T. Kodenkandath

Uniform performance of continuously processed MOD-YBCO-coated conductors using a textured Ni?W substrate

Second-generation coated conductor composite HTS wires have been fabricated using a continuous reel-to-reel process with deformation-textured Ni–W substrates and a metal-organic deposition process for YBa2Cu3O7−x. Earlier results on 1 m long and 1 cm wide wires with 77 K critical current performance greater than 100 A cm−1 width have now been extended to 7.5 m in length and even higher performance, with one wire at 132 and another at 127 A cm−1 width. Performance as a function of wire length is remarkably uniform, with only 2–4% standard deviation when measured on a 50 cm length scale. The length-scale dependence of the deviation is compared with a statistical calculation.

YBCO coated conductors by an MOD/RABiTS/spl trade/ process

Commercialization of YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) superconducting coated conductor composite (CCC) technology requires a cost-effective continuous manufacturing process. High critical current YBCO CCC wires with excellent uniformity over length have been fabricated using an all-continuous process. The conductor architecture consists of a metal organic derived YBCO layer, coated on a deformation-textured NiW alloy substrate buffered with Y/sub 2/O/sub 3//YSZ/CeO/sub 2/. Critical current at 77 K, self-field, of up to 118 A was achieved in 1 cm-wide tapes over 1.25 meter lengths, with a standard deviation of 3% measured on a 5 cm scale. The high uniformity and performance supports the feasibility of commercial long-length CCC wire based on deformation textured metal substrates and solution-based deposition of YBCO.

The Development of Second Generation HTS Wire at American Superconductor

Development of the second generation (2G) YBCO high temperature superconducting wire has progressed rapidly and its performance is approaching, and in some areas exceeding, that of first generation (1G) HTS wire. American Superconductors approach to the low-cost manufacturing of 2G wire is based on a wide-strip (4 cm) process using a metal organic deposition (MOD) process for the YBCO layer and the RABiTS (rolling assisted biaxially textured substrate) process for the template. In addition, the wide-strip RABiTS/MOD-YBCO process provides the flexibility to engineer practical 2G HTS wires with architectures and properties tailored for specific applications and operating conditions through slitting to custom widths and laminating with custom metallic stabilizers. This paper will review the status of the 2G manufacturing scale up at AMSC and describe the properties and architecture of the 2G wire being developed and tested for various applications including in cables, coils and fault current limiters. Performance of 100 meter class, 4 mm wide wires at 77 K, self-field has reached 100 A (250 A/cm-width) with single-coat YBCO and 140 A (350 A/cm-width) with double-coat YBCO. A 5 cm inner diameter coil fabricated from the latter wire achieved 1.5 T at 64 K, confirming the capability of the wire for coil applications.

YBCO coated conductors by an MOD/RABiTS™ process

Commercialization of YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) superconducting coated conductor composite (CCC) technology requires a cost-effective continuous manufacturing process. High critical current YBCO CCC wires with excellent uniformity over length have been fabricated using an all-continuous process. The conductor architecture consists of a metal organic derived YBCO layer, coated on a deformation-textured NiW alloy substrate buffered with Y/sub 2/O/sub 3//YSZ/CeO/sub 2/. Critical current at 77 K, self-field, of up to 118 A was achieved in 1 cm-wide tapes over 1.25 meter lengths, with a standard deviation of 3% measured on a 5 cm scale. The high uniformity and performance supports the feasibility of commercial long-length CCC wire based on deformation textured metal substrates and solution-based deposition of YBCO.

Enhanced in-field critical currents of YBCO second-generation (2G) wire by Dy additions

The addition of dysprosium oxide nanoparticles is shown to improve the critical current in perpendicular magnetic fields for second-generation (2G) wire formed by metal–organic deposition (MOD). Typical enhancements in Jc are from 0.17 MA cm−2 to over 0.33 MA cm−2 at 77 K and Bperp = 1.5 T. TEM analysis shows that we are introducing (Y,Dy)2O3 nanoparticles with dimensions of 10–50 nm. A simple theoretical analysis shows that the maximum pinning effect for additions is expected at excess concentrations of approximately 70% DyO1.5, i.e. for YBa2Cu3O7−δ+0.7DyO1.5 if the added nanoparticles are randomly dispersed and a strong pinning model is valid. An interesting feature is that the critical current in parallel field is reduced in these samples. We present evidence that shows this may be due to reduced planar defects in the YBCO.

