Jc (H, T). And TEM were used to characterize the spatial-dependent compositional fluctuations in this sample. Moreover, the diffusion of Sm from seed to IG-YBCO bulk was also observed, which is believed to form compositional fluctuations (Y,Sm)BCO and that is correlated to the effective pinning at high field (or peak effect) to change the superconductivity.This research is supported by NSC 96-2112-M-006 -012 -MY3.
9:00 PM - CC5.8
Superconducting Cuprates Films on Single Crystalline Manganite Substrates.
N. Haberkorn 1 , J. Guimpel 1 , Gladys Nieva 1 Show Abstract
1 , Centro Atómico Bariloche and Instituto Balseiro, S. C. de Bariloche Argentina
We present a study on the superconducting and structural properties ofGdBa2Cu3O7-δ thin films grown on Gd0.7Ca0.3MnO3 bulksingle crystals.The superconducting films were grown by sputtering on the (220) surfaceof the manganite. The films show epitaxial growth along the (103)direction and a critical temperature of 87K.Magnetization measurements evidence that the superconductingproperties of the films are influenced by the magnetic state of the ferrimagnetic substrate.
9:00 PM - CC5.9
Enhancing Superconducting Parameters by Array of External Magnetic Dots.
Wei Jiang Yeh 1 , Bo Cheng 1 Show Abstract
1 Department of Physics, University of Idaho, Moscow, Idaho, United States
Enhancing the pinning force in cuprates can be achieved by externally introduced magnetic dots. We have used a novel nanotechnology to create metal masks with sub-micron size holes that have a triangular lattice pattern. With this mask, magnetic dots with a periodic array were deposited onto the surface of YBCO thin films by a simple deposition. The current versus voltage characteristics of YBCO thin film trips with a uniform nickel dot array have been measured. The results show that as the magnetic field strength increased, the critical current value of the strip with magnetic dots reduced with a much slower pace in comparison with the values obtained from the bare sample. We also found as temperature reduced, the pinning force from the magnetic dots increased dramatically. These results are consistent with our numerical calculations.
Ron Feenstra Oak Ridge National Laboratory
David C. Larbalestier Florida State University
Boris Maiorov Los Alamos National Laboratory
Marina Putti University of Genova and CNR/INFM-LAMIA
Yi-Yuan Xie SuperPower, Inc.
CC6: Coated Conductors I: Fabrication
Thursday AM, April 16, 2009
Room 3012 (Moscone West)
10:00 AM - CC6.2
Visualization of Dissipation at Different Magnetic Field Orientations in RABiTS Coated Conductors.
Dmytro Abraimov 1 , Pei Li 1 , David Larbalestier 1 , Xiaoping Li 2 , Rupich Marty 2 Show Abstract
1 Applied Superconductivity Center, FSU, National High Magnetic Field Laboratory , Tallahassee, Florida, United States, 2 , American Superconductor Corporation, Devens, Massachusetts, United States
Application of YB2Cu3O(7-d) coated conductor (CC) in magnets and generators becomes much more promising due to the recent progress in engineering pinning centers, which allow better in-field YBCO properties. Since magnetic field orientation strongly affects Jc visualization of the local electric field in the CC for different external magnetic field orientations becomes important. To understand the influence of current limiting mechanisms (CLM) in TFA-MOD YB2Cu3O(7-d) CC on RABiTS at different magnetic fields (B) we employed Low Temperature Scanning Laser Microscopy (LTLSM), which allows direct imaging of the local electric field (E) distributions. LTLSM is combined with orientation imaging microscopy to reveal the grain boundary (GB) structure. We measured different links to understand the competitive role of strongly misoriented grains (SMGs) and the low angle misoriented GB network inherited from the Ni-W substrate on the local E at different B. For polycrystalline links, as the magnetic field is increased we observe a smooth transition from a GB to a bulk limited regime. At small B, the dissipation is strongly inhomogeneous and generally follows the GB network with enhanced values along low angle GBs and at the edges of bottlenecks defined by higher misoriented GBs. We observed that inhomogeneous flux jets can lose their structure at magnetic fields below 1 T. In links with an abundance of SMGs the SMGs are CLMs up to 5 T. For links with low concentrations of SMG, the dissipation pattern at 5 T is defined by the link geometry rather than the GBs, which means the risk of developing hot spots at GBs is considerably decreased. For narrow, one-dimensional CC links, the Ic distributions were calculated for different magnetic fields. In wider, two-dimensional links where we applied B//ab, the electric field is more homogeneous and appears as straight lines that follow the external magnetic field. In the nominal “Lorentz force free regime” where the field is nominally parallel to the current, the dissipation is highly sensitive to defects.
