Leonardo Civale Los Alamos National Laboratory
Claudia Cantoni Oak Ridge National Laboratory
Matthew Feldmann University of Wisconsin-Madison
Xavier Obradors CSIC
HH1: Overviews of CC Development -- IBAD Template - Buffer Layers
Tuesday PM, April 18, 2006
Room 2020 (Moscone West)
9:30 AM - **HH1.1
Recent Progress & Future Prospects for Applications in Coated Conductor Development of Japan
Yuh Shiohara 1 , Yutaka Yamada 1 , Teruo Izumi 1 Show Abstract
1 , SRL-ISTEC, Koto-ku, Tokyo Japan
The present 5-year national project since 2003 for development of coated conductors (CC) using Y-system superconductors has passed for almost a half term and achieved satisfactory results. In this paper, the current status and the future prospect are reviewed.The group of Fujikura and SRL has worked on the long tape with high performance in the PLD-YBCO superconducting tapes on the IBAD-GZO buffered substrates. Both have achieved almost the same IcxL product values of 19kAm, which were the champion data in the world at June 2005, by different combinations of Ic and L. Fujikura realized the longest tape of 200m with a reasonable high Ic value of 100A. On the other hand, the high Ic value of 200A was obtained in a 100m long tape by SRL. The values have been steadily improved and the trend is going to be continued. Then, the record was broken over 50kAm, which consists of 212m in length and high Ic value of 245A.In the other group, the long tape processing has been developed focusing on lowering the production cost. The extremely high Ic value of 470A was obtained in the film by the TFA-MOD method on CeO2(PLD)/GZO(IBAD)/Hastelloy substrate. In the effort for the long tape in the process, the 25m long tape with the Ic value of 100A by a continuous reel-to-reel system and 40m long tape with 150A by a batch system were realized. Additionally, 100m class long tapes were also obtained by the MOCVD and PLD-HoBCO processes.The both groups are aiming to achieve the final goals of 500m long tape with the high Ic value of 300A/cm-w by the production rate of 5m/h.Furthermore, the feasibility study for applications using coated conductors has been already started from the above mentioned success of long tape production. Several kinds of coils using the long coated conductors such as a solenoid and a pancake types and the spiral shaped conductors for the cable were firstly made. Reasonable high performances were confirmed in the trials.This work was supported by the New Energy and Industrial Technology Development Organization (NEDO) as Collaborative Research and Development Fundamental Technologies for Superconductivity Applications.
10:00 AM - HH1.2
Progress in Scale up of Second-generation HTS Conductors at SuperPower.
Venkat Selvamanickam 1 , Yimin Chen 1 , Xuming Xiong 1 , Yi-Yuan Xie 1 , Tom Salagaj 1 , Jodi Reeves 1 , Yunfei Qiao 1 , Yijie Li 1 , Ping Hou 1 , Michael Gardner 1 , Xun Zhang 1 , Ken Lenseth 1 Show Abstract
1 , SuperPower, Schenectady, New York, United States
SuperPower is scaling up second-generation (2G) HTS conductors to full-fledged manufacturing. We recently reported achievement of 22,000 A-m in lengths of 207 m conductor produced by MOCVD and IBAD. Critical current of 200 A/cm has been demonstrated in lengths over 70 m.IBAD MgO based buffer tapes have been scaled up to 100+ m lengths. Using LMO buffers, we demonstrated a linear tape speed of 10 m/h in every process step of IBAD MgO based buffers to produce 25 m long MOCVD tape with a critical current of 142 A/cm. Practical conductor configurations, namely 4 mm wide conductors produced by slitting followed by copper stabilizer application by electroplating have been produced in lengths of 100+ m. Our surround stabilizer geometry has been shown to result in superior overcurrent protection as well as dielectric strength. The thinnest 2G conductors have been demonstrated using 50 micron thick substrates, which have resulted in engineering current densities above 70,000 A/cm2 at 77 K, self field and above 18,000 A/cm2 at 65 K and 3 T. Superior tensile and bend properties have been achieved with the thin conductors. Twisting of 2G conductors has been demonstrated for low ac losses, down to twist pitches of 4.2 cm and 4.6 cm using 1 mm and 2 mm wide conductors respectively, while maintaining less than 5% reduction in critical current. Photolithographic patterning has been successfully used to achieve more than 100-fold reduction in ac losses. Several prototype devices have been demonstrated using our 2G conductor since 2004. This includes 1 m HTS cable made by Sumitomo Electric using 113 m of 2G conductor as well as a 7.5 h.p. motor made by Rockwell Automation using 4 race-track coils supplied by SuperPower. The 1 m cable showed a critical current of 2350 A and an ac loss of 0.16 W/kA-m in the 4 conductor layers and 0.18 W/kA-m in the 2 shield layers, which are the lowest values of ac losses reported yet. SuperPower has so far delivered 320 m of complete 2G conductor (4 mm wide, copper stabilized) to Sumitomo Electric for the Albany Cable project and is now embarking on preproduction operations to produce nearly 10 km of 2G conductor for a 30 m long HTS cable.
10:15 AM - **HH1.3
Coated Conductors. Where Do we Need Fundamental Knowledge?Developments in Europe.
Herbert Freyhardt 1 Show Abstract
1 Univ. Goettingen, Inst. Materialphysik, Goettingen Germany
10:45 AM - HH1.4
Fabrication of Long GdBCO Coated Conductor with High Production Rate by IBAD/MPMT-PLD Method.
Akira Ibi 1 , Hiroyuki Fukushima 1 , Yutaka Yamada 1 , Seiki Miyata 1 , Reiji Kuriki 1 , Kazuhiro Shiohara 1 , Yuh Shiohara 2 Show Abstract
1 , SRL-ISTEC Nagoya Coated Conductor Center, Nagoya Japan, 2 , SRL-ISTEC Division of Superconducting Tapes & Wires, Tokyo Japan
11:15 AM - **HH1.5
Development of IBAD Process for Y-123 Coated Conductors.
Yasuhiro Iijima 1 , Kazuomi Kakimoto 1 , Yasunori Sutoh 1 , Naoki Kaneko 1 , Satoru Hanyu 1 , Takashi Saitoh 1 Show Abstract
1 Material Technology Lab., Fujikura Ltd., Tokyo Japan
In the past decade, worldwide research efforts are concentrated on Y-123 coated conductors. Rapid progresses were observed in reel-to-reel long length continuous processing over 100-m, and elementary demonstrations of coils, cables, etc. have already started using coated conductors. This paper reviews development of Ion-Beam-Assisted Deposition (IBAD) technique of textured template films using fluorite like oxide of YSZ, Gd 2 Zr 2 O 7 , etc. for coated conductors.IBAD is first proposed method to form “biaxially aligned Y-123 films” on flexible metal substrates in 1991. It is characterized as direct deposition of sharply textured template films on non-textured metallic tapes. IBAD process showed faster progress than others in early 90s without using metallurgically textured metals that had problems of magnetism or hardness of substrates, heteroepitaxy at metal/oxide interface, etc. But it takes many years to develop reel-to-reel IBAD approach for long length processing, because of low growth rate for textured template. In late 90s, big national programs synchronously started to develop coated conductors, when quite rapid progress was observed in vacuum technology including large area RF-discharged ion sources. 100-250 m long reel-to-reel IBAD process was successfully completed with throughput of nearly 1.0 m/h. Several long high performance Y-123 tapes over 100-m were reported by several groups using templates formed by reel-to-reel IBAD. Recently new set of IBAD apparatus was developed which was equipped with a 110cm x 15cm ion source especially designed for coated conductors so as to get throughput over 5.0m/h for long length conductors over 500-m. Several advance of template materials were also observed in late years. Biaxially textured YSZ template films were formed with concurrent Ar ion beam bombardment of 200-300 eV. Unexpectedly low optimized ion energies suggest ion bombarding damage prevent texture evolution at higher ion energy. A series of ZrO2-RE2O3 oxide films were studied to search for better-optimized texture correlated with lattice bonding energy. The best results were obtained at mixing ratio of ZrO2:RE2O3=1:1, with RE=Gd. Quite highly textured templates with ΔΦ below 5 deg. were obtained by the combination of IBAD- Gd 2 Zr 2 O 7 films and CeO2 films deposited by Pulsed Laser Deposition (PLD) on them. High-Jc Y-123 films with ΔΦ of 3-4 deg. were deposited by many methods on those IBAD template. In this paper high-performance 100-200 m class Y-123 conductors were characterized by combination of IBAD and Pulsed Laser Deposition (PLD) method. Small solenoid coils were also demonstrated, operating in liquid nitrogen or with cryo-cooler, without degradation even using 1cm wide Y-123 tapes. This paper includes works supported by the New Energy and Industrial Technology Development Organization (NEDO) as Collaborative Research and Development of Fundamental Technologies for Superconductivity Applications.
11:45 AM - HH1.6
Ion Damage Anisotropy Investigations of MgO Crystals.
Paul Arendt 1 , Igor Usov 1 , Raymond DePaula 1 , James Groves 1 , Liliana Stan 1 Show Abstract
1 Superconductivity Technology Center, Los Alamos National Lab., Los Alamos, New Mexico, United States
MgO single crystals with (100), (110) and (111) orientations were implanted with 100 keV Ar + ions at doses ranging from 1X1014 to 1X1017/cm2. The resulting lattice damage was characterized using Rutherford Backscattering Spectrometry combined with Channeling (RBS/C). For a dose range 1015 to 1016 ions/cm2, the differences in damage accumulation for the three orientations varied according to the relation: (110) < (100) <(111). Rapid thermal annealing experiments were performed in a range of 600 to1300 °C. The annealing of defects occurred most effectively for the (110) oriented crystals according to the relation: (110) > (100) > (111). This anisotropy in damage annealing provides an explanation for the damage accumulation relation delineated above when dynamic annealing is taken into account. This damage anisotropy data also provides an explanation for the orientations that are empirically observed when MgO films are deposited under ion-assist conditions.
12:00 PM - HH1.7
Strategic Buffer Layer Development For Coated Conductors.
Mariappan Paranthaman 1 , Srivatsan Sathyamurthy 1 , Amit Goyal 1 , Tolga Aytug 1 , Venkat Selvamanickam 2 , Thomas Kodenkandath 2 , Xiaoping Li 3 , Martin Rupich 3 Show Abstract
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , SuperPower Inc, Schenectady, New York, United States, 3 , American Superconductor Corporation, Westborough, Massachusetts, United States
RABiTS based metal-organic deposition (MOD) buffer/YBCO and IBAD-MgO/MOCVD YBCO approach have been considered as the potential, low-cost processes to fabricate second generation YBa2Cu3O7 (YBCO) coated conductors. The most commonly used RABiTS architectures consisting of a starting template of biaxially textured Ni-5W substrate with a seed layer of Y2O3, a barrier layer of YSZ, and a CeO2 cap. In this three layer architecture, all the buffers were deposited using physical vapor deposition (PVD) techniques. Using these PVD templates, MOD-YBCO films with an Ic (critical current) of 250 A/cm have been achieved in short lengths. We have developed a low-cost, non-vacuum, MOD process to grow highly textured buffer layers on textured Ni-5W substrates. The main challenge is to match the performance of MOD templates to that of PVD templates. We have recently demonstrated the properties of La2Zr2O7 (LZO) layers can be improved by inserting a thin Y2O3 seed layer. Using MOD La2Zr2O7 and CeO2 layers, we have demonstrated the growth of high performance MOD-YBCO films with an Ic of 200 A/cm-width. For the IBAD-MgO template, we have developed the LaMnO3 cap layers and demonstrated an Ic of 272 A/cm. We will also discuss about our recent developments in buffer layer research.___________Research sponsored by the U.S. Department of Energy, Office of Electricity Delivery and Energy Reliability, Superconductivity Program for Electric Power Systems, and Division of Materials Sciences, Office of Science, under contract No. DE-AC05-00OR22725 with UT-Battelle, LLC.
12:15 PM - HH1.8
Scaling of Biaxial Texture Evolution during Ion-Beam Assisted Deposition of Rock-salt Materials
Vladimir Matias 1 , Konrad Gueth 1 , Alp Findikoglu 1 Show Abstract
1 MST-STC, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
We examine the evolution of biaxial texture during ion-beam assisted deposition (IBAD) of MgO and other rock-salt-structure materials using reflection high-energy electron diffraction (RHEED), in situ ion scattering, and x-ray diffraction. The IBAD-textured templates on metal tape are used for second generation high-temperature superconducting wires, also known as coated conductors. We find that the texture development is very sensitive to the nucleation surface conditions, such as elemental composition and surface morphology. In the best cases an in-plane texture of 3.5° and an out-of-plane texture of 1.5° are attainable. We have shown that 7° in-plane texture can be attained in an IBAD deposition time of 1.8 sec. We are utilizing a methodology of presenting data in terms of IBAD texture contour plots where we collect data as a function of ion-to-molecule ratios and film thicknesses. The striking conclusion from the data is that the texture development for different ion-to-molecule ratios can be scaled with the cumulative ion fluence. We discuss the results in terms of possible mechanisms for IBAD-MgO biaxial texturing and relationship to other IBAD texturing processes.This work is funded by the Department of Energy Office of Electric Transmission and Distribution.
