The Superconducting and Normal Heat Capacities of Niobium

Abstract

Data on the heat capacity of niobium in the normal and superconducting phases are presented in the temperature interval 2.5°K to 11°K. The normal heat capacity $c_n$ was found to be given by the usual relation: $c_n=\gamma T+\frac{464T^3}{{\Theta }^3}$, where $\gamma =20.4\mathrm{}\times {10}^{-4\mathrm{}}$ cal/M ${\mathrm{deg}}^2$ and $\Theta =252\mathrm{}°$K. The zero-field transition temperature $T_0$ was found to be 8.70°K±0.10°, and the heat capacity discontinuity $\Delta c$ at this temperature to be 0.0368 cal/M deg. The heat capacity in the superconducting phase was found to depart from a $T^3$ dependence below 5°K. The entire curve could not be represented by either the Koppe relation or the $\alpha$ model. The $H_T$ vs $T$ curve deduced from the heat capacity data was found to be very nearly parabolic, with the value of $H_0=2000\mathrm{}$ gauss and $\frac{d{H}_T}{\mathrm{dT}}$ at the zero-field transition temperature equal to 453 gauss/deg.