Electronic and lattice vibrational properties of thorium hydrides

The low temperature heat capacities of several bulk samples of Th4H15 and Th4D15 have been measured in the normal state over the temperature range from 1.4 to 20 K. Values of the electronic heat capacity coefficient, y, and the Debye temperature, eD' have been determined. No isotope effect upon the substitution of deuterium for hydrogen was found within experimental uncertainty in either y or eD. The specific heats of Th4H15 and Th4D15 in the superconducting states below 8 K have also been measured. The results indicate that these compounds are bulk superconductors whose properties do not deviate appreciably from the predictions of the BCS theory. Both the normalized specific heat discontinuity at Tc and the ratio of the energy gap to Tc are comparable to those of other weak-coupled superconductors. A re1ative1y large electronic density of states at the Fermi level suggests the possibility of occupied 5f electron states. By contrast, the dihydride of tporium was found to have a rather low density of states which presumab1y accounts for its lack of superconductivity. Anomalies in the heat capacities of several samples were observed at the melting temperatures of molecular hydrogen and deuterium. The static magnetic susceptibility of Th4H15 has been measured from 10 to 250 K. The results exhibit a large temperature dependence which is indicative of a substantial amount of structure in the electronic density of states near the Fermi level. The magnitude of the susceptibilities of Th4Hl5 and ThH2 corroborate the results obtained from specific heat measurements that Th4H15 has a much higher density of states than ThH2. The vibrational modes of hydrogen in Th4H15 have been investigated by neutron inelastic scattering. The optic phonon density of states derived from the observed scattering cross section is found to be very broad, ranging from 45 meV up to 150 meV. Two broad peaks centered about 70 and 135 meV are observed.U of I OnlyThesi