Platinum Metals Rev., 1975, 19, (1), 14
Superconductivity in Palladium-Hydrogen Alloys
Superconducting properties have not generally been associated with the platinum group metals. However, in 1972 T. Skoskiewicz of the Polish Academy of Sciences reported that palladium enriched with hydrogen possesses superconductivity, with a transition temperature Tc of ∼5 K when H:Pd=0.9.
Recent research in this field has been briefly summarised by R. Taylor (New Scientist, 1974, 64, (923, Nov. 14), 473), who comments on work by B. Stritzker et al . of the Nuclear Research Centre at Jülich aimed at raising Tc (Z. Physik, 1974, 268, (2), 261–264) and by C. A. Mackliet et al . at the Naval Research Laboratory at Washington, D.C., on the specific heat of superconducting Pd-H alloys (Solid State Commun., 1974, 15, (2), 207–210).
The Jülich team, which had first raised Tc to 9.4 K by H+ ion bombardment to increase the H:Pd ratio on the surface of palladium foils to more than 1, had also shown that the substitution of deuterium for hydrogen can raise Tc to 11 K. It is suggested that these additions may be modifying the lattice vibrations, or phonons, in the solids, thereby changing their coupling to the electrons, since it is the electron-phonon interaction which is believed to lead to superconductivity. Stritzker has now shown that alloying of suitable amounts of copper, silver or gold to Pd-H can raise Tc still more (to 16.6 K for 45 per cent Cu-Pd when H:Pd=0.7; the optimum silver and gold concentrations are smaller).
Mackliet and his co-workers have discovered that, whereas the peaks in the specific heat of superconductors usually drop sharply above Tc to the normal state, i.e. the superconducting state is more ordered, in Pd-H the drop is less marked.