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REBa2Cu3Ox ((REBCO), RE = rare earth) superconductor tapes with moderate levels of dopants have been optimized for high critical current density in low magnetic fields at 77 K, but they do not exhibit exemplary performance in conditions of interest for practical applications, i.e., temperatures less than 50 K and fields of 2-30 T. Heavy doping of REBCO tapes has been avoided by researchers thus far due to deterioration in properties. Here, we report achievement of critical current densities (Jc) above 20 MA/cm² at 30K, 3T in heavily doped (25 mol. % Zr-added) (Gd,Y)Ba2Cu3Ox superconductor tapes, which is more than three times higher than the Jc typically obtained in moderately doped tapes. Pinning force levels above 1000 GN/m3 have also been attained at 20 K. A composition map of lift factor in Jc (ratio of Jc at 30 K, 3 T to the Jc at 77 K, 0 T) has been developed which reveals the optimum film composition to obtain lift factors above six, which is thrice the typical value. A highly c-axis aligned BaZrO3 (BZO) nanocolumn defect density of nearly 7 Ã--1011 cmâ'2 as well as 2-3 nm sized particles rich in Cu and Zr have been found in the high Jc films. [ABSTRACT FROM AUTHOR]

Critical current (Ic) values of 1384 A/12 mm, corresponding to a critical current density of 12.47 MA cm−2 and a pinning force of 374 GN m−3, have been achieved at 30 K, 3 T in the orientation of field parallel to the c axis (B ∥ c) in (Gd, Y)BaCuO tapes with 15 mol% Zr addition made by metal organic chemical vapor deposition (MOCVD). These tapes show pinning force levels as high as 453 GN m−3 at 30 K. An analysis of the properties of 24–28 (Gd, Y)BaCuO tapes with 15 mol% Zr addition showed a lack of correlation between their critical currents at 30 K, 3 T (B ∥ c) and Ic values both at 77 K, zero field and at 77 K, 1 T (B ∥ c). However, a strong correlation was found between the critical currents at 30 K, 3 T and at 77 K, 3 T (B ∥ c). It has also been discovered that the minimum critical current (Ic, min) value at 77 K, 3 T has no influence on the Ic, min value at 30 K, 3 T, and it in turn depends on the ratio of the Ic values in the orientations of field parallel and perpendicular to the c axis at 77 K, 3 T. [ABSTRACT FROM AUTHOR]

The critical current and structural properties of (Gd,Y)BaCuO tapes made by metal organic chemical vapor deposition (MOCVD) with Zr addition levels up to 30 at.% have been investigated. The reduction in critical current beyond the previously optimized Zr addition level of 7.5 at.% was found to be due to structural deterioration of the (Gd,Y)Ba2Cu3Ox film. By a modified MOCVD process, enhanced critical current densities have been achieved with high levels of Zr addition, including 3.83 MA cm-2 in 15 at.% Zr-added 1.1 µm thick film at 77 K in zero magnetic field. Critical currents as high as 1072 A/12 mm have been reached in (Gd,Y)BaCuO tapes with 15 at.% Zr addition at 30 K in a field of 3 T applied perpendicular to the tape, corresponding to a pinning force value of 268 GN m-3. The enhanced critical currents achievable with a high density of nanoscale defects by employing high levels of second-phase additions enable the performance targets needed for the use of HTS tapes in coil applications involving high magnetic fields at temperatures below 50 K to be met. [ABSTRACT FROM AUTHOR]

Critical current performances of state-of-the-art Zr-added (Gd, Y)BaCuO tapes have been investigated over a temperature range of 20-77 K, in magnetic fields up to 9 T and over a wide angular range of magnetic field orientations. The peak in critical current that is commonly observed in the field orientation perpendicular to the tape in BaZrO3 (BZO) containing superconducting tapes is found to vanish at 30 K in magnetic fields at 1-9 T. While the critical current of 15% Zr-added tapes was about 40% lower than that of 7.5% Zr-added tapes at 77 K, the pinning force values of the former were found to be 18-23% higher than those of the latter in the temperature range of 20-40 K and in magnetic fields of 3-5 T. The results from this study emphasize the importance of optimization of coated conductor fabrication processes for optimum performance not just in low magnetic fields at 77 K but also at the operating conditions of low temperatures and high magnetic fields that are of interest, especially for rotating superconducting machinery applications. [ABSTRACT FROM AUTHOR]

The effect of changing Gd C+Y content from 1.2 to 1.6 in the precursor of (Gd,Y)Ba2Cu3O7 superconducting thin film tapes made by metal organic chemical vapor deposition (MOCVD) at a constant Gd:Y ratio and a fixed Zr content of 7.5% has been studied. The influence of changing the Gd:Y ratio from Gd=0 to Y= 0 in 0.2 mol steps at a constant Gd+Y content of 1.2 in the precursor has also been investigated at a fixed Zr content of 7.5%. The critical current of these films is found to vary significantly as a function of rare-earth content as well as a function of rare-earth type. Even for a fixed Zr content, it is found that the critical current in the orientation of magnetic field parallel to the a-b plane and that in the orientation of field perpendicular to the a-b plane can be systematically varied with changing Gd+Y content as well as with changing Gd:Y ratio. The nanoscale defect structures along the a-b plane and along the c-axis are found to be sensitive to these changes in rare-earth content and type. [ABSTRACT FROM AUTHOR]

