Cage structure and near room-temperature superconductivity in TbH_n(n = 1-12)

Hydrogen-rich compounds are considered most likely to achieve room-temperature superconductivity since the critical temperature (Tc) above 250 K was observed in lanthanum hydride. Exploring the high-temperature superconductivity in rare-earth metal hydrides becomes very interesting. Based on the particle swarm optimization for crystal structures and first-principles calculations, we investigate the crystal structures, phase stability, metallization, and possible superconducting properties of terbium hydride (TbHn, n = 1 - 12) under pressure. Our results show that terbium hydride is a potential high-temperature superconductor under high pressures. It stably exists at different pressure conditions by adjusting the H content. Specifically, the H atomic cage structure can be observed in most terbium hydrides, and the number of H atoms in the cage sublattice increases with the stoichiometry of H in TbHn. We demonstrate that the high Tc value is closely related to this cage sublattice and it increases with increasing H content in terbium hydride. The highest Tc above 270 K is predicted in TbH10 at 250 GPa for Fm3¯m and 310 GPa for R3¯m space group. This result indicates that the superconductivity with Tc close to or beyond lanthanum hydride can be achieved in other rare-earth metal hydrides.