Search

A low-cost, non-vacuum reel-to reel dip-coating system has been used to continuously fabricate epitaxial Gd2O3 buffer layers on mechanically strengthened, biaxially textured Ni- (3at.%W-1.7at%Fe), defined as Ni-alloy, metal tapes. X-ray diffraction analysis of the seed Gd2O3 layers indicated that well textured films can be obtained at processing temperatures (Tp) between 1100 and 1175°C. Processing speed did not significantly affect the crystalline quality of the Gd2O3. Scanning electron microscopy revealed a continuous, dense and crack-free surface morphology for these dip-coated buffers. The Gd2O3 layer thickness led to remarkable differences in the growth characteristics of the subsequent YSZ and CeO2 layers deposited by rfmagnetron sputtering. Epitaxial YBCO films grown by pulsed laser deposition on the short prototype CeO2/YSZ/Gd2O3/Ni-(3at%W-1.7at%Fe) conductors yielded self-field critical current densities (Jc) as high as 1.2×106 A/cm2 at 77 K. Pure Ni tapes were used to asses the viability of dip-coated buffers for long length coated conductor fabrication. The YBCO films, grown on 80 cm long and 1 cm wide CeO2/YSZ/Gd2O3 buffered Ni tapes by the industrially scalable ex-situ BaF2 precursor process, exhibited end-to-end self-field Jc of 6.25×105 A/cm2 at 77 K.

We report the fabrication and superconducting properties of ∼0.5 μm thick, fine-grained polycrystalline coatings of MgB2 on single-crystal substrate surfaces. The films exhibit large critical current densities, implying little effect from the grain boundaries. Analyses for thermal activation effects are inconclusive, and evidence is presented that the irreversibility line is dominated by the combined influences of Hc2 anisotropy and polycrystallinity. Comparative studies of the magnetic persistent currents and electrical transport properties reveal excellent agreement over a wide range of temperature and magnetic field. This result is contrary to similar comparisons on high-temperature cuprates, where disparities arise from the effects of large flux creep and the diverse electric field regimes probed by the two techniques. The MgB2 films exhibit extremely sharp voltage-current relations away from the irreversibility line, in qualitative agreement with observed large Jc values and low rates of magnetic flux creep.

The use of magnesium diboride in superconducting magnets, transmission lines, or other large-scale applications depends on the transport-current characteristics of this material in magnetic field, and how they compare to the properties of conventional and high-temperature superconductors. Thin films of boron grown on sapphire substrates during electron-beam evaporation were exposed to Mg vapor to produce 0.5-μm thick layers of the metallic compound MgB2. Four-terminal measurements of their voltagecurrent relations, E(J), were carried out before and after exposure to Bφ =1-T and higher doses of 1-Gev U ions. These doses lowered critical temperatures Tc≈39 K less than 0.1 degree, raised the normal-state resistivity, and reduced the loss-free critical current density, Jc. Higher doses added little. The reduction of current densities was greater in the presence of applied magnetic field greater than 0.1 T.

Thin superconducting films of magnesium diboride (MgB2) with Tc \approx 24K were prepared on various oxide substrates by pulsed laser deposition (PLD) followed by an in-situ anneal. A systematic study of the influence of various in-situ annealing parameters shows an optimum temperature of about 600C in a background of 0.7 atm. of Ar/4%H2 for layers consisting of a mixture of magnesium and boron. Contrary to ex-situ approaches (e.g. reacting boron films with magnesium vapor at 900C), these films are processed below the decomposition temperature of MgB2. This may prove enabling in the formation of multilayers, junctions, and epitaxial films in future work. Issues related to the improvement of these films and to the possible in-situ growth of MgB2 at elevated temperature are discussed., Comment: 5 pages, 4 figures

We analyze fundamental issues related to the thermal and electrical stability of a coated conductor during its operation. We address the role of conductive buffer layers in the stability of Ni-based coated conductors, and the effect of a metallic cap layer on the electrical properties of Ni alloy-based superconducting tapes. For the first case we report on the fabrication of a fully conductive RABiTS architecture formed of bilayers of conductive oxides SrRuO3 and LaNiO3 on textured Ni tapes. For the second case we discuss measurements of current-voltage relations on Ag/YBa2Cu3O7-d and Cu/Ag/ YBa2Cu3O7-d prototype multilayers on insulating substrates. Limitations on the overall tape structure and properties that are posed by the stability requirement are presented., Comment: 4 pages, 5 figures

Large enhancements in the critical current density Jc were produced in single crystals of the high‐temperature superconductor Bi2Sr2Ca1Cu2O8 by irradiation with high energy Sn ions. In addition, the irreversibility line was moved to considerably higher magnetic fields. In contrast with analogous studies on Y1Ba2Cu3O7, there was little, if any, selective pinning when the magnetizing field was applied parallel to the linear, ion‐damage‐produced tracks.

