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The new series of commercially produced high temperature superconducting (HTS) tapes based on the YBa 2 Cu 3 O 7 (YBCO) structure have attracted renewed attention for their performance under applied magnetic fields without significant loss in supercurrent compared to the earlier generation of conductors. This adaptability is achieved through rare earth substitution and dopants resulting in the formation of nanoparticles and extended defects within the superconducting film matrix. The electrical performance of Zr-(Gd x ,Y 1 − x )Ba 2 Cu 3 O 7 and (Y 1 − x ,Dy x )Ba 2 Cu 3 O 7 coated conductor tapes were tested prior to and after neutron exposures between 6.54 × 10 17 and 7.00 × 10 18 n/cm 2 ( E > 0.1 MeV). Results showed a decrease in superconducting current with neutron irradiation for the range of fluences tested, with losses in the Zr-(Gd x ,Y 1 − x )Ba 2 Cu 3 O 7 conductor being more rapid. Post-irradiation testing was limited to evaluation at 77 K and applied fields of up to 0.5 Tesla, and therefore testing at lower temperatures and higher applied fields may result in improved superconducting properties as shown in previous ion irradiation work. Under the conditions tested, the doped conductors showed a loss in critical current at fluences lower than that of undoped YBa 2 Cu 3 O 7 tapes reported on in literature.

Effects of low dose irradiation on the electrical transport current properties of commercially available high-temperature superconducting, coated-conductor tapes were investigated, in view of potential applications in the irradiative environment of fusion reactors. Three different tapes, each with unique as-grown flux-pinning structures, were irradiated with Au and Ni ions at energies that provide a range of damage effects, with accumulated damage levels near that expected for conductors in a fusion reactor environment. Measurements using transport current determined the pre- and post-irradiation resistivity, critical current density, and pinning force density, yielding critical temperatures, irreversibility lines, and inferred vortex creep rates. Results show that at the irradiation damage levels tested, any detriment to as-grown pre-irradiation properties is modest; indeed in one case already-superior pinning forces are enhanced, leading to higher critical currents.

The latest generations of rare-earth substituted and nano-doped YBa2Cu3O7-x (YBCO) high temperature superconductors (HTS) developed for applications in magnetic fields are being evaluated for poten...

The synthesis and some physical properties of a new quasi-one-dimensional tetracyanidoplatinate, Cs4[Pt(CN)4](CF3SO3)2 (CsCP(OTf)) are reported and described in comparison to the well-known K2[Pt(CN)4]Br0.30·3.2H2O (KCP). Single-crystal X-ray diffraction reveals Pt–Pt spacings to be greater than those of KCP by 5% longitudinal and 38% transverse, but much shorter than comparable spacings in other non-partially oxidized platinates. Anomalies are observed between temperatures 100 K and 200 K: (1) Longitudinal DC conductivity is two orders of magnitude higher and is non-monotonic with temperature, showing a minimum at around 170 K. (2) Nuclear magnetic resonance (NMR) longitudinal relaxation time T1 is at least three orders of magnitude higher than that of KCP, and is also non-monotonic with temperature, showing a sharp peak at around 120 K. Since X-ray diffraction reveals no structural transition at 120 K, these suggest a possible lattice freezing or stiffening at around 120 K.

By controlling the early stages of thin film growth during laser ablation (i.e. Volmer–Weber type growth), we have synthesized magnetic nanocomposites consisting of nickel (Ni) nanoparticulates in multiple layers of yttria stabilized zirconia. The magnetic properties are a strong function of the nickel particle size, showing a clear transition from superparamagnetic to ferromagnetic characteristics. The coercivity at 300 K varies from 0 to nearly 13 kA m − 1 (∼ 160 Oe) as the laser ablation time is increased. By applying the Scherrer formula to X-ray diffraction patterns, we estimated the average size of the Ni nanoclusters to be

