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In-field critical current Ic variations, detected using a short sample, angular Ic(77K, H=5.2kOe, Angle) measurement on the ends of a 20 m coated conductor tape fabricated by the MOD / RABiTS process, are shown to be variations in the Ic(H) anisotropy that exist on subcentimeter length scales. A Ic(75 K, H, Angle) study was performed on segments cut from the tape where the power law exponent of the field dependence, α, Ic ∼H−α was calculated for Ic(H, Angle) data. Two extrema behaviors, anisotropic and isotropic, were identified. The isotropic material is shown to outperform the anisotropic material for a wide range of fields and angles at T=26 K.
Coated conductor samples, prepared by reactive co-evaporation, are investigated with respect to the hole-doping dependence of the critical current density. The samples are annealed in an atmosphere of variable oxygen content after which critical currents, critical temperature and the c-axis lattice spacing are measured. The lattice spacing increases with decreasing oxygen content, consistent with literature data. These co-evaporated samples show hole overdoped behavior with respect to the maximum Tc. The achievable range of hole doping in these samples seems to depend on surface coverage. Both self-field and in-field Jc at 75.5 K have a maximum in the overdoped region but at less than maximum oxygen content. The reason for the overdoping of these samples is discussed briefly in terms of Y-Ba disorder.
Over current stabilization of YBa2Cu30x (YBCO) coated conductor high temperature superconductor tape is required in most applications. The conductor must carry currents in excess of the critical current, Ic, without damage during over current events. Conductor damage is the result of joule heating and excessive temperature rise in regions with low Ic. We have developed and applied a measurement technique using a locally applied magnetic field with a high spatial gradient to define a small area over which the Ic is depressed. By measuring the voltage and temperature as a function of current, power dissipation and temperature rise were determined. Unstabilized conductors experienced thermal runaway and are easily damaged. Copper stabilizers applied by electroplating decreased dramatically the temperature rise and increased the level of power dissipation compared with the unstabilized conductor.
Ion-assisted, ion-beam sputter deposition is used to obtain (00l) biaxially oriented films of cubic yttria-stabilized-zirconia (YSZ) on polycrystalline metal substrates. Yttrium-barium-copper-oxide (YBCO) is then heteroepitaxially-pulse-laser deposited onto the YSZ. Phi scans of the films show the full-width-half maxima of the YSZ (202) and the YBCO (103) reflections to be 14° and 10° respectively. Our best dc transport critical current density measurement for the YBCO is 800,000 A/cm2 at 75K and 0T. At 75K, the total dc transport current in a 1 cm wide YBCO film is 23 A.
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