Oxygen Deficiency in Ba sub 2 YCu sub 3 O sub 7-delta: The Need for a Microscopic Description.

The physical properties, such as crystal structure, resistivity, T sub c and normal state susceptibility have been studied in Ba sub 2 YCu sub 3 O sub 7-delta as a function of oxygen deficiency delta. Oxygen was removed in a controlled way at relatively low temperatures employing a Zr-gettering technique. Not only do we find a second superconducting phase with T sub c ~60 K and with new (short range) crystallographic periodicity along the b-direction, but we also find that all physical properties depend on the manner in at which oxygen is removed.