10:15 AM - CC6.3
All Chemical High Critical Current Coated Conductors From Modified Anhydrous TFA Precursor Solution.
Susagna Ricart 1 , Neus Roma 1 , Anna Llordes 1 , Fernando Martinez 1 , Xavier Palmer 1 , Roxana Vlad 1 , Albert Calleja 1 , Alberto Pomar 1 , Teresa Puig 1 , Xavier Obradors 1 Show Abstract
1 ICMAB, CSIC, Bellaterra Spain
Chemical solution deposition (CSD) has emerged in the last years as a very competitive technique to obtain epitaxial films of high quality with controlled nanostructures. In particular, the all CSD approach is considered as one of the most promising ways for low-cost production of second generation superconducting tapes.The TFA route is, at present, the most suitable chemical solution road to achieve epitaxial YBa2Cu3O7 layers with high critical currents. The use of anhydrous TFA precursors have allowed to greatly shorten the pyrolysis process while understanding the YBCO growth process leads to controlled crystal nucleation and microstructure and allows to achieve high critical currents (Jc ≈ 4 MA/cm2 at 77 K).Anhydrous TFA solution proved to be easily modified by means of changes on concentration (from 10-3 to 3M), solvent (methanol, ethanol or methoxyethanol), precursors (low fluorine content) and use of different organic and polymeric additives. In this communication we present also an approach based in an “all chemical” process in order to obtain nanocomposite thin films containing previously or simultaneously synthesized nanoparticles of non-superconducting second phases (Au, Ag, Y2O3, BaZrO3) in the YBCO matrix using the Metal Organic Decomposition. The growth of the YBCO chemical derived layers has been attained also on solution derived doped-CeO2 buffered substrates where the surface planarity has proven to be a crucial parameter for the ulterior growth of high performant YBCO layers . Control in the stability and rheology of the precursor solutions by means of different analytical and spectroscopic techniques showed to be very important to obtain good and reproducible results. In addition, the mechanisms controlling stress relief during the drying and pyrolysis processes of the different metal-organic precursors determine the film homogeneity after the pyrolysis stage. Hence, combined FT-IR and TGA studies have been undertaken. Finally, the growth process has been studied to achieve high critical current nanostructured YBa2Cu3O7 coated conductors.
10:30 AM - CC6.4
Improved Nucleation and Growth in Ex Situ RBCO Coated Conductors.
Ron Feenstra 1 , F. List 1 , D. Christen 1 , D. Miller 2 , V. Maroni 2 , X. Li 3 , S. Sathyamurthy 3 , M. Rupich 3 Show Abstract
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , Argonne National Laboratory, Argonne, Illinois, United States, 3 , American Superconductor Corporation, Devens, Massachusetts, United States
A critical moment in the ex situ conversion of fluoride-based HTS precursors occurs at the start of the high-temperature anneal when the RBCO first nucleates and starts to grow. This nucleation and growth follows complex physical and chemical changes in the precursor during the heating ramp. Therefore, it has been difficult to isolate the effects of key parameters on this sensitive part of the process. Using advanced processing and characterization techniques and building on a rapidly expanding knowledge base in the literature, we have succeeded in studying the nucleation and growth of ex situ RBCO films in renewed detail. Precursors were deposited on RABiTS templates by means of metal-organic deposition (MOD) and physical vapor deposition (PVD). We find that by manipulation of the nucleation, the RBCO growth mode may be changed from island-like to laminar. This change is pivotal to the optimization of critical current performance. In addition to adjustments in the processing parameters, it is found that a new “seed layer” approach provides an alternative means to control the nucleation and growth. Implications for the successful processing of thick films are discussed.*Research sponsored by the U.S. DOE, Office of Electricity Delivery and Energy Reliability, Superconductivity Program for Electric Power Systems, under contract DE-AC05-00OR22725 with ORNL, managed and operated by UT-Batelle, LLC. Work at Argonne was performed under contract DE-AC02-06CH11357 between UChicago Argonne, LLC and the DOE.
11:15 AM - **CC6.5
MOCVD Research at ORNL: Systematic Studies and Coordinated Characterization of REBCO Films.
