Effect of an Oxygen Gradient on the Ba sub 2 YCu sub 3 O sub x Superconductor.

The high-T sub c superconductor Ba sub 2 YCuO sub (7-delta) is observed to undergo demixing in the presence of an oxygen gradient. When a single phase polycrystalline disk is placed between 100% O sub 2 and 0.5% O sub 2 in N sub 2 at 800C it was found by SEM, EDAX and x-ray diffraction that Cu migrates away from the low Po sub 2 surface and the concentrations of Ba and Y are enriched at the low Po sub 2 surface. The temperature and values of Po sub 2 are such that the basic material would remain single phase in either atmosphere individually.