Over the past decade, pulsed-laser deposition (PLD) has proven to be one of the most versatile and effective methods for obtaining high-quality electronic oxide thin-film materials. Much of this success can be attributed to its initial use in depositing high temperature superconducting materials. However, pulsed-laser deposition is now a leading research tool in the development of various electronic oxide thin-film technologies, In this paper, recent progress in the deposition of oxide materials on dissimilar materials for both superconductor and semiconductor applications is discussed. Recent developments in the synthesis of superconducting wires via epitaxial growth of superconducting oxides on biaxially textured metal tapes is described. In addition, efforts to integrate high-k dielectric oxides on semiconductor surfaces using pulsed-laser deposition are highlighted.

Two new processes have been under development since 1991 that promise a new, cost- effective way to manufacture flexible, high current density wires made from YBa2Cu3O7 (YBCO). The key is to prepare a textured substrate, or “template,” on which the YBCO may be deposited as a biaxially aligned thick film. Ion beam assisted deposition (IBAD) of yttria stabilized zirconia or magnesium oxide on alloy tapes enables a final superconducting layer with grain-to-grain, in-plane alignment to within 3–5 degrees. Similar results are achieved on rolling-assisted, biaxially textured substrates (RABiTS) using a variety of oxide layers on textured nickel tapes. The performance of research lengths of prototype wires in strong magnetic fields at 65 K already exceeds that of NbTi and Nb3Sn in liquid helium. A scalable, ex-situ process for the YBCO coating has been demonstrated on both types of substrates. Consistent values of critical current density (Jc) greater than 1 106 A/cm2 are now obtained on RABiTS, and Jc’s in excess of 2 x 106 A/cm2 have been obtained on both substrates. A nonmagnetic variation of RABiTS (Ni-13% Cr) has also been shown to yield Jc greater than 1.5 106 A/cm2.Six private companies in the U.S. are scaling up YBCO coated conductors for power and physics applications.

Randomly oriented columnar defects can efficiently increase and stabilize the current density in many high-Tc superconductors. Irradiation with 0.8 GeV protons induces a prompt fission of heavy constituent nuclei, such as Hg, Tl, Pb, and Bi, in the cuprate compounds; then recoiling fragments generate randomly oriented columnar tracks. This markedly enhances the persistent current density J, elevates the irreversibility line to higher fields and temperatures, and reduces the temporal rate of current decay. The associated crystalline disorder depresses Tc by ~ 0.1–1 K per 1016 proton/cm2. At optimal proton fluency, J is enhanced by one or more orders of magnitude (compared with unirradiated virgin materials) and the logarithmic decay rate d ln(J)/d ln(i) is diminished. However, we show that while these vortex pins greatly reduce thermally activated current decay in the highly anisotropic material Bi-2212, significant temperature-independent current decay remains, due to quantum tunneling of vortices. An analysis of the thermally-induced current decay in a “Maley” framework provides the effective pinning energy U(J, T) of irradiated materials, for comparison with the virgin superconductors. The influence of quantum decay on this analysis is shown.

A self‐consistent critical current model in the Josephson mixed state is proposed for a series of c‐oriented, polycrystalline and for a series of epitaxial triaxially oriented YBCO thin films. The flux pinning activation energies were experimentally determined from electrical transport measurements over a wide range of temperatures and were found to behave quite differently for the two types of granular film. With these activation energies applied to a superconductor‐normal metal‐superconductor weak‐link system, thermally activated flux motion is shown to reproduce the experimentally measured critical current densities.

We investigated the stabilization of magnetic flux in a high‐temperature superconductor (a proton‐irradiated Y1Ba2Cu3O7 crystal), by operating with subcritical current density J. Using the thermal history to obtain an induced current density J≤Jc, we observed a drastically reduced relaxation rate dM/dt (M=magnetization), after ‘‘flux creep annealing.’’ The results show that the field gradient ∼J∼M determined the relaxation rate, independent of the sample’s H‐T history, in agreement with recent theory.

