The superconducting transition temperatures of the thorium-hydrides

The contributions to the quantity ² F() coming from the different vibration modes are calculated for the compounds Th₄H₁₅ and Th H₂. The electronic quantities have been evaluated in a cluster approximation while simple models are used for the phonons. The high transition temperature of Th₄H₁₅ is explained by the large contribution of the hydrogen modes to the McMillan, which overcompensates the deterioration of the Th-lattice in comparison to the Th-metal. In Th H₂ the hydrogen contribution turns out to be insufficient for a highT _c . An important property of these substances is the significant admixture off-states at the Fermi level.