Modulated structures of bismuth-based superconductors

A brief review is given of the modulated structures of bismuth-based high temperature superconductors and related materials. Three types of generally incommensurate modulations with distinct wave vector and symmetry will be discussed. Various cation substitutions, including Y3+, rare-earth trivalent cation, Pb2+ and 3d-metal element (Mn, Fe and Co) substitutions, and their impact on the modulations will be described. The origin of the modulation is ascribed to the lattice mismatch between the BiO and the CuO2 layers. The modulation periodicity is closely related to the extra oxygen insertion in the BiO layer. (orig.)