The structure of YBa2Cu3Ox thin films and YBa2Cu3Ox/PrBa2Cu3Ox superlattice films grown on (00L) SrTiO3 substrates has been studied using x‐ray diffraction and transmission electron microscopy. The films consist of four symmetry‐equivalent domains related by mutually perpendicular (hh0) and (hh0) twin boundaries. One twin orientation is often highly favored over the other. We have correlated this in‐plane symmetry breaking with small miscuts of the substrate surface towards the [HH0] direction and propose that interfacial steps act as nucleation sites for twins. Thus, by controlling the surface normal, a technique is described for producing films containing aligned twin boundaries.

We report the growth on polycrystalline yttria‐stabilized zirconia substrates of YBa2Cu3O7−x films with Jc (77 K)=11 000 A/cm2 and Jc (4.2 K)=122 000 A/cm2 by pulsed laser ablation. These Jc values are among the highest reported for YBa2Cu3O7−x on any polycrystalline substrate and approach the intrinsic upper limit for films with large‐angle grain boundaries, as indicated by recent bicrystal experiments. We find that the substrate temperature during film growth is most important in obtaining high Jc polycrystalline films. Although the magnetic field dependence of Jc indicates the presence of weak links, the behavior of Jc (4.2 K, H) suggests that a percolative path consisting of low‐angle grain boundaries exists in the films, resulting in Jc (4.2 K, 60 kOe)=4100 A/cm2.

In order to develop an alternative buffer layer architecture using the sol-gel process to produce YBCO (YBa2Cu3O7-δ) coated conductors, Yb2O3 has been chosen as the candidate material. Buffer layers of Yb2O3 were epitaxially grown on biaxially textured-Ni (100) substrates by the sol gel process for the first time. The Yb2O3 precursor solution was prepared from an alkoxide sol-gel route in 2-methoxyethanol and was deposited on textured-Ni (100) substrates by either spin coating or dip coating methods. The amorphous film was then processed at 1160°C under flowing (96%)Ar/H2(4%) gas mixture for one hour. The Yb2O3 film exhibited a strong c-axis orientation on the Ni (100) substrates. The phi and omega scans indicated good in plane and out of plane orientations. The X-ray (222) pole figure showed a cube-on-cube epitaxy. High current YBCO films were grown on the Yb2O3 sol-gel buffered-Ni substrates.

The critical current density of high-{Tc} superconducting thin films is found to be sensitive to the presence of flux-pinning defects, and particularly to the existence of grain boundaries which may act either as pinning centers for the vortices or as weak link junctions. Atomic resolution Z-contrast imaging and spatially resolved electron energy loss spectroscopy provide a method to obtain a direct image of the atomic grain boundary structure for correlation with its electronic structure. Using a combination of transport measurements and electron microscopy, the authors have begun to correlate superconducting properties with atomic scale grain boundary structure using YBCO thin films deposited on SrTiO{sub 3} bicrystals and on Ni substrates (RABiTS).

It is well established that high efficiency (20%) solar cells can be routinely fabricated using single crystal photovoltaic (PV) materials with low defect densities. Polycrystalline materials with small grain sizes and no crystallographic texture typically result in reduced efficiencies. This has been ascribed primarily to the presence of grain boundaries and their effect on recombination processes. Furthermore, lack of crystallographic texture can result in a large variation in dopant concentrations which critically control the electronic properties of the material. Hence in order to reproducibly fabricate high efficiency solar cells a method which results in near single crystal material is desirable. Bulk single crystal growth of PV materials is cumbersome, expensive and difficult to scale up. We present here a possible route to achieve this if epitaxial growth of photovoltaic materials on rolling-assisted-biaxially-textured-substrates (RABiTS) can be achieved. The RABiTS process uses well-established, industrially scaleable, thermomechanical processing to produce a biaxially textured or single-crystal-like metal substrate with large grains (50–100 μm). This is followed by epitaxial growth of suitable buffer layers to yield chemically and structurally compatible surfaces for epitaxial growth of device materials. Using the RABiTS process it should be possible to economically fabricate single-crystal-like substrates of desired sizes. Epitaxial growth of photovoltaic devices on such substrates presents a possible route to obtaining low-cost, high performance solar cells.

