A study of superconducting crystals by diffuse scattering measurement

Although the crystal structures of the Bi-based high- superconductor, which is distinguished by incommensurate modulations, were solved several years ago, their implications for superconductivity are as yet uncertain. This indicates that the deviation from the average structure also should be considered; this may play an important role in the superconductivity. For this purpose the contour maps of the scattering intensity in the plane for single crystals have been observed by both ordinary x-ray and synchrotron radiation. The characteristic feature was obtained in the experiments; that is, the intensity distribution around both the Bragg reflection and its satellites show a strong asymmetry. Both of them are elongated along the c axis, especially the satellites, connecting each other and almost forming a rod shape, which reveals the origin of the presence of the incompatible satellite reflections. This indicates that the structure has a strong two-dimensional feature, which is coincident with the two-dimensional characteristics of physical transportation. Our observation also confirms the previous results that the modulated wavevector is .