Thorium superconductivity

In the area of superconductivity, tetravalent thorium is used to replace trivalent lanthanides in n-ty e doped superconductors, R2 Th Cu0 g, where R = Pr, Nd, or Sm, producing a higher T superconductor. Thorium also forms alloys with a wide variety of metals. In particular, thorium is used in magnesium alloys to extend the temperature range over which stmctural properties are exhibited that are useful for the aircraft industry. More detailed discussions on thorium alloys are available (8,19). 

Properties. Pure thorium metal is a dense, bright silvery metal having a very high melting point. The metal exists in two allotropic modifications. Thorium is a reactive, soft, and ductile metal which tarnishes slowly on exposure to air (12). Having poor mechanical properties, the metal has no direct stmctural appHcations. A survey of the physical properties of thorium is summarized in Table 1. Thorium metal is diamagnetic at room temperature, but becomes superconducting below 1.3—1.4 K. 

Mixed hydrides with Zr and Ti were reported several years ago. It has now been shown that substantial replacement of thorium by lanthanum is possible in Th4His. The temperature at which superconduction appears falls as the lanthanum content rises (298). 

Superconductivity of actinides seems to be well understood (40) on the basis of recent progress in the calculation of their band structures and their vibrational spectra. Thorium and uranium are known to be superconductors. By using ac susceptibility techniques, superconductivity could be detected in both Am (41) and Pa (42). Vapour deposited Am was used as sample material ... 

Incorporation of elements other than thorium into yttrium sesquicarbide also leads to a resultant enhancement of the superconducting temperature (Krupka et al. 1969b). These elements include the group IV and VI transition metals, as well as gold, germanium and silicon. But, in these cases, it is necessary to ensure the solubiUty of these elements in the parent sesquicarbide lattice. 

There are a number of materials which have been studied but the two favorite ternary superconductors are the so called Chevrel phases, named after R. Chevrel (Universite de Rennes, France) who first prepared the MMo Sg or MMo Seg compounds (Chevrel et al. 1971), and the RRh4B4 compounds. In the Chevrel phases, M can be any number of metals including the rare earth metals, and in the latter compound R represents the rare earths and thorium. In both instances Matthias and his co-workers were the first to report the existence of superconductivity in the Chevrel phases (Matthias et al. 1972) and in RRh4B4 (Matthias et al. 1977),... 

Giorgi, A.L., E.G. Szklarz and M.C. Knipka, 1972, Superconductivity of Various Ternary Thorium Compounds, in Douglass, D.H., ed.. Superconductivity in d- and f-Band Metals, AlP Conf. Ifroc. No. 4 (American Inst, of Physics-New York 1972) p. 147. 

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