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Here we discuss the preparation and characterization of YBa2Cu3O7-δ high temperature superconductor through standard solid state reaction route and added with different (x = 0.0, 0.1, 0.3, 0.5, & 0.7) wt. % of graphene oxide (GO). The phase purity and surface morphology of the composite samples were examined through the X-ray powder diffraction and Field emission scanning electron microscopy respectively. The self field transport measurement and electric field versus current density measurement confirms the occurrence of superconductivity in the composite materials. The maximum value of critical temperature is found to be 96.42 K for 0.7 wt. % GO added sample. Similarly, the maximum value of critical current density is observed to be 412.92 A/cm² for 0.7 wt. % GO added sample at 77K. This may be attributed to enhancement in superconducting volume fraction of the sample, as GO resides near the grain boundary region to increase the weak link between the superconducting grains. [ABSTRACT FROM AUTHOR]

Y123 (YBa2Cu3O7-δ) cylinders were fabricated by Melt Texture Growth (MTG) technique using two different composites. First composite was prepared by addition of 25 wt% of Yttria and 1 % Pt to pre-reacted Y123, and the second composite was prepared by addition of 25 wt% of Yttria and 1wt % Ceria to pre-reacted Y-123. Cylinder shaped green compacts of both the composite were fabricated by pressing in cold isostatic press. These green compacts were sintered at 930oC before subjecting to MTG technique. The MTG cylinders were characterized by Scanning Electron Microscope (SEM), Electron Probe Micro Analysis (EPMA) and then correlated with electrical properties like Critical current density (Jc). [ABSTRACT FROM AUTHOR]

The effects of nano-sized Co0.5Ni0.5Fe2O4 addition on the superconducting and transport properties of Bi1.6Pb0.4Sr2Ca2Cu3O10 (Bi-2223) in bulk form has been investigated. Bi-2223 superconductor was fabricated using coprecipitation method and 0.01 - 0.05 wt% of Co0.5Ni0.5Fe2O4 nanoparticles with average size of 20 nm were added into the samples. The critical temperature (Tc) and critical current density (Jc) of the samples were measured by using the four-point probe method, while the phase formation and microstructure of the samples were examined using x-ray diffraction and SEM respectively. It was found that Jc of all samples added with Co0.5Ni0.5Fe2O4 were higher than nonadded sample, with x = 0.01 wt. % sample showing the highest Jc. This study showed that small addition of nano-Co0.5Ni0.5Fe2O4 can effectively enhance the transport critical current density in Bi-2223 superconductor. [ABSTRACT FROM AUTHOR]

When a magnetic field is applied to type II superconductors, such as YBa2Cu3O7-d (YBCO), the flux quanta penetrate the material as a regular array of vortices. However when transport currents are applied, they act to move these vortices, thus lowers the critical current density (Jc) as well as destroying superconductivity. The development of microstructures made of YBCO materials has enabled engineers to increase the critical current density, within Type II materials by introducing flux pinning centres into the material. The microstructure and flux pinning properties of YBa2Cu3O7-d system with varying levels (0-5 wt. %) of a nano perovskite ceramic insulator; YBa2HfO5.5 addition was studied in detail. Orthorhombic YBa2Cu3O7-d powder was prepared through conventional solid state route and a modified combustion method was used for synthesizing nanocrystalline YBa2HfO5.5. The structure and microstructure of the samples examined by X-ray diffraction and scanning electron microscopy showed that YBa2HfO5.5 and YBCO remained unreacted even at higher processing temperature without deteriorating the superconducting properties. The scanning electron microscope image shows that YBa2HfO5.5 forms an electrical-network between grains. These observations suggest that the YBa2HfO5.5 addition to the Y-123-compounds improve the electrical connection between superconducting grains and substantial improvements in the relative electrical transport properties of the composites. The variation of sintering temperature, density, critical transition temperature (Tc) and magnetic field dependence of critical current density (Jc) of YBa2Cu3O7-d having different proportions of YBa2HfO5.5 in the matrix were also studied in detail. It is found that the addition of these elements considerably enhances the flux pinning strength of the system, and there is also an increase of critical temperature (Tc) and critical current density (Jc) up to an optimum value of 8.76 x104 A/cm² for a concentration of 2 wt % addition of nano YBa2HfO5.5. The enhancement of the critical current density in the YBa2Cu3O7-d - YBa2HfO5.5 samples is attributed to the sustained formation of the insulating and non-reacting YBa2HfO5.5 phase acting as pinning center. The addition of YBa2HfO5.5 in YBa2Cu3O7-d bulk superconductor also enhances the pinning force density from 3 x106 N/m³ to 69.6 x 106N/m³ at 77 K. [ABSTRACT FROM AUTHOR]