12:30 PM - HH1.9
MOD YBCO on Electrodeposited LZO/CeO2/Ni-W Buffer Layer
Raghu Bhattacharya 1 , Sovannary Phok 1 , Tapas Chaudhuri 1 , Thomas Kodenkandath 2 , Marty Rupich 2 Show Abstract
1 , National Renewable Energy Laboratory, Golden, Colorado, United States, 2 , American Superconductor, Westborough, Massachusetts, United States
YBa2Cu3O7-x coated conductors prepared by MOD on complete electrodeposited LZO/CeO2/Ni-W buffer layer architecture will be reported in this meeting. The main goal of our work is to simplify the buffer layer architectures and also to prepare them by low-cost non-vacuum system. Complete two-layer buffer architecture consisting of LZO and CeO2 is prepared by electrodeposition. The electrodeposited buffer layers are crack-free and have improved biaxial texturing. The electrodeposition technique is easily scalable, non-vacuum and offers low cost advantage relative to physical deposition methods.
12:45 PM - HH1.10
Biaxially Textured SmxZr1-xOy (SZO) Films Grown by Reactive Sputtering as Buffers for YBa2Cu3O7-δ (YBCO) Coated Conductors
Liliana Stan 1 , Paul Arendt 1 , Igor Usov 1 , Haiyan Wang 1 , Stephen Foltyn 1 , Raymond DePaula 1 , Yuan Li 1 Show Abstract
1 MST-STC, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
YBa2Cu3O7-δ (YBCO) coated conductors that use ion beam assisted deposited (IBAD) MgO as a template have been identified as one of the viable approaches for large scale manufacturing. The biaxial texture of MgO is transferred to the superconductor through buffer layers which have both chemical and structural buffer properties. The main goal of this study is to develop a simplified coated conductor architecture using a single oxide buffer layer attainable using high-rate reactive sputter deposition. SmxZr1-xOy (SZO), with cubic phases ranging from x=0.02 to x=0.8, has been identified as a good candidate for this study. Well textured SZO films with different stoichiometries were epitaxially grown on IBAD MgO. YBCO films grown on SZO buffers using pulsed laser deposition (PLD) have self-field current densities (Jc) in the 1 to 4 MA/cm2 range. The present results demonstrate that SZO is a suitable buffer for the fabrication of lower cost YBCO coated conductors.
HH2: Issues in YBCO Film Growth
Tuesday PM, April 18, 2006
Room 2020 (Moscone West)
2:30 PM - **HH2.1
Issues Related to the Growth of Thick High Performance Superconducting Films.
Q. X. Jia 1 , S. R. Foltyn 1 , H. Wang 1 , Y. Lin 1 , B. Maiorov 1 , Y. Li 1 , C. Wetteland 1 , I. Usov 1 , G. W. Brown 1 , M. Hawley 1 , V. A. Maroni 2 , L. Civale 1 , P. Arendt 1 , J. L. MacManus-Driscoll 3 Show Abstract
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 , Argonne National Laboratory, Argonne, Illinois, United States, 3 , University of Cambridge, Cambridge United Kingdom
Second-generation coated conductors or flexible metal tapes coated with thick films of high temperature superconductors (HTS) are believed to represent the most cost-effective approach to the commercialization of HTS for a number of electric power applications, such as magnets, motors, and transmission lines. Tremendous efforts are being made worldwide to develop high performance coated conductors. In the development of such high performance coated conductors, it is desirable to obtain thick HTS films on flexible metal substrates with the highest critical current density possible, but a number of issues such as the materials used, the processes, and the architectures of the coatings will need to be addressed before the best performance can be achieved. For example, one of the main complications in the process of obtaining a higher current-carrying capacity is that the critical current density in the superconductor drops sharply as the coating thickness is increased. In this talk, we will discuss the interplays among the structure, the process, and the superconducting properties of thick HTS films. Based on our current understanding of the materials and the transport properties of coated conductors, we have implemented an approach to overcome thick HTS films’ dependence on critical current density. This allows us to achieve a current carrying capacity of over 1000 A per centimeter width for films that are as thin as three micrometers.
3:00 PM - HH2.2
High Rate High Jc YBCO Electron Beam Co-Evaporation Technique: Liquid Assisted Growth with Nano-Engineered Structure.
Jeong-uk Huh 1 , Gertjan Koster 1 , Malcolm Beasley 1 , Robert Hammond 1 Show Abstract
1 Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California, United States
Electron beam co-evaporation technique is used to deposit YBCO (YBa2Cu3O7-x) film at a high rate (10nm/s and higher) on single crystals and metal tapes (IBAD-MgO from LANL and RABiTS from AMSC). The oxygen pressure at the stage of depositing Y, Ba, Cu is 5x10-5 Torr and the process temperature is 810-850°C. In-situ Fourier Transform Infrared spectroscopy (FTIR) is used to monitor the optical properties of the YBCO during and after deposition. The deposit transforms to a glassy amorphous mixture of Y, Ba and Cu at 3mTorr of oxygen. YBCO crystallization occurs after extra oxygen is applied to several Torr. FTIR shows almost the same signature during the formation of YBCO and liquid Ba-Cu-O during deposition, which indicates the liquid plays an important role in determining the properties of YBCO in terms of providing epitaxy and fast transport of atoms to nucleate on the film-metal interface. The transformation is very rapid—seconds to minutes, compared to minutes to hours for other post-reaction processes. The oxygen partial pressure as well as the rate of oxidation (supersaturation) in the liquid region defined in the YBCO phase stability diagram determine the electrical and microstructural properties. In-situ X-ray diffraction heating stage with ambient control is utilized to study this supersaturation effect during YBCO growth. TEM analysis (Holesinger-LANL) shows a growth mode and microstructure suggestive of lateral growth. Jc(H) was measured (Feldmann-Wisconsin) (1 MA/cm2 at self-field, 0.2 at 1 Tesla) for a one micron thick film on RABiTS with nano-engineered defects. Sponsored by AFOSR, DOE and Netherlands Organization for Scientific Research
3:15 PM - HH2.3
Investigation of YBCO Phase Formation in BaF2-ex Situ Films.
Manisha Rane 1 , Hassa Bakhru 1 , Richard Moore 1 , Emilio Stinzianni 1 , Kathleen Dunn 1 , Pradeep Haldar 1 , Ron Feenstra 2 , Yifei Zhang 2 , David Christen 2 Show Abstract
1 , Albany NanoTech, Albany, New York, United States, 2 , ORNL, Oak Ridge, Tennessee, United States
3:30 PM - HH2.4
New Insights into the Nucleation Mechanism of TFA Derived YBCO Films.
Jaume Gazquez 1 , Felip Sandiumenge 1 , Mariona Coll 1 , Neus Roma 1 , Alberto Pomar 1 , Narcis Mestres 1 , Teresa Puig 1 , Xavier Obradors 1 , Carmen Ballesteros 2 , Marie-Jo Casanove 3 Show Abstract
1 , ICMAB-CSIC, Bellaterra Spain, 2 , Universidad Carlos III de Madrid, Leganes Spain, 3 , CEMES-CNRS, Toulouse France
The heteroepitaxial growth of YBa 2Cu3O7-x (YBCO) films prepared by the trifluoracetate route (MOD-TFA) was characterized by TEM/EELS, μ-Raman spectroscopy and X-Ray diffraction of specimens quenched from various temperatures. We find that after the pyrolysis, the film consists of a homogeneous, partly amorphous, nanocrystalline matrix of Ba1-xYxF 2+x (BYF) and CuO. Upon heating, such a precursor undergoes a strong phase segregation on a length scale of 200 nm. Simultaneously, the Ba1-xY xF2+x solid solution is decomposed into BaF2 and Y2O3, and part of this Y2O3 eventually reacts with CuO to give Y2Cu2O5. EELS analysis also reveals that part of Cu species are in form of nanocrystalline Cu2O, embedding larger CuO particles. In contrast with previous studies, our results strongly suggest that Y2Cu2O5 does not constitute a necessary step in the reaction path to YBCO. This means that the dominating feeding mechanism of the growing YBCO islands is via dissolution of CuO and Y2O3. Interestingly, CuO containing phases are typically observed far from the interface and therefore the film transformation requires long range diffusion. Our results make evident that the nucleation of YBCO takes place exclusively at the interface with the substrate, within the fluoride phase. By processing high resolution TEM images, we have detected a radial variation of lattice parameter of the fluoride phase around the YBCO islands, that is consistent with and Y enrichment just ahead of the growth front. The fluoride phase appears highly textured from the early stages of phase evolution, above 600°C, and determines the orientation of the YBCO.
4:15 PM - **HH2.5
F/Ba Trajectory-property Relationships in MOD-derived YBCO Coated Conductors.
Masateru Yoshizumi 1 , Daniel Wesolowski 1 , Yoda Patta 1 , Michael Cima 1 Show Abstract
1 , MIT, Cambridge, Massachusetts, United States
4:45 PM - HH2.6
Interfacial control and nanostructuration in all chemical TFA-YBCO based multilayers
Xavier Obradors 1 , Mariona Coll 1 , Gibert Marta 1 , Andrea Cavallaro 1 , Joffre Gutierrez 1 , Awateff Hassini 1 , Anna Llordes 1 , Sussagna Ricart 1 , Teresa Puig 1 , Alberto Pomar 1 , Felip Sandiumenge 1 Show Abstract
1 , ICMAB, CSIC, Bellaterra, Catalonia, Spain
The achievement of multilayered architectures based on YBCO layers grown by the trifluoroacetate (TFA) route and oxide buffers prepared by Chemical Solution Deposition (CSD) remains a critical issue in view of developing low-cost high critical current coated conductors. Particularly, controlling the interfacial quality of the oxide cap layers is very important to keep highly textured and dense YBCO layers. In this work we will present new results concerning the generation by CSD of low-roughness facetted oxide cap layers in the systems CeO2, SrTiO3 and La0.7Sr0.3MnO3 where high quality TFA-YBCO layers can be grown. We will particularly stress the influence of the processing conditions of the cap layers on the microstructural evolution and the critical currents of the TFA-YBCO films and we will show that high quality multilayers can be achieved. On the other hand, the development of new methodologies for nanostructuration of YBCO layers to induce artificial vortex pinning centers is a very hot topic at present. We will show that both, interfacial and bulk oxide nanodots of BaZrO3, CeO2 or Y2O3, can be grown based on CSD and they are compatible with the TFA-YBCO film processing conditions. The parameters controlling the nanoscale structure of the dots have been investigated and its influence on the critical currents of the YBCO layers will be presented.* This work has been supported by the European Union (SOLSULET project, GRD2-2000-30613 and HIPERCHEM project, NMP4-CT2005-516858)
5:00 PM - HH2.7
Key Microstructural Features of YBa2Cu3O7-∂ Films Based on the Solution Deposition and Ex-situ Conversion of Metalorganic Trifluoroacetate Precursors on Textured Nickel Substrates
Terry Holesinger 1 , Boris Maiorov 1 , J. Coulter 1 , Leonardo Civale 1 Show Abstract
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Large area, continuous solution deposition of YBa2Cu3Oy (YBCO) film precursors by metal organic deposition (MOD) of trifluoroacetate-based precursors and their ex-situ furnace conversion to YBCO are economically attractive processes for adding the superconducting layer during fabrication of second generation (coated conductor) superconductor wire. Long strips of 4 cm wide coated conductors exhibiting excellent length and width uniformity have been demonstrated. In this work, key features of the microstructure in high critical current density (Jc) MOD YBCO films on biaxially-textured nickel substrates with intervening buffer layers are presented. These 0.8 µm thick MOD YBCO films have 77K, self-field Jc and Ic values up to 3.5 MA/cm2 and 260 A/cm-width, respectively. The YBCO film forms during thermal processing from the decomposition of carboxylate precursors and the subsequent growth of the YBCO phase from the decomposition products. In contrast to the columnar structure of YBCO films made by pulsed laser deposition, MOD YBCO films have a laminar grain structure with a high density of YBa2Cu4Oy (Y124) intergrowths. The extensive intergrowth structures give rise to an enhanced peak in angular anisotropy measurements of Jc when the applied field is parallel to the ab planes of the YBCO films. Other key aspects of MOD YBCO films related to the laminar growth mode and layered microstructure are grain boundary overgrowth, grain boundary meandering, colony microstructures, incoherent precipitates of Y2O3 and Y2Cu2O5, and phase separations. The angular anisotropy or vortex pinning characteristics can be changed by rare-earth oxide additions to the baseline composition. These additions decrease the density of Y124 intergrowths while simultaneously increasing the density of incoherent precipitates.
5:15 PM - **HH2.8
Growth of Thick, High Critical Current YBa2Cu3O7 Films by HLPE.
