Superconducting and Normal Specific Heats of Niobium

Abstract

The measurements reported in this paper were undertaken to resolve differences in the published values of the low-temperature heat capacity of niobium and to determine the effect of high-temperature annealing (2340°C) and degassing on the same sample for which data had previously been published by Brown, Zemansky and Boorse. The new measurements cover the temperature interval 1.1 to 11.5°K and are significantly different from those obtained prior to the thermal treatment. The normal-phase heat capacity may be expressed by the usual relation, $C_n=\gamma T+\mathrm{const}{\left(\frac{T}{{\Theta }_D}\right)}^3$, with $\gamma =(7.53\mathrm{}\pm 2\%)$ mJ/mole ${\mathrm{deg}}^2$ and ${\Theta }_D=238\mathrm{}°\mathrm{K}\pm 1.5\%$. The zero-field transition temperature, determined from the midpoint of the transition interval, was found to be 9.09°K. In the superconducting phase below 1.7°K, the total heat capacity $C_s$ was found to be less than the lattice specific heat alone in the normal phase. This anomalous result, previously reported by the present authors, is comparable to that found in indium by Bryant and Keesom. This anomaly complicates the determination of the superconducting electronic specific heat $C_{\mathrm{es}}$ but by using a theory by Ferrell, it may be evaluated in the usual form, $a\gamma T_c\exp (-\frac{b{T}_c}{T})$, with $a=12.6\mathrm{}$ and $b=1.71\mathrm{}$.