Structural classification of superconducting cuprates

The concept of a homologous series in the case of cuprate superconductors can be defined as ''a family of layered copper oxides that differ from one another only by the number of pairs of CuO2 and bare cation planes in the so-called infinite-layer block''. During the last three years a large number of new homologous series has been discovered. Since the number of new phases is increasing so rapidly, it has become more and more important to develop an unambiguous classification system for the known structures. The present paper reviews and discusses the structures and classification of the existing cuprate families in general. Based on the accumulated knowledge the functions of each structural block in terms of charge balance and doping are more clearly understood. Categorization of the existing cuprate phases promotes also the design and synthesis steps of new materials and even of new structure types. In that respect, the synthesis and optimization of the so-called 01(n-1)n, 02(n-1)n, Cu-12(n-1)n and Pb-12(n-1)n series are discussed in more detail. (C) 1997 Academic Press Limited.