Synthesis and Stability of Lanthanum Superhydrides

Recent theoretical calculations predict that megabar pressure stabilizes very hydrogen-rich simple compounds having new clathrate-like structures and remarkable electronic properties including room-temperature superconductivity. We report x-ray diffraction and optical studies demonstrating that superhydrides of lanthanum can be synthesized with La atoms in an fcc lattice at 170 GPa upon heating to 1000 K. The results match the predicted cubic metallic phase of LaH₁₀ having cages of thirty-two hydrogen atoms surrounding each La atom. Upon decompression, the fcc-based structure of LaH₁₀ undergoes a rhombohedral distortion of the La sublattice. The superhydride phases consist of an atomic hydrogen sublattice with H-H distances of 1.1 Å, which are close to predictions for solid atomic metallic hydrogen at these pressures.

This research was supported by EFree, an EFRC funded by the US DOE (DE-SC0001057). The infrastructure and facilities used are supported by the US DOE/NNSA (Awards DE-NA-0002006, CDAC; and DE-NA0001974, HPCAT).