The epitaxial growth of CeO{sub 2} on various (001) metal surfaces using pulsed-laser deposition is discussed. In particular, the growth of (001) CeO{sub 2} on (001) Pd, Ag, and Ni is described. Emphasis is given to the specific deposition conditions which successfully alleviate the formation of native oxides at the metal/metal oxide interface. The control of the epitaxial relationships between the oriented oxides films and the underlying noble and oxidizing metal surfaces is addressed. In addition, recent use of these heterostructures in the epitaxial growth of high temperature superconducting films on biaxially-textured metal substrates for superconducting wire development is described.

The correlation between defect formation and carrier doping in epitaxial films of the infinite layer compound SrCuO{sub 2} has been studied via molecular beam epitaxy controlled layer-by-layer growth experiments, chemically resolved scanning transmission electron microscopy, scanning tunneling microscopy, x-ray diffraction, electrical transport measurements, and post-growth oxidation-reduction annealing. Based on the complementary information provided by these experiments, it is concluded that the carrier doping is dominated by the formation of an electron-doped, Sr and O deficient matrix under mildly oxidizing growth conditions. Hole-doping is induced by extended defects containing excess Sr atoms and may lead to superconductivity after high-temperature oxidation.

High-temperature superconductors could revolutionize the electrical power industry. New work shows how the introduction of BaZrO3 nanoparticles during growth leads to a dramatic increase of the critical current in the 'second generation' superconductor YBa2Cu3O7.

Microstructural and magnetoresistance properties of La0.6Y0.07Ca0.33MnOx (Y-doped LCMO) thin films grown in-situ by pulsed laser ablation have been studied. Transmission election microscopy and x-ray diffraction measurements have shown that the Y-doped LCMO thin films grow epitaxially on (100) LaAl03 substrates and are cubic with a lattice parameter of 3.849 ?. The as-deposited films exhibited a metal-insulator transition at 130 K and a giant magnetoresistance (GMR) at 125 K with a MR ratio (dR/RH) of 1500% in the presence of a magnetic field of 6 Tesla. Such a colossal value of MR ratio for as-deposited Y-doped LCMO films is quite promising keeping in view the fact that these films were unannealed and not optimized. We ascribe this magnetoresistance to spin-dependent electron scattering coupled with the presence of intervening O2. ions across Mn3+ and Mn4+ with suppressed separation between Mn-O layers caused by smaller sized Y-dopant. The effect of annealing on the positive-shift of metal-insulator transition temperature and the improvement in GMR ratio has also been discussed. We also report a non-ohmic response in the Y-doped LCMO films which is observed only in the region of the resistance peak and lends support to a conduction mechanism in these materials based on spin-dependent scattering of electrons.

Electrical, magnetic, and structural properties of the vortex lattice (VL) in single crystal V 3 Si were studied by transport, bulk magnetometry and small-angle neutron scattering. Studies focused on the ‘peak effect’ in critical current density just below the upper critical field of this weak-pinning system. The overall picture is a slightly disordered VL easily re-ordered by transport-current ‘shaking’ and ultimately softening at the peak effect.

When randomly oriented columnar defects (CDs) are added to Hg-1223 and Tl-2212 superconductors, their vortex state equilibrium magnetization Meq decreases substantially. Meq progressively deviates from the usual London ln(B) dependence and the curves become S-shaped. Vortex-defect interactions quantitatively account for this behavior.

We have investigated the superconductive transport properties of Y Ba2Cu3O7 films containing self-assembled columnar arrays of second phase SrZrO3 or BaSnO3 precipitates. A matching condition between columnar pinning sites (aligned at or near the c axis) and external magnetic flux, tilted with respect to them, is identified in the critical current JC(H) data. The results for the material containing SrZrO3-based pins are analyzed within a simple intuitive model. At matching, the critical current is enhanced above the model prediction. In complementary contact-free investigations of BaSnO3-doped material, matching effects are observed over a wide range of temperatures in the field dependence of JC(H). The deduced matching fields agree reasonably well with the densities of columnar pins directly observed by scanning electron microscopy.

