The Crystal Chemistry of High-Temperature Oxide Superconductors and Materials with Related Structures

Never before in human history has a chemical substance been the object of collaborative research by so many scientists of different disciplines as in the case of the first high-temperature (HT_c) oxide superconductor La_2?xSr_xCuO₄. If the importance of a class of materials is measured by the number of papers published in a given period, the new superconductors hold the all-time record; moreover, this flood of publications also reflects the high expectations that are held worldwide for this class of substances. Every day seems to bring further surprises. From the two phases of HT_c oxide superconductors that were recognized at the outset there have developed within a period of scarcely two years a series of new materials which all show superconductivity at temperatures above the boiling point of liquid nitrogen; this property is undoubtedly closely related to the crystal chemistry of the individual phases and compounds. This article will report and discuss the resemblances and differences between the HT_c superconductors and materials with related structures.