Superconducting transition temperature metals Table

The superconducting transition temperatures for selected chemical elements and certain metallic alloys are presented in Table 1. These data and those presented throughout this Chapter have been taken, for the most part, from the excellent compilation by B. W. Roberts (3). 

The superconducting transition temperatures of boron and selected borides are listed in Table 4.2-30. Boron itself, which is an isolator at ambient pressure, was recently found to become superconducting under high pressure [2.129]. The boron atoms in transition metal borides can form chains, nets, and three-dimensional networks. In this respect the borides differ markedly from other interstitial compounds such as carbides... 

Table II presents the DOS evaluated at the Fermi energy for fixed hydrogen concentration and a range of y values for each of the palladium-noble metal-hydrogen systems considered. These results have been used[14] to calculate the electron-phonon coupling and provide an explanation of the variation (as a function of y) of the superconducting transition temperature T found in Stritzker s[16] experiments.

As can be appreciated in the examples illustrated in Table 4.14, a number of superconductors based on the inclusion of alkali metals and thalium have been prepared. Superconducting transition temperatures in these compounds are significantly higher than those observed for the correponding graphite intercalates. Apparently, in the case of the fullerenes there is a near linear relationship between the superconducting transition temperature, Tp, and the alkali metal size. Such a relationship, deduced from the correlation between Tp and the... 

The relatively low transition temperatures of the metals shown in Table 18.3 mean that it would be impractical to make superconducting motors or transmission lines from them. Shortly after the superconductivity of metals was discovered, certain alloys (mixtures of metals) were prepared that had much higher transition temperatures than the metals themselves. Niobium alloys showed the most promise, but they still had to be cooled to below 23 K ( —250°G) to exhibit superconductivity. To maintain such a low temperature would require liquid helium, which costs about 6 per liter— an expensive proposition for all but the most exotic applications. 

Table 1. Structural and conductivity data of P-(ET)2X salts [length of anion X, room-temperature unit cell volume and superconducting critical temperature (or metal-to-insulator transition temperature Tj )]. 

Other elements become superconducting under pressure (e.g.. As, Ba, Ce, Ge). No alkali metals or noble metals are superconductors. Matthias pointed out that the transition temperature is generally higher if the electron per atom ratio is odd, as can be seen from the above tables (group IVA being the exception). 

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