Judith MacManus-Driscoll 1 , A Kursumovic 1 , B Maiorov 2 , L Civale 2 , H Wang 2 , Q Jia 2 , S Foltyn 2 Show Abstract
1 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom, 2 Superconductivity Technology Centre, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
5:45 PM - HH2.9
Phase Relations of High Tc Ba2RCu3O6+x Superconductors
Winnie Wong-Ng 1 , Lawrence Cook 1 , Igor Levin 1 , Zhi Yang 1 , Mark Vaudin 1 , Joseph Ritter 1 , Ron Feenstra 2 Show Abstract
1 Ceramics, NIST, Gaithersburg, Maryland, United States, 2 Condensed Matter Sciences, ORNL, Oak Ridge, Tennessee, United States
In recent years, accelerated global research in high Tc superconductors has lead to the success of a wide variety of industrial prototype applications, including power distribution, energy storage, and advanced motors and magnets. The availability of low-cost, long-length, and high performance wire/tape and cable is critical for implementing these applications. Since information on phase relations (commonly regarded as “road maps” for the optimization of processing) in various coated conductor-related film systems (BaF2 ex situ process) is important for processing, we have focused our efforts on determination of phase relationships in the Ba2RCu3O6+x (R=lanthanides and Y) systems. This talk will highlight our results in two areas: (1) Phase relations in films obtained using the ex situ BaF2 process, in particular, Ba2YCu3Ox prepared using the e-beam evaporation technique, and Ba2(Nd,Eu,Gd)Cu3Ox films prepared using the spin-coating technique. A comparison of these diagrams with those of the bulk systems will be presented. (2) The occurrence of low temperature melts in the Ba-Y-Cu-O-F-H2O system as related to the “BaF2 process” for long-length coated conductor processing. Recent results on phase equilibrium studies of the Ba-Y-Cu-O-F-H2O system will be summarized.
Leonardo Civale Los Alamos National Laboratory
Claudia Cantoni Oak Ridge National Laboratory
Matthew Feldmann University of Wisconsin-Madison
Xavier Obradors CSIC
HH3: Enhancing Flux Pinning in YBCO
Wednesday AM, April 19, 2006
Room 2020 (Moscone West)
9:30 AM - **HH3.1
Vortex Pins — BZO Columnar Defects or Non-Aligned Inclusions — in YBCO Coated Conductors.
James Thompson 1 2 , A. Goyal 2 , S. Kang 2 , K. Leonard 2 , P. Martin 2 , A. Gapud 2 , M. Varela 2 , M. Paranthaman 2 , A. Ijaduola 1 , E. Specht 2 , D. Christen 2 , S. Pennycook 2 , F. List 2 , R. Feenstra 2 , X. Song 3 Show Abstract
1 Dept. of Physics, University of Tennessee , Knoxville, Tennessee, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Applied Superconductivity Center, University of Wisconsin, Madison, Wisconsin, United States
With the great progress in minimizing weak links between YBaCuO grains in coated conductors, an understanding of vortex pinning is becoming ever more important. In this presentation, two cases of contrasting pinning morphologies will be presented and analyzed. I.BZO – based correlated disorder: the addition of BaZrO(3) nanoparticles (with volume fraction x) to a YBCO target for pulsed laser deposition (PLD) introduces non-superconducting BZO nanoparticles in the deposited layer. The particles self-assemble (presumably through the strain field associated with a 9% mismatch in ab-plane lattice parameters) and form extended stacks. These stacks are oriented roughly along the c-axis and resemble the columnar defects first formed in YBCO by heavy ion irradiation. The resulting critical current density Jc (H, T, θ) reflects this angularly-selection pinning, with a peak for H || c. Here the Jc will be analyzed using theoretical formalism developed for columnar defects.II.Large, sparse, ~ isotopic defects: in nominally stoichiometric YBCO layers prepared by BaF(2)-based ex-situ processing, TEM reveals a variety of non-superconductors inclusions (Y(2)O(3), voids, etc.). These approximate the large, sparse, uncorrelated pinning sites treated in the theory of Ovchinnikov – Ivlev and van der Beek et al. An analysis of experimental studies of Jc as a function of magnetic field, temperature, and layer thickness shows that the theory accounts reasonably for many observed features; resulting values for the characteristic size and density of pinning sites are comparable with those observed in TEM.Overall, these two cases with contrasting defect morphologies show the possibility of progressing beyond a purely qualitative, "hand waving" description of pinning in coated conductors.Oak Ridge National Laboratory is managed by UT-Battelle, LLC for the United States Department of Energy under contract No. DE-AC05-00OR22725.
10:00 AM - HH3.2
Artificial Flux Pinning of YBCO and Correlation With Pinning Mechanism Studies.
Timothy Haugan 1 , Paul Barnes 1 , Timothy Campbell 1 , Neal Pierce 1 , Srinivas Sathiraju 1 , Chakrapani Varanasi 1 , Michael Sumption 2 Show Abstract
1 Propulsion Directorate, AFRL/PRPG, The Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States, 2 Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio, United States
Recent experiments to enhance flux pinning of YBa2Cu3O7-z (YBCO or 123) by nanoparticle additions and chemical substitutions including Ca-doping will be summarized, and the results correlated with studies of flux pinning mechanisms. Nanoparticles were added to YBCO by pulsed laser deposition using nanoscale multilayer methods and mixed-composition single targets. Different pinning materials were considered with lattice mismatches varying from -12% to +10% compared to YBCO. Ca-doping was achieved with (Y1-xCax)2BaCuO5 phase nanoparticle additions, with x varying from 0.05 to 0.10 and overall Ca concentrations of the film varying from 0.25% to 1%. The flux pinning properties were studied to optimize critical current density (Jc) and pinning structures as a function of magnetic field (H), temperature (T) and angle of field applied (θ). It was found that each defect addition optimizes Jc(H,T,θ) properties at different H,T,θ regimes; e.g. some will enhance Jc at low H < 1T whereas others provide strong pinning at H > 3T. In technically important field regimes of 1-6T at 77 K, it is known that Jc is a function of H to the power -α. In this work, α values have been suppressed from typical 0.5 down to significantly lower values for various additions and for one case as low as 0.2. Additionally, various experiments have been performed to test the dimensionality of the pinning and to extract comparative pinning strengths by magnetic relaxation methods. Microstructural analysis by TEM was used to confirm the nature of the defect structures. A preliminary pinning model is being developed that describes the experimental features observed, including Jc(H,T,θ) properties, differences of pinning materials, varying Uo pinning strengths, and parameter studies such as the 123-layer-thickness effect in (M/123)xN multilayer films. A comparison of the pinning improvements will be presented, and correlated to proposed models of pinning mechanisms.
10:15 AM - HH3.3
Enhancement of Flux Pinning and Critical Currents in YBa2Cu3O7-δ Films byNanoscale Substrate Surface Modifications.
Tolga Aytug 1 4 , M Paranthaman 1 , H Christen 1 , S Kang 1 , K Leonard 1 , A Gapud 1 , P Martin 1 , A Goyal 1 , A Ijaduola 4 , J Thompson 4 1 , D Christen 1 , R. Meng 2 , S Chan 5 , I Rusakova 2 , C Chu 2 , T Johansen 3 Show Abstract
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 , University of Tennessee, Knoxville, Tennessee, United States, 2 , University of Houston, Houston, Tennessee, United States, 5 , Columbia University, New York, New York, United States, 3 , University of Oslo, Norway Norway
Nano-scale iridium, (MgO and BaZrO3), and CeO2 particles were applied to single crystal and biaxially textured metal substrate surfaces using dc-magnetron sputtering, solution- and suspension-based techniques, respectively. A combination of methods was used to document the superconducting and structural properties. Critical current levels of YBCO films grown on the modified substrates were measured over a wide range of field and temperature by transport, magnetization, and magneto optical imaging. Results have shown systematic enhancement in the critical current densities (Jc). Cross-sectional TEM analysis reveals nanoparticle induced defects and second-phase precipitates in proximity to surface nanoparticles. Details of the field-orientation dependence of Jc are related to the nanoparticle species. Nanoparticles applied by using suspension-based techniques revealed correlated c-axis pinning and improved in-field Jc performance, while for sputtered and solution processed nanoparticles, results show a more uniform dependence of Jc over all orientations of magnetic field, along with improved irreversibility behavior. Analysis of the scaling behavior of pinning force density, Fp, indicates consistency of pinning mechanism with respect to temperature and provides a powerful tool for predicting Jc at arbitrary B,T.
10:30 AM - HH3.4
Nature of High Critical Current Density in Epitaxial Films of HTS YBCO Cuprate and Coated Conductors
Vladimir Pan 1 , Ernst Pashitskii 2 , Yuriy Cherpak 1 , Alexei Semenov 2 1 Show Abstract
1 Superconductivity, Institute for Metal Physics, Kiev Ukraine, 2 Nonideal Solids, Institute of Physics, Kiev Ukraine
Currently a problem of crystal defects nano-engineering for pinning enhancement is extensively studied. A number of efforts were done to create nanodot-like and particulate-dispersive pins to enhance pinning and critical current density, Jc(77 K), in high-Tc cuprate films and coatings. Sometimes a desirable effect of Jc enhancement was really achieved. However it is very important to comprehend a real nature and mechanisms of such an enhancement. It is well-known the ensemble of randomly distributed point-like pins enables to provide only weak enough pinning and Jc not higher than 10 KAmps/cm2. Estimations give the maximum pinning force, i.e., its highest achievable value of about fmax = ε/ξab for linear nonsuperconducting extended defects with radius r ≥ ξab(T) when H||c. Here ε is the characteristic vortex energy. A consistent model of vortex pinning and supercurrent limitation is developed by us and discussed on the base of our detailed measurements of magnetic field and angle dependencies of the critical current density Jc(H,θ) in epitaxial c-oriented YBa2Cu3O7−δ (YBCO) films. Measurements are done by the four-probe transport current, low-frequency ac magnetic susceptibility and SQUID magnetometry. YBCO films under study are deposited by off-axis dc magnetron sputtering onto r-cut sapphire substrates buffered with CeO2. Films nano-structure is studied by SEM, TEM, HREM, AFM and X-ray diffractometry. Rows of growth-induced out-of-plane edge dislocations (EDs), forming low angle boundaries (LABs), are shown to play a key role in achievement of the highest critical current density Jc ≥ 2 MAmps/cm2 at 77 K. Our model takes into account transparency of LABs for supercurrent as well as pinning of vortex lattice on LABs network. Principal statistical parameters of film defect structure such as domain size distribution and mean misalignment angle are extracted from Jc(H)-curves measured in magnetic field H applied parallel to the c-axis and from X-ray diffraction data. Evolution of angle dependencies Jc(θ) with H is shown to be consistent with the model, supposing dominant pinning on EDs. Strongly pinned vortices parallel to c-axis appear to exist in tilted low magnetic field up to characteristic threshold field below which magnetic induction within film obeys simple relation B = H cosθ. This feature is shown to explain the absence of the maximum of Jc(θ), expecting at H||c in low applied field. Peaks evolution in Jc(H,θ) and an angular hysteresis of Jc(θ) observed in intermediate field range are discussed in terms of film thickness, surface quality and field orientation. Observed effects are found to be consistent with developed model. To our comprehension any nano-, micro- and macro-interfaces, emerging at the deposition process within film or coating (e.g., nanodot-like and particulate dispersive inclusions) coherently with YBCO-matrix, are a source of formation of a multitude of additional EDs and as a result promote the essential Jc-enhancement.
11:15 AM - **HH3.5
Identification and Engineering of Defects for Vortex Pinning Enhancement in YBa2Cu3O7 Films and Coated Conductors
Boris Maiorov 1 , H. Wang 1 , J. MacManus-Driscoll 2 1 , T Haugan 3 , T. Holesinger 1 , Q. Jia 1 , P. Arendt 1 , S. Foltyn 1 , P. Barnes 3 , L. Civale 1 Show Abstract
1 Superconductivity Technology Center, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Dept. of Materials Science, University of Cambridge, Cambridge, CB2 3QZ, United Kingdom, 3 , Air Force Research Laborator, Wright-Patterson Air Force Base, Ohio, United States
Recent efforts in the ''coated conductor" community have been focused on routes to improve the critical current density (Jc) under applied magnetic fields. In order to tailor pinning centers, it is important to determine the pinning mechanism responsible for enhancing Jc. Using angular and field dependent Jc measurements we have been able to isolate contributions coming from various types of defects that are characteristic of particular growth methods or are introduced artificially. The pinning mechanisms behind some of the successful approaches used to improve in-field Jc, will be presented and contrasted. Several of them consisting of nano-sized inclusions into the YBa2Cu3O7 matrix, namely BaZrO3, Y2BaCuO5 and Y2O3. The ability of the defects to pin vortices depends not only on the chemical composition but also on the deposition technique, growth mode, and process parameters, which correlates on the defects’ microstructure. Changes in the size or shape of the inclusions drastically affect the interaction between the vortices and the defects, resulting in very different angular and field dependences of Jc.
