Oxygen nonstoichiometry effect on structural modulation in Bi-2212 cuprate superconductors

The X-ray diffraction patterns for Bi2Sr2Ca1-xYxCu2O8+y sintered in air or Ar indicated that the reduction in the number of excess oxygen ions induced a structural change from orthorhombic to pseudotetragonal. When the oxygen contents decreased with the reducing treatment, the period of modulation in Bi2Sr2Ca1-xYxCu2O8+y increased. This result supported the model of excess oxygen ions in the Bi-O sheet. However, it was difficult to understand the change of modulation period with increasing Y contents using the model of excess oxygen ions in the Bi-O layers. Also, it is included that the Y substitution for Ca and La substitution for Sr in the Bi2Sr2CaCu2O8+y system result in parallel effects for the modulation structure. (orig.)