We identify a phase transition in the vortex system of a high-temperature superconductor with nano-columnar stacks of precipitates as strong vortex pinning centers. Above a particular, temperature-dependent field $B_X(T)$ the vortex response is no longer determined by the nano-columns, and is instead determined by point-like pinning. This phase transition leads to the change in the measured critical current density as a function of angle between the applied magnetic field and the nano-columns. Below the unbinding, there is a strong maximum in $J_C$ when field is aligned parallel to the columns. Above the unbinding, there is a minimum for this orientation., Comment: Formatted for APL

The critical current density Jc and the magnetic relaxation (‘creep’) properties have been studied for a set of NdBa2Cu3O7−δ (NdBCO) films doped with BaZrO3 (BZO) nanoparticles to form columnar defects. The dependence of Jc on the magnitude and orientation of the applied magnetic field Happ (0–6.5 T) and temperature T (5 K–Tc) was investigated. The normalized flux-creep rate S =− dln(J)/dln(t) was determined as a function of T. The current dependence of the effective activation energy Ueff(J) was derived using the formalism developed by Maley. The results are well described by an inverse power law type barrier of the form Ueff(J) ∼ U0(J0/J)μ with fitted values for the pinning energy scale U0 and the glassy exponent μ. When comparing values for these parameters in the BZO-doped samples with those for their undoped control counterparts, the most striking difference is the larger scale of current density J0 in the doped samples (a factor of 2.4 higher), while the other pinning parameters do not differ strongly. In the BZO-doped materials, the pinning energy scale U0 increases with vortex density and J0 decreases, with both following simple power law dependences on the field.

To obtain an engineered surface for deposition of high-Tc superconductors, nanoscale modulations of the surface of the underlying LaMnO3 (LMO) cap layer is a potential source for generating microstructural defects in YBa2Cu3O7−δ (YBCO) films. These defects may improve the flux pinning and consequently increase the critical current density, Jc. To provide such nanoscale modulation via a practical and scalable process, palladium (Pd) or tantalum (Ta) nano-islands were deposited using dc-magnetron sputtering on the surface of the cap layer of commercial metal tape templates for second-generation wires. The size and density of these nano-islands can be controlled by changing sputtering conditions such as the power and deposition time. Compared to the reference sample grown on an untreated LMO cap layer, the YBCO films grown on the LMO cap layers with Pd or Ta nano-islands exhibited improved in-field Jc performance. Atomic force microscopy and transmission electron microscopy were used to assess the evolving size and density of the nano-islands.

Pulsed-laser deposition was used to synthesize artificially layered high-temperature superconductors. Thin-film compounds were formed when the constraint of epitaxy was used to stabilize SrCuO(2)-BaCuO(2) superlattices in the infinite layer structure. Using this approach, two new structural families, Ba(2)Srn-1,Cun+1 O2n+2+delta and Ba(4)Srn-1 Cun+3O2n+6+delta have been synthesized; these families superconduct at temperatures as high as 70 kelvin.

A generalized methodology is described for determining both the intragranular and through-grain-boundary critical current densities in practical coated conductors from contact-free magnetic hysteresis measurements. The model incorporates the vector nature of current density J within the superconducting grains and current conservation with respect to the grain boundaries. Using physically observed values for the grain aspect ratio as input, the analysis yields the low-field intragranular critical current density JcG from a single field-dependent measurement of the global Jc and provides a consistent description that spans the entire range from the weak-link () to the single-grain () limit. Results are given for ex?situ processed RBCO coatings on RABiTS.

Bi2Sr2CaCu2O8+x and Bi2Sr1.6La0.4CuO6+x epitaxial films have been grown on (001) MgO and SrTiO3 substrates at different deposition rates by pulsed‐laser ablation (PLA). The surface morphology, crystallinity, and superconducting critical temperature, Tc , of the films depend sensitively on the deposition rate even though the ablation target composition and substrate temperature were kept almost constant. Furthermore, using scanning electron microscopy, we observed that the density of particles generated by PLA is reduced by decreasing the deposition rate. The results show that the highest quality films of the highly anisotropic Bi‐based materials are deposited by PLA at a low deposition rate, which results in film growth in a near‐equilibrium state.