Chemical solution deposition of lanthanum zirconate barrier layers applied to low-cost coated-conductor fabrication

Epitaxial lanthanum zirconate (LZO) buffer layers have been grown by sol-gelprocessing on Ni–W substrates. We report on the application of these oxide films asseed and barrier layers in coated conductor fabrication as potentially simpler, lowercost coated-conductor architecture. The LZO films, about 80–100-nm thick, werefound to have dense, crack-free surfaces with high surface crystallinity. Using 0.2- mYBCO deposited by pulsed laser deposition, a critical current density of 2 MA/cm

Control of Flux Pinning in MOD YBCO Coated Conductor

Two different types of defect structures have been identified to be responsible for the enhanced pinning in metal organic deposited YBCO films. Rare earth additions result in the formation of nanodots in the YBCO matrix, which form uncorrelated pinning centers, increasing pinning in all magnetic field orientations. 124-type intergrowths, which form as laminar structures parallel to the ab-plane, are responsible for the large current enhancement when the magnetic field is oriented in the ab-plane. TEM studies showed that the intergrowths emanate from cuprous containing secondary phase particles, whose density is partially controlled by the rare earth doping level. Critical process parameters have been identified to control this phase formation, and therefore, control the f 24 intergrowth formation. This work has shown that through process control and proper conductor design, either by adjusting the composition or by multiple coatings of different functional layers, the desired angular dependence can be achieved.

TEM observation of the microstructure of metal-organic deposited YBa2Cu3O7−δ with Dy additions

The microstructure of metal-organic deposited YBa2Cu3O7−δ with dysprosium (Dy) additions has been investigated by transmission electron microscopy (TEM). Dy additions which increase the density of normal-state nanoparticles in the YBCO have been demonstrated to enhance the critical current densities in moderate magnetic fields. The influence of nanoparticles, stacking faults and other planar defects on flux pinning is discussed. We observed a high density of nanoparticles in the size range of 10–50 nm, which may act as flux pinning centres to enhance the critical current density of the material. Stacking faults and planar defects are observed which may also be effective flux pinning centres in YBCO samples with and without Dy addition.

Improved YBCO coated conductors using alternate buffer architectures

The Rolling-Assisted Biaxially Textured Substrates (RABiTS) process has been identified as one of the leading candidates for the fabrication of high performance YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) coated conductors. The RABiTS process uses standard thermomechanical processing to obtain long lengths of flexible, biaxially oriented substrates with smooth surfaces. The strong biaxial texture of the metal is then transferred to the superconductor by the deposition of intermediate oxide buffers that serve both as a chemical and structural buffer. The typical three-layer RABiTS architecture consists of an e-beam Y/sub 2/O/sub 3/ seed, sputtered YSZ barrier and a sputtered CeO/sub 2/ cap layer. Chemical solution deposition of buffer layers offers potential cost advantage relative to physical vapor deposition (PVD) processes. Our main goal of this study is to develop simplified buffer architectures and demonstrate high J/sub c/ Metal-Organic Deposition (MOD)-YBCO films on all-MOD buffers. La/sub 2/Zr/sub 2/O/sub 7/ (LZO)/CeO/sub 2/ buffers have been identified as potential candidates for this study. MOD-YBCO films with a critical current, I/sub c/ of 212 A/cm have been achieved on MOD-LZO seeds with sputtered YSZ and CeO/sub 2/ cap layers. In addition, MOD-YBCO films with a critical current, I/sub c/ of 140 A/cm have been achieved on all MOD buffers of LZO/CeO/sub 2/ for the first time. This offers a potential toward fabrication of lower cost YBCO coated conductors.

MOD Buffer/YBCO Approach to Fabricate Low-Cost Second Generation HTS Wires

The metal organic deposition (MOD) of buffer layers on RABiTS substrates is considered a potential, low-cost approach to manufacturing high performance Second Generation (2G) high temperature superconducting (HTS) wires. The typical architecture used by American Superconductor in their 2G HTS wire consists of a Ni-W (5 at.%) substrate with a reactively sputtered Y2O3 seed layer, YSZ barrier layer and a CeO2 cap layer. This architecture supports critical currents of over 300 A/cm-width (77 K, self-field) with 0.8 mum YBCO films deposited by the TFA-MOD process. The main challenge in the development of the MOD buffers is to match or exceed the performance of the standard vacuum deposited buffer architecture. We have recently shown that the texture and properties of MOD - La2Zr2Ogamma (LZO) barrier layers can be improved by inserting a thin sputtered Y2O3 seed layer and prepared MOD deposited LZO layers followed by MOD or RF sputtered CeO2 cap layers that support MOD-YBCO films with Ics of 200 and 255 A/cm-width, respectively. Detailed X-ray and microstructural characterizations indicated that MOD - CeO2 cap reacted completely with MOD YBCO to form BaCeOs. However, sputtered CeO2 cap/MOD YBCO interface remains clean. By further optimizing the coating conditions and reducing the heat-treatment temperatures, we have demonstrated an Ic of 336 A/cm with improved LZO layers and sputtered CeO2 cap and exceeded the performance of that of standard vacuum deposited buffers.