Second-generation (2G) HTS wires are now being produced routinely in kilometer lengths using Metal Organic Chemical Vapor Deposition (MOCVD) process with critical currents of 300 A/cm. While this achievement is enabling several prototype devices, in order to reach a substantial commercial market, the cost-performance metrics of 2G HTS wires need to be significantly improved in device operating conditions. Zr-doping has been found to be an effective approach to improve in-field critical current performance of MOCVD-based HTS wires. In this work, we have explored modifications to the Zr-doped precursor compositions to achieve three and two-fold increase in deposition rate in research and production MOCVD systems respectively. Production wires made with modified Zr-doped compositions exhibit a self-field critical current density of 50 MA/cm^2 at 4.2 K and a 55 to 65% higher performance than our previous wires with Zr-doping, over magnetic field range of 0 to 30 T. We have also developed an alternate, low-cost technique, namely electrodeposition, to deposit silver overlayer on superconducting film. Wires made with electrodeposited silver are able to sustain the same level of overcurrent as sputtered silver layers. This process has been successfully scaled up to 100 m lengths. [ABSTRACT FROM AUTHOR]

Abstract: (Gd,Y)Ba2Cu3O x tapes have been fabricated by metal organic chemical vapor deposition (MOCVD) with Zr-doping levels of 0–15mol.% and Ce doping levels of 0–10mol.% in 0.4μm thick films. The critical current density (J c) of Zr-doped samples at 77K, 1T applied in the orientation of H ‖ c is found to increase with Zr content and shows a maximum at 7.5% Zr doping. The 7.5% Zr-doped sample exhibits a critical current density (J c) of 0.95MA/cm2 at H ‖ c which is more than 70% higher than the J c of the undoped sample. The peak in J c at H ‖ c is 83% of that at H ‖ a–b in the 7.5% Zr-doped sample which is more than twice as that in the undoped sample. Superconducting transition temperature (T c) values as high as about 89K have been achieved in samples even with 15% Zr and 10% Ce. Ce-doped samples with and without Ba compensation are found to exhibit substantially different J c values as well as angular dependence characteristics. [Copyright &y& Elsevier]

Abstract: High efficiencies have been achieved in photovoltaic cells based on III–V compounds grown on single crystal germanium substrates. Since the size of these substrates is limited and their cost is very high, such III–V photovoltaics have not found widespread terrestrial use. The objective of this work is to develop highly textured, epitaxial germanium thin films on inexpensive substrates suitable for roll-to-roll continuous processing to serve as templates for III–V compounds. Germanium films with a high degree of in-plane and out-of plane texture have been demonstrated on randomly textured, flexible nickel alloy substrates by epitaxial growth on template films made by ion beam-assisted deposition (IBAD). In order to achieve epitaxial growth, an intermediate layer of CeO2 was found to be required between the IBAD MgO template and the Ge film. Our study shows that structural match between Ge and the underlying oxide layer is the key to epitaxial growth. Room temperature optical bandgap of the Ge films was identified at 0.67eV suggesting minimal residual strain in the film. Refraction index and extinction coefficient values of the epitaxial Ge film were found to match well with that measured from a reference Ge single crystal. [Copyright &y& Elsevier]

Abstract: 2007 has marked yet another year of continued rapid progress in developing and manufacturing high-performance, long-length second-generation (2G) HTS wires at high speeds. Using ion beam assisted deposition (IBAD) MgO and associated buffer sputtering processes, SuperPower has now exceeded piece lengths of 1000m of fully buffered tape reproducibly with excellent in-plane texture of 6–7 degrees and uniformity of about 2%. These kilometer lengths are produced at high speeds of about 350m/h of 4mm wide tape. In combination with metal organic chemical vapor deposition (MOCVD), 2G wires up to single piece lengths to 790m with a minimum critical current value of 190A/cm corresponding to a Critical current×Length performance of 150,100Am have been achieved. Tape speeds up to 180m/h have been reached MOCVD while maintaining critical currents above 200A/cm in 100+ m lengths. Thick film MOCVD technology has been transitioned to Pilot manufacturing system where a minimum critical current of 320A/cm has been demonstrated over a length of 155m processed at a speed of 70m/h in 4mm width. Finally, nearly 10,000m of 2G wire has been produced, exhaustively tested, and delivered to the Albany Cable project. The average minimum critical current of the wire delivered in 225 segments of 43–44m is 70A in 4mm widths. A 30m cable has been fabricated with this wire by Sumitomo Electric and has been installed in the power grid of National Grid in downtown Albany and is the world’s first 2G device installed in the grid. [Copyright &y& Elsevier]

Abstract: Tremendous progress has been recently made in the achievement of high-performance, high-speed, long-length second-generation (2G) HTS conductors. Using ion beam assisted deposition (IBAD) MgO and metal organic chemical vapor deposition (MOCVD), SuperPower has scaled up tape lengths to 427m with a minimum critical current value of 191A/cm corresponding to a critical current×length performance of 81,550m. Tape speeds up to 120m/h have been reached with IBAD MgO, up to 80m/h with buffer deposition and up to 45m/h with MOCVD, all in single pass processing of 12mm wide tape. Critical current value of 227A/cm has been achieved in a 203m long tape produced in an all-high-speed fabrication process. Critical current values have been raised to 721A/cm, 592A/cm and 486A/cm in short, reel-to-reel processed tape, over 1m length and over 11.1m, respectively, using thicker MOCVD HTS films. Finally, over 10,000m of copper-stabilized, 4mm wide conductor has been produced and tested for delivery to the Albany Cable project. The average critical current of the 10,000m lot was 81A. [Copyright &y& Elsevier]

