Abstract

Knowledge of crystal structures is essential for understanding physical properties and of great help when defining guidelines for the exploration of new materials. The efforts invested since the discovery of superconductivity during low-temperature studies of mercury have led to the synthesis of more than one thousand different superconducting compounds, among which are several hundreds of high-temperature superconducting oxides. Classical superconductors cover a large spectrum of chemically different substances, ranging from metallic elements and alloys to borides, carbides, chalcogenides and organic compounds, and crystallize with very different structures. High-T _c superconducting oxides contain, in addition to copper and oxygen, which are always present, many other chemical elements, but show common structural features, e.g. a pronounced layer character.