Tolga Aytug 1 , M. Paranthaman 1 , L. Heatherly 1 , Y. Zhang 1 , E. Specht 1 , K. Kim 1 , C. Cantoni 1 , D. Christen 1 , A. Goyal 1 , Y. Chen 3 , V. Selvamanickam 3 , V. Maroni 2 Show Abstract
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 , SuperPower, Inc., Schenectady, New York, United States, 2 , Argonne National Laboratory, Argonne, Illinois, United States
The research-scale metal organic chemical vapor deposition (MOCVD) system, provided by SuperPower, Inc. has been used to investigate processing variables for MOCVD REBCO precursors as well as to understand the efficacy and effects of RE and other cation addition/substitution in the structural properties and pinning performance of these films. Systematic studies have revealed trends in the resulting property/performance correlations of these films, as characterized by conducting coordinated transport, XRD, SEM, TEM, XAFS, and Raman analyses. From the combination of these characterization techniques, an improved understanding for the growth characteristics of MOCVD REBCO films was established and will be discussed.
11:45 AM - CC6.6
In Field Low Temperature Laser Scanning Microscopy Study of IBAD YBCO Coated Conductors.
Pei Li 1 , Dmytro Abraimov 1 , David Larbalestier 1 , Yi-Yuan Xie 2 , Yimin Chen 2 , Venkat Selvamanickam 2 Show Abstract
1 , Applied Superconductivity Center, National High Magnetic Field Lab, Tallahassee, Florida, United States, 2 , SuperPower, Inc. , Schenectady, New York, United States
YBCO coated conductors fabricated with IBAD-MOCVD technique is one of the promising candidates for magnet application. Commercial coated conductors usually contain defects obstructing current flow. Application of YBCO coated conductors requires understanding of the local dissipation caused by these defects under different external magnetic field orientation. In our work, we used Low Temperature Laser Scanning Microscopy (LTLSM) to map the local electric field distribution on IBAD YBCO samples in both perpendicular and parallel magnetic field. Scanning Electron Microscopy (SEM) and Orientation Imaging Microscopy (OIM) maps were used to identify defects causing the dissipation. We also patterned artificial defects on IBAD YBCO samples with precisely controlled Focused Ion Beam (FIB) to simulate real grain boundaries (GB), which were common current-limiting defects in commercial YBCO coated conductors. Strong local dissipation was observed around artificial GBs caused by preferential flux penetration when GBs and the field were parallel. It was also found that dissipation maps became more non-uniform under Lorentz force-free (longitudinal magnetic field) configuration.
12:00 PM - CC6.7
Critical Current Anisotropy in Prototype 2G Wire with Flux Pinning Strongly Enhanced by Columnar Defects of BZO Nanoparticles
Yifei Zhang 1 , Yuri Zuev 1 , Claudia Cantoni 1 , Amit Goyal 1 , David Christen 1 , Eliot Specht 1 , John Sinclair 2 , James Thompson 2 1 , Mariappan Paranthaman 3 Show Abstract
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee, United States, 3 Chemical Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Magnetic field angular dependence of the critical current (Ic) and the I-V relationship power-law exponent (n) for the prototype 2G wires was experimentally studied. The Zr-doped rare-earth cuprate superconducting films were fabricated by MOCVD on IBAD-MgO templates. Transport measurements were configured with the electrical current either in the longitudinal or the transverse direction of the tape, but always perpendicular to the magnetic field (B). For both current transport directions, the angular dependence of Ic showed essentially two peaks, one corresponding to the pinning along the a-b plane and the other to the strongly-enhanced pinning near the c-axis due to the columnar defects of BaZrO3 nanoparticles created by the doping. The exact angular positions of the peaks differ for the two different transport directions. It was observed that the peak positions can shift away from the a-b plane and the c-axis when the current is in the longitudinal direction. The orientational dependence of Ic exhibiting this angular shift was studied in terms of the combined effects from the electronic anisotropy and the tilts in the lattice and columnar defects. XRD and cross-sectional TEM were used to investigate the structural details of the crystal lattice and the columnar defects. This work was sponsored by the U.S. Department of Energy, Office of Electricity Delivery and Energy Reliability as part of a DOE program to develop electric power technology. The materials studied were provided under a CRADA between SuperPower Inc. and Oak Ridge National Laboratory.