YBa2Cu3Ox (YBCO) second-generation (2G) HTS conductors have been produced in lengths over 300 m in pilot scale facilities established at SuperPower. High throughput pilot-scale manufacturing has been demonstrated with tape speeds at or above 30 m/h of 12 mm wide tape (corresponding to 90 m/h of 4mm wide conductor) in all steps. A 322 m long conductor with a minimum critical current value of 219 A/cm has been produced, which corresponds to a critical current × length value of 70,520 A-m. A 270 m long, 4 mm wide conductor with an end-to-end critical value of 100 A has also been demonstrated. In a campaign to manufacture 2G conductor for the Albany cable project, SuperPower has produced 12,470 m of conductor that meets or exceeds the specification for piece length (42.4 m) and critical current (100 A/cm). In fact, more than 55% of the conductor produced is at least 100 m in piece length and more than 27% greater than 200 m in piece length. In addition to scaling up 2G conductors to high-throughput pilot-scale manufacturing, we have demonstrated high critical currents in short samples produced by Metal Organic Chemical Vapor Deposition (MOCVD). Critical current values of 557 A/cm have been achieved in 2.1 micrometer thick films in 12 mm wide, 10 cm long tapes. These samples exhibit a critical current value of 116 A/cm at 1 T and 76 K, in the orientation of field parallel to the c-axis. We have also constructed a 4-pancake coil that generated a magnetic field of 1.1 T at 77 K and 2.4 T at 64 K. A Fault Current Limiter (FCL) assembly has been successfully constructed and tested at high power levels. A prospective current of 90 kA was successfully limited to 32 kA within 1 ms without any HTS element failure. [ABSTRACT FROM AUTHOR]

YBa2Cu3Ox (YBCO) coated conductors have been produced in 100 m lengths in pilot scale facilities established at SuperPower. In addition to scaling up coated conductors to long lengths with high critical current, we have modified the basic conductor for enhanced in-field performance and low ac losses. In addition, our coated conductors have been produced in practical configurations in 4 mm widths and with a surround topper stabilizer. The conductors were slit first to a 4 mm width and then subjected to electroplating to apply the copper stabilizer. Mechanical and electrical properties of the complete conductor have been elaborately tested. 61 m of 4 mm wide, surround copper stabilized conductor was provided to Sumitomo Electric Industries who fabricated a 1 m cable using the conductor. The cable exhibited the lowest ac losses reported with HTS conductors. SuperPower also fabricated a pancake coil with 7.4 m of coated conductor, which generated a maximum magnetic field of 0.28 T at 77 K. [ABSTRACT FROM AUTHOR]

SuperPower has been scaling up YBa2Cu3Ox-based second-generation superconducting tapes by techniques such as pulsed laser deposition (PLD) using industrial laser and metal organic chemical vapor deposition (MOCVD). Both techniques offer advantage of high deposition rates, which is important for high throughput. Using highly-polished substrates produced in a reel-to-reel polishing facility and buffer layers deposited in a pilot ion beam assisted deposition facility, meter-long second-generation high temperature superconductor tapes have been produced. 100 A class, meter-long coated conductor tapes have been reproducibly demonstrated in this work by both MOCVD and PLD. The best results to date are 148 A over 1.06 m by MOCVD and 135 A over 1.1 m by PLD using industrial laser. [Copyright &y& Elsevier]

YBa[sub 2]Cu[sub 3]O[sub x] (YBCO) coated conductors have been produced in meter lengths in pilot scale facilities established at IGC-SuperPower. Highly-smooth nickel alloy substrates have been polished in reel-to-reel polishing facility, with a uniform roughness of 2 nm. A pilot-scale ion beam assisted deposition (IBAD) facility has been used to produce 1 to 5 m lengths of buffered tapes with a uniform in-plane texture of 11 degrees and a surface roughness of 12 nm. YBCO has been deposited on meter-lengths of substrates by both pulsed laser deposition (PLD), and metal organic chemicalvapor deposition (MOCYD). End-to-end critical current of 43 A has been achieved in meter-long PLD-based YBCO. Meter-long YBCO tapes with a critical current of 90 A have been produced in MOCVD facility. [ABSTRACT FROM AUTHOR]

Describes the deposition of high temperature superconducting yttrium barium copper oxide films on buffered metal substrates by Metal Organic Chemical Vapor Deposition (MOVCD). Fabrication of cube-textured nickel substrates by a thermochemical process; Optimization of the MOVCD process; Critical current densities.

Tl-1223 conductors have been fabricated by the powder-in-tube (PIT) and surface-coated conductor (thick film) techniques. Current densities (J/sub c/) of 20,000 A/cm/sup 2/ and 12,000 A/cm/sup 2/ have been achieved at 77 K in short monofilament tapes and meter-long 37-filament tapes respectively. A large diameter test pancake coil was successfully fabricated with 17 m long PIT tapes. A new process has been developed to achieve grain alignment in PIT Tl-1223. Critical currents of 18 A and a J/sub c/ of 19000 A/cm/sup 2/ has been achieved at 77 K in surface-coated Tl-1223 conductor fabricated by an industrial process. [ABSTRACT FROM PUBLISHER]

Examines the deposition of YBCO superconductors films on buffered metal substrates through metal organic chemical vapor deposition (MOCVD) and ion-beam-assisted deposition. Comparison of solid- and liquid-precursor delivery systems; Critical current measurements; Fracture surface of a YBCO film on buffered metal substrates.

