Superconducting materials 1212 cuprate structures

In these and the other cuprate superconductors, the part of the structure that leads to superconductivity is the slab of Cu02 sheets. When more than one sheet is present, they are separated by cation layers, Q (usually Ca or Y) to give a sequence Cu02-(Q-Cu02) i, which forms the superconducting layer in the material. The index n is the total number of Cu02 layers in the phase, which is equal to the formula number of Cu atoms present (Fig. 8.5). 

Although the high-temperature superconducting phases are formed from insulating materials by the introduction of defects, the precise relationship between dopant, structure, and properties is not fully understood yet. For example, in most of the cuprate phases it is extremely difficult to be exactly sure of the charges on the individual ions, and because of this the real defect structures are still uncertain. 

The electron density in transition metal complexes is of unusual interest. The chemistry of transition metal compounds is of relevance for catalysis, for solid-state properties, and for a large number of key biological processes. The importance of transition-metal-based materials needs no further mention after the discovery of the high-Tc superconducting cuprates, the properties of which depend critically on the electronic structure in the CuOz planes. 

The first edition of this book published in 1986 was well received by the chemistry and materials science communities and this resulted in the paperback edition published in 1989. We are most gratified by this warm reception to the book which has been found useful by students and teachers as well as practising solid state chemists and materials scientists. Since we first wrote the book, there have been many new developments in the various aspects of solid state chemistry covering synthesis, structure elucidation, properties, phenomena and reactivity. The discovery of high-temperature superconductivity in the cuprates created a great sensation and gave a boost to the study of solid state chemistry. Many new types of materials such as the fullerenes and carbon nanotubes have been discovered. We have now revised the book taking into account the new developments so that it reflects the present status of the subject adequately and points to new directions. 

With the discovery of superconductivity (Tc = 15.5 K) in the Y-Ni-B-C system [6, 80], a new class of quaternary borocarbide superconductors has emerged. Superconductivity has been observed in several rare earth (Lu, Tm, Er and Ho) nickel borocarbides[80], and with transition metals such as Pd and Pt. The superconducting phase having the composition of YNi2B2C, crystallizes [81] in a tetragonal structure with alternating Y-C and Ni2B2 layers. Band structure calculations [82] indicate that these materials, unlike cuprate superconductors, are three-dimensional metals. 

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