Z-contrast images and electron energy loss spectra (EELS) were obtained from low angle grain boundaries in SrTiO3 and YBa2Cu3O7-x (YBCO). Z-contrast images are easy to interpret and especially useful for positioning the beam to acquire EELS data from small sample areas [1], because both these techniques can be performed simultaneously.In high-temperature superconductors even a single grain boundary can reduce the critical current by up to four orders of magnitude. The band-bending model can quantitatively explain this phenomenon. YBCO is a hole-doped superconductor with about one hole per unit cell for optimum doping at x close to zero. It has a structure closely related to the perovskite structure, and Z-contrast images have shown that the dislocation cores are made up of similar structural units as in SrTiO3.[2,3] Our EELS measurements show clear evidence for band bending effects around isolated dislocation cores in an undoped 8° low angle grain boundary.

Anisotropie electrical resistivity is studied in epitaxial superlattice films of YBa2Cu3O7-δ/PrBa2Cu3O7-ε grown in situ by laser ablation on SrTiO3 surfaces aligned slightly away from the [100] direction. Layer thicknesses of each compound range from two to eight atomic cells. Electrical resistivity of these superlattice films always shows a peak at some cryogenic temperature that decreases with increasing PrBa2Cu3O7-ε layer thickness. Clear evidence is seen of vortex pinning or of supercurrent blocking by the step edges or by twin boundaries. The ratio of electrical resistivities for current directions parallel and perpendicular to these boundaries shows a large step-like change just above the superconductive critical temperature. The possibility is discussed that the Kosterlitz-Thouless transition explains this anisotropy change.

Using ion irradiation techniques to create defects with point-like and line-like geometries, the pinning of vortices in single crystals of Y1Ba2Cu3O7 superconductor was increased greatly, as shown by magnetic studies of the vortex state magnetization and critical current density Jc. Complementary investigations of “flux creep” (the time dependence of magnetization), both conventional and long-term studies, were well described by recent vortex glass and collective pinning theories. Additional flux creep annealing experiments were quantitatively consistent with this work and demonstrated greater stability of operation with reduced current density. Linear defects, created by irradiation with energetic heavy ions, are particularly effective in pinning vortices that are aligned parallel to the damage tracks.

The Tc dependence on oxygen content was measured for YBa2Cu3O7-δ films grown with a variety of techniques (solid phase epitaxy, laser ablation, off-axis sputtering, co-evaporation) at oxygen pressures p(O2) ranging from 1.0 atm to 0.1 mTorr. Dissimilar dependences resulted for each film type, with Tc either increasing or decreasing for small increments in δ from maximum oxygen occupancy. Varying systematically with p(O2) during growth, the deviations are attributed to competing effects from hole-doping lattice defects (most likely on the Y-site) on the carrier density of the CuO2 planes and basal plane oxygen capacity, respectively, giving rise to overdoping or underdoping after low temperature oxidation in 1.0 atm of oxygen.

To increase the current density and pinning of magnetic flux in high temperature superconductors, defects with point‐like and line‐like geometries were created in controlled numbers using ion irradiation methods. Single crystals of Y1Ba2Cu3O7 and Bi2Sr2Ca1Cu2O8 superconductors were studied using dc magnetic methods. These studies showed greatly increased irreversibility in the vortex state magnetization and enhanced intergrain current density Jc following irradiation. Linear defects, created by irradiation with energetic heavy ions, are particularly effective in pinning vortices at higher temperatures and magnetic fields. Further investigations of ‘‘flux creep’’ (the time dependence of magnetization) are well described by recent vortex glass and collective pinning theories. Complementary investigations have delineated the role of oxygen deficiency δ on pinning in aligned Y1Ba2Cu3O7−δ materials.

We consider factors that limit the loss‐free conduction of electric current in the vortex state of high‐temperature superconductors (HTS). Simple arguments lead to an estimate of the maximum possible critical current densities arising from optimally‐sized linear defects that pin each vortex core over its entire length. In a series of model experiments, such linear defect structures have been tailored at controlled densities in several HTS materials by irradiation with high‐energy heavy ions. Results from these studies are compared with the estimated zero‐temperature theoretical limits. At higher temperatures, the irradiated materials provide unique systems for evaluation of the current theories of flux motion that account for both the intrinsic, anisotropic material properties and the unique defect structures. In particular, from measurements that relate the pinning to the angle between the vortex and defect lines, direct information can be obtained about the influence of material anisotropy on the vortex structure. Results will be compared for different classes of HTS materials.