Evaluates the uniformity of grain alignment in the production of yttrium-barium-copper-oxide (YBCO) superconductors with high current density. Use of directional solidification method in growing YBCO samples; Analysis of x-ray pole figures; Determination of the deviations of aligned planes.

The intergrain transport current density and its anisotropy have been studied in oriented grained bulk YBa2Cu3Ox superconductors fabricated by the liquid phase processing method. Current density measurements were performed on oriented grained samples with the transport current aligned at different angles to the a-b plane. In these measurements, the transport current passed through several oriented grain boundaries. The results indicate that the critical current density drops rapidly when the transport current flows at small angles to the a-b plane and then decreases slowly at larger angles. At 77 K and zero magnetic field, an anisotropy ratio of about 25 is observed between Jc along a-b plane and that perpendicular to the plane. Further, the critical current density in these samples is found to depend weakly on magnetic field even though the current crosses grain boundaries. These results support the notion that grain boundaries of these superconductors are different in nature from those of solid-state sintered samples. [ABSTRACT FROM AUTHOR]

A liquid phase processing method for the fabrication of bulk YBa2Cu3Ox superconductors with large current carrying capacity has been developed. Slow cooling through the peritectic transformation (1030–980 °C) has been shown to control the microstructure of these superconductors. A cooling rate of 1 °C/h in this temperature range has yielded a microstructure with long plate type, thick grains oriented over a wide area. Current density up to 18 500 A/cm2 has been obtained by continuous direct current measurements and in excess of 62 000 A/cm2 with pulse current of 10 ms duration and 75 000 A/cm2 using 1 ms pulse. The strong magnetic field dependence observed in sintered bulk 1-2-3 superconductors is also minimized to a large extent where a current density in excess of 37 000 A/cm2 is obtained in a field of 6000 G. [ABSTRACT FROM AUTHOR]

Examines the grain alignment in bulk YBa[sub 2]Cu[sub 3]O[sub x] superconductor by low temperature phase transformation method. Development of a quench and directional transformation process; Role of temperature in the formation of Y[sub 2]BaCuO[sub 5]; Comparison of the magnetic field dependence between the textured YBCO and melt-textured materials.

The influence of Zr doping in (Gd, Y)-Ba-Cu-O ((Gd, Y)BCO) tapes made by metal-organic chemical vapor deposition has been studied with a specific objective of uniform and reproducible enhancement in in-field critical current (Ic) over long lengths. 50 m long tapes with 7.5 and 10 at.% Zr doping in 1 um thick (Gd, Y)BCO films have been found to exhibit a sharply enhanced peak in Ic in the orientation of field parallel to the c-axis and retain 28% of their self-field Ic value at 77 K and 1 T. BaZrO3 (BZO) nanocolumn density in the cross-sectional microstructure was found to increase with increasing Zr addition. The end segments of the 50 m long tapes were found to display nearly identical angular dependence of critical current at 77 K and 1 T, indicative of the uniformity in in-field performance over this length. A 610 m long tape was fabricated with 10% Zr doping and a 130 m segment showed a 3.2% uniformity in critical current measured every meter in the orientation of B \parallel c -axis. A retention factor of 36% of the zero-field Ic value measured at 0.52 T over the 130 m is consistent with that obtained in short samples. [ABSTRACT FROM AUTHOR]

Large-scale, high-rate epitaxial growth technology for the second-generation superconducting wire brings unique technological challenges for the thin-film coating industry. One of the most difficult steps of the process is controlling nucleation of a complex compound over a km-long low-cost oxide template. Here, we analyze early stages of industrial-scale epitaxial metal organic chemical vapor deposition (MOCVD) growth of ReBa2Cu3Ox (REBCO, Re = rare-earth) on buffered metal substrates. The nucleation event is detected by high-flux synchrotron X-ray diffraction and confirmed by atomic force microscopy. REBCO nuclei exhibit a strong preference for edges of the buffer grain, indicating that (001) steps of the buffer grains are preferred nucleation sites. It is concluded that random nucleation of REBCO is caused by agglomerates of small buffer grains. [ABSTRACT FROM AUTHOR]

Digital speckle pattern interferometry has been used to detect inhomogeneous heating in YBa2Cu3O7-δ coated conductors. The analysis was performed in a sample with a controlled defect, which causes a significant local reduction in the critical current value, Ic. The experiments, which were performed with the sample surrounded by nitrogen vapor, have shown that the location of the initial hot spot leading to the complete transition to the normal state of the conductor (quench) is strongly dependent on the sample cooling configuration. When the sample is mainly cooled by gas convection, the quench always starts in the low-Ic region, while for improved cooling configurations the initial hot spot does not always coincide with this region. The results have been compared with those obtained by direct electric field measurements along the sample in nitrogen vapor and liquid. [ABSTRACT FROM AUTHOR]

Presents measurements of the direct current transport critical current of oriented-grained YBa[sub 2]Cu[sub 3]O[sub 7] (YBCO) superconductors. Production of high quality current contacts using thick silver pads; Formation of silver pads by sputter etching the YBCO surface; Details of the contact fabrication method.

Reports on measurements of the millimeter wave surface resistance of grain-aligned YBa[sub2]Cu[sub3]O[subx] bulk material grown by a liquid phase process. Effect of microstructure on surface resistance; Fabrication of grain-aligned polycrystalline samples of YBa[sub2]Cu[sub3]O[subx]; Determination of surface resistance.

