HIGH-RESOLUTION STM STS STUDIES OF THE ROLE OF OXYGEN IN SUPERCONDUCTIVITY OF BI-2122 AND OPTIMIZATION OF TC

The presence of excess oxygen intercalated in Bi-O redox layers has been found to be detrimental to the T(c) of the Bi-2122 phase. High resolution STM has been effectively used to locate intercalated oxygen and STS studies have revealed Bi-O layers becoming more insulating with intercalation. By suitable nitrogenation when the excess oxygen is depleted, more conducting redox layers give rise to an improved coupling between Cu-O planes of the neighbouring demi-unit cells in the c-direction, and it is this improved coupling that is responsible for enhanced T(c). In this way it has been possible to optimize T(c)(R = 0) for the single phase Bi-2122 cuprate at 96 K with a transition width of 3 K. which is the best value reported to date for the bulk ceramic sample of this material.