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A simple investigation into the properties of weakly linked filaments in striated YBa2Cu3O7-d (YBCO) coated conductors has been performed. Such weak-link connections may arise in two different contexts within the coated conductors, the one case being the occurrence of unintentional connections. However, it may be desirable to intentionally induce the weak-link connections in order to allow a current sharing between the filaments. This allows the localized degradation of a given filament to be circumvented at a small cost in terms of the added losses and magnetization. This problem has been treated mathematically with a comparison of the superconductor weak linking in contrast to the normal-metal-induced current sharing. The estimates for target values of filament coupling are deduced, and the results in terms of magnetization are then determined. The YBCO samples created, using the pulsed laser deposition, are described that have these properties. The samples consist of one control and one striated sample. The magnetization response of these samples is then considered in terms of the expressions developed. [ABSTRACT FROM AUTHOR]

The controlled growth of self-assembled second-phase nanostructures has been shown to be an essential tool for enhancing properties of several composite oxide thin film systems. Here, the role of Y2O3 nanoparticles on the growth of BaZrO3 (BZO) nanorods is investigated in order to understand the mechanisms governing their self-assembly in YBa2Cu3O7- x (YBCO) thin films and to more fully control the resulting defect landscape. By examining the microstructure and current-carrying capacity of BZO-doped YBCO films, it is shown that the nanorod growth dynamics are significantly enhanced when compared to films double-doped with BZO and Y2O3 nanoparticles. The average nanorod length and associated critical current densities are found to increase at a significantly higher rate in the absence of Y2O3 nanoparticles when the growth temperature is increased. Using microstructural data from transmission electron microscopy studies and the response in critical current density, the interactive effects of multiple dopants that must be considered to fully control the defect landscape in oxide thin films are shown. [ABSTRACT FROM AUTHOR]

We will discuss how stability and speed of normal zone propagation in YBCO-coated conductors is affected by interfacial resistance between the superconducting film and the stabilizer. Our numerical simulation has shown that the increased interfacial resistance substantially increases speed of normal zone propagation and decreases the stability margins. Optimization of the value of the resistance may lead to a better compromise between stability and quench protection requirements than what is found in currently manufactured coated conductors. [ABSTRACT FROM AUTHOR]

When grown on miscut SrTiO3 substrates, significant microstructural changes are observed in BaZrO3-doped YBa2Cu3O7-x thin films when compared to those on non-vicinal substrates. Scanning Electron Microscopy indicates a surface morphology strongly influenced by the vicinal angle, and an accumulation of BaZrO3 particles is observed near the step edges. Cross-sectional Transmission Electron Microscopy reveals that while the columnar formations of BaZrO3 rods typically seen on non-vicinal substrates are present, a significant increase in planar defects in a 100 vicinal film are observed. The effects observed with increasing miscut angle indicate that the modulated surface provided by the vicinal substrate influences the crystalline quality of the YBCO matrix and BZO columnar formation through the thickness of the film. [ABSTRACT FROM AUTHOR]

The superconducting properties of YBa2Cu3O7-δ (YBCO or 123) thin films doped with BaZrO3 (BZO) nanopartides by multilayer and single-target methods were studied and compared. Thin films of 123 + BZO were processed by pulsed laser deposition on LaA1O3 and SrTiO3 single crystal substrates. Multilayer (BZO0.6 nm-1.4/12315nm)19 structures were grown by alternating deposition from 123 and BZO targets, and BZO additions of 0–2 Vol% were deposited using (1231-xBZOx) single-targets. The multilayer and single-target methods of BZO addition caused significant differences of superconducting transition temperatures (Tc) measured by AC susceptibility, and critical current densities (Jc) measured by both magnetic and transport methods as a function of temperature (T), applied magnetic field (H) and angle of H field incidence (θ). Single-target films had almost linear decrease of Tc and self-field Jc with BZO vol% addition, and compared to multilayer films had lower Jc (77 K, H < 4 T) however had improved high-field properties for Jc (77 K, H > 4 T). Multilayer films had almost no decrease of Tc and self-field Jc for high BZO additions up to 10 Vol% and very strong peak of Jc(H//ab in — plane) and constant and high Jc(H,0 < θ < 80°). Single-target BZO-2 Vol% films had slightly enhanced Jc (H//c — axis), consistent with results by other authors. [ABSTRACT FROM AUTHOR]

