A STUDY OF BI2SR2CACU2O-DELTA SUPERCONDUCTING CRYSTALS BY DIFFUSE-SCATTERING MEASUREMENT

Although the crystal structures of the Bi-based high-T-c superconducto r, which is distinguished by incommensurate modulations, were solved s everal years ago, their implications for superconductivity are as yet uncertain. This indicates that the deviation from the average structur e also should be considered; this may play an important role in the su perconductivity: For this purpose the contour maps of the scattering i ntensity in the b-c* plane for Bi2Sr2CaCu2Odelta single crystals have been observed by both ordinary x-ray and synchrotron radiation. The c haracteristic feature was obtained in the experiments; that is, the in tensity distribution around both the Bragg reflection and its satellit es show a strong asymmetry. Both of them are elongated along the c axi s, especially the satellites, connecting each other and almost forming a rod shape, which reveals the origin of the presence of the incompat ible satellite reflections. This indicates that the structure has a st rong two-dimensional feature, which is coincident with the two-dimensi onal characteristics of physical transportation. Our observation also confirms the previous results that the modulated wavevector is q = q(2 )b + c* (q(2) = 2.0 similar to 2.1).