On the long period superstructure of the superconducting phase Bi₂Sr₂CaCu₂O_8+x

We have analyzed the structure of the superconducting phase Bi₂Sr₂CaCu₂O_8+x from the long-period superstructure point of view in the a-b plane. An incommensurate modulation along the b-axis has been found with mean size for the anti-phase boundaries of M= 5 2. Simulated electron diffraction patterns and images from these compounds are presented. It is concluded that the superstructure is consistent with a long period structure based on planar defects such as antiphase boundaries. Calculated diffraction patterns and images using this model are in full agreement with the experimental results obtained by several groups. We therefore conclude that the incommensurate structure along the b-axis observed in these materials can be explained in terms of a simple defect structure.