Fast Temperature Ramping Annealing (FTRA) combined with a cation-exchange process is applied in the fabrication of HgBa2Ca1Cu2Ox (Hg-1212) superconducting tapes in Rolling Assisted Biaxially Textured Substrates (RABiTSs). Tl2Ba2CaCu2Ox (Tl-2212) precursor films were synthesized on RABiTSs and then converted into Hg-1212 films. By employing the FTRA process in the synthesis of Tl-2212 films, significant improvement was achieved in terms of surface morphology as well as in-plane alignment. These features were retained in the Hg-1212 films during T1-Hg cation-exchange. Tc of Hg-1212 films is up to 124K and Jc is up to 105A/cm2 (0T) at 115K. Further improvements in Jc are expected for optimized synthesis conditions.

Epitaxial YSZ film was deposited directly on biaxially-textured (001) Ni tapes using pulsed-laser deposition. Nucleation of the YSZ film on Ni is achieved without the intentional removal of the native oxide from the Ni (001) surface. The epitaxial YSZ layer grown on the Ni (001) surface was used as a single buffer layer for a high temperature superconducting coated conductor architecture, yielding YBa 2 Cu 3 O 7 films with critical current density of 1 MA/cm 2 at 77 K. This architecture eliminates the necessity for a multilayer buffer architecture, as high J c superconducting films are achieved with no intermediate buffer layer between the (001) YSZ and the biaxially textured metal.

The magnetization M and heat capacity of clean, single crystal YNi2B2C superconductor have been studied with magnetic field H||c-axis. The magnetization M(H) deviates from conventional predictions, but is accurately described by recent non-local London theory, with well-behaved parameters. We show that the Ginzburg-Landau parameters κ1 and κ2 increase considerably as T decreases, similar to niobium, but with κ(Tc)≈7.

Systematic effects of Zr additions on the structural and flux pinning properties of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) films deposited by metal-organic chemical vapor deposition (MOCVD) have been investigated. Detailed characterization, conducted by coordinated transport, x-ray diffraction, scanning and transmission electron microscopy analyses, and imaging Raman microscopy have revealed trends in the resulting property/performance correlations of these films with respect to varying mole percentages (mol%) of added Zr. For compositions {le} 7.5 mol%, Zr additions lead to improved in-field critical current density, as well as extra correlated pinning along the c-axis direction of the YBCO films via the formation of columnar, self-assembled stacks of BaZrO{sub 3} nanodots.

Applications of coated conductors based on high- Tc superconductors often require detailed knowledge of their critical current density Jc as a function of magnetic field orientation as well as field strength and temperature. This work demonstrates experimental methods for obtaining the angularly dependent Jc using contact-free magnetic measurements, and qualifies those methods using several well defined conditions. The studies complement traditional transport techniques and are readily extended to conditions of field and temperature where the current density is very large and transport methods become difficult. Results on representative materials are presented.

We performed high-field magnetotransport and magnetization measurements on a single crystal of the 122-phase iron pnictide Ba(Fe1-xCox)2As2. Unlike the HTS cuprates and 1111-phase oxypnictides, Ba(Fe1-xCox)2As2 showed practically no broadening of the resistive transitions under magnetic fields up to 45 T. The mass anisotropy gamma = Hc2ab/Hc2c deduced from the slopes of the upper critical field dHc2ab/dT = 4.9T/K and dHc2c/dT = 2.5T/K decreases from ~2 near Tc, to ~1.5 at lower temperatures. We observed the irreversibility field close to Hc2, and a rather unusual symmetric volume pinning force curve Fp(H) suggestive of strong pinning nano-structure., Comment: 12 pages, 5 figures

The pulsed-laser deposition method has been used to fabricate epitaxial, nonsymmetric M(Y) x N(Pr) superlattices in which YBa2Cu3O7 (YBCO) layers either M = 1, 2, 3, 4, 8, or 16 c-axis unit cells thick are separated by insulating PrBa2Cu3O7 (PBCO) layers N unit cells thick (N = I to -32). The zero-resistance superconducting transition temperature, Tc0, initially decreases rapidly with increasing PBCO layer thickness, but then saturates at TcO 19 K, 54 K, 71 K, or 80 K, for structures containing 1-, 2-, 3-, or 4-cell-thick YBCO layers, respectively. Critical current density measurements carried out on structures with 16- or 32-cell thick YBCO layers show that the magnitude of Jc(H 0) 12 MA/cm2, as well as the magnetic field dependence and the anisotropy of Jc(H) all are in good agreement with corresponding measurements on thicker, single-layer YBCO films. Thus, there is no evidence of an enhanced Jc(H) due to the multi-layered structure, for the layer thicknesses investigated to date. The systematic variation of Tc0, as a function of the YBCO and PBCO layer thicknesses, is discussed in light of other recent experiments and theoretical model calculations. The superlattices' structural and compositional order are characterized using x-ray diffraction, transmission electron microscopy, and scanning tunneling microscopy, and details of the pulsed-laser deposition process are reported.

