Oxide ceramics superconductors

The copper oxide ceramic superconductors are two-dimensional conductors They can conduct a current parallel to the layers of Cu and O atoms but not between the layers. The fullerides, by contrast, are three-dimensional conductors that conduct equally in all directions. Because of this property, they may prove to be superior materials for making superconducting wires. 

The theoretical interpretation of the high temperature superconductors is still under development. The copper oxide ceramic superconductors obtain their paired conducting electrons from copper in mixed oxidation states of I and II or II and III, depending on the particular system. The paired conducting electrons are called Cooper pairs, after Leon N. Cooper. Cooper s name also gives us the C of BCS the BCS theory is an interpretation of superconductivity for low temperature superconductors (having Tc s of less than 40 K). 

The most important feature of these oxide ceramic superconductors is that superconductivity can be achieved in liquid nitrogen (77K). This is very... 

Before the discovery of high-temperature superconductors in 1986, there already existed oxide ceramic superconductors such as SrTi03 (Tc = 0.4 K) 7, BaPbOs (Tc = 0.4 K) and Ba(Pb,Bi)03 (Tc = 12K). They have a cubic perovskite structure. In those, the Ba(Pb, Bi)03 attracted much interest from scientists due to its high Tc despites of relatively small carrier density. In 1998, Cava et al. discovered that (Ba, K)Bi03 with same cubic perovskite structure has an extremely higher Tc of 40 K [8] in cubic perovskite superconductors. Figure 8.1.2 shows the crystal structure of cubic perovskite. The unit cell is... 

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. 

There are presently four famihes of high-temperature superconductors under investigation for practical magnet appheations. Table 11-25 shows that all HTS are copper oxide ceramics even though the oxygen content may vary. However, this variation generally has little effect on the phvsical properties of importance to superconductivity. 

As an example of the production of oxide systems, the ceramic superconductor YBa2Cu307 j has been prepared tlrrough the reaction... 

In the ceramics field many of the new advanced ceramic oxides have a specially prepared mixture of cations which determines the crystal structure, through the relative sizes of the cations and oxygen ions, and the physical properties through the choice of cations and tlreh oxidation states. These include, for example, solid electrolytes and electrodes for sensors and fuel cells, fenites and garnets for magnetic systems, zirconates and titanates for piezoelectric materials, as well as ceramic superconductors and a number of other substances... 

A unique application of the solid oxygen electrolytes is in dre preparation of mixed oxides from metal vapour deposits. For example, the ceramic superconductors described below, have been prepared from mixtures of the metal vapours in the appropriate proporhons which are deposited on the surface of a solid electrolyte. Oxygen is pumped tluough the electrolyte by the application of a polarizing potential across the electrolyte to provide the oxidant for the metallic layer which is formed. 

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... 

A common feature of all the new ceramic superconductors is that they are cuprates, that is, they are complex copper oxides. The structure of YBCO is given in Fig. 19.3, which also shows that it is related to the perovskite structure (Fig. 4.17). Synthesis of YBCO is remarkably easy appropriate amounts of dry yttrium oxide (Y203), copper oxide (CuO), and barium carbonate (BaC03) are ground together into a fine, well-mixed... 

The 1-2-3 ceramic superconductor YBa2Cu307 has been synthesized by the sol-gel method from a stoichiometric mixture of yttrium ethoxide, barium ethoxide, and cop-per(II) ethoxide in an appropriate organic solvent. The oxide product, before being heated in oxygen, has the formula YBa2Cu3065. Write a balanced equation for the hydrolysis of the stoichiometric mixture of metal ethoxides. 

Surface fluorination in various fluorinated media are currently used nowadays as processes that allow the modifications of many classes of materials, such as metals, intermetallics, semiconductors, carbons, superconductors, oxide ceramics. The above selected examples have illustrated some physical properties that can be drastically modified, including conduction, adhesion, passivation, superconductivity, hy drophobicity / wettability. 

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