11:45 AM - HH3.6
Enhanced Flux Pinning Properties in High-Temperature Superconductor Films by Introduction of Artificial Pinning Centers
Kaname Matsumoto 1 6 , Tomoya Horide 1 6 , Mele Paolo 1 6 , Yutaka Yoshida 2 6 , Masashi Mukaida 3 6 , Shigeru Horii 4 6 , Ataru Ichinose 5 6 Show Abstract
1 Department of Materials Science and Engineering, Kyoto University, Kyoto Japan, 6 , CREST-JST, Tokyo Japan, 2 , Nagoya University, Nagoya Japan, 3 , Kyushu University, Fukuoka Japan, 4 , University of Tokyo, Tokyo Japan, 5 , CRIEPI, Yokosuka Japan
The increase of flux pinning in magnetic fields at the liquid nitrogen temperature is very important for applications of the recently developed coated conductors, which are made of RE123 high-temperature superconductors. We improve the pinning properties of the RE123 films, which are grown on single crystal substrates or on metallic substrates, by introducing high-density artificial pinning centers into the films by using the nanostructure engineering. In YBCO films deposited on the substrates with the Y2O3 nanoislands the crossover field B*, which separates the single vortex pinning region from the plastic pinning region, becomes large with the increase of the dislocation density, and the flux pinning forces in the high magnetic fields are enhanced. The grain-size-controlled GdBCO thin films effectively increase the pinning density in the films and raise B* from 0.01 T to 0.7 T with the decrease of the grain size. As a result, the pinning forces in the high magnetic fields are also improved, though Jc values in the low magnetic field are slightly degraded. These behaviors are concerned on not only difference between the effective pinning densities but also difference between the dimensionalities of the pinning centers in the films. By the recent improvement in nanostructure control technology in high-temperature superconductor films and coated conductors, the quantitative control of Jc in the magnetic field becomes possible. Here, by referring to the latest results, design guidelines in the nanostructure control are discussed for increasing the flux pinning in high-temperature superconductors.
12:00 PM - HH3.7
Flux Pining Enhancement in Pulsed Laser Deposited YBa2Cu3O7-x Coated Conductors with BaSnO3 Nano Particle Additions.
Chakrapani Varanasi 2 1 , Jack Burke 1 , Paul Barnes 1 , Mike Sumption 3 , Iman Maartense 2 , Tim Haugan 1 Show Abstract
2 Metals and Ceramics, Univerisity of Dayton Research Institute, Dayton, Ohio, United States, 1 AFRL/PRPG (UDRI), Airforce Research Laboratory, WPAFB, Ohio, United States, 3 MSE, The Ohio State University, Columbus, Ohio, United States
For the high magnetic field applications, flux pinning enhancement in YBa2Cu3O7-x (YBCO) coated conductors is very important to achieve. In this work, a unique, specially made pulsed laser ablation target with a BaSnO3 second phase pie wedge was used to deposit coated conductor “composite” consisting of YBCO and random second phase particulates. This approach gives the flexibility of introducing the second phase particulates in an uninterrupted way in a growing YBCO film. The particles will be deposited in a non layered, random fashion which may be helpful to reduce the anisotropy in the flux pining enhancement. By selecting a proper laser scanning sequence, desired amount of BaSnO3 nano particles were introduced randomly in the growing YBCO films. Initial results show that YBCO films on lanthanum aluminate substrates can be made with significant improvement in magnetization critical current density (Jcm) at higher fields >3T but with slightly reduced Jcm at low fields. A cross over in the Jcm values as compared to regular YBCO was observed to occur at magnetic fields > 3T at both 77K and 65K measurements. Nearly an order of magnitude improvement in Jcm at 6T at 77K as compared to similarly processed regular YBCO was observed. The BaSnO3/YBCO films are compared to similarly processed Y2BaCuO5 (Y211)/YBCO films. Other results such as microstructure, texture, and transport current Jc on buffered metallic substrates etc. will be discussed.
12:15 PM - HH3.8
The Growth Mechanism of Pinning-effective Nanostructures Embedded in YBCO Superconducting Thin Film.
Albert Gapud 1 , Aurangzeb Khan 2 , M. Parans Paranthaman 3 , David Christen 3 Show Abstract
1 Department of Physics, University of South Alabama, Mobile, Alabama, United States, 2 Department of Electrical and Computer Engineering, University of South Alabama, Mobile, Alabama, United States, 3 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
12:30 PM - HH3.9
How Nanosized Defects Affect Current Percolation, Vortex Pinning, Irreversibility Field, and Ultimately the Critical Current Density in HTS.
Alberto Gandini 1 2 , Roy Weinstein 1 2 , Ravi-Persad Sawh 1 2 , Drew Parks 1 2 , Billy Mayes 1 Show Abstract
1 Department of Physics, University of Houston, Houston, Texas, United States, 2 Texas Center for Superconductivity at the University of Houston, University of Houston, Houston, Texas, United States
The optimization of nanodefects to achieve large Jc is a key issue in HTS applications. Present vortex pinning theory and early irradiation experiments on HTS suggested that the pinning potential energy, Up, should be maximized in order to achieve high Jc. Continuous columnar pinning centers, CCPCs, which maximize Up, have therefore been regarded as the optimum pinning centers, PCs. On the contrary, at the 2005 MRS spring meeting we reported the surprising experimental result, that Jc for discontinuous PCs is much higher than for continuous PCs. For example, Jc ~ 275 kA/cm2, at B = 1T and T = 77K, and Jc ~ 800 kA/cm2, at B = 1T and T = 60K, have been achieved with discontinuous PCs, in ordinary melt-textured YBCO. These record-high Jc values are comparable to those in YBCO 2G wires, under the same conditions, in spite of Jc typically being much smaller in melt-textured bulk samples than in 2G wires. This indicates that large improvements of the in-field Jc may be also achieved in 2G wires. We have now extended our analysis to the effect of discontinuous PCs on the irreversibility field, Hirr, and on Tc – which are also key issues with Jc in HTS theory and applications. For example, at 77K we found that discontinuous PCs yield Hirr ~ 9T, which is higher than for CCPCs, suggesting that discontinuous PCs promote fluxoids self-entanglement. Next, since very high values of Jc and Hirr for discontinuous PCs are not predicted by conventional vortex-pinning theory, which instead predicts Jc to be maximized by CCPCs, we ask the fundamental question of why discontinuous PCs yield the largest Jc, even though the Up is smaller than for CCPCs. To do that we have recently introduced a phenomenological theory that includes two novel elements: the effect on Jc of current percolation and of the Tc reduction, which typically follows the insertion of inhomogeneities in the HTS matrix. The latter, although previously suggested, was not directly implemented in theoretical calculation. In particular, we consider three leading effects of the interaction between nanodefects (e.g. pinning centers), vortices, and current flow: (1) defects reduce percolation paths, and thereby reduce Jc, (2) defects reduce Tc, and thereby decrease Jc, (3) defects pin the fluxoids thereby increase Jc. When these three effects are joined together, the optimum theoretical value of PC length, diameter, and density at which Jc is maximized is predicted, in good agreement with experimental data. This new phenomenological theory indicates that Jc is predominantly determined, not by Up, as expected at present, but by percolation limitations. Our analysis indicates that the superior percolation achieved by discontinuous PCs outweighs the decrease in Up, and thus in contrast with conventional pinning theory, that Jc does not depend primarily on Up. In conclusion, the present work provides a guideline to achieve through nano-engineering the optimum PC morphology for high in-field Jc.
12:45 PM - HH3.10
Temperature Dependent Vortex Pinning Regimes in YBa2Cu3O7 Coated Conductors.
Leonardo Civale 1 , Boris Maiorov 1 , Jason Mantei 3 1 , Steve Foltyn 1 , Haiyan Wang 1 , Judith MacManus-Driscoll 2 1 , Quanxi Jia 1 , Paul Arendt 1 Show Abstract
1 Superconductivity Technology Center, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 Dept. Material Science and Engeneering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 Dept. of Materials Science , University of Cambridge, Cambridge, CB2 3QZ, United Kingdom
The field dependence of the critical current density (Jc) in YBa2Cu3O7(YBCO) films usually exhibits three regimes. At low fields and up to a certain H* field, Jc is field-independent. Above H*, Jc starts to decay following a power-law Jc ∼ H-α, and beyond a second crossover field Hcr it drops faster as the irreversibility line is approached. We had previously found that at liquid nitrogen temperatures and for H//c-axis α depends on the fabrication method and structural properties of the YBCO film, and that it can be reproducibly improved (i.e., reduced) by appropriate nano-engineering of the vortex pinning centers. Moreover, the Jc ∼ H-α regime extends over a field range that is particularly relevant for applications of coated conductors (CC), thus α is a technologically important characterization parameter of the in-field performance. As the most likely temperatures for applications of CC are between 20K and 50K, it is important to explore the in-field Jc in that range. To that end magnetization measurements of Jc(T,H) were performed for temperatures between 4K and 75K on a variety of YBCO films and CC with different structural properties and engineered vortex pinning centers. These data was used to extract H*(T) and Hcr(T) and build a H-T phase diagram of the pinning regimes. In most cases α exhibits a small but systematic temperature dependence. These results will be discussed in the framework of the combined effects of various types of pinning mechanisms.
HH4: MgB2 and Bi2223 Conductors and Novel Materials
Wednesday PM, April 19, 2006
Room 2020 (Moscone West)
2:30 PM - **HH4.1
Critical Currents of Nb3Sn and MgB2 Wires under Uniaxial Strain and Compressive Stress, With and Without Steel Reinforcement.
Rene Flukiger 1 , D. Uglietti 1 , B. Seeber 1 , C. Senatore 1 , V. Abacherli 1 Show Abstract
1 MANEP, University of Geneva, Geneva Switzerland
The effects of both, uniaxial strain and compressive stress on long, high current superconductors at fields up to 21 T, as determined by the modified Walters Spring. The long measuring length (up to 80 cm) of the conductors allowed the measurement of the V - I relation under uniaxial strain over three decades of electric field, down to 0.01 mV/cm (measuring currents up to 1’000 A). Measurements on Nb3Sn wires, prepared by various techniques (Bronze Route, Internal Sn diffusion and Powder-in-Tube) are presented and discussed. The results are analyzed in the light of various models. The analysis is extended to stainless steel reinforced wires. The mechanical properties of MgB2 wires and tapes prepared by both, the in situ and ex situ technique are analyzed, and the effect of various sheath materials (Fe, Ni alloys, stainless steel) is compared. A particular attention is given on the limits of strain reversibility. The effect of compressive stress on the critical current density of various conductors by using an inverse Walters spiral is presented. The possibility to measure the strain sensitivity at currents up to 1000 A is very useful when characterizing the thermo-mechanical properties of industrial conductors
3:00 PM - HH4.2
Ex-Situ MgB2/Al Tape with High Jc Exceeding 10,000 A/cm2 at 4.2K, 4T.
Hitoshi Kitaguchi 1 , Takayuki Nakane 1 , Hiroaki Kumakura 1 Show Abstract
1 Superconducting Materials Center, National Institute for Materials Science, Tsukuba Japan
Magnesium diboride, MgB2, has a possibility to be very light-weight superconducting wires and tapes in addition to its advantages such as higher Tc and lower material costs than conventional superconductors. MgB2 has another possibility as one of the candidate superconductors suitable for the magnet coils in future fusion reactors because of its low induced activity. In order to realize these possibilities, it is desirable to use light metal(s) with low induced activity as the sheath material (or stabilizer.) Therefore, we are developing MgB2 tapes using aluminum-based metal sheath. As Mg and Al react very easily to MgAl2 at high temperatures, we applied an ex-situ PIT process to fabricate MgB2/Al tapes. A serious problem in MgB2/Al tapes prepared through the ex-situ route using commercial MgB2 powder is their poor Jc-B performance (typically, around 100 A/cm2 at 4 T and 4.2 K.) Recently, we found that the performance of ex-situ MgB2 conductors can be improved by using MgB2 powder fabricated from a mixture of MgH2 and amorphous boron. We applied this technique to fabricate ex-situ MgB2/Al tapes. For comparison, we prepared another ex-situ MgB2/Al tape using a commercial MgB2 powder. These powders were tightly packed into Al tubes, and then the tubes were cold-rolled into tapes. The highest Jc value at 4 T and 4.2 K was 1.1x104 A/cm2 for our ex-situ MgB2/Al tape using MgB2 powder fabricated from a mixture of MgH2 and amorphous boron. This Jc is higher in two orders of magnitude than that of the ex-situ tape fabricated using commercial MgB2 powder. Our ex-situ MgB2/Al tape carries 1.0x103 A/cm2 even in 10 T (4.2 K), whereas the ex-situ MgB2/Al tape prepared using commercial MgB2 powder is no longer superconducting in 10T. The Jc of our ex-situ MgB2/Al tape is on the same order as that of in-situ MgB2/Fe tape prepared using a powder mixture of Mg and amorphous boron. These results indicate that the Jc-B performance of ex-situ MgB2/Al tape can be enhanced much by improving the quality of the starting powder.
