Classification of superconducting oxide structures

There are approximately 35 superconducting oxide structures and structurally related compounds. These are analysed as symmetrical combinations of u or u' (Ca,Sr)CuO2, v CaTiO3, w' SrO and W' CeO2 structural subunits. A 'crystallographic' notation of the metal atoms according to the sequence of different layers gives more information than the common characterization by the ratio of metal atoms. The oxygen coordination numbers of the metal atoms allow the classification of isomorphous compounds and the search for new compounds. Physical properties can be predicted from the sequence of u, v, w' and W' units. The structures with a maximum of eight subunits can be classified according to the different hole-donating elements u' (9 structures), w' (21 structures) or electron-donating element W' (4 structures). There are 15 structures containing two donating elements (u'+w'), (u'+W') or (w'+W'). The superconducting layers v of 11 structures with a Tc>40 K are separated by insulating layers u. Six non-symmetrical structures can be considered as a combination of two different structures. A two-dimensional connection of u and v units yields metallic, but non-superconducting oxides with oxygen vacancies in the CuO2 planes. The non-metallic Aurivillius phases are closely related to the structures of superconducting oxides. (author)