Y. Akin

Textured growth of multi-layered buffer layers on Ni tape by sol-gel process

Textured Cerium Oxide (CeO/sub 2/)/Yttrium-Stabilized Zirconia (YSZ)/CeO/sub 2/ buffer layers structure were grown by sol-gel dip coating process on bi-axially textured Ni tapes for processing of YBCO coated conductors. CeO/sub 2//YSZ/CeO/sub 2/ buffer layer structure has been demonstrated by vacuum techniques, but first time textured CeO/sub 2//YSZ/CeO/sub 2/ structure were grown by sol-gel on biaxially textured Ni tape. The buffer layer structure promoted c-axis oriented sol-gel YBCO films and prevented oxidation of nickel during YBCO processing. After each layer was coated, the layer was annealed. CeO/sub 2/ layers were annealed at 950 /spl deg/C for 30 min. and YSZ layers were annealed at 1150 /spl deg/C for 10 min. under 4% H/sub 2/ - Ar gas flow. Texture analysis of Ni substrates and bottom CeO/sub 2/ were done by Philips diffractometer. Sol-gel YBCO layers were coated on CeO/sub 2//YSZ/CeO/sub 2/ structure and critical current density was about 0.5 /spl times/ 10/sup 5/ A/cm/sup 2/. Microstructure of the buffer layer was investigated by Environmental Scanning Electron Microscope (ESEM).

Non-vacuum YBCO films on buffer layered Ni tapes: processing, growth and properties

YBCO thin films on buffer layered Ni tapes were investigated via a sol-gel technique. YBCO films were prepared using solutions of various Y, Ba, and Cu precursor compounds. SrTiO/sub 3/ was used on Ni tapes as a buffer layer, ESEM, EDS, and XRD analysis were used to characterize the YBCO films. Sol-gel YBCO coated conductors on buffer layered Ni tapes yielded a T/sub c/ of 90 K by a transport 4-wire resistance measurement. The films produced in this manner were homogeneous, and free of pinholes and cracks.

Textured CeO/sub 2/ thin films on nickel tape by sol-gel process

Cerium oxide (CeO/sub 2/) is one of the preferred buffer layer for fabrication of coated conductors, especially when e-beam evaporation technique is used for YBCO processing. Therefore, processing of CeO/sub 2/ buffer layers has been extensively studied by several vacuum deposition techniques. However, a nonvacuum process is desired for fabrication of coated conductors to make coated conductors widely available in the market. In order to develop a nonvacuum process for fabrication of coated conductors, we fabricated textured cerium oxide (CeO/sub 2/) buffer layers on biaxially textured-Ni [100] substrates by sol-gel process. The solution was prepared from metal-organic precursor, Cerium 2,4-pentanedionate, and was deposited on the Ni substrates using a reel-to-reel sol-gel dip coating system. The textured films were annealed at 1150 /spl deg/C for 10 min under 4% H/sub 2/-Ar gas flow. Extensive texture analysis has been done to characterize the texture of CeO/sub 2/ buffer layers. X-ray diffraction (XRD) of the buffer layer showed strong out-of-plane orientation on Ni tape. The CeO/sub 2/ [111] pole figure indicated a single cube-on-cube textured structure. The omega and phi scans revealed good out-of-plane and in-plane alignments. The full-width-at-half-maximum (FWHM) values of omega and phi scans of CeO/sub 2/ films were 6.47/spl deg/ and 7.26/spl deg/, respectively. ESEM micrographs of the CeO/sub 2/ films revealed pinhole free, crack-free and dense microstructures.

Development of 100% lattice match buffer layers on RABiTS Ni tapes by sol-gel

Gd/sub 2/O/sub 3/-Yb/sub 2/O/sub 3/ and Gd/sub 2/O/sub 3/-Ho/sub 2/O/sub 3/ mixed RE oxides were used to produce buffer layers with a perfect lattice match with superconducting layer. Since these RE oxides are 100% miscible in each other, pseudocubic lattice parameter of the buffer layers can be modified by changing the ratio of components to perfectly match with any superconducting RE-123. Texture and the microstructure of the buffer layers were studied by XRD, Pole Figure and ESEM.

Textured buffer layers for YBCO coated conductors by continuous sol-gel processing

In order to develop alternative buffer layers for YBCO coated conductors, RE/sub 2/O/sub 3/ (RE=La, Pr, Sm, Eu, Gd, Tb, Ho, Yb, and Lu) thin films were studied as candidate materials. Buffer layers were grown on Ni tapes using organometallic compounds that are 2,4-pentanedionates, isopropoxides, and acetates by a continuous, non-vacuum sol-gel process. Films were annealed at 900/spl deg/C-1200/spl deg/C under 4%H/sub 2/-Ar gas mixture. The buffer layers were characterized by means of ESEM, SEM, EDS, XRD and pole figure analysis. Textured, pinhole free crack free, continuous buffer layers were obtained by using 2,4-pentanedionates.

