Specific Heat of Niobium-Tin

The specific heat of ${\mathrm{Nb}}_{3}$Sn has been measured over the temperature range 1-42\ifmmode^\circ\else\textdegree\fi{}K, and in magnetic fields up to 52.5 kG. The data can be interpreted to give $\ensuremath{\gamma}=13.1$ mJ/g atom \ifmmode^\circ\else\textdegree\fi{}${\mathrm{K}}^{2}$, $\frac{\ensuremath{\Delta}C}{\ensuremath{\gamma}{T}_{c}}=2.4$, ${H}_{0}=5350 \mathrm{G}$, and $\ensuremath{\kappa}({T}_{c})=21.7$. The Debye temperature $\ensuremath{\Theta}$ appears to increase at the rate of 1\ifmmode^\circ\else\textdegree\fi{}K/\ifmmode^\circ\else\textdegree\fi{}K over most of the range of the measurements, with $\ensuremath{\Theta}(0)={228}^{\ensuremath{\circ}}$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.