12:15 PM - CC6.8
Epitaxial, Phase-separated, Nanostructured Cap Layers for Propagation of Columnar Defects into REBCO Films to Enhance Flux-pinning.
Junsoo Shin 1 , S. Wee 1 2 , H. Meyer III 1 , C. Cantoni 1 , Y. Zuev 1 , A. Goyal 1 Show Abstract
1 , Oak Ridge National Lab., Oak Ridge, Tennessee, United States, 2 , University of Tennessee, Knoxville, Tennessee, United States
Ordered, epitaxial, surface decoration of controllable nanostructures can result in reproducible generation of columnar defects within superconducting films. We have fabricated epitaxial, phase-separated, nanostructured cap layers on coated conductor substrates in order to achieve this goal. Epitaxial, phase-separated, nanocomposite cap layer comprised of LaMnO3 (LMO) + MgO or BaTiO3 (BTO) + CoFe2O4 (CFO) were fabricated using pulsed laser deposition (PLD). The nanocomposite films were grown on standard LMO buffered, IBAD-MgO metallic templates or (100) SrTiO3 substrates. Scanning Auger spectroscopy maps of the phase separated layers, atomic force microscopy (AFM) micrographs, and cross-section transmission electron microscopy (TEM) images confirmed the nanoscale, spatial surface modulation in the phase separated layers. Preliminary results on YBCO films grown using PLD on LMO + 25 vol% MgO phase-separated cap layers show enhanced flux-pinning characteristics with a smaller α value of ~0.38 (in J c ~ H-α), compared to typical values of 0.5-0.6 for pure YBCO films. Detailed morphological features of BTO-CFO nanocomposite films with different CFO additions, and superconducting properties for YBCO films grown on BTO-CFO nanocomposite cap layers will be also discussed in this presentation. Research was sponsored by the US Department of Energy, Office of Electricity Delivery and Energy Reliability - Superconductivity Program, under contract DE-AC05-00OR22725 with UT-Battelle, LLC managing contractor for Oak Ridge National Laboratory.
12:30 PM - CC6.9
Development of IBAD MgO Based HTS Coated Conductor with a Simplified Architecture.
Liliana Stan 1 , Bowan Tao 2 , Terry Holesinger 1 , Hao Yang 1 , David Feldmann 1 , Boris Maiorov 1 , Leonardo Civale 1 , Raymond DePaula 1 , Quanxi Jia 1 Show Abstract
1 MPA-STC, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 , University of Electronics Science and Technology, Chengdu China
The development of a simpler architecture for high temperature superconducting (HTS) coated conductors (CCs) is of great significance since fewer processing steps can increase the production yields and reduce the production cost of the HTS CCs. The HTS CCs based on IBAD MgO have five nonsuperconductive layers between the metal substrate and the superconducting film. By using Y-Al-O composite instead of Y2O3 and Al2O3 separate layers and growing the LaMnO3 buffer directly on the IBAD MgO, the number of non-superconducting layers between the polycrystalline metal substrate and the YBCO is reduced to three. The excellent stability of the 3-layer stack is proved by minimal interfacial mixing and no detectable diffusion of substrate materials into the superconductor layer. The textures of YBCO films grown by PLD on the 3-layer stack are as good as those of films on standard 5-layer architecture. The transport properties of the CCs based on such 3-layer stack are similar with those of the CCs with standard architecture. This represents a step forward towards achieving DOE’s cost/performance goal for HTS CCs.
12:45 PM - CC6.10
Simplification of IBAD-MgO/LMO architectures for High Performance YBCO Coated Conductors
Mariappan Paranthaman 1 , Tolga Aytug 1 , Ozgur Polat 1 , Claudia Cantoni 1 , Amit Goyal 1 , Venkat Selvamanickam 2 , Xuming Xiong 2 , Yimin Chen 2 , L. Stan 3 , Raymond DePaula 3 , Terry Holesinger 3 , Quanxi Xia 3 Show Abstract
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , SuperPower Inc., Schenectady, New York, United States, 3 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
The SuperPower/ORNL high performance LMO-enabled, high temperature superconducting tape is a robust, high-current second-generation superconducting wire. This superconducting wire can be fabricated at high throughput rates using reel-to-reel processes. The main objective of this research is to simplify the SuperPower’s standard five-layer architecture of Ni-alloy/Al2O3/Y2O3/IBAD-MgO/Homoepi-MgO/LMO. This will result in reduced manufacturing cost of these 2G wires. In this research, we will address (i) whether we can eliminate the need for the homo-epi MgO layer? (ii) can we replace the vacuum deposited Al2O3/Y2O3 layers with a low-cost solution layer? and (3) can we eliminate the need for the Ni-alloy substrate electropolishing step? A high-rate, reactive sputter deposition process was developed at SuperPower for the deposition of LMO buffer layers directly on the IBAD-MgO without the need for a homo-MgO layer and demonstrated the growth high current MOCVD REBCO films. Our preliminary results show that it is possible to replace the vacuum Al2O3 layer with a solution Al2O3 layer. We will discuss in detail about the results achieved towards planarization of the substrate using solution layers. Research sponsored by the US Department of Energy, Office of Electricity Delivery and Energy Reliability - Superconductivity Program, under contract DE-AC05-00OR22725 with UT-Battelle, LLC managing contractor for Oak Ridge National Laboratory.
