STRUCTURE FAMILIES OF SUPERCONDUCTING OXIDES AND INTERSTITIAL ALLOYS

Ising-type analysis of superconducting cuprates shows that the layered structures are composed of perovskite, SrO and CaCuO<INF>2</INF> stru ctural units with different interactions between oxygen atoms. The 45 structures for a combination of a maximum of eight structural units ca n be classified into 13 structural families which are named after the authors who synthesized the first compound or found superconducting pr operties, e.g. the Ruddlesden-Popper, Muller-Bednorz family with the s equence of coordination numbers (CN) of metal atoms 12 6<INF>2</INF> 1 2<INF>2</INF> 6<INF>2</INF> 9<INF>2</INF> 6<INF>n</INF>'. The number o f layers is reduced if segregation, for example of a perovskite with C N 12 6 or of SrO with 6' coordination, is considered. Other compounds such as F>2</INF>Fe<INF>2</INF>Sr<INF>2</INF>O<INF>9</INF> of the Luca s, Raveau series with the CN sequence 6<INF>n</INF>', 9<INF>2</INF> 6< INF>2</INF> 9<INF>2</INF> 6<INF>n</INF>'<INF></INF> occur only in a fe w cases because of a similar composition and lower stability. Another five structural families are obtained if the CaCuO<INF>2</INF> structu ral unit (4 8) is replaced by Cu(Nd, Ce)<INF>2</INF>O<INF>4</INF> (4 8 <INF>2</INF>') or if SrO (6') is replaced by WBi<INF>2</INF>O<INF>6</I NF> (6 12<INF>2</INF>') in the Aurivillius family.