Superconducting ternary hydrides in Ca-U-H under high pressure.

The research on hydrogen-rich ternary compounds attract tremendous attention for it paves new route to room-temperature superconductivity at lower pressures. Here, we study the crystal structures, electronic structures, and superconducting properties of the ternary Ca-U-H system, combining crystal structure predictions withcalculations under high pressure. We found four dynamically stable structures with hydrogen clathrate cages: CaUH-, CaUH--3, CaUH--31, and CaUH--3. Among them, the CaUH--31 and CaUH--3are likely to be synthesized below 1 megabar. Theelectrons in U atoms make dominant contribution to the electronic density of states around the Fermi energy. The electron-phonon interaction calculations reveal that phonon softening in the mid-frequency region can enhance the electron-phonon coupling significantly. Thevalue of CaUH--31 is estimated to be 57.5-65.8 K at 100 GPa. Our studies demonstrate that introducing actinides into alkaline-earth metal hydrides provides possibility in designing novel superconducting ternary hydrides.