Examines thermally activated flux creep of oriented grained and single-crystalline YBa[sub2]Cu[sub3]O[subx]. Preparation of the samples; Results.

Highlights • The (Ba+Zr)/Cu composition of REBCO superconductors with 25% Zr addition affects its c-axis lattice parameter. • Increasing (Ba+Zr)/Cu content decreases lattice parameter mismatch relative to BZO nanocolumns. • The c-axis lattice parameter value significantly affects J c at (77 K, 0 T), (30 K, 3 and 9 T (B ||c)). • The reduction in BZO/REBCO mismatch increases BZO nanocolumn density leading to an improvement of in-field J c at 30 K. • The optimum c-axis value is temperature and field dependent, 11.74, 11.76 and 11.78 Å at (77 K, 0 T), (30 K, 3 T and 9 T (B ||c)). Abstract The relation between the c-axis lattice parameter of REBa 2 Cu 3 O 7−δ (REBCO and RE = Gd, Y) superconductors with 25 mol.% Zr addition and the critical current density (J c) was determined at (77 K, 0 T), (30 K, 3 T (B ||c)), and (30 K, 9 T (B ||c)). In this work, heavily doped Zr-added REBCO films with the thickness of 0.9 µm were fabricated by metal organic chemical vapor deposition (MOCVD) using a roll-to roll process. An increase in REBCO c-axis lattice parameter and a decrease in elastic mismatch strain relative to self-assembled BZO nanocolumns were observed with increasing (Ba + Zr)/Cu content. The optimum c-axis lattice parameter for achieving the highest J c in magnetic field was found to be temperature and field dependent, with optimum values of 11.74, 11.76 and 11.78 Å at (77 K, 0 T), (30 K, 3 T (B ||c)), and (30 K, 9 T (B ||c)), respectively. [ABSTRACT FROM AUTHOR]

In this report, we demonstrate heteroepitaxial growth of single-crystalline-like Si thin films on inexpensive and lightweight flexible metal foil substrates using radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD). Single-crystalline-like Ge thin film on ion-beam textured templates on metal foils served as epitaxy enabling substrates for Si growth. The epitaxial Si films were oriented along (004) direction and strongly biaxially-textured with narrow in-plane and out-of-plane spreads. Surface morphology was granular with 300–400 nm diameter grains having very low-angle grain boundaries (average ∼ 0.5°). Raman spectroscopy revealed near 100% crystallinity and high structural quality, comparable to bulk c-Si wafer. Controllable in-situ gas phase doping was carried out to achieve n- and p-type Si films with high electron and hole mobilities of 230 and 65 cm 2 /V-s respectively and carrier concentrations suitable for electronic device application. Direct deposition of high mobility single-crystalline-like Si thin films on flexible and inexpensive metal foils can be a potential route towards roll-to-roll scalable manufacturing of high-performance flexible electronics applications. [ABSTRACT FROM AUTHOR]

Provides information on a study which detailed the measurement of magnetic levitation and stiffness in several systems composed of a permanent magnet elastically suspended above a stationary melt-textured sample of Y-Ba-Cu-O. Calculation of the levitation force and vertical stiffness; Prediction in the force and magnetization measurements; Areas in which high-temperature superconductors are used.

We demonstrate heteroepitaxial growth of single-crystalline-like n and p-type doped GaAs thin films on inexpensive, flexible, and light-weight metal foils by metal-organic chemical vapor deposition. Single-crystalline-like Ge thin film on biaxially textured templates made by ion beam assisted deposition on metal foil served as the epitaxy enabling substrate for GaAs growth. The GaAs films exhibited strong (004) preferred orientation, sharp in-plane texture, low grain misorientation, strong photoluminescence, and a defect density of ~107cm-2. Furthermore, the GaAs films exhibited hole and electron mobilities as high as 66 and 300 cm² /V-s, respectively. High mobility single-crystalline-like GaAs thin films on inexpensive metal substrates can pave the path for roll-to-roll manufacturing of flexible III-V solar cells for the mainstream photovoltaics market. [ABSTRACT FROM AUTHOR]

Pre-fabrication of metallic nanorods on biaxially textured templates has been explored in this study to introduce flux pinning centers in RE-Ba-Cu-O (REBCO, RE D rare earth) based superconductors. Pt nanorods were deposited by an electron beam assisted deposition method on LaMnO3-capped biaxially textured IBAD-(ion beam assisted deposition) substrates. Well-controlled nanorods with varying diameter (50-120 nm), length (up to 1 µm), orientation and unit cell size were grown over an area of 120-150 µm². The nanorod-decorated samples were then deposited with Gd-Y-Ba-Cu-O ((Gd, Y)BCO) by metal organic chemical vapor deposition (MOCVD). The Pt nanorods remain in their positions during MOCVD and become embedded in the (Gd, Y)BCO matrix, although they suffer creep-induced shape deformation due to exposure to elevated temperature. Higher unit cell size, longer nanorods, and nanorods oriented at an angle to the substrate normal adversely affect the epitaxy of the (Gd, Y)BCO film due to formation of a-axis grains. The observed current-carrying capacity of the Pt nanorod sample is lower than its corresponding reference sample without any nanorods and processed under identical conditions, but it decreases at a slower rate with increasing magnetic field. Potential routes to improve the performance while retaining the desirable characteristics of controlled nanorod direction and density are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Single-crystalline-like epitaxial germanium thin films with hall mobility values as high as 833cm2/Vs have been demonstrated on inexpensive polycrystalline metallic substrates. The dependence of mobility of p-type and n-type germanium films on the deposition temperature has been examined and correlated to microstructural changes. The importance of crystallographic orientation of Ge to achieve these high mobility values has been verified. The mobilities of the epitaxial germanium films on the film thickness for p-type and n-type films with multi-layer architecture with different epitaxial intermediate layers have been investigated. Results show that the increased mobility with increasing germanium film thickness is not just due to crystallographic texture improvement, but could also be a result of decreasing defect density. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Abstract: A peel test was used to study the adhesion strength of a commercial grade 2G HTS wire which features a characteristic multilayer structure with the rare earth-based MOCVD superconducting film deposited on an IBAD-MgO template. The peel test could be carried out at various peeling angles (from 90° to 180°) and the peel strength of a wire was defined as the steady-state peeling load determined from a load–displacement curve. The test results had good reproducibility and accuracy, making the test a reliable and useful method for studying the adhesion strength of the wire. By characterizing the peeled surfaces the weakest interface in a wire could be identified. The peel strength data of the wire was analyzed together with the performance of the experimental magnet coils fabricated using the wire. The effect of the silver contact layer annealing on the peel strength is discussed. [Copyright &y& Elsevier]