By controlling the early stages of thin film growth during laser ablation (i.e. Volmer–Weber type growth), we have synthesized magnetic nanocomposites consisting of nickel (Ni) nanoparticulates in multiple layers of yttria stabilized zirconia. The magnetic properties are a strong function of the nickel particle size, showing a clear transition from superparamagnetic to ferromagnetic characteristics. The coercivity at 300 K varies from 0 to nearly 4 A m − 1 (∼ 300 Oe) as the laser ablation time is increased. By applying the Scherrer formula to X-ray diffraction patterns, we estimated the average size of the Ni nanoclusters to be

We have demonstrated improved critical current density, Jc, in YBa2Cu3O7-delta (YBCO) films through a controlled study of substrate surface modifications with nano-sized second-phase pre-formed CeO2 particles. Nanoparticles were applied to single crystal SrTiO3 surfaces using suspension-based techniques prior to YBCO film growth. With the introduction of CeO2 nanoparticles, YBCO films showed more robust field dependence at intermediate fields (Jc prop B-prop), where a smaller power law exponent of alpha ~ 0.3 is obtained. The self-flefd Jc(77K, Bparc) values of the YBCO films on reference and CeO2 modified substrates are 1.1 and 1.9 MA/cm2 ; and at 1 Tesla 0.1 and 0.52 MA/cm2 , respectively. Consistent with this alpha-value, angular field dependent Jc and transmission electron microscopy studies indicate the presence of c-axis aligned correlated defects in these modified samples.

The physical and electrical characteristics of oxide buffer layers for Cu-based coated conductors are reviewed, with emphasis on the need for conductive buffers and advanced Cu-based substrates. Methods for preventing Cu oxidation are discussed because it is an anticipated problem for applications using Cu-based rolling assisted biaxially textured substrates (RABiTS).

The development of biaxially textured, second-generation, high-temperature superconducting (HTS) wires is expected to enable most large-scale applications of HTS materials, in particular electric-power applications. For many potential applications, high critical currents in applied magnetic fields are required. It is well known that columnar defects generated by irradiating high-temperature superconducting materials with heavy ions significantly enhance the in-field critical current density. Hence, for over a decade scientists world-wide have sought means to produce such columnar defects in HTS materials without the expense and complexity of ionizing radiation. Using a simple and practically scalable technique, we have succeeded in producing long, nearly continuous vortex pins along the c-axis in YBa2Cu3O7?? (YBCO), in the form of self-assembled stacks of BaZrO3 (BZO) nanodots and nanorods. The nanodots and nanorods have a diameter of ~2?3?nm and an areal density ('matching field') of 8?10?T for 2?vol.% incorporation of BaZrO3. In addition, four misfit dislocations around each nanodot or nanorod are aligned and act as extended columnar defects. YBCO films with such defects exhibit significantly enhanced pinning with less sensitivity to magnetic fields H. In particular, at intermediate field values, the current density, Jc, varies as Jc~H??, with ?~0.3 rather than the usual values 0.5?0.65. Similar results were also obtained for CaZrO3 (CZO) and YSZ incorporation in the form of nanodots and nanorods within YBCO, indicating the broad applicability of the developed process. The process could also be used to incorporate self-assembled nanodots and nanorods within matrices of other materials for different applications, such as magnetic materials.

Nanodot arrays of Y2O3 were dispersed in thin films of YBa2Cu3O7−δ (YBCO) by growing alternating layers of these two species using a pulsed laser deposition method. As a result, critical current density Jc both in applied magnetic field and self-field is enhanced by as much as an order of magnitude, along with a significant increase in the irreversibility field Hirr. High-resolution scanning transmission electron microscopy (STEM) and Z -contrast STEM show that the nanoparticles are crystalline and coherent with the YBCO matrix. Whereas in most other studies pinning has been attributed to the strain fields around the nanoparticles, in this case pinning may actually be due to the nanoparticles themselves ,s incethe delineation between the two species is very sharp and STEM reveals no discernible strain fields in the superconducting material around the nanoparticles. (Some figures in this article are in colour only in the electronic version)

Deposition of (Y2BaCuO5–0.5 nm/YBa2Cu3O7−x∼15 nm) × N multilayer films on rolling-assisted biaxially textured Ni-alloy (RABiTSTM) substrates was investigated, as a new candidate coated conductor architecture for improved flux pinning. Significant enhancements of critical current density (Jc) > 6-fold were measured for applied magnetic fields up to 7 T at 77 K, for multilayer films compared to YBa2Cu3O7−x—only films. By comparing Jc(H)/Jc(0 T) plots of films deposited on RABiTS and single-crystal substrates, the relative increase of Jc(H) from pinning was the same as measured on both substrates. This indicates the varying microstructural properties of the RABiTS templates were, on average, not adversely affecting the pinning enhancements.