3:15 PM - HH4.3
Superconducting characteristics of MgB2 wires obtained by Reactive Liquid Mg Infiltration
Giovanni Giunchi 1 , Giovanni Ripamonti 1 , Elena Perini 1 , Tommaso Cavallin 2 , Enrico Bassani 2 , Umberto Gambardella 3 , Yifeng Yang 4 , Edward Young 4 , Marco Bianchetti 4 , Carlo Beduz 4 Show Abstract
1 R&D, EDISON SpA, Milano Italy, 2 Sezione di Lecco, CNR-IENI, Lecco Italy, 3 INFN, University of Salerno, Salerno Italy, 4 Department of Cryogenics, University of Southampton, Southampton United Kingdom
Superconducting MgB2 wires, of different diameter and length, have been produced by the reactive Liquid Mg Infiltration process, implemented with the addition of extra Mg, to completely fill the internal hole created from the normal infiltration process. The actual wires have an Iron external lining and the metallic Mg internally added has a twofold effect: to avoid Mg deficiency during the reaction and to increase the quenching resistance of the wire. The superconducting characteristics of the wires have been measured either at the liquid He and at the liquid Ne temperatures, on small samples cut from meter long wires. The typical critical current density in self field, at 27.2 K is about 1000 A/mm2, a value of interest for current leads application. The extension of the manufacturing process to longer wire will be discussed as well as the effect of the metallic lining of the wires on the contact resistance and on the current injection length. - Giunchi,G;Ceresara,S;Ripamonti,G;DiZenobio,A;Rossi,S; Chiarelli,S;Spadoni,M; Wesche,R ;Bruzzone,PL “High performance new MgB2 superconducting hollow wires” SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 16(2): 285-291 FEB 2003
3:30 PM - HH4.4
Hot Deformation Processing of MgB2
Harry Jones 1 , Mike Osofsky 1 , Chia Feng 1 , Khershed Cooper 1 , Chandra Pande 1 , Robert Soulen 1 Show Abstract
1 Physical Metallurgy Branch, Naval Research Laboratory, Washington, District of Columbia, United States
MgB2 exhibits an interesting and potentially useful mechanical behavior when hot rolled inside a steel sheath at 900°C. Somewhat surprisingly, 90% reductions in area of the MgB2 core have been achieved without significant "sausageing", or pinch off, of the core by the sheath. This was accomplished utilizing a two step process. First, a length of black iron pipe having an inside diameter of 11.8 mm was packed with granular magnesium and powdered boron, and then sealed by arc welding steel plugs into the ends. This container, or "billet", was heated to 900°C, and then repeatedly hot rolled through grooves of decreasing size in a hot rolling mill with rectangular, or "diamond" grooved rolls. The billet was reheated to 900°C after each of the eighteen passes required to deform the billet into a 5.6 mm square rod 610 mm in length. Inside this rod a 3.9 mm diameter MgB2 core was formed which was free of the voids that are common to the "in situ" PIT process. In the second step, a length of this rod was inserted inside a steel bar which had a hole drilled into it. This container was sealed by welding in a plug, and then hot rolled as described above. The resulting core diameter after hot rolling was 1.3 mm, which represents a nearly 90% reduction in area, again without pinch off by the sheath. Three stochiometric ratios, ranging from 10% excess Mg to 10% excess B by weight were explored. In each case nearly 90% reductions in area were achieved despite dramatic changes in the core microstructure. The mechanisms by which these deformations are accommodated are not clearly understood. On the Mg rich side the reduction may be the result of the deformation of a "slush" of MgB2 crystallites suspended in liquid Mg. For the stochiometric ratio, however, this is not the case, yet the same amount of deformation is achieved. A crush and resintering mechanism may also be a possibility, but the hardness of steel at 900°C places limits on this. Additionally, a four strand wire was fabricated using a simple recanning process which exhibited promising transport properties, and a pack of 25 PIT wires was hot rolled to produce a 25 strand conductor.
4:15 PM - HH4.5
Global and Local Flux Jumps in Superconducting MgB2 Films: Magneto-optical Imaging and Theory.
Daniel Shantsev 1 3 , Dmitry Denisov 1 3 , Alexander Rakhmanov 2 , Alexander Bobyl 3 , Yuri Galperin 1 3 , Sung-Ik Lee 4 , Tom Johansen 1 Show Abstract
1 Department of Physics, University of Oslo, Oslo Norway, 3 , A. F. Ioffe Physico-Technical Institute, St. Petersburg Russian Federation, 2 , Institute for Theoretical and Applied Electrodynamics, Moscow Russian Federation, 4 Department of Physics, Pohang University of Science and Technology, Pohang Korea (the Republic of)
MgB2 is one of the most unstable superconducting materials, where flux jumps are commonly observed at low temperatures jeopardizing its potential for applications. We present a detailed magneto-optical imaging study of the jumps in MgB2 films, where branched dendritic flux patterns are observed. In addition to large dendrites, with length close to the sample size and width ~ 100 micron, we find simultaneously also much smaller jumps down to 50 flux quanta. We have developed a theory for the dendritic instability in thin superconducting films assuming that the jumps are of thermal origin. It is based on the Maxwell and thermal diffusion equations, and takes into account the nonlocal electrodynamics in films, and also the thermal coupling to the substrate. A linear analysis of the equations gives a criterion for the onset of the instability, and the conditions under which dendritic patterns are developed. We derive the build-up time for the instability, the characteristic dendrite width, and reproduce precisely the experimental temperature dependence of the threshold field. It is shown that in thin films the instability starts at lower fields, and is more likely to result in dendritic flux pattern than in bulk superconductors . Furthermore, we determine the size of flux jumps in the adiabatic approximation. The field dependence of the jump size, as well as the flux density profiles after jumps, are in very good agreement with the direct observations .  Denisov et al., cond-mat/0508679 Shantsev et al. Phys. Rev. B 72, 024541 (2005)
4:30 PM - **HH4.6
Progress in Bi-2212 Wire and Coils for Superconducting Magnets.
Ken Marken 1 , H. Miao 1 , M. Meinesz 1 , B. Czabaj 1 , S. Hong 1 Show Abstract
1 , Oxford Instruments, Inc., Carteret, New Jersey, United States
Partial melt processing of BSCCO-2212 enables the fabrication of round multifilamentary wire which displays no anisotropy in critical current with respect to applied field orientation. The high field critical current density (Jc) and engineering current density (JE) in these wires continue to improve. Recent efforts have focused on the effect of precursor composition combined with separate heat treatment optimization for each composition. Variations in the starting precursor cation ratios have several effects on conductor processing and properties, including the ceramic melt temperature, the relative sharpness of the melting event, the crystallization behavior including secondary phase formation and growth, and the peak Jc attainable. We systematically varied melt temperature, cooling rate, annealing temperature, and annealing time. Average Jc was determined from multiple samples for each parameter set. Dependence of Jc on cation ratio and these heat treatment parameters will be presented and discussed. Wind-and-react coil trials are underway using these improved wires. The combination of round wire and wind-and-react coils shows substantial potential for superconducting magnets, particularly high field insert coils.
5:00 PM - HH4.7
Processing of Bi2Sr2CaCu2O8+x Ag-clad Conductors Applying the React-Wind and Sinter Approach.
Gary Merritt 1 2 , Justin Schwartz 1 2 , Ulf Trociewitz 2 Show Abstract
1 Mechanical Engineering, The Florida State University, Tallahassee, Florida, United States, 2 Magnet Science & Technology, National High Magnetic Field Laboratory, Tallahassee, Florida, United States
5:15 PM - HH4.8
Strain Dependence Transport and Mechanical Characteristics of High-current and High-strength type Ag/Bi2223 Composite Superconductors.
Malik Adam 1 , Kozo Osamura 2 Show Abstract
1 Electrical and Electronics Engineering, University Technology Petronas, UTP, Seri Skandar, 37150 Tronoh, Perak, Malaysia, 2 2Department of Materials Science and Engineering, Kyoto University, , Yoshida- Honmachi, Sakyo-Ku, 606-8501 Kyoto, , Kyoto, Japan
5:30 PM - HH4.9
Nanoscale Epitaxial Films of Cu2O2-x (cubic CuO).
Gertjan Koster 1 , W Siemons 1 , H Yamamoto 2 , R Hammond 1 , P Grant 3 , T Geballe 1 , M Beasley 1 Show Abstract
1 GLAM, Stanford University, Stanford, California, United States, 2 , NTT Basic Research Laboratories, Kanagawa Japan, 3 , W2AGZ technologies, San Jose, California, United States
Here we present a detailed study on the growth of epitaxial Cu2O2-x thin films on single crystal substrates by MBE as a possible metastable model system for correlated electronic behavior related to the cuprates. In situ photoelectron spectroscopy (XPS and UPS) is used to establish the degree of oxidation of Cu while in situ electron diffraction (X-ray photoelectron diffraction and RHEED) monitor the crystal structure and morphology of the growing thin film. We pay particular attention to the valence state of Cu and the crystal symmetry as influenced by a combination of activated oxygen (O*) and/or a collimated flux of low energy Ar+ ions. We observe a rich variety of epitaxial relationships as a function of the flux ratios of three species on the substrate surface (i.e., Cu, O* and Ar+) which will be used to explore the possibility of the highest crystal symmetry attainable in the CuOx system. In recent experiments we observed a new divalent copper oxide phase for the first few deposited cubic-like unit cell layers with the direction pointed along the  diagonal of the SrTiO3 substrate lattice. Both RHEED as well as preliminary X-ray photoelectron diffraction confirm a four-fold symmetric structure. In addition to these experimental efforts, we have undertaken computational efforts in an attempt to establish a relationship between relative electronic stability and crystal structure symmetry at different copper-oxygen bond length scales. Although the copper cation system is the focus of this paper, we also address whether such an approach is feasible for other oxide materials, for example dielectric materials.
5:45 PM - HH4.10
Bulk CaC6 Superconductivity.
Nicolas Emery 1 , Claire Herold 1 , Matteo d'Astuto 2 , Chirstophe Bellin 2 , Jean-Francois Mareche 1 , Philippe Lagrange 1 , Genevieve Loupias 2 Show Abstract
1 , LCSM, Vandoeuvre-les-Nancy Cedex France, 2 , IMPMC, Paris France
We have obtained bulk samples of the CaC6 graphite intercalation compound (GIC) by a novel method of synthesis. Using magnetization measurements, we have clearly shown the occurrence of superconductivity at 11.5K, the highest Tc observed among all the GICs.GICs are synthesized by inserting foreign atoms between graphite sheets, leading to strictly ordered structures. Superconductivity in the KC8 GIC was reported forty years ago(1) with a critical temperature Tc of 0.14K(2). The BCS behavior of KC8 leads to two kinds of attempts to increase Tc: a larger charge transfer to graphene planes or a larger graphite interlayer spacing. The highest Tc, of only 5.5K, was reached by KC4, a metastable compound obtained by a high-pressure method(3). Very recently, Tc of 6.5K was discovered in YbC6 as well as a Tc as high as 11.5K was suggested in CaC6 but the “reduced quality sample” has not allowed to clearly evidence Meissner effect(4). We have succeeded in synthesizing bulk CaC6 from highly oriented pyrolytic graphite and a molten lithium-calcium alloy. We have carried out the first CaC6 structural study and pointed out that this compound is the only one to possess a rhombohedral symmetry instead of the hexagonal symmetry of all the others MC6 GICs(5). We have evidenced a very sharp drop of magnetization below 11.5 K with a strong diamagnetic signal(6). In order to study details of CaC6 superconductivity, magnetization was measured as a function of temperature and of directionnal magnetic field, applied parallel or perpendicular to graphene c-axis. From these results, we have evidenced a true Meissner effect, a type-II superconductor behavior and an anisotropic CaC6 superconducting state but clearly three-dimensional, in spite of its layered structure. Recent ab initio calculations(7) indicate that the substantial amount of charge left in the metal plays a major role in CaC6 superconductivity and evidence a noticeable 3D character of its metallic bands.In present case, CaC6 Tc is the highest observed among all the GICs and represents an increase of Tc by almost two orders of magnitude over that of KC8. This leads to renew interest in GICs, with their wide variety of intercalant species. 1 – N.B. Hannay, T.H. Geballe, B.T. Matthias, K. Andres, P. Schmidt, D. MacNair, Phys. Rev. Lett. 14, 225 (1965).2 - Y. Koike, S. Tanuma, H. Suematsu, K. Higuchi, J. Phys. Chem. Solids 41, 1111 (1980).3 – V.V. Avdeev, O.V. Zharikov, V.A. Nalimova, A.V. Pal’nichenko, K.N. Semenenko, Pis’ma Zh. Eksp. Teor. Fiz. 43, 376 (1986).4 - T.E. Weller, M. Ellerby, S.S. Saxena, R.P. Smith, N.T. Skipper, Nat. Phys. 1, 39 (2005).5 - N. Emery, C. Hérold, P. Lagrange, J. Solid State Chem. 178, 2947 (2005).6 - N. Emery, C. Hérold, M. d’Astuto, V. Garcia, Ch. Bellin, J.F. Marêché, P. Lagrange, G. Loupias, Phys. Rev. Lett. 95 087003 (2005).7 - M. Calandra and F. Mauri, cond-mat/050682.
HH5: Poster Session
Thursday AM, April 20, 2006
Salons 8-15 (Marriott)
9:00 PM - HH5.1
Fabrication of MgB2 Superconductors on Polycrystalline Cu Substrates.