It was shown that the current-carrying capacity of a superconducting DC power cable could be dramatically increased using the longitudinal magnetic field effect. That is, the force-free structure was assumed for the conductor in the cable to use a significant enhancement of the critical current density in a parallel magnetic field observed in metallic superconductors. However, the critical current density of present commercial coated conductors decreases slightly with increasing the longitudinal magnetic field. Hence, the fundamental design of the cable must be changed to obtain a higher current-carrying capacity. In spite of a poor critical current density in the longitudinal magnetic field, it is still appreciably higher than that in a transverse magnetic field. A new design is introduced for a superconducting DC power cable suitable for present coated conductors. It is shown that the current-carrying capacity can be remarkably increased from conventional cables. [ABSTRACT FROM AUTHOR]

The effect of nanosized PbO additions on the superconducting properties of (Bi, Pb)-2223(PbO)x (x = 0 - 0.15 wt. %) prepared by the co-precipitation method was studied. The structure and the microstructure of samples were examined by powder XRD and SEM, respectively. The transport critical current density (Jc), onset transition temperature (Jc onset) and zero resistance temperature (Jc zero) were determined by using four-probe method. It was observed that PbO additions enhanced Jc for all added samples. The x = 0.05 wt. % sample showed the highest Jc (19.3 and 11.3 A/cm² at 30 and 77 K, respectively) This study showed that the addition of PbO, as a result of existence of the effective artificial pinning, provided extra flux pinning centers in the (Bi, Pb)-2223 superconductor. [ABSTRACT FROM AUTHOR]

Effect of SiC, as carbon source doping, by diffusion method on the lattice parameter, critical temperature (Tc) and critical current density (Jc) has been studied. The broadening of full width at half maximum (FWHM) values in XRD patterns with increasing of the doping level indicates smaller grains and imperfect MgB2 crystallinity, whereas the carbon substitution into the boron site was confirmed by the shrinkage of the lattice parameter a. Despite of lower Tc's, Jcs of the doped samples are higher than the undoped sample over 4 T at 20 K and over 7 T at 5 K, respectively. MgB2 with the 10 % of SiC doping showed the highest Jc with the value of 105 A/cm2 at 5 K and 4 T while the 2.5% SiC doped sample showed 7 factor of Jc enhancement compared to pristine sample at 20 K and 4.5 T. Jc enhancement by different doping level at respective temperature suggests, impurities such as Mg2Si, MgB2C2 and MgO play a significant role in 20 K while carbon substitution effect dominances the flux pinning in 5 K. Our results also demonstrate that flux pinning and the Jc can be tailored for various applications depending on the operating temperature and external magnetic field. [ABSTRACT FROM PUBLISHER]

The effects of sintering temperature on the superconducting properties of Ti-sheathed MgB2 wires have been studied. The wires were fabricated by in situ powder-in-tube (PIT) method and characterized by x-ray diffraction, magnetization, scanning electron microscopy and transport measurements. Samples were sintered for 30 minutes at the following temperatures: 650° C, 700° C, 750° C, 800° C, and 850° C. It is found that the cores of these wires are almost in pure MgB2 superconducting phase, indicating that the Ti-sheath does not react with Mg or B. The superconducting transition temperature Tc decreases from 36 K to 34.2 K with the decrease of the sintering temperature from 850° C to 650° C. At 5 K and 20 K, critical current density Jc peaks up for samples sintered at 800° C, which is in sharp contrast with previously reported result that for Fe-sheathed MgB2 wires, Jc peaks up at sintering temperature of 650° C. [ABSTRACT FROM AUTHOR]

A15 stoichiometry was investigated and compared for two different Nb3Sn strand designs, “tube type” and high-performance, distributed-barrier RIT type. The focus of the study was to attain fine grain A15 with maximal Sn stoichiometry. Tube type conductors were compared to RIT conductors, each after the application of two-step HTs with plateaus ranging from 615° C to 675° C for various times. The resulting transport values were compared to those arising from standard HTs, namely 3476 A/mm2 for the RIT conductors and 2231 A/mm2 for the tube type conductors. The influence of strand geometry and reaction route was related to the resulting A15 stoichiometries. Short sections of strand were encapsulated and then HT, after which SEM (BSE) and EDS were used to observe the structures and obtain Sn concentration profiles. Fractography was performed to investigate the effect of a two-step reaction on the morphology, the ratio of coarse/fine grain area and grain size of fine grain A15. [ABSTRACT FROM AUTHOR]