Striation of wide YBCO coated conductor tapes is necessary to reduce the hysteresis losses. However, the processes used to striate the films may adversely affect the overall critical current of the tape not only by simple removal of superconducting material, but by introducing additional defects. We studied the transport properties of individual filaments of a filamentary YBCO tape on Hastelloy substrate striated by laser ablation. The tape consisted of 24 parallel filaments 0.5 mm wide, covered by thin Ag layer. I–V curves on 9 cm long filament sections as well as the changes of the critical current along the filament were measured at 77 K in magnetic fields up to 70 mT. 8 of 24 filaments were experimentally characterized by the mean value of the critical current and the associated n-value. The best filament had a critical current of ∼7 A at 1 microvolt/cm and B = 0. [ABSTRACT FROM AUTHOR]

Abstract: This work focuses on the development of high power density generators for airborne applications by bridging the chasm between generator and high temperature superconducting (HTS) wire developmental efforts. Benefits of HTS power generation include improved efficiency, thermal management reduction, improved power handling, reduced life cycle costs, and size and weight reduction. Superconducting generator development from the 1970s is outlined, and the basic types of ac synchronous generators are described. The benefits of HTS conductors in general and HTS coated conductors in particular are discussed. Critical issues for the employment of HTS coated conductors are then considered and recommendations made for enhancements to the HTS coated conductor for implementation in the more advanced superconducting power generators. [Copyright &y& Elsevier]

The possibility of a substantial reduction of weight and size of electrical generators is the main incentive behind the effort to develop superconducting armature windings based on Y1Ba2Cu3O6+x (YBCO) coated conductors in the form of wide tapes with large aspect ratio. The main obstacle to the application of coated superconductors in stator windings is the large losses incurred due to the ac magnetic field produced by the rotor's dc coils of the field windings. In the range of frequencies typical for aircraft generators, the hysteretic losses in wide tapes are unacceptably high. They can be reduced by dividing the YBCO layer into multiple filaments separated by non-superconducting barriers. However, the lack of current sharing between the filaments makes the conductor vulnerable to the localized defects, so that a single blockage can impede the flow of transport current through the whole length of a given filament. We present estimates of reliability as well as the magnetization losses in multiply connected superconductors. In this type of superconducting tape, a sparse network of superconducting bridges, which allows for current sharing, connects the filaments. The trade-off between the different types of losses and the connectivity requirement imposes restrictions on the number of filaments and properties of the network of bridges. [ABSTRACT FROM AUTHOR]

An YBCO coated conductor with a zipper pattern striation is investigated by scanning laser microscopy (SLM). The distribution of transport current deduced from the VTSLM images shows that striations act as artificial harriers forcing the current to flow around them. Current sharing and redistribution are observed at the zipper area. We find the major dissipation mechanism in the sample in the superconducting state to be the current crowding at bottleneck areas. The bottleneck seems to be caused by the disabled filaments at and around the zipper area. Some filaments show the dissipation away from the zipper area. In general, we find that the lower Jc* areas have lower Tc* and high δVm, which we consider as a sign of the current crowding. For the first time, we have demonstrated that there is a high temperature signature of the lower Jc* (high dissipation) area and VTSLM can detect the signature. [ABSTRACT FROM AUTHOR]

One of the methods to reduce magnetization loss of YBCO coated conductors in a perpendicular magnetic field is subdividing the YBCO layer into filaments and twisting them as a whole. A 10 mm wide multifilamentary YBCO coated conductor with 200 μm wide filaments was prepared by striation using the laser ablation technique. The number of filaments was 40. The sample length was varied from 100 mm to 25 mm, and their magnetization loss was measured at various frequencies. The measured magnetization losses were scaled using sample length, frequency, and field amplitude. This clarifies the magnetization loss characteristics of multifilamentary YBCO coated conductors and obtains empirical expressions for the magnetization loss. The measured loss was compared with the loss calculated numerically using a two dimensional FEM model. The experimentally confirmed effect of striation to reduce the magnetization loss was compared with theoretical predictions. [ABSTRACT FROM AUTHOR]

