High-temperature ceramic oxide superconductors

Abstract

High-temperature superconductivity in oxides of the type $La_{2-x}Ba_x(Sr_x)CuO_4$, $YBa_2Cu_30_{7-\delta}$, $La_{3-x}Ba_{3+x}Cu_60_{14}$ and Bi (Tl)- Ca-Sr(Ba)-Cu-0 systems is discussed, with special emphasis on the experimental findings from the author's laboratory. The importance of holes on oxygen and of the $Cu^{1+} (d^{10})$ state is examined. A transition is shown to occur from chain- to sheet-superconductivity in $YBa_2CU_3O_{7-\delta}$ 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 $T_c$ close to room temperature will be discovered in the near future. All the high $T_c$ oxides found hitherto have perovskite-related structures with two-dimensional Cu-0 sheets.