Normal and Superconducting Heat Capacities of Lanthanum

Abstract

The heat capacities of three samples of lanthanum have been measured in the temperature range 1.6 to to 6.5\ifmmode^\circ\else\textdegree\fi{}K. A four-constant formula was found which represented to high precision the resistance-temperature relation of the carbon composition resistance thermometer from 1.6 to 7.2\ifmmode^\circ\else\textdegree\fi{}K. Two superconducting transitions were found in each sample: one at 4.8\ifmmode^\circ\else\textdegree\fi{}K and the other at 5.9\ifmmode^\circ\else\textdegree\fi{}K. These are associated respectively with the hexagonal close-packed and face-centered cubic modifications of the metal. Below 2.5\ifmmode^\circ\else\textdegree\fi{}K, a magnetic field of 10 000 gauss was found insufficient to quench completely the superconducting phase. The values of the normal heat capacity constants for the purest sample, averaged over the two crystal structures present, were determined by a thermodynamic analysis of the data to be $\ensuremath{\gamma}=(24.1\ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ cal/mole ${(\mathrm{\ifmmode^\circ\else\textdegree\fi{}}\mathrm{K})}^{2}$, $\ensuremath{\Theta}=142\ifmmode\pm\else\textpm\fi{}3\ifmmode^\circ\else\textdegree\fi{}$K. The data are further analyzed for evidence of a law of corresponding states among superconductors.