Toshiya Doi 1 , Hitoshi Kitaguchi 2 Show Abstract
1 , Kagoshima University, Kagoshima, Kagoshima, Japan, 2 , National Institute for Materials Science, Tsukuba, Ibaraki, Japan
9:00 PM - HH5.10
Scaling of Superconducting Gap and Critical Temperature in Doped Bi-2212, Bi-2201 and Hg-1201
Yaroslav Ponomarev 1 , Svetoslav Kuzmichev 1 , Mikhail Mikheev 1 , Marina Sudakova 1 , Sergeii Tchesnokov 1 Show Abstract
1 Faculty of Physics, Moscow State University, Moscow Russian Federation
9:00 PM - HH5.11
Transport AC Losses of Ag-Sheathed Bi-2223 Tapes with Different Twist-Pitch using Electrical Methods
Mi-hye Jang 1 , Winnie Wong-Ng 1 , Tae Ko 2 Show Abstract
1 Ceramics, NIST, gaithersburg , Maryland, United States, 2 Electrcial and Electronic Engineering, Yonsei University, Seoul, Seadeamoon Ku, Korea (the Republic of)
At present, BSCCO-based tapes are the only high Tc superconductors that have a commercial market. Improvement of processing of these tapes, however, is still needed in order to maximize the superconducting properties which in turn will lead to the minimization of cost of production. In this study, a series of Bi-2223 ([Bi, Pb] : Sr : Ca : Cu :O = 2:2:2:3) tapes with 37 superconducting core filaments were investigated in an attempt to correlate critical current and alternating current (AC) losses with twist-pitch. The twist-pitch of these multi-filamentary tapes which were produced by the powder-in-(Ag)tube (PIT) method vary from 8, 10, 13, 30, 50, 70, to infinite (non-twist) mm. Critical current (Ic) measurements which were conducted in zero-field by a 4-probe method under liquid-nitrogen temperature showed that Ic is greater in the non-twist filament than that in twisted filaments. Among these tapes, three (twist-pitch of 10 mm, 13 mm, and 70mm) were selected for AC loss experiments under a time-varying transport current. The results of AC loss measurements in general agree with that of the AC loss simulation using the ellipse model of Norris Equation. Simulation results show that the hysteretic AC loss is lowest in the non-twist tape and increases as the twist-pitch decreases. A much greater loss was found in tapes with small twist-pitch, i.e. 10 mm and 8 mm. Among different possible loss contributions to the total AC losses, the hysteretic loss was determined to be the main source. In addition, microstructural damage of tapes with small twist-pitch appears to contribute to the overall AC losses as well.
9:00 PM - HH5.12
Electrical Devices Obtained From Polymeric Precursors Process.
Claudio Carvalho 1 , Raphael Peruzzi 1 , Rudi Solano 1 Show Abstract
1 Physics and Chemistry, Universidade Estadual Paulista - UNESP, Ilha Solteira, SP, Brazil
Nowadays, many investments have been made in the area of superconductor materials, with the aim to improve theirs potential technological applications. Applications on the energy transport using cables, to get high resolution images in the medicine use high magnetic fields, high speed signals use superconductor devices all of them are in crescent evidence and they are showing that the future is coming and next for this new kind of materials.Obviously that everything of this is possible due to the increasing of research with new materials, where the synthesis, characterization and applications are of the mainly objective of these researches.The production of cable for the energy transport has been in advanced stage as the bulks production is too. However, the film production that to aim at the electronic devices area are not so developed or its still need expensive investments.Thinking about that, we are developing a research where we may increase the relation of cost/benefits. Thereby, we are applying the polymeric precursors method to obtain films that will be used in the built of electronic devices. Thin films (mono and multilayers, on crystalline or metallic substrates, controlled thickness) of the BSCCO system have been obtained from dip coating deposition process with excellent results in terms of preferential orientation, controlled thickness, large area, what may indicate future applications.Based on these results, we present an electrical circuit and their principal characteristics as superconductor transition (85K), transport current density and structure. DC four probes method, scanning electron microscopy, digital optical microscopy, X-ray diffractometry were some techniques used for the characterization of this superconductor electric device.
9:00 PM - HH5.13
Biomimetic Synthesis of High-Tc Type-II Superconductor Nanowires.
Simon Hall 1 Show Abstract
1 School of Chemistry, University of Bristol, Bristol United Kingdom
This work demonstrates the first biomimetic synthesis of a Type-II, high-Tc single crystal superconducting nanowire. Using the biopolymer chitosan from crab shells, control of crystal morphology through a matrix mediated vapour-liquid-solid growth mechanism is shown. This interdisciplinary approach not only produces high yields of the first Type-II superconductor in this much sought after morphology, but at the same time raises the record critical temperature for superconducting nanowires from 39K to 85K. A general theory of the growth of nanowires in biomatrices is presented.
9:00 PM - HH5.14
Study of Biaxial Texture Development in Copper Rich, Cu–Ni Alloy (Cu 55 wt%, Ni 45 wt%) Substrates for Coated Conductor Applications.
Chakrapani Varanasi 3 1 , Jack Burke 1 , Paul Barnes 1 , Haralabos Efstathiadis 2 , Pradeep Haldar 2 , Andrew Chaney 1 Show Abstract
3 Metals and Ceramics, University of Dayton Research Institute, Dayton, Ohio, United States, 1 AFRL/PRPG, Airforce Research Laboratory, WPAFB, Ohio, United States, 2 College of Nanoscale Science and Engineering , University at Albany-SUNY, Albany, New York, United States
Biaxially textured Cu-based substrates are attractive as they can be a cheaper alternative to the widely used Ni-based substrates in high temperature superconducting (HTS) coated conductors. Although excellent biaxial texture can be obtained in pure Cu, it needs to be alloyed with other elements to improve the yield strength to make it useful as a practical substrate. Often these alloying elements in Cu can affect the stacking fault energy and reduce the ability to obtain the needed (001) biaxial texture. In addition to improving the yield strength without adversely affecting the bi-axial texture development, the alloying elements must provide a good lattice match, maintain low magnetic properties etc. Once these properties can be obtained, then appropriate architectures can be developed to improve the substrate’s tolerance to an oxygen environment. In this study, a non magnetic (at room temperature) copper rich composition of Cu- Ni alloy is used as opposed to previously studied compositions that are mostly Ni rich. Cu-Ni alloy rods of the composition Cu 55 wt%, Ni 45 wt% have been rolled to get nearly 99% reduction in the thickness and the texture development was studied in a systematic way as a function of annealing treatment at different temperatures. It was found that the total percentage of (001) biaxial texture (as determined by OIM) can be increased from 72% to >96% as the annealing temperature was increased from 750 C to 1150 C. The saturation magnetization value of a textured Cu-Ni substrate was found to be only 13% of the value of a Ni-5%W substrate measured at 77K. Initial results of the texture development in the buffer layers (nitrides and oxides) grown on these Cu-Ni substrates will be presented.
9:00 PM - HH5.15
Comparison of Texture Evolution in Nickel Deformed by Equal Channel Angular Pressing and Rolling
Predrag Kisa 1 , Andreas Kulovits 1 , Jorg Wiezorek 1 , Nicholas Eror 1 Show Abstract
1 Materials Science and Egineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
9:00 PM - HH5.16
Crystal Chemistry and Crystallography of the Ba2RCu3O6+x - SrTiO3 System.
Zhi Yang 1 , Winnie Wong-Ng 1 , Qingzhen Huang 1 , Lawrence Cook 1 , James Kaduk 2 Show Abstract
1 , NIST/MS-8520, Gaithersburg, Maryland, United States, 2 , BP Chem, Naperville, Illinois, United States
Continued world-wide research in high Tc superconductors has lead to the promise of a wide variety of industrial applications. To implement these applications, the availability of low-cost, long-length, and high performance superconductor wire/tape and cable is critical. Preparation of these wires/tapes involve deposition of Ba2RCu3O6+x (R-213, R=lanthanides and Y) films on biaxially-textured buffer/substrates. Two promising processes for preparing buffer/substrates are the Ion Beam Assisted Deposition (IBAD) and the Rolling Assisted Biaxially Textured Substrates Buffer (RABiTS). For a given combination of buffer layers that has been found to promote epitaxial growth of Ba2RCu3O6+x, there may be unavoidable reactions at the interface between layers. Understanding of interfacial reactions of R-213 phase with the buffer layers will provide information about how to avoid and/or control the formation of second phases. Crystallographic and phase equilibrium data will assist analysis of coated conductor interfaces. This paper describes the phase equilibria, crystal chemistry and crystallography of the multi-component (Ba,Sr)-R-Ti-Cu-O system and selected subsystems representing the interaction of Ba2RCu3O6+x with the SrTiO3 buffer. X-ray and neutron Rietveld refinements were employed for structural studies. Examples of phases that will be discussed include (Ba,Sr)3RTi2O8.5, (Ba,Sr)R2CuO5, and (Ba,Sr)2RCu3O6+x, etc.
9:00 PM - HH5.17
Monte Carlo Simulations of ion implanted YBa2Cu3O7-d for High Tc Josepshon Junctions
Charles Cheung 1 , Shane Cybart 1 , Robert Dynes 1 Show Abstract
1 Physics, University of California, San Diego, La Jolla, California, United States
High Tc Josephson junctions fabricated from a narrow area of reduced Tc by ion implantation has been studied in the last decade as an alternative to other junction types. The advantages of a-b plane conduction, the use of widely available industry tools for fabrication, and the lack of a need for special metallurgical techniques have made ion damaged junctions an area of focus. Ion implantation simulations of thin-film YBa2Cu3O7-d Josephson junctions were carried out to compare the reduction of Tc with experimental results. With increasing damage the coherence length inside of the junction is decreased, complicating Josephson junction devices.
9:00 PM - HH5.2
Ag and Au Borides Prepared by Magnetron Sputtering.
Michael Rotman 1 , Joshua Pelleg 1 , Michael Sinder 1 Show Abstract
1 Materials Eng, Ben Gurion University, Beer Sheva Israel
9:00 PM - HH5.3
Characterization and Mitigation of Oxide Phases in Bulk Magnesium Diboride.
Scot Bohnenstiehl 2 , Michael Sumption 2 , Ted Collings 2 Show Abstract
2 Materials Science and Engineering, Ohio State University, Columbus, Ohio, United States
Bulk magnesium diboride has made significant advances in magnetic field stability but current densities are still significantly less than magnesium diboride thin films. If optimal processing of bulk MgB2 could be achieved, then it would further wire development and applications. The discrepancy in current densities may be due in part to various oxide and impurity phases that affect the connectivity of MgB2 grains and thus contribute to a lower Jc of the bulk. These oxide phases include MgO and B2O3 although various suboxides may be present. A study of these oxide phases and their effect on MgB2 connectivity was carried out using the liquid infiltration process for bulk MgB2 synthesis. A variety of methods for mitigating the formation of these oxide phases was also explored with the prospect of increasing MgB2 connectivity and thus Jc.
9:00 PM - HH5.4
Optimising Critical Current Density in MgB2 Through Stoichiometry Control, and Novel Nano-particle inclusions
S Chen 1 , K Yates 1 , M Blamire 1 , Judith MacManus-Driscoll 1 Show Abstract
1 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
With a Tc of nearly 40K, and strongly linked grains in polycrystalline form, there are good prospects for MgB2 for open-aperture, low-field (<2T) MRI applications at 20K. However, Jc needs to be increased in the low field regime through enhanced pinning, and intergrain connectivity. While much work has been focusing on doping to control interband scattering in the B-plane (most useful for high-field applications), the issue of ‘intrinsic doping’ through control of stoichiometry has yet to be explored. In this work, we demonstrate enhanced Jc by up to an order of magnitude through control of the Mg stoichiometry. We also demonstrate the addition of very small (<1 wt. %) oxide phase to give strong intragranular nano-scale pinning and a factor of more than 3 improvement in Jc.
9:00 PM - HH5.8
Magnetic Field Enhanced Texture of Bi2Sr2CaCu2O8+x During Partial-melt Processing.
Manuel Ramos 1 2 , Justin Schwartz 1 2 , Sastry Pamidi 3 , Ulf Trociewitz 2 , Timotthy Effio 1 2 Show Abstract
1 Mechanical Engineering, FSU-FAMU College of Engineering, Tallahassee, Florida, United States, 2 , The National High Magnetic Field Laboratory, Tallahassee, Florida, United States, 3 , The Center for the Advance Power Systems, Tallahassee, Florida, United States
9:00 PM - HH5.9
Observation of Leggett’s Mode in Mg1-xAlxB2
Yaroslav Ponomarev 1 , Svetoslav Kuzmichev 1 , Mikhail Mikheev 1 , Marina Sudakova 1 , Sergei Tchesnokov 1 , Boris Bulychev 2 , Evgenii Maksimov 3 , Sergei Krasnosvobodtsev 3 Show Abstract
1 Faculty of Physics, Moscow State University, Moscow Russian Federation, 2 Faculty of Chemistry, Moscow State University, Moscow Russian Federation, 3 , P.N.Lebedev Institute of Physics, RAS, Moscow Russian Federation
Leonardo Civale Los Alamos National Laboratory
Claudia Cantoni Oak Ridge National Laboratory
Matthew Feldmann University of Wisconsin-Madison
Xavier Obradors CSIC
HH6: Doping and Processing of MgB2
Thursday AM, April 20, 2006
Room 2020 (Moscone West)
9:30 AM - **HH6.1
High-field Superconductivity in the Two-gap MgB2 Near the Paramagnetic Limit.