The anisotropic irreversibility field BIrr of two YBa2Cu3O7-x thin films doped with additional rare earth (RE) = (Gd, Y) and Zr and containing strong correlated pins (splayed BaZrO3 nanorods and RE2O3 nanoprecipitates) has been measured over a very broad range up to 45 T at temperatures 56 K < T < Tc. We found that the experimental angular dependence of BIrr (θ) does not follow the mass anisotropy scaling BIrr (θ) = BIrr (0)(cos² θ + γ-2 sin² θ)-1/2, where γ = (mc/mab)1/2 = 5-6 for the RE-doped YBa2Cu3O7-x (REBCO) crystals, mab and mc are the effective masses along the ab plane and the c-axis, respectively, and θ is the angle between B and the c-axis. For B parallel to the ab planes and to the c-axis correlated pinning strongly enhances BIrr, while at intermediate angles, BIrr (θ) follows the scaling behavior BIrr (θ) ∝ (cos² θ + γRP-2sin² θ)-1/2 with the effective anisotropy factor γRP ≈ 3 significantly smaller than the mass anisotropy would suggest. In spite of the strong effects of c-axis BaZrO3 nanorods, we found even greater enhancements of BIrr for fields along the ab planes than for fields parallel to the c-axis, as well as different temperature dependences of the correlated pinning contributions to BIrr for B//ab and B//c. Our results show that the dense and strong pins, which can now be incorporated into REBCO thin films in a controlled way, exert major and diverse effects on the measured vortex pinning anisotropy and the irreversibility field over wide ranges of B and T. In particular, we show that the relative contribution of correlated pinning to BIrr for B//c increases as the temperature increases due to the suppression of thermal fluctuations of vortices by splayed distribution of BaZrO3 nanorods. [ABSTRACT FROM AUTHOR]

The dependence of the critical current density Jc on temperature, magnetic field, and film thickness has been investigated in (Gd-Y)-Ba-Cu-O materials of 0.7, 1.4, and 2.8 μm thickness. Generally the Jc decreases with film thickness at investigated temperatures and magnetic fields. The nature and strength of the pinning centers for vortices have been identified through angular and temperature measurements, respectively. These films do not exhibit c-axis correlated vortex pinning, but do have correlated defects oriented near the ab planes. For all film thicknesses studied, strong pinning dominates at most temperatures. The vortex dynamics were investigated through magnetic relaxation studies in the temperature range of 5-77 K in 1 and 3 T applied magnetic fields, H ∥ surface normal. The creep rate S is thickness dependent at high temperatures, implying that the pinning energy is also thickness dependent. Maley analyses of the relaxation data show an inverse power law variation for the effective pinning energy Ueff ∼ (J0/J)μ. Finally, the electric field-current density (E-J) characteristics were determined over a wide range of dissipation by combining experimental results from transport, swept field magnetometry (VSM), and superconducting quantum interference device (SQUID) magnetometry. We develop a self-consistent model of the combined experimental results, leading to an estimation of the critical current density Jc0(T) in the absence of flux creep. [ABSTRACT FROM AUTHOR]

In the present work, composite LaMnO3:MgO (LMO:MgO) cap buffer layers with varying MgO contents 5 vol% up to 75 vol% have been grown on homo-epi MgO/IBAD(MgO) substrates to enhance the performance of YBa2Cu3O7-x (YBCO) films. Results showed formation of phase separated MgO nanocolumns within the LMO matrix. The impact of these nanocolumns on the superconducting properties of YBCO films deposited using pulsed laser deposition (PLD) on the nanostructured layer was investigated by electrical transport measurements. Such YBCO films showed better in-field performance compared to that of YBCO films on standard LMO cap films. In particular, measurements of the field-angle dependence revealed c-axis correlated pinning for YBCO films on these composite cap layers. The present results demonstrate a practical approach to obtain high performance superconducting wires. [ABSTRACT FROM AUTHOR]

