Specific Heat of Niobium-Tin

The specific heat of ${\mathrm{Nb}}_3$Sn has been measured over the temperature range 1-42°K, and in magnetic fields up to 52.5 kG. The data can be interpreted to give $\gamma =13.1\mathrm{}$ mJ/g atom °${\mathrm{K}}^2$, $\frac{\Delta C}{\gamma T_c}=2.4\mathrm{}$, $H_0=5350\mathrm{} \mathrm{G}$, and $\kappa \left(T_c\right)=21.7\mathrm{}$. The Debye temperature $\Theta$ appears to increase at the rate of 1°K/°K over most of the range of the measurements, with $\Theta \mathrm{}\left(0\right)={228}^{\circ }$K. Measurements have also been made on a sample of composition ${\mathrm{Nb}}_4$Sn, and on vapor-grown ${\mathrm{Nb}}_3$Sn similar to that exhibiting the cubic-tetragonal lattice transformation. The specific heat of ${\mathrm{Nb}}_3$Sn can be reconciled with elastic-constant data only if it is assumed that the lattice softening implied by the decreasing velocity of sound with decreasing temperatures is limited to frequencies considerably below the Debye frequency.