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ABSTRACT: We present results of Raman scattering studies of superconducting YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-x</sub> (YBCO) films grown by a high-rate electron-beam co-evaporation method. It is shown by X-ray diffraction that the as-grown YBCO films have a highly c-axis oriented and in-plane aligned texture. Raman scattering measurements were used to study optical phonon modes, oxygen content and second phases of the YBCO coated conductors. Raman spectra of YBCO films with lower-transport properties exhibit additional phonon modes at ~ 300 cm<sup>-1</sup>, ~ 600 cm<sup>-1</sup>, and ~ 630 cm<sup>-1</sup>, which are related to second-phases such as Ba<sub>2</sub>Cu<sub>3</sub>O<sub>5.9</sub> and BaCuO<sub>2</sub>. We also performed micro-Raman scattering measurements, which enable the local characterization of the material over a few micrometer scales. We could clearly determine the chemical homogeneities of the films on which we could not have information using XRD. Our results strongly suggest that micro-Raman scattering can be a very effective tool for characterizing structural and chemical properties, which is essential for optimizing growth conditions.
IEEE Transactions on Appiled Superconductivity 07/2007; · 1.04 Impact Factor
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ABSTRACT: Bi-2212/SrSO<sub>4</sub> bulk superconductors were fabricated using a casting process, and the effects of the powder mixing method, annealing temperature, and SrSO<sub>4</sub> content on the texture, microstructure, and critical properties were evaluated. The Bi-2212 powders were mixed with SrSO<sub>4</sub> either by hand-mixing (HM) or planetary ball milling (PBM), followed by melting at 1100degC-1200degC, solidification, and annealing. The rod produced by PBM had a more homogeneous microstructure and smaller grain size of SrSO<sub>4</sub> and minor phases, resulting in increased I<sub>c</sub>, than the rod made by HM. The I<sub>c</sub> of the rod was also dependent on the annealing temperature with the highest I<sub>c</sub> of 200 A being obtained at an annealing temperature of 810degC. This was attributed to the moderate density and 2212 texture as well as the smaller and less minor phase than that observed at higher temperature. In addition, the optimum SrSO<sub>4</sub> content was found to be 6 wt.% for an increased I<sub>c</sub>. SEM, EPMA, and DTA analyses indicated that the differences in microstructural evolution caused the variations of the I<sub>c</sub> with the powder mixing method, annealing temperature, and SrSO<sub>4</sub> addition.
IEEE Transactions on Appiled Superconductivity 07/2007; · 1.04 Impact Factor
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ABSTRACT: We present results of Raman scattering studies of superconducting YBa 2 Cu 3 O 7 x (YBCO) films grown by a high-rate electron-beam co-evaporation method. It is shown by X-ray diffraction that the as-grown YBCO films have a highly c-axis oriented and in-plane aligned texture. Raman scattering measurements were used to study optical phonon modes, oxygen content and second phases of the YBCO coated conductors. Raman spectra of YBCO films with lower-transport properties exhibit additional phonon modes at 300 cm 1 , 600 cm 1 , and 630 cm 1 , which are related to second-phases such as Ba 2 Cu 3 O 5 9 and BaCuO 2 . We also performed micro-Raman scattering measurements, which enable the local characterization of the material over a few micrometer scales. We could clearly determine the chemical homogeneities of the films on which we could not have information using XRD. Our results strongly suggest that micro-Raman scattering can be a very effective tool for characterizing structural and chemical properties, which is essential for optimizing growth conditions.
IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY. 01/2007; 17.
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S.H. Kim,
W.S. Kim,
W.G. Min,
C.B. Park,
S.J. Lee,
J.T. Kim,
D.K. Lee,
K.D. Choi,
H.G. Joo, G.W. Hong,
J.H. Han,
S. Hahn
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ABSTRACT: In high temperature superconducting (HTS) transformer with double pancake windings, the perpendicular component of leakage magnetic flux density (B<sub>r</sub>) applied to HTS tapes of double pancake windings is larger than that of solenoid windings, which acts as a cause to decrease the critical current in HTS tape and increase AC loss. In this paper, in order to reduce the B<sub>r</sub> applied to HTS windings, the use of ferrite flux diverters is presented. Flux diverters are located in between the primary windings and the secondary windings, and must be made of low-loss materials to minimize the heat. And electromagnetic analysis of a single-phase 1 MVA 22.9 kV/6.6 kV HTS transformer with flux diverters in HTS windings was accomplished. The variation of B<sub>r</sub> applied to the secondary windings and magnetic flux density in flux diverters were analyzed by changing their relative permeability of flux diverters respectively. Suitable relative permeability of flux diverters to reduce B<sub>r</sub> applied to HTS windings was selected, considering flux diverter losses by increment of B in flux diverters.
IEEE Transactions on Appiled Superconductivity 07/2004; · 1.04 Impact Factor
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Journal of Materials Science Letters 01/2002; 21(22):1797-1801.