Implementation of improved processing for BaF/sub 2/ ex situ YBCO coatings from e-beam evaporated precursors enables faster conversion with rates up to 12 /spl Aring//s and critical currents I/sub c/ at 77 K greater than 350 A/cm-width on a RABiTS template. Details of the faster processing are described and compared to an earlier slower process. A linear relation between I/sub c/ and YBCO layer thickness provides evidence of new opportunities to further improve I/sub c/.

Several applications of high-temperature super-conducting wire require high currents at intermediate magnetic fields B and over a range of orientations; however, such conditions are at present achievable only at low temperatures (/spl sim/30 K). The goal of this study is to determine the feasibility of higher operating temperatures for these applications by investigating temperature dependent, low- and high-field pinning properties of YBCO coated conductor samples. The YBCO films were grown on RABiTS templates by a PVD ex situ BaF/sub 2/ process. Variations in pinning properties were induced by introducing excess yttrium (Y) in the precursor and controllably increasing the growth rate. The main result is a more uniform dependence of J/sub c/ over all orientations of B, along with high irreversibility field B/sub irr/ and high critical current densities J/sub c/. Results also show that for films with various pinning properties and processed under different conditions the self-field J/sub c/ at 77 K is an effective indicator of performance in the temperatures and fields of interest.

Sharpening of the substrate texture is key to obtain critical current densities approaching single crystal values in coated conductors. In particular, great improvements in J/sub c/ are obtained by narrowing the substrate texture down to values of 3-4/spl deg/ for both phi-scan and omega-scan FWHM. The best Ni-alloy substrates used today for RABiTS show FWHM's of 6-5/spl deg/. Although the majority of buffer layers deposited on these tapes by various techniques approximately duplicate the substrate's grain alignment, some materials have been found to develop much sharper out-of-plane texture. Here we report on growth and structural characterization of TiN seed layers on various textured metal tapes. TiN seed layers deposited by PLD have consistently shown tilting of the c-axis toward the direction of the sample's surface normal. We address the extent of such tilt and discuss feasibility of alternative RABiTS architectures that use a TiN seed layer to provide very sharp out-of-plane texture and serve as an effective metal-ion diffusion barrier.

For power applications of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) coated conductors, it is necessary to electrically stabilize the conductor. An economic way to achieve this, which also benefits the engineering J/sub E/, is to grow conductive buffer layers directly on textured Cu or Ni metal surfaces. However, due to poor oxidation resistance and high reactivity/diffusivity of Cu or Ni, an insulating oxide layer usually forms at the metal/substrate interface, degrading the electrical connectivity of the entire architecture. To overcome this problem, we have developed a new conductive, nonmagnetic buffer layer architecture of La/sub 0.7/Sr/sub 0.3/MnO/sub 3//Ir on textured Ni-based tapes. This structure serves as a barrier to both inward diffusion of oxygen and outward diffusion of metal cations. Using PLD to grow YBCO, we demonstrate ideal electrical coupling to the metal substrate. Critical current (I/sub c/) values for 1 /spl mu/m thick YBCO coatings exceed 100 A/cm-width at 77 K on a Ni-W RABiTS template.

