Superconductive ceramics structures

In the system Ba(Pb1.xBix)Os, the compound with x = 0.25 must be considered the first discovered ceramic material showing high-temperature superconductivity (7). Structure determinations have been carried out over the entire range of composition (8)-(ll) and the refined parameters are presented in Table 2. Superconductivity in this system exists only for values of x between 0.05 and 0.35. The value of the critical temperature increases with x, reaches a maximum value Tc 13K for x = 0.25, and then decreases. For x > 0.35, the material becomes a semiconductor. 

A significant step in the history of the HTSs was the discovery in 1966 of superconductivity in the oxygen-deficient perovskite SrTi03 5, containing some barium or calcium substituted for strontium. Although the Tc value was very low (0.55 K), in retrospect it can be seen as the first superconducting ceramic. In 1979 a Tc of approximately 13 K was discovered for BaPb075Bi025O3, which also has the perovskite structure. 

But even though crystallographers have pulled the ceramic structure apart, can track the path of a current along their chains and planes, and can speculate as to where superconductivity actually takes place, this doesn t yet tell... 

Because the function of semiconductors, like the new superconducting ceramics, is dependent on the way their crystalline structure is arranged, transistor makers can control the function of the devices by deliberately adding small amounts of certain impurities to the crystals. Such impurities control the flow of electricity through the device either by providing extra electrons or by not supplying enough. 

Some selected superconducting carbides, nitrides, borides, and sulfides are presented in Table 1 with their values. Among these superconducting ceramics, the most influential factor was the crystal structure. Many of the important superconductors were based on the NaCl-type structure (also referred to as the B1 structure by metallurgists) and the... 

Colloidal dispersions of 33-nm-diameter trimetallic Au-Pb-Cd particles, containing gold core surroimded with a 18-nm-thick lead shell are formed by y-irradiation of corresponding metals salts." Nanocomposites with three or more different metals are multimetallic nanohybrids. Studies of their structures is a challenging task. Nevertheless, these materials have aheady been used as precursors in the production of superconducting ceramics, special multicomponent steels, etc. Traditionally, polymer is formed in a previously prepared inorganic matrix or the polymer is inserted into the latter. Multimetallic nanocomposites are prepared in situ within a polymeric matrix or simultaneously with polymer matrix formation. 

Note that the issue of the brittleness of ceramics restricting their application is not limited to structural applications. For instance, the brittleness of superconducting ceramics had to be resolved by employing them either as thin films on ductile metal wires or embedded within ductile metal casings. Thus the understanding of how to defeat the brittleness of the ceramics impacts their use in a host of applications. 

The superconducting oxides include both perovskites and Ruddlesden-Popper compounds which have an orthorhombic arrangement of cubic cells, alternatively of the perovskite and sodium chloride structures. The common feature of all of these is the presence of copper as a major component. The first ceramic superconductor was a lanthanum-strontium substituted cuprate (Lai Sr Cu04 z), which is a perovskite, but subsequently the inter-oxide compound Y203 2BaO 3CuO, commonly referred to as a 123 compound, was shown to have superior performance. The speculation concerning the conduction mechanism is that this involves either Cu3+-Cu2+ positive hole... 

Influence of Electron Correlation on the Electronic Structure of Superconducting Y-Ceramics... 

After more than ten years of extensive experimental and theoretical studies of the phenomenon of the high Tc superconductivity (HTSC) [1], we still do not know a microscopic mechanism responsible for this phenomenon. Numerous theories of pairing, which lead to high Tc values, are based on models [2-9] and cannot connect a specific chemical composition of HTSC ceramics with the value of the transition temperature Tc. For creating a quantitative theory of the HTSC phenomenon further comparative studies of the electronic structure and their relative properties of SC and non-SC ceramics are needed. In this paper, we confine ourselves to calculations of the electronic structure of the SC yttrium ceramics. 

Influence of Electron Correlation on the Electronic Structure of Superconducting Y-Ceramics Table 6 Self-consistent charge and spin distributions at different electron correlation levels... 

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