Abstract: The dependence of the critical current density (J c) on the orientation of an applied magnetic field was studied for a prototype (Gd,Y)Ba2Cu3O7− x (GdYBCO) coated conductor fabricated by MOCVD on an IBAD-MgO template. Additional rare-earth cations (Y and Gd) and Zr were incorporated into the superconducting film to form (Y,Gd)2O3 and BaZrO3 nanoparticles extended nearly parallel to the a–b planes and to the c-axis, respectively, to enhance the flux pinning. In-field measurement of J c was carried out with electrical current flowing either along or perpendicular to the longitudinal axis of the tape, while a maximum Lorentz force configuration was always maintained. Details in the angular dependence of J c were related to the unique structure of the film, specifically the tilt in the GdYBCO lattice and the tilts in the extended (Y,Gd)2O3 and BaZrO3 nanoparticles. XRD and TEM were used to study the structure of the coated conductor. The effect of the misalignment between the external field H and the internal field B on the angular dependence of J c is discussed. [Copyright &y& Elsevier]

Abstract: The properties of discontinuous aligned pinning centers (PCs) created by high-energy heavy-ions are compared for bulk melt-textured and coated conductor HTS. Properties of PCs, which increase J c (pinning potential and entanglement), and negative properties which decrease J c (e.g., decreased T c and percolation paths) are evaluated. Mechanisms are proposed to explain the very large increases in J c resulting from multiple-in-line-damage (MILD) compared to continuous columnar pinning centers (CCPC). In particular, a mechanism which results in fluxoid entanglement, even for parallel (unsplayed) PCs, is discussed. The same mechanism is found to also account for restoration of much of the pinning potential expected to be lost due to the gaps in MILD PCs. It also accounts for the fact that at high fluence, J c increases as fluence is increased, instead of decreasing as expected. The very low self-field in coated conductor permits separation of the negative and positive effects of PCs. It is found that parameters developed to quantify the negative effects in bulk melt-textured YBCO, by 63GeV U238 ions, successfully describe damage to 2.1μm thick coated conductor by 1GeV Ru44 ions. Coated conductor at 77K and self-field is generally known to have J c about 100 times that of melt-textured YBCO. However, at 77K and applied field of 1T, when both forms of HTS are processed with comparable numbers of near-optimum MILD PCs, the difference in J c is reduced to a factor of 1.3–2. Whereas J c for melt-textured YBCO increased sharply, by a factor of up to 16.8 for high-fluence MILD PCs, J c in coated conductor increased by a smaller factor of 2.5–3.0. Nevertheless, 2.1μm thick coated conductor, with near-optimum MILD PCs, exhibits J c =543kA/cm2 at 77K and applied field of 1.0T, and I c =114 A/cm-width of conductor. This is the highest value we find in the literature. The phenomenology developed indicates that for optimum MILD PCs in coated conductor, J c ∼700±70kA/cm2 should be achievable at 77K, 1.0T. [Copyright &y& Elsevier]

Ic-strain characteristic of YBCO coated conductor was measured using a Walters spring (WASP). In this technique, additional bending and thermal strains induced to the YBCO layer should be considered. In order to produce different initial bending strain to the YBCO layer, the conductor was wound around the springs with different diameters and in the different bending directions. The clear evidence was obtained that Ic-strain curves using a WASP strongly depend on the initial bending strain state. However, when Ic-strain curves were normalized by a maximum Ic value, all of the curves even including the data measured by uniaxial strain method for a short sample fall on to the same curve. Strain analysis based on the rule of mixture probes that the shift along the strain axis for each Ic-strain curve can be explained by the bending and thermal strain during soldering. This result suggests that combined strain of bending and tensile strains can be regarded as simple summation in the present YBCO coated conductor. [ABSTRACT FROM AUTHOR]

Abstract: Reduction of ac losses in applied ac fields can be accomplished through either the creation of filaments and bridging in YBCO coated conductors or by an assembly of narrow width YBCO tapes. The ac losses for each of these geometries were measured at 77K in perpendicular ac fields up to 100mT. Despite physical isolation of the filaments, coupling losses were still present in the samples when compared to the expected hysteretic loss. In addition to filamentary conductors the assembly of stacked YBCO conductor provides an alternative method of ac loss reduction. When compared to a 4-mm wide YBCO coated conductor with a critical current of 60A, the ac loss in a stack of 2-mm wide YBCO coated conductors with a similar total critical current was reduced. While the reduction in ac loss in a 2-mm wide stack coincided with the reduction in the engineering current density of the conductor, further reduction of ac loss was obtained through the splicing of the 2-mm wide tapes with low resistance solders. [Copyright &y& Elsevier]

Abstract: The synthesis and properties of CuAl2O4 thin films have been examined. The CuAl2O4 films were deposited via reactive direct current magnetron sputter using a CuAl2 target. As-deposited films were amorphous. Post-deposition annealing at high temperature in oxygen yielded solid-phase epitaxy on MgO. The film orientation was cube-on-cube epitaxy on (001) MgO single-crystal substrates. The films were transparent to visible light. The band gap of crystalline CuAl2O4 was determined to be ∼4 eV using a Tauc plot from the optical transmission spectrum. The dielectric constant of the amorphous films was determined to be ∼20–23 at 1–100 kHz. [Copyright &y& Elsevier]

