Bismuth-copper-calcium based systems

The high temperature superconductivity discovered in the Bi-Sr-Ca-Cu-O system was found to be related to a homologous series of compounds with an idealized formulation Bi2Sr2Ca iCu 02n+4 (n = 1 to 3 or more). The n = I, 2, 3 phases have Tc values of 10-20, 90 and 11 K, respectively. The presence of superstructure modulations which are, in general, incommensurate with the basic structure was first discovered by HRTEM and ED (Shaw et al 1988, Gai et al 1988). The periodicity of the modulation is found to be about 4.7 multiplied by the a-lattice parameter. The compounds can be prepared from solid state reactions of the component oxides in stoichiometric proportions and heating between 800-900 °C in air. 

The fundamental structure of Bi2Sr2CaCu20g (or the 2212 phase), ignoring the modulations, is orthorhombic, with a = 5.39 A, = 5.41 A and c = 30.8 A. A schematic diagram of the structure is shown in figure 6.4(a). It consists of a Bi202 double layer and a perovskite layer containing two Cu02, 

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