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Critical Current Density (critical + current_density)
Selected AbstractsInterfacial Strain-Induced Oxygen Disorder as the Cause of Enhanced Critical Current Density in Superconducting Thin FilmsADVANCED FUNCTIONAL MATERIALS, Issue 6 2009Stuart C. Wimbush Abstract To understand the origin of the increase in critical current density of rare earth barium cuprate superconductor thin films with decreasing thickness, a series of sub-300-nm EuBa2Cu3O7,, thin films deposited on SrTiO3 substrates are studied by X-ray diffraction and electrical transport measurements. The out-of-plane crystallographic mosaic tilt and the out-of-plane microstrain both increase with decreasing film thickness. The calculated density of c -axis threading dislocations matches the extent of the observed low-field enhancement in critical current density for fields applied parallel to c. The in-plane mosaic twist and in-plane microstrain are both around twice the magnitude of the out-of-plane values, and both increase with decreasing film thickness. The results are consistent with the observed stronger field enhancement in critical current density for fields applied parallel to ab. The lattice parameter variation with thickness is not as expected from consideration of the biaxial strain with the substrate, indicative of in-plane microstrain accommodation by oxygen disorder. Collectively, the results point to an enhancement of critical current by interfacial strain induced oxygen disorder which is greatest closest to the film-substrate interface. The findings of this study have important implications for other thin functional oxide perovskite films and nanostructures where surface and interfacial strains dominate the properties. [source] Progress in Nanoengineered Microstructures for Tunable High-Current, High-Temperature Superconducting Wires,ADVANCED MATERIALS, Issue 3 2008G. Holesinger Abstract High critical current densities (Jc) in thick films of the Y1Ba2Cu3O7,, (YBCO, Tc , 92 K) superconductor directly depend upon the types of nanoscale defects and their densities within the films. A major challenge for developing a viable wire technology is to introduce nanoscale defect structures into the YBCO grains of the thick film suitable for flux pinning and the tailoring of the superconducting properties to specific, application-dependent, temperature and magnetic field conditions. Concurrently, the YBCO film needs to be integrated into a macroscopically defect-free conductor in which the grain-to-grain connectivity maintains levels of inter-grain Jc that are comparable to the intra-grain Jc. That is, high critical current (Ic) YBCO coated conductors must contain engineered inhomogeneities on the nanoscale, while being homogeneous on the macroscale. An analysis is presented of the advances in high-performance YBCO coated-conductors using chemical solution deposition (CSD) based on metal trifluoroacetates and the subsequent processing to nano-engineer the microstructure for tuneable superconducting wires. Multi-scale structural, chemical, and electrical investigations of the CSD film processes, thick film development, key microstructural features, and wire properties are presented. Prospects for further development of much higher Ic wires for large-scale, commercial application are discussed within the context of these recent advances. [source] Interfacial Strain-Induced Oxygen Disorder as the Cause of Enhanced Critical Current Density in Superconducting Thin FilmsADVANCED FUNCTIONAL MATERIALS, Issue 6 2009Stuart C. Wimbush Abstract To understand the origin of the increase in critical current density of rare earth barium cuprate superconductor thin films with decreasing thickness, a series of sub-300-nm EuBa2Cu3O7,, thin films deposited on SrTiO3 substrates are studied by X-ray diffraction and electrical transport measurements. The out-of-plane crystallographic mosaic tilt and the out-of-plane microstrain both increase with decreasing film thickness. The calculated density of c -axis threading dislocations matches the extent of the observed low-field enhancement in critical current density for fields applied parallel to c. The in-plane mosaic twist and in-plane microstrain are both around twice the magnitude of the out-of-plane values, and both increase with decreasing film thickness. The results are consistent with the observed stronger field enhancement in critical current density for fields applied parallel to ab. The lattice parameter variation with thickness is not as expected from consideration of the biaxial strain with the substrate, indicative of in-plane microstrain accommodation by oxygen disorder. Collectively, the results point to an enhancement of critical current by interfacial strain induced oxygen disorder which is greatest closest to the film-substrate interface. The findings of this study have important implications for other thin functional oxide perovskite films and nanostructures where surface and interfacial strains dominate the properties. [source] Influences of passivating elements on the corrosion and biocompatibility of super stainless steelsJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2008Young-Ran Yoo Abstract Biometals need high corrosion resistance since metallic implants in the body should be biocompatible and metal ion release should be minimized. In this work, we designed three kinds of super stainless steel and adjusted the alloying elements to obtain different microstructures. Super stainless steels contain larger amounts of Cr, Mo, W, and N than commercial alloys. These elements play a very important role in localized corrosion and, thus, their effects can be represented by the "pitting resistance equivalent number (PREN)." This work focused on the behavior which can arise when the bare surface of an implant in the body is exposed during walking, heavy exercise, and so on. Among the experimental alloys examined herein, Alloy Al and 316L stainless steels were mildly cytotoxic, whereas the other super austenitic, duplex, and ferritic stainless steels were noncytotoxic. This behavior is primarily related to the passive current and pitting resistance of the alloys. When the PREN value was increased, the passivation behavior in simulated body solution was totally different from that in acidic chloride solution and, thus, the Cr2O3/Cr(OH)3 and [Metal oxide]/[Metal + Metal oxide] ratios of the passive film in the simulated body solution were larger than those in acidic chloride solution. Also, the critical current density in simulated body solution increased and, thus, active dissolution may induce metal ion release into the body when the PREN value and Ni content are increased. This behavior was closely related to the presence of EDTA in the simulated body solution. