Measurements of the specific heat of aluminum and its dilute alloys below 4°K show that the electronic specific-heat coefficient $\gamma$ changes linearly with the valence electron concentration from below to above the pure-aluminum value, in contradiction to previous work. The difference is attributed to undetected precipitation of the solutes Ge or Si in the previous work. Good agreement is found between $\gamma$ values for $\mathrm{Al}\mathrm{Zn}$ alloys and the previous $\mathrm{Al}\mathrm{Mg}$ alloys. The rate of increase of $\gamma$ is three times that expected from free-electron theory. For pure Al, $\gamma =1.362\mathrm{}$ mJ ${\mathrm{mole}}^{-1\mathrm{}}$ °${\mathrm{K}}^{-2\mathrm{}}$, and the Debye temperature =431°K.

• Received 18 July 1966

DOI:https://doi.org/10.1103/PhysRev.153.800