CC7: Coated Conductors II: Properties, Applications
Thursday PM, April 16, 2009
Room 3012 (Moscone West)
2:30 PM - **CC7.1
Microstructural Issues Affecting Connectivity and Pinning in Thick Film RBCO Coated Conductors.
Terry Holesinger 1 Show Abstract
1 Materials Physics and Applications, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
High critical current densities in YBa2Cu3Oy (YBCO) coated conductors depend directly upon the connectivity and defect density within the films. Hence, one needs to develop methodologies for controllably introducing defect structures that are sufficient for tailoring the superconducting properties while, on the other hand, maintaining high critical current properties over lengths exceeding several hundred meters. Aspects of thick film development for physical and chemical deposition processes will be discussed with respect to the types of defects that can be expected to form and effects of thick film growth on connectivity.
3:00 PM - **CC7.2
Low Angle Grain Boundaries in YBCO with Very High CriticalCurrent Densities.
Rainer Held 1 , Christof Schneider 1 3 , Jochen Mannhart 1 , Larry Allard 2 , Karen More 2 , Amit Goyal 2 Show Abstract
1 Experimentalphysik VI, Center for Electronic Correlations and Magnetism, Center for Electronic Correlations and Magnetism , Augsburg Germany, 3 , Paul Scherrer Institute, Villegen Switzerland, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
High-Tc coated conductors rely on supercurrent-flow across networks of low angle grain boundaries. The knowledge of the critical current densities of these boundaries provides the basis of the requirements on the grain alignment of coated conductors. However, while the critical current densities of -tilt boundaries are well known, only sparse information is available on the properties of low angle boundaries with other types of misorientations. We have therefore performed systematic bicrystal measurements of the critical current densities of low-angle YBa2Cu3O7 grain boundaries with in-plane and out-of-plane misorientations. We find that low angle grain boundaries with out-of-plane misorientations reduce the critical current density much less than previously known.We show that grain boundary networks in biaxially-textured, superconducting wires fabricated via epitaxial growth on cube-textured metals have numerous boundaries with out-of-plane misorientations > 4° and few boundaries with in-plane misorientations > 4°. The high critical current density of these wires is explained by the fact that critical current density is determined primarily by in-plane misorientations.
3:30 PM - CC7.3
Understanding Grain Boundaries in YBCO bi-crystal by Advanced Scanning Transmission Electron Microscopy Techniques.
