Compounds, superconductivity

Fulde, P., and J. Keller, 1982, in Superconductivity in Ternary Compounds, Superconductivity and Magnetism, eds M.B. Maple and 0. Fischer (Springer, Berlin) p. 249. 

The (rare-earth)-PSYCO compounds [12], Pb r (JtE) i Qa Qi Qb iq which RE is a rare-earth ion or Y, superconduct for all the common rare-earth ions (for which the material is p-type) except for RE=Ce, which naturally becomes Ce+4 in its crystal-held and then dopes the material n-type, and the material does not superconduct [13]. The same happens for Am+4 doping. Clearly, the PSYCO compounds superconduct when doped p-type, but not when doped n-type. 

The compounds of the type YBa2Cu307 are broadly known as a family of 1,2,3-compounds. These are compounds consisting of multiple phases. It is also disturbing to note that the precise composition and constitution of these compounds and their role in exhibiting the properties are not completely clear. It also appears that the properties of the compound are independent of the rare earth present in the compound. Superconductivity has been observed at relatively high temperature in the case of all the rare earths in 1,2,3-compounds. One of the stringent requirements is that the starting materials from which the 1,2,3-compounds are synthesized have to be pure. 

Fascinating it was, but few people paid attention—except for the Japanese. They had read Powell and Danby s paper with the same keen interest with which years later, they would read the obscure journal detailing the discovery by IBM scientists of a ceramic compound superconducting at a record-high Kelvin. In 1970, they exhibited a model of the train at the Osaka World s Fair. By 1979, they tested another at speeds that hit a top of 321 miles per hour, a world record. In 1985, another maglev carried more than a half-million passengers on short runs at the science fair at Tsukuba. 

Table 2. Selected organic metals [39]. None of these compounds superconduct. The temperature of maximum conductivity is in parentheses if it is a broad conductivity maximum...

Using the knowledge that one of the strongest Jahn-Teller ions, Cu(+2), should have the largest electron-phonon interactions and thus should lead to high temperature superconductivity, Bednorz and Muller (1) discovered that a K2NiF4 structured La-Ba-Cu-0 compound superconducts near 30K. 

Despite the initial excitement, this class of high-temperature superconductors has not fully lived up to its promise. After more than 20 years of intense research and development, scientists still puzzle over how and why these compounds superconduct. It has also proved difficult to make wires of these compounds, and other technical problems have hmited their large-scale commercial applications thus far. 

Additives used in final products Fiiiers aramid fiber, caicium carbonate, carbon black, carbon fiber, carbon nanotubes, glass beads, glass fiber, iron powder, metal flakes, nano-CaCOj (nucleating agent), PTFE fiber, talc, zinc whisker Antistatics polyetheresteramide, quaternary ammonium compound, superconductive carbon black Release fluoropolymer, N,N -ethylene bisstearamide, paintable silicone Slip PTFE Thermal stabilizer triethanolamine ... 

This suggestion theoretically explains the metal and intermetallic compound superconductivity phenomenon (J. Bardin, L.N. Cooper and R. Schrieffer, Nobel Prize 1972), discovered earlier by H. Kamerling-Onnes (Nobel Prize, 1913). This phenomenon occurs only at very low temperatures (—20 K). However, superconductivity has been discovered in nonmetalhc, oxide-type chemical compounds with critical points of superconductivity up to ==140 K (in hquid nitrogen region) (so-called high-temperature super conductors, HTSC) (J.G. Bednorz and K.A. Muller, Nobel Prize, 1987). Intensive attempts to synthesize new materials of this kind are in progress. 

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