YBa2Cu3Oy (YBCO) films produced by the ex situ conversion of BaF2-based precursors deposited by physical vapor deposition on ion-beam assisted deposited (IBAD) yttrium-stabilized zirconia (YSZ) and rolling-assisted biaxially textured substrates (RABiTS) templates are characterized by a bi-axially aligned, laminar grain structure that results from the anisotropic growth characteristics of the YBCO phase and its precipitation from a transient liquid phase during the conversion process. A bimodal microstructure characterizes these films and is defined by large, well-formed YBCO grains with Y2O3 precipitates in the bottom region of the film and small YBCO grains with a high density of stacking faults in the upper half. Ba2Cu3Oy or Ba–O–F/CuO second phase layers were often found between large YBCO grains in the bottom half of the films. YBCO grain sizes exceeded 50 μm within the plane of the film in some cases. Conversely, discrete secondary phases of Y2Cu2O5, Y2O3, and Ba2Cu3Oy/Ba–O–F could be found among the much smaller YBCO grains in the top portion of the bimodal structure. The dividing line of the bimodal structure was generally at one half of the film thickness, although exceptions to this trend were found. The highest critical current densities (Jc) and best film alignments for a given film thickness were found in samples where the layers of Ba2Cu3Oy or Ba–O–F were minimized or eliminated from the films. Samples quenched after partial conversion show the segregation of CuO to the top region of the film and the lateral growth of large YBCO grains from a precursor mix of Y2Cu2O5 and Ba–O–F. The data demonstrate that transient liquid phases are part of the conversion process of BaF2-based YBCO films. The control of both CuO segregation and the amount of liquid phases generated during the initial stages of phase formation is needed for optimizing the ex situ conversion process for high-Jc coated conductors.

The growth of 0.9–1.0 µm thick Y Ba2Cu3O7−δ (YBCO) films on biaxially textured Ni–3 at.% W (NiW) substrates using the BaF2 ex situ process was investigated at reduced pressures. By varying the water vapour pressure (PH2O), Y–BaF2–Cu–O (YBFCO) precursor films deposited by e-beam co-evaporation were converted at a reduced total pressure (Ptotal) of 50–55 Torr and conversion temperature (TS) of 740 °C for a wet conversion time (tW) of 60 min. Critical current density (JC) values greater than 1 MA cm−2 for the thick YBCO films were obtained under the condition of varying PH2O from low pressure to 10 Torr. The transition temperatures (TC) of the samples were over 90 K with ΔTC = 1.8–2.5 K. Pre-heat treatment of the precursor films on CeO2/Y SZ/Y2O3/Ni/NiW substrates under an O2 atmosphere condition before the conversion resulted in smooth surfaces without large secondary phase particles embedded in the films.

There is interest in probing the feasibility and possible advantages of making uniform and cost-effective long-length coated conductors through a low-pressure processing approach. The low-pressure approach, eliminating the boundary layer and gas flow considerations, consumes much less of the processing gases and offers the possibility of improved uniformity and faster growth rate of superconducting films. Here, we have fabricated Y Ba2Cu3O7?? (YBCO) epitaxial films of thickness 0.1?1.0??m on SrTiO3 single crystal substrates using ex situ post-deposition processing of co-evaporated Y, BaF2 and Cu precursors in a controlled low-pressure gas mixture of oxygen and water vapour. Partial pressures of oxygen (PO2) and water vapour (PH2O) as low as 10 and 0.1?mTorr, respectively, were used. X-ray diffraction and scanning electron microscopy inspection were conducted for structure characterization of the films. High critical current densities (Jc) of at 77?K in self-field were obtained, yielding properties comparable to those of in situ films and ex situ films processed under atmospheric pressure condition.

A rapid decrease in the critical current density (Jc) of YBa2Cu3O7-x (YBCO) films with increasing film thickness has been observed for multiple YBCO growth processes. While such behavior is predicted from 2D collective pinning models under certain assumptions, empirical observations of the thickness dependence of Jc are believed to be largely processing dependent at present. To investigate this behavior in ex situ YBCO films, 2.0 and 2.9 um thick YBCO films on ion beam assisted deposition (IBAD) - yttria stabilized zirconia (YSZ) substrates were thinned and repeatedly measured for rho(T) and Jc(H). The 2.9 um film exhibited a constant Jc(77K,SF) through thickness of ~1 MA/cm2 while the 2.0 um film exhibited an increase in Jc(77K,SF) as it was thinned. Neither film offered evidence of significant dead layers, suggesting that further increases in critical current can be obtained by growing thicker YBCO layers., To appear in Applied Physics Letters

