Cage Structure and Near Room-Temperature Superconductivity in TbHₙ (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 Fm3m and 310 GPa for R3m 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.