Elements superconducting properties

It is used in arc-welding rods for stabilized grades of stainless steel. Thousands of pounds of niobium have been used in advanced air frame systems such as were used in the Gemini space program. The element has superconductive properties superconductive magnets have been... 

Practically all HTSC materials contain chemically active elements with the consequence that various degradation processes are bound to proceed accompanied by the loss of superconducting properties in air, and especially in moist atmospheres and electrolyte solution. Hence, it is essential to carry out electrochemical studies only in media for which degradation does not proceed or is very slow. These are, primarily, aprotic solvents, and also aqueous alkaline solutions of sufficiently high concentration, including those to which have been added salts of the elements of the HTSC components. Thus, in ordinary aqueous solutions, at not too low a pH one can study relatively stable thallium- and bismuth-based HTSCs, and also LCO and certain of its derivatives. 

Roberts ( 1 1) surveyed the superconductive properties of the elements and recommended a critical temperature of 1.175 0.002 K for Al(cr). Since this temperature is so low, the effects of superconductivity on the thermodynamic functions are not considered. The entropy contribution due to superconductivity will be less than 0.002 J X mol . The data of Giauque and Meads (j ) and Downie and Martin (3) agree at temperatures up to 150 K but drift apart by 0.2 J X mol at 200 X and 0.17 J X mol at 300 K, with the Downie and Martin study being lower. The Takahashi (4, 5) study is even lower at 298 X. The high temperature heat capacity values are derived from the enthalpy study of Ditmars et al. (9). Their curve is intermediate between those derived from previous studies (4, 5, 6, 7, 8) and implies a flatter Cp curve near the melting point (in comparison to previous interpretations). Numerous other heat capacity and enthalpy studies are available but were omitted in this analysis. A detailed discussion of the Group IIIA metals (B, Al, and Ga) is in preparation by the JANAF staff. 

Properties Lustrous metal. D 7.87, mp 1312C, bp 3000C reacts slowly with water. Soluble in dilute acid insoluble in water. Exhibits a high degree of magnetism, especially at low temperatures salts are colorless has highest neutron absorption cross-section of any known element has superconductive properties, burns in air to form the oxide. Combustible. 

The composition, structure and superconducting properties of high Tc oxide superconductors, La-Sr-Cu-0 and Y-Ba-Cu-0 systems have been investigated. From comparative studies of effects of partial replacements of metal sites by other elements, a low dimensional nature of conduction path was suggested in both oxide systems. Critical relevance of oxygen deficiency and the conditions of heat treatments to the evolution of superconductivity, is discussed in terms of the relatively large nonstoichiometry found in these systems. 

The fact that Tc is essentially unchanged by replacement of Y with the magnetic rare earth elements points to the Cu-O sublattice as the source of the superconducting properties of Y,Ba2Cu309 y. Mixtures of rare earths or alkaline earths (2,13) also do not affect Tc, again emphasizing the key role of the Cu-O sublattice. 

The following tables include superconductive properties of selected elements, compounds, and alloys. Individual tables are given for thin fUms, elements at high pressures, superconductors with high critical magnetic fields, and high critical temperature superconductors. 

The nature and origin of superconductivity was described in 1957 by John Bardeen, Leon Neil Cooper, and John Robert Schrieffer. Together they created the Bardeen Cooper Schrieffer (BCS) model. It occurs for many metals, alloys, intermetallic compounds, and doped semiconductors. The transition temperatures range from 92.5 K for Ybc CUjOg j, down to 0.001 K for the element Rh. And there are some materials that become superconducting only under high-pressure conditions. These materials all have to be extremely pure, even just one impurity in 10,000 atoms can severely affect the superconducting property. 

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