First-Principles Study of the Dynamics in Face-Centered Cubic CeH₉ and CeH₁₀ under High Pressure

Rare-earth metal superhydrides have attracted much attention because of their high-temperature superconductivity. Since experimental measurements can only determine the structures of rare-earth metal atoms in the superhydrides, first-principles calculations have become an important complementary method for a comprehensive understanding on their structures and physical properties. In this work, the elasticity, lattice dynamics and proton dynamics properties of face-centered cubic CeH₉ and CeH₁₀ with different hydrogen contents but the same Ce lattice structure are investigated comparatively by first-principles calculations. The low hydrogen content is found to favor the elastic and phonon stabilization of face-centered cubic cerium superhydrides expanding to low pressures. At 100–140 GPa, CeH₉ and CeH₁₀ do not have significant proton diffusion at room temperature, but fully transform into the superionic state at 1500 K with diffusion coefficients of 1.6×10⁻⁴−1.2×10⁻⁴ cm²/s and 1.9×10⁻⁴−1.5×10⁻⁴ cm²/s; the diffusion coefficient is positively correlated with temperature and hydrogen content, but negatively correlated with pressure. The findings on the laws of pressure, temperature and hydrogen content affecting the structure and dynamics of cerium superhydrides are obtained, which can be used as a reference for the study of other superhydrides.