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008 [source] Synthesis of bulk MgB2 superconductors by pulsed electric currentAICHE JOURNAL, Issue 7 2006A. M. Locci Abstract A preparation method to simultaneously synthesize and consolidate bulk MgB2 superconductors from Mg and B commercial elemental powders by means of the spark plasma sintering technique is reported. The influence of process parameters on sintering process dynamics as well as product characteristics, determined by transport and magnetic measurements, is investigated. The superconducting properties of the obtained samples, and particularly the critical current density, are comparable or better than those corresponding to other MgB2 preparation techniques. Thus, the superconductive properties of the bulk MgB2 materials synthesized in this work are suitable for selected applications, such as magnetic levitation, magnetic screening, and fault current limiters. It should be finally noted that the proposed method represents a particularly rapid preparation route as compared to other techniques. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] Processing Dependence of Texture, and Critical Properties of YBa2Cu3O7,, Films on RABiTS Substrates by a Non-Fluorine MOD MethodJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2006Y. Xu YBa2Cu3O7,, (YBCO or Y123) films on rolling-assisted biaxially textured substrates (RABiTS) were prepared via a fluorine-free metallorganic deposition (MOD) through spin coating, burnout, and high temperature anneal. The effects of substrate texture and surface energy of the CeO2 cap layer were investigated. Except for the commonly accepted key factors, such as the textures of substrate and buffer layers, we found some other factors, for example, the deposition temperature of the cap layer, are also critical to the epitaxial growth of Y123 phase. With the CeO2 cap layer deposited at relative high temperature of 700°C, a critical current density, Jc, over 1 MA/cm2 has been demonstrated for the first time on Ni-RABiTS by a fluorine-free MOD method. Whereas for samples with CeO2 cap layers deposited at a lower temperature of 600°C, even though XRD data showed a better texture on these buffer layers, texture degradations of YBCO grains under the optimized processing conditions were observed and a lower oxygen partial pressure around 40 ppm was necessary for the epitaxial growth of Y123 phase. As a result, Jc fell to 0.45 MA/cm2 at 77 K. The observed phenomena points to the change of surface energy and reactivity of the CeO2 cap layer with respect to the CeO2 deposition temperature. In this paper, the YBCO phase diagram was also summarized. [source] RE (RE = Sm, Eu, Gd)-doped CeO2 single buffer layers for coated conductors prepared by chemical solution depositionPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2009Ruiping Sun Abstract Textured RE (RE = Sm, Eu, Gd)-doped CeO2 single buffer layers for coated conductors were prepared by a polymer assisted chemical solution deposition (PACSD) approach. The as-grown buffer layers on biaxially textured NiW(5%) alloy tapes were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) as well as atomic force microscopy (AFM). The thicknesses of these buffer layers have been determined to be over 150 nm, on which a YBCO film has been deposited with an onset transition temperature above 90 K and a critical current density of 1 MA cm,2. These results indicate that RE doping can increase the critical thickness of CeO2 and PACSD may be a cost-effective way to deposit CeO2. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Fishtail effect in twinned and detwinned YBCO single crystalsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2006M. Boudissa Abstract We have studied the magnetization hysteresis loops of a twinned and detwinned single crystals in a temperature range between 4.2 and 100 K and a magnetic field (H) range between 0 and 6 T. We carried out relaxation measurements on the samples at different temperatures and magnetic fields. We investigated the twin pinning as a function of temperature (T) and the fishtail anomaly in the critical current density of the two samples. We tried in this study to confirm or infirm the different models which explain the fishtail effect by confronting them to our experimental results We found that the collective creep theory is consistent with the results of our experiment in the field region where the magnetization is at its minimum. This field marks a crossover between the small and large bundle pinning regimes. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Critical current of Nb and NbN thin-film structures: The cross-section dependencePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2005K. Il'in Abstract We present results of a systematic study of the critical current in superconducting Nb and NbN thin film bridges. The bridges with a width from 50 nm to 10 µm were patterned from thin superconducting films by means of electron-beam lithography and ion milling. For both materials the nominal critical current density extrapolated to zero temperature varied with the bridge width and thickness. We attribute these variations to a fabrication-enhanced reduction of the effective, superconducting cross-section of the bridges with respect to their geometric cross-section and to an uneven distribution of the super-current over the superconducting core of the bridge. In very thin bridges, i.e. 5 nm and 8 nm for NbN and Nb, respectively, the nominal current density increased drastically when the bridge width became smaller than 500 nm. We associate the enhancement of the critical current density in narrow bridges with the crossover from depinning of magnetic vortices to either their nucleation or breaking of Cooper pairs. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||