The use of nitrogen dioxide to improve the superconducting properties of YBa2Cu3O7

The elemental homogeneity of YPa2Cu3O7 powders can be improved substantially by heating the powder in a nitrogen dioxide-containing atmosphere, followed by annealing in oxygen above 750 degrees C, and slow cooling to room temperature. The improved homogeneity results in a substantially larger flux exclusion signal for the NO2-treated powder, as measured by ac susceptibility. A substantial advantage of the NO2 process is that this process is easily scaled to larger batches and the results are highly reproducible. This is not the case for solid-state reaction processes requiring repeated heating and grinding. The effects of the various process variables on the properties of the treated powder, and the reproducibility of the process, are discussed