Alex Gurevich 1 Show Abstract
1 Applied Superconductivity Center, University of Wisconsin, Madison, Wisconsin, United States
Anomalous temperature dependence of the upper critical field Hc2 in a dirty anisotropic two-gap superconductor MgB2 is addressed. A theory based on generalized Usadel equations shows that multiple scattering channels in MgB2 offer special opportunities for Hc2 increase by tuning the intraband and interband impurity scattering rates due to selective atomic substitutions on Mg and B sites. As a result, Hc2(T) can exhibit a temperature dependent anisotropy and a strong upward curvature inconsistent with the one-band BCS dirty limit theory and the Ginzburg-Landau angular scaling. In particular, the upward curvature of Hc2(T) leads to a significant (up to 10 fold) enhancement of Hc2 observed on dirty MgB2 films and bulk samples, for which Hc2(0) already exceeds Hc2 of Nb3Sn. The theory explains recent high field transport measurements done by the UW-PSU-ASU-U.Genova groups on C-doped and irradiated MgB2 films, for which Hc2(0) along the ab planes may approach the weak coupling BCS paramagnetic limit of 64 -73 Tesla. Features of the paramagnetic limit in dirty two-gap superconductors are discussed.
10:00 AM - HH6.2
Carbon Nanotube Doping Effect on Superconducting Properties of MgB2.
Adriana Serquis 1 , German Serrano 1 , Leonardo Civale 2 , Boris Maiorov 2 , Jack Kennison 2 , Marcelo Jaime 2 , Fedor Balakirev 2 Show Abstract
1 Temadi, CONICET - Centro Atomico Bariloche, S. C. de Bariloche Argentina, 2 Materials Science and Technology, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
10:15 AM - HH6.3
Dependence of Uptake and Homogeneity of Carbon on Mg(B,C)2 Synthesis Conditions.
Lance Cooley 1 , Antonio Zambano 1 2 , Arnold Moodenbaugh 1 Show Abstract
1 Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York, United States, 2 Materials Science and Engineering and Center for Superconductivity Research, University of Maryland, College Park, Maryland, United States
10:30 AM - HH6.4
Mechanisms of MgB2 formation by reaction of solid B with liquid Mg
John DeFouw 1 , John Quintana 2 , David Dunand 1 Show Abstract
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States, 2 Advanced Photon Source, Argonne National Lab, Argonne, Illinois, United States
MgB2 synthesis by reaction of solid B with liquid Mg is studied for the case where excess Mg is used, thus providing a metallic matrix upon solidification after the end of the synthesis. The Mg+2B=MgB2 reaction kinetics were studied in-situ using synchrotron x-ray diffraction, and the microstructure of the phases formed during the reaction was examined using secondary ion mass spectrometry, showing intermediate phase formation, reaction layer thicknesses, phase morphology and cracks, the latter resulting from the volume expansion associated with MgB2 formation. Doping MgB2 with carbon has become technologically important for the high field applications of MgB2. Reaction kinetics were found to slow dramatically for boron fibers doped with carbon but were not significantly changed when reacting doped powders. Other factors influencing kinetics are discussed, including internal stresses, boron purity, size and shape (cylindrical fibers vs. irregular polygonal powders) and cracks.
11:15 AM - **HH6.5
MgB2 Thin Films by HPCVD for High Field and Electronic Applications.
Xiaoxing Xi 1 Show Abstract
1 , Penn State University, University Park, Pennsylvania, United States
11:45 AM - HH6.6
Nanoscale Structure and Chemistry in SiC–Doped MgB2 Tapes
Ye Zhu 1 , Akiyoshi Matsumoto 2 3 , David Larbalestier 1 2 , Paul Voyles 1 Show Abstract
1 Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 Applied Superconductivity Center, University of Wisconsin-Madison, Madison, Wisconsin, United States, 3 , National Institute for Materials Science, Tsukuba, Ibaraki, Japan
Large–scale superconducting magnet applications of MgB2 require long lengths of conductor with high critical current density (Jc) and upper critical magnetic field (Hc2). We have characterized SiC–doped MgB2/Fe tapes fabricated by in situ reaction powder–in–tube process using MgH2, B, and nanoscale–SiC powder mixtures as a function of SiC content from 0 to 10 mol. % and heat treatment temperature from 600 to 900 C. Tc and connectivity increase, while resistivity ρ(40K) decreases with increasing heat treatment temperature and decreasing SiC content. With the highest resistivity among all samples, the 600 C 10% doped sample exhibits excellent Jc at high magnetic fields (Jc(4.2K)∼104 A/cm2 at 10 T) and Hc2 reaches 42 T at 2.3K. We have characterized the nanoscale structure and chemistry of these tapes using bright–field and dark–field TEM imaging, Z–contrast STEM imaging, and EELS and EDS microanalysis in the STEM. The MgB2 grains in all these samples are quite small (<100 nm), although the samples processed at 900 C have more large grains. Adding SiC leads to smaller grains at 900 C, possibly because second phases inhibit grain growth. Z–contrast imaging shows significant contrast variation at a length scale of ∼10 nm, suggesting a high density of impurity phases which could act as pinning centers. In the pure samples, we find MgO, despite the reducing MgH2 precursor. In the SiC–containing samples, we find a higher concentration of O, and phases including Mg2Si and various Si–O–C phases. The 600 C sample contains significant unreacted SiC, but the 900 C sample contains much less. The C concentration inside MgB2 grains is <5 at.% from EELS, consistent with the lattice parameters measured by XRD. Taken together, these results suggest a more complicated role for SiC that just as a source of C in the MgB2 lattice. Detailed correlations between the microstructural and electromagnetic results will be presented.This work is supported by the FRG on MgB2 through the US National Science Foundation (DMR–0514592).
12:00 PM - HH6.7
Numerical Modeling of Superconductivity Phase Transition using Anisotropic Effective Medium Theory.
Enis Tuncer 1 , David Christen 1 Show Abstract
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
The superconductivity phase transition in polycrystalline, anisotropic materials, e.g.MgB2, show a broad resistance transition region in its temperature dependence due to the orientation of the grains. In thin-films of these superconductors, the grain size in the lateral dimensions is comparable to the thickness of the sample (two-dimensional), and the grains are oriented randomly. To have a better understanding of the superconductivity transition and resistance broadening in the transition, we study the influence of the micro-structure, random orientation of the grains, on the superconducting phase transition in the two-dimensions. In order to achieve this, we adopt a critical magnetic field-temperature (H-T) phase diagram and a variation of resistance with orientation of the applied field (R-H dependence) using the effective mass anisotropic dependence Hc2 on crystal orientation. The effective medium approximation is employed to calculate the direct-current resistance of the considered polycrystalline system. In this approximation the grain sizes are much smaller than the wavelength of the applied field, therefore the mixture of normal and superconductor states can be approximated as an effective medium. The Laplace equation for the electrical potential (Ohm's law) is solved by utilizing the finite element method on a square lattice with grains as square tiles. The resistance of the system is calculated from the current at one of the applied potential boundaries. The orientation of the grains are picked at random, and the H-T phase diagram and R-H dependences are used to assign the tile states, normal or superconducting. Several different sets of grain orientations are assumed by implementing a Monte Carlo procedure. We compare our numerical results with the observed superconducting phase transition of MgB2. Finally, the size of the lattice is varied to show the finite-size effects in the numerical model.
12:15 PM - HH6.8
A Simple High-yield Synthesis of Pure MgB2 Superconducting Nanowires.
Bruce Parkinson 1 , Manashi Nath 1 Show Abstract
1 Department of Chemistry, Colorado State University, Fort Collins, Colorado, United States
Magnesium boride (MgB2) has been an interesting material for study ever since the discovery of superconductivity in this compound. Several researchers have tried to synthesize nano-structures of this material mostly by solid-state synthesis methods or slight variations thereof. We have been successful in synthesizing MgB2 nanowires and some unusual open nanostructures by a combination of simple sol-gel chemistry and pyrolysis. The starting reactants are ethanolic solutions of MgBr2 and NaBH4 that upon mixing form a gel when left open to the atmosphere for several hours. Adding a small amount of cetyltrimethyl ammonium bromide (CTAB) in the ethanolic solution speeds up the gel formation. Nanowires can be prepared either by heating the thickened gel under an atmosphere of N2 and diborane (B2H6) gas or by loading the gel into the pores of an alumina membrane before pyrolysis. The scanning electron microscopy shows a high yield of the nanowires. The product morphology differs depending on the pre-pyrolysis treatment of the gel. While the black powder, obtained by heating the as-formed gel, is composed of a mesh of nanowires, the product obtained when the gel is heated in the alumina membranes shows unusual open nanostructures in addition to the nanowires. The diameter of the MgB2 nanowires obtained from the as-synthesized gel is in the range of 50-100 nm while the length exceeds several micrometers. The MgB2 nano-structures obtained from the synthesis involving alumina membranes are, however, much shorter in length while the diameter varies between 150-400 nm between different structures and different parts of the same structure. These porous structures are thin-walled, generally open at one end, and sometimes show beautiful shapes. The DC susceptibility measurement (performed with a SQUID magnetometer) acquired on an ensemble of the MgB2 nanowires shows a strong Meissner effect indicating the onset of superconductivity at 39K. The rapid drop in the susceptibility at 39 K indicates that the nanowires are chemically quite pure.
12:30 PM - HH6.9
Superconducting Properties Of Mgb2 Electroplating Films On Iron Substrates.
Abe Hideki 1 2 , Shibayama Isao 3 , Takeshi Aoyagi 1 , Motoharu Imai 1 , Hideaki Kitazawa 1 , Kenji Yoshii 4 , Jun Akimitsu 3 Show Abstract
1 , NIMS, Tsukuba, Ibaraki, Japan, 2 , Cornell University, Ithaca, New York, United States, 3 , Aoyama Gakuin University, Sagamihara, Kanagawa, Japan, 4 , JAERI, Mikadzuki, Hyogo, Japan
The superconductive boride, MgB2, is one of the most promising practical superconductive materials because of its high superconducting transition temperature of 39 K and high critical current density (Jc) under magnetic fields. In recent we have developed an electroplating technique of superconducting MgB2 films by electrolysis on a molten mixture of MgCl2, KCl, NaCl and MgB2O4 (Molten Salts Electroplating: MSEP) [*]. MSEP has advantages over the conventional fabrication methods of MgB2 films that superconducting MgB2 films can be prepared on conductive substrates using cost-effective and highly scalable synthetic equipment.We report the superconducting properties of MgB2 electroplating films on iron tape substrates. Electrical transport measurements have shown that Jc of the MgB2 films electroplated to iron substrates reaches Jc = 240,000 A/cm2 at 5 K. The high Jc of the MgB2 electroplating films on iron substrates suggests strongly that MSEP is applicable to the fabrication of practical superconducting MgB2 power lines.[*]...H.Abe, K. Nishida, M. Imai, H. Kitazawa, and K. Yoshii, Appl. Phys. Lett. 85, 6197 (2004).
HH7: GB Properties in HTS Films
Thursday PM, April 20, 2006
Room 2020 (Moscone West)
2:30 PM - **HH7.1
Structure and Properties of Extended Defects in HTCS Films: Interfaces and Grain Boundaries.
Maria Varela 1 , Stephen Pennycook 1 , Robert Klie 2 , Yimei Zhu 2 , Alberto Franceschetti 3 1 , Sokrates Pantelides 3 1 , Vanessa Pena 4 , Zouhair Sefrioui 4 , Jacobo Santamaria 4 Show Abstract
1 Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , Brookhaven National Laboratory, Upton, New York, United States, 3 , Vanderbilt University, Nashville, Tennessee, United States, 4 , Universidad Complutense, Madrid, Madrid, Spain
The presence of interfaces and grain boundaries is unavoidable in coated conductors and HTCS based devices, and their role in current transport remains a major scientific and technological issue. The combination of atomic-resolution Z-contrast scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) represents a powerful method to link the atomic and electronic structure of such interfaces to macroscopic properties. Recent developments in aberration correction have pushed the achievable spatial resolution and the sensitivity for imaging and spectroscopy in the STEM into the sub-angstrom regime, allowing us to analyze in great detail the crystal and electronic structures of HTCS materials. This work will present several examples of atomic resolution studies of the relationship between structure, chemistry and electronic properties of YBa2Cu3O7 thin films and interfaces, with complementary density-functional calculations.
3:00 PM - HH7.2
Comparative Study of Grain Orientations and Grain Boundary Networks for YBa2Cu3O7-d Films Deposited by Metalorganic and Pulsed Laser Deposition on Biaxially Textured Ni-W Substrates.
