High-temperature ceramic oxide superconductors

High-temperature superconductivity in oxides of the type La2-xBax(Srx)CuO4, YBa2Cu3O7-δ, La3-xBa3+xCu6O14 and Bi(Tl)(-Ca-Sr(Ba)-Cu-O systems is discussed, with special emphasis on the experimental findings from the author's laboratory. The importance of holes on oxygen and of the Cu1+ (d10) state is examined. A transition is shown to occur from chain- to sheet-superconductivity in YBa2Cu3O7-δ accompanying a change in oxygen stoichiometry. Some of the important material parameters and technological applications are briefly presented. There is every hope that materials with Tc close to room temperature will be discovered in the near future. All the high Tc oxides found hitherto have perovskite-related structures with two-dimensional Cu-O sheets.