Bismuth-Containing Superconductors

Bi2Sr2CaCu2Og but containing a commensurate modulated superstructure has been prepared and characterized (19) and gives further insight into the structures of the Bi-O layers. This is discussed in further detail below. A material containing three copper-oxygen sheets, with ideal formula Bi2Sr2Ca2Cu3O10, can also be made. The Tc s of the one, two, and three copper-sheet compounds are 10, 85, and 110 K, respectively. 

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Rojo and coworkers have explored the use of ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) salts as precursors for the preparation of bismuth-containing superconductors. The pyrolysis of the mixed lead-bismuth complex PbBi(DTPA)-3 H2O was shown to proceed in three stages firstly the dehydration of the complex (32-150 °C) followed by the loss of organics starting at 300 °C, and finally the decomposition of the residual ill-defined carbonates up to 500 °C affording a mixture of PbO and an unidentified new Bi—Pb—O phase. 

Some aspects of bismuth chemistry have been known and studied for many decades but in recent years there has been a resurgence of interest in the properties of this element not least because of its application in a number of important yet often disparate fields. These fields include bismuth containing pharmaceuticals, superconductors, ferroelectrics, heterogeneous catalysts and, of particular relevance to this book, reagents for organic synthesis. 

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... 

Oxides containing bismuth oxygen atom double layers include the bismuth calcium copper oxide series of superconductors exemplified by Bi2Sr2CaCu20g (Bi-2212) and the beta phase oxide ion conductors based on the composition Sr Big j 0(2 j)/2. While the details of these two stmcture types are quite different, they have the common feature of containing BiMT double layers that are only weakly bonded. In Bi-2212, the bismuth atoms are four + one coordinated by oxygen atoms whereas, in Srj Bi9 j 0(2 j)/2 they are three + one coordinated and form square and hexagonal layers of Bi-O bonds. Both classes of compounds and be intercalated by iodine atoms that are inserted between the Bi-O double layers. 

The manufacture of bismuth-, copper-alkaline earth oxide high-tem-perature superconductors is carried out through calcination and/or sintering in ozone-containing atmosphere with Bi(OH)2, Ca(N03)2 and Sr(N03)2 and subsequent treatment by CuC03(0H)2 the components are dried, calcinated in ozone containing air, molded and dried in air atmosphere. Their temperature of superconductivity is 107K and the critical current density is 405 A/cm2[153]. 

To date, many of the ceramic superconductors contain copper and share a common structural feature copper and oxygen atoms bonded together in planar sheets. In YBCO superconductors, the Cu—O planes are widely separated. In bismuth superconductors, the Cu—O planes occur in "sandwiches" consisting of two closely spaced sheets separated by a layer of group 2 ions. These sandwiches are separated from one another by several layers of bismuth oxide. In the thallium superconductors, the Cu—O planes are stacked in groups of three, like triple-decker sandwiches. 

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