Yan Xin 1 , Sang-Il Kim 1 , Alex Gurevich 1 , David Larbalestier 1 , Larry Allard 2 , Doug Blom 3 Show Abstract
1 , FSU, Tallahassee, Florida, United States, 2 Materials Science and Technology Division, ORNL, Oak Ridge, Tennessee, United States, 3 EM Center, Coker Life Sciences 001, University of South Carolina, Columbia, South Carolina, United States
The critical current density Jc of present high Tc cuprate superconductors is mainly hindered by the grain boundaries (GB) due to the exponential decrease of Jc with increasing misorientation angle across the grain boundaries. Even though the in-plane texture of the YBCO coated conductors made by RABiTS route is improved, but the GB effects still persists particularly at low magnetic field, where most electric utility applications use. It is therefore essential to develop a unified understanding of the low angle grain boundaries found in coated conductors. It has been shown that Ca doping improves the boundary property, leading to the increase of Jc across the GB (1). The most direct way to probe or observe the GBs is to use advanced scanning transmission electron microscopy techniques with sub-Angstrom resolution. Atomic scale microstructural analysis on pure and 20% to 30% Ca doped YBCO low angle GBs has been carried out by several groups recently (2), yet still, a mutual consensus on the physical model of the GBs, and the effect of Ca doping on the dislocations, which are the core issues of our understanding towards the GB properties in Ca doped YBCO remains to be underpinned. In this work, we will present our microstructural characterization work concentrated on the 15% Ca doped 7 degree tilt GBs in comparison to the pure, undoped sample. This sample shows no GB signature in the I-V curve. STEM techniques, such as HAADF imaging and spectrum imaging/electron energy loss spectroscopy with probe Cs corrected TEM/STEM are used to get structural information on the dislocation cores, in an attempt to answer questions of core size, atomic configuration of cores, dopant Ca position and concentration along the cores, hole concentration at GB, all of which will give us a better understanding of the mechanism behind of the GB behavior and Ca doping effects.(1) G. Hammerl, A. Schmehl, R. R. Schulz, et al., Nature 407, 162 (2000); G. A. Daniels, A. Gurevich, and D. C. Larbalestier, Appl Phys Lett 77, 3251 (2000)(2) X. Y. Song, G. Daniels, D. M. Feldmann, et al., Nat Mater 4, 470 (2005); R. F. Klie, J. P. Buban, M. Varela, et al., Nature 435, 475 (2005).
3:45 PM - CC7.4
Strong Enhancment of Transport Current across Grain Boundaries of YBCO Superconductor with Nanoparticle Additions
Timothy Haugan 1 , Paul Barnes 1 , Matthew Mullins 1 , Francisco Baca 1 , Eric Brewster 1 , Joshua Reichart 1 , Michael Sumption 2 Show Abstract
1 , The Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States, 2 , The Ohio State University, Columbus, Ohio, United States
Transport currents across misoriented grain boundaries (GB’s) of YBa2Cu3O7-delta (YBCO) superconductor are well-known to decrease exponentially as the average misorientation angle (theta) between grains increases; e.g. I = Ico*exp(-alpha*theta). Thus far, only one method was demonstrated to increase Ic across low-angle GB’s < 12°; so-called GB meandering with fractal-growth achieved by metal-organic-deposition. Herein we demonstrate a new approach of adding nanoparticles to YBCO, which gives world-record 2-40 times increases transport critical currents across bicrystal GB angles of 4°-36° and for both  ab in-plane and  c-axis tilts. The addition of nanoparticles was achieved by pulsed laser deposition of (M/YBCO)N multilayer and (YBCO)1-xMx mixed-composition films deposited onto SrTiO3 bicrystals, with M = Y2O3, Y2BaCaO5 (211), (Y1-xCax)2BaCuO5, and BaZrO3 and x = 0 to 0.1. Several microstructural mechanisms observed are suggested to produce the critical current increases; including almost perfect healing of GB fissures for all misorientations, and a higher density of nanosize defects formed right at the GB. The increase of nanosize defects right at the GB suggests enhancement of Abrikosov-Josephson vortex pinning can also play a role for some GB angles. The results and significance of these experiments will be presented.
4:30 PM - CC7.5
Persistent Coils Made Out of Coated Conductors.
George Levin 1 , Paul Barnes 1 , John Murphy 1 Show Abstract
1 , AFRL, Dayton, Ohio, United States
We report the results of an experimental study of a persistent coil made out of YBCO coated conductors. The magnitude of the persistent current and the rate of decay were investigated. We will discuss the ways to reduce the relaxation rate of the induced current. Our conclusion is that the persistent current in such a coil can be large enough and decay slowly enough so that coated conductors can be used to make persistent coils for variety of applications.