Fe-sheathed MgB2 wires doped with C and TiC nanoparticles in the formula MgB2-xCx+yTiC (x = 0, 0.05, 0.1, 0.15, 0.2, and y = 0, 2.5 wt.%, 5 wt.%) were investigated. X-ray diffraction patterns indicate that the core materials in the wires contain small amount of Fe2B and MgO impurity phases, and the peaks shift with the variation of doping amount. It is found that the critical temperature Tc decreases with the increase of doping amount. Strong in-field current carrying capability enhancement was observed on MgB1.95C0.05+2.5 wt.% TiC. [ABSTRACT FROM AUTHOR]

One of the main requirements for ITER Nb3Sn Toroidal Field (TF) conductor is a temperature margin of 0.7 K under 11.8 T peak field, 68 kA operating current, and operating temperature of 5 K, i.e. current sharing temperature Tcs = 5.7 K, while the performance of Nb3Sn strands used for the fabrication of the conductor is evaluated by critical current density Jc(4.2 K, 12 T). This work represents an analysis of experimentally revealed correlation between Jc(4.2 K, 12 T) and Tcs of several Nb3Sn strands and short sample of the TF conductor RFTF2 tested in SULTAN facility (SULTAN sample). The performance of the strands used for SULTAN sample fabrication is investigated in details. The paper includes the analysis of voltage-current and voltage-temperature characteristics. An assessment of strain influence on the performance and transition parameters (n and T0) of the strands is also presented. The results obtained for strands are compared with the test results of SULTAN sample RFTF2. [ABSTRACT FROM AUTHOR]

YBa2Cu3O7-x (YBCO)+BaSnO3 (BSO) thin films with BSO nanocolumns have been shown to have improved critical current density (Jc) in applied magnetic fields. Previously, a sectored target was used to grow thick (>2.5 μm) YBCO+BSO films. In the present study, a premixed YBCO+BSO (20 mol%) target was used to grow thick films (>3 μm) to determine if similar high quality thick films can be obtained as with the sectored target approach. In the case of the premixed target, BSO material is continuously supplied as opposed to the sectored target method. YBCO+BSO thick film samples processed using a premixed target were also found to have high Jc at high fields with Jc>104 A/cm2 at 8 T at 77 K, whereas typical YBCO films carry only 102 A/cm2. Transmission electron microscopy (TEM) on these films indicated that BSO nanocolumns with a diameter of ∼8–11 nm extend through the thickness of the films. The critical transition temperature (Tc) for the films was found to be ∼87 K, regardless of thickness. [ABSTRACT FROM AUTHOR]

Understanding the real mechanism responsible for achieving high transport critical current density (Jc) in the high temperature (high-Tc) cuprate superconductors has been one of the primary goal. The only promising way is to tailor the high-Tc cuprate material during preparation stage incorporating suitable non-superconducting particles within superconducting matrix, which are known to serve as effective pining centers. Incorporation of non-superconducting particle like silver with dimension down to micron/submicron size in the superconducting matrix is very stable and form a homogenous solid solution matrix, which has got the better stability on aging and found to be effective in enhancing flux pining in high-Tc superconducting system. In this paper, studies have been made to investigate and review the effect of non-superconducting micron size Ag particle in to the matrix of RE-Ba-Cu-O (RE = Sm, Gd & Y) 123 high-Tc ceramic superconducting system. XRD, SEM, magnetization, magnetotransport and microwave induce DC voltage measurements were carried out to study the effect of Ag into 123-superconducting system. It is observed that controlled addition of Ag into Sm-Ba-Cu-O (SBCO), Gd-Ba-Cu-O (GBCO) and Y-Ba-Cu-O (YBCO) ceramic superconductor do not react with the decomposed phases but remains in the metallic form. This brings about a lowering of the normal-state resistivity. The increase of magnetic critical current density (Jmc), transport critical current density (Jtc), and, hence pinning force density (Fp) with Ag addition into above three systems suggest the creation of an SNS-type proximity junction at the intergranular region and stronger Josephson current paths between the superconducting intergrains. This is attributed to the physical densification and consequent reduction of the total number of weak links by Ag addition into the above mentioned ceramic superconducting system. [ABSTRACT FROM AUTHOR]