High-density direct currents are used to drive flux quanta via the Lorentz force toward a highly ordered ``free flux flow'' (FFF) dynamic state, made possible by the weak-pinning environment of high-quality, single-crystal samples of two low-${T}_{c}$ superconducting compounds, ${\text{V}}_{3}\text{Si}$ and ${\text{LuNi}}_{2}{\text{B}}_{2}\text{C}$. We report the effect of the magnetic field-dependent fluxon-core size on flux flow resistivity ${\ensuremath{\rho}}_{f}$. Much progress has been made in minimizing the technical challenges associated with the use of high currents. Attainment of a FFF phase is indicated by the saturation at highest currents of flux flow dissipation levels that are well below the normal-state resistance and have field-dependent values. The field dependence of the corresponding ${\ensuremath{\rho}}_{f}$ is shown to be consistent with a prediction based on a model for the decrease of fluxon-core size at higher fields in weak-coupling BCS $s$-wave materials.

The critical current density ${J}_{c}$ flowing in thin $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ (YBCO) films of various thicknesses $d$ has been studied magnetometrically, both as a function of applied field $H$ and temperature $T$, with a central objective to determine the dominant source of vortex pinning in these materials. The films, grown by a $\mathrm{Ba}{\mathrm{F}}_{2}$ ex situ process and deposited on buffered rolling assisted biaxially textured substrates (``RABiTS'') substrates of $\mathrm{Ni}\text{\ensuremath{-}}5%\phantom{\rule{0.3em}{0ex}}\mathrm{W}$, have thicknesses $d$ ranging from $28\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ to $1.5\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$. Isothermal magnetization loops $M(H;T)$ and remanent magnetization ${M}_{\mathit{rem}}(T)$ in $H=0$ were measured with $H\ensuremath{\Vert}c$-axis (i.e., normal to film plane). The resulting ${J}_{c}(d)$ values (obtained from a modified critical state model) increase with thickness $d$, peak near $d\ensuremath{\sim}120\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, and thereafter decrease as the films get thicker. For a wide range of temperatures and intermediate fields, we find ${J}_{c}\ensuremath{\propto}{H}^{\ensuremath{-}\ensuremath{\alpha}}$ with $\ensuremath{\alpha}\ensuremath{\sim}(0.56--0.69)$ for all materials. This feature can be attributed to pinning by large random defects, which theoretically has power-law exponent $\ensuremath{\alpha}=5∕8$. Calculated values for the size and density of defects are comparable with those observed by TEM in the films. As a function of temperature, we find ${J}_{c}(T,sf)\ensuremath{\sim}{[1\ensuremath{-}{(T∕{T}_{c})}^{2}]}^{n}$ with $n\ensuremath{\sim}1.2--1.4$. This points to ``$\ensuremath{\delta}{T}_{c}$ pinning'' (pinning that suppresses ${T}_{c}$ locally) in these YBCO materials.

In ${\mathrm{V}}_{3}\mathrm{Si}$, a first-order structural phase transition from hexagonal to square flux-line lattice occurs at approximately 1 T with $H\ensuremath{\Vert}$ to the $a$ axis. In this paper, we demonstrate the reentrant structural transition in the flux-line lattice, which reverts to hexagonal symmetry as the magnetic field approached ${H}_{c2}(T)$. This behavior is described very well by a nonlocal London theory with thermal fluctuations. The phase diagram of the flux lattice topology is mapped out for this geometry.

The peak effect in critical current density ${J}_{c}$ is investigated by studying the flux dynamics in ${\mathrm{V}}_{3}\mathrm{Si}$ using bulk magnetometry, small-angle neutron scattering, and transport measurements on clean single-crystal samples from the same ingot. For a field-cooled history, well-defined structure in the vortex lattice was found for fields and temperatures (H,T) below the peak-effect line ${H}_{P}(T);$ above this line, the structure disappeared. History-dependent, metastable disorder is found only for (H,T) below ${H}_{P}(T)$ but the vortex system is reproducibly re-ordered either by field cooling or a low-frequency, pulsed ``shaking'' transport current. The latter is shown to attain Bardeen-Stephen flux flow. In addition, flux flow is observed at ${H}_{P}(T)$ at high current levels. The results support the traditional picture of ${H}_{P}(T)$ as an order-disorder transition due to the competition between elasticity and pinning.

