Bismuth cuprate superconductors

Preparation of Bismuth- and Thallium-Based Cuprate Superconductors... 

A number of chemical reviews of cuprate superconductors have included the bismuth and thallium families (11)-(14). Reviews focussing on the structural chemistry of these two series are also available (15),(16). On the thallium cuprates, an overview of structural studies has appeared (17), and a detailed review of... 

The layer-type structures and chemical nature of the constituents of the bismuth and thallium-based cuprate superconductors - notably the lone-pair stereochemistry of Bis+, variable valence of copper, and considerable exchange among some of the cation sites - combine to make structural non-ideality, nonstoichiometry, and phase intergrowth the rule rather that the exception in these families of materials. These features, as well as the probable metastability of the phases (and possibly all high-temperature oxide superconductors), also contribute to the difficulties typically encountered in preparing single-phase samples with reproducible properties and compositions. 

This chapter presents an overview of our understanding of phase relationships and a summary of synthetic techniques for the synthesis of phase-pure superconducting samples in the bismuth-and thallium-based families of high Tc cuprate superconductors. 

The volatility of the reactants is a concern in some solid state syntheses. This may be a slight problem in bismuth cuprates synthesized at high temperatures because Bi2Os has an appreciable vapor pressure at these temperatures (i.e. 900-950°C) however, chemical analyses of samples of bismuth-based superconductors before and after reactions at temperatures up to 900°C indicate no detectable loss of bismuth. This problem is much more severe in the case of thallium chemistry. 

The following sections will outline specific methods for the synthesis of Bi- and Tl-based cuprate superconductors. Because the synthetic methods and historical evolution of the compounds are different, the bismuth and thallium families are described separately. 

A review of the synthetic methods used to prepare the bismuth and thallium families of cuprate superconductors has been presented. An overview of our current knowledge of phase relationships in the bismuth systems is also given such studies of... 

While this chapter has focussed on synthesis of polycrystalline samples, other aspects of the bismuth and thallium cuprate superconductors are discussed elsewhere. An introduction to synthesis and crystal growth is given in Chapter 5, and a review of the crystal chemistry of the two families is presented in Chapter... 

Figure 7.30 The ab plane resistivity in cuprate superconductors as a function of temperature (a) Bismuth cuprate (2201) (b) Laj gjSro jjCuO (c) Bismuth cuprate (2212) (d) YBajCujO,.

Bismuth cuprates of the general formula Bi2(Ca,Sr)n+1Cu 02 +4 possessing an orthorhombic structure and containing two rock-salt type layers of BiO constitute an important family of superconductors, with the n = 2 and the n = 3 members showing Tcs of 90 K and 110 K respectively (figure 10). The n = 1 member of the formula Bi2+2.Sr2 a.Cu06 (without Ca) shows a maximum Tc of around 20 K. The n = 1 member containing calcium has been reported, but it does not appear to be... 

One of main thrusts in organic-perovskite hybrids has been in the preparation of stable delaminated perovskite sols as the building blocks of nanocomposite materials. A well-known process for exfoliation is to weaken the attractive interaction of the layers through intercalation of bulky organic components. A representative example is exfoliation of bismuth-based cuprate superconductors (Figure 14.12). °3... 

---