Ultrafine precursor powder of YBa2Cu3O7-δ was prepared via co-precipitation method. Synthesis route is developed by saturated solution of metal acetates and 2-isopropanol solution of oxalic acid. The thermal treatment (24 hrs calcinations at 920 °C, 24 hrs sintering at 920 °C) gives a superconductor YBa2Cu3O7-δ with a transition temperature at 90 K. These ultrafine powders can be useful in wide application especially in fabricating high temperature superconductor tape. [ABSTRACT FROM AUTHOR]

For the first time, molecular dynamic simulations based on dense nanostructured periodic arrays of pinning sites were carried out. The variables in the simulations were the vortex density, the temperature, the pinning strength, the size of pinning sites. An interesting dip was found to occur in the critical current density but only at zero temperature and for specific values of pinning strength. The properties of the dip were found to depend strongly on the initial positions of the vortices with respect to the positions of the pinning sites. The occurrence of the dip is attributed to the formation of one dimensional linear channels of moving vortices in the direction of the applied current. The pinning strength was also found to have an important role in determining the relative depth of the dip. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Cycled applied field magnetization curves contain a wealth of information on critical current density and flux pinning that is not commonly exploited. Detailed magnetization data for magnesium boride wire cores have been analyzed for critical state model consistency. The iron-sheathed silicon nitride doped magnesium boride wires were prepared from pure magnesium and boron powders with nano-scale silicon nitride additions (MgB2-x(Si3N4)x/7 with x = 0 – 0.4). A subsequent short annealing heat treatment, 800 degrees C and of 1 hour duration in Argon, was applied to create the desired phase. Magnetization critical current densities were up to ∼340 kA/cm2 at 5K and 1T. Major and minor loop analysis will be described, for field sweeps up to 3 tesla at fixed temperatures and for temperature sweeps from 5K to 45K in fixed fields, with respect to parameters describing the critical state model. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper reports on the fabrication and testing of a MgB2 coil made using a wind & react method. We made a 130m-long Fe/Cu-composite sheathed, SiC-doped MgB2-superconducting round wire using an in-situ PIT method. Using a 92m-long wire, we fabricated a solenoid coil with 722 turns. In the coil test, we measured the Ic of the coil under various external fields and temperatures. The Ic of the coil reached 162 A (Je = 340 A/mm2) at 4.2 K and in the external field of 2 T. The coil generated 2.2 T (the center magnetic field, Bo); thus the total field reached 4.2 T. The Je exceeded 100 A/mm2 in the external fields of 4 T, 2.5 T, and 1 T at 15 K, 20 K, and 25 K, respectively. The Jc of the coil was almost equal to that of the short sample. This indicates that the 92m-long wire has a very homogeneous Jc distribution. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Multifilament Nb3Sn superconductor has been produced by the internal-tin-tube approach. In this method tubular niobium filaments containing either solid or powder cores of high tin content are processed into multifilament conductors containing filament diameters as small as 30 μm. The recent emphasis has been on incorporating Nb-7.5Ta filaments in an effort to raise the upper critical field and hence increase the critical current density. Comparison to recent results with our powder-in-tube A15 conductor is made. Niobium-tantalum tube fabrication, wire processing, filament quality and Nb3Sn microstructure are discussed and the superconducting properties are presented. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The critical current of Nb3Sn strands used in Fermilab’s high field magnets was measured at low and high fields under various experimental conditions using the voltage-current (V-I) and voltage-field (V-H) methods. The strands were commercially produced using Restack Rod Process (RRP) and Powder-in-Tube (PIT) technologies. Both round and deformed strands were studied. Measurements were performed at the Fermilab’s Short Sample Test Facility using a 2-kA sample holder with a low contact resistivity. V-I characteristics at fields above 10–12T with a smooth transition from the superconducting to normal phase allowed determining strand critical current. V-I and V-H measurements at low fields showed premature quenches due to magnetic instability in strands with high critical current density and large effective filament size. The effects of strand deformation and RRR as well as test temperature were studied. This paper describes the Nb3Sn strand parameters, the equipment and measurement methods used, and the results of the critical current measurements at low and high fields. The effect of magnetic instabilities is analyzed for different measurement conditions and compared to the predictions of an instability model. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The reactive liquid Mg infiltration of Boron powders preforms is an easy technique to obtain high density and large superconducting bulk MgB2 manufacts, in which the supercurrents can percolate without obstacles by grains boundaries. The microstructure of these manufacts, as well their superconducting characteristics, can be tailored according to the Boron powders used and the particular arrangements of the reactants in a stainless steel container. A discussion of the superconducting characteristics of prototype manufacts of various shape will be given. The practical application of these manufacts, as permanent magnets for bearings or as current leads, will be discussed with reference to other superconducting bulk options. The expected temperature range for the use of this material will be between 15K and 30K and that calls for the development of reliable and cheap cryogenic systems. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Bulk YBCO components were prepared using Melt Texture Growth (MTG) technique. Components were fabricated using MTG by addition of Y2BaCuO5 (Y211) and Ag to YBCO, which leads to improved grain size without affecting superconducting properties. Green compacts prepared by cold isostatic pressing were pre-sintered at 930°C before subjecting melt texturing. Cooling rates lower than 1 °C.h-1 was used, in between (peritectic) temperature of about 995 and 1025°C, to obtain large grained components. Microstructure studies in details were carried out by Scanning Electron Microscope (SEM), Electron Probe Micro Analysis (EPMA), Orientation Imaging Microscope (OIM) and TEM correlated with electrical properties like Critical current density (Jc). [ABSTRACT FROM AUTHOR]