Many future military systems will depend heavily on high electrical power input ranging from hundreds of kilowatts up to the multimegawatt level. These weapon systems include electromagnetic launch applications as well as electrically driven directed energy weapons (DEW), such as high-power microwaves and solid-state lasers. These power generation subsystems must often be packaged using limited space and strict weight units on either ground mobile or airborne platforms. Superconducting generators made of high-temperature superconductors (HTS) will enable megawatt-class airborne power systems that are lightweight and compact. Also discussed briefly are new advances in HTS conductors and refrigeration systems furthering the development of HTS power systems. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy (XPS) depth profiling was used to investigate the compositional and chemical profile of a typical YBCO coated conductor architecture. Results of the process revealed that the Y(3d) photoelectronic peak shape in these films is very different from bulk YBCO. To investigate this, several samples of Y[sub 1]Ba[sub 2]Cu[sub 3]O[sub 7-x] thin films were intentionally created of varying quality. The films were deposited on LaAlO[sub 3] by pulsed laser deposition with J[sub c] values ranging from poorly conducting up to several MA/cm². Initial results indicated a potential correlation between the Y(3d) XPS peak shape (full-width-half-maximum) of the YBCO and the film quality. A potential correlation may also exist with the Cu(2p)/Ba(3d) ratio indicating an interrelationship to the FWHM of the Y(3d) peak. Film quality was determined by current transport, resistive T[sub c], and AC magnetic susceptibility measurements. [ABSTRACT FROM AUTHOR]

Magnetization vs. applied field measurements (M-H loops) were taken on YBCO thin films with filaments patterned into them. The YBCO was deposited onto LaAlO[sub 3] substrates using PLD, and the filaments were formed by laser ablation. M-H loops were taken at 4.2 K in fields up to ±9 T using a vibrating sample magnetometer technique, the field applied perpendicular to the film width, d. The losses were seen to be greatly reduced by filament width reductions following the standard expression Q[sub h]/H[sub m] ∝ dJ[sub c]/10. The penetration field was also well described by the standard "high field" expression H[sub p] = (0.4J[sub c]t) ln(d/t + 1), where t is the film thickness. The regimes of applicability of the loss expression were investigated, in particular near H[sub m] ≈ H[sub p]. A more general form of the loss equation was obtained and compared with the high-field approximation. The result was that although Q[sub h]/H[sub m] still increased in proportion to d, the rate of increase decreased as H[sub m] approached H[sub p]. [ABSTRACT FROM AUTHOR]

Magnetization vs. applied field measurements (M–H loops) were taken on short samples of YBa2Cu3O7−δ (YBCO) thin films which were divided into narrow filaments. The YBCO was deposited using pulsed laser deposition onto single-crystal LaAlO3 substrates, with a range of film thicknesses from 0.25 to 0.33 μm. Using a YAG laser, the thin films were patterned into linear striations by removing strips of the superconductor by laser ablation. The resulting striated filamentary structure serves to reduce the effective width of the YBCO films and hence the hysteresis loss in the superconducting samples. The magnetization measurements were taken over the temperature range of 4.2–77 K in applied fields of 0–17 kOe using a vibrating sample magnetometer. The measured hysteresis losses show a highly linear relationship between superconductor filament width and hysteresis loss as anticipated. However, the laser ablation process did result in the redeposition of YBCO along the edges of individual filaments. Degradation of Tc and Jc due to the ablation process is discussed. [Copyright &y& Elsevier]

Studies the development of nickel alloy substrates for Y-Ba-Cu-O coated superconductor applications. Physical and mechanical properties of typical alternate substrate materials; Induced magnetization in Ni and Ni alloys; Recrystallization textures of nickel alloys.

YBa[sub 2]Cu[sub 3]O[sub 7-δ] and YbBa[sub 2]Cu[sub 3]O[sub 7-δ] layers were coated by sol-gel and PLD on Gd[sub 1.91]Er[sub 0.09]O[sub 3] (100% lattice match with Y- and Yb-123) textured buffer layer on Ni substrates. Different thickness of buffer layers and superconducting layer were tried to see the thickness effect on superconducting properties. Buffer layers were prepared with different lattice parameters for Y-123 and Yb-123. Coated conductors were characterized by means of XRD, ESEM and T[sub c] and J[sub c] measurement. Since the perfect lattice match can be achieved between buffer layer and superconducting layer, texture of superconducting film was improved, and consequently critical current density of Y- and Yb-123 were improved. [ABSTRACT FROM AUTHOR]

Abstract: We have studied the transport current distributions in striated YBa2Cu3O7−x (YBCO) films and coated conductors using variable temperature scanning laser microscopy (VTSLM). VTSLM images reveal the location of incomplete separation between filaments due to un-optimized sample processing parameters. When the current flows parallel to the completely separated striations, the current seems to flow within a strip without inter-mixing via the substrate. Initial resistivity measurements on metallic inter-filamentary connections (gold dots) exhibit a semiconducting behavior. VTSLM images clearly show that the current flows between filaments via the metallic inter-connect, indicating the semiconducting resistive behavior is due to the interface between YBCO and metallic layer. The results demonstrate the potential of VTSLM technique in investigating current sharing and normal metal inter-connect issues for the coated conductor development for ac applications. [Copyright &y& Elsevier]