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

Abstract 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 with ab-initio calculations under high pressure. We found four dynamically stable structures with hydrogen clathrate cages: CaUH 12 - Cmmm , CaUH 12 - Fd -3 m , Ca 2 UH 18 - P -3 m 1, and CaU 3 H 32 - Pm -3 m . Among them, the Ca 2 UH 18 - P -3 m 1 and CaU 3 H 32 - Pm -3 m are likely to be synthesized below 1 megabar. The f electrons 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. The T c value of Ca 2 UH 18 - P -3 m 1 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.