Low-temperature heat capacity of normal and superconducting thorium hydride and thorium deuteride

Abstract

The low-temperature heat capacities of several bulk samples of ${\mathrm{Th}}_{4}$${\mathrm{H}}_{15}$ and ${\mathrm{Th}}_{4}$${\mathrm{D}}_{15}$ have been measured over the temperature range from 1.4 to 20 K in both the normal and superconducting states. Average values of the electronic-heat-capacity coefficient $\ensuremath{\gamma}$ and Debye temperature ${\ensuremath{\Theta}}_{D}$ are found to be 8.07 \ifmmode\pm\else\textpm\fi{} 0.14 mJ ${\mathrm{K}}^{\ensuremath{-}2}$/mole Th and 211.5 \ifmmode\pm\else\textpm\fi{} 1.1 K, respectively, for ${\mathrm{Th}}_{4}$${\mathrm{H}}_{15}$. Corresponding values for ${\mathrm{Th}}_{4}$${\mathrm{D}}_{15}$ are 7.84 \ifmmode\pm\else\textpm\fi{} 0.25 mJ ${\mathrm{K}}^{\ensuremath{-}2}$/mole Th and 216.5 \ifmmode\pm\else\textpm\fi{} 6.6 K. A relatively large density of states at the Fermi level suggests the possibility of occupied $5f$ electronic states. Anomalies in the heat capacities of several samples were observed at the melting temperatures of molecular hydrogen and deuterium.