L. Arda

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).

Irreversibility field and flux pinning in MgB2 with and without SiC additions

The critical current density (Jc) was measured at 4.2?K for MgB2 strands with and without SiC additions. In some cases measurements were performed on long (1?m) samples wound on barrels, the transport results being compared to the results of magnetic measurements. Most measurements were performed on short samples in fields of up to 18?T. It was found that in?situ processed strands with 10% SiC additions heat treated at 700?800??C showed improved irreversibility fields (Hr) and bulk pinning strengths (Fp) as compared to control samples; an increase in Hr of 1.5?T was noted. Heat treatment to 900??C gave even larger improvements, with Hr reaching 18?T and Fp values maximizing at 20?GN?m?3.

Structure and microstructure characterization of the mixed sesquioxides (Gd1−xYbx)2O3 and (Gd1−xHox)2O3 prepared by sol–gel process

Polycrystalline samples of (Gd 1-x Yb x ) 2 O 3 and (Gd 1-x HO x ) 2 O 3 (0.0 ≤ x ≤ 1.0) were synthesized by a sol-gel process. X-ray diffraction data were collected and crystal structure and microstructure analyses were performed using the Rietveld refinement method. All samples were found to have the same crystal system and formed solid solutions over the whole range of x. For the system (Gd 1-x HO x ) 2 O 3 , the cationic distribution over the two non-equivalent sites 8b and 24d of the space group Ia3 were found to be random for all values of x. For (Gd 1-x Yb x ) 2 O 3 , the distribution is random in the range 0.0 < x ≤ 0.5 and preferential in the range 0.5 < x ≤ 1.0. The lattice parameters are found to vary linearly with the composition x. Replacing Gd 3+ and Yb 3+ , or Gd 3+ and Ho 3+ , by each other introduces slight changes in relative atomic coordinates. Crystallite size and microstrain analyses were performed along different crystallographic directions and both are found to vary anisotropically with the composition parameter (x). The obtained values of microstrain are correlated with the distribution of the rare earth ions over the two cationic sites of the structure. The average crystallite size ranges from 45 to 144 nm and the root mean square (r.m.s.) strain from 0.018 to 0.409 × 10 -2 .

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.

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/.

YbBa/sub 2-x/Sr/sub x/Cu/sub 3/O/sub 7-/spl delta// coated conductor development by sol-gel process

YbBa/sub 2-x/Sr/sub x/Cu/sub 3/O/sub 7-/spl delta// coated conductors were grown on Gd/sub 1.8/Ho/sub 0.2/O/sub 3/ buffer layered biaxially textured-Ni (100) substrates by the reel-to-reel sol-gel dip coating system. Sample with different Sr substitution ratio (x=0.0, 0.1, 0.2, 0.3, 0.4, and 0.6) were heat treated using varying heat treatment parameters. The surface morphologies and microstructure of all samples were investigated by ESEM, EDS and XRD. The critical current measurements were performed using four-wire method with the 1 /spl mu/V/cm criterion. The critical current density, J/sub c/ was measured to be 10/sup 5/ A/cm/sup 2/ at 4.2 K and 10/sup 4/ A/cm/sup 2/ at 75 K in-self field for YbB/sub 1.9/Sr/sub 0.1/Cu/sub 3/O/sub 7-/spl delta// sample.YbBa 2-x Sr x Cu 3 O 7-δ coated conductors were grown on Gd 1.8 Ho 0.2 O 3 buffer layered biaxially textured-Ni (100) substrates by the reel-to-reel sol-gel dip coating system. Sample with different Sr substitution ratio (x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.6) were heat treated using varying heat treatment parameters. The surface morphologies and microstructure of all samples were investigated by ESEM, EDS and XRD. The critical current measurements were performed using four-wire method with the 1 μV/cm criterion. The critical current density, J c was measured to be 10 5 A/cm 2 at 4.2 K and 10 4 A/cm 2 at 75 K in-self field for YbB 1.9 Sr 0.1 Cu 3 O 7-δ sample.

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.

Characterization of MgB2 Conductors for Coil Development

The effects of the heat treatment conditions on microstructure and the transport critical current density of MgB2 wires, which were fabricated by the Continuous Tube Forming and Filling (CTFF) process, have been investigated. Two types of MgB2 conductors, Fe/MgB2 and Cu/MgB2, were studied. It was found that the sheath materials affect the optimum annealing profile of MgB2 conductor. The annealing temperature for Cu/MgB2 conductors was lower than that for the Fe/MgB2 conductors. The critical current density, Jc was measured to be 1.1×105 A/cm2 at 20 K in‐self field for Cu/MgB2 conductor of 1.25 mm in diameter. The processing, microstructure and superconducting properties are presented.

Textured Growth of Buffer Layer Structures for YBCO Coated Conductors

Textured growth of Cerium oxide (CeO2) and 100% lattice matched (Eu0.893Yb0.107)2O3 buffer layers were investigated for YBCO coated conductors as cap layers on Gd2O3 thin films by chemical solution deposition technique. CeO2 is one of the most widely used cap layer for fabrication of coated conductors, especially when e‐beam evaporation technique is used for YBCO processing. (Eu0.893Yb0.107)2O3 was designed as a perfect lattice matched cap layer, and CeO2 and (Eu0.893Yb0.107)2O3 cap layers have been fabricated on biaxially textured Ni substrates by chemical solution deposition technique in our laboratory. This time we presented textured growth of CeO2 on a Gd2O3 thin film and textured growth of (Eu0.893Yb0.107)2O3 on the CeO2/Gd2O3/Ni buffer layers structure by chemical solution deposition technique.