4:45 PM - CC7.6
Dynamical Study of Flux and Current Distributions in Multi-Filamentary YBCO Thin Films
Gunter Luepke 1 , Andrea Lucarelli 1 , Ran Yang 1 , Francesco Grilli 2 , Timothy Haugan 3 , Paul Barnes 3 Show Abstract
1 Applied Science, College of William & Mary, Williamsburg, Virginia, United States, 2 , Ecole Polytechnique de Montreal, Montreal, Quebec, Canada, 3 , Air Force Research Laboratory, Wright-Patterson AFB, Dayton, Ohio, United States
The adoption of multi-filamentary geometries in YBCO second-generation tapes has been proposed as a viable solution to reduce the hysteretic losses. Despite recent significant improvements in the striation process and the use of insulating substrates the losses of the finely striated tapes are still noticeably larger than analytical expressions predicted. The discrepancy tends to increase with increasing filament density due to the influence of the magnetic field distribution inside the non-superconducting trenches. We studied magnetic flux and current distributions in multi-filamentary YBCO thin films exposed to an ac current and/or dc magnetic field using time-resolved magneto-optical imaging (TRMOI). High-resolution maps of magnetic field and current density obtained from TRMOI data show how defects, homogeneity and geometry of the multi-filamentary sample affect the flux dynamics. We also investigated the effect of magnetic coupling between filaments by studying the flux dynamics with an applied ac current only and simultaneously with a dc magnetic field applied perpendicular to the film. The magnetic coupling between filaments strongly affects screening and transport current distributions. The measured current and flux dynamics are in very good agreement with simulations based on a 2D finite-element model (FEM). The FEM simulations show that increasing the distance between filaments alters the transport and screening current distributions and reduces magnetic coupling and ac losses.This work was supported in part by DOE through grant DE-FG02-99ER45781 and AFOSR/AFRL through grant F33615-02-D-2299.
5:00 PM - **CC7.7
Epitaxial Growth of Superconductor on Structural, Single-Crystal, Faceted Fibers (SSIFFS): A Potential Route Towards Low ac-loss Wire
A. Goyal 1 , Sung-Hun Wee 1 , Eliot Specht 1 , Jim Thompson 1 , Yuri Zuev 1 , Claudia Cantoni 1 Show Abstract
1 , ORNL/UT-Battelle, Oak Ridge, Tennessee, United States
A potential route towards a low ac-loss wire is developed via epitaxial growth of the superconductor (REBCO) on Structural, Single-Crystal, Faceted, Fibers (SSIFFS). “Structural” implies a higher dislocation density than optical fibers. “Single-crystal” implies that the fiber is crystallographically a single-crystal. “Faceted” implies that the fiber has certain crystallographic facets for growth of an epitaxial superconductor layer. “Fiber” implies a long, flexible, low-aspect ratio substrate. SSIFFS have a composition of Al2O3 and the crystallographic facets have an R-plane orientation. Such crystallographically faceted, sapphire fibers are grown high speeds via extraction from the melt using edge-defined film growth. A single buffer layer of CeO2 is then deposited epitaxially on the R-plane facets formed on the fiber. Superconducting films are then deposited epitaxially on the CeO2-buffered, R-plane facets of the fibers. The ac-losses are reduced because of the “low-aspect ratio” of the fiber which eliminates the need for filamentization (diameter of the fiber is 100-300 μm). In addition, because the fiber is non-magnetic and non-conducting, there are no ferromagnetic or eddy current losses from the substrate. This talk will provide an overview of the SSIFFS concept and technology. A potential route to scale-up the fabrication of such faceted fibers will also be discussed. Latest results obtained on superconducting films deposited epitaxially on SSIFFS will be presented. Research sponsored by the US Department of Energy, Office of Electricity Delivery and Energy Reliability - Superconductivity Program, under contract DE-AC05-00OR22725 with UT-Battelle, LLC managing contractor for Oak Ridge National Laboratory.
5:30 PM - CC7.8
YBCO Films Grown On Fibers By Magnetron Sputtering and Modified TFA-MOD Process.
Yongli Xu 1 , Zongqi Qian 1 , Ziyang Xu 1 , Peng He 1 , Rabi Bhattacharya 1 Show Abstract
1 , UES Inc, Dayton, Ohio, United States
Due to the high aspect ratio, AC loss is a severe problem for the traditional coated conductors (CCs) on metal tapes. Technical approaches of cutting the wide CC tapes into small strips have been explored and confirmed to be effective in reducing AC loss. Also, substrate magnetic and eddy current losses are unavoidable in the current CC technologies. From the application stand point, customers need thin round wire (like commonly used copper wire) or multi-filament cables rather than wide tape CCs. Low aspect ratio, non-magnetic, non-conductive, and low dielectric constant nature of oxide single crystal fiber will provide extremely low AC loss in CC application. By using these oxide fibers, substrate magnetic and eddy current losses are completely eliminated. In this research, YBa2Cu3O7-δ (YBCO) films have been grown successfully on single crystal fibers of sapphire and LaAlO3 by magnetron sputtering and modified TFA-MOD Process. Critical current density over 1MA/cm2 has been demonstrated at 77K self-field.