In superconductors

This experiment outlines a potentiometric titration for determining the valency of copper in superconductors in place of the visual end point used in the preceding experiment of Harris, Hill, and Hewston. The analysis of several different superconducting materials is described. 

CERAMCS-ELECTRONIC PROPERTIES AND MATERIALSTHUCTURE] (Vol5) -in superconductors [CERAMICS AS ELECTRICAL MATERIALS] (Vol5)... 

Coppet(II) oxide [1317-38-0] CuO, is found in nature as the black triclinic tenorite [1317-92-6] or the cubic or tetrahedral paramelaconite [71276-37 ]. Commercially available copper(II) oxide is generally black and dense although a brown material of low bulk density can be prepared by decomposition of the carbonate or hydroxide at around 300°C, or by the hydrolysis of hot copper salt solutions with sodium hydroxide. The black product of commerce is most often prepared by evaporation of Cu(NH2)4C02 solutions (35) or by precipitation of copper(II) oxide from hot ammonia solutions by addition of sodium hydroxide. An extremely fine (10—20 nm) copper(II) oxide has been prepared for use as a precursor in superconductors (36). 

Thiophenes continue to play a major role in commercial applications as well as basic research. In addition to its aromatic properties that make it a useful replacement for benzene in small molecule syntheses, thiophene is a key element in superconductors, photochemical switches and polymers. The presence of sulfur-containing components (especially thiophene and benzothiophene) in crude petroleum requires development of new catalysts to promote their removal (hydrodesulfurization, HDS) at refineries. Interspersed with these commercial applications, basic research on thiophene has continued to study its role in electrocyclic reactions, newer routes for its formation and substitution and new derivatives of therapeutic potential. New reports of selenophenes and tellurophenes continue to be modest in number. 

R. Chevrel, in Superconductor Materials Sciences Metallurgy, Fabrication and Applications (S. Foner, B.B. Schwarz, eds.), Chap. 10. Plenum Press, 1981. 

Scientists are interested in superconductors because they have a number of properties that arise from their lack of resistance. For example, once a current is induced in a circuit made with a superconducting material, the current continues to flow through the circuit indefinitely, without ever diminishing. Also, superconductors have the ability to completely repel magnetic field lines. This means that a magnet placed over a superconductor hovers in mid-air, as shown in Figure 4.25. 

Uses. Yttrium is mixed with rare earths as phosphors for color television receivers oxide for mantles in gas and acetylene lights in ceramics in superconductors... 

Giaever, I. (1960). Energy gap in superconductors measured by electron tunneling. Phys. Rev. Lett. 5, 147-148. 

The quest for higher transition temperatures in superconductors took a strange turn when ceramic materials, possessing good, room-temperature metallic conductivity, were investigated. A study of simple binary compounds such as ZrN (Tc = 10.7 K), NbC (Tc =... 

Discovery of the 90+ K Superconductor "Paul" Chu and coworkers at the University of Houston (during October 1986) carried out the synthesis of (La1.xBax)CuOs.y (Type I) and (La1.xBax)2 Cu04.y (Type II) compounds and isolated superconducting phases exhibiting a sharp decrease in resistivity at 32 K. The best materials, however, showed only a 2% Meissner fraction. By applying pressure to one such product, their forte in superconductor research, they observed an increase in transition temperature of 8 degrees at 14 kbar pressure (see Figure 29). Chu, et al., submitted (156) these results to Physical Review Letters on 15 December 1986, and the publication appeared in the January 26, 1987 issue. 

Various substitution studies (171-173) were conducted in the early stages of research on these new oxide superconductors. One most dramatic result was the facile substitution of other (magnetic) lanthanide ions for yttrium in the VUI-coordinated site of the structure. The incorporation of these magnetic ions had no effect on the superconductivity nor the Tc of the material— quite astounding, since the presence of magnetic ions in superconductors was previously believed to destroy the phenomenon entirely Table 13 presents several examples of such substituted compounds. 

Tinkham, M., 1970b. Far infrared absorption in superconductors, in Far-Infrared Properties of Solids, S. S. Mitra and S. Nudelman (Eds.), Plenum, New York, pp. 223-246. 

A breakthrough in superconductor technology came with the discovery24 of yttrium barium copper oxide, YBa2Cu307, whose crystal structure is shown here. When heated, the material readily loses oxygen atoms from the Cu-O chains, and any composition between YBa2Cu307 and YBa2Cu3Ob is observable. 

Figure 8 Slipped and staggered relationship of TMTSF molecules in superconductors the relative positions are approximate...

More recently, other metals such as thallium, bismuth, and lead have been included in superconductor formulation. In one interesting series, the critical temperature has been found to increase with increasing n in susperconductors of the type HBa2Can CunO ,l+2 to a max,mum 122 K for n = 4 (Fig. 7.34).45 The current maximum critical temperature is 125 K for a closely related TUBa2CujO,v-... 

Giaever, I Energy Gap in Superconductors Measured by Electron Tunneling. Physical Review Letters, 5(4), 147-148 (August 15, 1960). 

But with the metal at a temperature below 7.2 K before the external field is removed, this current shows no sign of decay even when observations extend over a period of a year. As a result of such measurements, it has been estimated that it would require 10 years for the supercurrent to decay. Such persistent or frictionless currents in superconductors were observed in the early 1900s—hence they are not a recent discovery. 

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