In this paper, we report the results from evaluation on the use of 2nd generation high-temperature superconducting wires, or 2G HTS conductors, as elements for superconducting fault current limiter (SFCL). The unique features of 2G HTS conductors such as high N-values, superior electromechanical performance, large surface area available for cooling, and their availability in long-lengths that could be produced by high-throughput and low-cost manufacturing, may provide advantages for SFCL applications. We tested SuperPower's standard ion-beam-assisted-deposition based 2G HTS conductors under various conditions. First, individual conductors 10–20 cm long with dc critical current (Ic) ranging from 180 amps to 277 amps were tested at prospective fault current up to 3 kA (peak). 2G HTS conductors demonstrated good fault current limiting performance, including first peak limitation. Quench current was in the range of 1.8 to 3 times Ic, and the response time was within 1 ms. Secondly, 3–5 conductors in parallel connections demonstrated uniform current sharing and fast recovery under no-load condition. Finally, an assembly consisted of 12 elements in series connection was tested at high-power condition at KEMA PowerTest. Each element had four 40 cm long conductors with Ic ∼120 A in parallel connection. With 1080 V supply voltage and 90 kA prospective fault peak current, the fault current was limited to 32 kA at the 1st peak with 3.2 kA in the HTS elements. The response time was less than 1 ms. All these testing results indicate that our 2G HTS conductors are promising for practical SFCL applications. [ABSTRACT FROM AUTHOR]

Abstract: SuperPower is focused on scaling up second-generation (2-G) high-temperature superconductor (HTS) technology to pilot-scale manufacturing. The emphasis of this program is to develop R&D solutions for scale-up issues in pilot-scale operations to lay the foundation for a framework for large-scale manufacturing. Throughput continues to be increased in all process steps including substrate polishing, buffer and HTS deposition. 2-G HTS conductors have been produced in lengths up to 100m. Process optimization with valuable information provided by several unique process control and quality-control tools has yielded performances of 6000–7000Am (77K, 0T) in 50–100m lengths using two HTS fabrication processes: metal organic chemical vapor deposition (MOCVD) and pulsed laser deposition (PLD). Major progress has been made towards the development of practical conductor configurations. Modifications to the HTS fabrication process have resulted in enhanced performance in magnetic fields. Industrial slitting and electroplating processes have been successfully adopted to fabricate tapes in width of 4mm and with copper stabilizer for cable and coil applications. SuperPower’s conductor configuration has yielded excellent mechanical properties and overcurrent carrying capability. Over 60m of such practical conductors with critical current over 100A/cm-width have been delivered to Sumitomo Electric Industries, Ltd. for prototype cable construction. [Copyright &y& Elsevier]

On the basis of previously reported 10 m long YBCO tape with over 100 A/cm performance, we are working toward scaling up the YBCO coating process to 100 m lengths. We are using a high tape speed of 15 m/h for fabrication of long lengths. To understand the mechanism of high growth rates of YBa2Cu3O7-x (YBCO) on buffered metal substrates, the relationship between critical current density and YBCO film thickness has been systematically investigated. When YBCO thickness was below one micrometer, the critical current density (Jc) was over 2 MA/cm². As YBCO thickness was increased, Jc decreased gradually. However, Jc still remained 0.91 MA/cm² at a YBCO thickness of 4.2 μm. Critical current (Ic) was 380 A across 1 cm wide tape at 77 K. To scale up the YBCO coating process, the deposition rate was increased to a growth rate of 70 nm/s, corresponding to a tape speed of 15 m/h. The average phi-scan rocking curve of YBCO films was ∼ 3° on 11° buffered metal tape. The omega scan rocking curve (FWHM) was just 1.5°. Jc of 2 MA/cm°²² at 77 K and self-field was achieved at a high deposition rate of 70 nm/s and a tape speed of 15 m/h by optimizing deposition parameters. The high rate process has been transferred to long lengths and results will be discussed in this manuscript. [ABSTRACT FROM AUTHOR]

The microstructural and compositional evolution of thick (>1 μm) high temperature superconducting YBa2Cu3O7-x (YBCO) films grown on single crystal SrTiO3 substrates by the metal organic chemical vapor deposition (MOCVD) process was investigated by focused ion beam microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and atomic force microscopy. This study showed that as the MOCVD YBCO film thickness increased above 0.5 μm, defects such as second phase particles, pores, and misaligned grains preferentially nucleated and grew at the YBCO surface. A portion of this defective top layer was eliminated from all the samples using a gas cluster ion beam (GCIB) process that first removed material with a focused argon cluster beam. Next, an oxygen cluster beam was used to smooth the surface and re-oxygenate the YBCO. Comparing the critical current (Ic) measured before and after GCIB processing showed that the Ic remained the same, and even improved, when part of the defective top layer was removed. This microstructural and electromagnetic “dead layer” is believed to be responsible for the overall Ic decrease of MOCVD YBCO films thicker than 0.5 μm. [Copyright &y& Elsevier]

YBa[sub 2]Cu[sub 3]O[sub 7-x] (YBCO) thick films have been grown on buffered metal substrates at different deposition rates by pulsed laser deposition (PLD). In-plane texture and supeconducting properties of YBCO films have been systematically investigated. It was observed that the in-situ epitaxial growth of YBCO films on buffered metal substrates could be achieved at a very high deposition rate. Under the optimized deposition conditions, X-ray diffraction measurements showed that both in-plane and out-plane texture of YBCO films were mainly dependent on the texture quality of the buffer-layer not the deposition rate. As the deposition rate increased from 1 nm/s to 30 nm/s, the average phi-scan rocking curve of YBCO films was only increased from 10 degree to 12 degree. The omega scan rocking curves kept the same FWHM value of 2 degree. Critical current densities J[sub c] of the order of 10[sup 6] A/cm² at 77 K and self-field have been achieved at high deposition rate of 30 nm/s by optimizing deposition parameters. Our results demonstrate the practical possibility of YBCO thick film processing at very high deposition rate by PLD on buffered metal substrates. [ABSTRACT FROM AUTHOR]