Superconductivity in the Alloy System Cadmium-Mercury and the Effect of Ordering upon Superconductivity

The superconducting transition temperatures of Cd-Hg alloys covering the complete composition range have been determined. The solubility of Cd in Hg has been accurately determined; it is 1.5±0.25 at.% at 193°K. The terminal solid solubility of Hg in Cd is found to be 26±2 at.% at 418°K. Boundaries of the $\omega$ phase occur at 88±1 at.% Hg at 193°K and at 35±2 at.% Hg at 383°K. Ordering occurs in the intermediate $\omega$ phase at compositions based on ${\mathrm{Cd}}_2$Hg and Cd${\mathrm{Hg}}_2$. The effect of ordering upon the superconducting transition temperature is observed for the first time. The transition temperature for the ordered phase is lower than the one for the disordered. This is presumably caused either by a reduced electron-phonon interaction, which is reflected also in a lower measured normal-state resistivity of the ordered phase, or by changes in the electronic density of states at the Fermi surface, which would be expected as a consequence of the subdivision of the Brillouin zones by the superlattice formation.