Superconductivity, yttrium role

Superconductivity is no stranger to the rare earths, in particular La and several of its compounds. Under pressure, Ce also becomes a superconductor as do Y, Lu (see Probst and Wittig 1978) and certain alloys however, for those lanthanides in which well-defined local 4f moments are present, superconductivity is inhibited by the pair breaking associated with the spins. And yes,- rare earths play a role, albeit not central, in what has been described as the condensed matter event of the 1980s -the remarkable discovery of superconductivity above 90 K in YBaCuO (Wu et al. 1987, Cava et al. 1987). In this case the rare earth is electronically isolated from the superconducting electrons, and as a result the substitution of heavy lanthanides with large 4f spins for the yttrium (Fisk et al. 1987) has virtually no dfect on the superconducting properties. 

Measurements on LaY alloys (Ohtsuka and Satoh 1966) failed to shed light on the role of the 4f electrons in the superconductivity of lanthanum. But we can say a few more words about y. The variation of y with yttrium content shows values of 10.0 mJ/mole-K at 100% a-La and 10.5 mJ/mole-K at 100% Y. The y versus concentration curve falls from either end, but shows an irregularity in the region of Lao.sYos where the alloy has the complex a-Sm structure. Thus y for the rare earths is perhaps more closely structure dependent than was first assunted, and care must be taken when adopting a y value for separating off the electronic term in the heat capacity (see also section 1.3 above). 

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