BaZrO3 insulation coatings for HTS coils

Abstract Barium zirconium oxide (BaZrO 3 ) thick films were grown on Ag and AgMg sheathed Bi 2 Sr 2 CaCu 2 O 8+ δ (Bi-2212) superconducting tapes for electrical insulation purposes. A BaZrO 3 (BZO) precursor solution was prepared by sol–gel synthesis using Ba and Zr based alkoxide. Reel-to-reel continuous sol–gel dip coating method was used to grow BZO coatings on superconducting tapes. Processing, microstructure and electrical properties of high temperature BZO insulation coatings have been studied. The BZO coatings were grown in the temperature range of 450 and 600 °C in air. ESEM and X-ray diffraction were used to investigate microstructure and crystallinity of the coatings. Room temperature resistance, dielectric constant, and high voltage breakdown strength of the coatings were measured to be 13 M Ω , 22.5 and 1.0 kV at 1.5 mA, respectively.

Y-and Yb-123 coated conductor development by PLD and sol-gel on (Gd/sub 1-x/Er/sub x/)/sub 2/O/sub 3/ buffered Ni tapes

YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// and YbBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// 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.

Silver doped YBCO coated conductor development by sol-gel process

The nonfluorinated YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) coated conductors with 1-3 wt%Ag have been fabricated by sol-gel process. Ag doped YBCO films were fabricated on CeO/sub 2//YSZ/CeO/sub 2/ buffer layered Ni tapes by continuous sol-gel dip coating process. Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD) analysis were used to characterize the YBCO coated conductor. The superconducting properties (T/sub c/ and J/sub c/) of Ag doped YBCO coated conductors were found to be higher than those of the un-doped conductors. The Ag doped YBCO has a T/sub c,zero/ of 88 K and J/sub c/ of 1.0/spl times/10/sup 5/ A/cm/sup 2/.

Sol-gel Tb/sub 2/O/sub 3/ buffer layers on Ni tapes for YBCO coated conductors

In this study, processing of Tb/sub 2/O/sub 3/ buffer layers on textured Ni tapes were evaluated for YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) coated conductor. A solution deposition process was used to grow textured Tb/sub 2/O/sub 3/ buffer layers on the Ni tapes. The solution was prepared using Tb-2, 4-pentanedionate precursor, methanol as solvent, chelating agents and a solution modifying chemical, triethanolamine (TEA). Biaxially textured Ni substrates were dipped into the solution by a reel-to-reel sol-gel dip coating system. The amorphous thin films were dried at 300 /spl deg/C for 30 sec and then heat-treated at 500 /spl deg/C for 2 min in air using an in-line three-zone furnace. The films were annealed at temperature range of 900 /spl deg/C and 1170 /spl deg/C for 10 to 20 min under 4%H/sub 2/ - Ar gas flow. The textured buffer layers were obtained using TEA onto the textured Ni tapes at 1150 /spl deg/C for 10 minutes. The Tb/sub 2/O/sub 3/ (222) pole figure revealed a single cube-on-cube texture. The omega and phi scans indicated good out-of-plane and in-plane orientations. DTA results pointed out that Tb based gel film transformed to oxide structure at temperature range of 350 /spl deg/C and 410 /spl deg/C. Microstructures of the Tb/sub 2/O/sub 3/ films were investigated by Environmental Scanning Electron Microscope (ESEM), and the films were dense, smooth and free from cracks and pinholes.

Fabrication and Testing of W&R MgB2 Coils Using CTFF Cu/MgB2 Wires and the Sol‐Gel Insulation Process

We have sol‐gel insulated and characterized short samples of the Cu CTFF in Cu tube MgB2 wire with a view to fabricate the first US MgB2 coil from this conductor. The optimum heat treatment condition for this conductor was found to be half an hour at 700 °C under 4%H2‐Ar gas flow. We have sol‐gel insulated 25 meters of Cu/MgB2 wire with SnO2‐ZrO2, layer wound the coil, impregnated with stycast and then tested it between 4.2 K and 30 K together with a sister sample which was heat treated with the coil. The coil had a Jc of 66190 A/cm2 at 4.2 K and 21428 A/cm2 at 20 K in its self field. This is almost identical to that of the sister sample when the self field effect is considered. This is very significant, as it demonstrate that with CTFF process which is readily scalable, one can produce any lengths of MgB2 conductor which would demonstrate the short sample Jc which is unheard of in the HTS conductors.