Mark Rikel

Simplified Procedure for Estimating Epitaxy of -Buffered NiW RABITS Using XRD

A procedure is developed for assessing the epitaxy of La2- xZr2+ xO7 (LZO) layers on NiW RABITS. Comparing XRD patterns ( thetas -2thetas scans and 2D rocking curves) of LZO films of known thickness (ellipsometry or reflectometry measurements) with those of standard samples (100% epitaxial LZO film and an isotropic LZO pellet of known density), we estimate the epitaxial (EF), and polycrystalline (PF) fractions of LZO within the layer. The procedure was tested using MOD-LZO(100 nm)/NiW tape samples with EF varied from 3 to 90% (reproducibly prepared by varying the humidity of Ar - 5%H2 gas during heat treatment). A qualitative agreement with RHEED and quantitative (within plusmn 10%) agreement with the EBSD results was shown. Correlation between EF and J c in 600 nm thick YBCO layer deposited on MOD-LZO/NiW using thermal coevaporation enables us to impose the EF = 80% margin on the quality of LZO layer for the particular conductor architecture.

Development of All-CSD Processes for Coated Conductors at Nexans: Limitations and Possible Solutions

Nexans experience in developing all CSD processes for coated conductors with the YBCO/CGO/LZO/Ni-5% W RABITS architecture is summarized. The chosen CC architecture has a principal disadvantage that the next layer only clones, but more often deteriorates the out-of-plane texture of the previous layer (in average by ~ 20% for LZO). Depending on the quality of RABITS, this may increase the amount of grain boundaries (GBs) not transparent for the supercurrent close to the percolation limit for the current-breaking path, which explains low and poorly reproducible Jc. Modifying the buffer architecture by introducing CGO seed layer suppresses deterioration of the out-of-plane texture. Another approach, extending the range of acceptable grain misorientations by selective doping YBCO GBs with Ca is shown not possible using the current MOD-TFA process because of decomposition of initial Y123 to disordered Y124 and Y247 during pyrolysis of the second MOD layer. Possible ways of further development are discussed.

Effect of precursor phase composition on 2223 phase formation in Ag-sheathed tapes

Metastable phase states of BPSCCO 2223 precursor were studied as a function of annealing temperature, time, and oxygen partial pressure. Reproducible, but path-dependent changes in precursor phase composition during annealing are mostly governed by changes in Pb solubility in the (Bi,Pb)2212 phase. Studying phase formation upon heat treatment of tapes made by Nexans customers, we found that BPSCCO phase composition affects melting behavior of (Bi,Pb)2223/Ag tapes, phase recrystallization upon heating, and early stages of Bi2223 phase formation.

Simplified Procedure for Estimating Epitaxy of

A procedure is developed for assessing the epitaxy of La2- xZr2+ xO7 (LZO) layers on NiW RABITS. Comparing XRD patterns ( thetas -2thetas scans and 2D rocking curves) of LZO films of known thickness (ellipsometry or reflectometry measurements) with those of standard samples (100% epitaxial LZO film and an isotropic LZO pellet of known density), we estimate the epitaxial (EF), and polycrystalline (PF) fractions of LZO within the layer. The procedure was tested using MOD-LZO(100 nm)/NiW tape samples with EF varied from 3 to 90% (reproducibly prepared by varying the humidity of Ar - 5%H2 gas during heat treatment). A qualitative agreement with RHEED and quantitative (within plusmn 10%) agreement with the EBSD results was shown. Correlation between EF and J c in 600 nm thick YBCO layer deposited on MOD-LZO/NiW using thermal coevaporation enables us to impose the EF = 80% margin on the quality of LZO layer for the particular conductor architecture.

{\rm La}_{2}{\rm Zr}_{2}{\rm O}_{7}

A procedure is developed for assessing the epitaxy of La2- xZr2+ xO7 (LZO) layers on NiW RABITS. Comparing XRD patterns ( thetas -2thetas scans and 2D rocking curves) of LZO films of known thickness (ellipsometry or reflectometry measurements) with those of standard samples (100% epitaxial LZO film and an isotropic LZO pellet of known density), we estimate the epitaxial (EF), and polycrystalline (PF) fractions of LZO within the layer. The procedure was tested using MOD-LZO(100 nm)/NiW tape samples with EF varied from 3 to 90% (reproducibly prepared by varying the humidity of Ar - 5%H2 gas during heat treatment). A qualitative agreement with RHEED and quantitative (within plusmn 10%) agreement with the EBSD results was shown. Correlation between EF and J c in 600 nm thick YBCO layer deposited on MOD-LZO/NiW using thermal coevaporation enables us to impose the EF = 80% margin on the quality of LZO layer for the particular conductor architecture.