Matt Feldmann 1 , T.G. Holesinger 2 , C. Cantoni 3 , R. Feenstra 3 , D.C. Larbalestier 1 Show Abstract
1 , University of Wisconsin, Madison, Wisconsin, United States, 2 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
We report a detailed study of the grain orientations and grain boundary (GB) networks in YBa2Cu3O7-d (YBCO) films ~0.8 microns thick grown by both the in-situ pulsed laser deposition (PLD) process and the ex-situ metalorganic deposition (MOD) process on rolling-assisted biaxially textured substrates (RABiTS). In the MOD-processed sample [full-width critical current density Jc(0 T, 77 K) = 3.4 MA/cm2], we observed an improvement in both the in-plane and out-of-plane alignment of the YBCO relative to the template that resulted in a significant reduction of the total grain boundary misorientation angles. YBCO GBs were observed to meander extensively about their corresponding template GBs and through the thickness of the film. In contrast, the PLD-processed film [full width Jc(0 T, 77 K) = 0.9 MA/cm2] exhibited nearly perfect epitaxy, replicating the substrate grain orientations and GB network, including the values of the misorientation angles of the GBs. The PLD and MOD-processed films were deposited on similarly processed templates, and the distribution of total GB misorientation angles in the template was very similar for both samples. Direct transport measurement of the intra-grain Jc(0 T, 77 K) values of PLD and MOD-processed films on RABiTS revealed values up to 4.5 MA/cm2 and 5.1 MA/cm2 respectively. While intra-grain Jc values were very similar, the significantly higher full-width Jc for the MOD-processed YBCO film is believed to be due to the improved grain alignment and extensive GB meandering.
3:15 PM - HH7.3
Grain Boundaries in REBaCuO (RE=Er,Y,Yb) Ca-doped YBaCuO thin films: Mechanisms of Current Suppression and Current Enhancement.
Christian Jooss 1 , Eva Brinkmeier 1 , Karsten Guth 1 , Yimei Zhu 2 , Felip Sandiumenge 3 Show Abstract
1 Institute of Materials physics, University of Goettingen, Goettingen Germany, 2 , Brookhaven National Laboratory, Upton NY, New York, United States, 3 Institut de Ciencia de Materials de Barcelona CSIC, Universitat Autonoma de Barcelona, Bellaterra Spain
Recent results on low-angle grain boundaries in high-temperature superconductors give fascinating insight into their interplay of atomic structure, electronic properties and transport properties [1-3]. It was shown that Ca doping can reduce atomic strain and the related size of space charge layers and therefore can significantly improve the transport properties in a wide angular range. However, our experimental data suggests that this mechanism does not work for all types of grain boundaries. Furthermore, we present experiments on ErBaCuO and YbBaCuO bi-crystalline films, where charge balance arguments suggests an increased hole density in the electronic conduction bands and, in the framework of specific models, an increased critical current density. The different types of experiments will be summarized to determine the atomic mechanism determining the grain boundary transport properties. Furthermore, we will demonstrate experimentally the significant difference of mechanisms that determine the "intrinsic" depairing current density of a grain boundary and "extrinsic properties" like flux pinning for understanding their transport properties.  R. F. Klie, J. P. Buban, M. Varela, A. Franceschetti, C. Jooss, Y. Zhu, N. D. Browning, S. T. Pantelides, S. J. Pennycook, Nature, 435 (2005) 475.  M. A. Schofield, M. Beleggia, Y. Zhu, K. Guth, Ch. Jooss, Phys. Rev. Lett. 92 (2004) 195502 Ch. Jooss, E. Brinkmeier, H. Heese, Phys. Rev. B, accepted.
3:30 PM - HH7.4
Weak Thickness Dependence of the Critical Current Density in Strong Pinning Ex Situ Metal-organic-deposition Route YBa2Cu3O7-x Coated Conductors.
Sang-il Kim 1 , D. M. Feldmann 1 , Alex Gurevich 1 , Xueyan Song 1 , X. Li 2 , W. Zhang 2 , T. Kodenkandath 2 , M. W. Rupich 2 , T. G. Holesinger 3 , David Larbalestier 1 Show Abstract
1 Applied Superconductivity Center, University of Wisconsin - Madison, Madison, Wisconsin, United States, 2 , American Superconductor Corp., Westborough, Massachusetts, United States, 3 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
4:15 PM - **HH7.5
A New Dimension in Coordinated Characterization: Three Dimensional Characterization of Microstructure in High Temperature Superconductors
Dean Miller 1 , Jon Hiller 1 Show Abstract
1 , Argonne National Laboratory, Argonne, Illinois, United States
Characterization of microstructure in three dimensions offers many advantages over analysis based on more traditional 2-D imaging, providing, for example, measurement of phase distribution, volume fractions, and interfacial area that can profoundly influence properties in high temperature superconducting materials. A variety of approaches have been developed to provide this information, but the advent of focused ion beam (FIB) techniques, especially associated with dual ion- and electron-beam instruments, has greatly facilitated such 3-D characterization that can provide useful information at length scales between that of TEM and x-ray-based techniques. In this work we have used FIB-based approaches to characterize the microstructure of high temperature superconducting tapes in three dimensions. 3-D visualization can often provide a unique, albeit qualitative, perspective of microstructure beyond that offered from a single 2-D image. 3-D reconstruction advances visualization into a quantitative regime and provides a useful way to visualize important microstructural characteristics. One key to such reconstruction is reliable, high quality volumetric data collection that can be interrogated to provide such 3-D information. The specific approach to data collection and analysis may vary depending on the microstructural features of interest, and various approaches will be presented using our work on high temperature superconducting tapes as examples.This work was supported by the U. S. Department of Energy, Offices of Science and of Electric Transmission and Distribution, under Contract W-31-109-ENG-38.
4:45 PM - **HH7.6
Pinning of Grain Boundary Vortices: A key Issue to Enhance the Critical Current Density of YBCO Coated Conductors.
Teresa Puig 1 , Anna Palau 1 , Joffre Gutierrez 1 , Xavier Obradors 1 , Francisco De la Cruz 2 Show Abstract
1 Institut de Ciencia de Materials de Barcelona, CSIC, Bellaterra Spain, 2 Instituto Balseiro and Centro Atomico Bariloche, CNEA, San Carlos de Bariloche Argentina
Coated conductors have emerged as a promising fabrication route of long-length, flexible superconducting YBCO tapes and complex processing techniques based on replicating the texture of a buffered metallic substrate into the superconducting layer have been developed accordingly. Therefore, a coated conductor can be considered as a superconducting network of low-angle grain-boundaries (GB) through which a percolative current flows, separating superconducting grains. In order to understand the physical mechanisms governing the critical current density (Jc) of coated conductors we must analyze deeply the physics of GB vortices (Abrikosov-Josephson vortices), their pinning capabilities within the GB and their interaction with the Abrikosov vortices (AV) of the grains. .By analyzing the magnetic field dependence of the critical current density of several YBCO coated conductors, we have built up a general magnetic phase diagram where three different AJV motion regimes have been identified depending on the balance between the GB pinning force and the AJV-AV interaction force. This work was motivated by the results obtained in coated conductors of different thickness where a clear correlation between the grain and GB vortices was obtained at low magnetic fields*, as determined by the inductive dc-magnetometry methodology developed in the group. Furthermore, angular dependent critical current density measurements performed at several temperatures and magnetic fields have enabled us to separate and even model the temperature and magnetic field dependence of the random pinning and correlated pinning contributions of Jc. All this knowledge is being now applied to nanostructured coated conductors where artificial pinning centers are introduced. We will present the approaches we are using by chemical solution deposition to generate an artificial network of pinning centers in YBCO films grown by the trifluor-acetate route. * A. Palau, T. Puig, X. Obradors, R. Feenstra, submitted to APL
5:15 PM - HH7.7
Improving Jc of Coated Conductors by High Aspect Ratio Grains and RE123 Based Quasi-multilayers.
Bernhard Holzapfel 1 , Chuanbing Cai 1 , Joerg Eickemeyer 1 , Jens Haenisch 1 , Ruben Huehne 1 , Dietmar Selbmann 1 , Ludwig Schultz 1 Show Abstract
1 , IFW Dresden, Dresden Germany
5:30 PM - HH7.8
Magnetotransport And Flux Pinning Characteristics In High Quality NdBa2Cu3O7-y Thin Films Grown By Tri-Phase Epitaxy.
KyungSung Yun 1 , Shunichi Arisawa 1 , Akira Ishii 1 , Yoshihiko Takano 1 , Takeshi Hatano 1 , Masashi Kawasaki 2 1 , Hideomi Koinuma 1 Show Abstract
1 Nanomaterials Laboratory, National Institute for Materials Science, Tsukuba Japan, 2 Institute for Materials Research, Tohoku University, Sendai Japan
We have proposed and developed the fabrication of single crystalline thin films of REBa2Cu3O7-y (REBCO, RE: rare earth elements) using a novel process of Tri-Phase Epitaxy (TPE). Previously, we reported the successful fabrication of the high-quality crack-free NdBa2Cu3O7-y (NBCO) thin film on SrTiO3/BaTiO3 buffered MgO (100) substrate by TPE and this enhanced endeavor has also realized NBCO grain boundary Josephson junctions (GBJJs) on SrTiO3/BaTiO3 buffered MgO (100) bicrystal substrates. In the present study, we report on the magnetotransport and flux pinning characteristics of high quality NBCO films grown by TPE.The improvement of the critical current density (JC) as well as irreversibility fields (Birr) value, are still important issues. Initial research suggested several possible types of effective pinning source in REBCO films, including low-angle grain boundaries, precipitates, twins, surface roughness, screw dislocations etc. It is well known that the disorders correlated along the c-axis can enhance both the critical current density (JC) and irreversibility fields (Birr) value through the vortex phase transition from the vortex glass to the Bose glass state. Columnar defects and twin boundaries are prime candidates for such c-axis correlated disorders. With an advantage of single crystallinity of NBCO films on various substrates, we can obtain the large domains containing the same orientation of twin planes. The magnetoresistance of single crystalline NBCO films was systematically investigated as a function of magnetic field strength, orientation, and temperature to determine the pinning properties of twin boundaries and to clarify the nature of the NBCO thin film by using submicro-fabrication techniques on these high quality NBCO films.
5:45 PM - HH7.9
The Effect of Twin Spacing and Twin Intersection on Critical Current Densities in Bulk YBa2Cu3O7-x.
Siu-Wai Chan 1 , Manoj Chopra 1 , Linfeng Mei 1 , Vladimir Boyko 1 Show Abstract
1 Dept. of Appl. Physics, Columbia University, New York, New York, United States
We have exploited the positive entropy of the twin boundary energy to refine twin structure in YBa2Cu3O7-x (Y123) which is the matrix phase in melt-textured grown (MTG) Y-Ba-Cu-O (YBCO) pellets. Refinement of twin spacing in MTG pellets is achieved by annealing at higher temperatures. Decrease of twin spacing with increasing temperature is confirmed by electron microscopy. The critical current density (Jc), the pinning force and the magnetic field at maximum pinning-force all increase with increasing annealing temperature of oxygenation. Twin intersections have been identified as possibly better pinning centers because of their geometric circumvention of the anisotropy of flux-pinning by twin boundaries. Preliminary results on pinning by twin intersections will be presented. Conditions for generating twin intersections are examined.
HH8: Poster Session
Friday AM, April 21, 2006
Salons 8-15 (Marriott)
9:00 PM - HH8.1
Chemically Deposited Buffer Layers for YBCO Coated Conductors.
Md Bhuiyan 1 Show Abstract
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
We have developed a chemical solution deposition (CSD) process, to deposit single layer oxide buffer layers on biaxially textured Ni-W (3 at.%) substrates. A new series of rare earth niobate, RE3NbO7 (RE = La, Ce, Nd, Sm, Eu, Gd, Ho, Y, and Yb) and rare earth tantalate RE3TaO7 (RE = La, Ce, Eu, and Gd) buffer layers have been developed for the growth of superconducting YBa2Cu3O7-δ (YBCO) films. Sharper out-of-plane and in-plane textures were achieved for lanthanum-based buffers compared to the underlying texture of the Ni-W substrate. Using CSD, smooth, crack-free and epitaxial RE3NbO7 and RE3TaO7 films were grown on cube textured Ni-W substrate. YBCO films with critical current densities exceeding 1 MA/cm2 at 77 K and self-field were achieved on single layer solution buffers using pulsed laser deposition. This demonstration promises a route for producing low-cost all-solution second generation YBCO coated conductors.
9:00 PM - HH8.10
Investigation of Magnetic Characteristics of YBCO Film with Artificial Pinning Centers on PLD/IBAD Metal Substrate.
Hiroyoshi Kobayashi 1 , Satoru Ishida 1 , Kazuhiro Takahashi 1 , Masaya Konishi 1 , Akira Ibi 1 , Seiki Miyata 1 , Yutaka Yamada 1 , Yu Shiohara 2 , Takeharu Kato 3 , Tsukasa Hirayama 3
1 , ISTEC-SRL Nagoya Coated Conductor Center, Nagoya, Aichi, Japan, 2 , ISTEC-SRL, Tokyo Japan, 3 , JFCC, Nagoya