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.

Critical current density Jc in polycrystalline or granular superconducting material is known to be hysteretic with applied field H due to the focusing of field within the boundary between adjacent grains. This is of concern in the so-called coated conductors wherein superconducting film is grown on a granular, but textured surface of a metal substrate. While previous work has mainly been on Jc determined using induced or magnetization currents, the present work utilizes transport current via an applied potential in strip geometry. It is observed that the effect is not as pronounced using transport current, probably due to a large difference in criterion voltage between the two types of measurements. However, when the films are narrowed by patterning into 200-, 100-, or 80-micron, the hysteresis is clearly seen, because of the forcing of percolation across higher-angle grain boundaries. This effect is compared for films grown on ion-beam-assisted-deposited (IBAD) YSZ substrate and those grown on rolling-assisted-biaxially-textures substrates (RABiTS) which have grains that are about ten times larger. The hysteresis is more pronounced for the latter, which is more likely to have a weak grain boundary spanning the width of the microbridge. This is also of concern to applications in which coated conductors will be striated in order to reduce of AC losses., Comment: text-only: 10 pages, plus 5 figures on 5 pages

Irradiation by 1MeV electron of InAsxP1−x∕InP multiquantum well (MQW) solar cells results in the appearance of a dominant electron-emitting level E1, in the upper half of the band gap. The level E1, however, exhibits an interesting behavior as it was found to completely anneal out with storage at room temperature with no change in other majority carrier levels. No any other defect has been observed in electron-irradiated n-type InAsxP1−x∕InP MQW solar cell structures, which contrasts to conventional n-InP solar cell counterparts (structures without QWs). The study reveals that introduction of QWs in the intrinsic region of p-i-n structures enhances significantly the device radiation tolerance well beyond what has been thus far reported for conventional Si or III-V semiconductor-based solar cells.

The superconducting grain-boundary (GB) network of coated conductors (CCs) is usually assumed to be a replica of the substrate network. In this letter, we analyze IBAD and RABITS CCs, where such replica either do or do not exist. We have analyzed the effect of GB overgrowth on the critical currents by quantifying the average superconducting grain size and determining the intragrain and grain-boundary critical current densities, JcG and JcGB. We have employed a recently developed inductive methodology enabling the simultaneous determination of these three parameters. We show that the percolative JcGB may be reduced by 50% if the GB networks do not correlate, while JcG and the grain pinning properties appear unaffected.

The dependence of the percolative critical current density at low magnetic fields on YBa2Cu3O7−δ (YBCO) layer thickness is studied by comparing grain, JcG, and grain-boundary, JcGB, critical current densities for a series of ex situ processed YBCO films on a RABiTS template. Both critical current densities decrease as a function of thickness and the values of JcG and JcGB show a clear correlation which suggests the existence of an interaction between Abrikosov–Josephson vortices on the grain boundaries and Abrikosov vortices in the bulk of the grains. This opens the possibility to improve JcGB by optimizing the pinning capabilities of the grains.

We have acquired positive results in a controlled study to investigate the effects of substrate surface modification on the growth-induced flux-pinning nanostructures in YBa2Cu3O7−δ (YBCO) films. Nanoscale iridium (Ir) particles were applied to single-crystal SrTiO3 substrate surfaces using dc-magnetron sputtering. Superconducting properties of YBCO films grown on the Ir-modified substrates, measured by transport and magneto-optical imaging, have shown substantial improvement in the critical current densities (Jc) at 77 K over those on untreated, control substrates. Results also show a nearly uniform enhancement of Jc over all orientations of magnetic field. Present results are found to be consistent with cross-sectional transmission electron microscopy investigations. Ultimately, the objective of this approach is to produce enhancements in the properties of coated conductors by a simple pretreatment of the substrate surface.