Relation of Oxygen Content and Modulation Structure in Bi2201 System

Two series of samples of Bi1.8Pb0.2Sr2CuO y and Bi1.9Sr1.6La0.4CuO y systems with different oxygen content were prepared. The microstructure of these samples was investigated by means of X-ray diffraction (XRD) and electron diffraction (ED). The analysis of XRD indicates that a progressive change in lattice parameters takes place with the removal of oxygen. The analysis of ED patterns reveals that for the Bi1.8Pb0.2Sr2CuO y system, the orthorhombic modulation (Pb-type modulation) is strongly related to the oxygen in Bi2O2 layers, which implies that the orthorhombic modulation is not compositional (Pb) modulation, and the periodic distribution of oxygen in Bi2O2 layers induced by Pb doping may be the real origin of orthorhombic modulation. While for the Bi1.9Sr1.6La0.4CuO y system, the monoclinic incommensurate modulation is independence of the variation of oxygen in Bi2O2 layers, which suggests that the intercalation or removal of extra oxygen atoms was only the result of the monoclinic modulation structure changing, and the crystal misfit between Bi2O2 layers and perovskite blocks was the real driving force of the Bi-concentrated band superstructural modulation.