For YBCO epitaxial thin films the basal plane transport critical current density Jc, flowing perpendicular to an applied magnetic field H, depends sensitively on the orientation of the crystal with respect to H. In particular, Jc is sharply peaked and greatly enhanced when H is precisely parallel to the copper‐oxygen planes. Experiments on a series of epitaxial monolithic and superconductor‐insulator multilayer thin films provide clear evidence that the enhancement is a bulk, rather than surface or thin sample, phenomenon. Measurements of the orientation dependence are presented and compared with a model of ‘‘intrinsic flux pinning’’ by the layered crystal structure.

Among the most informative and facile methods for investigations of a superconductor are measurements of its static magnetization. The objective of this paper is to analyze some experimental features frequently observed in static (dc) magnetization studies of conventional and high-Tc superconductors. We shall discuss investigations employing measurement protocols in which the sample is cooled through the superconductive transition temperature in a finite magnetic field (“field-cooled”) and compare this with zero-field-cooled studies. Also considered are reversible and irreversible materials; particle size effects; some effects of granular and multiply-connected materials; penetration depth studies of type II materials in the vortex state; and fine scale “multiconnected” materials formed by heavy ion irradiation that produces very significant enhancements of the critical current density Jc in the high temperature superconductor Y1Ba2Cu307. Many of these superconductors are “non-ideal” in that they may contain defects and inhomogeneities or may have small dimensions comparable with microscopic superconductive lengths. Practically speaking, however, such materials are often encountered experimentally and can have very desirable physical properties, such as the high Jc values that developed in the ion-irradiated crystal. In the following, we assume that the reader is familiar with the fundamentals of superconductivity, which are thoroughly treated in many sources.1–4

High-temperature superconductors (HTS) are finding use as high - current wires for potential application in power devices. The dependence of their basal-plane critical current properties on orientation in a magnetic field can pose important design problems. Here we report material and operating parameter conditions where prototype HTS tape conductors exhibit critical current characteristics that are essentially field-orientation independent. The novel phenomenon is observed for specific magnetic field intensities that depend on the operating temperature, and in materials having strong flux pinning by extended nanoscale structures aligned roughly along the HTS crystalline c-axis. The effect can be described by a simple model for the field dependence of critical current density, generalized for anisotropic electronic response. This description may provide insight into means to fine-tune the material properties for nearly isotropic performance characteristics at a preferred field and temperature., 7 pages, 6 figures

Interfacial engineering via nanoparticle substrate surface decoration has been extended to coated conductor templates. Preformed BaTiO3 and BaZrO3 nanoparticles were applied to substrate surfaces, prior to YBa2Cu3O7−δ (YBCO) deposition, by using a scalable and inexpensive technique of solution-based suspension. Compared to untreated reference samples, nanodecoration yields improved in-field critical current density (Jc) as well as strong correlated pinning along the c-axis direction of the YBCO film. Accordingly, a much reduced falloff of Jc with magnetic field strength was observed in all of the modified samples. In addition, scaling behavior of the normalized volume pinning force density (Fp) with respect to temperature provided insight as to the differences in flux pinning mechanisms dependent on the decoration technique. Finally, with these results our earlier proof-of-concept demonstrations on nanoparticle modified single crystal substrates were replicated on technological substrates, pointing to the...

The conduction of supercurrents in a short-segment state-of-the-art coated conductor prototype has been studied over ∼8 decades of dissipation. A combination of conventional transport methods, magnetometry in a swept magnetic field, and “flux creep” measurements was used to obtain current density J versus electric field E characteristics over a span E∼10−5–10−13V∕cm. The inductive measurements allow facile exploration of current conduction over a wide range of temperatures, magnetic fields, and dissipation levels where future applications are envisioned.