191 superconductor composition

Ho CT, Chung DDL, Carbon fiber reinforced tin-superconductor composites, Bhagat RB, Clauer AH, Kumar P, Ritter AM eds., Minerals, Metals <6 Materials Society Metal Ceramic Matrix Composites, Processing, Modelling <6 Mechanical Behaviour, Minerals, Metals Materials Society Anaheim, 525-533, Feb 19-22, 1990. 

A number of researchers have begun to prepare poly-mer/superconductor composites with the hope of improving the processibility and properties of the hybrid materials (see Table 37.1) [1-8], For example, polymeric matrices loaded with ceramic superconductor components have been used in a plastic extrusion process to prepare superconducting wires and filaments [5,6]. Moreover, hydrophobic polymers have been used as environmentally protective layers [7,8] to slow the parasitic corrosion reactions that occur when cuprate compounds are exposed to water, acids, carbon dioxide, and carbon monoxide. 

Table 37.1 Summary of Polymer/Superconductor Composite Systems...

H, Crystal Engineering of Organic Superconductor/ Inorganic Superconductor Composite Structures... 

In summary, effective methods have been identified for the preparation of conductive polymer/superconductor and molecular metal/superconductor composite structures. Here both solution-processing strategies and electrochemical deposition techniques for the preparation of the composite structures have been developed. Moreover, a powerful new high-Tc self-assembly method based on the spontaneous adsorption of amine reagents onto cuprate surfaces has been developed that affords precise control of the synthesis of polymer/superconductor composite systems. With these methods, the hybrid structures can be prepared with little chemical or physical damage to either conductor component material. Convincing evidence for the clean combination of the molecular and superconductor components has been obtained from electrochemical, conductivity, contact resistance, and electron microscopic measurements. 

S. G. Haupt, D. R. Riley, and J. T. McDevitt, Conductive polymers/high-temperature superconductors composite structures, Adv. Mater. 5 755 (1993). 

Electrical and Electronic Applications. Silver neodecanoate [62804-19-7] has been used in the preparation of a capacitor-end termination composition (110), lead and stannous neodecanoate have been used in circuit-board fabrication (111), and stannous neodecanoate has been used to form patterned semiconductive tin oxide films (112). The silver salt has also been used in the preparation of ceramic superconductors (113). Neodecanoate salts of barium, copper, yttrium, and europium have been used to prepare superconducting films and patterned thin-fHm superconductors. To prepare these materials, the metal salts are deposited on a substrate, then decomposed by heat to give the thin film (114—116) or by a focused beam (electron, ion, or laser) to give the patterned thin film (117,118). The resulting films exhibit superconductivity above Hquid nitrogen temperatures. 

Oxide superconductors have been known since the 1960s. Compounds such as niobium oxide [12034-57-0] NbO, TiO, SrTi02, and AWO, where A is an alkah or alkaline earth cation, were found to be superconducting at 6 K or below. The highest T observed in oxides before 1986 was 13 Kin the perovskite compound BaPb Bi O, x = 0.27. Then in 1986 possible superconductivity at 35 K in the La—Ba—Cu—O compound was discovered (21). The compound composition was later determined to be La 85 A the Y—Ba—Cu—O system was pubUshed in 1987 and reported a transition... 

XPS has been used in almost every area in which the properties of surfaces are important. The most prominent areas can be deduced from conferences on surface analysis, especially from ECASIA, which is held every two years. These areas are adhesion, biomaterials, catalysis, ceramics and glasses, corrosion, environmental problems, magnetic materials, metals, micro- and optoelectronics, nanomaterials, polymers and composite materials, superconductors, thin films and coatings, and tribology and wear. The contributions to these conferences are also representative of actual surface-analytical problems and studies [2.33 a,b]. A few examples from the areas mentioned above are given below more comprehensive discussions of the applications of XPS are given elsewhere [1.1,1.3-1.9, 2.34—2.39]. 

The generally accepted theory of electric superconductivity of metals is based upon an assumed interaction between the conduction electrons and phonons in the crystal.1-3 The resonating-valence-bond theory, which is a theoiy of the electronic structure of metals developed about 20 years ago,4-6 provides the basis for a detailed description of the electron-phonon interaction, in relation to the atomic numbers of elements and the composition of alloys, and leads, as described below, to the conclusion that there are two classes of superconductors, crest superconductors and trough superconductors. 

Given the potential future importance of ceramics in areas as diverse as electronics (see Chapter 4), machine tools, heat engines, and superconductors (see Chapter 4), the United States can ill afford to surrender technical leadership to its competitors. The dominant trend in the field is toward materials with finer microstractures, fewer defects, and better interactions at interfaces (particularly in composites). Chemical processes provide important tools to capture the promise of ceramics for the benefit of our society and to maintain our international competitive position in technology. 

MATERIALS SCIENCE IS A CRITICAL TECHNOLOGY for America. In 1987 and again in 1990, the U.S. Department of Commerce included advanced materials such as ceramics, polymers, advanced composites, and superconductors in a short list (1) of very important emerging technologies. The world market based on these advanced materials was estimated conservatively at 600 million by the year 2000. 

This should come as no surprise, since the physical behavior of materials is non-linear and unpredictable, especially when materials are formulated or in combination. Two examples will suffice high temperature ceramic superconductors and insulators above their critical temperatures or at non-ideal stoichiometries composite structures may show several times the strength or impact resistance than would be expected from their component materials. Materials discovery will always require a good deal of trial and error, factors that may be mitigated by techniques that permit the simultaneous synthesis of large numbers of materials, followed by rapid or parallel screening for desired properties. 

The important and widely studied copper-oxide-derived high-temperature superconductors, known as cuprate superconductors, are basically insulators. Doping converts these into metallic materials, many of which are superconductors over rather more restricted composition ranges. Several of these materials have already been discussed La2Cu04 and Sr2Cu02F2 (Section 4.3.3), La2 A.SrxCu04 (Section 8.5.1), and Nd2, Ce,Cu04 (Section 8.5.2). 

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