Polycrystalline MgB2 with addition of 0, 1, 3, and 5 wt. % of Bi-2223(Bi1.8Pb0.26Sr2Ca2Cu3O10+x) powder has been synthesized by solid reaction process. The effect of Bi-2223 addition on current transport and superconducting properties of polycrystalline MgB2 superconductor is discussed. Four probe DC resistivity measurement shows that low level of Bi-2223 addition hardly affects the superconducting transition temperature, Tc of MgB2. The modified Bloch- Gruneisen (B-G) analysis of normal state resistivity data reveals a decrease in intergrain connectivity and increase in intragrain connectivity of MgB2 by Bi-2223 addition. The critical current density of present set of samples is estimated from M- H hysteresis loop in the light of Bean's model. MgB2 added with 1 wt. % of Bi- 2223 added gives the best performance (~ 2 times enhancement in Jc) amongst the studied samples. [ABSTRACT FROM AUTHOR]

Interlayer transport properties are measured for electron‐doped Sm1.86Ce0.14CuO4−δ by using 30 nm‐high small mesa structures to elucidate intrinsic characteristics of this material without influence of the partial epitaxial decomposition phase parallel to the layers. We find that the mesas show some properties quite diffrent from those of the bulk single crystals, providing intriguing insight into the electronic states in electron‐doped cuprates analogous to overdoped Bi2Sr2CaCu2O8+δ. [ABSTRACT FROM AUTHOR]

The nano-powder additives of SiC (11nm) and diamond (6 nm) were mixed with Mg and amorphous B powders in the production route of MgB2 bulk and wires samples. Special attention was paid to the precursor powders with the respect to chemical purity, grain morphology and secondary phases. Commercially available MgB2 powders (ex-situ technology) and also mixtures of MgH2 and amorphous B powders (in-situ technology) were applied as the starting precursors. Electron microscopy was used extensively for the characterization of these powders applying both SEM and TEM analysis. Superconducting bulks and wires samples have been produced, by hot pressing, hot isostatic pressing and hydrostatic extrusion processes. High grain refinement and density in the final wire samples have been achieved by the severe plastic deformation (reduction over 99.98%) with the use of the cumulative (multi-step) hydrostatic extrusion. Superconducting properties of these samples were measured, with particular attention paid to the Jc(B) characteristics. Critical currents at lower and higher magnetic fields depended sensitively on the amount of the additives and grain refinement. TEM imaging and electron spectroscopic imaging were used to evaluate the size and distribution of the both of additives within the microstructure. The strain field of the additives resulted from the misfit in thermal expansion coefficient between the additives and the MgB2 matrix was imaged in bright and dark field TEM and is particularly important for the flux-pinning properties of these materials. Influence of such synthesis parameters as pressure, temperature and time on the superconducting properties and the morphology of the products were examined and obtained results were compared. This allowed to choose the optimal conditions for the improvement of the bulk MgB2 characteristics of the wire samples. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Analyzing the critical state problem for a thin superconducting strip, we explain how one can determine the critical current density jc from the magnetic-field profiles measured by magneto-optical imaging at the upper surface of the strip in the case when this jc depends on the magnitude and direction of the local magnetic field H. We show that measurements of the profiles and their asymmetry in oblique magnetic fields enable one to determine the H-dependent jc. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]