Specific Heats of Au andAuSnat Low Temperatures

Specific heats of high-purity Au and $\mathrm{Au}\mathrm{Sn}$ alloys have been measured between 2 and 4°K. The electronic coefficient $\gamma$ rises strongly with tin concentration; expressed in terms of electron concentration $\frac{e}{a}$, $\gamma =(0.730\mathrm{}\pm 0.007)+(0.60\pm 0.08)(\frac{e}{a}-1)$ mJ ${\mathrm{mole}}^{-1\mathrm{}}$ °${\mathrm{K}}^{-2\mathrm{}}$ for $\alpha$-phase $\mathrm{Au}\mathrm{Sn}$. Hence a rise of $\gamma$ with $\frac{e}{a}$ is a universal characteristic of noble metals alloyed with polyvalent nontransition elements, and this slope appears to depend on the solute/solvent mass ratio. The lattice contribution has the form $A{T}^3+B{T}^5$. For Au, the Debye temperature ${\Theta }_0$ (at $T=0\mathrm{}°$K) is 162.5±0.4°K, while $B$ is - (1.08±0.07)×${10}^{-3\mathrm{}}$ mJ ${\mathrm{mole}}^{-1\mathrm{}}$ °${\mathrm{K}}^{-6\mathrm{}}$. With increasing Sn concentration, ${\Theta }_0$ falls and $B$ rises. Current theory does not seem to account for these trends.