Letter | Published:

Transition Temperatures of Superconductive Alloys

Nature volume 142, page 611 (01 October 1938) | Download Citation



THE transition between the normal and the superconductive state of a metal is a phase transition of the second kind, that is, there is no latent heat but a discontinuous jump in the specific heat, as at the λ-point of liquid helium or at the Curie point of a ferromagnetic. At the transition temperature in such phase changes, the entropy of the two phases as well as the free energy is equal. Thus if the entropies of the superconductive and the normal states are plotted as functions of the temperature T, the intersection of these curves determines the transition temperature. In the normal state the entropy is known to depend linearly on T at low temperatures. The entropy of the superconductive state can be determined from the magnetic threshold curve1 and is found for most superconductors to vary approximately as T2. There is a fairly well established theory which gives the entropy in the normal state, and we can predict with fair certainty how this will change when small quantities of other metals are added in solid solution. It is the purpose of this letter to show that the change in the normal state which can be roughly calculated is by itself sufficient to account rather satisfactorily for the observed changes in the transition temperature. The conclusion is therefore that the entropy-temperature curve for the superconductive state is not sensitively affected by the addition of small quantities of other metals in solid solution.

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  1. 1.

    , and , Physica, 1, 305 (1934).

  2. 2.

    and , "The Theory of Metals and Alloys", Oxford, 1936.

  3. 3.

    , Erg. Exakten Nat., 11, 219 (1932).

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  1. Royal Society Mond Laboratory, Cambridge. Aug. 26.

    • H. JONES


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