Superconductivity and Electronic Properties of Mg-Cd and Some hcp Mg Alloys

The superconducting transition temperature $T_c$, electronic specific heat $\gamma$, and Debye temperature $\Theta$ have been measured in the Mg-Cd alloy system and in some other Mg-rich hcp alloys. No superconductivity could be detected in the latter above 0.013°K. On the Cd-rich side of the Cd-Mg system $T_c$ drops rapidly on alloying with Mg, and if one correlates this with the drop in $\frac{c}{a}$, one may expect Mg to have $T_c$ around 1 × ${10}^{-4\mathrm{}}$°K. A subsidiary maximum in $T_c$ occurs at $x=0.20\mathrm{}$ (in ${\mathrm{Mg}}_x{\mathrm{Cd}}_{1-x}$), where $\gamma$ and $\Theta$ have a marked maximum and minimum, respectively. At $x=0.50\mathrm{}$, the $\gamma$ has a minimum and $\Theta$ has a maximum if the mass factor is divided out. The possible origin of the anomaly at $x=0.20\mathrm{}$ is discussed in terms of ordering and an incipient instability reflected in the rapid variation of $\frac{c}{a}$.