ABSTRACT
There are some characteristic features in the structures of high-Tc superconductive oxides. The first one is that the species of component elements are many in number, at least 4. The second one is that the crystal structures are of new types. They seem to be rather complicated, but there is a common structural element, a Cu02 plane, in which the superconductive current runs. Atomic planes of the remaining part, sandwiching the Cu02 plane, also play an important role in that they accommodate additional oxygen atoms or defects to provide carriers (positive holes in the case of Bi-based superconductors) to the Cu02 planes. They are then called the charge reservoir. The transition temperature between superconductive and nonsuperconductive states, Tc, strongly depends on the concentration of carriers in the Cu02 planes, which closely relates to structures in the charge reservoirs and the number of the Cu02 planes.
