Kevin J. Leary

Local magnetic field distribution in polycrystalline YBa 2 Cu 3 O 7 and its influence on bulk critical currents

The transport critical current density J c has been measured in high quality polycristalline YBa 2 Cu 3 O 7 samples made from extruded preforms. The hysteretic response of J c to applied magnetic fields was studied as a function of temperature (77-87 K) and sample morphology for various field sweeps in the 0-5 KOe range. A variety of samples show a basic J c ∼H −n behavior where n depends on temperature, but is independent of the other variables. A simple model of the local magnetic field distribution is presented and compared to te data, and the theoretical implications of the power law behavior are considered

The production of high performance YBa 2 Cu 3 O 7 using nitrogen dioxide

Energy dispersive x-ray spectroscopy (EDS) was used to show that the elemental homogeneity of YBa{sub 2}Cu{sub 3}O{sub 7} powders can be improved substantially by heating the powder in a nitrogen dioxide-containing atmosphere (e.g., 950 {degree}C), followed by annealing in oxygen at 950 {degree}C, and slow-cooling to room temperature. The improved homogeneity results in a substantially larger flux exclusion signal for the NO{sub 2}-treated powder, as measured by both ac and dc techniques. The experimental results suggest a mechanism which involves the formation of a small amount of molten Ba(NO{sub 3}){sub 2}, which acts as a flux that dissolves the constituents and reprecipitates them as high purity YBa{sub 2}Cu{sub 3}O{sub 7}.

The production of high performance YBa sub 2 Cu sub 3 O sub 7 using nitrogen dioxide

Energy dispersive x-ray spectroscopy (EDS) was used to show that the elemental homogeneity of YBa{sub 2}Cu{sub 3}O{sub 7} powders can be improved substantially by heating the powder in a nitrogen dioxide-containing atmosphere (e.g., 950 {degree}C), followed by annealing in oxygen at 950 {degree}C, and slow-cooling to room temperature. The improved homogeneity results in a substantially larger flux exclusion signal for the NO{sub 2}-treated powder, as measured by both ac and dc techniques. The experimental results suggest a mechanism which involves the formation of a small amount of molten Ba(NO{sub 3}){sub 2}, which acts as a flux that dissolves the constituents and reprecipitates them as high purity YBa{sub 2}Cu{sub 3}O{sub 7}.